The advance notice procedures of our bylaws generally provide that, to be timely, a stockholder's notice with respect to director nominations or proposals for an annual meeting must be delivered to our corporate secretary at our principal executive office not less than 90 nor more than 120 days prior to the first anniversary of the date of our preceding year's annual meeting.

The general applicability of the business combination provisions of the MGCL, the provisions of our charter on removal of directors and the advance notice provisions of the bylaws could delay, defer or prevent a transaction or a change in control of our company that might involve a premium price for holders of our common stock or otherwise be in their best interest. Likewise, if our board of directors were to opt in to certain of the provisions of Title 3, Subtitle 8 of the MGCL, or if the provision in the bylaws opting out of the control share acquisition provisions of the MGCL were rescinded, these provisions of the MGCL could have similar anti-takeover effects.

The transfer agent and registrar for our common stock is Computershare Trust Company, N.A.

Our shares of common stock are listed for trading on the Nasdaq Global Market under the symbol "PTX."

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DESCRIPTION OF OUR WARRANTS

We may issue warrants to purchase shares of our common stock, preferred stock and/or debt securities in one or more series together with other securities or separately, as described in each applicable prospectus supplement or free writing prospectus. Below is a description of certain general terms and provisions of the warrants that we may offer. Particular terms of the warrants will be described in the applicable warrant agreements and the applicable prospectus supplement or free writing prospectus for the warrants.

The applicable prospectus supplement or free writing prospectus will contain, where applicable, the following terms of and other information relating to the warrants:

• the specific designation and aggregate number of, and the price at which we will issue, the warrants;
• the currency or currency units in which the offering price, if any, and the exercise price are payable;
• the designation, amount and terms of the securities purchasable upon exercise of the warrants;
• if applicable, the exercise price for shares of our common stock and the number of shares of common stock to be received upon exercise of the warrants;
• if applicable, the exercise price for shares of our preferred stock, the number of shares of preferred stock to be received upon exercise of the warrants, and a description of that series of our preferred stock;
• if applicable, the exercise price for our debt securities, the amount of our debt securities to be received upon exercise of the warrants, and a description of that series of debt securities;
• the date on which the right to exercise the warrants will begin and the date on which that right will expire or, if the warrants may not be continuously exercised throughout that period, the specific date or dates on which the warrants may be exercised;
• whether the warrants will be issued in fully registered form or bearer form, in definitive or global form or in any combination of these forms, although, in any case, the form of a warrant included in a unit will correspond to the form of the unit and of any security included in that unit;
• any applicable material U.S. federal income tax or foreign tax consequences;
• the identity of the warrant agent for the warrants and of any other depositaries, execution or paying agents, transfer agents, registrars or other agents;
• the proposed listing, if any, of the warrants or any securities purchasable upon exercise of the warrants on any securities exchange or market;
• if applicable, the date from and after which the warrants and the common stock, preferred stock and/or debt securities will be separately transferable;
• if applicable, the minimum or maximum amount of the warrants that may be exercised at any one time;
• information with respect to book-entry procedures, if any
• the anti-dilution provisions of the warrants, if any;
• any redemption, put or call provisions;
• whether the warrants are to be sold separately or with other securities as parts of units; and
• any additional terms of the warrants, including terms, procedures and limitations relating to the exchange and exercise of the warrants.

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Transfer Agent and Registrar

The transfer agent and registrar for any warrants will be set forth in the applicable prospectus supplement or free writing prospectus.

As of November 22, 2017, there were 32,992 warrants to purchase shares of our common stock outstanding. See "Description of Our Capital Stock - Common Stock Warrants."

As of September 30, 2017, we have outstanding (a) $172,069,814 of 12% Senior Secured Notes due 2020, (b) $78,225,000 of 4.25% Convertible Senior Notes due 2021, and (c) $36,242,500 of 4.25%/5.25% Exchangeable Notes due 2022.

We will issue any senior debt securities under the senior indenture that we will enter into with the trustee named in the senior indenture. We will issue any subordinated debt securities under the subordinated indenture that we will enter into with the trustee named in the subordinated indenture. We have filed forms of these documents as exhibits to the registration statement, of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The indentures will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We use the term "trustee" to refer to either the trustee under the senior indenture or the trustee under the subordinated indenture, as applicable.

The following summaries of material provisions of the senior debt securities, the subordinated debt securities and the indentures are subject to, and qualified in their entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplement or free writing prospectus related to the debt securities that we may offer under this prospectus, as well as the complete applicable indenture that contains the terms of the debt securities. Except as we may otherwise indicate, the terms of the senior indenture and the subordinated indenture are identical.

We will describe in the applicable prospectus supplement or free writing prospectus the terms of the series of debt securities being offered, including:

• the title of the series;

• the aggregate principal amount being offered, and if a series, the total amount authorized and the total amount outstanding;

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• the issue price or prices, expressed as a percentage of the aggregate principal amount of the debt securities;

• any limit on the aggregate principal amount that may be issued;

• whether or not we will issue the series of debt securities in global form, and, if so, the terms and who the depository will be;

• the maturity date;

• whether and under what circumstances, if any, we will pay additional amounts on any debt securities held by a person who is not a United States person for tax purposes, and whether we can redeem the debt securities if we have to pay such additional amounts;

• the annual interest rate, which may be fixed or variable, or the method for determining the rate and the date interest will begin to accrue, the dates interest will be payable and the regular record dates for interest payment dates or the method for determining such dates;

• whether or not the debt securities will be secured or unsecured, and the terms of any secured debt;

• the terms of the subordination of any series of subordinated debt;

• the place where payments will be payable;

• restrictions on transfer, sale or other assignment, if any;

• our right, if any, to defer payment of interest and the maximum length of any such deferral period;

• the date, if any, after which, the conditions upon which, and the price at which, we may, at our option, redeem the series of debt securities pursuant to any optional or provisional redemption provisions and the terms of those redemption provisions;

• the date, if any, on which, and the price at which we are obligated, pursuant to any mandatory sinking fund or analogous fund provisions or otherwise, to redeem, or at the holder's option, to purchase, the series of debt securities and the currency or currency unit in which the debt securities are payable;

• whether the indenture will restrict our ability or the ability of our subsidiaries to:
• incur additional indebtedness;
• issue additional securities;
• create liens;
• pay dividends or make distributions in respect of our capital stock or the capital stock of our subsidiaries;
• redeem capital stock;
• place restrictions on our subsidiaries' ability to pay dividends, make distributions or transfer assets;
• make investments or other restricted payments;
• sell or otherwise dispose of assets;
• enter into sale-leaseback transactions;
• engage in transactions with stockholders or affiliates;
• issue or sell stock of our subsidiaries; or
• effect a consolidation or merger;

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• whether the indenture will require us to maintain any interest coverage, fixed charge, cash flow-based, asset-based or other financial ratios;

• a discussion of certain material or special United States federal income tax considerations or foreign tax considerations applicable to the debt securities;

• information describing any book-entry features;

• provisions for a sinking fund purchase or other analogous fund, if any;

• the applicability of the provisions in the indenture on discharge;

• whether the debt securities are to be offered at a price such that they will be deemed to be offered at an "original issue discount" as defined in paragraph (a) of Section 1273 of the Internal Revenue Code of 1986, as amended;

• the denominations in which we will issue the series of debt securities, if other than denominations of $1,000 and any integral multiple thereof;

• the currency of payment of debt securities if other than U.S. dollars and the manner of determining the equivalent amount in U.S. dollars; and

• any other specific terms, preferences, rights or limitations of, or restrictions on, the debt securities, including any additional events of default or covenants provided with respect to the debt securities, and any terms that may be required by us or advisable under applicable laws or regulations or advisable in connection with the marketing of the debt securities.

We will set forth in the applicable prospectus supplement or free writing prospectus the terms on which a particular series of debt securities may be convertible into or exchangeable for our common stock, our preferred stock or other securities (including securities of a third-party). We will include provisions as to whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock, our preferred stock or other securities (including securities of a third-party) that the holders of the series of debt securities receive would be subject to adjustment.

Unless we provide otherwise in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, the indentures will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of all or substantially all of our assets. However, any successor to or acquirer of such assets must assume all of our obligations under the indentures or the debt securities, as appropriate. If the debt securities are convertible into or exchangeable for other securities of ours or securities of other entities, the person with whom we consolidate or merge or to whom we sell all of our property must make provisions for the conversion of the debt securities into securities that the holders of the debt securities would have received if they had converted the debt securities before the consolidation, merger or sale.

Unless we provide otherwise in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, the following are events of default under the indentures with respect to any series of debt securities that we may issue:

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• if we fail to pay interest when due and payable and our failure continues for 90 days and the time for payment has not been extended;

• if we fail to pay the principal, premium or sinking fund payment, if any, when due and payable at maturity, upon redemption or repurchase or otherwise, and the time for payment has not been extended;

• if we fail to observe or perform any other covenant contained in the debt securities or the indentures, other than a covenant specifically relating to another series of debt securities, and our failure continues for 90 days after we receive notice from the trustee or holders of at least 25% in aggregate principal amount of the outstanding debt securities of the applicable series; and

• if specified events of bankruptcy, insolvency or reorganization occur.

We will describe in each applicable prospectus supplement or free writing prospectus any additional events of default relating to the relevant series of debt securities.

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the unpaid principal, premium, if any, and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indentures, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity or security satisfactory to it against any loss, liability or expense. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

• the direction so given by the holder is not in conflict with any law or the applicable indenture; and

• subject to its duties under the Trust Indenture Act, the trustee need not take any action that might involve it in personal liability or might be unduly prejudicial to the holders not involved in the proceeding.

A holder of the debt securities of any series will have the right to institute a proceeding under the indentures or to appoint a receiver or trustee, or to seek other remedies if:

• the holder has given written notice to the trustee of a continuing event of default with respect to that series;

• the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made written request, and such holders have offered reasonable indemnity to the trustee or security satisfactory to it against any loss, liability or expense or to be incurred in compliance with instituting the proceeding as trustee; and

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• the trustee does not institute the proceeding, and does not receive from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series other conflicting directions within 90 days after the notice, request and offer.

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities, or other defaults that may be specified in the applicable prospectus supplement or free writing prospectus.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indentures.

Subject to the terms of the indenture for any series of debt securities that we may issue, we and the trustee may change an indenture without the consent of any holders with respect to the following specific matters:

• to fix any ambiguity, defect or inconsistency in the indenture;

• to comply with the provisions described above under "Description of Our Debt Securities-Consolidation, Merger or Sale;"

• to comply with any requirements of the SEC in connection with the qualification of any indenture under the Trust Indenture Act;

• to add to, delete from or revise the conditions, limitations, and restrictions on the authorized amount, terms, or purposes of issue, authentication and delivery of debt securities, as set forth in the indenture;

• to provide for the issuance of and establish the form and terms and conditions of the debt securities of any series as provided under "Description of Our Debt Securities- General," to establish the form of any certifications required to be furnished pursuant to the terms of the indenture or any series of debt securities, or to add to the rights of the holders of any series of debt securities;

• to evidence and provide for the acceptance of appointment hereunder by a successor trustee;

• to provide for uncertificated debt securities and to make all appropriate changes for such purpose;

• to add to our covenants such new covenants, restrictions, conditions or provisions for the benefit of the holders, to make the occurrence, or the occurrence and the continuance, of a default in any such additional covenants, restrictions, conditions or provisions an event of default or to surrender any right or power conferred to us in the indenture; or

• to change anything that does not materially adversely affect the interests of any holder of debt securities of any series.

In addition, under the indentures, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, subject to the terms of the indenture for any series of debt securities that we may issue or as otherwise provided in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

• extending the stated maturity of the series of debt securities;

• reducing the principal amount, reducing the rate of or extending the time of payment of interest, or reducing any premium payable upon the redemption or repurchase of any debt securities; or

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• reducing the percentage of debt securities, the holders of which are required to consent to any amendment, supplement, modification or waiver.

Each indenture provides that, subject to the terms of the indenture and any limitation otherwise provided in the prospectus supplement or free writing prospectus applicable to a particular series of debt securities, we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

• register the transfer or exchange of debt securities of the series;

• replace stolen, lost or mutilated debt securities of the series;

• maintain an office or agency with respect to each series of debt securities;

• maintain paying agencies;

• make, or cause to be made, payment of principal (and premium, if any) and interest due on each series of debt securities and hold monies for payment in trust;

• recover excess money held by the trustee;

• compensate and indemnify the trustee; and

• appoint any successor trustee.

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium and interest on, the debt securities of the series on the dates payments are due.

We will issue the debt securities of each series only in fully registered form without coupons and, unless we otherwise specify in the applicable prospectus supplement or free writing prospectus, in denominations of $1,000 and any integral multiple thereof. The indentures provide that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company or another depository named by us and identified in a prospectus supplement or free writing prospectus with respect to that series.

At the option of the holder, subject to the terms of the indentures and the limitations applicable to global securities described in the applicable prospectus supplement or free writing prospectus, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indentures and the limitations applicable to global securities set forth in the applicable prospectus supplement or free writing prospectus, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will make no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

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We will name in the applicable prospectus supplement or free writing prospectus the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

• issue, register the transfer of, or exchange any debt securities of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption of any debt securities that may be selected for redemption and ending at the close of business on the day of the mailing; or

• register the transfer of or exchange any debt securities so selected for redemption, in whole or in part, except the unredeemed portion of any debt securities we are redeeming in part.

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs.

Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indentures at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement or free writing prospectus, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement or free writing prospectus any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

The indentures and the debt securities will be governed by and construed in accordance with the laws of the State of New York, except to the extent that the Trust Indenture Act is applicable.

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Ranking of Debt Securities

The subordinated debt securities will be subordinate and junior in priority of payment to certain of our other indebtedness to the extent described in a prospectus supplement or free writing prospectus.  The subordinated indenture does not limit the amount of subordinated debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

The senior debt securities will rank equally in right of payment to all our other senior unsecured debt. The senior indenture does not limit the amount of senior debt securities that we may issue. It also does not limit us from issuing any other secured or unsecured debt.

On February 21, 2014, we issued $65.0 million aggregate principal amount of our 8.00% Convertible Senior Notes due 2019, or the 8.00% Convertible Notes, in accordance with each of the Securities Purchase Agreements dated February 4, 2014, by and between us and the investors party thereto, and the related Indenture, dated February 21, 2014, by and between us and the trustee.  During the year ended December 31, 2015, the holders of the 8.00% Convertible Notes converted the outstanding notes at a conversion price of $36.00 per share. We issued 1.8 million shares pursuant to this conversion and retired the $65.0 million of the outstanding 8.00% Convertible Notes.

On August 19, 2014, we issued $220,000,000 aggregate principal amount of our 12% Senior Secured Notes due 2020, or the August 2014 Notes, pursuant to an Indenture, or the August 2014 Indenture, dated as of August 19, 2014 among us, certain of our subsidiaries, or the Treximet Guarantors, and U.S. Bank National Association, or the August 2014 Trustee, as trustee and collateral agent.

The August 2014 Notes mature on August 1, 2020 and bear interest at a rate of 12% per annum, payable in arrears on February 1 and August 1 of each year, beginning on February 1, 2015.  On each payment date, commencing August 1, 2015, we will pay an installment of principal of the August 2014 Notes in an amount equal to 50% of net sales of Treximet, as such term is defined in the August 2014 Indenture, for the two consecutive fiscal quarters immediately preceding such payment date (less the amount of interest paid on the August 2014 Notes on such payment date).

The August 2014 Notes are unconditionally guaranteed, jointly and severally, by the Treximet Guarantors.  The August 2014 Notes and the guarantees of the Treximet Guarantors are secured by a continuing first-priority security interest in substantially all of our assets and the assets of the Treximet Guarantors related to Treximet®, other than inventory and certain inventory related assets, including accounts arising from the sale of the inventory.

We may redeem the August 2014 Notes at our option, in whole at any time or in part from time to time, on any business day, on not less than 30 days' nor more than 60 days' prior notice provided to each holder's registered address.  The redemption price will equal 100% of the outstanding principal amount of the August 2014 Notes being redeemed plus accrued and unpaid interest thereon.

The August 2014 Indenture contains covenants that limit our ability and the ability of the Treximet Guarantors to, among other things: incur certain additional indebtedness; pay dividends on, redeem or repurchase stock or make other distributions in respect of its capital stock; repurchase, prepay or redeem certain indebtedness; make certain investments; create restrictions on the ability of the Treximet Guarantors to pay dividends to us or make other intercompany transfers; create liens; transfer or sell assets; consolidate, merge or sell or otherwise dispose of all or substantially all of its assets and enter into certain transactions with affiliates. Upon the occurrence of certain events constituting a change of control, we are required to make an offer to repurchase all of the August 2014 Notes (unless otherwise redeemed) at a purchase price equal to 101% of their principal amount, plus accrued and unpaid interest, if any to the repurchase date.

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The August 2014 Indenture provides that an event of default will occur if, among other things, (a) we default in any payment of interest on any August 2014 Note when due and payable, and such default continues for a period of 30 days; (b) we default in the payment of principal of or premium, if any, on any August 2014 Note when due and payable on the maturity date, upon declaration of acceleration or otherwise, or to pay the change of control repurchase price, when due and payable, and such default continues for a period of five days; (c) we fail to make a repurchase offer in the event of a change in control when required under the August 2014 Indenture, which continues for three business days; (d) we or any Treximet Guarantor fails to comply with certain covenants after receiving written notice from the August 2014 Trustee or the holders of more than 25% of the principal amount of the outstanding August 2014 Notes; (e) we or any Treximet Guarantor defaults with respect to other indebtedness for borrowed money in excess of $8,000,000 and such default is not cured within 30 days after written notice from the August 2014 Trustee or the holders of more than 25% of the principal amount of the outstanding August 2014 Notes; (f) we or any Treximet Guarantor has rendered against it a final judgment for the payment of $8,000,000 (or its foreign currency equivalent) or more (excluding any amounts covered by insurance) under certain circumstances; (g) certain bankruptcy, insolvency, liquidation, reorganization or similar events occur with respect to us or any Treximet Guarantor; (h) a guarantee of the August 2014 Notes (with certain exceptions) is held to be unenforceable or invalid in a judicial proceeding or ceases to be in full force and effect or a Treximet Guarantor disaffirms its obligations under its guarantee of the August 2014 Notes; or (i) certain changes in control of a Treximet Guarantor.

On April 21, 2015, we and the August 2014 Trustee entered into a First Supplemental Indenture to the August 2014 Indenture, or the August 2014 First Supplemental Indenture, to among other things, allow us to incur up to $42.2 million of additional debt. On July 21, 2017, we, certain of our subsidiaries, or the New Guarantors, and the August 2014 Trustee entered into a Second Supplemental Indenture to the August 2014 Indenture, or the August 14 Second Supplemental Indenture, pursuant to which the New Guarantors provided guarantees of our obligations with respect to August 2014 Notes. On November 2, 2017, we, certain holders of the August 2014 Notes and the August 2014 Trustee entered into a Waiver, Amendment and Consent Agreement, pursuant to which such holders of the August 2014 Notes, representing a majority in aggregate principal amount of the August 2014 Notes then outstanding, agreed to waive compliance with, and modify certain provisions of, the August 2014 Indenture in order to permit and facilitate the distribution and marketing of an authorized generic version of Treximet in the United States by one of our wholly-owned subsidiaries, Macoven. In connection with the Waiver, Amendment and Consent Agreement, the Required Holders, as such term is defined in the August 2014 Indenture, were granted, among other things, certain consent rights with respect to the termination provisions in the Intercompany Distribution Agreements, as such term is defined in the August 2014 Indenture.

On April 22, 2015, we issued $130.0 million aggregate principal amount of our 4.25% Convertible Senior Notes due 2021, or the 4.25% Convertible Notes. The 4.25% Convertible Notes mature on April 1, 2021, unless earlier converted, redeemed or repurchased. The 4.25% Convertible Notes are governed by the terms of an Indenture, or the April 2015 Indenture, between us and Wilmington Trust, National Association, or the April 2015 Trustee, which was entered into on April 22, 2015.

The 4.25% Convertible Notes are our general unsecured obligations and bear interest at a rate of 4.25% per annum, payable semiannually in arrears on April 1 and October 1 of each year, beginning on October 1, 2015. The 4.25% Convertible Notes will mature on April 1, 2021, unless earlier converted, redeemed or repurchased. The Notes will be convertible into shares of our common stock at a conversion rate of 8.7237 shares of common stock per $1,000 principal amount of the 4.25 % Convertible Notes, which represents a conversion price of approximately $114.63 per share.  The conversion rate is subject to adjustment from time to time upon the occurrence of certain events, including, but not limited to, the issuance of certain stock dividends on common stock, the issuance of certain rights or warrants, subdivisions, combinations, distributions of capital stock, indebtedness, or assets, the payment of cash dividends and certain tender or exchange offers.

We may not redeem the 4.25% Convertible Notes prior to April 6, 2019. However, the holders may convert their 4.25% Convertible Notes at any time prior to the close of business on the business day immediately preceding January 1, 2021 only under certain circumstances. Upon conversion, we will deliver a number of shares of our common stock equal to the conversion rate in effect on the conversion date. In addition to the holder option to convert, the 4.25% Convertible Notes may be redeemed upon the occurrence of certain events.

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No "sinking fund" is provided for the 4.25% Convertible Notes, which means that we are not required to periodically redeem or retire the 4.25% Convertible Notes.  If we undergo a "fundamental change", as defined in the April 2015 Indenture, subject to certain conditions, holders may require us to repurchase for cash all or part of their 4.25% Convertible Notes in principal amounts of $1,000 or an integral multiple thereof. The fundamental change repurchase price will be equal to 100% of the principal amount of the 4.25% Convertible Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.  The April 2015 Indenture does not contain any financial or operating covenants or restrictions on the payments of dividends, the incurrence of indebtedness or the issuance or repurchase of securities by us or any of our subsidiaries. The April 2015 Indenture does not contain covenants or other provisions to afford protection to holders of the 4.25% Convertible Notes in the event of a fundamental change or other corporate transaction involving it except to the extent described above.

The April 2015 Indenture also provides for customary events of default. If an event of default (other than certain events of bankruptcy, insolvency or reorganization involving us) occurs and is continuing, the April 2015 Trustee by notice to us, or the holders of at least 25% in principal amount of the outstanding 4.25% Convertible Notes by written notice to us and the April 2015 Trustee, may declare 100% of the principal of and accrued and unpaid interest, if any, on all of the 4.25% Convertible Notes to be due and payable. Upon such a declaration of acceleration, such principal and accrued and unpaid interest, if any, will be due and payable immediately. Upon the occurrence of certain events of bankruptcy, insolvency or reorganization involving us, 100% of the principal of and accrued and unpaid interest, if any, on all of the 4.25% Convertible Notes will become due and payable automatically. Notwithstanding the foregoing, the April 2015 Indenture provides that, to the extent we elect and for up to 270 days, the sole remedy for an event of default relating to certain failures by us to comply with certain reporting covenants in the Indenture consists exclusively of the right to receive additional interest on the 4.25% Convertible Notes.

On July 20, 2017, we entered into the July 2017 Exchange Agreement with certain holders of the 4.25% Convertible Notes, or the Supporting Holders, pursuant to which, among other things, our wholly-owned subsidiary, Pernix Ireland Pain Limited, or PIPL, issued $36,242,500 aggregate principal amount of PIPL's 4.25%/5.25% Exchangeable Senior Notes due 2022, or the Exchangeable Notes, in exchange for the tender to PIPL of $51.8 million aggregate principal amount of the 4.25% Convertible Notes held by the Supporting Holders. The Exchangeable Notes are governed by the terms of an Indenture, or the July 2017 Indenture, among PIPL, us and our subsidiaries party thereto as guarantors and Wilmington Trust, National Association, or the July 2017 Trustee, which was entered into on July 21, 2017. Subsequent to the execution of the July 2017 Indenture, on August 9, 2017, PIPL changed its name and form of organization under Irish law to Pernix Ireland Pain Designated Activity Company, or PIP DAC, remaining the primary obligor with respect to the July 2017 Indenture.

The Exchangeable Notes are senior, unsecured obligations of PIP DAC. Interest on the Exchangeable Notes will be paid in cash or a combination of cash and in-kind interest at PIP DAC's election. Interest paid in cash, or the All Cash Method, will accrue at a rate of 4.25% per annum, while interest paid in a combination of cash and in-kind will accrue at a rate of 5.25% per annum, with 2.25% per annum of interest (plus additional interest, if any) capitalized to the principal amount of the Exchangeable Notes, and the balance paid in cash. The maturity date of the Exchangeable Notes Indenture is July 15, 2022.

The Exchangeable Notes initially are exchangeable into shares of our common stock at an exchange price per share of $5.50, or the Exchange Price. The Exchange Price is subject to adjustment from time to time upon the occurrence of certain events, including, but not limited to, the issuance of certain stock dividends on our common stock, the issuance of certain rights or warrants, subdivisions, combinations, distributions of capital stock, indebtedness, or assets, the payment of cash dividends or certain tender or exchange offers.

Holders may exchange all or a portion of their Exchangeable Notes at their option at any time prior to the close of business on the second scheduled trading day immediately preceding the maturity date.

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Upon not less than 30 nor more than 45 trading days' notice, if the daily VWAP, as defined in the July 2017 Indenture, of our common stock has been at least 120% of the Exchange Price then in effect for at least 20 trading days (whether or not consecutive) during any 30 consecutive trading day period ending on, and including, the trading day immediately preceding the date on which such notice of redemption is provided, we will have the right to redeem any or all of the Exchangeable Notes at a price equal to 100% of the principal amount thereof (including any interest capitalized thereto) plus accrued interest that has not been paid or capitalized to, but excluding, the date on which the Exchangeable Notes are to be redeemed. The redemption price will be paid in cash.

No "sinking fund" will be provided for the Exchangeable Notes, which means that PIP DAC will not be required to periodically redeem or retire the Exchangeable Notes. If we or PIP DAC undergoes a fundamental change, as defined below, subject to certain conditions, holders of the Exchangeable Notes may require PIP DAC to repurchase for cash all or part of their Exchangeable Notes. The fundamental change repurchase price will be equal to 100% of the principal amount (including any interest capitalized thereto) of the Exchangeable Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the date, chosen by PIP DAC, that is not less than 20 business days or more than 35 business days following the date on which notice of the fundamental change was provided by PIP DAC.

Under the July 2017 Indenture, a "fundamental change" will be deemed to have occurred if, among other events, any of the following occurs: (i) any "group" or "person," within the meaning of Section 13(d) of the Exchange Act, other than a permitted holder under the July 2017 Indenture, becomes the direct or indirect "beneficial owner," as defined in Rule 13d-3 under the Exchange Act, of our common stock representing more than 50% of our voting power; (ii) we consummate any recapitalization, reclassification or change of our common stock, subject to certain exceptions as contained in the July 2017 Indenture; (iii) we effect any share exchange, consolidation or merger pursuant to which our common stock will be converted into cash, securities or other property or assets; (iv) we effect any sale, lease or other transfer in one transaction or a series of transactions of all or substantially all of our consolidated assets to a person or entity other than a permitted holder under the July 2017 Indenture; (v) our stockholders approve a plan or proposal for our liquidation or dissolution or the liquidation or dissolution of PIP DAC; or (vi) our common stock ceases to be listed on The New York Stock Exchange, The Nasdaq Global Select Market or The Nasdaq Global Market (or any of their respective successors).

Holders of the Exchangeable Notes are entitled to receive, in certain circumstances, additional shares of our common stock upon exchanges of Exchangeable Notes in connection with a provisional redemption or certain fundamental changes.

Subject to certain limited exceptions, the Exchangeable Notes contain covenants which prohibit or limit the ability of PIP DAC and the guarantors under the July 2017 Indenture to, among other things: (i) pay cash dividends or make distributions on our capital stock or redeem or repurchase our capital stock; (ii) create, assume or suffer to exist at any time any lien upon any of our properties or assets; (iii) incur any debt other than debt permitted under the terms of the Exchangeable Notes Indenture; (iv) enter into transactions with affiliates other than on terms and conditions that, taken as a whole, would be obtained in an arm's-length transaction with non- affiliates; or (v) make any sale of our assets and the assets of our subsidiaries except in accordance with the terms of the July 2017 Indenture.

The July 2017 Indenture also provides for customary events of default. If an event of default (other than certain events of bankruptcy, insolvency or reorganization involving PIP DAC) occurs and is continuing, the July 2017 Trustee by notice to PIP DAC, or the holders of at least 25% in principal amount of the then outstanding Exchangeable Notes by written notice to PIP DAC and the July 2017 Trustee, may declare 100% of the accreted principal of and accrued and unpaid interest, if any, on all of the Exchangeable Notes to be due and payable immediately. Upon the occurrence of certain events of bankruptcy, insolvency or reorganization involving PIP DAC, 100% of the principal of and accrued and unpaid interest, if any, on all of the Exchangeable Notes will become due and payable automatically, including a make-whole premium in an amount equal to the present value of the interest that would accrue on such Exchangeable Notes (assuming the All Cash Method) from, and including, such date of acceleration until the maturity date of the Exchangeable Notes, with such present value computed using a discount rate equal to the sum of (i) the yield to maturity of United States Treasury securities with remaining maturity equal to that of the Exchangeable Notes (as determined in a commercially reasonable manner by PIP DAC) on such date of acceleration and (ii) 50 basis points. Notwithstanding the foregoing, for up to 270 days after the occurrence of an event of default, PIP DAC may elect to have the sole remedy for an event of default relating to certain of PIP DAC's failures to comply with certain reporting covenants in the July 2017 Indenture consist exclusively of the right to receive additional interest on the Exchangeable Notes.

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Holders of Exchangeable Notes will not be entitled to receive shares of our common stock upon exchange of any Exchangeable Notes to the extent such holder (or group of which such holder is a part) would beneficially own more than 9.99% of the outstanding shares of our common stock. Subject to such limitation, at the initial Exchange Price, the Exchangeable Notes will be exchangeable into approximately 40% of our outstanding common stock as of the date hereof (after giving effect to the issuance of 1,100,498 shares of our common stock to certain Holders of the Exchangeable Notes in connection with the July 2017 Exchange Agreement and the common stock underlying the Exchangeable Notes).

The following, together with the additional information we may include in the applicable prospectus supplement or free writing prospectus, summarizes the material terms and provisions of the units that we may offer under this prospectus. While the terms summarized below will apply generally to any units we may offer, we will describe the particular terms of any series of units in more detail in the applicable prospectus supplement or free writing prospectus.

We may, from time to time, issue units comprised of one or more of the other securities that may be offered under this prospectus, in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately at any time, or at any time before a specified date.

We will describe in the applicable prospectus supplement or free writing prospectus the terms of the series of units, including:

We may issue units in such amounts and in numerous distinct series as we determine.

As specified in any applicable prospectus supplement or free writing prospectus, we may issue subscription rights consisting of one or more debt securities, shares of preferred stock, shares of common stock or any combination of such securities.

We may sell the securities being offered by this prospectus separately or together:

• directly to purchasers;
• through agents;
• to or through underwriters;

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• through dealers;
• through a block trade in which the broker or dealer engaged to handle the block trade will attempt to sell the securities as agent, but may position and resell a portion of the block as principal to facilitate the transaction; or
• through a combination of any of these methods of sale.

In addition, we may issue the securities being offered by this prospectus as a dividend or distribution or in a subscription rights offering to our existing security holders. This prospectus may be used in connection with any offering of our securities through any of these methods or other methods described in the applicable prospectus supplement or free writing prospectus.

We may effect the distribution of the securities from time to time in one or more transactions:

• at a fixed price, or prices, which may be changed from time to time;
• at market prices prevailing at the time of sale;
• at prices related to such prevailing market prices; or
• at negotiated prices.

For example, we may engage in at-the-market offerings into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act. We may also sell securities through a rights offering, forward contracts or similar arrangements. In any distribution of subscription rights to shareholders, if all of the underlying securities are not subscribed for, we may then sell the unsubscribed securities directly to third parties or may engage the services of one or more underwriters, dealers or agents, including standby underwriters, to sell the unsubscribed securities to third parties.

The securities issued and sold under this prospectus will have no established trading market, other than our common stock, which is listed on Nasdaq. Any shares of our common stock sold pursuant to this prospectus will be eligible for listing and trading on the Nasdaq, subject to official notice of issuance. Any underwriters to whom securities are sold by us for public offering and sale may make a market in the securities, but the underwriters will not be obligated to do so and may discontinue any market making at any time without notice. The securities, other than our common stock, may or may not be listed on a national securities exchange or other trading market.

We will set forth in a prospectus supplement or free writing prospectus:

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If we sell directly to institutional investors or others, they may be deemed to be underwriters within the meaning of the Securities Act with respect to any resale of the securities. Unless otherwise indicated in a prospectus supplement or free writing prospectus, if we sell through an agent, such agent will be acting on a best efforts basis for the period of its appointment. Any agent may be deemed to be an "underwriter" of the securities as that term is defined in the Securities Act.  If a dealer is used in the sale of the securities, we or an underwriter will sell securities to the dealer, as principal. The dealer may resell the securities to the public at varying prices to be determined by the dealer at the time of resale.

We may authorize agents, underwriters and dealers to solicit offers by certain institutional investors to purchase offered securities under contracts providing for payment and delivery on a future date specified in a prospectus supplement or free writing prospectus. The prospectus supplement or free writing prospectus will also describe the public offering price for the securities and the commission payable for solicitation of these delayed delivery contracts. Delayed delivery contracts will contain definite fixed price and quantity terms. The obligations of a purchase under these delayed delivery contracts will be subject to only two conditions:

• that the institution's purchase of the securities at the time of delivery of the securities is not prohibited under the law of any jurisdiction to which the institution is subject; and
• that we shall have sold to the underwriters the total principal amount of the offered securities, less the principal amount covered by the delayed contracts.

To the extent permitted by and in accordance with Regulation M under the Securities Exchange Act of 1934, as amended, or the Exchange Act, in connection with an offering an underwriter may engage in over-allotments, stabilizing transactions, short covering transactions and penalty bids. Over-allotments involve sales in excess of the offering size, which creates a short position. Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum. Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a covering transaction to cover short positions. Those activities may cause the price of the securities to be higher than it would be otherwise. If commenced, the underwriters may discontinue any of the activities at any time.

To the extent permitted by and in accordance with Regulation M under the Exchange Act, any underwriters who are qualified market makers on Nasdaq may engage in passive market making transactions in the securities on Nasdaq during the business day prior to the pricing of an offering, before the commencement of offers or sales of the securities. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker's bid, however, the passive market maker's bid must then be lowered when certain purchase limits are exceeded.

The specific terms of any lock-up provisions in respect of any given offering will be described in the applicable prospectus supplement or free writing prospectus.

The underwriters, dealers and agents may engage in transactions with us, or perform services for us, in the ordinary course of business for which they receive compensation.

No securities may be sold under this prospectus without delivery, in paper format or in electronic format, or both, of the applicable prospectus supplement or free writing prospectus describing the method and terms of the offering.

The validity of the issuance of the securities offered hereby will be passed upon for us by Hogan Lovells US LLP, Philadelphia, Pennsylvania. As appropriate, legal counsel representing the underwriters, dealers or agents will be named in the accompanying prospectus supplement and may opine to certain legal matters.

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EXPERTS

Cherry Bekaert LLP, independent registered public accounting firm, has audited our consolidated financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2016, which is incorporated by reference in this prospectus and elsewhere in the registration statement. These financial statements are incorporated by reference in reliance on Cherry Bekaert LLP's report, given on their authority as experts in accounting and auditing.

The SEC allows us to "incorporate by reference" information from other documents that we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus.

We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC:

• our Annual Report on Form 10-K for the fiscal year ended December 31, 2016 filed with the SEC on March 28, 2017, as amended by our Annual Report on Form 10-K/A filed with the SEC on May 1, 2017;
• our Quarterly Reports on Form 10-Q for the fiscal quarters ended March 31, 2017, June 30, 2017 and September 30, 2017, filed with the SEC on May 15, 2017, July 27, 2017 and November 7, 2017, respectively;
• our Current Reports on Form 8-K as filed on February 3, 2017, March 21, 2017, April 20, 2017, July 20, 2017 (including Item 2.02 and Exhibit 99.1), July 20, 2017 (except Item 7.01 and Exhibits 99.1 and 99.2), as amended by our Current Report on Form 8-K/A filed with the SEC on July 21, 2017, August 15, 2017, September 22, 2017, October 17, 2017, November 7, 2017 (except Item 2.02 and Exhibit 99.1) and November 15, 2017; and
• the description of our capital stock contained in Form 8-A filed with the SEC on February 7, 1997, as amended by that certain Form 8-A filed with the SEC on March 15, 2010, including any amendment or report filed for the purpose of updating such description.

In addition, all documents that we file with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of the initial registration statement of which this prospectus is a part and prior to the effectiveness of such registration statement and all such documents that we file with the SEC after the date of this prospectus and before the termination of the offering of our securities shall be deemed incorporated by reference into this prospectus and to be a part of this prospectus from the respective dates of filing such documents.

Any statement contained in a document incorporated by reference in this prospectus shall be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus or in any other subsequently filed document that also is or is deemed to be incorporated by reference in this prospectus modifies or supersedes such statement. Any statement so modified or superseded shall not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

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You may request, orally or in writing, a copy of any or all of the documents incorporated herein by reference. These documents will be provided to you at no cost, by contacting our investor relations department at the following address and telephone number: Pernix Therapeutics Holdings, Inc., 10 North Park Place, Suite 201, Morristown, New Jersey 07960, (800) 793-2145. In addition, copies of any or all of the documents incorporated herein by reference may be accessed at our website at http://www.pernixtx.com. The information on such website is not incorporated by reference and is not a part of this prospectus.

We file annual, quarterly and current reports, proxy statements and other information with the SEC. You may read and copy any document we file with the SEC at the SEC's public reference room at 100 F Street NE, Room 1580, Washington, D.C. 20549. You may obtain information on the operation of the SEC's public reference facilities by calling the SEC at 1-800-SEC-0330. You can request copies of these documents, upon payment of a duplicating fee, by writing to the SEC at its principal office at 100 F Street NE, Room 1580, Washington, D.C. 20549-1004. The SEC maintains an Internet website at http://www.sec.gov that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the SEC. Our SEC filings are accessible through the Internet at that website. Our reports on Forms 10-K, 10-Q and 8-K, and amendments to those reports, are also available for download, free of charge, as soon as reasonably practicable after these reports are filed with the SEC, at our website at http://www.pernixtx.com. The content contained in, or that can be accessed through, our website is not a part of this prospectus.

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