Exhibit 99.1

AMENDMENT TO ARRANGEMENT AGREEMENT

This amendment (the “Amendment”) is made as of the 16th day of January, 2024,

BETWEEN:

CEAPRO INC., a corporation existing under the federal laws of Canada (“Ceapro”);

AND:

AETERNA ZENTARIS INC., a corporation existing under the federal laws of Canada (“Aeterna Zentaris”)

WHEREAS Ceapro and Aeterna Zentaris (the “Parties”) entered into an arrangement agreement dated December 14, 2023 (the “Arrangement Agreement”) setting out the terms and conditions of a plan of arrangement (as amended from time to time, the “Plan of Arrangement”) which provides for, among other things, and subject to the terms and conditions thereof (i) the acquisition by Aeterna Zentaris of all of the issued and outstanding common shares in the share capital of Ceapro (the “Shares”) from the shareholders of Ceapro (the “Shareholders”), which Shares will be exchanged for common shares of Aeterna Zentaris (the “Aeterna Zentaris Shares”) at the exchange ratio (the “Exchange Ratio”) set forth in the Arrangement Agreement, and (ii) the replacement of each of the outstanding options to purchase Shares granted under or otherwise subject to the 2023 amended and restated stock option plan of the Corporation approved by the Shareholders on June 6, 2023, as amended from time to time, for replacement options allowing their holders to acquire Aeterna Zentaris Shares on similar terms, as adjusted by the Exchange Ratio, by way of a statutory plan of arrangement (the “Arrangement”) under Section 192 of the Canada Business Corporations Act, a copy of which is attached as Schedule A to the Arrangement Agreement;

AND WHEREAS on the date hereof the Parties wish to amend the Plan of Arrangement in accordance with Section 5.01(a) of the Plan of Arrangement;

NOW THEREFORE THIS AMENDMENT WITNESSES THAT in consideration of the respective covenants and agreements of the Parties herein contained and for other good and valuable consideration (the receipt and sufficiency of which are hereby acknowledged), the Parties agree as follows:

1. Amended and Restated Plan of Arrangement

The Parties hereby agree to replace the Plan of Arrangement in its entirety by the amended and restated Plan of Arrangement attached hereto as Schedule A.

2. General

The Parties hereby confirm that the Arrangement Agreement remains in full force and effect, unamended, other than as provided in Section 1 hereof.

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IN WITNESS WHEREOF this Amendment has been executed by the Parties as of the date first above written.

SCHEDULE A

PLAN OF ARRANGEMENT

UNDER SECTION 192 OF THE

CANADA BUSINESS CORPORATIONS ACT

ARTICLE 1 DEFINITIONS AND INTERPRETATION

Section 1.01 Definitions

In this Plan of Arrangement, any capitalized term used herein and not defined in this Section 1.01 shall have the meaning ascribed thereto in the Arrangement Agreement. Unless the context otherwise requires, the following words and terms with the initial letter or letters thereof capitalized shall have the meanings ascribed to them below:

In addition, words and phrases used herein and defined in the CBCA and not otherwise defined herein shall have the same meaning herein as in the CBCA unless the context otherwise requires.

Section 1.02 Interpretation Not Affected by Headings

The division of this Plan of Arrangement into Articles, Sections, paragraphs and the insertion of headings are for convenience of reference only and shall not affect in any way the meaning or interpretation of this Plan of Arrangement. Unless the contrary intention appears, references in this Plan of Arrangement to an Article, Section or paragraph by number or letter or both refer to the Article, Section or paragraph, respectively, bearing that designation in this Plan of Arrangement.

Section 1.03 Number, Gender and Persons

In this Plan of Arrangement, unless the context otherwise requires, words importing the singular shall include the plural and vice versa, words importing gender include all genders and the word person and words importing persons shall include a natural person, firm, trust, partnership, association, corporation, joint venture or government (including any governmental agency, political subdivision or instrumentality thereof) and any other entity or group of persons of any kind or nature whatsoever.

Section 1.04 Date for any Action

Unless otherwise expressly stated, if the date on or by which any action is required or permitted to be taken hereunder by a Party is not a Business Day, such action shall be required or permitted to be taken on the next succeeding day which is a Business Day.

Section 1.05 Statutory References

Any reference to a statute refers to such statute, or successor thereto, and all rules, resolutions and regulations made under it, or its successor, respectively, as it or its successor, or they, may have been or may from time to time be amended or re-enacted, unless stated otherwise.

Section 1.06 Currency

Unless otherwise stated, all references herein to sums of money are expressed in lawful money of the United States and “$” or “USD$” refers to United States dollars.

Section 1.07 Governing Law

This Plan of Arrangement shall be governed, including as to validity, interpretation and effect, by the laws of the Province of Alberta and the laws of Canada applicable therein. All questions as to the interpretation or application of this Plan of Arrangement and all proceedings taken in connection with the Plan of Arrangement shall be subject to the exclusive jurisdiction of the Court.

ARTICLE 2 ARRANGEMENT

Section 2.01 Arrangement Agreement

This Plan of Arrangement is made pursuant to, and is subject to the provisions of, and forms part of, the Arrangement Agreement. If there is any inconsistency or conflict between the provisions of this Plan of Arrangement and the provisions of the Arrangement Agreement, the provisions of this Plan of Arrangement shall govern.

Section 2.02 Binding Effect

This Plan of Arrangement constitutes an arrangement as referred to in section 192 of the CBCA. The Arrangement will become effective at, and be binding at and after, the times referred to in Section 2.04 of this Plan of Arrangement on: (i) Ceapro; (ii) Aeterna Zentaris (iii) all Ceapro Securityholders (including Dissenting Shareholders); and (iv) the Depositary, without any further act or formality required on the part of any person, except as expressly provided herein.

Section 2.03 Prior Issuance of Aeterna Zentaris New Warrants

Immediately prior to the Effective Date and not through the effect of the filing of the Articles of Arrangement and the issuance of the Certificate of Arrangement, Aeterna Zentaris shall issue 2,534,424 Aeterna Zentaris New Warrants to the holders of Aeterna Zentaris Shares and the holders of Aeterna Zentaris Adjusted Warrants.

Section 2.04 Arrangement

The following events shall occur and shall be deemed to occur sequentially as set out below, and, except as otherwise set forth herein, without any further authorization, act or formality, in each case, unless stated otherwise, effective as at two-minute intervals starting at the Effective Time (unless otherwise indicated):

Section 2.05 No Liens

Any exchange or transfer of securities pursuant to this Plan of Arrangement shall be free and clear of any Liens or other claims of third parties of any kind.

Section 2.06 No Fractional Consideration

No fractional Aeterna Zentaris Shares shall be issued to Former Ceapro Shareholders under this Plan of Arrangement. The number of Aeterna Zentaris Shares to be issued to Former Ceapro Shareholders shall be rounded down to the nearest whole Aeterna Zentaris Share in the event that a Former Ceapro Shareholder is entitled to a fractional share without any additional compensation in lieu of such fractional share.

Section 2.07 U.S. Tax Matters

For U.S. federal (and applicable state and local) income tax purposes, (i) the Arrangement is intended to be treated as a “reorganization” within the meaning of Section 368(a) of the Code and (ii) the Arrangement Agreement and this Plan of Arrangement are intended to constitute a “plan of reorganization” within the meaning of the United States Treasury Regulation Section 1.368-2(g) (clauses (i) and (ii), collectively, the “Intended U.S. Tax Treatment”). The Parties (i) agree to report consistently with the Intended U.S. Tax Treatment on their income tax returns, and to not take any position for applicable income tax purposes (whether in the conduct of an audit, preparation of tax returns, or otherwise; provided that such position shall not preclude a Party from settling or otherwise resolving an audit) that is inconsistent therewith and (ii) agree to not take any action, or knowingly fail to take any action, if such action or failure to act would reasonably be expected to prevent the Arrangement from being treated inconsistently with the Intended U.S. Tax Treatment.

ARTICLE 3 DISSENT RIGHTS

Section 3.01 Dissent Rights

Each registered holder of Ceapro Shares may exercise dissent rights with respect to Ceapro Shares held by such Dissenting Shareholder (“Dissent Rights”), in connection with the Arrangement pursuant to and in the manner set forth in Section 190 of the CBCA, as modified by the Interim Order and this Section 3.01; provided that, notwithstanding Section 190(5) of the CBCA, the written objection to the Arrangement Resolution referred to in Section 190(5) of the CBCA must be received by Ceapro not later than 48 hours (excluding Saturday, Sundays and statutory holidays in Edmonton, Alberta) prior to the Ceapro Meeting. Each Dissenting Shareholder who duly exercises its Dissent Rights in accordance with this Section 3.01, shall be deemed to have transferred all Ceapro Shares held by such Dissenting Shareholder and in respect of which Dissent Rights have been validly exercised, to Ceapro, as provided in Section 2.04(b) of this Plan of Arrangement and if such Dissenting Shareholder:

Section 3.02 Recognition of Dissenting Shareholders

ARTICLE 4 DELIVERY OF AETERNA ZENTARIS SHARES

Section 4.01 Delivery of Aeterna Zentaris Shares

Section 4.02 Lost Certificates

In the event any certificate, that immediately prior to the Effective Time represented one or more outstanding Ceapro Shares that were exchanged for Aeterna Zentaris Shares in accordance with Section 2.04 of this Plan of Arrangement, shall have been lost, stolen or destroyed, upon the making of an affidavit of that fact by the holder claiming such certificate to be lost, stolen or destroyed, the Depositary shall deliver in exchange for such lost, stolen or destroyed certificate, a certificate or DRS Advice representing the Aeterna Zentaris Shares that such holder is entitled to receive in accordance with Section 2.04 of this Plan of Arrangement. When authorizing such delivery of certificates or DRS Advice representing Aeterna Zentaris Shares that such holder is entitled to receive in exchange for such lost, stolen or destroyed certificate, the holder to whom certificates or DRS Advice representing such Aeterna Zentaris Shares is to be delivered shall, as a condition precedent to the delivery of such Aeterna Common Zentaris Shares, give a bond satisfactory to Aeterna Zentaris and the Depositary in such amount as Aeterna Zentaris and the Depositary may reasonably direct, or otherwise indemnify Aeterna Zentaris and the Depositary in a manner satisfactory to Aeterna Zentaris and the Depositary, each acting reasonably, against any claim that may be made against Aeterna Zentaris or the Depositary with respect to the certificate alleged to have been lost, stolen or destroyed.

Section 4.03 Distributions with Respect to Unsurrendered Certificates

No dividend or other distribution declared or made after the Effective Time with respect to Aeterna Zentaris Shares with a record date after the Effective Time shall be delivered to the holder of any unsurrendered certificate or DRS Advice that, immediately prior to the Effective Time, represented outstanding Ceapro Shares unless and until the holder of such certificate or DRS Advice shall have complied with the provisions of Section 4.01 or Section 4.02 of this Plan of Arrangement. Subject to applicable law and to Section 4.04 of this Plan of Arrangement, at the time of such compliance, there shall, in addition to the delivery of certificates or DRS Advice representing Aeterna Zentaris Shares to which such holder is thereby entitled, be delivered to such holder, without interest, the amount of the dividend or other distribution with a record date after the Effective Time theretofore paid with respect to such Aeterna Zentaris Shares.

Section 4.04 Adjustment to Share Consideration

The number of Aeterna Zentaris Shares, if any, that a Ceapro Shareholder is entitled to receive as Consideration pursuant to Section 2.04(c) of this Plan of Arrangement shall be adjusted to reflect fully the effect of any share split, reverse split or split dividend (including any dividend or distribution of securities convertible into Aeterna Zentaris Shares), consolidation, reorganization, recapitalization or other similar change with respect to Aeterna Zentaris Shares occurring after the date of the Arrangement Agreement and prior to the Effective Time; provided, however, for the avoidance of doubt, no adjustment shall be made as a result of the issuance of Aeterna Zentaris New Warrants or any Aeterna Zentaris Shares issuable upon the exercise thereof.

Section 4.05 Withholding Rights

Aeterna Zentaris, Ceapro and the Depositary shall be entitled to deduct and withhold from any consideration payable or otherwise deliverable to any person hereunder and from all dividends or other distributions otherwise payable to any Former Ceapro Shareholders such amounts as Aeterna Zentaris, Ceapro or the Depositary may be required or permitted to deduct and withhold therefrom under the Tax Act, the Code or any provision of any other applicable Laws. To the extent that such amounts are so deducted, withheld and remitted, such amounts shall be treated for all purposes under this Agreement as having been paid to the person to whom such amounts would otherwise have been paid, provided that such deducted or withheld amounts are actually remitted to the appropriate taxation authority. To the extent the amount required to be deducted or withheld from any consideration payable or otherwise deliverable to any person hereunder exceeds the amount of cash consideration, if any, otherwise payable to the person, any of Aeterna Zentaris, Ceapro or the Depository is hereby authorized to sell or otherwise dispose of any non-cash consideration payable to the person as is necessary to provide sufficient funds to Aeterna Zentaris, Ceapro or the Depository, as the case may be, to enable it to comply with all deduction or withholding requirements applicable to it, and Aeterna Zentaris, Ceapro and the Depository shall notify such person and remit to such person any unapplied balance of the net proceeds of such sale. If any withholding Tax is assessed against and paid by Aeterna Zentaris, Ceapro or the Depositary, then the Former Ceapro Shareholders in respect of which such deduction or withholding should have been made will indemnify and hold harmless such withholding agent from and against such Tax, but only to the extent such Former Ceapro Shareholders actually received the amount that should have been deducted or withheld.

Section 4.06 U.S. Securities Laws Matters

Notwithstanding any provision herein to the contrary, this Plan of Arrangement will be carried out with the intention that all Aeterna Zentaris Shares issued to Ceapro Shareholders in exchange for Ceapro Shares and all Replacement Options issued to Ceapro Optionholders in exchange for Ceapro Options pursuant to this Plan of Arrangement, as applicable, will be issued and exchanged in reliance on the exemption from the registration requirements of the U.S. Securities Act as provided by section 3(a)(10) thereof and applicable state securities laws, and pursuant to the terms, conditions and procedures set forth in the Arrangement Agreement.

Section 4.07 Extinction of Rights

To the extent that a Former Ceapro Shareholder shall not have complied with the provisions of Section 4.01 or Section 4.02 of this Plan of Arrangement on or before the date that is six years after the Effective Date, then the certificate or DRS Advice which immediately prior to the Effective Time represented outstanding Ceapro Shares held by such Former Ceapro Shareholder shall cease to represent a claim or interest of any kind or nature whatsoever, whether as a securityholder or otherwise and whether against Ceapro, Aeterna Zentaris, the Depositary or any other person. On such date, the Consideration to which such Former Ceapro Shareholder would otherwise have been entitled to receive, together with any distributions or dividends such holder would otherwise have been entitled to receive shall be deemed to have been surrendered for no consideration to Aeterna Zentaris. Neither Ceapro nor Aeterna Zentaris will be liable to any person in respect of any cash or securities which is forfeited to Aeterna Zentaris or delivered to any public official pursuant to any applicable abandoned property or similar law.

ARTICLE 5 AMENDMENTS AND WITHDRAWAL

Section 5.01 Amendments to Plan of Arrangement

Section 5.02 Withdrawal

This Plan of Arrangement may be withdrawn prior to the Effective Time in accordance with the terms of the Arrangement Agreement. Upon termination of this Plan of Arrangement pursuant to the terms of the Arrangement Agreement, no Party shall have any liability or further obligation to any other Party hereunder other than as set out in the Arrangement Agreement.

ARTICLE 6 MISCELLANEOUS

Section 6.01 Further Assurances

Notwithstanding that the transactions and events set out herein shall occur and shall be deemed to occur in the order set out in this Plan of Arrangement without any further act or formality, each of the parties to the Arrangement Agreement shall make, do and execute, or cause to be made, done and executed, all such further acts, deeds, agreements, transfers, assurances, instruments or documents as may reasonably be required by either of them in order further to document or evidence any of the transactions or events set out herein.

Section 6.02 Paramountcy

From and after the Effective Time: