Exhibit 10.46

[Idenix Letterhead]

September 9, 2013

David Standring

205 Gun Hill Street

Milton, MA 02186

Dear David:

As we have discussed, your employment with Idenix Pharmaceuticals, Inc.
(“Idenix” or the “Company”) will end on September 9, 2013. The Company will
provide you with the severance benefits described in paragraph 2 below if you
sign and return this letter agreement (the “Agreement”) to me on or before
October 25th, 2013 (i.e. within 45 days from your receipt of this Agreement) —
but no earlier than the close of business on September 9, 2013, and the
Agreement becomes binding between you and the Company.

By timely signing and returning this Agreement and not revoking your acceptance,
you will be entering into a binding agreement with the Company and will be
agreeing to the terms and conditions set forth in the numbered paragraphs below,
including the release of claims set forth in paragraph 3. Therefore, you are
advised to consult with an attorney before signing this Agreement and you have
been given up to forty-five (45) days to do so. If you sign this Agreement, you
may change your mind and revoke your agreement during the seven (7) day period
after you have signed it by notifying me in writing. If you do not so revoke,
this Agreement will become a binding agreement between you and the Company upon
the expiration of the seven (7) day revocation period.

If you choose not to sign and return this Agreement in a timely manner as set
forth above, or if you timely revoke your acceptance in writing, you shall not
receive any of the severance payments or benefits under your restated employment
letter dated as of December 9, 2010 (the “Employment Letter”) from the Company.
Whether or not this Agreement becomes effective, you will receive payment on
your Termination Date, as defined herein, for (i) your final wages and (ii) any
unused vacation time accrued through the Termination Date. You may also, if
eligible, elect to continue receiving group medical insurance pursuant to the
federal “COBRA” law, 29 U.S.C. § 1161 et seq. Please consult the COBRA materials
to be provided by the Company under separate cover for details regarding these
benefits. Except as provided for herein, all other benefits and all unvested
stock rights will be cancelled on the Termination Date.

The following numbered paragraphs set forth the terms and conditions that will
apply if you timely sign and return this Agreement and do not revoke it in
writing within the seven (7) day period.

 

1. Termination Date — Your effective date of termination from the Company is
September 9, 2013 (the “Termination Date”). As of the Termination Date, all
salary payments from the Company will cease and any benefits you had as of the
Termination Date under Company-provided benefit plans, programs, or practices
will terminate, except as required by federal or state law.

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Description of Severance Benefits — If you timely sign and return this Agreement
and do not revoke your acceptance, the Company will provide the severance
benefits in accordance with Section 7 of your Employment Letter with the Company
dated December 9, 2010 (the “Severance Benefits”). The Company shall pay any
severance pay in one lump sum cash payment (pursuant to the Employment Letter)
on the first payroll following the date that is six months after the Termination
Date.

In addition, outplacement services will be arranged for you for up to 6 months.
The use of the outplacement services must occur within the 12-week period
following your Termination Date. The cost of these outplacement services will be
paid by the Company.

 

2. You will not be eligible for, nor shall you have a right to receive, any
payments or benefits from the Company following the Termination Date other than
as described in this paragraph 2.

 

3.

Release — In consideration of the Severance Benefits, which you acknowledge you
would not otherwise be entitled to receive, you hereby fully, forever,
irrevocably and unconditionally release, remise and discharge the Company, its
affiliates, subsidiaries, parent companies, predecessors, and successors, and
all of their respective past and present officers, directors, stockholders,
partners, members, employees, agents, representatives, plan administrators,
attorneys, insurers and fiduciaries (each in their individual and corporate
capacities) (collectively, the “Released Parties”) from any and all claims,
charges, complaints, demands, actions, causes of action, suits, rights, debts,
sums of money, costs, accounts, reckonings, covenants, contracts, agreements,
promises, doings, omissions, damages, executions, obligations, liabilities, and
expenses (including attorneys’ fees and costs), of every kind and nature that
you ever had or now have against any or all of the Released Parties, including,
but not limited to, any and all claims arising out of or relating to your
employment with and/or separation from the Company, including, but not limited
to, all claims under Title VII of the Civil Rights Act of 1964, 42 U.S.C. §
2000e et seq., the Americans With Disabilities Act of 1990, 42 U.S.C. § 12101 et
seq., the Age Discrimination in Employment Act, 29 U.S.C. § 621 et seq., the
Genetic Information Nondiscrimination Act of 2008, 42 U.S.C. § 2000ff et seq.,
the Family and Medical Leave Act, 29 U.S.C. § 2601 et seq., the Worker
Adjustment and Retraining Notification Act (“WARN”), 29 U.S.C. § 2101 et seq.,
the Rehabilitation Act of 1973, 29 U.S.C. § 701 et seq., Executive Order 11246,
Executive Order 11141, the Fair Credit Reporting Act, 15 U.S.C. § 1681 et seq.,
and the Employee Retirement Income Security Act of 1974 (“ERISA”), 29 U.S.C. §
1001 et seq., all as amended; all claims arising out of the Massachusetts Fair
Employment Practices Act., Mass. Gen. Laws ch. 151B, § 1 et seq., the
Massachusetts Civil Rights Act, Mass. Gen. Laws ch. 12, §§ 11H and 11I, the
Massachusetts Equal Rights Act, Mass. Gen. Laws. ch. 93, § 102 and Mass. Gen.
Laws ch. 214, § 1C, the Massachusetts Labor and Industries Act, Mass. Gen. Laws
ch. 149, § 1 et seq., Mass. Gen. Laws ch. 214, § 1B (Massachusetts right of
privacy law), the Massachusetts Wage Payment Act, M.G.L. c. 149, § 148 et seq.
(the Massachusetts law regarding payment of wages), the Massachusetts Minimum
Fair Wages Act, Mass. Gen. Laws ch. 151, § 1 et seq. (the Massachusetts law
regarding minimum wages and overtime), the Massachusetts Maternity Leave Act,
Mass. Gen.

 

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  Laws ch. 149, § 105D, and the Massachusetts Small Necessities Leave Act, Mass.
Gen. Laws ch. 149, § 52D, all as amended; all common law claims including, but
not limited to, actions in defamation, intentional infliction of emotional
distress, misrepresentation, fraud, wrongful discharge, and breach of contract;
all claims to any non-vested ownership interest in the Company, contractual or
otherwise, and any claim or damage arising out of your employment with and/or
separation from the Company (including a claim for retaliation) under any common
law theory or any federal, state or local statute or ordinance not expressly
referenced above; provided, however, that nothing in this Agreement prevents you
from filing a charge with, cooperating with, or participating in any proceeding
before the Equal Employment Opportunity Commission or a state fair employment
practices agency (except that you acknowledge that you may not recover any
monetary benefits in connection with any such claim, charge or proceeding).

Notwithstanding any provision of this Agreement to the contrary, by executing
this Agreement, you are not releasing (i) any claims that cannot be waived by
law, (ii) your right of indemnification as provided by, and in accordance with
the terms of, the Company’s by-laws or a Company insurance policy providing such
coverage, as any of such may be amended from time to time, or (iii) any claims
relating to your rights as an equity holder of the Company.

 

4. Post-Separation Obligations — You acknowledge and reaffirm your obligation to
keep confidential and not to disclose any and all non-public information
concerning the Company that you acquired during the course of your employment
with the Company, including, but not limited to, any non-public information
concerning the Company’s business affairs, business prospects, and financial
condition. Your further acknowledge and reaffirm your obligations under Sections
11 and 12 of the Employment Letter, which remain in full force and effect and
the Employment Letter is fully incorporated herein by reference. You further
agree that you will, at the Company’s request, promptly execute a written
assignment of title for any development required to be assigned by the
Employment Letter, and perform all acts deemed necessary or desirable by the
Company to assist it (at its expense) in obtaining and enforcing the full
benefits, enjoyment, rights and title throughout the world in any such
developments, including without limitation executing declarations, affidavits,
etc. Such acts may include, but are not limited to, execution of documents and
assistance or cooperation in legal proceedings. Should the Company be unable to
secure your signature on any document necessary to apply for, prosecute, obtain,
or enforce any patent, copyright, or other right or protection relating to any
development, whether due to my mental or physical incapacity or any other cause,
you hereby irrevocably designate and appoint the Company and each of its duly
authorized officers and agents as your agent and attorney-in-fact, to undertake
such acts in your name as if executed and delivered by you, and you waive and
quitclaim to the Company any and all claims of any nature whatsoever that you
may now have or may later have for infringement of any intellectual property
rights in the Development. The Company or its representative will compensate you
$350.00 an hour for time you actually spend at the Company’s request on such
assistance at any time following the Termination Date.

 

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5. Non-Disparagement — You understand and agree that, in consideration of the
Severance Benefits, you shall not make any false, disparaging or derogatory
statements to any person or entity, including, without limitation, any media
outlet, industry group, financial institution or current or former employee,
consultant, client or customer of the Company, regarding the Company or any of
its directors, officers, employees, agents or representatives or about the
Company’s business affairs or financial condition; provided, however, that
nothing herein shall be construed as preventing you from making truthful
disclosures to any governmental entity or in any litigation or arbitration or as
otherwise required by applicable law.

 

6. Cooperation — To the full extent permitted by law, you agree to cooperate
with the Company in the defense or prosecution of any claims or actions which
already have been brought, are currently pending, or which may be brought in the
future against or on behalf of the Company, whether before a state or federal
court, any state or federal government agency, a mediator or arbitrator, U.S. or
foreign patent office, or foreign court or tribunal (“Litigation Assistance
Services”). The Company or its representative will pay you $350.00 per hour as a
consultant for provision of Litigation Assistance Services. The Company or its
representative shall reimburse you for reasonable out-of-pocket expenses
incurred at the request of the Company with respect to your compliance with this
section. Your full cooperation in connection with such claims or actions shall
include, but not be limited to, being available to meet with counsel to prepare
its claims or defenses, to prepare for trial or discovery or an administrative
hearing or a mediation or arbitration, to act as a witness, prepare affidavits,
declarations or otherwise provide assistance, when requested by the Company at
reasonable times. You agree that you will notify the Company promptly in the
event that you are served with a subpoena or in the event that you are asked to
provide a third party with information concerning any actual or potential
complaint or claim against the Company.

 

7. Return of Company Property — You represent and confirm that you have returned
to the Company all Company-owned property in your possession or control,
including, without limitation, all keys, files, documents and records (and
copies thereof), equipment (including, but not limited to, computer hardware,
software and printers, wireless handheld devices, cellular phones, pagers,
etc.), Company identification and Company vehicles, and that you have left
intact all electronic Company documents, including, without limitation, those
that you developed or helped to develop during your employment. You further
confirm that you have cancelled all accounts for your benefit, if any, in the
Company’s name, including, without limitation, credit cards, telephone charge
cards, cellular phone and/or pager accounts, and computer accounts.

 

8. Business Expenses and Compensation — You acknowledge that you have been
reimbursed by the Company for all business expenses incurred in conjunction with
the performance of your employment and that no other reimbursements are owed to
you. You further acknowledge that you have received payment in full for all
services rendered in conjunction with your employment by the Company, including,
without limitation, payment for all wages, bonuses, commissions and accrued,
unused vacation time, and that no other compensation is owed to you.

 

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9. Amendment and Waiver — This Agreement shall be binding upon the parties and
may not be modified in any manner, except by an instrument in writing of
concurrent or subsequent date signed by duly authorized representatives of the
parties hereto. This Agreement is binding upon and shall inure to the benefit of
the parties and their respective agents, assigns, heirs, executors, successors
and administrators. No delay or omission by the Company in exercising any right
under this Agreement shall operate as a waiver of that or any other right. A
waiver or consent given by the Company on any one occasion shall be effective
only in that instance and shall not be construed as a bar to or waiver of any
right on any other occasion.

 

10. Validity — Should any provision of this Agreement be declared or be
determined by any court of competent jurisdiction to be illegal or invalid, the
validity of the remaining parts, terms or provisions shall not be affected
thereby and said illegal or invalid part, term or provision shall be deemed not
to be a part of this Agreement.

 

11. Confidentiality — To the extent permitted by law, you understand and agree
that as a condition of the severance benefits herein described, the terms and
contents of this Agreement, and the contents of the negotiations and discussions
resulting in this Agreement, shall be maintained as confidential by you and your
agents and representatives and shall not be disclosed except to the extent
required by federal or state law, or as otherwise agreed to in writing by the
Company. Additionally, the Company may make such disclosure as part of its
filings pursuant to the federal securities regulations.

 

12. Tax Provision — In connection with the Severance Benefits to be provided to
you pursuant to this Agreement, the Company shall withhold and remit to the tax
authorities the amounts required under applicable law, and you shall be
responsible for all applicable taxes with respect to such Severance Benefits
under applicable law. You acknowledge that you are not relying upon advice or
representation of the Company with respect to the tax treatment of any of the
Severance Benefits.

 

13. Compliance with Section 409A — The severance payment and benefits shall be
subject to and compliant with any requirements provided under Section 409A of
the Internal Revenue Code of 1986, as amended (“Section 409A”). The Company
shall have no liability to you or any other person if the payments and benefits
provided that are intended to be exempt from or compliant with Section 409A are
not so exempt or compliant.

 

14. Nature of Agreement — You understand and agree that this Agreement is a
severance agreement and does not constitute an admission of liability or
wrongdoing on the part of the Company.

 

15.

Eligibility for Severance Program. Attached to this Agreement as Attachment A is
a description of (i) any class, unit or group of individuals covered by the
program of severance benefits which the Company has offered to you, and any
applicable time limits regarding such severance benefit program; and (ii) the
job title and ages of all individuals eligible or selected for such severance
benefit program, and the ages of all individuals in

 

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  the same job classification or organizational unit who are not eligible or who
were not selected for such severance benefit program.

 

16. Acknowledgments — You acknowledge that you have been given at least
forty-five (45) days to consider this Agreement, including Attachment A, and
that the Company advised you to consult with an attorney of your own choosing
prior to signing this Agreement. To the extent that you sign this Agreement
within less than forty-five (45) days, you acknowledge that such decision was
entirely voluntary and that you had a full forty-five (45) days in which to
consider the Agreement. You understand that you may revoke this Agreement for a
period of seven (7) days after you sign this Agreement by notifying me in
writing, and the Agreement shall not be effective or enforceable until the
expiration of this seven (7) day revocation period. You understand and agree
that by entering into this Agreement, you are waiving any and all rights or
claims you might have under The Age Discrimination in Employment Act (the
“ADEA”),, as amended by The Older Workers Benefit Protection Act, and that you
have received consideration beyond that to which you were previously entitled.
You also understand that this Agreement has no effect on any rights or claims
under the ADEA arising after the date that you sign this Agreement.

 

17. Voluntary Assent — You affirm that no other promises or agreements of any
kind have been made to or with you by any person or entity whatsoever to cause
you to sign this Agreement, and that you fully understand the meaning and intent
of this Agreement. You state and represent that you have had an opportunity to
fully discuss and review the terms of this Agreement, including Attachment A,
with an attorney. You further state and represent that you have carefully read
this Agreement, including Attachment A, understand the contents herein, freely
and voluntarily assent to all of the terms and conditions hereof, and sign your
name of your own free act.

 

18. Applicable Law — This Agreement shall be interpreted and construed by the
laws of the Commonwealth of Massachusetts, without regard to conflict of laws
provisions. You hereby irrevocably submit to and acknowledge and recognize the
jurisdiction of the courts of the Commonwealth of Massachusetts, or if
appropriate, a federal court located in Massachusetts (which courts, for
purposes of this Agreement, are the only courts of competent jurisdiction), over
any suit, action or other proceeding arising out of, under or in connection with
this Agreement or the subject matter hereof.

 

19. Entire Agreement — This Agreement, including Attachment A, contains and
constitutes the entire understanding and agreement between the parties hereto
with respect to your severance benefits and the settlement of claims against the
Company and cancels all previous oral and written negotiations, agreements,
commitments and writings in connection therewith. Nothing in this paragraph,
however, shall modify, cancel or supersede your obligations set forth in
paragraph 4 herein.

If you have any questions about the matters covered in this Agreement, please
call me at (617) 995-9884.

Very truly yours,

 

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IDENIX PHARMACEUTICALS, INC.

By:

  /s/ Paul Fanning   Paul Fanning   Senior Vice President, Human Resources

I hereby agree to the terms and conditions set forth above and in Attachment A.
I have been given at least forty-five (45) days to consider this Agreement
(including Attachment A) and I have chosen to execute this on the date below. I
intend that this Agreement become a binding agreement between me and the Company
if I do not revoke my acceptance in seven (7) days. I further understand that if
I do revoke my acceptance of the Agreement within the time allotted, it shall be
void, and I shall not receive any of the benefits described in paragraph 2.

 

/s/David Standring

   Date November 8, 2013

David Standring

  

To be returned by October 25th, 2013 but no earlier than the close of business
on September 9th, 2013.

 

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ATTACHMENT A

OLDER WORKERS BENEFIT PROTECTION ACT

NOTICE TO EMPLOYEES

As a result of the Company’s reorganization of its Executive Staff due to
business conditions, your employment with the Company is being terminated and
you have been selected to receive an offer of severance benefits in exchange for
signing a release and waiver of claims. Employees were selected for termination
and eligibility for this severance program based on the Company’s decision to
eliminate certain positions as part of its restructuring efforts based on a
variety of factors, including the Company’s assessment of its need for
particular skill sets, relative and absolute performance, and the Company’s
projection of its other future business needs.

In connection with the severance program, you are being provided with
information as to: (i) any class, unit or group of individuals terminated and
covered by such program, any eligibility factors for such termination and,
therefore, eligibility for such program, and any time limits applicable to such
program; and (ii) the job title and ages of all individuals terminated and,
therefore, eligible or selected for the program, and the ages of all individuals
in the same job classification or organizational unit who are not terminated
and, therefore, are not eligible or selected for the program.

All persons in your Department who are being terminated in connection with this
reduction in force have been selected for the program and their job titles and
ages have been indicated in the chart below. The job titles and ages of
individuals in your Department who were not selected for the program are also
indicated in the below chart.

 

Class/Unit/
Department

  

Job Title and Ages of
Employees Selected

  

Job Title and Ages of Employees Not Selected

CEO Executive Staff    EVP and CSO (62)   

Sr. Vice President & General Counsel (43)

Sr. Vice President, CFO & Treasurer (35)

Vice President, Corporate & Business Development (43)

EVP, Clinical Development & CMO (59)

Sr. Vice President, Human Resources (55)

Vice President, Chemistry Manufacturing Controls (60)

 

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