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                                                                   EXHIBIT 10.31

CERTAIN CONFIDENTIAL INFORMATION CONTAINED IN THIS DOCUMENT, MARKED BY
ASTERISKS, HAS BEEN OMITTED AND FILED SEPARATELY WITH THE SECURITIES AND
EXCHANGE COMMISSION PURSUANT TO RULE 406 UNDER THE SECURITIES ACT OF 1933, AS
AMENDED.

[NABI LOGO]

                 FIRST AMENDMENT TO PRODUCTION AGREEMENT BETWEEN
                            NABI AND INHIBITEX, INC.
                             DATED DECEMBER 5, 2001

The parties to this First Amendment to the Production Agreement dated December
5, 2001 are Nabi Biopharmaceuticals, formerly Nabi, a Delaware corporation
("Nabi"), and Inhibitex, Inc., a Delaware corporation ("Inhibitex").

Background:

         WHEREAS, Nabi and Inhibitex entered into a Production Agreement having
an Effective Date of December 5, 2001 (the "Agreement"), pursuant to which Nabi
has agreed to manufacture Product for Inhibitex (capitalized terms used herein
shall have the meanings defined in the Agreement unless otherwise defined
herein); and

         WHEREAS, Nabi and Inhibitex desire to amend the Agreement as
hereinafter provided to define the structure for profit sharing in connection
with the sale of a By-Product, Fraction V, in accordance with Section 10 of the
Agreement, and acknowledge that no previous amendments to the Agreement have
been made; and

         WHEREAS, the parties hereby agree and confirm that the Agreement is
currently in full force and effect as between them, and further agree that all
terms and conditions as they previously applied shall continue to apply to the
Agreement, except as hereby amended.

         NOW, THEREFORE, in consideration of the mutual premises contained
herein and other valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, and intending to be legally bound hereby, the parties
hereto agree as follows:

Amendments:

         1.       Each of Sections 1.26, 2.5(b), 2.5(e), 2.5(f), 2.5(h) and 9.2
is hereby amended by inserting the phrase "and any By-Product" immediately after
each reference to "Product" contained therein. Each of Sections 2.5(d), 2.5(m),
2.5(n), 2.5(p), 2.5(q), 2.5(r), 3.3 and 17.5 is hereby amended by inserting the
phrase "or any By-Product" immediately after each reference to "Product"
contained therein.

         2.       Section 2.5 is hereby amended by adding new subsection (z) to
read in its entirety as follows:

         "(z)     have sole responsibility for the manufacture, testing,
filling, labeling, storage and shipping of any By-Product."

         3.       Section 10 is hereby amended by numbering the existing
paragraph "10.1" and adding new subsection 10.2 to read in its entirety as
follows:

"10.2    Terms of Sale for Fraction V By-Product:

         Nabi shall have the exclusive right to sell Fraction V By-Product
throughout the term of the Agreement on behalf of Inhibitex pursuant to the
following terms:

                                                                  [NABI ADDRESS]

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         (a)               For purposes of this Section 10.2, "Profits" shall be
                  defined as the amount remaining after (i) direct costs
                  incurred by Nabi (calculated in accordance with Nabi's cost
                  accounting practices for other manufactured products) for
                  labor, raw materials and supplies used specifically in the
                  process of producing Fraction V from Fraction II + III
                  centrifugate and (ii) reasonable deductions for cash or other
                  discounts or uncollected accounts on the sale of Fraction V
                  are subtracted from (iii) Nabi's gross receipts from the sale
                  of Fraction V. No other overheads or non-direct cost
                  allocations are to be deducted from gross receipts from the
                  sale of Fraction V in the calculation of Profits.

         (b)               Inhibitex and Nabi shall share the Profits from the
                  sale of Fraction V as follows:

                  [ *** ] to Nabi
                  [ *** ] to Inhibitex

         (c)               Nabi shall be responsible for negotiating all sales
                  terms and conditions with customers, and shall have the right
                  to enter into contracts for the sale of Fraction V without the
                  prior approval of Inhibitex.

         (d)               Nabi will remit payment of monies owed to Inhibitex
                  on the sale of Fraction V within fifteen (15) days of receipt
                  of payment from Nabi's customer. Nabi will certify, if
                  requested, that the gross receipts used to calculate Profits
                  include all amounts remitted to Nabi in consideration of the
                  sale of Fraction V to the customer and that Nabi will not be
                  receiving any other remuneration from the customer or any
                  other party in consideration of such sale (such as free goods,
                  add-on values, etc.).

         (e)               At the beginning of each calendar year, Nabi shall
                  provide Inhibitex with a goof faith estimate of its direct
                  costs and the selling price it expects to be used in the
                  calculation of Profits for the next year. With each payment of
                  monies made by Nabi to Inhibitex pursuant to 10.2 (d) Nabi
                  will provide an accounting statement that reflects the actual
                  calculation of Profits, including the actual direct costs and
                  selling price obtained in those particular sales of Fraction
                  V. and an explanation of any material variances from its good
                  faith estimate. Inhibitex shall have the right to make
                  enquiries and ask for reasonable support relative to any
                  material variances in the calculation of Profits included in
                  the accounting statement. In the event that Inhibitex and Nabi
                  cannot reach agreement as to the reasonableness or accuracy of
                  the calculation of Profits as it relates to a payment or
                  payments, the parties agree to retain an independent public
                  accountant, satisfactory to both parties, to resolve the
                  dispute. The parties agree to accept the decision of the
                  independent public accountants as final. The fees and expenses
                  of the independent account will be borne by the parties in
                  proportion to the differences between the respective estimates
                  of Profits and Profits as finally determined by the
                  independent public accountant.

         4.       Section 17.3 is hereby amended by adding new subsection (d) to
read in its entirety as follows:

         "(d)     any claim brought by a third party arising out of or in
                  connection with the use or sale of any By-Product."

Miscellaneous:

Each Party represents and warrants that each of its representations and
warranties set forth in the Agreement is true and correct as of the date hereof
as though made on the date hereof.

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Except as expressly provided herein, all terms and conditions set forth in the
Agreement remain unchanged and continue in full force and effect.

The Parties agree that they and their employees shall execute all documents and
do all other things necessary to carry out the intent to implement the
provisions of this First Amendment.

This First Amendment to the Agreement is effective the 6th day of May, 2002.

IN WITNESS WHEREOF, the parties hereby have caused this First Amendment to the
Agreement to be executed and the persons signing the same warrant that they are
duly authorized to sign for and on behalf of the respective parties.

Nabi Biopharmaceuticals                           Inhibitex, Inc.

By: /s/ Thomas H. McLain                          By: /s/Robert Schweiger
    --------------------                              --------------------------
                                                      R. Schweiger
Title: Exec VP and COO                            Title: VP Business Development