Portions of this exhibit were omitted and filed separately with the Secretary of the Commission pursuant to an
application for confidential treatment filed with the Commission pursuant to Rule 24b-2 under the Securities
Exchange Act of 1934. Such portions are marked by a series of asterisks.
AMENDMENT TO STOCK PURCHASE AGREEMENT
This Amendment (the "Amendment") to the Stock Purchase Agreement dated December 9, 1999, by and
between ViroPharma Incorporated ("ViroPharma"), a Delaware corporation with its principal place of business
at 405 Eagleview Boulevard, Exton, PA 19341, and American Home Products Corporation, a Delaware
corporation with its principal place of business at 5 Giralda Farms, Madison, NJ 07940 (the "Agreement"),
American Home Products Corporation now being known as Wyeth ("Wyeth"), is made this June 26, 2003, by
and between ViroPharma and Wyeth. All capitalized terms used in this Amendment that are not defined in this
Amendment shall have the meanings ascribed to them in the Agreement.
In consideration of the mutual covenants and agreements contained herein, ViroPharma and Wyeth, intending to
be legally bound, do hereby agree as follows:
1.1 Amendment of Section 1.30. Section 1.30 of the Agreement is amended by replacing current Section 1.30
with the following:
1.30 "*******" means the first date on which the JSC determines that *******.
1.2 Amendment of Section 2.3. Section 2.3 is amended by appending to the end of current Section 2.3 the
Notwithstanding the foregoing, if Wyeth's receipt of the Third Shares would increase Wyeth's total ownership of
Common Stock and other voting securities of ViroPharma to more than 19.9% of the outstanding Common
Stock and other voting securities of ViroPharma, then:
(i) Wyeth shall pay ViroPharma the entire Third Purchase Price of Ten Million Dollars ($10,000,000),
(ii) Wyeth shall purchase the maximum number of shares of Common Stock such that Wyeth's total ownership of
Common Stock and