Registration No. 333-44756

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C.  20549

____________________________

POST-EFFECTIVE AMENDMENT NO. 1

TO

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933
____________________________
 

PHARSIGHT CORPORATION

(Exact Name of Registrant as Specified in Its Charter)

____________________________

Delaware		77-0401273
(State or Other Jurisdiction of Incorporation or Organization)		(I.R.S. Employer Identification Number)
	321 E. Evelyn Avenue, 3rd Floor Mountain View, CA  94041 (650) 314-3800
(Address and Zip Code of Principal Executive Offices)

____________________________

2000 Equity Incentive Plan

2000 CEO Non-Qualified Stock Option Plan

1997 Stock Option Plan

1995 Stock Option Plan

(Full Title of the Plan)

______________________

James Hopkins

President

Pharsight Corporation

321 E. Evelyn Avenue, 3rd Floor

Mountain View, CA  94041

(650) 314-3800

(Name and Address of Agent for Service)

(Telephone Number, Including Area Code, of Agent for Service)

Copies to:

Martin A. Wellington, Esq.

Davis Polk & Wardwell

1600 El Camino Real

Menlo Park, California 94025

(650) 752-2000

RECENT EVENTS:  DEREGISTRATION

The Registration Statement on Form S-8 (Registration No. 333-44756) (the “Registration Statement”) of Pharsight Corporation (“Pharsight”), pertaining to the registration of certain shares of Pharsight’s common stock, par value $0.001 per share (“Pharsight Common Stock”), issuable to eligible employees of Pharsight under the 2000 Equity Incentive Plan, 2000 CEO Non-Qualified Stock Option Plan, 1997 Stock Option Plan and 1995 Stock Option Plan, to which this Post-Effective Amendment No. 1 relates, was filed with the Securities and Exchange Commission on August 29, 2000.

Pharsight, Tripos (DE), Inc. (“Tripos”) and Pearson Merger Corporation, a wholly-owned subsidiary of Tripos (“Merger Sub”), entered into an Agreement and Plan of Merger dated as of September 8, 2008, pursuant to which, among other things, Merger Sub would be merged with and into Pharsight, Pharsight would survive as a wholly-owned subsidiary of Tripos and each outstanding share of Pharsight Common Stock would be converted into the right to receive $5.50 in cash, without interest (the “Merger”).

On October 31, 2008, Pharsight effected the Merger pursuant to Section 251 of the General Corporation Law of the State of Delaware.  The Merger became effective as specified in a Certificate of Merger filed with the Secretary of State of the State of Delaware on October 31, 2008 (the “Merger Date”).

As a result of the Merger, Pharsight has terminated all offerings of Pharsight Common Stock pursuant to its existing registration statements, including the Registration Statement.  In accordance with an undertaking made by Pharsight in the Registration Statement to remove from registration, by means of a post-effective amendment, any shares of Pharsight Common Stock which remain unsold at the termination of the offering, Pharsight hereby removes from registration all shares of Pharsight Common Stock registered under the Registration Statement which remain unsold as of the Merger Date.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this Post-Effective Amendment No. 1 to the Registration Statement on Form S-8 to be signed on its behalf by the undersigned, thereunto duly authorized, in the city of St. Louis, state of Missouri, on this 31st day of October, 2008.

PHARSIGHT CORPORATION
By:	/s/ James Hopkins
	Name:	James Hopkins
	Title:	President

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment No. 1 to the Registration Statement on Form S-8 has been signed by the following persons on October 31, 2008 in the capacities indicated.

Signature	Title
/s/ James Hopkins	President, Director
James Hopkins	(Principal Executive Officer)
/s/ John D. Yingling	Vice President and Chief Financial Officer, Director
John D. Yingling	(Principal Financial and Accounting Officer)
/s/ James Munn	Secretary, Director
James Munn