Document:

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                                                                     EXHIBIT 4.1

    UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO WORLDCOM, INC. (THE
"COMPANY") OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND
ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER
NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS
MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED
REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR
OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

    THIS CERTIFICATE IS ONE OF THE GLOBAL SECURITIES REFERRED TO IN THE
INDENTURE DESCRIBED HEREIN. UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART
FOR SECURITIES IN DEFINITIVE FORM, THIS SECURITY MAY NOT BE TRANSFERRED EXCEPT
AS A WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF
THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE
DEPOSITARY OR ANY NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF ANY
SUCCESSOR DEPOSITARY.

                                 WORLDCOM, INC.
                           FLOATING RATE NOTE DUE 2002

PRINCIPAL AMOUNT                                                      NO. R-___
$                                                             CUSIP 98157D AE 6
                                                             ISIN: US98157DAE67

    WORLDCOM, INC., a corporation duly organized and existing under the laws of
the State of Georgia (herein called the "Company," which term includes any
successor corporation under the Indenture referred to below), for value
received, hereby promises to pay to CEDE & CO., or registered assigns, the
principal sum of _____________________ DOLLARS on June 11, 2002 (the "Stated
Maturity"), and to pay interest thereon from and including the most recent
Interest Payment Date to which interest has been paid or duly provided for, or,
if no interest has been paid, from and including June 12, 2000, payable in
arrears on March 11, June 11, September 11 and December 11 and at Maturity
(each, an "Interest Payment Date"), commencing on September 11, 2000. The rate
of interest payable from time to time in respect of the Notes (the "Rate of
Interest") will be a floating rate subject to adjustment on a quarterly basis
and determined by reference to LIBOR for three-month U.S. dollar deposits,
determined as described below, plus a spread of 0.16% per annum. The interest so
payable, and paid or duly provided for, on any Interest Payment Date shall, as
provided in the Indenture, be paid to the Person in whose name this Note (or one
or more Predecessor Securities) is registered at the close of business on the
Regular Record Date for such interest, which shall be the 28th day (whether or
not a Business Day) of February, May, August and November, respectively,
preceding such Interest Payment Date at the office or agency of the Trustee
maintained for such purpose in the City of New York, New York; provided, that
interest payable at Maturity will be payable to the registered Noteholder to
whom principal is payable.

    Except as otherwise provided in the Indenture, any such interest not so paid
or duly provided for shall forthwith cease to be payable to the Holder on the
related Regular Record Date and may either be paid to the Person in whose name
this Note (or one or more Predecessor Securities) is registered at the close of
business on a Special Record Date for the payment of such Defaulted Interest to
be fixed by the Trustee, notice whereof shall be given to Holders of Notes (as
defined below) not less than 10 days prior to such Special Record Date, or be
paid at any time in any other lawful manner not inconsistent with the
requirements of any securities exchange on which the Notes may be listed, and
upon such notice as may be required by such exchange, all as more fully provided
in the Indenture.

<PAGE>

    If any Interest Payment Date, the Stated Maturity or the Maturity shall not
be a Business Day (as hereinafter defined), payment of the amount due on this
Note on such date may be made on the next succeeding Business Day; and, if such
payment is made or duly provided for on such Business Day, no interest shall
accrue on such amounts for the period from and after such Interest Payment Date,
the Stated Maturity, or the Maturity as the case may be, to such Business Day.

    Payment of the principal of (and premium, if any) and interest on this Note
at Maturity shall be made upon presentation hereof at the office or agency of
the Company, one of which will be maintained in Pittsburgh, Pennsylvania (which
initially will be the Corporate Trust Office of Chase Manhattan Trust Company,
National Association, in Pittsburgh, Pennsylvania) or at such other office or
agency permitted under the Indenture, including the office or agency of the
Company maintained for such purpose in the City of New York, New York. Payment
of the principal of (and premium, if any) and interest on this Note shall be
payable in immediately available funds; provided however, that payment of
interest may be made at the option of the Company by check mailed to the address
of the Person entitled thereto as such address shall appear in the Security
Register. Payment of the principal of (and premium, if any) and interest, if
any, on this Note, as aforesaid, shall be made in such coin or currency of the
United States of America as at the time of payment shall be legal tender for the
payment of public and private debts. Interest payable on any Interest Payment
Date will be paid to DTC, Euroclear and/or CEDEL, as the case may be, with
respect to the portion of this Note held for its account by Cede & Co. or a
successor depositary, as the case may be, for the purpose of permitting such
party to credit the interest received by it in respect of this Note to the
accounts of the beneficial owners hereof.

    This Note is one of a duly authorized issue of unsecured senior debt
securities of the Company known as the Company's Floating Rate Notes Due 2002,
initially in the aggregate principal amount of $60,000,000 (herein called the
"Notes" or the "Securities"), issued under an Indenture dated as of May 15, 2000
(such Indenture as originally executed and delivered and as hereafter
supplemented or amended, together with the Board Resolution setting forth
certain terms of the Notes adopted on May 31, 2000 and delivered to the Trustee
by the Company pursuant to Section 301 of such Indenture, being herein called
the "Indenture") from the Company to Chase Manhattan Trust Company, National
Association, as trustee (herein called the "Trustee," which term includes any
other successor trustees under the Indenture), to which Indenture, all
indentures supplemental thereto and all Board Resolutions relating thereto
reference is hereby made for a statement of the respective rights, limitations
of rights, duties and immunities thereunder of the Company, the Trustee and the
Holders of the Notes and of the terms upon which the Notes are, and are to be,
authenticated and delivered. The acceptance of this Note shall be deemed to
constitute the consent and agreement of the Holder hereof to all of the terms
and provisions of the Indenture. All capitalized terms used in this Note which
are not defined herein shall have the meaning assigned to them in the Indenture.

    The Notes may not be redeemed prior to their Maturity and do not have the
benefit of any sinking fund obligations.

    If an Event of Default with respect to the Notes shall occur and be
continuing, the principal of all Notes may be declared due and payable in the
manner and with the effect provided in the Indenture.

    The Company's obligations under this Note and under the covenants provided
in the Indenture are subject to defeasance and discharge as provided in the
Indenture.

    Reference is made to the further provisions of this Note set forth on the
reverse hereof, which provisions shall for all purposes have the same effect as
if set forth at this place.

    Unless the certificate of authentication hereon has been executed by the
Trustee by manual signature, this Note shall not be entitled to any benefit
under the Indenture or be valid or obligatory for any purpose.

<PAGE>

    IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed under its corporate seal. WORLDCOM, INC.

Attested:

                                       By:
--------------------------                -------------------------
    Secretary                             President and
                                          Chief Executive Officer

This is one of the Securities of the series designated therein referred to in
the within-mentioned Indenture.

Dated: June 12, 2000                   CHASE MANHATTAN TRUST COMPANY,
                                       NATIONAL  ASSOCIATION, as Trustee

                                       By:
                                          -------------------------
                                          Authorized Representative

<PAGE>

                                 WORLDCOM, INC.
                           FLOATING RATE NOTE DUE 2002
                                 REVERSE OF NOTE

    The Rate of Interest shall be determined in accordance with the following
provisions:

    (i) At approximately 11:00 a.m. (London time) on the second day on which
commercial banks are open for business, including dealings in deposits in U.S.
dollars in London (or, for purposes of paragraph (iii)(B) below, New York),
prior to the commencement of the Interest Period (defined below) for which such
rate will apply (each such day an "Interest Determination Date") The Chase
Manhattan Trust Company, National Association, as the calculation agent, or its
successors in this capacity (the "Calculation Agent") will calculate the rate of
interest (the "Rate of Interest") for such Interest Period as, subject to the
provisions described below, the rate per annum equal to 0.16% above the rate
appearing on the Dow Jones Telerate Page 3750 (or such other page as may replace
that page on the Dow Jones Telerate Service) for three-month U.S. dollar
deposits in the London inter-bank market on such Interest Determination Date.
The period beginning on, and including, June 12, 2000, and ending on, but
excluding, the first Interest Payment Date and each successive period beginning
on, and including, an Interest Payment Date and ending on, but excluding, the
next succeeding Interest Payment Date is herein called an "Interest Period".

    (ii) If on any Interest Determination Date an appropriate rate cannot be
determined from the Dow Jones Telerate Service, the Rate of Interest for the
next Interest Period shall, subject to the provisions described below, be the
rate per annum that the Calculation Agent certifies to be 0.16% per annum above
the arithmetic mean of the offered quotations, as communicated to and at the
request of the Calculation Agent by not less than two major banks in London
selected by the Calculation Agent (the "Reference Banks," which term shall
include any successors nominated by the Calculation Agent), to leading banks in
London by the principal London offices of the Reference Banks for three-month
U.S. dollar deposits in the London inter-bank market as at 11:00 a.m. (London
time) on such Interest Determination Date.

    (iii) If on any Interest Determination Date fewer than two of such offered
rates are available, the Rate of Interest for the next Interest Period shall be
whichever is the higher of:

    (A) The Rate of Interest in effect for the last preceding Interest Period to
  which (i) or (ii) above shall have applied; and

    (B) The Reserve Interest Rate. The "Reserve Interest Rate" shall be the rate
  per annum which the Calculation Agent determines to be 0.16% per annum above
  either (i) the arithmetic mean of the U.S. dollar offered rates which at least
  two New York City banks selected by the Calculation Agent are or were quoting,
  on the relevant Interest Determination Date, for three-month deposits to the
  Reference Banks or those of them (being at least two in number) to which such
  quotations are or were, in the opinion of the Calculation Agent, being so
  made, or (ii) in the event that the Calculation Agent can determine no such
  arithmetic mean, the arithmetic mean of the U.S. dollar offered rates which at
  least two New York City banks selected by the Calculation Agent are or were
  quoting on such Interest Determination Date to leading European banks for a
  period of three months; provided, however, that if the banks selected as
  aforesaid by the Calculation Agent are not quoting as mentioned above, the
  Rate of Interest shall be the Rate of Interest specified in (A) above.

    The Calculation Agent shall, as soon as practicable after 11:00 a.m. (London
time) on each interest Determination Date, determine the Rate of Interest and
calculate the amount of interest payable in respect of the following Interest
Period (the "Interest Amount"). The Interest Amount shall be calculated by
applying the Rate of Interest to the principal amount of each Floating Rate Note
outstanding at the commencement of the Interest Period, multiplying each such
amount by the actual number of days in the

<PAGE>

Interest Period concerned (which actual number of days shall include the first
day but exclude the last day of such Interest Period) divided by 360 and
rounding the resultant figure upwards to the nearest cent. The determination of
the Rate of Interest and the Interest Amount by the Calculation Agent shall (in
the absence of willful default, bad faith or manifest error) be final and
binding on all parties. Notwithstanding anything herein to the contrary, the
rate of interest on the Floating Rate Notes shall in no event be higher than the
maximum rate permitted by New York law, as the same may be modified by United
States law of general application.

    The Company shall provide that, so long as any of the Floating Rate Notes
remain outstanding, there shall at all times be a Calculation Agent for the
purpose of the Floating Rate Notes. In the event of the Calculation Agent being
unable or unwilling to continue to act as the Calculation Agent or in the case
of the Calculation Agent failing duly to establish the Rate of Interest for any
Interest Period, the Company shall appoint another leading bank engaged in the
London inter-bank market to act as such in its place. The Calculation Agent may
not resign its duties without a successor having been appointed as aforesaid.

    All certificates, communications, opinions, determinations, calculations,
quotations and decisions given, expressed, made or obtained for the purposes of
the provisions relating to the payment and calculation of interest on the
Floating Rate Notes, whether by the Reference Banks (or any of them) or the
Calculation Agent, shall (in the absence of willful default, bad faith or
manifest error) be binding on the Company, the Calculation Agent and all of the
Holders and no liability shall (in the absence of willful default, bad faith or
manifest error) attach to the Calculation Agent in connection with the exercise
or non-exercise by it of its powers, duties and discretions.

    Interest shall cease to accrue on any Note on Maturity unless, upon
presentation of such Note, payment of principal is improperly withheld or
refused, in which case, interest shall continue to accrue.

    The Indenture permits, with certain exceptions as thereby provided, the
Trustee to enter into one or more supplemental indentures for the purpose of
adding any provisions to, or changing in any manner or eliminating any of the
provisions of, the Indenture or of modifying in any manner the rights of the
Holders of Securities, in any such case, with the consent of the Holders of not
less than majority in aggregate principal amount of all Outstanding Securities
affected by such supplemental indenture; provided, however, that no such
supplemental indenture shall, without the consent of the Holder of each of the
Outstanding Securities affected thereby, affect certain rights of such Holders
as more fully described in the Indenture.

  The Indenture also contains provisions permitting the Holders of specified
percentages in principal amount of the Securities then Outstanding, on behalf of
the Holders of all Securities affected thereby, to waive certain past defaults
of the Company under the Indenture and their consequences. In addition, without
the consent of any Holder of a Security, the Indenture and the Securities may be
amended and supplemented to cure any defect, ambiguity or inconsistency, make
other changes which will not adversely affect in any material respect the rights
of the Holders or certain other matters specified in the Indenture. Any such
consent or waiver by the Holder of this Note shall be conclusive and binding
upon such Holder and upon all future Holders of this Note and of any Note issued
upon the registration of transfer hereof or in exchange herefor or in lieu
hereof, whether or not notation of such consent or waiver is made upon this
Note.

    As provided in and subject to the provisions of the Indenture, the Holder of
this Note shall not have the right to institute any proceeding with respect to
the Indenture or for the appointment of a receiver or trustee, or for any other
remedy thereunder, unless such Holder shall have previously given the Trustee
written notice of a continuing Event of Default with respect to the Notes, the
Holders of not less than 25 percent in principal amount of the Notes Outstanding
shall have made written request to the Trustee to institute proceedings in
respect of such Event of Default as Trustee and offered the Trustee reasonable

<PAGE>

indemnity and the Trustee shall not have received from the Holders of a majority
in principal amount of the Notes Outstanding a direction inconsistent with such
request, and shall have failed to institute any such proceeding, for 60 days
after receipt of such notice, request and offer of indemnity. The foregoing
shall not apply to certain suits described in the Indenture, including any suit
instituted by the Holder of this Note for the enforcement of any payment of
principal hereof or any premium or interest hereon on or after the respective
due dates expressed herein.

    No reference herein to the Indenture and no provision of this Note or of the
Indenture shall alter or impair the obligation of the Company, which is absolute
and unconditional, to pay the principal of (and premium, if any) and interest,
if any, on this Note at the times, place and rate, in the coin or currency, and
in the manner, herein prescribed.

    The Notes are issuable only in registered form, without coupons, in
denominations of $1,000 and any integral multiple of $1,000, and in book-entry
form. The Notes may be represented by one or more global Notes deposited with
DTC and registered in the name of the nominee of DTC, with certain limited
exceptions. So long as DTC or any successor depository or its nominee is the
registered Holder of a global Note, DTC, such depository or such nominee, as the
case may be, will be considered to be the sole Holder of the Notes for all
purposes of the Indenture. Except as provided below, an owner of a beneficial
interest in a global Note will not be entitled to have Notes represented by such
global Note registered in such owner's name, will not receive or be entitled to
receive physical delivery of the Notes in certificated form and will not be
considered the owner or Holder thereof under the Indenture. Each person owning a
beneficial interest in a global Note must rely on DTC's procedures and, if such
person is not a participant, on the procedures of the participant through which
such person owns its interest, to exercise any rights of a Holder under the
Indenture. If the Company requests any action of Holders or if an owner of a
beneficial interest in a global Note desires to take any action that a Holder is
entitled to take under the Indenture, DTC will authorize the participants
holding the relevant beneficial interests to give or take such action, and such
participants will otherwise act upon the instructions of beneficial owners
holding through them.

    If at any time DTC notifies the Company that it is unwilling or unable to
continue as depository for the global Note or Notes or if at any time DTC ceases
to be a clearing agency registered under the Securities Exchange Act of 1934, as
amended, if so required by applicable law or regulation, the Company shall
appoint a successor depository with respect to such global Note or Notes. If (x)
a successor depository for such global Note or Notes is not appointed by the
Company within 90 days after the Company receives such notice or becomes aware
of such unwillingness, inability or ineligibility, (y) an Event of Default has
occurred and is continuing and the beneficial owners representing a majority in
principal amount of the Notes represented by such global Note or Notes advise
DTC to cease acting as depository for such global Note or Notes or (z) the
Company, in its sole discretion, determines at any time that all Outstanding
Notes (but not less than all) issued or issuable in the form of one or more
global Notes shall no longer be represented by such global Notes, then the
Company shall execute, and the Trustee shall authenticate and deliver,
definitive Notes of like series, rank, tenor and terms in definitive form in an
aggregate principal amount equal to the principal amount of such global Note or
Notes. If any beneficial owner of an interest in a permanent global Note is
otherwise entitled to exchange such interest for Notes of such series and of
like tenor and principal amount of another authorized form and denomination, as
contemplated by the Indenture and provided that any applicable notice provided
in the permanent global Note shall have been given, then without unnecessary
delay but in any event not later than the earliest date on which such interest
may be so exchanged, the Company shall execute, and the Trustee shall
authenticate and deliver, definitive Notes in aggregate principal amount equal
to the principal amount of such beneficial owner's interest in such permanent
global Note. On or after the earliest date on which such interests may be so
exchanged, such permanent global Note shall be surrendered for exchange by DTC
or such other

<PAGE>

depository as the Company shall specify to the Trustee.

    Initially, the Trustee will be the Security Registrar and the Paying Agent
for this Note. The Company reserves the rights at any time to remove any Paying
Agent or Security Registrar without notice, to appoint additional or other
Paying Agents and other Security Registrars without notice and to approve any
change in the office through which any Paying Agent or Security Registrar acts.
None of the Company, the Trustee, any Paying Agent or the Security Registrar
will have any responsibility or liability for any aspect of the records relating
to or payments made on account of beneficial ownership interests in this Note in
global form or for maintaining, supervising or reviewing any records relating to
such beneficial ownership interests. Notwithstanding the foregoing, nothing
herein shall prevent the Company, the Trustee, or any agent of the Company or
the Trustee, from giving effect to any written certification, proxy or other
authorization furnished by any depository, as a Holder, with respect to this
Note in global form or impair, as between such depository and owners of
beneficial interests in such global Note, the operation of customary practices
governing the exercise of the rights of such depository (or its nominee) as
Holder of such global Note.

    THE INDENTURE AND THE SECURITIES SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT REGARD TO CONFLICTS
OF LAW PRINCIPLES THEREOF.

    As used herein, "Business Day," when used with respect to any Place of
Payment or any other particular location referred to in this Note or in the
Indenture, means any day, other than a Saturday or Sunday, that is neither a
legal holiday nor a day on which banking institutions are authorized or required
by law or regulation to close in the City of New York or in the place of
presentation.

    The Company may cause CUSIP or ISIN numbers to be printed on the Notes as a
convenience to Holders of Notes. No representation is made as to the accuracy of
such numbers as printed on the Notes, and reliance may be placed only on the
other identification numbers printed thereon.

    This Note shall not be entitled to any benefit under the Indenture or be
valid or obligatory until the Trustee or authenticating agent signs the
certificate of authenticity on the Notes.

    No recourse shall be had for the payment of the principal of (or premium, if
any) or interest, if any, or Additional Amounts, if any, on this Note, or any
part hereof, or for any claim based hereon or otherwise in respect hereof, or of
the indebtedness represented hereby, or upon any obligation, covenant or
agreement under the Indenture, against, and no personal liability whatsoever
shall attach to, or be incurred by, any incorporator, shareholder, officer or
director, as such, past, present or future, of (i) the Company or (ii) any
predecessor or successor corporation (either directly or through the Company or
a predecessor or successor corporation), whether by virtue of any constitutional
provision, statute or rule of law, or by the enforcement of any assessment or
penalty or otherwise; it being expressly agreed and understood that the
Indenture and all of the Notes are solely corporate obligations and that any
such personal liability is hereby expressly waived and released as a condition
of, and as part of the consideration for, the execution of the Indenture and the
issuance of the Notes.<PAGE>

                                                                 EXHIBIT 10.11.1

                                 AMENDMENT NO. 1

This Amendment No. 1 (the "Amendment") to the parties' Data Set License
Agreement dated as of March 1, 2000 is entered into as of April 11, 2000 by and
between Pharsight Corporation, a California corporation, (hereinafter
"Pharsight") and the Lovelace Respiratory Research Institute (hereinafter
"Lovelace").

         WHEREAS, Pharsight and Lovelace have entered into an Agreement dated as
of March 1, 2000 (the "Agreement") whereby the parties agreed on the terms and
conditions under which Lovelace would grant Pharsight the right to use certain
Data Sets in its products; and

         WHEREAS, the parties have determined that certain of the terms and
conditions set forth in the Agreement should be modified;

         NOW, THEREFORE, the parties agree as follows:

1. All capitalized terms used but not defined in this Amendment shall have the
meaning specified therefor in the Agreement. All section and exhibit numbers
refer to sections and exhibits of the Agreement unless otherwise specified.

2. Section 6.4 is hereby amended to read in its entirety as follows:

         6.4 LOSS OF DATA ACCESS. In the event that at any time during the term
         of this Agreement there is a period of at least sixty (60) days in
         which the number of Consortium members having access to data to
         contribute to the Data Set is less than three (3), Lovelace shall so
         notify Pharsight and shall have the option to substitute for the
         missing Consortium member's data, equivalent years of data from one or
         more of the existing Consortium members, and in the event of such
         substitution, all rights and obligations with respect to the Data Set
         shall continue unchanged. In the event that Lovelace is unable to make
         such a substitution or determines not to exercise its option to do so,
         then Lovelace shall so notify Pharsight and shall thereafter have no
         obligation to provide Updates. Pharsight's rights with respect to the
         Data Set shall continue for one year from the date of such notice, but
         the royalties due under Sections 4.2 and 4.3 shall be reduced to fifty
         percent (50%) of the amount set forth in such sections during such
         one-year period.

3. Section 5.2 is hereby amended to read in its entirety as follows:

         5.2 INDEMNIFICATION. Pharsight will defend, indemnify, and hold
         Lovelace harmless from and against any action or other proceeding
         brought against Lovelace arising from Pharsight's use of the Data Set,
         except where such action arises from negligence or willful misconduct
         on the part of Lovelace or from Lovelace's breach of the
         representations and warranties set forth in Section 5.1. Lovelace will
         defend, indemnify, and hold Pharsight harmless from and against any
         action or other proceeding brought against Pharsight to the extent that
         it is based on (i) Lovelace's negligence or willful misconduct; (ii) a
         claim that any part of the Data Set or Documentation infringes any
         copyright or patent or incorporates any misappropriated trade secrets
         of any third party; or (iii) an action arising from Lovelace's breach
         of the warranties set forth in Section 5.1.

<PAGE>

4. The first paragraph of Part II.C. of Appendix E is hereby amended to read
in its entirety as follows:

         "The health care data that underlie the Pharsight (PRODUCT/CONSULTING
         SERVICE) are currently derived from two health care organizations that
         are members of the Lovelace Data Consortium. This Consortium was
         created and is managed by the Southwest Center for Managed Care
         Research of the Lovelace Respiratory Research Institute. The
         patient-level data from these two organizations have been merged into
         one combined database. One of the contributing organizations is a
         managed care organization in the southwestern United States. The second
         organization is a network model managed health care plan in the
         mid-Atlantic region of the United States."

5. Except as set forth herein, the Agreement shall remain unmodified and in full
force and effect in accordance with its terms.

IN WITNESS WHEREOF, THE PARTIES HAVE EXECUTED THIS AMENDMENT AS OF THE DATE
FIRST ABOVE WRITTEN.

PHARSIGHT CORPORATION                   LOVELACE RESPIRATORY RESEARCH INSTITUTE

By: /s/ Robin A. Kehoe                  By:   /s/ Patricia J. Marx
   -------------------                     -----------------------
Robin A. Kehoe                          Name:  Patricia J. Marx
Chief Financial Officer                 Title:  Chief Operating Officer

                                      -2-

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