<PAGE>
                                                                   Exhibit 10.07

[***] indicates the omission of confidential portions for which confidential
treatment has been requested. Such confidential information has been filed
separately with the Commission.

                               THIRD AMENDMENT TO
                             PRIME VENDOR AGREEMENT

         THIS THIRD AMENDMENT TO PRIME VENDOR AGREEMENT ("THIRD AMENDMENT") is
among Cardinal Health*, formerly known as Cardinal Distribution, ("CARDINAL"),
and Express Scripts, Inc. ("BUYER").

         WHEREAS, Cardinal and Buyer executed a Prime Vendor Agreement, dated
July 1, 2001, executed a First Amendment to Prime Vendor Agreement, dated
January 15, 2003 ("FIRST AMENDMENT"), and a Second Amendment to Prime Vendor
Agreement, dated November 19, 2003 ("SECOND AMENDMENT"), (collectively, the
"AGREEMENT").

         WHEREAS, the parties desire to further amend the Agreement as further
set forth herein.

         NOW THEREFORE, in consideration of the foregoing recitals, the parties
hereby agree as follows:

     1. SECTION 2, SALE OF MERCHANDISE. The following language shall be deleted
in its entirety from the definition of Primary Requirements as set forth in
Section 2, Sale of Merchandise, as amended by the First Amendment: "and
Monthly".

     2. SECTION 3, PURCHASE PRICE. The second paragraph of Section 3 shall be
amended to add "[***]" to the definition of [***].

     3. SECTION 5, PAYMENT TERMS. Section 5(a)(i), as amended by the First
Amendment, shall be deleted in its entirety and replaced with the following:

     "The payment terms applicable to Buyer for all DIRECT STORE DELIVERY
     PURCHASES shall be [***] calculated pursuant to either of the options set
     forth below. Buyer will notify Cardinal of its desire to switch from one
     option to the other no less than thirty (30) days prior to the effective
     date of such change, unless otherwise agreed to in writing by Buyer and
     Cardinal. In the event a payment due date falls on a Saturday, that payment
     due date will become the preceding Friday. In the event a payment due date
     falls on a Sunday, that payment due date will become the following Monday.
     In the event a due date falls on a Monday holiday, invoices due on Sunday
     and Monday will be due on Tuesday. In the event a due date falls on a
     Tuesday through Friday holiday, payment will be due the preceding day.

          OPTION 1

          The payment terms applicable to Buyer for all DIRECT STORE DELIVERY
          PURCHASES shall be [***] as follows: Buyer will cause Cardinal to
          receive payment in full: (1) by the [***] of each calendar month of
          the amount due for all invoiced Merchandise delivered and services
          provided during the first (1st) [***] of such calendar month; (2) by
          the [***] of each calendar month, of the amount due for all invoiced
          Merchandise delivered and services provided during the [***] through
          the [***] of such calendar month; and (3) by the [***] of each
          calendar month, of the amount due for all invoiced Merchandise
          delivered and services provided during the period beginning on the



<PAGE>



          [***] day of the preceding calendar month and ending on the last day
          of such preceding calendar month.

          OPTION 2

          The payment terms applicable to Buyer for all DIRECT STORE DELIVERY
          PURCHASES shall be [***] as follows: Buyer will cause Cardinal to
          receive payment in full: (1) by the [***] of each calendar month of
          the amount due for all invoiced Merchandise delivered and services
          provided from and including the [***] calendar day of each calendar
          month through and including the [***] of each calendar month; (2) by
          the [***] of each calendar month of the amount due for all invoiced
          Merchandise delivered and services provided from and including the
          [***] calendar day of each calendar month through and including the
          [***] calendar day of each calendar month; (3) by the last Business
          Day (as hereinafter defined) of each calendar month of the amount due
          for all invoiced Merchandise delivered and services provided from and
          including the [***] calendar day of each calendar month through and
          including the [***] calendar day of each calendar month; (4) by the
          [***] day of each calendar month of the amount due for all invoiced
          Merchandise delivered and services provided from and including the
          [***] calendar day of each preceding calendar month through and
          including the [***] calendar day of each preceding calendar month; (5)
          by the [***] day of each calendar month of the amount due for all
          invoiced Merchandise delivered and services provided from and
          including the [***] of each preceding calendar month through and
          including the [***] of the each calendar [***].

     For purposes of this Agreement, the term "Business Day" shall be defined as
     Monday through Friday, with the exception of the following holidays: New
     Year's Day, Memorial Day, Independence Day, Labor Day, Thanksgiving Day and
     Christmas Day."

     4. SECTION 5, PAYMENT TERMS. The first sentence of the third paragraph of
Section 5(b) shall be deleted in its entirety and replaced with the following:

     "All payments for invoiced Merchandise delivered and services provided by
Cardinal will be made to the applicable servicing division specified in
Cardinal's invoice (or as otherwise specified by Cardinal) by electronic funds
transfer or other method acceptable to Cardinal so as to provide Cardinal with
good funds by the due date; provided, however, if Option 2 (as set forth in
Section 5(a)(i)) is chosen by Buyer, then Buyer will have the option to make the
payment due on the last Business Day of the month via check (instead of
ACH/electronic funds transfer) as long as the check is delivered to Cardinal on
the last Business Day of the month at the address designated by Cardinal for
these payments."

     5. SECTION 6, ORDERING AND DELIVERY. The third sentence of Section 6,
Ordering and Delivery, as amended by the First Amendment shall be deleted in its
entirety and replaced with the following:



                                       2
<PAGE>



     "Pharmacies having Qualified Monthly Purchases in excess of $[***] (except
     Pharmacies located outside of the contiguous United States or other
     Pharmacies mutually agreed upon by the parties from time to time) will have
     two delivery options:

     OPTION 1

     [***] In addition, Pharmacies may receive [***] deliveries; provided,
     however, such deliveries will be at a charge equal to Cardinal's cost for
     such delivery.

     OPTION 2

     [***].

     All [***] deliveries will be subject to the order cut-off times at the
     applicable servicing distribution center."

     5. SECTION 12, SERVICE LEVEL. Section 12, Service Level, as amended by the
First Amendment, shall be further amended as follows: all references to the
average monthly service level on Rx Products (excluding Buyer's Top [***] Items
(as defined in the First Amendment)) shall be changed from [***] percent
([***]%) to [***] percent ([***]%), and all references to the average monthly
service level on Buyer's Top [***] Items shall be changed from [***] percent
([***]%) to [***] percent ([***]%).

     6. SECTION 13, RETURNED GOODS POLICY. The second paragraph and items 1-6 of
Section 13 related to the annual inventory clean-ups shall be deleted in their
entirety. The following paragraph shall be added to Section 13 of the Agreement,
as if fully rewritten therein:

     "Subject to the requirements of the Cardinal Returns Policy, Buyer may
     return Merchandise for up to [***] from the date of purchase for [***]% of
     original invoice amount paid by Buyer (i.e., Buyer's contract or other
     "cost" plus the applicable mark-up or less the applicable mark down),
     provided: (i) [***]; (ii) [***]; (iii) [***]; (iv) [***]; (v) and [***].
     After [***] months from the date of purchase, Merchandise may not be
     returned; provided, however, this [***] limitation shall not apply for
     [***]."

     In addition, the following paragraph shall be added to Section 13, as if
fully rewritten therein:

     "Unless otherwise notified by the servicing distribution center, returned
     goods will be processed within five (5) Business Days of receipt of the
     returned goods at the Cardinal distribution center, and credit for those
     returned goods will be issued within three (3) Business Days following
     processing."



                                       3
<PAGE>



     7. SECTION 14, TERM. The initial term of the Agreement shall be extended
[***].

     8. NEW SECTION 30, GENERIC PURCHASE REQUIREMENT. The following paragraph
shall be added to the Agreement as a new Section 30, titled "Generic Purchase
Requirement":

     "During calendar years 2004 and 2005, calculated on a quarterly basis,
     Buyer will use commercially reasonable efforts to cause not less than
     [***]% of Buyer's total Qualified Purchases from Cardinal to be generic Rx
     Products. During calendar year 2006 and the initial six (6) months of
     calendar year 2007, calculated on a quarterly basis, Buyer will use
     commercially reasonable efforts to cause not less than [***]% of Buyer's
     total Qualified Purchases from Cardinal to be generic Rx Products. The
     foregoing requirements shall be referred to as the "Generic Purchase
     Requirements." To support Buyer's achievement of the Generic Purchase
     Requirements, Cardinal will use commercially reasonable efforts to make
     generic Rx Products available to Buyer at prices that are equal to or
     better than those prices that Buyer can obtain directly from the generic Rx
     Product manufacturers. Pricing for Buyer's purchases of generic Rx Products
     shall be pursuant to Cardinal's Mail Order Preferred Source program.

     If Buyer does not achieve the Generic Purchase Requirements, Cardinal and
     Buyer will meet to review Buyer's purchases of generic Rx Products and
     develop a strategy to support Buyer's achievement of the Generic Purchase
     Requirements during the quarter following the quarter in which the Generic
     Purchase Requirements were not met. If, during such following quarter,
     Buyer does not achieve the Generic Purchase Requirements, Buyer shall be
     considered in breach of the then current agreement between Buyer and
     Cardinal, pursuant to Section 14 of this Agreement, and Buyer shall have
     [***]([***]) days to cure such breach to the reasonable satisfaction of
     Cardinal. In the event that Buyer does not cure such breach within such
     [***] ([***]) day period, Cardinal may terminate this Agreement immediately
     in accordance with Section 14 hereof."

     9. NEW SECTION 31, EDI INITIATIVES. The following sentence shall be added
to the Agreement as a new Section 31, titled "EDI Initiatives":

     "Cardinal will support mutually agreed upon Buyer standards, policies and
     service level agreements for all existing business-to-business processes
     and new initiatives. These processes and initiatives include, but are not
     limited to, EDI, VAN, Direct Connect, Collaborative Commerce, and adding
     new transactions (e.g., 832). Buyer will work closely with Cardinal to
     ensure seamless connectivity and smooth processing of data between the two
     parties is achieved."

     10. EXHIBIT A, PHARMACIES. The following Pharmacies shall be deleted from
Exhibit A, as amended by the First Amendment:

                  Express Access Pharmacy, Inc.
                  dba Express Scripts, Inc.
                  767 Electronic Drive
                  Horsham, Pennsylvania 19020




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                  Central Fill, Inc.
                  721 Ridgedale Avenue
                  East Hanover, New Jersey 07936

     11. EXHIBIT B, PRICING MATRIX. Section 1 of Exhibit B, Pricing Matrix, as
amended by the First Amendment, shall be deleted in its entirety and replaced
with Section 1 of Exhibit A attached to this Amendment.

     12. EXHIBIT D, DEDICATED RESOURCES. The Dedicated Resource section of
Exhibit D shall be amended to provide [***] Cardinal employees who will be
dedicated to servicing Buyer's account and will act as a liaison between Buyer
and Cardinal in order to enhance Buyer-Cardinal relations. The Cardinal
employees will be based in the St. Louis, Bensalem and Tempe Pharmacies.

     13. MISCELLANEOUS. Capitalized terms not defined herein will have the same
meaning ascribed to them in the Agreement, it being the intent of the parties
that the Agreement and this Third Amendment will be applied and construed as a
single instrument. The Agreement, as modified by this Third Amendment,
constitutes the entire agreement between Cardinal and Buyer regarding the
subject matter of the Agreement and this Third Amendment and supersedes all
prior or contemporaneous writings and understandings between the parties
regarding the same. This Third Amendment will be binding upon the parties, their
heirs, legal representatives, successors and assigns. The terms and provisions
of this Third Amendment are severable. If any term or provision of this Third
Amendment is determined to be illegal or unenforceable by a court of competent
jurisdiction, the remaining terms and provisions of this Third Amendment and the
Agreement will remain in full force and effect. This Third Amendment may only be
amended in a writing signed by Cardinal and Buyer.

     14. EFFECTIVE DATE. This Third Amendment shall be effective as of January
1, 2004 ("EFFECTIVE DATE"). Except as otherwise amended herein, the terms and
conditions of the Agreement shall remain in full force and effect.


CARDINAL HEALTH*                            EXPRESS SCRIPTS, INC.

BY:    /s/ Mark W. Parrish                  BY:    /s/ Barrett Toan
       -------------------------------             -----------------------------

NAME:  Mark W. Parrish                      NAME:  Barrett Toan
       -------------------------------             -----------------------------

TITLE: Group President                      TITLE: CEO
       -------------------------------             -----------------------------

DATE:  4/9/04                               DATE:  3-30-04
       -------------------------------             -----------------------------

*The term "CARDINAL HEALTH" means the following pharmaceutical distribution
companies including: Cardinal Health 106, Inc. (formerly known as James W. Daly,
Inc.), a Massachusetts corporation (Peabody, Massachusetts); Cardinal Health
103, Inc. (formerly known as Cardinal Southeast, Inc.), a Mississippi
corporation (Madison, Mississippi); Cardinal Health 110, Inc. (formerly known as
Whitmire Distribution Corporation), a Delaware corporation (Folsom, California)
and any other subsidiary of Cardinal Health, Inc., an Ohio corporation ("CHI"),
as may be designated by CHI.



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<PAGE>



                                                                       EXHIBIT A

1. [***] The [***] has been established based upon [***]:

(a) [***] (as defined in Section 2 of this Agreement) and Generic Purchase
Requirements (as defined in Section 8 of the Third Amendment) [***];

(b) [***] Dollars ($[***]).

(collectively referred to herein as the "[***]"). If, for any reason, [***]
Dollars ($[***]) [***]%. [***], beginning on the Commencement Date of this
Agreement.

         Subject to the [***] of this Agreement regarding [***] (that is [***]
or subject to a Manufacturer Contract) for [***]:

<Table>
<Caption>
                               [***]                                                 [***]
                           =============                                             ======
<S>                                                                                  <C>
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - [***]                                             [***]%
                           [***] - greater                                           [***]%
</Table>



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<PAGE>



         Buyer's pricing will be reviewed on a [***] basis and any [***] based
on [***] during such [***]; provided, however, that such [***]. [***] of the
[***]. In all instances, [***]. For example, [***].

         The pricing set forth above [***] (as hereinafter defined) [***]. [***]
that include, but are not limited to, [***]. In the event that [***] during the
term of this Agreement [***], or in the event the [***], then [***]. In such
event, [***]. If the [***]; provided, however, [***] to [***] shall be the
pricing in effect as of the date of the notice to Buyer hereunder.

ANNUAL DISCOUNT. Within seven (7) calendar days of January 1, 2004, 2005 and
2006, provided Buyer is in compliance with the terms and conditions of this
Agreement, Buyer will be eligible to receive a discount in an amount equal to
[***] Dollars ($[***]) to be applied to Buyer's purchases of Merchandise under
this Agreement during such month. The discount will be provided in the form of a
credit memo. This discount constitutes a "discount or other reduction in price,"
as such terms are defined under the Medicare/Medicaid Anti-Kickback Statute, on
the Merchandise purchased by Buyer under the terms of this Agreement. Cardinal
and Buyer agree to use their best efforts to comply with any and all
requirements imposed on sellers and buyers, respectively, under 42 U.S.C.
Section 1320a-7b(b)(3)(A) and the "safe harbor" regulations regarding discounts
or other reductions in price set forth in 42 C.F.R. Section 1001.952(h). In this
regard, Buyer may have an obligation to accurately report, as may be required,
under any state or federal program which provides cost or charge based
reimbursement for the products or services covered by this Agreement, or as
otherwise requested or required by any governmental agency, the net cost
actually paid by Buyer.





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