Document:

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                                                                 Exhibit 10.5(b)

                                                                  EXECUTION COPY

                                 AMENDMENT NO. 1
                                       TO
                              AMENDED AND RESTATED
                             MANAGED CARE AGREEMENT

     Amendment No. 1, dated as of July 23, 2003 ("Amendment No. 1") to the
Amended and Restated Managed Care Agreement between Merck & Co., Inc., a New
Jersey corporation ("Merck"), and Medco Health Solutions, Inc., a Delaware
corporation ("Medco"), dated as of May 28, 2003 (the "Agreement"). Capitalized
terms used but not defined herein shall have the meanings ascribed to them in
the Agreement. All section references used herein are to the Agreement.

     WHEREAS, Medco, an independently managed wholly-owned subsidiary of Merck,
is in the business of providing PBM Services to corporations, health maintenance
organizations, unions, insurance carriers, government employee plans and others;

     WHEREAS, Merck is a pharmaceutical company engaged in the discovery,
development, manufacturing and marketing of pharmaceutical products;

     WHEREAS, the parties desire to amend the Agreement to clarify the terms
upon which Medco would be entitled to receive market share rebates from Merck
for the utilization, from and after the Effective Date, of Merck Products by
Medco Plans; and

     WHEREAS, this Amendment No. 1 shall be deemed to be effective as of the
Effective Date.

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

          1. The definition of "Target MAS Premium Percentage" as set forth in
Annex B of the Agreement is hereby amended to read in its entirety as follows:

          "Target MAS Premium Percentage" shall be, with respect to the Calendar
     Quarter ended December 31, 2001, the sum of all of the Weighted Medco
     Market Share Premium Percentages for the Calendar Quarter ended December
     31, 2001, excluding from such calculation Prinivil(R)/Prinzide(R) and the
     Therapeutic Category that includes Prinivil(R)/Prinzide(R), and utilizing a
     Weighted Medco Market Share Premium Percentage for Zocor(R) that is
     calculated assuming a Medco Market Share for Zocor(R) for the Calendar
     Quarter ended December 31, 2001 that is equal to the actual Medco Market
     Share for Zocor(R) for the Calendar Quarter ended December 31, 2001 less
     the Zocor(R) Permitted Percentage Point Reduction set forth on Schedule 4
     to this Annex B. Medco shall deliver to Merck

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     within 30 days from the Effective Date the Quarterly Data with respect to
     the Calendar Quarter ended December 31, 2001. Within 30 days after receipt
     of complete and accurate Quarterly Data for the Calendar Quarter ended
     December 31, 2001, Merck shall calculate the initial Target MAS Premium
     Percentage referred to in the first sentence of this definition. With
     respect to each given Calendar Quarter beginning with the Calendar Quarter
     ended March 31, 2002, the "Target MAS Premium Percentage" shall be
     adjusted, if necessary, to be equal to the sum of (x) the Target MAS
     Premium Percentage for the immediately preceding Calendar Quarter, (y) the
     Outgoing Medco Plans Adjustment Percentage for such given Calendar Quarter
     and (z) the Incoming Medco Plans Adjustment Percentage for such given
     Calendar Quarter. (It is understood that Schedules 1 and 3 to this Annex B
     operate to adjust each of the percentages set forth under "Rebate Tiers" in
     Schedule 3 to this Annex B and under "MAS Premium Percentage" in Schedule 1
     to this Annex B simultaneously with any adjustments to the Target MAS
     Premium Percentage in accordance with the foregoing.) If, at the end of any
     Calendar Quarter ending after the Effective Date, the Cumulative Incoming
     Sales Adjustment Amount exceeds 20% of the sum of the Aggregate Medco Cost
     of all Eligible Prescriptions of all Merck Products dispensed during the
     Calendar Quarter ended December 31, 2001 under all Eligible Medco Plans,
     Merck shall have the right, at any time thereafter, to renegotiate with
     Medco the adjustment methodology reflected above in this paragraph.
     Notwithstanding the foregoing, with respect to Calendar Quarters after the
     Final Zocor(R) Calendar Quarter, (a) the Target MAS Premium Percentage for
     such Calendar Quarter shall be equal to the "Target (Ex-Zocor(R)) MAS
     Premium Percentage (as calculated in accordance with the definition
     thereof) and (b) the percentages under "Rebate Tiers" in Schedule 3 to this
     Annex B and under "MAS Premium Percentage" in Schedule 1 to this Annex B
     shall be adjusted so that the increment (expressed as a percentage) between
     each consecutive tier shall be equal to the increment between such tiers as
     of the execution date of this Restated Agreement (one percent) multiplied
     by the Ex-Zocor(R) Reduction Factor (rounded to the nearest hundredth
     decimal place). (It is understood that, after such adjustment to those
     increments, Schedules 1 and 3 to this Annex B will operate to adjust each
     of the percentages set forth under "Rebate Tiers" in Schedule 3 to this
     Annex B and under "MAS Premium Percentage" in Schedule 1 to this Annex B
     simultaneously with any adjustments to the Target (Ex-Zocor(R)) MAS Premium
     Percentage in accordance with the foregoing.)

          2. The parties agree and acknowledge that, notwithstanding anything to
     the contrary contained in the Restated Agreement, in the event that, for
     any Calendar Quarter, Medco is not entitled to receive a Formulary Access
     Rebate Amount in respect of Eligible Prescriptions of a Merck Product
     dispensed during such Calendar Quarter under a Medco Plan for any reason,
     Medco shall also not be entitled to receive any MAS Rebate in respect of
     such Eligible Prescriptions of

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     such Merck Product dispensed during such Calendar Quarter under such Medco
     Plan.

          3. All references in the Agreement to "the Restated Agreement" are
references to the Agreement as amended by this Amendment No. 1. The definition
of Restated Agreement in the Agreement is hereby amended to read in its entirety
as follows:

          "Restated Agreement" means this Amended and Restated Managed Care
     Agreement, dated and executed on May 28, 2003, between Merck and Medco, as
     further amended by Amendment No. 1 dated as of July 23, 2003, and effective
     as of the Effective Date.

          4. This Amendment No. 1 may be executed simultaneously in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

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         IN WITNESS WHEREOF, the parties have executed this Amendment No. 1 to
the Agreement as of the date set forth above.

                                             MERCK & CO., INC.

                                             By:    /s/ Margaret G. McGlynn
                                                 ----------------------------
                                             Name:  Margaret G. McGlynn
                                             Title: President, U.S. Human
                                                    Health Division

                                             MEDCO HEALTH SOLUTIONS, INC.

                                             By:    /s/ David B. Snow, Jr.
                                                 -------------------------
                                             Name:  David B. Snow, Jr.
                                             Title: President and Chief
                                                    Executive Officer<PAGE>

             FORM OF INDEMNIFICATION AND INSURANCE MATTERS AGREEMENT

     THIS INDEMNIFICATION AND INSURANCE MATTERS AGREEMENT (this "Agreement") is
entered into as of __________, 2003, by and between Merck & Co., Inc., a New
Jersey corporation ("Merck"), and Medco Health Solutions, Inc., a Delaware
corporation ("Medco"). Certain capitalized terms used herein are defined in
Article VI. Capitalized terms used herein and not otherwise defined herein shall
have the meanings ascribed to such terms in the Distribution Agreement (defined
below).

                                    RECITALS

     WHEREAS, the Merck Board has determined that it is appropriate and
desirable for Merck to separate the Medco Group from the Merck Group; and

     WHEREAS, as part of the foregoing, Merck and Medco have entered into the
Master Separation and Distribution Agreement, dated as of __________, 2003 (the
"Distribution Agreement"), which provides, among other things, for the
declaration of the Merck Dividend prior to the Distribution Date, the pro-rata
distribution by Merck of all of its shares of Medco Common Stock to the holders
of Merck Common Stock, and the execution and delivery of certain other
agreements in order to facilitate and provide for the foregoing; and

     WHEREAS, in connection therewith, the parties desire to set forth certain
agreements regarding indemnification and insurance.

     NOW, THEREFORE, in consideration of the foregoing and the covenants and
agreements set forth below, the parties hereto agree as follows:

                                   ARTICLE I

                                 INDEMNIFICATION

     Section 1.1 Indemnification by Medco.

     (a) Indemnification. Except as otherwise provided in this Agreement, Medco
shall, for itself and as agent for each member of the Medco Group, indemnify,
defend and hold harmless the Merck Indemnitees from and against any and all
Liabilities that any third party seeks to impose upon any of the Merck
Indemnitees, or which are imposed upon any of the Merck Indemnitees, if and to
the extent such Liabilities relate to, arise out of or result from any of the
following items (without duplication):

               (i) any breach by Medco or any member of the Medco Group of the
          Distribution Agreement or any of the Ancillary Agreements (including
          this Agreement), other than breaches of the Amended and Restated
          Managed Care Agreement between Merck and Medco, dated as of May 28,
          2003 (the "Restated Agreement"), as further amended from time to time,
          or the original Managed Care Agreement between Merck and Medco, dated
          as of June 28, 2002 (the "Original Agreement" together with the
          Restated Agreement, the "Managed Care Agreement"), which shall be
          covered by the provisions thereof; or

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               (ii) any Medco Liability.

     (b) Reduction of Liability. In the event that any member of the Medco Group
makes a payment to any Merck Indemnitee hereunder, and the Liabilities on
account of which such payment was made are subsequently diminished or reduced,
either directly or through a third-party recovery (other than as a result of a
recovery under a Merck Insurance Policy, unless such recovery is pursuant to the
Credit Support Insurance Coverage, if any), Merck will promptly repay (or will
procure the relevant Merck Indemnitee promptly to repay) such member of the
Medco Group the amount by which the payment made by such member of the Medco
Group exceeds the actual cost of the associated indemnified Liabilities.

     (c) Joint and Several Liability; No Modification to Other Agreements. The
liability of the members of the Medco Group under this Section 1.1 shall be
joint and several. Nothing in this Section 1.1 shall modify or limit the rights
and remedies of Merck under the Distribution Agreement or any of the Ancillary
Agreements (other than this Agreement) relating to, arising out of or resulting
from any breach by Medco or any member of the Medco Group of the Distribution
Agreement or any of the Ancillary Agreements (other than this Agreement),
including without limitation, any provisions relating to the measure of damages,
consequential damages, liquidated damages, limitation of damages and/or specific
performance.

     Section 1.2 Indemnification by Merck.

     (a) Indemnification. Except as otherwise provided in this Agreement, Merck
shall, for itself and as agent for each member of the Merck Group, indemnify,
defend and hold harmless the Medco Indemnitees from and against any and all
Liabilities that any third party seeks to impose upon any of the Medco
Indemnitees, or which are imposed upon any of the Medco Indemnitees, if and to
the extent such Liabilities relate to, arise out of or result from (without
duplication):

               (i)  any breach by Merck or any member of the Merck Group of the
          Distribution Agreement or any of the Ancillary Agreements (including
          this Agreement), other than breaches of the Managed Care Agreement,
          which shall be covered by the provisions thereof; or

               (ii) any Merck Liability;

provided, however, that notwithstanding anything to the contrary herein, in no
event shall Merck or any member of the Merck Group be obligated to indemnify,
defend or hold harmless the Medco Indemnitees from, against or in respect of any
Medco Liability.

     (b) Reduction of Liability. In the event that any member of the Merck Group
makes a payment to any Medco Indemnitee hereunder, and the Liabilities on
account of which such payment was made are subsequently diminished or reduced,
either directly or through a third-party recovery, Medco will promptly repay (or
will procure a Medco Indemnitee to promptly repay) such member of the Merck
Group the amount by which the payment made by such member of the Merck Group
exceeds the actual cost of the associated indemnified Liabilities.

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            (c)  Joint and Several Liability; No Modification to Other
Agreements. The liability of the members of the Merck Group under this Section
1.2 shall be joint and several. Nothing in this Section 1.2 shall modify or
limit the rights and remedies of Medco under the Distribution Agreement or any
of the Ancillary Agreements (other than this Agreement) relating to, arising out
of or resulting from any breach by Merck or any member of the Merck Group of the
Distribution Agreement or any of the Ancillary Agreements (other than this
Agreement), including without limitation, any provisions relating to the measure
of damages, consequential damages, liquidated damages, limitation of damages
and/or specific performance.

     Section 1.3 Procedures for Defense, Settlement and Indemnification of Third
Party Claims.

            (a)  Notice of Claims. If an Indemnitee shall receive notice or
otherwise learn of the assertion of any Third Party Claim with respect to which
a party may be obligated to provide indemnification to such Indemnitee pursuant
to Section 1.1 or 1.2, Merck or Medco (as applicable) shall ensure that such
Indemnitee shall give the potential Indemnifying Party written notice thereof
(including any pleadings relating thereto) within twenty (20) days after
becoming aware of such Third Party Claim. Any such notice shall describe the
Third Party Claim in reasonable detail. Notwithstanding the foregoing, any delay
or failure of any Indemnitee to give notice as provided in this Section 1.3(a)
shall not relieve the Indemnifying Party of its obligations under this Article
I, except to the extent that the Indemnifying Party is actually and
substantially prejudiced by such delay or failure to give notice.

            (b)  Defense by Indemnifying Party. For any Third Party Claim
concerning which notice is required to be given under Section 1.3(a), the
Indemnifying Party may elect to defend and, subject to Section 1.3(f), may
settle or compromise the Third Party Claim using counsel appointed by the
Indemnifying Party, which counsel shall be reasonably satisfactory to the
Indemnitee. An Indemnifying Party electing to defend a Third Party Claim must
(i) notify the Indemnitee of its election to defend within twenty (20) days of
receipt of notice of such claim pursuant to Section 1.3(a) or sooner if the
nature of the Third Party Claim so requires and (ii) subject to Section 1.3(c),
acknowledge and agree in writing that if such Third Party Claim is adversely
determined, such Indemnifying Party will have an obligation to indemnify the
Indemnitee in respect of all Liabilities relating to, arising out of or
resulting from such Third Party Claim and that such Indemnifying Party
irrevocably waives in full all defenses it may have to contest such obligation.

            (c)  Defense by Merck. Notwithstanding Section 1.3(b), Merck, in its
sole discretion, upon written notice to Medco, may elect to defend (or may at
any time assume the defense of) and, subject to Section 1.3(f), may settle or
compromise, any Third Party Claim or series of related Third Party Claims,
regardless of whether Merck is obligated to indemnify any member of the Medco
Group in respect of such Third Party Claim or series of related Third Party
Claims or whether Merck acknowledges any obligation to indemnify any Medco
Indemnitee if:

                 (i) any member of the Merck Group is named as a party to any of
            such Third Party Claims; or

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                 (ii) both Merck and Medco may be Indemnifying Parties with
            respect to such Third Party Claim(s).

     Except as otherwise provided in the definition of "Merck Share of the
Shared Liability Actions," if Merck elects to defend against a Third Party Claim
pursuant to this Section 1.3(c) all costs and expenses incurred by members of
the Merck Group in connection with such defense shall be paid by Merck and Medco
pro rata based on their respective proportionate liability for any Liabilities
relating to, arising out of or resulting from such Third Party Claim (after
taking into account the parties' respective indemnification obligations under
this Agreement, other than with respect to payment of defense costs).

            (d)  Defense By Non-Electing Party. If the party having the right to
elect to defend a Third Party Claim pursuant to Section 1.3(b) or 1.3(c) elects
not to defend, or does not within any time frame required thereunder elect to
defend, a particular claim, the other party shall defend such Third Party Claim.
In such case, (i) the other party shall have the right, subject to Sections
1.3(c) and 1.3(f) and the provisions contained in the definition of "Merck Share
of the Shared Liability Actions," to compromise, settle or consent to the entry
of any judgment with respect to such Third Party Claim (but such compromise,
settlement or judgment shall not necessarily be determinative of which party
hereunder is entitled to indemnification) and (ii) the Indemnifying Party shall
bear all costs and expenses of defending such Third Party Claim; provided,
however, that if both parties may be Indemnifying Parties with respect to such
Third Party Claim, except as otherwise provided in the definition of "Merck
Share of the Shared Liability Actions," the Non-Defending Party (defined below)
shall reimburse the Defending Party for the Non-Defending Party's pro rata share
of all costs and expenses incurred by the Defending Party in connection with its
defense of such Third Party Claim, based on the Non-Defending Party's
proportionate liability for any Liabilities relating to, arising out of or
resulting from such Third Party Claim (after taking into account the parties'
indemnification obligations under this Agreement, other than with respect to
payment of defense costs).

            (e)  Participation by Non-Defending Party. In the event that a party
(a "Defending Party") elects or is required to defend a particular Third Party
Claim pursuant to Section 1.3(b), 1.3(c) or 1.3(d), the other party (the
"Non-Defending Party") shall have the right to participate in the defense of
such Third Party Claim; provided, however, that (i) the Defending Party shall
control, manage and direct the defense of such Third Party Claim; and (ii) the
costs and expenses of participating in such defense by the Non-Defending Party
shall be the sole responsibility of the Non-Defending Party. Nothing in this
Section 1.3(e) shall affect the rights of Merck under Section 1.3(c) at any time
to assume the defense of any Third Party Claim and to be indemnified for costs
and expenses of such defense in accordance with Section 1.3(c).

            (f)  No Settlement, Compromise or Consent to Judgments.

                 (i)  No Non-Defending Party may compromise or settle or consent
            to the entry of judgment or determination of liability with respect
            to any Third Party Claim without the consent of the Defending Party.

                 (ii) Notwithstanding anything to the contrary herein (but
            subject to the provisions contained in the definition of "Merck
            Share of the Shared Liability

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            Actions"), no Defending Party shall compromise, settle or consent to
            the entry of judgment or determination of liability concerning any
            Third Party Claim without providing at least 10 days' prior written
            notice of such compromise, settlement or consent to the Indemnitor
            (if the Indemnitor is other than the Defending Party) and without
            the consent of the Non-Defending Party (such approval not to be
            unreasonably withheld) if the terms or conditions of such
            compromise, settlement or consent would have a Material Adverse
            Effect on the Non-Defending Party's Group.

     Section 1.4 Additional Matters.

            (a)  Other Claims for Indemnification. Any claim in respect of a
Liability which does not relate to, arise out of or result from a Third Party
Claim shall be asserted by written notice from the Indemnitee to the
Indemnifying Party stating the specific provisions of this Agreement or any
Ancillary Agreement upon which such claim is based. Such Indemnifying Party
shall have a period of twenty (20) days from actual receipt of the notice within
which to respond thereto. If such Indemnifying Party does not respond within
such 20-day period, then such Indemnifying Party shall be deemed to have denied
responsibility for such claim.

            (b)  Contribution. If with respect to any Securities Liabilities an
Indemnitee's right to indemnification therefor contained in this Article I is
for any reason held by a court or other tribunal to be unavailable on policy
grounds or otherwise, the Indemnifying Party shall contribute to any amount
payable by the Indemnitee as a result of such Securities Liabilities in such
proportion as to reflect the relative benefit received by the members of the
Indemnifying Party's Group and such Indemnitee from the transaction or
disclosure giving rise to such Securities Liability. If the contribution
provided above is not permitted by applicable law, the Indemnifying Party shall
contribute to any amount payable by the Indemnitee as a result of such
Securities Liabilities in such proportion as to reflect the relative benefit
received by the members of the Indemnifying Party's Group and such Indemnitee
from the transaction and the statements and omissions giving rise to such
Securities Liability, and the relative fault of such members and the Indemnitee
in connection with such statements or omissions. The relative fault of the
members of the Indemnifying Party's Group and such Indemnitee shall be
determined by reference to, among other things, their relative intent,
knowledge, access to information and opportunity to prevent or correct the
statements or omissions giving rise to such Securities Liability.

            (c)  Subrogation. In the event of payment by or on behalf of any
Indemnifying Party to or on behalf of any Indemnitee in connection with any
Third Party Claim, such Indemnifying Party shall be subrogated to and shall
stand in the place of such Indemnitee, in whole or in part based upon whether
the Indemnifying Party has paid all or only part of the Indemnitee's Liability,
as to any events or circumstances in respect of which such Indemnitee may have
any right, defense or claim relating to such Third Party Claim against any
claimant or plaintiff asserting such Third Party Claim or against any other
Person. Such Indemnitee shall cooperate with such Indemnifying Party in a
reasonable manner, and at the cost and expense of such Indemnifying Party, in
prosecuting any subrogated right, defense or claim.

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            (d)  Effect of Insurance on Indemnification/Contribution
Obligations. No Indemnitee shall be required to pursue any claim under any
Insurance Policies of which it is a beneficiary in connection with any Liability
for which such Indemnitee is entitled to indemnification hereunder. The amount
of indemnification or contribution to which such Indemnitee may be entitled
hereunder shall not be reduced as a result of any claim such Indemnitee may
pursue, or have the right to pursue, under any Insurance Policy in respect of
the Liability to which such right to indemnification or contribution relates,
unless the Indemnitee shall have actually recovered any portion of such
Liability from its insurance carrier(s), in which case, whether or not the
amount of indemnification or contribution to such Indemnitee shall be reduced
shall be determined in accordance with Sections 1.1(b) and 1.2(b), as
applicable.

            (e)  Not Applicable to Taxes. Notwithstanding anything to the
contrary contained herein, this Agreement shall not apply to Taxes (which are
covered by the Tax Agreement).

     Section 1.5 Survival of Indemnities. Subject to Section 5.4, the rights and
obligations of the members of the Merck Group and the Medco Group under this
Article I shall survive the sale or other transfer by any party of any assets or
businesses or the assignment by it of any Liabilities or the sale by any member
of the Merck Group or the Medco Group of the capital stock or other equity
interests of any Subsidiary to any Person.

                                   ARTICLE II

                                INSURANCE MATTERS

     Section 2.1 Medco Insurance Coverage. Medco, and Medco alone, shall be
responsible for obtaining and maintaining insurance programs for its risk of
loss and such insurance arrangements shall be separate and apart from Merck's
insurance programs. Merck shall not be required to maintain any insurance
coverage for the benefit of the members of the Medco Group or the directors,
officers or employees of any member of the Medco Group for any period prior to
or after the Distribution.

     Section 2.2 Cooperation and Agreement Not to Release Carriers. Each of
Merck and Medco will share such information as is reasonably necessary in order
to permit the other to manage and conduct its insurance matters in an orderly
fashion. Medco, at the request of Merck, shall cooperate with and use
commercially reasonable efforts to assist Merck in recoveries for claims made
under any Merck Insurance Policy for the benefit of members of the Merck Group.
Neither Medco nor any of its Subsidiaries shall take any action which would
intentionally jeopardize or otherwise interfere with the ability of any member
of the Merck Group to collect any proceeds payable pursuant to any insurance
policy. Nothing in this Agreement shall be interpreted to require Merck to
maintain any insurance coverage for any Member of the Medco Group or any of
their officers, directors or employees.

     Section 2.3 No Liability. Medco does hereby, for itself and as agent for
each other member of the Medco Group, agree that no member of the Merck Group or
any Merck Indemnitee shall have any Liability whatsoever as a result of the
insurance policies and practices

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of Merck and its Subsidiaries as in effect at any time prior to the Distribution
Date, including as a result of the level or scope of any such insurance, the
creditworthiness of any insurance carrier, the terms and conditions of any
policy, the adequacy or timeliness of any notice to any insurance carrier with
respect to any claim or potential claim or otherwise.

     Section 2.4 No Restrictions. Nothing in this Agreement shall be deemed to
restrict any member of the Medco Group from acquiring at its own expense any
other insurance policy in respect of any Liabilities or covering any period.

     Section 2.5 Further Agreements. Medco, the members of the Medco Group, and
the directors, officers and employees of any member of the Medco Group, shall
not make any claims under Merck Insurance Policies, including in respect of
events that occurred when Medco and the members of the Medco Group were
subsidiaries of Merck, without Merck's approval, which may be granted or
withheld in Merck's sole discretion.

                                   ARTICLE III

                               DISPUTE RESOLUTION

     EXCEPT AS OTHERWISE SET FORTH IN THE DISTRIBUTION AGREEMENT OR ANY
ANCILLARY AGREEMENT, ANY DISPUTES ARISING OUT OF OR RELATING TO THE DISTRIBUTION
AGREEMENT OR ANY ANCILLARY AGREEMENT (INCLUDING THIS AGREEMENT BUT EXPRESSLY
EXCLUDING THE MANAGED CARE AGREEMENT), INCLUDING, WITHOUT LIMITATION, DISPUTES
CONCERNING THE VALIDITY, INTERPRETATION AND PERFORMANCE OF OR UNDER ANY SUCH
AGREEMENT, SHALL BE EXCLUSIVELY GOVERNED BY AND SETTLED IN ACCORDANCE WITH THE
PROVISIONS OF THIS ARTICLE III.

     Section 3.1 Negotiation. The parties shall make a good faith attempt to
resolve any Dispute through negotiation. Within fifteen (15) days after notice
of a Dispute is given by either party to the other party, each party shall
select one or more representatives who are vice presidents, senior vice
presidents or executive vice presidents of such party and shall notify the other
party in writing of the names and contact details of its representatives, which
representatives shall meet and make a good faith attempt to resolve such Dispute
and shall continue to negotiate in good faith in an effort to resolve the
Dispute without the necessity of any formal proceedings. The specific format for
such negotiations will be left to the discretion of the designated
representatives but may include the preparation of agreed upon statements of
fact or written statements of position furnished to the other party.

     Section 3.2 Binding Arbitration.

            (a)  If such representatives fail to resolve a Dispute within ten
(10) days after the date of delivery of the later of the notices of selection of
the representatives, unless otherwise mutually agreed, either party shall have
the right to submit such Dispute to final and binding arbitration. It is the
intent of the parties that any such arbitration be structured in such a way as
to result in a resolution of such Dispute as promptly as practicable in
accordance herewith.

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Except as otherwise provided in this Article III, any arbitration shall be
conducted pursuant to the then current Rules for Non-Administered Arbitration of
the Center for Public Resources ("CPR Rules") and the site of the arbitration
shall be in New York County, New York.

         (b) A party (a "Disputing Party") shall institute any arbitration
proceeding hereunder by providing written notice thereof to the other party (the
"Arbitration Demand") which shall describe in reasonable detail the nature of
the Dispute, the claims of the Disputing Party and the requested relief and, if
the Disputing Party is Merck, setting forth a list of at least five potential
independent and impartial arbitrators selected by Merck, each of whom shall not
have a personal or financial interest in the result of the arbitration or the
parties to the arbitration (provided that the ownership of shares in a mutual
fund that owns securities of either of the parties shall not be considered a
personal or financial interest for this purpose) and shall be experienced in
representing clients in commercial arbitration. Within thirty (30) days after
the other party's receipt of the Arbitration Demand, such other party shall
furnish the Disputing Party with a written statement (a "Response Statement")
(1) answering the claims set forth in the Arbitration Demand, (2) asserting any
counterclaim, describing in reasonable detail the nature of the Dispute relating
to such counterclaim and the requested relief for such counterclaims, and (3) if
such other party is Medco, selecting as the sole arbitrator for the proceeding
one of the potential arbitrators listed in the Arbitration Demand or if such
other party is Merck setting forth a list of at least five potential impartial
arbitrators selected by Merck, each of whom shall not have a personal or
financial interest in the result of the arbitration or the parties to the
arbitration (provided that the ownership of shares in a mutual fund that owns
securities of either of the parties shall not be considered a personal or
financial interest for this purpose) and shall be experienced in representing
clients in commercial arbitration. If the Disputing Party is Medco, Medco shall
notify Merck within ten (10) days of Medco's receipt of the Response Statement
of Medco's selection as the sole arbitrator for the proceeding from the
potential arbitrators listed in the Arbitration Demand. If Medco fails within
the applicable time period to select an arbitrator from the list of potential
arbitrators included in Merck's Arbitration Demand or Response Statement, as
applicable, an arbitrator shall be selected in accordance with the CPR Rules
from such list of potential arbitrators.

         (c) The arbitrator shall be instructed to use best efforts to complete
all arbitration hearings no later than three (3) months from the date of the
arbitrator's appointment and use best efforts to render a decision within four
(4) months from such date.

         (d) With respect to discovery in an arbitration proceeding, the
arbitrator must allow either party to make discovery requests for documents of
the other party where the information sought is reasonably calculated to lead to
the discovery of admissible evidence, and each party agrees to respond to such
discovery request within a reasonable time. The arbitrator is obligated to
construe the term "document" literally to encompass data compilations in any
form.

         (e) The prevailing party in any arbitration as determined by the
arbitrator shall be entitled to expenses, including costs and reasonable
attorneys' and other professional fees, incurred in connection with the
arbitration.

                                       8

<PAGE>

            (f)  In connection with any Dispute, the arbitrator shall be
obligated to apply solely principles of law.

            (g)  The decision of the arbitrator shall be final and
non-appealable and may be enforced in any court of competent jurisdiction.

            (h)  The use of any alternative dispute resolution procedures will
not be construed under the doctrine of laches, waiver or estoppel to adversely
affect the rights of either party.

     Section 3.3 Specific Performance. The parties agree and acknowledge that
each would suffer irreparable harm in the event that the other fails to perform
any of its obligations under Article IV hereunder in accordance with its
specific terms or otherwise breaches any of such obligations. Each of the
parties further agrees and acknowledges that money damages may be an inadequate
remedy for such failure to perform or breach of Article IV by it. Accordingly,
notwithstanding anything herein to the contrary, and without waiving any remedy
hereunder, each of the parties shall be entitled to seek specific performance by
the other of its obligations under Article IV hereunder and/or injunctive or
other equitable relief to prevent or cure breaches of Article IV hereunder in an
arbitration proceeding (without first complying with the negotiation provision
of Section 3.1) or in court (subject to Section 5.2).

                                   ARTICLE IV

                             PRIVILEGED INFORMATION

     Section 4.1 Privileged Information. In furtherance of the rights and
obligations of the parties set forth in the Distribution Agreement and the
Ancillary Agreements:

            (a)  Each party hereto acknowledges that (i) each of the Merck Group
on the one hand, and the Medco Group on the other hand, has or may obtain
Information regarding a member of the other Group, or any of its operations,
employees, assets or liabilities (whether in documents or stored in any other
form or known to its employees or agents), as applicable, that is or may be
protected from disclosure pursuant to the attorney-client privilege, the work
product doctrine or other applicable privileges ("Privileged Information"); (ii)
there are a number of actual, threatened or future litigations, investigations,
proceedings (including arbitration proceedings), claims or other legal matters
that have been or may be asserted by or against, or otherwise affect, each or
both of Merck and Medco (or members of either Group) ("Litigation Matters");
(iii) Merck and Medco have a common legal interest in Litigation Matters, in the
Privileged Information, and in the preservation of the confidential status of
the Privileged Information, in each case relating to the Merck Business or the
Medco Business or any former businesses or the assets or liabilities of each
party as it or they existed prior to the Distribution Date or relating to or
arising in connection with the relationship between the constituent elements of
the Groups on or prior to the Distribution Date; and (iv) Merck and Medco intend
that the transactions contemplated by the Related Agreements and any transfer of
Privileged Information in connection herewith or therewith shall not operate as
a waiver of any potentially applicable privilege.

                                       9

<PAGE>

            (b)  Each of Merck and Medco agrees, on behalf of itself and each
member of the Group of which it is a member, not to disclose or otherwise waive
any privilege attaching to any Privileged Information relating to the Merck
Business or the Medco Business or any former businesses or the assets or
liabilities of either party as it or they existed prior to the Distribution Date
or relating to or arising in connection with the relationship between the Groups
on or prior to the Distribution Date, without providing prompt written notice to
and obtaining the prior written consent of the other, which consent shall not be
unreasonably withheld and shall not be withheld if the other party certifies
that such disclosure is to be made in response to a likely threat of suspension,
debarment, criminal indictment or similar action; provided, however, that Merck
may make such disclosure or waiver with respect to Privileged Information if
such Privileged Information relates solely to the Merck Business, its former
businesses (other than the Medco Business), its assets or liabilities (other
than assets or liabilities of the Medco Business), and Medco may make such
disclosure or waiver with respect to Privileged Information if such Privileged
Information relates solely to the Medco Business, or assets or liabilities
exclusively of the Medco Business. The parties will use commercially reasonable
efforts to limit any such disclosure or waiver to the maximum extent possible
and shall seek the execution of a confidentiality agreement by the party or
parties to which such disclosure or waiver is made.

            (c)  Upon any member of the Merck Group or any member of the Medco
Group receiving any subpoena or other compulsory disclosure notice from any
Governmental Authority or otherwise which requests disclosure of Privileged
Information, in the case of the Medco Group, relating to the Merck Business, its
former businesses (other than the Medco Business), its assets or liabilities
(other than assets or liabilities of the Medco Business), or, in the case of the
Merck Group, relating to the Medco Business, or assets or liabilities
exclusively of the Medco Business, as it or they existed prior to the
Distribution Date or, in either case, relating to or arising in connection with
the relationship between the constituent elements of the Groups on or prior to
the Distribution Date, the recipient of the notice shall promptly provide to
Merck, in the case of receipt by a member of the Medco Group, or to Medco, in
the case of receipt by a member of the Merck Group, a copy of such notice, the
intended response, and all materials or information relating to the other Group
that might be disclosed. In the event of a disagreement as to the intended
response or disclosure, unless and until the disagreement is resolved as
provided in Article III, Merck and Medco shall cooperate to assert all defenses
to disclosure claimed by either Group, at the cost and expense of the Group
claiming such defense to disclosure, and shall not disclose any disputed
documents or information until all legal defenses and claims of privilege have
been finally determined.

                                    ARTICLE V

                                  MISCELLANEOUS

     Section 5.1 Entire Agreement. This Agreement, the Distribution Agreement,
the other Ancillary Agreements and any Annexes, Exhibits and Schedules attached
hereto and thereto, constitutes the entire agreement among the parties with
respect to the subject matter hereof and thereof and shall supersede all prior
written and oral and all contemporaneous oral agreements and understandings with
respect to the subject matter hereof and thereof.

                                       10

<PAGE>

     Section 5.2 Governing Law; Forum. This Agreement, the Distribution
Agreement and all other Ancillary Agreements shall be construed in accordance
with, and all Disputes hereunder shall be governed by, the procedural (except to
the extent inconsistent with the procedures set forth in Article III of this
Agreement) and substantive laws of the State of New York as to all matters
regardless of the laws that might otherwise govern under principles of conflicts
of laws applicable thereto. Under no circumstances may any party seek or be
awarded punitive damages under this Agreement, the Distribution Agreement or any
other Ancillary Agreement. Any state court sitting in New York county, New York
and/or the United States District Court for the Southern District of New York
shall have exclusive jurisdiction and venue, and each party hereto hereby
submits to such jurisdiction and venue and irrevocably waives, to the fullest
extent permitted by applicable law, any objection it may now or hereafter have
to such jurisdiction or the laying of such venue over any Disputes between the
parties that are permitted to be brought in a court, or the enforcement of any
decision of arbitrators, pursuant to Article III above. Each of the parties
hereby irrevocably waives any right to a jury trial with respect to a Dispute.

     Section 5.3 Notices. All notices and other communications required or
permitted to be given by any party pursuant to the terms of this Agreement shall
be in writing to and shall be deemed to have been duly given when delivered in
person, by express or overnight mail delivery by a nationally recognized courier
(delivery charges prepaid), or by registered or certified mail (postage prepaid,
return receipt requested), as follows:

         if to Merck:

                 Merck & Co., Inc.
                 One Merck Drive
                 P.O. Box 100
                 Whitehouse Station, New Jersey 08889
                 Attention: General Counsel

         if to Medco:

                 Medco Health Solutions, Inc.
                 100 Parsons Pond Drive
                 Franklin Lakes, New Jersey 07417
                 Attention: General Counsel

or to such other address as the party to whom notice is given may have
previously furnished to the other in writing in the manner set forth above. All
notices and other communication shall be deemed to have been given and received
on the date of actual delivery.

     Section 5.4 Binding Effect; Assignment; Third-Party Beneficiaries. Medco
may not, directly or indirectly, in whole or in part, whether by operation of
law or otherwise, assign or transfer this Agreement or its rights or obligations
hereunder, without Merck's prior written consent and, except as otherwise
permitted hereby, any attempted assignment, transfer or delegation without such
prior written consent shall be voidable at the sole option of Merck. Nothing in
this Agreement shall restrict any transfer of this Agreement by Merck, whether
by

                                       11

<PAGE>

operation of law or otherwise. Without limiting the foregoing, this Agreement
shall be binding upon Merck and the other members of the Merck Group and Medco
and the other members of the Medco Group and inure solely to the benefit of the
Medco Indemnitees and the Merck Indemnitees and their respective legal
representatives, successors and permitted assigns, and nothing in this
Agreement, express or implied, is intended to confer upon any other Person any
rights or remedies of any nature whatsoever under or by reason of this
Agreement.

     Section 5.5 Offset. In addition to, and not in limitation of, any other
remedies any member of the Merck Group or any Merck Indemnitee may be entitled
to under the Distribution Agreement, any Ancillary Agreement (including this
Agreement) or any Intercompany Agreement, any member of the Merck Group or any
Merck Indemnitee may satisfy any amounts owed to such member of the Merck Group
or Merck Indemnitee by any member of the Medco Group by means of an offset
against any amounts any member of the Merck Group may from time to time owe to
any member of the Medco Group or an Medco Indemnitee, whether under the
Distribution Agreement, any Ancillary Agreement (including this Agreement), any
Intercompany Agreement, any other agreement or arrangement existing between any
member of the Merck Group and any member of the Medco Group, or otherwise.

     Section 5.6 Other Agreements Evidencing Indemnification Obligations. Merck
hereby agrees to execute, for the benefit of any Medco Indemnitee, such
documents as may be reasonably requested by such Medco Indemnitee, evidencing
Merck's agreement that the indemnification obligations of Merck set forth in
this Agreement inure to the benefit of and are enforceable by such Medco
Indemnitee. Medco hereby agrees to execute, for the benefit of any Merck
Indemnitee, such documents as may be reasonably requested by such Merck
Indemnitee, evidencing Medco's agreement that the indemnification obligations of
Medco set forth in this Agreement inure to the benefit of and are enforceable by
such Merck Indemnitee.

     Section 5.7 Counterparts. This Agreement, including any Annexes, Schedules
and Exhibits hereto, and the other documents referred to herein, may be executed
in counterparts, each of which shall be deemed to be an original but all of
which shall constitute one and the same agreement.

     Section 5.8 Severability. If any term or other provision of this Agreement
or any Annexes, Schedules or Exhibits attached hereto is determined by a court,
administrative agency or arbitrator to be invalid, illegal or incapable of being
enforced by any rule of law or public policy, all other conditions and
provisions of this Agreement will nevertheless remain in full force and effect
so long as the economic or legal substance of the transactions contemplated
hereby is not affected in any manner materially adverse to any party hereto.
Upon such determination that any term or other provision is invalid, illegal or
incapable of being enforced, the parties hereto shall negotiate in good faith to
modify this Agreement so as to effect the original intent of the parties hereto
as closely as possible in an acceptable manner to the end that transactions
contemplated hereby are fulfilled to the fullest extent possible. If the parties
are unable to reach an agreement on any such modification, the arbitrator
selected in accordance with Article III of this Agreement shall have the
authority to determine such modification.

     Section 5.9 Failure or Indulgence Not Waiver. No failure or delay on the
part of any party hereto in the exercise of any right hereunder shall impair
such right or be construed to be a

                                       12

<PAGE>

waiver of, or acquiescence in, any breach of any representation, warranty or
agreement herein, nor shall any single or partial exercise of any such right
preclude other or further exercise thereof or of any other right.

     Section 5.10 Amendment. No change or amendment will be made to this
Agreement except by an instrument in writing signed on behalf of each of the
parties to this Agreement.

     Section 5.11 Interpretation. The headings contained in this Agreement, in
any Annex, Exhibit or Schedule hereto and in the table or contents to this
Agreement are for reference purposes only and shall not affect in any way the
meaning or interpretation of this Agreement. Any capitalized term used in any
Annex, Schedule or Exhibit but not otherwise defined therein, shall have the
meaning assigned to such term in this Agreement. When a reference is made in
this Agreement to an Article or Section, or an Annex, Exhibit or Schedule, such
reference shall be to an Article or Section of, or an Annex, Exhibit or Schedule
to, this Agreement unless otherwise indicated.

                                   ARTICLE VI

                                   DEFINITIONS

     Section 6.1  Action. "Action" means any claim, demand, action, suit,
countersuit, arbitration, inquiry, proceeding or investigation by or before any
federal, state, local, foreign or international governmental authority or any
arbitration or mediation tribunal.

     Section 6.2  Dispute. "Dispute" means a dispute arising from or in
connection with the Distribution Agreement, this Agreement or any other
Ancillary Agreement, whether based on contract, tort, or otherwise.

     Section 6.3  Indemnitee. "Indemnitee" means a Merck Indemnitee or a Medco
Indemnitee.

     Section 6.4  Indemnifying Party. "Indemnifying Party" means any party who
is required to indemnify any other Person pursuant to this Agreement.

     Section 6.5  Insurance Policies. "Insurance Policies" means insurance
policies pursuant to which a Person makes a true risk transfer to an insurer.

     Section 6.6  Intercompany Agreements. "Intercompany Agreements" means any
written agreement, arrangement or understanding between any member of the Merck
Group and any member of the Medco Group which is in effect prior to, as of or
after the Distribution Date.

     Section 6.7  Liabilities. "Liabilities" means all debts, liabilities,
guarantees, assurances, commitments and obligations, whether fixed, contingent
or absolute, asserted or unasserted, matured or unmatured, liquidated or
unliquidated, accrued or not accrued, known or unknown, due or to become due,
whenever or however arising (including, without limitation, whether arising out
of any contract or tort based on negligence or strict liability) and whether or
not the same would be required by generally accepted principles and accounting
policies to be

                                       13

<PAGE>

reflected in financial statements or disclosed in the notes thereto. For
purposes of any indemnification hereunder, "Liabilities" shall be deemed also to
include any and all damages, claims, suits, judgments, fines, penalties, costs
and expenses of any kind or character, including attorney's fees and expenses,
costs of investigation and preparation, expert witness costs and any other fees
and expenses associated with the defense of any Action whether relating to Third
Party Claims or Actions against the other party hereto.

     Section 6.8  Material Adverse Effect. "Material Adverse Effect" means, with
respect to either Group, a material adverse effect on the business, results of
operations or financial conditions of the members of such Group, taken as a
whole, provided that, without limiting the events, circumstances or conditions
which may constitute or result in a Material Adverse Effect on the Merck Group,
any compromise, settlement or consent affecting the Merck Group that, if applied
to Medco or any member of the Medco Group, would result in a Material Adverse
Effect on the Medco Group, shall be deemed to result in a Material Adverse
Effect on the Merck Group.

     Section 6.9  Medco Assets. "Medco Assets" means all assets of the Medco
Group following the consummation of the Distribution.

     Section 6.10 Medco Balance Sheets. "Medco Balance Sheets" means the
consolidated balance sheets of Medco and its Subsidiaries included in the Form
10.

     Section 6.11 Medco Business. "Medco Business" means (a) the business and
operations of Medco, Merck-Medco LLC and its Subsidiaries and Affiliates (other
than members of the Merck Group), and (b) except as otherwise expressly provided
herein, any terminated, divested or discontinued businesses or operations that
at the time of termination, divestiture or discontinuation primarily related to
the Medco Business as then conducted; provided, that the Medco Business shall
not include the business or operations of Merck Capital Ventures LLC, Merck
Liability Management Company or Merck Medco Holdings II Corp.

     Section 6.12 Medco Indemnitees. "Medco Indemnitees" means Medco, each
member of the Medco Group and each of their respective directors, officers,
employees, agents or representatives.

     Section 6.13 Medco Liabilities. "Medco Liabilities" means, collectively,
all of the Liabilities of Medco and each of the other members of the Medco
Group, including without limitation:

                  (i)   all of the Liabilities reflected on the Medco Balance

               Sheet;

                  (ii)  all Liabilities relating to, arising out of or resulting
               from any of the Credit Support Arrangements, including, without
               limitation, any payment required to be made by a member of the
               Merck Group under any of the Credit Support Arrangements;

                  (iii) all Liabilities which are incurred or arise, or which
               accrue or exist or are accrued at any time on, prior to or after
               the date of the Medco Balance

                                       14

<PAGE>

         Sheets and which arise or arose out of, or in connection with, or
         otherwise relate to or result from, the Medco Assets or the Medco
         Business;

             (iv)    all Liabilities of each member of the Medco Group under,
         allocated to or to be retained or assumed by Medco or any of the other
         members of the Medco Group pursuant to the Distribution Agreement, this
         Agreement or any Ancillary Agreements, or Intercompany Agreements;
         provided that nothing in this Agreement shall adversely affect the
         rights and remedies of Merck or Medco under the Managed Care Agreement
         relating to, arising out of or resulting from a breach of the Managed
         Care Agreement, or any Liability of either party to the other relating
         to, arising out of or resulting from such breach;

             (v)     all of the Liabilities of any member of the Merck Group or
         Medco Group (whenever arising whether prior to, on or following the
         Distribution Date) arising out of or in connection with or otherwise
         relating to the management or conduct prior to, on or following the
         Distribution Date of the Medco Business or the Medco Assets; provided
         that nothing in this Agreement shall adversely affect the rights and
         remedies of Merck or Medco under the Managed Care Agreement relating
         to, arising out of or resulting from a breach of the Managed Care
         Agreement, or any Liability of either party to the other relating to,
         arising out of or resulting from such breach;

             (vi)    Subject to the proviso set forth after clause (x) of this
         Section 6.13, all Liabilities relating to, arising out of or resulting
         from (a) the Shared Liability Actions, any Actions in respect of which
         as of the date of this Agreement any member of the Medco Group has been
         named as a defendant (including, without limitation, the Actions
         captioned U.S.A. ex rel. Hunt and Gauger v. Medco and U.S.A. ex rel. v.
         Piacentile v. Medco) or any amendments to such Actions (the "Existing
         Actions"), (b) any of the facts, circumstances and events giving rise
         to Shared Liability Actions or any of the Existing Actions, and (c) any
         Actions involving similar claims or which are based upon similar facts,
         circumstances or events, whether involving the same parties or other
         parties, in each case whether relating to, arising out of or resulting
         from facts, circumstances or events prior to, on or after the
         Distribution Date;

             (vii)   all Liabilities relating to, arising out of or resulting
         from, any Third Party Claim relating to, arising out of or resulting
         from (1) the Managed Care Agreement or (2) any infringement or alleged
         infringement by the Patents or the Patent License (or the use thereof)
         on any intellectual property or other rights of any Person;

             (viii)  all Liabilities relating to, arising out of or resulting
         from the Actions, Third Party Claims, the examinations, notices,
         letters, reviews and investigations by Governmental Authorities,
         referred to in the Form 10 under "Business - Legal Proceedings and
         Government Investigations", and "Management - Retirement Benefits -
         Cash Balance Plan" and Liabilities relating to, arising out of, or
         resulting from the facts, circumstances or events giving rise

                                       15

<PAGE>

         to any of such Actions, Third Party Claims, examinations, notices,
         letters, reviews or investigations (subject to the proviso set forth
         after clause (x) of this Section 6.13);

             (ix)    all Securities Liabilities relating to, arising out of or
         resulting from (A) the Notes Offering, the Distribution and any
         documents, information or data (financial or otherwise) furnished or
         provided, orally or in writing, to purchasers or transferees or
         potential purchasers and transferees (or any of their respective
         representatives), in connection therewith or filed or furnished in
         connection therewith with or to any Governmental Authority or any
         securities exchange or securities market, including, without
         limitation, the Registration Statements, (B) any other offer, issuance,
         sale, exchange or other transfer of securities of or by Medco or any
         member of the Medco Group prior to, on or after the Distribution Date,
         or any documents, information or data (financial or otherwise)
         furnished or provided, orally or in writing, to transferees or
         purchasers or potential transferees or purchasers (or any of their
         respective representatives) of such securities or filed or furnished in
         connection therewith with or to any Governmental Authority or
         securities exchange or securities market, including, without
         limitation, any registration statement, (C) any oral or written
         disclosure made, whether or not included in documents filed with or
         furnished to any Governmental Authority or securities exchange or
         securities market, by Medco or any member of the Medco Group, or on
         behalf of Medco or any Member of the Medco Group, prior to, on or after
         the Distribution Date or any disclosure made (other than by a member of
         the Merck Group), orally or in writing, of information or data
         (financial or otherwise) relating to or concerning Medco or any other
         member of the Medco Group, the business, operations and management of
         the Medco Business and/or Medco or any other member of the Medco Group,
         and (D) any oral or written disclosure made, whether or not included in
         documents filed with or furnished to any Governmental Authority or
         securities exchange or securities market, by Merck or any member of the
         Merck Group prior to, on or after the Distribution Date based on any
         information or data (financial or otherwise) provided by or on behalf
         of Medco or any member of the Medco Group; and

             (x)     all other Liabilities arising out of, relating to or
         resulting from any Action or Third Party Claim by any Governmental
         Authority or any other Person that is based on (A) any violations or
         alleged violations by Medco, its Subsidiaries and/or any of their
         respective directors, officers, employees, agents or representatives of
         any of the provisions of the Securities Act, Exchange Act, or the rules
         and regulations of the Commission promulgated thereunder, any other
         securities or similar law or any other law, rule or regulation,
         including, without limitation, the federal False Claims Act and state
         False Claims Acts, or (B) any breach or alleged breach of fiduciary
         duty by the Medco Board or any Committee of the Medco Board (or any
         member of the Medco Board or any Committee thereof) or the board of
         directors or similar body or any Committee of the board of directors or
         similar body (or any member of any such board or similar body or

                                       16

<PAGE>

            any Committee thereof) of any other member of the Medco Group, or by
            any officer or employee of any member of the Medco Group.

provided, however, that (i) Medco Liabilities shall not include the Merck
Defendant Robinson-Patman Act Liabilities (as defined in Section 6.16), and (ii)
Merck shall be responsible for the Merck Share of the Shared Liability Actions.

     Section 6.14 Merck Indemnitees. "Merck Indemnitees" means Merck, each
member of the Merck Group and each of their respective directors, officers,
employees, agents and representatives.

     Section 6.15 Merck Insurance Policy. "Merck Insurance Policy" shall mean
each Insurance Policy owned or maintained by a member of the Merck Group.

     Section 6.16 Merck Liabilities. "Merck Liabilities" means

                  (i)   all Liabilities of any member of the Merck Group under,
            allocated to or to be retained or assumed by Merck or any of the
            other members of the Merck Group pursuant to the Distribution
            Agreement, this Agreement or any other Ancillary Agreement (other
            than Liabilities resulting from a breach of the Managed Care
            Agreement, which shall be subject to the terms thereof);

                  (ii)  all Liabilities incurred by members of the Merck Group
            in connection with the management or conduct prior to, on or
            following the Distribution Date of the Merck Business (other than
            Liabilities resulting from a breach of the Managed Care Agreement,
            which shall be subject to the terms thereof); and

                  (iii) all monetary Liabilities arising out of those Actions
            set forth on Schedule 6.16 (but not including any lost sales or
            profits resulting from any of such Actions) (the "Merck Defendant
            Robinson-Patman Act Liabilities");

provided, however, that Merck Liabilities shall not include any Liability that
constitutes a Medco Liability.

     Section 6.17 Merck Share of the Shared Liability Actions. "Merck Share of
the Shared Liability Actions" shall have the meaning set forth on Schedule 6.17.

     Section 6.18 Privileged Information. "Privileged Information" has the
meaning set forth in Section 4.1(a).

     Section 6.19 Securities Liabilities. "Securities Liabilities" means any and
all losses, liabilities, penalties, claims, damages, demands, costs or expenses
or other Liabilities whatsoever that are assessed, imposed, awarded against,
incurred or accrued by a Person arising out of or relating in whole or in part
to any Action, any potential or threatened Action, any Third Party Claim or any
potential or threatened Third Party Claim by any Governmental Authority or any
other Person that is based on any violations or alleged violations of the
Securities Act, the

                                       17

<PAGE>

Exchange Act, and any of the rules or regulations of the Commission promulgated
under the Securities Act or Exchange Act, or any other securities or other
similar laws, rules or regulations, including, without limitation, state
securities or "blue sky" laws, rules or regulations, foreign securities laws,
rules or regulations and rules or regulations of any securities exchange or
market.

     Section 6.20 Distribution Agreement. "Distribution Agreement" has the
meaning set forth in the Recitals hereof.

     Section 6.21 Shared Liability Actions. "Shared Liability Actions" has the
meaning set forth on Schedule 6.21.

     Section 6.22 Subsidiary. "Subsidiary" has the meaning set forth in the
Distribution Agreement.

     Section 6.23 Taxes. "Taxes" has the meaning set forth in the Tax Agreement.

     Section 6.24 Third Party Claim. "Third Party Claim" means an Action
brought, asserted, commenced or pursued by a Person (including any Governmental
Authority) other than a member of the Merck Group or the Medco Group.

     Section 6.25 Other Definitions. Any capitalized terms used but not defined
herein shall have the meanings assigned to them in the Distribution Agreement.

                         [SIGNATURES ON FOLLOWING PAGE]

                                       18

<PAGE>

     IN WITNESS WHEREOF, each of the parties has caused this Indemnification and
Insurance Matters Agreement to be executed on its behalf by its officers
thereunto duly authorized on the day and year first above written.

                                    MERCK & CO., INC.

                                    By:_________________________________
                                    Name:
                                    Title:

                                    MEDCO HEALTH SOLUTIONS, INC.

                                    By:_________________________________
                                    Name:
                                    Title:

                                       19

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