Document:

<PAGE>   1

                                                                    EXHIBIT 10.2

                     AMENDMENT NO. 18 TO THE LOAN DOCUMENTS

         AMENDMENT NO. 18 TO THE LOAN DOCUMENTS dated as of May 2, 2000 to the
Amended and Restated Credit Agreement dated as of June 9, 1998 (as amended and
otherwise modified by Amendment and Waiver No. 1 to the Loan Documents dated as
of December 4, 1998, Amendment No. 2 to the Loan Documents dated as of January
13, 1999, Amendment No. 3 to the Loan Documents dated as of February 9, 1999,
Amendment and Waiver No. 4 to the Loan Documents dated as of March 18, 1999,
Amendment and Waiver No. 5 to the Loan Documents dated as of April 1, 1999,
Amendment No. 6 to the Loan Documents dated as of April 14, 1999, Amendment No.
7 to the Loan Documents dated as of June 29, 1999, Amendment No. 8 to the Loan
Documents dated as of August 2, 1999, Amendment No. 9 to the Loan Documents
dated as of August 16, 1999, Amendment No. 10 to the Loan Documents dated as of
August 23, 1999, Amendment No. 11 to the Loan Documents dated as of August 30,
1999, Amendment No. 12 to the Loan Documents dated as of September 14, 1999,
Amendment No. 13 to the Loan Documents dated as of November 5, 1999, Amendment
No. 14 to the Loan Documents dated as of December 16, 1999, Amendment No. 15 to
the Loan Documents dated as of January 20, 2000, Amendment No. 16 to the Loan
Documents dated as of February 3, 2000, and Amendment No. 17 to the Loan
Documents dated as of April 10, 2000, (the "CREDIT AGREEMENT") among Caremark
Rx, Inc. (formerly known as MedPartners, Inc.), a Delaware corporation (the
"BORROWER"), the Lenders party thereto, Bank of America, N.A. (formerly
NationsBank, N.A.; "BOFA"), as the Initial Issuing Bank and the Swing Line Bank
thereunder, Credit Lyonnais New York Branch, The First National Bank of Chicago
and Morgan Guaranty Trust Company of New York, as the Syndication Agents
therefor, Banc of America Securities LLC (formerly NationsBanc Montgomery
Securities LLC), as the Arranger therefor, and BofA, as the Administrative Agent
for the Lender Parties thereunder. Capitalized terms not otherwise defined in
this Amendment have the same meanings as specified therefor in the Credit
Agreement.

                             PRELIMINARY STATEMENTS

         (1) The Borrower has requested that the Lender Parties agree to amend
the Credit Agreement as provided herein in order to increase the aggregate
amount of cash and noncash charges that are permitted to be excluded from the
determination of the Consolidated EBITDA of the Borrower and its Subsidiaries
for all Fiscal Quarters ending on or after December 31, 1998 as a result of the
reclassification of certain physician practice management businesses of the
Borrower and its Subsidiaries as "discontinued operations."

         (2) The Lender Parties have indicated their willingness to agree to
amend the Credit Agreement and to waive such default on the terms and subject
to the satisfaction of the conditions set forth herein.

         NOW, THEREFORE, in consideration of the premises and of the mutual
covenants and agreements contained herein and in the Loan Documents, the
parties hereto hereby agree as follows:

         SECTION 1. Amendments of Certain Provisions of the Credit Agreement.
The Credit Agreement is, upon the occurrence of the Amendment Effective Date
(as hereinafter defined), hereby amended as follows:

         (a) Paragraph (1) of Schedule II to the Credit Agreement is hereby
amended (i) to delete the figure "$233,453,000" in subclause (x) thereof and to
substitute therefor the figure

<PAGE>   2

"$431,453,000" and (ii) to delete the figure "$1,351,490,000" in subclause (y)
thereof and to substitute therefor the figure "$1,549,490,000."

         SECTION 2. Conditions Precedent to the Effectiveness of this
Amendment. This Amendment shall become effective as of the date hereof if on or
before May 2, 2000, each of the following conditions have been satisfied (such
date when the conditions are satisfied being the "AMENDMENT EFFECTIVE DATE"):

                  (a) The Administrative Agent shall have received on or before
         5:00 p.m. (Charlotte time) on May 2, 2000, (i) counterparts of this
         Amendment executed by the Borrower and the Required Lenders or, as to
         any of the Lender Parties, advice satisfactory to the Administrative
         Agent that such Lender Party has executed this Amendment, (ii)
         counterparts of the Consent attached hereto executed and delivered by
         each of the Loan Parties (other than the Borrower) and (iii) for the
         benefit of each Lender Party that has executed this Amendment on or
         before 5:00 p.m. (Charlotte time) on May 2, 2000, a fee from the
         Borrower in an amount equal to 0.15% of the aggregate Commitment of
         such Lender Party, in each case as of the Business Day immediately
         preceding the Amendment Effective Date, which amount will be
         distributed to the respective Lender Party no later than the Business
         Day immediately succeeding the Amendment Effective Date.

                  (b) The representations and warranties set forth in each of
         the Loan Documents shall be correct in all material respects on and as
         of the Amendment Effective Date, before and after giving effect to this
         Amendment, as though made on and as of such date (except (i) for any
         such representation and warranty that, by its terms, refers to a
         specific date other than the Amendment Effective Date, in which case as
         of such specific date, (ii) that the Consolidated financial statements
         of the Borrower and its Subsidiaries referred to in Sections 4.01(f)
         and 4.01(g) of the Credit Agreement shall be deemed to refer to the
         Consolidated financial statements of the Borrower and its Subsidiaries
         comprising part of the Required Financial Information most recently
         delivered to the Administrative Agent and the Lender Parties pursuant
         to Sections 5.03(b) and 5.03(c), respectively, on or prior to the
         Amendment Effective Date and (iii) that the forecasted Consolidated
         financial statements of the Borrower and its Subsidiaries referred to
         in Section 4.01(h) of the Credit Agreement shall be deemed to refer to
         the forecasted Consolidated financial statements of the Borrower and
         its Subsidiaries most recently delivered to the Administrative Agent
         and the Lender Parties prior to the Amendment Effective Date).

                  (c) No event shall have occurred and be continuing, or shall
         result from the effectiveness of this Amendment, that constitutes a
         Default.

                  (d) All of the reasonable fees and expenses of the
         Administrative Agent and the Arranger (including the reasonable fees
         and expenses of counsel for the Administrative Agent) due and payable
         on or before the Amendment Effective Date shall have been paid in full.

         The effectiveness of this Amendment is further conditioned upon the
accuracy of all of the factual matters described herein. This Amendment is
subject to the provisions of Section 8.01 of the Credit Agreement.

         SECTION 3. Reference to and Effect on the Loan Documents. (a) On and
after the Amendment Effective Date, each reference in the Credit Agreement to
"this Agreement," "hereunder," "hereof" or words of like import referring to the
Credit Agreement, and each reference in the Notes and

                                       2

<PAGE>   3

each of the other Loan Documents to "the Credit Agreement," "thereunder,"
"thereof" or words of like import referring to the Credit Agreement, shall mean
and be a reference to the Credit Agreement, as amended by this Amendment.

         (b) The Credit Agreement, the Notes and each of the other Loan
Documents, as amended by the amendments specifically provided above in Section
1, are and shall continue to be in full force and effect and are hereby in all
respects ratified and confirmed. The execution, delivery and effectiveness of
this Amendment shall not, except as expressly provided herein, operate as a
waiver of any right, power or remedy of any of the Guaranteed Parties or the
Administrative Agent under any of the Loan Documents, or constitute a waiver of
any provision of any of the Loan Documents.

         SECTION 4. Costs and Expenses. The Borrower hereby agrees to pay, upon
demand, all of the reasonable costs and expenses of the Administrative Agent and
the Arranger (including, without limitation, the reasonable fees and expenses of
counsel for the Administrative Agent) in connection with the preparation,
execution, delivery, administration, modification and amendment of this
Amendment and all of the agreements, instruments and other documents delivered
or to be delivered in connection herewith, all in accordance with the terms of
Section 8.04 of the Credit Agreement.

         SECTION 5. Execution in Counterparts. This Amendment may be executed
in any number of counterparts and by different parties hereto in separate
counterparts, each of which when so executed shall be deemed to be an original
and all of which taken together shall constitute one and the same agreement.
Delivery of an executed counterpart of a signature page to this Amendment by
telecopier shall be effective as delivery of a manually executed counterpart of
this Amendment.

         SECTION 6. Governing Law. This Amendment shall be governed by, and
construed in accordance with, the laws of the State of New York.

                                       3

<PAGE>   4
         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective officers, thereunto duly authorized, as of the date
first written above.

                                          THE BORROWER

                                          CAREMARK RX, INC.
                                          (formerly known as MEDPARTNERS, INC.)

                                          By   /s/ JAMES H. DICKERSON, JR.
                                            ----------------------------------
                                            Name:  James H. Dickerson, Jr.
                                            Title: President and COO

                                          THE ADMINISTRATIVE AGENT

                                          BANK OF AMERICA, N.A.

                                          By   /s/ WILLIAM C. NELSON
                                            -----------------------------------
                                            Name:  William C. Nelson
                                            Title: Managing Director

                                       4

<PAGE>   5

               CONSENT TO AMENDMENT NO. 18 TO THE LOAN DOCUMENTS

                                As of May 2, 2000

         Reference is made to Amendment No. 18 to the Loan Documents dated as of
May 2, 2000 (the "AMENDMENT") to the Amended and Restated Credit Agreement dated
as of June 9, 1998 (as amended and otherwise modified by Amendment No. 1 to the
Loan Documents dated as of December 4, 1998, Amendment No. 2 to the Loan
Documents dated as of January 13, 1999, Amendment No. 3 to the Loan Documents
dated as of February 9, 1999, Amendment and Waiver No. 4 to the Loan Documents
dated as of March 18, 1999, Amendment and Waiver No. 5 to the Loan Documents
dated as of April 1, 1999, Amendment No. 6 to the Loan Documents dated as of
April 14, 1999, Amendment No. 7 to the Loan Documents dated as of June 29, 1999,
Amendment No. 8 to the Loan Documents dated as of August 2, 1999, Amendment No.
9 to the Loan Documents dated as of August 16, 1999, Amendment No. 10 to the
Loan Documents dated as of August 23, 1999, Amendment No. 11 to the Loan
Documents dated as of August 30, 1999, Amendment No. 12 to the Loan Documents
dated as of September 14, 1999, Amendment No. 13 to the Loan Documents dated as
of November 5, 1999, Amendment No. 14 to the Loan Documents dated as of December
16, 1999, Amendment No. 15 to the Loan Documents dated as of January 20, 2000,
Amendment No. 16 to the Loan Documents dated as of February 3, 2000, and
Amendment No. 17 to the Loan Documents dated as of April 10, 2000, the "CREDIT
AGREEMENT") among Caremark Rx, Inc. (formerly known as MedPartners, Inc.), a
Delaware corporation, the Lenders party thereto, Bank of America, N.A. (formerly
NationsBank, N.A.), as the Initial Issuing Bank and Swing Line Bank thereunder,
Credit Lyonnais New York Branch, The First National Bank of Chicago and Morgan
Guaranty Trust Company of New York, as the Syndication Agents therefor, Banc of
America Securities LLC (formerly NationsBanc Montgomery Securities LLC), as
Arranger therefor, and Bank of America, N.A. (formerly NationsBank, N.A.), as
the Administrative Agent for the Lender Parties thereunder. Capitalized terms
not otherwise defined herein shall have the same meanings as specified therefor
in the Credit Agreement.

         Each of the undersigned, as a guarantor under the Subsidiaries
Guarantee dated as of June 9, 1998 (as modified to the date hereof, the
"SUBSIDIARIES GUARANTEE") in favor of the Guaranteed Parties, hereby consents
to the execution and delivery of the Amendment and the performance of the
Credit Agreement, as amended thereby, and hereby confirms and agrees that,
notwithstanding the effectiveness of the Amendment, the Subsidiaries Guarantee
is, and shall continue to be, in full force and effect and is hereby in all
respects ratified and confirmed, except that each reference in the Subsidiaries
Guarantee to "the Credit Agreement," "thereunder," "thereof" or words of like
import referring to the Credit Agreement shall mean and be a reference to the
Credit Agreement, as amended by the Amendment.

         This Consent may be executed in any number of counterparts and by
different parties hereto in separate counterparts, each of which when so
executed shall be deemed to be an original and all of which taken together
shall constitute one and the same Consent. Delivery of an executed counterpart
of a signature page to this Consent by telecopier shall be effective as
delivery of a manually executed counterpart of this Consent.

         This Consent shall be governed by, and construed in accordance with,
the laws of the State of New York.

<PAGE>   6

                                       THE LENDER PARTIES

                                       BANK OF AMERICA, N.A., as a Lender,
                                       the Swing Line Bank and the Issuing Bank

                                       By  /s/ WILLIAM C. NELSON
                                         ------------------------------------
                                         Name: William C. Nelson
                                         Title: Managing Director

                                       AMSOUTH BANK

                                       By /s/ RICK HAMILTON
                                         ------------------------------------
                                         Name: Rick Hamilton
                                         Title: Commercial Banking Officer

                                       THE CHASE MANHATTAN BANK

                                       By /s/ DAWN LEE LUM
                                         ------------------------------------
                                         Name: Dawn Lee Lum
                                         Title: VP

                                       CITIBANK, N.A.

                                       By /s/ JOHN DORANS
                                         ------------------------------------
                                         Name: John Dorans
                                         Title: VP

                                       CREDIT LYONNAIS NEW YORK BRANCH

                                       By /s/ HENRY J. REUKAUF
                                         ------------------------------------
                                         Name: Henry J. Reukauf
                                         Title: VP

                                       DEBT STRATEGIES FUND, INC.

                                       By /s/ COLLEEN M. CUNNIFFE
                                         ------------------------------------
                                         Name: Colleen M. Cunniffe
                                         Title:

                                       5

<PAGE>   7
                                       BANK ONE, NA (f/k/a THE FIRST NATIONAL
                                       BANK OF CHICAGO)

                                       By /s/ L. Richard Schiller
                                         ------------------------------------
                                         Name: L. Richard Schiller
                                         Title: VP

                                       FIRST UNION NATIONAL BANK

                                       By /s/ Keith S. Law
                                         ------------------------------------
                                         Name: Keith S. Law
                                         Title: VP

                                       FLOATING RATE PORTFOLIO
                                       BY: INVESCO Senior Secured Management,
                                           Inc., as attorney in fact

                                       By /s/ Gregory Stoeckle
                                         ------------------------------------
                                         Name: Gregory Stoeckle
                                         Title:

                                       KZH HIGHLAND-2 LLC

                                       By /s/ Susan Lee
                                         ------------------------------------
                                         Name: Susan Lee
                                         Title:

                                       MERRILL LYNCH DEBT STRATEGIES
                                        PORTFOLIO, INC.
                                        BY: MERRILL LYNCH ASSET
                                            MANAGEMENT L.P., as Investment
                                            Advisor

                                       By /s/ Colleen M. Cunniffe
                                         ------------------------------------
                                         Name: Colleen M. Cunniffe
                                         Title:

                                       6

<PAGE>   8

                                       MERRILL LYNCH GLOBAL INVESTMENT
                                        SERIES: INCOME STRATEGIES PORTFOLIO
                                        BY: MERRILL LYNCH ASSET MANAGEMENT,
                                            L.P., as Investment Advisor

                                       By /s/ Colleen M. Cunniffee
                                         ------------------------------------
                                         Name: Colleen M. Cunniffee
                                         Title:

                                       MERRILL LYNCH SENIOR FLOATING
                                        RATE FUND, INC.

                                       By /s/ Colleen M. Cunniffee
                                         ------------------------------------
                                         Name: Colleen M. Cunniffee
                                         Title:

                                       MERRILL LYNCH PRIME RATE PORTFOLIO
                                        BY: MERRILL LYNCH ASSET MANAGEMENT,
                                            L.P., as Investment Advisor

                                       By /s/ Colleen M. Cunniffee
                                         ------------------------------------
                                         Name: Colleen M. Cunniffee
                                         Title:

                                       ML CBO IV (CAYMAN) LTD.
                                       BY: HIGHLAND CAPITAL MANAGEMENT L.P.,
                                           as Collateral Manager

                                       By /s/ Todd Travers
                                         ------------------------------------
                                         Name: Todd Travers
                                         Title: Senior Portfolio Manager

                                       ML CLO XX PILGRIM AMERICA
                                        (CAYMAN) LTD.
                                        BY: PILGRIM INVESTMENTS, INC.,
                                            as Investment Manager

                                       By /s/ Jason T. Groom
                                         ------------------------------------
                                         Name: Jason T. Groom
                                         Title: Asst. VP

                                       7

<PAGE>   9

                                       MORGAN GUARANTY TRUST COMPANY
                                        OF NEW YORK

                                       By
                                         ------------------------------------
                                         Name:
                                         Title:

                                       PAM CAPITAL FUNDING, LP
                                        BY: HIGHLAND CAPITAL MANAGEMENT, L.P.,
                                             as Collateral Manager

                                       By  /s/ Todd Travers
                                         ------------------------------------
                                         Name: Todd Travers
                                         Title: Sr. Portfolio Manager

                                       PAMCO CAYMAN, LTD.
                                        BY: HIGHLAND CAPITAL MANAGEMENT, L.P.,
                                                 as Collateral Manager

                                       By  /s/ Todd Travers
                                         ------------------------------------
                                         Name: Todd Travers
                                         Title: Sr. Portfolio Manager

                                       PILGRIM PRIME RATE TRUST
                                        BY: PILGRIM INVESTMENTS, INC.,
                                                as Investment Manager

                                       By /s/ Jason T. Groom
                                         ------------------------------------
                                         Name: Jason T. Groom
                                         Title: Asst. VP

                                       SCOTIABANC INC.

                                       By /s/ Dana Maloney
                                         ------------------------------------
                                         Name: Dana Maloney
                                         Title: Relationship Manager

                                       8

<PAGE>   10

                                            SRV-HIGHLAND, INC.

                                            By  /s/ Kelly C. Walker
                                              --------------------------------
                                              Name: Kelly C. Walker
                                              Title: VP

                                            STEIN ROE & FARNHAM INCORPORATED,
                                              as Agent for KEYPORT LIFE
                                                INSURANCE COMPANY

                                            By  /s/ Kathleen A. Zarn
                                              --------------------------------
                                              Name: Kathleen A. Zarn
                                              Title: VP

                                            TORONTO DOMINION (TEXAS), INC.

                                            By  /s/ Mark A. Baird
                                              --------------------------------
                                              Name: Mark A. Baird
                                              Title: VP

                                            TRANSAMERICA LIFE INSURANCE AND
                                               ANNUITY CO.

                                            By
                                              --------------------------------
                                              Name:
                                              Title:

                                            TRANSAMERICA PREMIER HIGH YIELD FUND

                                             By
                                               --------------------------------
                                               Name:
                                               Title:

                                             VAN KAMPEN PRIME RATE INCOME TRUST

                                             By  /s/ Douglas C. Winchell
                                               --------------------------------
                                               Name: Douglas C. Winchell
                                               Title: VP

                                       9

<PAGE>   11

                                           VAN KAMPEN SENIOR INCOME TRUST

                                           By /s/ Douglas C. Winchell
                                             --------------------------------
                                             Name: Douglas C. Winchell
                                             Title: VP

                                           VAN KAMPEN CLO II, LIMITED
                                           BY:  VAN KAMPEN MANAGEMENT, INC.,
                                                as Collateral Manager

                                           By /s/ Douglas C. Winchell
                                             --------------------------------
                                             Name: Douglas C. Winchell
                                             Title: VP

                                           WACHOVIA BANK, N.A.

                                           By
                                             --------------------------------
                                             Name:
                                             Title:

                                       10
<PAGE>   12

                                       MEDPARTNERS ACQUISITION CORPORATION

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name: James H. Dickerson, Jr.
                                         Title: President & Treasurer

                                       MEDPARTNERS AVIATION, INC.

                                       By   /s/ SARA J. FINLEY
                                         ------------------------------------
                                         Name: Sara J. Finley
                                         Title: Vice President & Secretary

                                      MEDPARTNERS EAST, INC.

                                       By   /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name: James H. Dickerson, Jr.
                                         Title: President & Treasurer

                                      MEDPARTNERS INTEGRATED NETWORK-
                                      CHANDLER, INC.

                                       By   /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name: James H. Dickerson, Jr.
                                         Title: President & Treasurer

                                       MEDPARTNERS PROFESSIONAL
                                       MANAGEMENT CORPORATION

                                       By   /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name: James H. Dickerson, Jr.
                                         Title: President & Treasurer

                                      HEALTHWAYS, INC.

                                       By   /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name: James H. Dickerson, Jr.
                                         Title: President & Treasurer

                                       2
<PAGE>   13
                                       BAY AREA PRACTICE MANAGEMENT GROUP, INC.

                                       By    /s/ SARA J. FINLEY
                                         ------------------------------------
                                         Name:  Sara J. Finley
                                         Title: Vice President & Secretary

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: Vice President & Treasurer

                                       CHS MANAGEMENT, INC.

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: President & Treasurer

                                       CAREMARK INTERNATIONAL INC.

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: President & Treasurer

                                       CAREMARK INC.

                                       By    /s/ SARA J. FINLEY
                                         ------------------------------------
                                         Name:  Sara J. Finley
                                         Title: Vice President & Secretary

                                       By    /s/ LEISA KIZER
                                         ------------------------------------
                                         Name:  Leisa Kizer
                                         Title: Treasurer

                                       3
<PAGE>   14
                                       PRESCRIPTION HEALTH SERVICES, INC.

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name: James H. Dickerson, Jr.
                                         Title: Vice President & Treasurer

                                       By    /s/ SARA J. FINLEY
                                         ------------------------------------
                                         Name:  Sara J. Finley
                                         Title: Vice President & Secretary

                                       CAREMARK INTERNATIONAL HOLDINGS INC.

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: Vice President & Treasurer

                                       MEDPARTNERS PHYSICIAN SERVICES INC.

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: Vice President & Treasurer

                                       FRIENDLY HILLS HEALTHCARE NETWORK INC.

                                       By    /s/ SARA J. FINLEY
                                         ------------------------------------
                                         Name:  Sara J. Finley
                                         Title: Vice President & Secretary

                                       MEDPARTNERS NSC LTD.

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         ------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: Vice President & Treasurer

                                       4
<PAGE>   15
                                        MEDPARTNERS ADMINISTRATIVE
                                        SERVICES, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: James H. Dickerson, Jr.
                                          Title: Vice President & Treasurer

                                        MEDPARTNERS MANAGED CARE, INC.

                                        By /s/ SARA J. FINLEY
                                          -------------------------------------
                                          Name: Sara J. Finley
                                          Title: Vice President & Secretary

                                        ACUTE CARE MEDICAL MANAGEMENT, INC.

                                        By /s/ SARA J. FINLEY
                                          -------------------------------------
                                          Name: Sara J. Finley
                                          Title: Vice President & Secretary

                                        BGS HEALTHCARE, INC.

                                        By /s/ SARA J. FINLEY
                                          -------------------------------------
                                          Name: Sara J. Finley
                                          Title: Vice President & Secretary

                                        HOME HEALTH AGENCY OF GREATER
                                        MIAMI, INC.

                                        By /s/ SARA J. FINLEY
                                          -------------------------------------
                                          Name: Sara J. Finley
                                          Title: Vice President & Secretary

                                        PACIFIC MEDICAL GROUP, INC.

                                        By /s/ SARA J. FINLEY
                                          -------------------------------------
                                          Name: Sara J. Finley
                                          Title: Vice President & Secretary

                                       5
<PAGE>   16
                                        PACIFIC PHYSICIAN SERVICES, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        PPS EAST, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        PPS NORTH CAROLINA MEDICAL
                                        MANAGEMENT, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        PPS RIVERSIDE DIVISION ACQUISITION
                                        AND MANAGEMENT CORP. I

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        PPS VALLEY MANAGEMENT, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        By /s/ SARA J. FINLEY
                                          -------------------------------------
                                          Name: Sara J. Finley
                                          Title: Vice President & Secretary

                                       6

<PAGE>   17
                                        PACIFIC PHYSICIAN SERVICES
                                        ARIZONA, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        PACIFIC PHYSICIAN SERVICES
                                        NEVADA, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        PHYSICIAN'S HOSPITAL MANAGEMENT
                                        CORPORATION

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: Vice President & Treasurer

                                        RELIANT HEALTHCARE SYSTEMS, INC.

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: President & Treasurer

                                        By /s/ SARA J. FINLEY
                                          -------------------------------------
                                          Name: Sara J. Finley
                                          Title: Vice President & Secretary

                                        MEDPARTNERS/TALBERT MEDICAL
                                        MANAGEMENT CORPORATION

                                        By /s/ JAMES H. DICKERSON, JR.
                                          -------------------------------------
                                          Name: JAMES H. DICKERSON, JR.
                                          Title: Vice President & Treasurer

                                       7

<PAGE>   18

                              TALBERT MEDICAL MANAGEMENT
                              CORPORATION

                              By   /s/  JAMES H. DICKERSON, JR.
                                 -------------------------------------------
                                 Name:  James H. Dickerson, Jr.
                                 Title: Vice President & Treasurer

                              TALBERT HEALTH SERVICES
                              CORPORATION

                              By   /s/  JAMES H. DICKERSON, JR.
                                 -------------------------------------------
                                 Name:  James H. Dickerson, Jr.
                                 Title: Vice President & Treasurer

                              MEDPARTNERS ADMINISTRATION, L.P.

                              By   /s/  JAMES H. DICKERSON, JR.
                                 -------------------------------------------
                                 Name:  James H. Dickerson, Jr.
                                 Title: Executive Vice President & Treasurer
                                        of Caremark Rx, Inc., the General
                                        Partner

                              MEDPARTNERS PHYSICIAN
                              MANAGEMENT, L.P.

                              By   /s/  JAMES H. DICKERSON, JR.
                                 -------------------------------------------
                                 Name:  James H. Dickerson, Jr.
                                 Title: Executive Vice President of
                                        Caremark Rx, Inc., the General
                                        Partner

                              MED TENNESSEE, INC.

                              By   /s/  JAMES H. DICKERSON, JR.
                                 -------------------------------------------
                                 Name:  James H. Dickerson, Jr.
                                 Title: President & Treasurer

                                       8
<PAGE>   19
                                       MEDPARTNERS PHYSICIAN SERVICES OF
                                       ILLINOIS L.L.C.

                                       By  /s/ JAMES H. DICKERSON, JR.
                                         ---------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: Vice President & Treasurer of
                                                North Suburban Clinic, Ltd.,
                                                a Member

                                       CERRITOS INVESTMENT GROUP

                                       By  /s/ JAMES H. DICKERSON, JR.
                                         ---------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: Executive Vice President & Chief
                                                Financial Officer of Caremark
                                                Rx, Inc., a Partner

                                       By  /s/ SARA J. FINLEY
                                         ---------------------------------------
                                         Name:  Sara J. Finley
                                         Title: Corporate Secretary of
                                                Caremark Rx, Inc., a Partner

                                       CERRITOS INVESTMENT GROUP II

                                       By  /s/ JAMES H. DICKERSON, JR.
                                         ---------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: Executive Vice President & Chief
                                                Financial Officer of Caremark
                                                Rx, Inc., a Partner

                                       By  /s/ SARA J. FINLEY
                                         ---------------------------------------
                                         Name:  Sara J. Finley
                                         Title: Corporate Secretary of Caremark
                                                Rx, Inc., a Partner

                                       9

<PAGE>   20
                                       5000 AIRPORT PLAZA, L.P.

                                       By    /s/ JAMES H. DICKERSON, JR.
                                         --------------------------------------
                                         Name:  James H. Dickerson, Jr.
                                         Title: President & Chief Operating
                                                Officer of Caremark Rx, Inc.
                                                the General Partner

                                       By    /s/ SARA J. FINLEY
                                         --------------------------------------
                                         Name:  Sara J. Finley
                                         Title: Corporate Secretary of Caremark
                                                Rx, Inc., the General Partner

                                       10<PAGE>   1
                                                                    EXHIBIT 10.4

                                 THIRD AMENDMENT
                                       TO
                              EMPLOYMENT AGREEMENT

         THIS THIRD AMENDMENT TO EMPLOYMENT AGREEMENT (this "Amendment") is made
and entered into as of March 8, 2000 by and between Caremark Rx, Inc., a
Delaware corporation (f/k/a MedPartners, Inc.) ("Caremark Rx") and E. Mac
Crawford ("Executive"). Capitalized terms used herein and not otherwise defined
herein shall have the meanings ascribed to them in that certain Employment
Agreement by and between Caremark Rx and Executive dated March 18, 1998 (the
"Employment Agreement" and as amended by the First Amendment (as hereinafter
defined) and the Second Amendment (as hereinafter defined), the "Amended
Employment Agreement").

         WHEREAS, Caremark Rx and Executive entered in the Employment Agreement
whereby Executive agreed to serve as President and Chief Executive Officer of
Caremark Rx;

         WHEREAS, on August 6, 1998, Caremark Rx and Executive entered into that
certain First Amendment to Employment Agreement (the "First Amendment") whereby
Caremark Rx and Executive agreed to reduce the exercise price of an option to
purchase 3,250,000 shares of Caremark Rx Common Stock (as hereinafter defined)
which option is evidenced by that certain Nonqualified Stock Option Agreement
dated August 6, 1998 (the "Stock Option Agreement");

         WHEREAS, on December 1, 1998, Caremark Rx and Executive entered into
that certain Second Amendment to Employment Agreement (the "Second Amendment"),
which acknowledged that Executive was elected to serve as Chairman of the Board
of Directors of Caremark Rx;

         WHEREAS, pursuant to the Amended Employment Agreement, Executive is
entitled to receive a bonus for each year of the term of the Amended Employment
Agreement of at least two times the Executive's base salary;

         WHEREAS, the Executive has agreed to forego the payment of any bonus
for calendar year 2000 and all future calendar years during the term of the
Amended Employment Agreement in exchange for and as consideration for the grant
by Caremark Rx of an option (the "New Option") to purchase 3,875,000 shares of
Caremark Rx common stock, par value $.001 per share (the "Common Stock") at an
exercise price equal to 115% of the closing price of the Common Stock on March
8, 2000, the day the Compensation Committee of the Board of Directors and the
Board of Directors recommended and approved the New Option;

<PAGE>   2

         WHEREAS, the Board of Directors has determined that the grant of the
New Option in consideration for the Executive's agreement to forego the bonus
payable pursuant to the Amended Employment Agreement is fair and in the best
interest of Caremark Rx and its stockholders; and

         WHEREAS, Caremark Rx and Executive desire to amend the Amended
Employment Agreement as provided herein.

         NOW, THEREFORE, in consideration of the foregoing recitals and of the
mutual covenants and agreements contained in this Amendment, the parties agree
as follows:

         1.       AMENDMENT OF CORPORATE NAME. References to "MedPartners, Inc."
contained throughout the Amended Employment Agreement shall be amended to read
"Caremark Rx, Inc." and references to "MedPartners" contained throughout the
Amended Employment Agreement shall be amended to read "Caremark Rx."

         2.       AMENDMENT TO SECTION 5. Section 5(c) of the Amended Employment
Agreement is hereby deleted in its entirety and shall be of no further force or
effect. Executive does hereby relinquish and waive any bonus or claims for bonus
pursuant to Section 5(c) of the Amended Employment Agreement for the year 2000
and for all subsequent years, whether such amounts are currently due and payable
or to become due and payable following the date hereof pursuant to Section 5(c)
of the Amended Employment Agreement. In no event shall the deletion of Section
5(c) of the Amended Employment Agreement affect any bonus payments previously
paid to Executive prior to the year 2000.

         3.       AMENDMENT TO SECTION 8(D). Section 8(d)(iv) of Amended
Employment Agreement shall be amended to read in its entirety as follows:

                  "(iv) the failure to continue the Executive as Chairman of the
                  Board and Chief Executive Officer of Caremark Rx."

         4.       AMENDMENTS TO SECTION 10.

                  (a)      Sections 10(b)(i), 10(c)(i), and 10(d)(i) of the
Amended Employment Agreement shall each be amended to read in their entirety as
follows:

                           "(i)     payment of (a) any previously unpaid base
                           salary and (b) an amount equal to one-twelfth of the
                           Separation Payment applicable to the fiscal year in
                           which such termination event has occurred multiplied
                           by the number of whole calendar months between the
                           first day of the fiscal year in which such
                           termination event has occurred and the date of such
                           termination event;"

                  (b)      Section 10(b)(ii) of the Amended Employment Agreement
shall be amended to read in its entirety as follows:

                                       2
<PAGE>   3

                           "(ii)    lump-sum payment equal to the sum of (a)
                           Executive's then-current base salary for the
                           then-remaining term of this Agreement (but in no
                           event less than three years), and (b) an amount equal
                           to the Separation Payment multiplied by the greater
                           of three (3) or the number of years (including
                           fractions thereof) remaining in the term of this
                           Agreement;"

                  (c)      Section 10(d)(ii) of the Amended Employment Agreement
shall be amended to read in its entirety as follows:

                           "(ii)    lump-sum payment equal to the sum of (a)
                           Executive's then-current base salary for the
                           then-remaining term of this Agreement (but in no
                           event less than three years), and (b) an amount equal
                           to the Separation Payment multiplied by the greater
                           of three (3) or the number of years (including
                           fractions thereof) remaining in the term of this
                           Agreement, provided that such lump-sum payment shall
                           be offset by any amount payable to Executive's
                           beneficiaries under any executive life insurance
                           policy paid for by Caremark Rx (excluding amounts
                           payable under any life insurance policy generally
                           provided to employees of Caremark Rx);"

                  (d)      Section 10(e) shall be added to the Amended
Employment Agreement and shall read in its entirety as follows:

                           "(e) As used in this Section 10, the term `Separation
                           Payment' shall mean an amount equal to at least two
                           (2) times the base salary in effect for the year to
                           which the Separation Payment relates."

         5.       GRANT OF OPTION. As consideration for the Executive's
foregoing of any and all bonus payable or to be paid pursuant to Section 5(c) of
the Amended Employment Agreement, Caremark Rx does hereby grant executive the
option to purchase 3,875,000 shares of Common Stock at an exercise price of
$4.46 per share of Common Stock, which New Option shall be evidenced by and
subject to the additional terms and conditions of the Nonqualified Stock Option
Agreement attached hereto as Exhibit A (the "Additional Stock Option
Agreement"). The parties hereto acknowledge and agree that the $4.46 exercise
price represents 115% of the closing price of the Common Stock on the date
hereof.

         6.       NO OTHER AMENDMENT. Except as expressly modified by this
Amendment, all other terms and conditions of the Amended Employment Agreement
shall not be modified or amended and shall remain in full force and effect.

         7.       MISCELLANEOUS.

                  (a)      Entire Agreement. This Amendment, together with the
Amended Employment Agreement, the Stock Option

                                       3
<PAGE>   4

Agreement, and the Additional Stock Option Agreement, contains the entire
agreement of the parties relating to the subject matter hereof and thereof, and
it replaces and supersedes any prior agreements between the parties relating to
said subject matter. If the Additional Stock Option Agreement is terminated or
deemed invalid or unenforceable for any reason other than the expiration of the
Option Term (as defined in the Additional Stock Option Agreement) or the
purchase of all of the Option Shares (as defined in the Additional Stock Option
Agreement) (i) Sections 2, 4, and 5 of this Amendment shall be null and void,
(ii) Executive shall be promptly paid all bonuses under the Amended Employment
Agreement that would have been due and payable if this Amendment and the
Additional Stock Option Agreement had never been executed, and (iii) Executive
shall promptly upon written notice from Caremark Rx (a "Rescission Notice")
surrender all Option Shares purchased by Executive and deliver the certificate
or certificates evidencing such purchased Option Shares to Caremark Rx. Such
Rescission Notice shall be accompanied by a payment from Caremark Rx to
Executive of the aggregate exercise price paid by Executive for such purchased
Option Shares. Upon such termination of the Additional Stock Option Agreement,
Caremark Rx shall cancel the certificate or certificates evidencing such
purchased Option Shares and shall place stop transfer instructions on such
certificate or certificates.

                  (b)      Waiver and Amendment. No provision of this Amendment
may be waived except by a written agreement signed by the waiving party. The
waiver of any term or of any condition of this Amendment shall not be deemed to
constitute the waiver of any other term or condition. This Amendment may be
amended only by a written agreement signed by each of the parties hereto.

                  (c)      Captions. Captions have been inserted solely for the
convenience of reference and in no way define, limit or describe the scope or
substance of any provisions of this Amendment.

                  (d)      Severability. If this Amendment shall for any reason
be or become unenforceable by any party, this Amendment shall thereupon
terminate and become unenforceable by the other party as well. In all other
respects, if any provision of this Amendment is held invalid or unenforceable,
the remainder of this Amendment shall nevertheless remain in full force and
effect and, if any provision is held invalid or unenforceable with respect to
particular circumstances, it shall nevertheless remain in full force and effect
in all other circumstances.

                  (e)      Governing Law. This Amendment shall be governed by
the laws of the State of Alabama.

                                       4
<PAGE>   5

         IN WITNESS WHEREOF, the parties have executed this Amendment as of the
date first above written.

Attest:                                     CAREMARK RX, INC.

By: /s/ Amy Holliman                        By: /s/ Kirk McConnell
   -------------------------                   ----------------------------
Name: Amy Holliman                          Name: Kirk McConnell
     -----------------------                     --------------------------

Title: Director, Benefits                   Title: EVP/CAO
      ----------------------                      -------------------------

                                            /s/ Charles W. Newhall III
                                            -------------------------------
                                            Charles W. Newhall III
                                            Compensation Committee Chairman

                                            /s/ E. Mac Crawford
                                            --------------------------------
                                            E. Mac Crawford

                                       5

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