<PAGE>   1
                                                                    EXHIBIT 4.6



         THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE
HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF THE DEPOSITORY TRUST
COMPANY (THE "DEPOSITARY") OR A NOMINEE OF THE DEPOSITARY. THIS SECURITY IS
EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A PERSON OTHER THAN THE
DEPOSITARY OR ITS NOMINEE ONLY IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE
INDENTURE, AND NO TRANSFER OF THIS SECURITY (OTHER THAN A TRANSFER OF THIS
SECURITY AS A WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A
NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE
DEPOSITARY) MAY BE REGISTERED EXCEPT IN LIMITED CIRCUMSTANCES.

         UNLESS THIS SECURITY IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
THE DEPOSITORY TRUST COMPANY (55 WATER STREET, NEW YORK) TO THE TRUST OR ITS
AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY SECURITY
ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS REQUESTED
BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY AND ANY PAYMENT
HEREON IS MADE TO CEDE & CO., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR
VALUE OR OTHERWISE BY A PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

         THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
1933, AS AMENDED (THE "SECURITIES ACT"), OR UNDER THE SECURITIES LAWS OF ANY
STATE OR OTHER JURISDICTION. NEITHER THIS SECURITY NOR ANY INTEREST OR
PARTICIPATION HEREIN MAY BE REOFFERED, RESOLD, ASSIGNED, TRANSFERRED, PLEDGED,
ENCUMBERED OR OTHERWISE DISPOSED OF IN THE ABSENCE OF SUCH REGISTRATION OR
UNLESS SUCH TRANSACTION IS EXEMPT FROM, OR NOT SUBJECT TO, SUCH REGISTRATION.
THE HOLDER HEREOF MAY NOT ENGAGE IN HEDGING TRANSACTIONS IN THIS SECURITY
UNLESS SUCH TRANSACTIONS ARE IN COMPLIANCE WITH THE SECURITIES ACT.

         THE HOLDER OF THIS SECURITY BY ITS ACCEPTANCE HEREOF AGREES TO OFFER,
RESELL OR OTHERWISE TRANSFER SUCH SECURITY, PRIOR TO THE DATE (THE "RESALE
RESTRICTION TERMINATION DATE") WHICH IS THE LATER OF (X) TWO YEARS AFTER THE
LATER OF THE ORIGINAL ISSUE DATE HEREOF AND THE LAST DATE ON WHICH CAREMARK RX,
INC. (THE "COMPANY") OR ANY AFFILIATE OF THE COMPANY WAS THE OWNER OF THIS
SECURITY (OR ANY PREDECESSOR OF SUCH SECURITY), AND (Y) SUCH LATER DATE, IF
ANY, AS MAY BE REQUIRED BY APPLICABLE LAW ONLY (A) TO THE COMPANY, (B) PURSUANT
TO A REGISTRATION STATEMENT THAT HAS BEEN DECLARED EFFECTIVE UNDER THE
SECURITIES ACT, (C) FOR SO LONG AS THE SECURITIES ARE ELIGIBLE FOR RESALE
PURSUANT TO RULE 144A, TO A PERSON IT REASONABLY BELIEVES IS A "QUALIFIED
INSTITUTIONAL BUYER" AS DEFINED IN RULE144A UNDER THE SECURITIES ACT THAT
PURCHASES FOR ITS OWN ACCOUNT OR FOR THE ACCOUNT OF A QUALIFIED INSTITUTIONAL
BUYER TO WHOM NOTICE IS GIVEN THAT THE TRANSFER IS BEING MADE IN RELIANCE ON
RULE 144A, (D) PURSUANT TO OFFERS AND SALES THAT OCCUR OUTSIDE THE UNITED
STATES IN ACCORDANCE WITH REGULATION S UNDER THE SECURITIES ACT, OR (E)
PURSUANT TO ANY OTHER AVAILABLE EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF
THE SECURITIES ACT, SUBJECT TO THE COMPANY'S AND THE TRANSFER AGENT'S RIGHT
PRIOR TO ANY SUCH OFFER, SALE OR TRANSFER PURSUANT TO CLAUSES (D) OR (E) TO
REQUIRE THE DELIVERY OF AN OPINION OF COUNSEL, CERTIFICATION
<PAGE>   2

AND/OR OTHER INFORMATION SATISFACTORY TO EACH OF THEM. THIS LEGEND WILL BE
REMOVED UPON THE REQUEST OF THE HOLDER AFTER THE RESALE RESTRICTION TERMINATION
DATE. ANY TRANSFER OF THIS SECURITY IS REQUIRED TO BE MADE IN COMPLIANCE WITH
THE APPLICABLE STATE SECURITIES LAWS AND APPLICABLE SECURITIES LAWS OF OTHER
JURISDICTIONS.

         EACH PURCHASER OR HOLDER OF THE SECURITY EVIDENCED HEREBY WILL BE
DEEMED TO HAVE REPRESENTED EITHER THAT (A) IT IS NOT AN EMPLOYEE BENEFIT PLAN
SUBJECT TO PART 4 OF SUBTITLE B OF TITLE I OF THE EMPLOYEE RETIREMENT INCOME
SECURITY ACT OF 1974, AS AMENDED, ("ERISA") OR A PLAN DESCRIBED IN SECTION 4975
OF THE INTERNAL REVENUE CODE OF 1986, AS AMENDED (THE "CODE") OR AN ENTITY
WHOSE UNDERLYING ASSETS INCLUDE THE ASSETS OF ANY SUCH ERISA PLAN OR OTHER PLAN
OR (B) ITS ACQUISITION, HOLDING AND DISPOSITION OF THE SECURITY EVIDENCED
HEREBY WILL NOT RESULT IN A PROHIBITED TRANSACTION UNDER SECTION 406 OF ERISA
OR SECTION 4975 OF THE CODE BY REASON OF PROHIBITED TRANSACTION CLASS EXEMPTION
("PTCE") 91-38, PTCE 84-14, PTCE 90-1, PTCE 95-60 OR PTCE 96-23.

         THE HOLDER OF THIS SECURITY AGREES THAT IT WILL DELIVER TO EACH PERSON
TO WHOM THIS CAPITAL SECURITY IS TRANSFERRED A NOTICE SUBSTANTIALLY TO THE
EFFECT OF THIS LEGEND.
<PAGE>   3

CERTIFICATE NUMBER: REG S P-1                 NUMBER OF PREFERRED SECURITIES: 0
CUSIP NO.  U 14164 10 4
ISIN NO. USU 141 641 048
COMMON CODE: 010254752


                  Certificate Evidencing Preferred Securities

                                       of


                          CAREMARK RX CAPITAL TRUST I

            7.0% Shared Preference Redeemable Preferred Securities,
                (Liquidation Amount $50 per Preferred Security)

                  Caremark Rx Capital Trust I, a statutory business trust
created under the laws of the State of Delaware (the "Trust"), hereby certifies
that Cede & Co. (the "Holder") is the registered owner of 0 preferred
securities of the Trust representing an undivided beneficial ownership interest
in the assets of the Trust and designated the Caremark Rx Capital Trust I
Shared Preference Redeemable Securities (SPuRS SM) (Liquidation Amount $50 per
Preferred Security unit redeemable) (the "Preferred Securities"). The Preferred
Securities are transferable on the books and records of the Trust, in person by
a duly authorized attorney, upon surrender of this certificate duly endorsed
and in proper form for transfer as provided in Section 5.4 of the Trust
Agreement (as defined below). The designations, rights, privileges,
restrictions, preferences and other terms and provisions of the Preferred
Securities are set forth in, and this certificate and the Preferred Securities
represented hereby are issued and shall in all respects be subject to, the
terms and provisions of, the Amended and Restated Trust Agreement of the Trust
dated as of September 29, 1999, as the same may be amended from time to time
(the "Trust Agreement") including the designation of the terms of Preferred
Securities as set forth herein. The Holder is entitled to the benefits of (i)
the Guarantee Agreement entered into by Caremark Rx, Inc., a Delaware
corporation ("Caremark"), and Wilmington Trust Company, a Delaware corporation
("Preferred Guaranty Trustee"), as guarantee trustee, dated as of September 29,
1999 (the "Guarantee") and (ii) the Registration Rights Agreement dated as of
September 29, 1999 among the Trust, Caremark and Warburg Dillon Read LLC (the
"Registration Rights Agreement"), in each case to the extent provided therein.
The Trust will furnish a copy of the Trust Agreement, the Guarantee and the
Registration Rights Agreement to the Holder without charge upon written request
to the Trust at its principal place of business or registered office.

                  Upon receipt of this certificate, the Holder is bound by the
Trust Agreement and is entitled to the benefits thereunder and by acceptance
hereof agrees to the provisions of (i) the Guarantee, (ii) the Indenture
entered into by Caremark and Wilmington Trust Company, as trustee, dated as of
September 29, 1999 and (iii) the Registration Rights Agreement.

                  This Certificate shall be construed in accordance with and
governed by the laws of the State of Delaware (without regard to conflict of
laws principles).
<PAGE>   4

                  IN WITNESS WHEREOF, one of the Administrative Trustees of the
Trust has executed this certificate.


Dated:  September 29, 1999

                                   CAREMARK RX CAPITAL TRUST I



                                   By: /s/ James H. Dickerson, Jr.
                                       ----------------------------------------
                                       Name:  James H. Dickerson, Jr.
                                       Title: Administrative Trustee


                  This is one of the Securities referred to in the within
mentioned Trust Agreement.


Date of Authentication:


September 29, 1999

                                   WILMINGTON TRUST COMPANY,
                                   as Property Trustee



                                   By: /s/ Mary C. St. Amand
                                       ----------------------------------------
                                       Name:  Mary C. St. Amand
                                       Title: Assistant Vice President
<PAGE>   5

                                   ASSIGNMENT

         FOR VALUE RECEIVED, the undersigned assigns and transfers this Trust
Security to:



---------------------------------------------------------------

---------------------------------------------------------------

---------------------------------------------------------------

(Insert assignee's social security or tax identification number)


---------------------------------------------------------------

---------------------------------------------------------------

---------------------------------------------------------------

(Insert address and zip code of assignee)

and irrevocably appoints

---------------------------------------------------------------

---------------------------------------------------------------

---------------------------------------------------------------

agent to transfer this Preferred Securities Certificate on the books of the
Trust. The agent may substitute another to act for him or her.

Date:
     -------------------------------

Signature:
          -----------------------------------------
(Sign exactly as your name appears on the other side of this Trust Security
certificate)



Signature Guarantee*:
                     ------------------------------


------------------

*(Signature must be guaranteed by an "eligible guarantor institution" that is,
a bank, stockbroker, savings and loan association or credit union meeting the
requirements of the Registrar, which requirements include membership or
participation in the Securities Transfer Agents Medallion Program ("STAMP") or
such other "signature guarantee program" as may be determined by the Registrar
in addition to, or in substitution for, STAMP, all in accordance with the
Securities Exchange Act of 1934, as amended)
<PAGE>   6

                               CONVERSION REQUEST

To:      Wilmington Trust Company, as Conversion Agent under the Trust
         Agreement of Caremark Rx Capital Trust I

                  The undersigned owner of these Preferred Securities hereby
irrevocably exercises the option to convert these Preferred Securities, or the
portion below designated, into Common Stock of CAREMARK RX, INC. (the "Common
Stock") in accordance with the terms of the Trust Agreement. Pursuant to the
aforementioned exercise of the option to convert these Preferred Securities,
the undersigned hereby directs the Conversion Agent (as that term is defined in
the Trust Agreement) to (i) exchange such Preferred Securities for a portion of
the Debentures (as that term is defined in the Trust Agreement) held by the
Trust at the Conversion Price specified in the Trust Agreement, and (ii)
immediately convert such Debentures on behalf of the undersigned, into Common
Stock at the Conversion Price specified in the Trust Agreement.

                  The undersigned also hereby directs the Conversion Agent that
the shares issuable and deliverable upon conversion, together with any check in
payment for fractional shares, be issued in the name of and delivered to the
undersigned, unless a different name has been indicated in the assignment
below. If shares are to be issued in the name of a person other than the
undersigned, the undersigned will pay all transfer taxes payable with respect
thereto.

                  If the undersigned is a BHCA Person (as that term is defined
in the Trust Agreement, the undersigned certifies that it is in compliance with
Section 4.3(a) of the Trust Agreement.

Date:
     -------------------------

Number of Preferred Securities to be converted:
                                               -----------------

If a name or names other than the undersigned, please indicate in the spaces
below the name or names in which the shares of Common Stock are to be issued,
along with the address or addresses of such person or persons.


--------------------------------------------

--------------------------------------------

--------------------------------------------

(Sign exactly as your name appears on the other side of this Trust Security
certificate) (for conversion of definitive Preferred Securities only)

Please Print or Typewrite Name and Address,
Including Zip Code, and Social Security or
Other Identifying Number.

--------------------------------------------

--------------------------------------------

--------------------------------------------
<PAGE>   7

Signature Guarantee:*
                     -----------------------


-------------------

*(Signature must be guaranteed by an "eligible guarantor institution" that is,
a bank, stockbroker, savings and loan association or credit union meeting the
requirements of the Registrar, which requirements include membership or
participation in the Securities Transfer Agents Medallion Program ("STAMP") or
such other "signature guarantee program" as may be determined by the Registrar
in addition to, or in substitution for, STAMP, all in accordance with the
Securities Exchange Act of 1934, as amended)
<PAGE>   8

                      CERTIFICATE FOR EXCHANGE OR TRANSFER

Re:  7.0% Shared Preference Redeemable Securities ("SPuRS" or "Preferred
     Securities)

         This Certificate relates to _________ Preferred Securities held by
_________ (the "Transferor").

         The Transferor has requested the Trustee by written order to exchange
or register the transfer of a Preferred Security or Preferred Securities.

         In connection with such request and in respect of each such security,
the Transferor does hereby certify to the Depositor and the Trustee that
Transferor is familiar with the Trust Agreement relating to the above captioned
Preferred Securities and, as provided in Section 5.4 and Section 5.5 of such
Trust Agreement, the transfer of this Preferred Security does not require
registration under the Securities Act (as defined below) because:

         [ ]   Such Preferred Security is being acquired for the Transferor's
own account, without transfer.

         [ ]   Such Preferred Security is being transferred pursuant to an
effective registration statement under the Securities Act.

         [ ]   Such Preferred Security is being transferred to a "qualified
institutional buyer" (as defined in Rule 144A under the Securities Act of 1933,
as amended (the "Securities Act")) in reliance on Rule 144A.

         [ ]   Such Preferred Security is being transferred in reliance on and
in compliance with an exemption from the registration requirements of the
Securities Act pursuant to Regulation S, Rule 144 or otherwise (other than
pursuant to Rule 144A) under the Securities Act. An opinion of counsel to the
effect that such transfer does not require registration under the Securities
Act accompanies this Certificate.

         If this certificate is being delivered in connection with a transfer
or exchange of Preferred Securities held by a BHCA Person (as that term is
defined in the Trust Agreement), such BHCA Person certifies that this transfer
or exchange complies with Section 4.3(a) of the Trust Agreement.

         You are entitled to rely upon this certificate and you are irrevocably
authorized to produce this certificate or a copy hereof to any interested party
in any administrative or legal proceeding or official inquiry with respect to
the matters covered hereby.



                                        ----------------------------
                                        [INSERT NAME OF TRANSFEROR]


                                        By:
                                           -------------------------



Date:
     -------------------------------
<PAGE>   9
                       OPTION OF HOLDER TO ELECT PURCHASE

         If you wish to have Preferred Securities represented by this
certificate purchased by the Depositor pursuant to Article X of the Trust
Agreement, check the Box: [ ]

         If you wish to have a portion of the Preferred Securities represented
by this certificate purchased by the Depositor pursuant to Article X of the
Trust Agreement, state the number of Preferred Securities you wish to have
purchased: ___________________________


      Date:                        Your Signature(s):
           ---------------------                      -------------------------

                            Tax Identification No.:

(Sign exactly as your name appears on the face of this Security)

Signature Guarantee*:
                     --------------------------------------

---------------------

*(Signature must be guaranteed by an "eligible guarantor institution" that is,
a bank, stockbroker, savings and loan association or credit union meeting the
requirements of the Registrar, which requirements include membership or
participation in the Securities Transfer Agents Medallion Program ("STAMP") or
such other "signature guarantee program" as may be determined by the Registrar
in addition to, or in substitution for, STAMP, all in accordance with the
Securities Exchange Act of 1934, as amended)