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                           Offer to Purchase For Cash
                     All Outstanding Shares of Common Stock
                                       of
                         AMERICAN MEDSERVE CORPORATION
                                       at
                              $18.00 NET PER SHARE
                                       by
                           OMNICARE ACQUISITION CORP.
                          a wholly owned subsidiary of
                                 OMNICARE, INC.
 
  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
      TIME, ON THURSDAY, SEPTEMBER 11, 1997, UNLESS THE OFFER IS EXTENDED.
 
                                                                 August 14, 1997
 
To Our Clients:
 
     Enclosed for your consideration is an Offer to Purchase dated August 14,
1997 (the "Offer to Purchase") and the related Letter of Transmittal relating to
an offer by Omnicare Acquisition Corp. (the "Purchaser"), a Delaware corporation
and a wholly owned subsidiary of Omnicare, Inc., a Delaware corporation
("Parent"), to purchase all outstanding shares of Common Stock, par value $0.01
per share (the "Shares"), of American Medserve Corporation, a Delaware
corporation (the "Company"), at a purchase price of $18.00 per Share, net to the
seller in cash, without interest thereon, upon the terms and subject to the
conditions set forth in the Offer to Purchase and in the related Letter of
Transmittal (which, as amended or supplemented from time to time, together
constitute the "Offer"). Holders of Shares whose certificates for such Shares
are not immediately available or who cannot deliver their certificates and all
other required documents to the Depositary (as defined in the Offer to
Purchase), or complete the procedures for book-entry transfer, if applicable,
prior to the Expiration Date (as defined in Section 1 of the Offer to Purchase)
must tender their Shares according to the guaranteed delivery procedures set
forth in Section 3 of the Offer to Purchase. WE ARE THE HOLDER OF RECORD OF
SHARES HELD BY US FOR YOUR ACCOUNT. A TENDER OF SUCH SHARES CAN BE MADE ONLY BY
US AS THE HOLDER OF RECORD AND PURSUANT TO YOUR INSTRUCTIONS. THE LETTER OF
TRANSMITTAL IS FURNISHED TO YOU FOR YOUR INFORMATION ONLY AND CANNOT BE USED BY
YOU TO TENDER SHARES HELD BY US FOR YOUR ACCOUNT.
 
     We request instructions as to whether you wish to have us tender on your
behalf any or all of such Shares held by us for your account, pursuant to the
terms and subject to the conditions set forth in the Offer.
 
     Please note the following:
 
          1. The Offer price is $18.00 per Share, net to the seller in cash,
     without interest, upon the terms and subject to the conditions set forth in
     the Offer.
 
          2. The board of directors of the Company has unanimously determined
     that the Offer and the Merger (as defined in the Offer to Purchase) are
     fair to, and in the best interests of, the Company's stockholders, has
     approved the Merger Agreement (as defined in the Offer to Purchase) and the
     transactions contemplated thereby, including the Offer and the Merger, and
     recommends that the Company's stockholders accept the Offer and tender
     their Shares pursuant to the Offer.
 
          3. The Offer is conditioned upon, among other things, there being
     validly tendered and not withdrawn prior to the Expiration Date that number
     of Shares which represents at least a majority of the
<PAGE>   2
 
     Shares outstanding on a fully diluted basis. The Offer also is subject to
     certain other conditions, which are set forth in the Offer to Purchase.
 
          4. The Offer and withdrawal rights will expire at 12:00 midnight, New
     York City time, on Thursday, September 11, 1997, unless the Offer is
     extended.
 
          5. The Offer is being made for all of the outstanding Shares.
 
          6. Tendering stockholders who hold Shares in their names will not be
     obligated to pay brokerage fees or commissions to the Dealer Manager, the
     Depositary or the Information Agent or, except as otherwise provided in
     Instruction 6 of the Letter of Transmittal, transfer taxes on the purchase
     of Shares by the Purchaser pursuant to the Offer. However, backup federal
     income tax withholding at a rate of 31% may be required, unless an
     exemption applies or unless the required taxpayer identification
     information is provided. See Instruction 10 of the Letter of Transmittal.
 
          7. Notwithstanding any other provision of the Offer, payment for
     Shares accepted for payment pursuant to the Offer will in all cases be made
     only after timely receipt by the Depositary of (a) certificates for (or a
     timely Book-Entry Confirmation (as defined in Section 3 to the Offer to
     Purchase) with respect to) such Shares, (b) the Letter of Transmittal (or a
     facsimile thereof), properly completed and duly executed with any required
     signature guarantees or an Agent's Message (as defined in the Offer to
     Purchase) in connection with a book-entry transfer, and (c) any other
     documents required by the Letter of Transmittal. Accordingly, payment to
     all tendering stockholders may not be made at the same time depending upon
     when certificates for Shares or Book-Entry Confirmation with respect to
     Shares are actually received by the Depositary.
 
     If you wish to have us tender any or all of your Shares, please so instruct
us by completing, executing and returning to us the instructions form contained
in this letter. An envelope in which to return your instructions to us is
enclosed. If you authorize the tender of your Shares, all such Shares will be
tendered unless otherwise specified on the instruction form contained in this
letter. Your instructions should be forwarded to us in ample time to permit us
to submit a tender on your behalf prior to the expiration of the Offer.
 
     THE OFFER IS MADE SOLELY BY THE OFFER TO PURCHASE AND THE RELATED LETTER OF
TRANSMITTAL.
 
     The Offer is not being made to (nor will tenders be accepted from or on
behalf of) holders of Shares residing in any jurisdiction in which the making of
the Offer or the acceptance thereof would not be in compliance with the
securities, blue sky or other laws of such jurisdiction. However, the Purchaser
may, in its discretion, take such action as it may deem necessary to make the
Offer to holders of Shares in such jurisdiction.
 
     In any jurisdiction where the securities, blue sky or other laws require
the Offer to be made by a licensed broker or dealer, the Offer will be deemed to
be made on behalf of the Purchaser by one or more registered brokers or dealers
that are licensed under the laws of such jurisdiction.
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          INSTRUCTIONS WITH RESPECT TO THE OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
                                       OF
 
                         AMERICAN MEDSERVE CORPORATION
 
     The undersigned acknowledge(s) receipt of your letter and the enclosed
Offer to Purchase, dated August 14, 1997 (the "Offer to Purchase"), and the
related Letter of Transmittal (which, as amended or supplemented from time to
time, together constitute the "Offer"), in connection with the Offer by Omnicare
Acquisition Corp., a Delaware corporation (the "Purchaser") and a wholly owned
subsidiary of Omnicare, Inc., a Delaware corporation, to purchase all
outstanding shares of Common Stock, par value $0.01 per share (the "Shares"), of
American Medserve Corporation, a Delaware corporation (the "Company"), at a
price of $18.00 per Share, net to the seller in cash, without interest thereon.
 
     This will instruct you to tender to the Purchaser the number of Shares
indicated below (or, if no number is indicated below, all Shares) held by you
for the account of the undersigned, upon the terms and subject to the conditions
set forth in the Offer to Purchase.
 
Number of Shares Tendered:*
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Certificate Nos. (if available):
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Check ONE box if Shares will be tendered by book-entry transfer:
[ ]  The Depository Trust Company
[ ]  Philadelphia Depository Trust Company
 
Account No:
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Dated:
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                                   SIGN HERE
 
Signature(s):
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Please type or print address(es):
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Area Code and Telephone Number:
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Taxpayer Identification or Social Security Number(s):
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* Unless otherwise indicated, it will be assumed that all Shares held by us for
your account are to be tendered.
