
<PAGE>   1
 
[CREDIT SUISSE FIRST BOSTON LOGO]

CREDIT SUISSE FIRST BOSTON CORPORATION
 
Eleven Madison Avenue
New York, New York 10010  Telephone 212 325 2000


 
                           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 Brokers, Dealers, Commercial Banks,
     Trust Companies and Other Nominees:
 
     We have been engaged by Omnicare Acquisition Corp. (the "Purchaser"), a
Delaware corporation and a wholly-owned subsidiary of Omnicare, Inc., a Delaware
corporation ("Parent"), to act as Dealer Manager in connection with the
Purchaser's offer to purchase for cash all of the 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") enclosed herewith. The Offer is being
made in connection with the Agreement and the Plan of Merger, dated as of August
7, 1997, by and among Parent, the Purchaser and the Company. Holders whose
certificates evidencing such Shares (the "Certificates") are not immediately
available or who cannot deliver their Certificates and all other required
documents to the Depositary (as defined below) prior to the Expiration Date (as
defined in Section 1 of the Offer to Purchase), or who, if applicable, cannot
complete the procedures for book-entry transfer on a timely basis, must tender
their Certificates according to the guaranteed delivery procedures set forth in
Section 3 of the Offer to Purchase.
 
     Please furnish copies of the enclosed materials to those of your clients
for whose accounts you hold Shares registered in your name or in the name of
your nominee.
 
     The Offer is subject to there being validly tendered and not withdrawn
prior to the Expiration Date that number of Shares which represents at least a
majority of the Shares outstanding on a fully diluted basis. The Offer is also
subject to other terms and conditions. See the "Introduction" and Section 14 of
the Offer to Purchase.
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The following are enclosed herewith:
 
     1. The Offer to Purchase, dated August 14, 1997.
 
     2. The Letter of Transmittal to tender Shares for your use and for the
information of your clients. Facsimile copies of the Letter of Transmittal may
be used to tender Shares.
 
     3. The Notice of Guaranteed Delivery for Shares to be used to accept the
Offer if Share Certificates are not immediately available, if such Certificates
and all other required documents cannot be delivered to First Chicago Trust
Company of New York (the "Depositary") prior to the Expiration Date, or, if
applicable, the procedure for book-entry transfer cannot be completed by the
Expiration Date.
 
     4. A printed form of letter which may be sent to your clients for whose
accounts you hold Shares registered in your name or in the name of your nominee,
with space provided for obtaining your clients' instructions with regard to the
Offer.
 
     5. Guidelines of the Internal Revenue Service for Certification of Taxpayer
Identification Number on Substitute Form W-9 providing information relating to
backup federal income tax withholding.
 
     6. A return envelope addressed to First Chicago Trust Company of New York,
the Depositary.
 
     YOUR PROMPT ACTION IS REQUIRED. WE URGE YOU TO CONTACT YOUR CLIENTS AS
PROMPTLY AS POSSIBLE. PLEASE NOTE THAT 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.
 
     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 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
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     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.
 
     In order to take advantage of the Offer, (i) a duly executed and properly
completed Letter of Transmittal with any required signature guarantees, or an
Agent's Message (as defined in Section 3 of the Offer to Purchase) in connection
with a book-entry delivery of Shares, and any other required documents should be
sent to the Depositary, and (ii) Certificates representing the tendered Shares
should be delivered to the Depositary, or, if applicable, Shares should be
tendered by book-entry transfer into the Depositary's account maintained at one
of the Book-Entry Transfer Facilities (as described in Section 3 of the Offer to
Purchase), all in accordance with the instructions set forth in the Letter of
Transmittal and the Offer to Purchase.
 
     If Holders of Shares wish to tender, but it is impracticable for them to
forward their Certificates or other required documents on or prior to the
Expiration Date or, if applicable, to comply with the book-entry transfer
procedures on a timely basis, a tender may be effected by following the
guaranteed delivery procedures specified in Section 3 of the Offer to Purchase.
 
     The Purchaser will not pay any commissions or fees to any broker, dealer or
other person (other than the Information Agent and the Dealer Manager) in
connection with the solicitation of tenders of Shares pursuant to the Offer. The
Purchaser will, however, upon request, reimburse you for customary clerical and
mailing expenses incurred by you in forwarding any of the enclosed materials to
your clients. The Purchaser will pay or cause to be paid any stock transfer
taxes payable on the transfer of Shares to it, except as otherwise provided in
Instruction 6 of the Letter of Transmittal.
 
     Any inquiries you may have with respect to the Offer should be addressed to
Credit Suisse First Boston Corporation, the Dealer Manager, at its address and
telephone numbers set forth on the back cover of the Offer to Purchase. Requests
for additional copies of the enclosed materials may be directed to the
Information Agent, D.F. King & Co., Inc. at its address and telephone numbers
set forth on the back cover of the Offer to Purchase.
 
                                          Very truly yours,
 
                                          Credit Suisse First Boston Corporation
 
     NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU
OR ANY OTHER PERSON THE AGENT OF THE PURCHASER, PARENT, THE COMPANY, THE
DEPOSITARY OR THE DEALER MANAGER, OR ANY AFFILIATE OF ANY OF THEM, OR AUTHORIZE
YOU OR ANY OTHER PERSON TO MAKE ANY STATEMENT OR USE ANY DOCUMENT ON BEHALF OF
ANY OF THEM IN CONNECTION WITH THE OFFER OTHER THAN THE ENCLOSED DOCUMENTS AND
THE STATEMENTS CONTAINED THEREIN.
