<PAGE>
 
                      PREFERRED STOCK AND WARRANT AGREEMENT

        THIS AGREEMENT (this "Agreement") is made and entered into as of
December 6, 1996, by and among ZYNAXIS, INC., a Pennsylvania corporation
("Zynaxis"), CYTRX CORPORATION, a Delaware corporation ("CytRx"), Vaxcel, Inc.,
a Delaware corporation and a wholly owned subsidiary of CytRx ("Vaxcel") and the
persons listed in Exhibit A (the "Securityholders").
                  ---------

                              W I T N E S S E T H:
                              -------------------

        WHEREAS, the Securityholders collectively hold all of the outstanding
shares of Series A Convertible Preferred Stock of Zynaxis (the "Series A Stock")
and each Securityholder holds the number of shares of Series A Stock and the
number of warrants to purchase additional shares of Common Stock of Zynaxis set
forth beside such Securityholder's name in Exhibit A (the "Warrants");
                                           ---------
        WHEREAS, the Series A Stock and the Warrants were issued pursuant to
that certain Preferred Stock and Warrant Purchase Agreement dated March 29,
1995, as amended (the "Preferred Stock and Warrant Purchase Agreement"), and in
connection with bridge loans extended by certain of the Securityholders to
Zynaxis;

        WHEREAS, simultaneously with the execution of this Agreement Zynaxis is
entering into an Agreement and Plan of Merger and Contribution (the "Merger and
Contribution Agreement") with CytRx, Vaxcel, and Vaxcel Merger Sub, Inc., a
Georgia corporation and a newly formed, wholly owned subsidiary of Vaxcel
("Vaxcel Merger Sub"), and certain other agreements, including, among other
things, a Liquidation Agreement (the "Liquidation Agreement") contemplating the
sale of Assets (as defined therein) of Zynaxis and documents (the "Secured Loan
Documents") relating to a secured loan being extended to Zynaxis by CytRx (the
"Secured Loan"). The Merger and Contribution Agreement provides for the issuance
of shares of Vaxcel Common Stock and a warrant to purchase shares of Vaxcel
Common Stock to CytRx in exchange for CytRx's contribution to Vaxcel of the
Secured Loan and a cash payment in an amount equal to Four Million Dollars
($4,000,000) minus the aggregate principal and interest balance outstanding
under the Secured Loan, subject to adjustment for payments made to shareholders
of Zynaxis pursuant to Section 3.3 of the Merger and Contribution Agreement. The
Merger and Contribution Agreement also provides for the issuance of shares of
Vaxcel Common Stock to the existing shareholders of Zynaxis in exchange for the
contribution to Vaxcel by the existing shareholders of Zynaxis of all of the
outstanding shares of capital stock of Zynaxis by means of a merger of Vaxcel
Merger Sub with and into Zynaxis. At the effective time of such merger, the
outstanding shares of the capital stock of Zynaxis will be converted into the
right to receive shares of the common stock of Vaxcel (except as provided
herein). As a result, shareholders of Zynaxis will become shareholders of Vaxcel
and Zynaxis will continue to conduct its business and operations as a wholly
owned subsidiary of Vaxcel.
<PAGE>
 
        WHEREAS, CytRx is unwilling to enter into the Merger and Contribution
Agreement unless the rights of the Securityholders are modified as set forth in
this Agreement;

        NOW, THEREFORE, in consideration of the foregoing and the mutual
promises, covenants, and agreements contained herein and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto, intending to be legally bound, hereby agree as follows:

                1.    Treatment of Transactions. Each of the undersigned elects
                      -------------------------
that the consummation of the transactions contemplated by the Merger and
Contribution Agreement and the other agreements contemplated by the Merger and
Contribution Agreement, including but not limited to the Liquidation Agreement,
will not be deemed a liquidation for purposes of Sections 3.1 and 3.2 of the
Statement with Respect to Shares filed by Zynaxis in the Department of State of
the Commonwealth of Pennsylvania on April 6, 1995.

                2.    Consent to Secured Loan. Each of the undersigned consents
                      -----------------------
to the Secured Loan and all liens, pledges, mortgages, security interests and
other encumbrances to which the assets or properties of Zynaxis may become
subject as part of the Secured Loan.

                3.    Exchange of Warrants. Each of the undersigned agrees that
                      --------------------
upon consummation of the merger between Zynaxis and Vaxcel Merger Sub pursuant
to the Merger and Contribution Agreement (the "Merger"), each Warrant held by
the undersigned shall be exchanged for a new warrant substantially in the form
attached hereto as Exhibit B to purchase a number of shares of Vaxcel Common
Stock equal to: (i) the number of shares of Common Stock of Zynaxis as the
Warrants held by such undersigned are exercisable to purchase at that time
multiplied by (ii) the Exchange Ratio (the "New Warrant"). Each of the
undersigned Securityholders agrees that such undersigned Securityholder shall
surrender the Warrants held by such undersigned Securityholder and shall receive
in exchange therefor a New Warrant. Zynaxis shall not honor any warrant
agreement representing a Warrant after the Merger.

                4.    Termination of Preferred Stock and Warrant Purchase
                      ---------------------------------------------------
Agreement and Registration Rights. Each of the undersigned agrees that the
---------------------------------
Preferred Stock and Warrant Purchase Agreement and all rights of the
Securityholders thereunder shall terminate upon the Merger. Each of the
undersigned further agrees that: (i) upon execution of this Agreement all rights
that the undersigned Securityholder may have to require Zynaxis to register
securities of Zynaxis for sale under applicable state and federal securities
laws, whether granted pursuant to the Preferred Stock and Warrant Agreement or
otherwise ("Registration Rights"), are suspended pending the Merger, and (ii)
upon occurrence of the Merger all such Registration Rights will be terminated
and such Securityholder will have such Registration Rights as are provided for
such Securityholder in the Merger and Contribution Agreement. If the Merger and
Contribution Agreement is terminated for any reason, beginning at the time of
such termination the undersigned Securityholder shall have such Registration
Rights as such Securityholder would have had at such time if such Registration
Rights had not been suspended pursuant to the preceding sentence.

                                      -2-
<PAGE>
 
                5.    Accredited Investor Status of Securityholder. Each of the
                      --------------------------------------------
undersigned Securityholders represents and warrants to CytRx, Vaxcel and Zynaxis
that he or it is an "accredited investor" within the meaning of Regulation D
promulgated under the Securities Act of 1933, as amended (the "Securities Act"),
and that he or it is acquiring New Warrants for himself or itself and not for
other persons. Each Securityholder understands that the New Warrants and any
Securities purchased upon exercise of New Warrants (the "Warrant Securities")
have not been registered under the Securities Act and, therefore, cannot be
resold unless such Warrant Securities are registered under the Securities Act or
unless an exemption from such registration is available.

                6.    Notices. All notices, requests, claims, demands and other
                      -------
communications under this Agreement shall be in writing and shall be deemed
given if delivered personally or sent by overnight courier (providing proof of
delivery) to the parties at the following addresses (or at such other address
for a party as shall be specified by like notice): (i) if to Zynaxis, CytRx or
Vaxcel, to the address set forth in Section 11.8 of the Merger and Contribution
Agreement; and (ii) if to a Securityholder, to its address shown below its
signature on the last page hereof.

                7.    Headings. The headings contained in this Agreement are for
                      --------
reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement.

                8.    Counterparts. This Agreement may be executed in two or
                      ------------
more counterparts, all of which shall be considered one and the same agreement.

                9.    Entire Agreement. This Agreement (including the documents
                      ----------------
and instruments referred to herein) constitutes the entire agreement, and
supersedes all prior agreements and understandings, both written and oral, among
the parties with respect to the subject matter hereof.

                10.   Governing Law. This Agreement shall be governed by, and
                      -------------
construed in accordance with, the laws of the Commonwealth of Pennsylvania,
regardless of the laws that might otherwise govern under applicable principles
of conflicts of laws thereof.

                11.   Assignment. Neither this Agreement nor any of the rights,
                      ----------
interests or obligations under this Agreement shall be assigned, in whole or in
part, by operation of law or otherwise, by any of the parties without the prior
written consent of the other parties. Any assignment in violation of the
foregoing shall be void.

                12.   Equitable Remedies. Each Securityholder agrees that
                      ------------------
irreparable damage would occur and that CytRx and Vaxcel would not have any
adequate remedy at law in the event that any of the provisions of this Agreement
were not performed in accordance with their specific terms or were otherwise
breached. It is accordingly agreed that CytRx and Vaxcel shall be entitled to an
injunction or injunctions to prevent breaches by a Securityholder of this
Agreement and to enforce specifically the terms and provisions of this
Agreement.

                                      -3-
<PAGE>
 
                13.   Severability. If any term, provision, covenant or
                      ------------
restriction herein, or the application thereof to any circumstance, shall, to
any extent, be held by a court of competent jurisdiction to be invalid, void or
unenforceable, the remainder of the terms, provisions, covenants and
restrictions herein and the application thereof to any other circumstances,
shall remain in full force and effect, shall not in any way be affected,
impaired or invalidated, and shall be enforced to the fullest extent permitted
by law.

                14.   Defined Terms. Capitalized terms used in this Agreement
                      -------------
but not defined herein shall have the meanings given such terms in the Merger
and Contribution Agreement.






                  [Remainder of page intentionally left blank.]

                                      -4-
<PAGE>
 
[First of Three Signature Pages to Preferred Stock and Warrant Agreement 
 dated December 6, 1996]

        IN WITNESS WHEREOF, the undersigned have duly executed this Agreement
under seal as of the day and year first above written.

ZYNAXIS, INC.                               CYTRX CORPORATION

By: /s/ Martyn Greenacre                    By: /s/ Jack J. Luchese
   --------------------------------            ---------------------------------
Name:  M.D. Greenacre                       Name: Jack J. Luchese
     ------------------------------              -------------------------------
Title: Chairman, President & CEO                Title: Chairman, President & CEO
      -----------------------------                   --------------------------


VAXCEL, INC.                                S.R. ONE, LTD.

By:    /s/ Paul J. Wilson                   By:      /s/ Brenda D. Gavin
   --------------------------------            ---------------------------------
Name:  Paul J. Wilson                       Name:    Brenda D. Gavin
     ------------------------------              -------------------------------
Title: President & CEO                      Title:   Vice President
      -----------------------------               ------------------------------

                                            Address: 565 E. Swedesford Rd -# 315
                                                    ----------------------------
                                                     Wayne, PA  19087
                                                    ----------------------------

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

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

EUCLID PARTNERS III, L.P.                   ALPHI FUND L.P.

BY: Euclid Associates III, L.P.
     General Partner
By: /s/ Stephen K. Reidy                    By: Alphi Investment Management Co.
   -------------------------------             ---------------------------------
Name:    Stephen K. Reidy                      General Partner
     -----------------------------
Title:   General Partner
      ----------------------------
                                            By:      /s/ Philip R. Smith
                                               ---------------------------------
Address: Euclid Partners Corp.              Name:    Philip R. Smith
        --------------------------               -------------------------------
         50 Rockefeller Plaza               Title:   President
        --------------------------                ------------------------------
         New York, NY  10020
        --------------------------
                                            Address: 155 Pfingsten Rd
        --------------------------                  ----------------------------
                                                     Suite 360
                                                    ----------------------------
                                                     Deerfiled, IL 60015
                                                    ----------------------------
JAVELIN CAPITAL FUND, L.P.

By: /s/ Lyle A. Hohnke
   -------------------------------
Name:    Lyle A. Hohnke
     -----------------------------
Title:   General Partner
      ----------------------------

Address: 1075 13th Street South
        --------------------------
         Birmingham, AL  35294
        --------------------------

                                      -5-
<PAGE>
 
[Second of Three Signature Pages to Preferred Stock and Warrant Agreement dated 
 December 6, 1996]

SENMED MEDICAL VENTURES                     CIP CAPITAL L.P.

                                            By: CIP Capital Management Inc.,
                                                General Partner

By: /s/ Vincent M. Paglino                  By: /s/ Joseph M. Corr
   -------------------------------             ---------------------------------
Name: Vincent M. Paglino                    Name: Joseph M. Corr
     -----------------------------               -------------------------------
Title: Vice President, Business Dev.        Title: President
      ------------------------------              ------------------------------

Address: 4445 Lake Forest Drive # 600       Address: 20 Valley Stream Parkway
        -----------------------------               ----------------------------
         Cincinnati, OH  45242                       Suite 265
        --------------------------                  ----------------------------
                                                     Malvern, PA 19355
        --------------------------                  ----------------------------

        --------------------------                  ----------------------------
         
THE WEST COMPANY                            WILLIAM M. SPENCER, III

By: /s/ Donald E. Morel                     By: /s/ William M. Spencer, III
   -------------------------------             ---------------------------------
Name:  Donald E. Morel                      Name: William M. Spencer
     -----------------------------               -------------------------------
Title: Corporate Vice President,            Title:
      ----------------------------                ------------------------------
       Scientific Services
      ----------------------------  

Address: 101 Gordon Drive                   Address: 3300 Cahaba Rd- Suite 105
        --------------------------                  ----------------------------
         Lionville, PA  19341                        Birmingham, AL  35223
        --------------------------                  ----------------------------

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

BIOTECHNOLOGY VENTURE                       COMMONWEALTH VENTURE
FUND S.A.                                   PARTNERS I, L.P.


By:                                         By: /s/ Charles A. Burton
   -------------------------------             ---------------------------------
Name:                                       Name: Charles A. Burton
     -----------------------------               -------------------------------
Title:                                      Title:   General Partner
      ----------------------------                ------------------------------

Address:                                    Address: The Bellevue
        --------------------------                  ----------------------------
                                                     200 S. Broad Street
        --------------------------                  ----------------------------
                                                     Phila, PA  19102
        --------------------------                  ----------------------------

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

                                      -6-
<PAGE>
 
[Third of Three Signature Pages to Preferred Stock and Warrant Agreement dated 
 December 6, 1996]

PLEXUS VENTURES, INC.                       PHILADELPHIA VENTURES - JAPAN I,
                                            L.P.

By: /s/ John F. Chappell                    By: /s/ Charles A. Burton
   -------------------------------             ---------------------------------
Name:    John F. Chappell                   Name:     Charles A. Burton
     -----------------------------               -------------------------------
Title:   President                          Title:    General Partner
      ----------------------------                ------------------------------

Address: 1787 Sentry Parkway West           Address:  The Bellevue
        --------------------------                  ----------------------------
         Building 18, Suite 301                       200 S. Broad Street
        --------------------------                  ----------------------------
         Blue Bell, PA  19422                         Phila, PA  19102
        --------------------------                  ----------------------------


GROTECH PARTNERS II, L.P.                   GROTECH PARTNERS III, L.P.
                                            GROTECH III COMPANION FUND, L.P.
By: Mid Atlantic Ventures II, L.P.,         GROTECH III PENNSYLVANIA FUND, L.P.
    General Partner

                                            By: Grotech Capital Group, Inc.,
By: Grotech Capital Group, Inc.,                General Partner
    General Partner

By: /s/ Matthew D. Brunner                  By: /s/ Matthew D. Brunner
   -------------------------------             ---------------------------------
Name:    Matthew D. Brunner                 Name:    Matthew D. Brunner
     -----------------------------               -------------------------------
Title:   Partner                            Title:   Partner
      ----------------------------                ------------------------------

Address: 9690 Deereco Road                  Address: 9690 Deereco Road
        --------------------------                  ----------------------------
         Timonium, MD  21093                         Timonium, MD  21093
        --------------------------                  ----------------------------

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

    /s/ Gus S. Casten, M.D.
----------------------------------
Dr. Gus G. Casten

Address: 238 Meadowcroft Circle
        --------------------------
         Birmingham, AL  35242-2956
        --------------------------

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

                                      -7-
<PAGE>
 
                                   EXHIBIT A

               HOLDERS OF PREFERRED STOCK AND WARRANTS ISSUED BY
                                 ZYNAXIS, INC.

<TABLE> 
<CAPTION>
                                       Series A 
     Name                              Shares                 Warrants
     ----                              ------                 --------
<S>                                    <C>                    <C> 
Euclid Partners III, L.P.              260,000                680,775
S.R. One, Ltd.                         257,500                540,000
Javelin Capital Fund, L.P.             250,000                500,000
Alphi Fund L.P.                        150,000                300,000
Senmed Medical Ventures                135,000                270,000
The West Company                       125,000                250,000
William M. Spencer, III                 55,000                110,000
Biotechnology Venture Fund S.A.         50,000                100,000
CIP Capital L.P.                        45,000                265,000 
Grotech Partners III, L.P.              26,490                 52,980
Plexus Ventures, Inc.                   25,000                150,000
Dr. Gus G. Casten                       12,500                 25,000
Commonwealth Venture Partners I, L.P.   10,000                 20,000
Grotech Partners II,L.P.                 3,455                  6,910
Grotech III Companion Fund, L.P.         3,155                  6,310
Philadelphia Ventures - Japan I, L.P.    2,500                  5,000
Grotech III Pennsylvania Fund, L.P.      1,900                  3,800
                                     ---------              ---------
     Totals                          1,412,500              3,285,775
</TABLE> 

<PAGE>
 
                                   EXHIBIT B
                                   ---------

THE WARRANTS REPRESENTED HEREBY HAVE BEEN ACQUIRED FOR INVESTMENT AND HAVE NOT 
BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933. THE WARRANTS MAY NOT BE SOLD 
OR TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR AN EXEMPTION THEREFROM.

THE WARRANTS REPRESENTED HEREBY AND THE RIGHTS OF HOLDERS THEREOF ARE SUBJECT TO
CERTAIN RESTRICTIONS ON TRANSFER AND OTHER RESTRICTIONS, AND THE HOLDER OF THE
WARRANTS REPRESENTED HEREBY (INCLUDING ANY HOLDERS) ARE BOUND BY THE TERMS OF A
PREFERRED STOCK AND WARRANT AGREEMENT DATED NOVEMBER 25, 1996 AMONG ZYNAXIS,
INC., A PENNSYLVANIA CORPORATION, CYTRX CORPORATION, A DELAWARE CORPORATION,
VAXCEL, INC., A DELAWARE CORPORATION, AND THE HOLDERS OF SHARES OF SERIES A
CONVERTIBLE PREFERRED STOCK OF ZYNAXIS, INC. (THE "PREFERRED STOCK AND WARRANT
AGREEMENT") (COPIES OF WHICH MAY BE OBTAINED FROM THE COMPANY).


           Void after 5:00p.m. (Eastern Standard Time), on the last
                  day of the Warrant Term, as provided herein.


Date:____________, 1996                     Warrant to
                                            Purchase_________________
                                            Shares of Common Stock



                                  WARRANT 
                         TO PURCHASE COMMON STOCK OF
                                VAXCEL, INC.


    THIS CERTIFIES THAT, FOR VALUE RECEIVED, ______________ or such person's
registered assigns (herein called "Warrant Holder"), is the holder of a warrant
(this "Warrant") to purchase, subject to the provisions of this Warrant, from
Vaxcel, Inc., a Delaware corporation (the "Company"), at any time and from time
to time during the Warrant Term, __________ fully paid, validly issued and
nonassessable shares of Common Stock, par value $.001 per share, of the Company
("Common Stock"), at the Warrant Price. The Warrant Price and number and kind of
securities issuable hereunder are subject to adjustment as provided herein.























 














<PAGE>
 
     1.  Definitions. For the purpose of this Warrant:
         -----------

         (a)  "Additional Shares of Capital Stock" means all shares of capital 
stock issued by the Company, except shares of capital stock of the Company 
issued and outstanding at the time of issuance of this Warrant or expressly 
authorized to be issued in the future pursuant to any contract, option, warrant 
or benefit or compensation plan in existence and/or outstanding at the time of 
issuance of this Warrant.

         (b)  "Capital Stock" means the Company's Common Stock, and any other 
stock of any class, whether now or hereafter authorized, which has the right to 
participate in the distribution of earnings and assets of the Company without 
limit as to amount or percentage.

         (c)  "Merger and Contribution Agreement" means that certain Agreement 
and Plan of Merger and Contribution entered into by and among CytRx Corporation,
a Delaware corporation, the Company, Vaxcel Merger Subsidiary, Inc., a Georgia 
corporation, and Zynaxis, Inc., a Pennsylvania corporation.

         (d)  "Per Share Price" means the Per Share Price as defined in the 
Merger and Contribution Agreement.

         (e)  "Warrants" mean the warrants to purchase Common Stock of the 
Company issued by the Company pursuant to the Preferred Stock and Warrant 
Agreement and any and all warrants which are issued in exchange or substitution 
for any outstanding Warrant pursuant to the terms of that Warrant.

         (f)  "Warrant Price" means the price per share at which shares of 
Common Stock are purchasable hereunder, as such price may be adjusted from time 
to time hereunder. The Warrant Price shall initially be equal to: (i) the Per 
Share Price divided by (ii) the Exchange Ratio, and beginning at 5:00 p.m. 
            ----------
Eastern Time on the sixtieth (60th) day following the Closing Date, as such term
is defined in the Merger and Contribution Agreement, shall be equal to two (2) 
times the Warrant Price in effect immediately prior to such time.

         (g)  "Warrant Shares" mean shares of Common Stock or other securities 
purchased upon exercise of this Warrant.

         (h)  "Warrant Term" means a period of one year commencing on the 
Closing Date and ending at 5:00 p.m. Eastern Time on the first anniversary of 
the Closing Date, as such term is defined in the Merger and Contribution 
Agreement.

     2.  Exercise of Warrants. This Warrant may be exercised during the Warrant
         --------------------
Term in whole or in part by the surrender of the Warrant, with the purchase 
agreement attached hereto as Exhibit A properly completed and executed, at the 
principal office of

                                     - 2 -
<PAGE>
 
the Company at 154 Technology Parkway, Norcross, Georgia 30092 or such other 
location which shall at that time be the principal office of the Company (the 
"Principal Office"), and upon payment to it by certified check or bank draft to 
the order of the Company for the purchase price for the shares to be purchased 
upon such exercise. The persons entitled to the shares so purchased shall be 
treated for all purposes as the holders of such shares as of the close of 
business on the date of exercise and certificates for the shares of stock so 
purchased shall be delivered to the persons so entitled within a reasonable 
time, not exceeding thirty (30) days, after such exercise. Unless this Warrant 
has expired, a new Warrant of like tenor and for such number of shares as the 
holder of subject to the restrictions on transfer set forth below.

     (a)  Registration Restrictions. This Warrant and any Warrant Shares that 
          -------------------------
may be issued upon exercise thereof have not been registered under the
Securities Act of 1933, as amended (the "Securities Act"), by reason of their
issuance in a transaction exempt from the registration requirements of the
Securities Act pursuant to the exemption provided in Section 4(2) thereof, and
have not been registered under state securities laws by reason of their issuance
in a transaction exempt from such registration requirements. This Warrant and
such Warrant Shares may not be sold, transferred or otherwise disposed of unless
registered under the Securities Act and applicable state securities laws (the
Company being under no obligation so to register such Warrant or Warrant Shares
except as set forth in the Merger and Contribution Agreement) or exempted from
such registration. Warrant Shares issuable upon exercise of this Warrant will
bear a legend to this effect. The restrictions contained herein shall be binding
on any transferee of this Warrant and the Company may require any such
transferee to execute an instrument agreeing in writing to be so bound by these
restrictions as a condition to transfer.

     (b)  Notice of Transfer and Opinion of Counsel. Warrant Holder agrees that,
          -----------------------------------------
prior to any transfer of this Warrant, such holder will give written notice to 
the Company of such holder's intention to effect such transfer and to comply in 
all other respects with the provisions of this Section 4. Each such notice shall
contain (i) a statement setting forth the intention of such holder's prospective
transferee with respect to its retention or disposition of this Warrant, and 
(ii) unless waived by the Company, an

                                     - 3 -
<PAGE>
 
opinion of counsel for such holder (who may be the inside or staff counsel 
employed by such holder), as to the necessity or non-necessity for registration 
under the Securities Act and applicable state securities laws in connection with
such transfer and stating the factual and statutory bases relied upon by 
counsel. The following provisions shall then apply: 

          (A) If in the opinion of counsel for the Company the proposed transfer
     of this Warrant may be effected without registration or qualification under
     the Securities Act and any applicable state securities laws, then the
     registered holder of this Warrant shall be entitled to transfer this
     Warrant in accordance with the intended method of disposition specified in
     the statement delivered by such holder to the Company.

          (B) If in the opinion of counsel for the Company the proposed transfer
     of this Warrant may not be effected without registration under the
     Securities Act or registration or qualification under any applicable state
     securities laws, the registered holder of this Warrant shall not be
     entitled to transfer this Warrant until the requisite registration or
     qualification is effective.

        (c) Transfer. Subject to the restrictions on transfer set forth in this 
            --------
Section 4 and in Section 11 hereof, this Warrant is transferable, in whole or in
part, at the Principal Office by the registered holder thereof, in person or by 
duly authorized attorney, upon presentation of this Warrant, properly endorsed, 
for transfer. Each holder of this Warrant, by holding it, agrees that this 
Warrant, when endorsed in blank, may be deemed negotiable, and that the holder 
thereof, when the Warrant shall have been so endorsed, may be treated by the 
Company and all other persons dealing with the Warrant as the absolute owner 
thereof for any purpose and as the person entitled to exercise the rights 
represented by this Warrant, or to the transfer thereof on the books of the 
Company, any notice to the contrary notwithstanding.

     5. Certain Covenants of the Company. The Company covenants and agrees that 
        --------------------------------
all shares which may be issued upon the exercise of this Warrant, will, 
upon issuance, be duly and validly issued, fully paid and nonassessable and free
from all taxes, liens and charges with respect to the issue thereof, and without
limiting the generality of the foregoing, the Company covenants and agrees that 
it will from time to time take all such action as may be required to assure that
the par value per share of the Common Stock is at all times equal to or less
than the then effective purchase price per share of the Common Stock issuable
pursuant to this Warrant. The Company further covenants and agrees that during
the period within which the rights represented by this Warrant may be exercised,
the Company will at all times have authorized, and reserved for the purpose of
issue upon exercise of the purchase rights evidenced by this Warrant, a
sufficient number of shares of its Common Stock to provide for the exercise of
the rights represented by this Warrant.

     6. Adjustments of Warrant Price. In the event that the Company at any time 
        ----------------------------
or from time to time after the issuance of the Warrants shall declare any 
dividend on the Common Stock payable in Common Stock or in any right to acquire 
Common Stock for 

                                      -4-
<PAGE>
 
any consideration less than the Warrant Price, or shall effect a subdivision of 
the outstanding shares of Common Stock into a greater number of shares of Common
Stock (by stock split, reclassification or otherwise than by a payment of a
dividend in Common Stock or in any right to acquire Common Stock) or in the
event the outstanding shares of Common Stock shall be combined or consolidated,
by reverse stock split, reclassification or otherwise, into a lesser number of
shares of Common Stock, then the Warrant Price shall, concurrently with the
effectiveness of such event, be proportionately decreased or increased, as
appropriate, to avoid dilution of the exercise rights hereunder. In the event
that the Company shall declare or pay any dividend on the Common Stock payable
in any right to acquire Common Stock for no consideration, then the Company
shall be deemed to have made a dividend payable in Common Stock in an amount of
shares equal to the maximum number of shares issuable upon exercise of such
rights to acquire Common Stock. The Warrant Price will be adjusted on a 
weighted-average basis in the event of the sale of Additional Shares of Capital
Stock for consideration less than the Warrant Price (except in connection with
corporate partnership or research and development agreements). For the purposes
of this Section 6, the value of consideration other than cash received for the
issuance of Additional Shares of Capital Stock shall be computed at the fair
value thereof at the time of such issuance, as determined in good faith by the
Board of Directors of the Company.

        7.  Adjustments for Reclassification and Reorganization. In case of any 
            ---------------------------------------------------
reclassification or change of outstanding securities issuable upon exercise of 
this Warrant (other than a change in par value, or from par value to no par 
value, or from no par value to par value or as a result of a subdivision or 
combination) or in case of any consolidation or merger of the Company with or 
into another corporation or in case of any sale or transfer to another 
corporation of the property of the Company as an entirety or substantially as an
entirety, the Company, or such successor or purchasing corporation, as the case 
may be, shall, without payment of any additional consideration therefor, execute
or require the execution of new warrants providing that the holders of the 
Warrants shall have the right to exercise such new warrants (upon terms not less
favorable to the holders than those then applicable to the Warrants) and to 
receive upon such exercise, in lieu of each share of Common Stock theretofore 
issuable upon exercise of the Warrants, the kind and amount of shares of stock, 
other securities, money or property receivable upon such reclassification, 
change, consolidation, merger, sale or transfer by the holder of one share of 
Common Stock issuable upon exercise of the Warrants had the Warrants been 
exercised immediately prior to such reclassification, change, consolidation, 
merger, sale or transfer. Such new warrant shall provide for adjustments which 
shall be as nearly equivalent as may be practicable to the adjustments provided 
for in Section 6 hereof and this Section 7. The provisions of this Section 7 
shall similarly apply to successive reclassifications, changes, consolidations, 
mergers, sales and transfers.

        8.  Notices. Whenever the Warrant Price shall be adjusted pursuant to 
            -------
Section 6 hereof, or there shall be a reclassification, reorganization or other 
event specified in Section 7 hereof, the Company shall promptly prepare a 
certificate signed by its President or a Vice President and by its Treasurer or 
Assistant Treasurer or its
                                      -5-
<PAGE>
 
Secretary or Assistant Secretary, setting forth in reasonable detail, as the 
case may be, the event requiring the adjustment, the amount of the adjustment, 
the method by which such adjustment was calculated, the Warrant Price after 
giving effect to such adjustment, and information regarding the execution of new
warrants, and shall promptly cause copies of such certificate to be mailed (by 
first class mail and postage prepaid) to the registered holders of the Warrants.
 
     In the event the Company shall take any action which pursuant to Section 6 
may result in an adjustment of the Warrant Price, or pursuant to Section 7 may 
result in the execution of new warrants, the Company will give to the registered
holders of the Warrants at their last addresses known to the Company written 
notice of such action ten (10) days in advance of its effective date in order to
afford to such holders of the Warrants an opportunity to exercise the Warrants 
and to purchase shares of Common Stock of the Company prior to such action 
becoming effective.

     9.  Fractional Shares. No fractional shares of Common Stock will be issued
         -----------------
in connection with any purchase hereunder.

     10.  Loss, Theft, Destruction or Mutilation. Upon receipt by the Company of
          --------------------------------------
reasonable evidence satisfactory to it of the ownership of and the loss, theft, 
destruction or mutilation of this Warrant and (in the case of loss, theft or 
destruction) of reasonable indemnity and (in case of mutilation) upon surrender 
and cancellation thereof, the Company will execute and deliver, in lieu thereof 
a new Warrant of like tenor.

     11.  Restrictions on Transfer. This Warrant is, and any Warrant Shares 
          ------------------------
issued upon the exercise of this Warrant will be, issued subject to the 
restrictions on transfer contained in this Warrant or any certificate for 
Warrant Shares issued in exchange or substitution for this Warrant or any 
outstanding certificate for Warrant Shares and shall bear the restrictive 
legend(s), if any, on this Warrant or such outstanding certificate for Warrant 
Shares unless, in the opinion of counsel for the Company, such legend(s) may be 
removed therefrom.

     12.  Headings. The description headings of the several sections of this 
          --------
Warrant are inserted for convenience only and do not constitute a part of this 
Warrant.

                                     - 6 -
<PAGE>
 
     IN WITNESS WHEREOF, the Company has caused this Warrant to be signed by its
duly authorized officer under its corporate seal, attested by its duly 
authorized officer, on the date of this Warrant.

                                        VAXCEL, INC.


                                        By:
                                           -------------------------------------
                                           As its:

ATTEST:

                                     - 7 -
<PAGE>
 
EXHIBIT A
---------

                              PURCHASE AGREEMENT
                              ------------------

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

TO:

     The undersigned, pursuant to the provisions set forth in the attached 
Warrant, hereby agrees to purchase shares of Common Stock covered by such 
Warrant, and makes payment herewith in full therefor at the price per share 
provided by this Warrant.

                                           Signature:
                                                     ------------------------

                                           Address:
                                                   --------------------------

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

                            *          *          *

                                  ASSIGNMENT
                                  ----------

     For Value Received, __________________________________________ hereby
sells, assigns and transfers all of the rights of the undersigned under the 
within Warrant, with respect to the number of shares of Common Stock covered by 
such Warrant to:

     NAME OF ASSIGNEE           ADDRESS             NO. OF SHARES
     ----------------           -------             -------------


, and appoints ______________Attorney to make such transfer of the books of 
Vaxcel, Inc. maintained for such purpose, with full power of substitution in the
premises.

Dated:                                     Signature:
                                                     ------------------------

                                           Witness:
                                                   --------------------------