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                                   EXHIBIT 4.5
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                             STOCK PURCHASE WARRANT

                   THE SECURITIES REPRESENTED BY THIS INSTRUMENT HAVE BEEN
ACQUIRED FOR INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
1933, AS AMENDED, OR THE SECURITIES LAWS OF ANY STATE OR OTHER JURISDICTION.
WITHOUT SUCH REGISTRATION, SUCH SECURITIES MAY NOT BE SOLD, PLEDGED,
HYPOTHECATED OR OTHERWISE TRANSFERRED, EXCEPT UPON DELIVERY TO ATRIX
LABORATORIES, INC. OF AN OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT
REGISTRATION IS NOT REQUIRED FOR SUCH TRANSFER, OR SUBMISSION TO THE COMPANY OF
SUCH OTHER EVIDENCE AS MAY BE SATISFACTORY TO THE COMPANY TO THE EFFECT THAT ANY
SUCH TRANSFER SHALL NOT BE IN VIOLATION OF THE SECURITIES ACT OF 1933, AS
AMENDED, OR ANY APPLICABLE STATE OR FOREIGN SECURITIES LAW OR ANY RULE OR
REGULATION PROMULGATED THEREUNDER.

         WHEREAS, Atrix Laboratories, Inc., a Delaware corporation (the
"Company"), has agreed to acquire ViroTex Corporation ("ViroTex") pursuant to
the terms of the Agreement and Plan of Reorganization by and among the Company,
Atrix Acquisition Corporation, a Delaware corporation and ViroTex, dated
November 24, 1998 (the "Merger Agreement") whereby ViroTex will merge with a
wholly owned subsidiary of the Company (the "Merger"); and

         WHEREAS, Warrant Holder (as defined below) is the holder of a warrant
to purchase 52,936 shares of the common stock of ViroTex, at a price of $1.65
per share, pursuant to a Stock Purchase Warrant (the "Original Warrant") between
Warrant Holder and ViroTex dated April 28, 1995 (the "Prior Option"); and

         WHEREAS, pursuant to the terms of the Original Warrant and Section 2.04
of the Merger Agreement, the Warrant Holder is entitled to receive a substitute
stock purchase warrant (the "Warrant") in exchange for the Warrant Holder's
agreement to cancel and surrender the Original Warrant; and

         WHEREAS, the Warrant Holder is desirous of obtaining the Warrant in
exchange for canceling and surrendering the Original Warrant on the terms and
conditions herein contained.

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants herein contained and for other good and valuable consideration, the
Company and Warrant Holder agree as follows:

         1. Subject to and effective upon the consummation of the Merger, the
Company hereby grants to GulfStar Investments, Limited, ("Warrant Holder"), the
right to purchase (and the Company shall be obligated to issue and sell to the
Warrant Holder),


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at the option of the Warrant Holder and on the terms and conditions hereinafter
set forth, all or any part of an aggregate of 6,750 shares ("Shares") of Common
Stock, $.001 par value per share ("Common Stock"), of the Company, such Shares
to be exercisable at a purchase price per share equal to $12.94 ("Exercise
Price"). This Warrant may be exercised at any time, or from time to time, until
five (5) years from April 28, 1995 (the "Expiration Date). The number of Shares
subject to this Warrant and the Exercise Price therefor shall be subject to
adjustment as set forth in Section 6. In consideration therefore, Warrant Holder
agrees to cancel and surrender the Original Warrant in exchange for issuance of
this replacement Warrant, as provided in Section 2.04(f) of the Merger
Agreement. Such cancellation and surrender shall become effective automatically
and without further action on the part of the Warrant Holder upon receipt by the
Company of an executed copy of this Warrant and upon the consummation of the
Merger. The Warrant Holder further acknowledges that the cancellation and
surrender of the Original Warrant held by the Warrant Holder releases absolutely
and irrevocably the Warrant Holder's interest in the Original Warrant.

         2. (a) The Warrant Holder may exercise this Warrant, in whole or in
part, upon surrender to the Company of this Warrant with the Subscription Form
attached hereto duly executed, together with payment in full of the Exercise
Price for the Shares to be purchased in cash or by certified or cashier's check
to the order of the Company.

                  (b) Upon receipt of this Warrant with the Subscription Form
duly executed and accompanied by payment of the Exercise Price for the Shares
for which this Warrant is then being exercised, the Company will cause to be
issued certificates for the total number of whole shares of Common Stock for
which this Warrant is being exercised in such denominations as are required for
delivery to the Warrant Holder and the Company shall thereupon deliver such
certificates to the Warrant Holder.

                  (c) In case the Warrant Holder shall exercise this Warrant
with respect to less than all of the Shares that may then be purchased under
this Warrant, the Company will execute a new Warrant in the form of this Warrant
for the balance of such Shares and deliver such new Warrant to the Warrant
Holder.

         3. The Company shall at all times during the term of this Warrant have
authorized, reserve and keep available, free from preemptive rights, such number
of shares of its Common Stock as will be sufficient to satisfy the requirements
of this Warrant, and shall pay all fees and expenses necessarily incurred by the
Company in connection therewith. The reserved shares may be either authorized
and unissued shares of its Common Stock or shares of Common Stock held in its
treasury, or partly unissued and partly treasury shares, at the Company's sole
discretion. Upon issuance to the Warrant Holder, all of the Shares shall be duly
authorized, validly issued, fully paid and nonassessable and free and clear from
all liens, charges, security interests and encumbrances created by the Company.

         4. (a) This Warrant, and the rights and privileges conferred hereby,
may be exercised only by the Warrant Holder and its or his legal
representatives, successors or 


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permitted assignees. This Warrant may be transferred in whole to any person or
entity or in part to any partner or partners of GulfStar Investments, Limited or
members of any of their families and/or trusts established for their behalf
(subject to the provisions hereof including the provisions of Section 5 below).

                  (b) Prior to due presentment for registration of transfer of
this Warrant, the Company may deem and treat the Warrant Holder as the absolute
owner of this Warrant (notwithstanding any notation of ownership or other
writing hereon) for the purpose of any exercise hereof and for all other
purposes, and the Company shall not be affected by any notice to the contrary.

                  (c) Subject to and limited by the provisions of Section 5
hereof, this Warrant may be split up, combined or exchanged for another Warrant
or Warrants containing the same terms and entitling the Warrant Holder to
purchase a like aggregate number of Shares. If the Warrant Holder desires to
split up, combine or exchange this Warrant, he or it shall make such request in
writing delivered to the Company and shall surrender to the Company this Warrant
and any other Warrants to be so split up, combined or exchanged. Upon any such
surrender for a split-up, combination or exchange, the Company shall execute and
deliver to the person entitled thereto a Warrant or Warrants, as the case may
be, as so requested. The Company shall not be required to effect any split-up,
combination or exchange which will result in the issuance of a Warrant entitling
the Warrant Holder to purchase upon exercise a fraction of a share of Common
Stock or a fractional Warrant. The Company may require such Warrant Holder to
pay a sum sufficient to cover any tax or governmental charge that may be imposed
in connection with any split-up, combination or exchange of Warrants.

                  (d) If this Warrant shall be mutilated, upon request by the
Warrant Holder the Company shall issue a new Warrant containing the same terms
and entitling the Warrant Holder to purchase the same number of Shares, in
exchange for and upon cancellation of the mutilated Warrant. If this Warrant
shall be lost, stolen or destroyed, upon request by the Warrant Holder and upon
receipt of evidence satisfactory to the Company of such loss, theft or
destruction of this Warrant Certificate and, if required by the Company,
indemnity also satisfactory to it, the Company shall issue a new Warrant
containing the same terms and entitling the Warrant Holder to purchase the same
number of Shares, in substitution for the lost, stolen or destroyed Warrant.

         5. Neither this Warrant nor the underlying Shares have been registered
under the Securities Act of 1933 ("Act), or registered or qualified under the
securities laws of any state. Neither this Warrant nor the underlying Shares may
be sold or offered for sale in the absence of the effective registration or
qualification thereof under the Act and any applicable state securities laws or
an opinion of counsel acceptable to the Company that such registration or
qualification is not required. Any certificates representing the shares of
Common Stock issued hereunder shall bear a restrictive legend in conformity with
the provisions of this Section 5. The Company will not recognize or give effect
to any purported transfer of this Warrant or any interest herein, or the
underlying Shares, unless and until the provisions of this Section 5 shall have
been satisfied.

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         6. (a) (i) if at any time prior to the full exercise of this Warrant,
the Company shall: (A) pay a dividend or make a distribution on its shares of
Common Stock in shares of Common Stock; (B) subdivide, reclassify or
recapitalize its outstanding shares of Common Stock into a greater number of
shares; or (C) combine, reclassify or recapitalize its outstanding shares of
Common Stock into a smaller number of shares, the number of Shares in effect at
the time of the record date of such dividend, subdivision, combination,
reclassification or recapitalization shall be proportionately adjusted so that
the Warrant Holder shall be entitled to receive the aggregate number and type of
shares that, if this Warrant had been exercised in full immediately prior to
such time, it would have owned upon such exercise and been entitled to receive
upon such dividend, subdivision, combination, or recapitalization. Such
adjustment shall be made successively whenever any event listed in this
paragraph (a) shall occur.

                           (ii) Whenever the number of Shares issuable upon 
exercise of this Warrant is adjusted pursuant to paragraph (a) of this Section
6, the Exercise Price payable for such Shares shall simultaneously be adjusted
by multiplying the number of Shares initially issuable upon exercise of each
Warrant by the Exercise Price in effect on the date thereof and dividing the
product so obtained by the number of Shares, as adjusted.

                           (iii) No adjustment in the Exercise Price shall be
required unless such adjustment would require an increase or decrease of at
least five cents ($.05) in such price, provided, however, that any adjustments
which by reason of this paragraph (iii) are not required to be made shall be
carried forward and taken into account in any subsequent adjustment. All
calculations under this Section 6 shall be made to the nearest cent or to the
nearest one-hundredth of a share, as the case may be.

                           (iv) If at any time, as a result of any adjustment 
made pursuant to paragraph (a) of this Section 6, the Warrant Holder thereafter
shall become entitled to receive any securities of the Company other than shares
of Common Stock, thereafter the number of such other securities so receivable
upon exercise of any Warrant shall be subject to adjustment from time to time in
a manner and on terms as nearly equivalent as practicable to the provisions with
respect to the Common Stock contained in paragraph (a) of this Section 6.

                  (b) No adjustment in respect of any cash dividends in the
ordinary course out of current earnings of the Company shall be made during the
term of this Warrant or upon the exercise of this Warrant.

                  (c) In case of any consolidation of the Company with or merger
of the Company into another corporation or any sale, lease or other transfer or
conveyance to another corporation of all or substantially all the property of
the Company, the corporation resulting from such consolidation or surviving such
merger or to which such sale or transfer shall be made, as the case may be,
shall make suitable provision (which shall be fair and equitable to the holders
of the Warrants) and shall assume the 

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obligations of the Company hereunder (by written instrument executed and mailed
to each holder of the Warrants then outstanding) pursuant to which, upon
exercise of the Warrants, at any time during the duration of the Warrants after
such consolidation, merger, or sale, lease or other transfer or conveyance the
holder shall be entitled to receive the stock or other securities or property
that such holder would have been entitled to receive upon consummation if such
holder had executed the Warrants immediately prior thereto, all subject to
further adjustment as provided in this Section 6.

                  (d) Whenever the number of Shares or the Exercise Price is
adjusted as herein provided, the Company shall prepare and deliver to the
Warrant Holder a certificate signed by its President, or any Vice President,
Treasurer or Secretary, setting forth the adjusted number of shares purchasable
upon the exercise of this Warrant and the Exercise Price of such shares after
such adjustment, setting forth a brief statement of the facts requiring such
adjustment and setting forth the computation by which such adjustment was made.

                  (e) The form of this Warrant need not be changed because of
any adjustments in the Exercise Price or the number or kind of the Shares, and
Warrants theretofore and thereafter issued may continue to express the same
price and number and kind of shares as are stated in this Warrant as initially
issued.

                  (f)      In case at any time:

                           (i) the Company shall declare any cash dividend on 
its Common Stock;

                           (ii) the Company shall pay any dividends payable in
stock upon its Common Stock or make any distribution (other than regular cash 
dividends) to the holders of its Common Stock;

                           (iii) the Company shall offer for subscription pro
rata to the holders of its Common Stock any additional shares of stock of any 
class or other rights;

                           (iv) the Company shall authorize the distribution to
all holders of its Common Stock of evidences of its indebtedness or assets 
(other than cash dividends or cash distributions payable out of current 
earnings or dividends payable in Common Stock);

                           (v) there shall be any capital reorganization, or 
reclassification of the capital stock of the Company, or consolidation or merger
of the Company with another corporation (other than a subsidiary of the Company
in which the Company is the surviving or continuing corporation and no change
occurs in the Company's Common Stock), or sale of all or substantially all of
its assets to, another corporation;


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                           (vi) there shall be a voluntary or involuntary 
dissolution,  liquidation, bankruptcy, assignment for the benefit of creditors,
or winding up of the Company, or

                           (vii) the Company proposes to take any other action
or an event occurs which would require an adjustment pursuant to subsections 
(a) or (c) of this Section 6;

then, in any one or more of said cases, the Company shall give written notice to
the holder of this Warrant, of (A) the date on which the books of the Company
shall close or a record shall be taken for such dividend, distribution or
subscription rights, or (B) the date (or, if not then known, a reasonable
approximation thereof by the Company) on which such reorganization,
reclassification, consolidation, merger, sale, dissolution, liquidation,
bankruptcy, assignment for the benefit of creditors, winding up or other action,
as the case may be, shall take place. Such notice shall also specify (or, if not
then known, reasonably approximate) the date as of which the holders of Common
Stock of record shall participate in such dividend, distribution or subscription
rights, or shall be entitled to exchange their Common Stock for securities or
other property deliverable upon such reorganization, reclassification,
consolidation, merger, sale, dissolution, liquidation, bankruptcy, assignment
for the benefit of creditors, winding up, or other action, as the case may be.
Such written notice shall be given at least 20 days prior to the action in
question and not less than 20 days prior to the record date or the date on which
the Company's transfer books are closed in respect thereto.

                  (g) The number of shares of Common Stock which may be acquired
upon exercise of this Warrant and the Exercise Price payable hereunder shall be
subject to adjustments from time to time in the event that the Company sells or
issues any shares of equity securities, or securities exercisable for or
convertible into equity securities, at a price less than the Exercise Price
(such securities being referred to as "Additional Shares of Common Stock").
Notwithstanding anything contained herein to the contrary, the Company shall not
be required to make any adjustment of the Exercise Price in the case of: (i) the
issuance or exercise of shares of Common Stock or any other securities which may
now or hereafter be granted or exercised under the Company's Amended and
Restated Performance Stock Option Plan, 1997 Employee Stock Purchase Plan and
Non-qualified Stock Option Plan (the "Plans") or under any other employee
benefit plan or stock option plan of the Company approved by the Company's Board
of Directors; (ii) the issuance of any shares of Common Stock of the Company or
other securities or instruments convertible into shares of Common Stock of the
Company issued in connection with corporate collaborations with pharmaceutical,
life science or biotechnology corporations or entities; (iii) the issuance of
shares of Common Stock in connection with a bona fide merger (other than the
Merger), acquisition or other similar transactions involving the Company with or
into a corporation or other entity if the Board of Directors of the Company has
obtained a fairness opinion with respect to the issuance of such Common Stock
from a nationally recognized investment banking firm indicating that the
financial terms of such merger, acquisition or other similar transaction are
fair to the Company when taken as a whole; (iv) the issuance or sale of shares
of Common 

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Stock upon conversion or exchange of any Convertible Securities, whether or not
any adjustment in the Exercise Price was made or required to be made upon the
issuance or sale of such Convertible Securities and whether or not such
Convertible Securities were outstanding on the date of the original sale of the
Warrants or were thereafter issued or sold; (v) the issuance of or sale of
securities to consultants or third parties providing consulting, marketing,
investor relations and other services to the Company; and (vi) issuance of
securities under the Merger Agreement. If, at any time or from time to time
after the date of issuance of this Warrant, the Company issues or sells any
Additional Shares of Common Stock, other than as a dividend or other
distribution on its shares of Common Stock as provided in Section 6(a)(i)(A),
and other than a combination, reclassification or recapitalization of its
outstanding shares of Common Stock as provided in Section 6(a)(i)(C), for a per
share price less than the then applicable Exercise Price, then, and in each such
case, the Exercise Price shall be reduced to a price determined by multiplying
the Exercise Price by a fraction, (i) the numerator of which shall be (A) the
number of shares of Common Stock deemed outstanding (as defined below)
immediately prior to such issuance or sale, plus (B) the number of shares of
Common Stock which the aggregate consideration received by the Company for the
total number of Additional Shares of Common Stock so issued or sold would
purchase at such Exercise Price, and (ii) the denominator of which shall be the
number of shares of Common Stock deemed outstanding (as defined below)
immediately prior to such issue or sale plus the total number of Additional
Shares of Common Stock so issued. For the purposes of the preceding sentence,
the number of shares of Common Stock deemed outstanding as of a given date shall
be the sum of (A) the number of shares of Common Stock actually outstanding, and
(B) the number of shares of Common Stock underlying all outstanding options,
warrants (including this Warrant) and convertible securities on the day
immediately preceding the given date.

                  (h) The shares of Common Stock which may be acquired upon
exercise of this Warrant shall be entitled to the registration rights on the
same terms and conditions as the principal stockholders of ViroTex pursuant to
the terms of the Merger Agreement.

         7. Neither the Warrant Holder nor its legal representatives, successors
or assignees shall be or have any rights or privileges of a shareholder of the
Company in respect to the shares issuable upon exercise of the Warrants granted
hereunder, unless and until the Warrant Holder shall have delivered the notice
and tendered payment for the Exercise Price to the Company, as required under
the provisions of Sections 1 and 2 hereof.

         8. The Company shall pay all taxes and other governmental charges
(other than taxes or governmental charges levied in respect of the income of the
Warrant Holder) that may be imposed on the Company or on the Warrants or the
Shares; provided, however, that the Company shall not be required to pay any tax
or other charge imposed in respect of the transfer of Warrants or the issuance
or delivery of certificates for Shares or other securities in respect of the
Shares upon the exercise of Warrants to a person or entity other than the then
holder of Warrants.


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         9. This Warrant shall be construed and enforced in accordance with the
laws of the State of Colorado. Any notices to be given under the terms of this
Warrant shall be addressed to the Company at 2579 Midpoint Drive, Fort Collins,
Colorado 80525, Attention: Chief Executive Officer, and notice to be given to
the Warrant Holder shall be addressed to it at the address last shown on the
books of the Company for such Warrant Holder or at any such other address as
either party may hereafter designate, by notice in writing, to the other. Any
such notice shall be deemed duly given when enclosed in a properly sealed
envelope or wrapper addressed as aforesaid, registered or certified, and
deposited, postage and registry or certification fee prepaid, in a post office
or branch post office regularly maintained by the United States Postal Service.

         10. This Warrant shall be binding upon and inure to the benefit of any
successor or successors of the Company, and shall inure to the benefit of and
shall be enforceable by the Warrant Holder and its legal representatives,
successors, heirs and permitted assigns.

Dated this 24th day of November, 1998.

ATTEST:                                    ATRIX LABORATORIES, INC.

/s/ Brian G. Richmond                      By: /s/ John E. Urheim
- ----------------------------                  --------------------------------
Brian G. Richmond                             John E. Urheim, Vice Chairman and
Assistant Secretary                           Chief Executive Officer



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                                   ASSIGNMENT

                (To be executed only upon assignment of Warrant )

                  For value received, ______________________ hereby sells,
assigns and transfers unto ________________________ the within Warrant, together
with all right, title and interest therein, and does hereby irrevocably
constitute and appoint ______________________ attorney, to transfer said Warrant
on the books of the within-named Company with respect to the number of Warrant
Shares set forth below, with full power of substitution in the premises:



                  Name(s) of
                  Assignee(s)               Address           No. of Shares
                  -----------               -------           -------------
                                                        






                   And if said number of Shares shall not be all the Shares
issuable upon exercise of the Warrant, a new Warrant is to be issued in the name
of said undersigned for the balance remaining of the Shares issuable upon
exercise of said Warrant.

Dated:  ___________________, 19___



                                      By:
                                         --------------------------------------
                                         The above signature should correspond
                                         exactly with the name of the Warrant 
                                         Holder set forth in this Warrant.



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                                SUBSCRIPTION FORM
                    (To be executed upon exercise of Warrant)

Atrix Laboratories, Inc.:


                  The undersigned hereby irrevocably elects to exercise the
right of purchase represented by the within Warrant for, and to purchase
thereunder, __________ shares of Common Stock, as provided for therein, and
tenders herewith payment of the Exercise Price in full in the form of cash or a
certified or cashier's check in the amount of $___________.

                  Please issue a certificate, or certificates for such shares of
Common Stock in the name of:


                       Name:                                       
                            --------------------------------
                       Address:                                    
                               -----------------------------
                       Social Security No.:                        
                                           -----------------

                                        Signature: 
                                                  -------------------------
                                        NOTE:     The above signature should  
                                                  correspond exactly with the
                                                  name of the Warrant Holder 
                                                  set forth in this Warrant or 
                                                  with the name of the assignee
                                                  appearing in the assignment 
                                                  form below.


And if said number of shares shall not be all the shares purchasable under the
within Warrant, a new Warrant is to be issued in the name of said undersigned
for the balance remaining of the shares purchasable thereunder.


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