<PAGE>   1
                                                                 EXHIBIT 10.4

                   THE TRANSFER OF THIS WARRANT IS SUBJECT TO
                   RESTRICTIONS CONTAINED HEREIN. THIS WARRANT
                      HAS BEEN ISSUED IN RELIANCE UPON THE
                  REPRESENTATION OF THE HOLDER THAT IT HAS BEEN
                  ACQUIRED FOR INVESTMENT PURPOSES AND NOT WITH
                 A VIEW TOWARD THE RESALE OR OTHER DISTRIBUTION
                  THEREOF. NEITHER THIS WARRANT NOR THE SHARES
              ISSUABLE UPON THE EXERCISE OF THIS WARRANT, HAVE BEEN
               REGISTERED UNDER THE SECURITIES ACT OF 1933 OR ANY
                             STATE SECURITIES LAWS.

                              DEPOTECH CORPORATION

                          COMMON STOCK PURCHASE WARRANT


To Subscribe for and Purchase                                  February 25, 1998
Shares of Common Stock
of DEPOTECH CORPORATION



                              VOID AFTER 5:00 P.M.,
                                  PACIFIC TIME
                                FEBRUARY 24, 2001

        THIS CERTIFIES that, for value received, SANDERLING MANAGEMENT COMPANY,
LLC, or its registered assigns (the "Holder"), is entitled to subscribe for and
purchase from DEPOTECH CORPORATION, a California corporation (hereinafter called
the "Corporation"), up to One Hundred Thousand (100,000) shares (subject to
adjustment as hereinafter provided) of fully paid and non-assessable Common
Stock of the Corporation, (the "Common Stock"), at $4.375 per share (such price
as from time to time to be adjusted as hereinafter provided being hereinafter
called the "Warrant Price"), at any time from May 25, 1998 but at or prior to
5:00 p.m. Pacific time on February 24, 2001 (the "Exercise Period") subject,
however, to the provisions and upon the terms and conditions hereinafter set
forth.

        This Warrant and any Warrant or Warrants subsequently issued upon
exchange or transfer hereof are hereinafter collectively called the "Warrant."

        Section 1. Exercise of Warrant. The rights represented by this Warrant
may be exercised by the Holder, in whole or in part (but not as to fractional
shares) at any time or from time to time in part, but not as to a fractional
share of Common Stock, by the



<PAGE>   2

completion of the purchase form attached hereto and by the surrender of this
Warrant (properly endorsed) at the office of the Corporation as it may designate
by notice in writing to the Holder hereof at the address of the Holder appearing
on the books of the Corporation, and by payment to the Corporation of the
Warrant Price for each share purchased, in cash, or by certified or official
bank check, or by tender of shares of Common Stock held for the required period
of time, if any, along with a written statement specifying that the Holder
intends to pay the Exercise Price by tender of such shares (such shares to be
valued at fair market value (as such term is defined below) on the date on which
the Corporation receives the Warrant, the shares of Common Stock and such
written statement, or such later date as specified therein). In the event of any
exercise of the rights represented by this Warrant, a certificate or
certificates for the shares of Common Stock so purchased, registered in the name
of the Holder, or its nominee or other party designated in the purchase form by
the Holder hereof, shall be delivered to the Holder within a reasonable time,
but in no event more than thirty (30) business days after the date in which the
rights represented by this Warrant shall have been so exercised; and, unless
this Warrant has expired or has been exercised in full, a new Warrant
representing the number of shares (except a remaining fractional share), if any,
with respect to which this Warrant shall not then have been exercised shall also
be issued to the Holder within such time. The person in whose name any
certificate for shares of Common Stock is issued upon exercise of this Warrant
shall for all purposes be deemed to have become the Holder of record of such
shares on the date on which this Warrant was surrendered and payment of the
Warrant Price, except that, if the date of such surrender and payment is a date
on which the stock transfer books of the Corporation are closed, such person
shall be deemed to have become the Holder of such shares at the close of
business on the next succeeding date on which the stock transfer books are open.
No fractional shares shall be issued upon exercise of this Warrant and no
payment or adjustment shall be made upon any exercise on account of any cash
dividends on the Common Stock issued upon such exercise. If any fractional
interest in a share of Common Stock would, except for the provision of this
Section 1, be delivered upon such exercise, the Corporation, in lieu of delivery
of a fractional share thereof, shall pay to the Holder an amount in cash equal
to the current market price of such fractional share as determined pursuant to
Section 2(c) below.

        Section 2.  Net Issuance.

               (a) Right to Convert. In addition to and without limiting the
rights of the Holder under the terms of this Warrant, the Holder shall have the
right to convert this Warrant or any portion thereof (the "Conversion Right")
into shares of Common Stock as provided in this Section 2 at any time or from
time to time during the Exercise Period. Upon exercise of the Conversion Right
with respect to a particular number of shares subject to the Warrant (the
"Converted Warrant Shares"), the Corporation shall deliver to the Holder
(without payment by the Holder of any exercise price or any cash or other
consideration) that number of shares of fully paid and nonassessable Common
Stock computed using the following formula:


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        X = Y (A - B)
               -----
                 A

        Where  X =    the number of shares of Common Stock to be delivered to 
                      the holder

               Y =    the number of Converted Warrant Shares

               A =    the fair market value of one share of the Corporation's
                      Common Stock on the Conversion Date (as defined below)

               B =    the per share exercise price of the Warrant (as adjusted
                      to the Conversion Date)

The Conversion Right may only be exercised with respect to a whole number of
shares subject to the Warrant. No fractional shares shall be issuable upon
exercise of the Conversion Right, and if the number of shares to be issued
determined in accordance with the foregoing formula is other than a whole
number, the Corporation shall pay to the Holder an amount in cash equal to the
fair market value of the resulting fractional share on the Conversion Date (as
defined below). Shares issued pursuant to the Conversion Right shall be treated
as if they were issued upon the exercise of the Warrant.

               (b) Method of Exercise. The Conversion Right may be exercised by
the Holder by the surrender of the Warrant at the principal office of the
Corporation together with a written statement specifying that the Holder thereby
intends to exercise the Conversion Right and indicating the total number of
shares under the Warrant that the Holder is exercising through the Conversion
Right. Such conversion shall be effective upon receipt by the Corporation of the
Warrant together with the aforesaid written statement, or on such later date as
is specified therein (the "Conversion Date"). Certificates for the shares
issuable upon exercise of the Conversion Right and, if applicable, a new warrant
evidencing the balance of the shares remaining subject to the Warrant, shall be
issued as of the Conversion Date and shall be delivered to the Holder promptly
following the Conversion Date.

               (c) Determination of Fair Market Value. For purposes of this
Section 2, fair market value of a share of Common Stock on the Conversion Date
shall mean:

                        (i)  If traded on a stock exchange, the fair market 
value of the Common Stock shall be deemed to be the average of the closing
selling prices of the Common Stock on the stock exchange determined by the Board
to be the primary market for the Common Stock over the ten (10) trading day
period (or such shorter period immediately following the closing of an initial
public offering) ending on the date prior to the Conversion Date, as such prices
are officially quoted in the composite tape of transactions on such exchange;

                       (ii) If traded over-the-counter, the fair market value of
the Common Stock shall be deemed to be the average of the closing bid prices
(or, if such information is available, the closing selling prices) of the Common
Stock over the ten (10) trading day


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period (or such shorter period immediately following the closing of an initial
public offering) ending on the date prior to the Conversion Date, as such prices
are reported by the National Association of Securities Dealers through its
Nasdaq system or any successor system; and

                      (iii) If there is no public market for the Common Stock,
then the fair market value shall be determined by the Board of Directors of the
Corporation.

        Section 3. Stock Splits, Consolidation, Merger and Sale. In the event
that the outstanding shares of Common Stock shall be split, combined or
consolidated, by dividend, reclassification or otherwise, into a greater or
lesser number of shares of Common Stock, the Warrant Price in effect immediately
prior to such combination or consolidation and the number of shares purchasable
under this Warrant shall, concurrently with the effectiveness of such
combination or consolidation, be proportionately adjusted. If there shall be
effected any consolidation or merger of the Corporation with another
corporation, or a sale of all or substantially all of the Corporation's assets
to another corporation, and if the holders of Common Stock shall be entitled
pursuant to the terms of any such transaction to receive stock, securities or
assets with respect to or in exchange for Common Stock, then, as a condition of
such consolidation, merger or sale, lawful and adequate provisions shall be made
whereby the Holder of this Warrant shall thereafter have the right to receive,
upon the basis and upon the terms and conditions specified herein and in lieu of
the shares of Common Stock immediately theretofore receivable upon the exercise
of such Warrant, such shares of stock, securities or assets as may be issuable
or payable with respect to or in exchange for a number of outstanding shares of
such Common Stock equal to the number of shares of such Common Stock immediately
theretofore so receivable had such consolidation, merger or sale not taken
place, and in any such case appropriate provisions shall be made with respect to
the rights and interests of the Holder to the end that the provisions hereof
shall thereafter be applicable, as nearly as may be, in relation to any shares
of stock, securities or assets thereafter deliverable upon the exercise of this
Warrant.

        Section 4.  Stock to Be Reserved; Issue Tax; Books.

               (a) The Corporation will at all times reserve and keep available
out of its authorized Common Stock, solely for the purpose of issue upon the
exercise of this Warrant as herein provided, such number of shares of Common
Stock as shall then be issuable upon the exercise of this Warrant. The
Corporation shall from time to time in accordance with applicable law increase
the authorized amount of its Common Stock if at any time the number of shares of
Common Stock remaining unissued and available for issuance shall not be
sufficient to permit exercise of this Warrant. The Corporation covenants that
all shares of Common Stock which shall be so issued shall be duly and validly
issued and 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 Corporation will take all such action as may be necessary
to assure that all such shares of Common Stock may be so issued without
violation of any applicable law or regulation, or of any requirements of any
national securities exchange upon which shares of capital stock of the
Corporation may be listed.


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               (b) The issuance of certificates for shares of Common Stock upon
exercise of this Warrant shall be made without charge to the Holders of this
Warrant for any issuance tax in respect thereof provided that the Corporation
shall not be required to pay any tax which may be payable in respect of any
transfer involved in the issuance and delivery of any certificate in a name
other than that of the Holder of this Warrant.

               (c) The Corporation will at no time close its transfer books
against the transfer of the shares of Common Stock (or Common Stock issued upon
the conversion of Common Stock) issued or issuable upon the exercise of this
Warrant in any manner which interferes with the timely exercise of this Warrant.

        Section 5.  Notices of Record Dates.  In the event of

               (a) any taking by the Corporation of a record of the Holders of
any class of securities for the purpose of determining the Holders thereof who
are entitled to receive any dividend or other distribution (other than cash
dividends out of earned surplus), or any right to subscribe for, purchase or
otherwise acquire any shares of stock of any class or any other securities or
property, or to receive any other right, or

               (b) any capital reorganization of the Corporation, any
reclassification or recapitalization of the capital stock of the Corporation or
any transfer of all or substantially all the assets of the Corporation to or
consolidation or merger of the Corporation with or into any other corporation,
or

               (c) any voluntary or involuntary dissolution, liquidation or
winding-up of the Corporation, then and in each such event the Corporation will
give notice to the Holder of this Warrant specifying (i) the date on which any
such record is to be taken for the purpose of such dividend, distribution or
right and stating the amount and character of such dividend, distribution or
right, and (ii) the date on which any such reorganization, reclassification,
recapitalization, transfer, consolidation, merger, dissolution, liquidation or
winding-up is to take place, and the time, if any is to be fixed, as of which
the Holders of record of Common Stock will be entitled to exchange their shares
of Common Stock for securities or other property deliverable upon such
reorganization, reclassification, recapitalization, transfer, consolidation,
merger, dissolution, liquidation or winding-up. Such notice shall be given at
least ten (10) days and not more than ninety (90) days prior to the date therein
specified, and such notice shall state that the action in question or the record
date is subject to the effectiveness of a registration statement under the
Securities Act of 1933, as amended (the "Securities Act") or to a favorable vote
of shareholders, if either is required.

        Section 6. No Shareholder Rights or Liabilities. This Warrant shall not
entitle the Holder hereof to any voting rights or other rights as a shareholder
of the Corporation. No provision hereof, in the absence of affirmative action by
the Holder hereof to purchase shares of Common Stock, and no mere enumeration
hereon of the rights or privileges of the Holder hereof, shall give rise to any
liability of such Holder for the Warrant Price or as a shareholder of the
Corporation, whether such liability is asserted by the Corporation or by
creditors of the Corporation.


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        Section 7.  Representations of Holder.  The Holder hereby represents and
acknowledges to the Corporation that:

               (a) this Warrant, the Common Stock issuable upon exercise of this
Warrant and any securities issued with respect to any of them by way of a stock
dividend or stock split or in connection with a recapitalization, merger,
consolidation or other reorganization will be "restricted securities" as such
term is used in the rules and regulations under the Securities Act and that such
securities have not been and will not be registered under the Securities Act or
any state securities law, and that such securities must be held indefinitely
unless registration is effected or transfer can be made pursuant to appropriate
exemptions;

               (b) the Holder has read, and fully understands, the terms of this
Warrant set forth on its face and the attachments hereto, including the
restrictions on transfer contained herein;

               (c) the Holder has either a pre-existing personal or business
relationship with the Corporation or one of its officers, directors or
controlling persons;

               (d) the Holder is purchasing for investment for its own account
and not with a view to or for sale in connection with any distribution of this
Warrant, the Common Stock of the Corporation issuable upon exercise of this
Warrant or the Common Stock of the Corporation issuable upon conversion of the
Common Stock and it has no intention of selling such securities in a public
distribution in violation of the federal securities laws or any applicable state
securities laws; provided that nothing contained herein will prevent Holder from
transferring such securities in compliance with the terms of this Warrant and
the applicable federal and state securities laws;

               (e) the Holder is an "accredited investor" within the meaning of
paragraph (a) of Rule 501 of Regulation D promulgated by the Securities and
Exchange Commission (the "Commission") and an "excluded purchaser" within the
meaning of Section 25102(f) of the California Corporate Securities Law of 1968;
and

               (f) the Corporation may affix the following legend (in addition
to any other legend(s), if any, required by applicable state corporate and/or
securities laws) to certificates for shares of Common Stock (or other
securities) issued upon exercise of this Warrant and the shares of Common Stock
issued upon conversion of the Common Stock ("Warrant Shares"):

               "These securities have not been registered under the Securities
               Act of 1933, as amended. They may not be sold, offered for sale,
               pledged or hypothecated in the absence of a registration
               statement in effect with respect to the securities under such Act
               or an opinion of counsel satisfactory to the Company that such
               registration is not required or unless sold pursuant to Rule 144
               of such Act."

        Section 8. Notice of Proposed Transfers. The Holder of this Warrant, by
acceptance hereof, agrees to comply in all respects with the provisions of this
Section 7. Prior to any


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<PAGE>   7

proposed transfer of this Warrant or any Warrant Shares, unless there is in
effect a registration statement under the Securities Act covering the proposed
transfer, the Holder of such securities shall give written notice to the
Corporation of such Holder's intention to effect such transfer. Each such notice
shall describe the manner and circumstances of the proposed transfer in
sufficient detail, and shall be accompanied (except in transactions in
compliance with Rule 144) by either (i) a written opinion of legal counsel which
shall be reasonably satisfactory to the Corporation addressed to the Corporation
and reasonably satisfactory in form and substance to the Corporation's counsel,
to the effect that the proposed transfer of the Warrant and/or Warrant Shares
may be effected without registration under the Securities Act, or (ii) a "no
action" letter from the Commission to the effect that the transfer of such
securities without registration will not result in a recommendation by the staff
of the Commission that enforcement action be taken with respect thereto,
whereupon the Holder of such securities shall be entitled to transfer such
securities in accordance with the terms of the notice delivered by the Holder to
the Corporation. Each new certificate evidencing the Warrant and/or Warrant
Shares so transferred shall bear the appropriate restrictive legends set forth
in Section 7 above, except that such certificate shall not bear such restrictive
legend if, in the opinion of counsel for the Corporation, such legend is not
required in order to establish or assist in compliance with any provisions of
the Securities Act or any applicable state securities laws.

        Section 9. Lost, Stolen, Mutilated or Destroyed Warrant. If this Warrant
is lost, stolen, mutilated or destroyed, the Corporation may, on such terms as
to indemnity or otherwise as it may in its discretion reasonably impose (which
shall, in the case of a mutilated Warrant, include the surrender thereof), issue
a new Warrant of like denomination and tenor as the Warrant so lost, stolen,
mutilated or destroyed. Any such new Warrant shall constitute an original
contractual obligation of the Corporation, whether or not the allegedly lost,
stolen, mutilated or destroyed Warrant shall be at any time enforceable by
anyone.

        Section 10. Presentment. Prior to due presentment of this Warrant
together with a completed assignment form attached hereto for registration of
transfer, the Corporation may deem and treat the Holder as the absolute owner of
the Warrant, notwithstanding any notation of ownership or other writing thereon,
for the purpose of any exercise thereof and for all other purposes, and the
Corporation shall not be affected by any notice to the contrary.

        Section 11. Notice. Notice or demand pursuant to this Warrant shall be
sufficiently given or made, if sent by first-class mail, postage prepaid,
addressed, if to the Holder of this Warrant, to the Holder at its last known
address as it shall appear in the records of the Corporation, and if to the
Corporation, at 10450 Science Center Drive, San Diego, California 92121,
Attention: Secretary. The Corporation may alter the address to which
communications are to be sent by giving notice of such change of address in
conformity with the provisions of this Section 11 for the giving of notice.

        Section 12. Governing Law. The validity, interpretation and performance
of this Warrant shall be governed by the laws of the State of California without
regard to principles of conflicts of laws.



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<PAGE>   8



        Section 13. Successors, Assigns. Subject to the restrictions on transfer
by Holder set forth in Section 8 hereof, all the terms and provisions of the
Warrant shall be binding upon and inure to the benefit of and be enforceable by
the respective successors and assigns of the parties hereto.

        Section 14. Amendment. This Warrant may be modified, amended or
terminated by a writing signed by the Corporation and the Holder.

        Section 15. Severability. Should any part but not the whole of this
Warrant for any reason be declared invalid, such decision shall not affect the
validity of any remaining portion, which remaining portion shall remain in force
and effect as if this Warrant had been executed with the invalid portion thereof
eliminated, and it is hereby declared the intention of the parties hereto that
they would have executed the remaining portion of this Warrant without including
therein any such part which may, for any reason, be hereafter declared invalid.

        IN WITNESS WHEREOF, the Corporation has caused this Warrant to be duly
executed and delivered on and as of the day and year first above written by one
of its officers thereunto duly authorized.

                                        DEPOTECH CORPORATION, a California
                                        corporation



Dated: February 25, 1998                By:   /s/ John P. Longenecker
                                           -------------------------------------
                                           John P. Longenecker
                                           President and Chief Operating Officer



               The undersigned Holder agrees and accepts this Warrant and
        acknowledges that it has read and confirms each of the representations
        contained in Section 7.



                                        By:      /s/ FRED A. MIDDLETON
                                               ---------------------------------
                                               Fred A. Middleton
                                               General Partner

                                        Its:    Sanderling Management Company
                                               ---------------------------------
                                        Address:  2730 Sand Hill Road
                                               ---------------------------------
                                                  Suite 200
                                               ---------------------------------
                                                  Menlo Park, CA 94025
                                               ---------------------------------


                               [SIGNATURE PAGE TO
                     DEPOTECH COMMON STOCK PURCHASE WARRANT]


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<PAGE>   9

                                  PURCHASE FORM



(To be executed by the Warrant Holder if he desires to exercise the Warrant in
whole or in part)

To:  DEPOTECH CORPORATION

                      The undersigned, whose Social Security or other
identifying number is ________, hereby irrevocably elects the right of purchase
represented by the within Warrant for, and to purchase thereunder,
_________________________________ shares of securities provided for therein and
tenders payment herewith to the order of

                              DEPOTECH CORPORATION
                                in the amount of

                                   $__________

The undersigned requests that certificates for such shares be issued as follows:

Name: _____________________________
Address: __________________________
Deliver to: _______________________
Address: __________________________

and, if said number of shares shall not be all the shares purchasable hereunder,
that a new Warrant for the balance remaining of the shares purchasable under the
within Warrant be registered in the name of, and delivered to, the undersigned
at the address stated below Address: _____________________________



Dated: _________________ , 19__


                          Signature___________________  (Signature must
                          conform in all respects to the name of the
                          Warrant Holder as specified on the face of
                          the Warrant, without alteration,
                          enlargement or any change whatsoever)


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<PAGE>   10

                                   ASSIGNMENT



(To be executed by the Warrant Holder if he desires to effect a transfer of the
Warrant)

                      FOR VALUE RECEIVED, the undersigned hereby sells, assigns
and transfers unto _________________________________ whose Social Security or
other identification number is____________________________ [residing/located] at
______________________ the attached Warrant, and
appoints_____________________________ residing at
________________________________________

_________________________________________
the undersigned's attorney-in-fact to transfer said Warrant on the books of the
Corporation, with full power of substitution in the premises.


Dated: ________________ , 19  .

In the presence of:


----------------------------                 ______________________________
                                            (Signature must conform in all
                                            respects to the name of the Warrant
                                            Holder as specified on the face of
                                            the Warrant, without alteration,
                                            enlargement or any change
                                            whatsoever).


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