<PAGE>   1

                                                                     EXHIBIT 4.5

NEITHER THESE SECURITIES NOR THE SECURITIES INTO WHICH THESE SECURITIES ARE
EXERCISABLE HAVE BEEN REGISTERED WITH THE SECURITIES AND EXCHANGE COMMISSION OR
THE SECURITIES COMMISSION OF ANY STATE IN RELIANCE UPON AN EXEMPTION FROM
REGISTRATION UNDER SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"),
AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT PURSUANT TO AN EFFECTIVE
REGISTRATION STATEMENT UNDER THE SECURITIES ACT OR PURSUANT TO AN AVAILABLE
EXEMPTION FROM THE REGISTRATION REQUIREMENTS THEREUNDER AND IN COMPLIANCE WITH
APPLICABLE STATE SECURITIES OR BLUE SKY LAWS.


                              NEOTHERAPEUTICS, INC.

                                 CLASS A WARRANT

Warrant No. A-2                                           Dated: April 6, 2000


         NeoTherapeutics, Inc., a Delaware corporation (the "Company"), hereby
certifies that, for value received, Strong River Investments, Inc., or its
registered assigns ("Holder"), is entitled, subject to the terms set forth
below, to purchase from the Company up to a total of 157,500 shares of common
stock, $.001 par value per share (the "Common Stock"), of the Company (each such
share, a "Warrant Share" and all such shares, the "Warrant Shares") at an
exercise price equal to $19.672 per share (as adjusted from time to time as
provided in Section 9, the "Exercise Price"), at any time and from time to time
from and after the date hereof and through and including April 6, 2005 (the
"Termination Date"), and subject to the following terms and conditions:

                  1. Registration of Warrant. The Company shall register this
Warrant, upon records to be maintained by the Company for that purpose (the
"Warrant Register"), in the name of the record Holder hereof from time to time.
The Company may deem and treat the registered Holder of this Warrant as the
absolute owner hereof for the purpose of any exercise hereof or any distribution
to the Holder, and for all other purposes, and the Company shall not be affected
by notice to the contrary.

                  2. Registration of Transfers and Exchanges.

                        (a) This Warrant may only be transferred pursuant to an
effective registration statement under the Securities Act, to the Company or
pursuant to an available exemption from or in a transaction not subject to the
registration requirements of the Securities Act. In connection with any transfer
of this Warrant other than pursuant to an effective registration statement or to
the Company, the Company may require the transferor thereof to provide to the


                                                                 Class A Warrant
<PAGE>   2
Company an opinion of counsel selected by the transferor, the form and substance
of which opinion shall be reasonably satisfactory to the Company, to the effect
that such transfer does not require registration of such Warrant under the
Securities Act. Holder agrees to the imprinting, so long as is required by this
Section 2(a), of a legend substantially similar to that first above written on
any New Warrant (as defined below). Any such transferee shall agree in writing
to be bound by the terms of this Warrant and shall have the rights of Holder
under this Warrant.

                        (b) The Company shall register the transfer of any
portion of this Warrant in the Warrant Register, upon surrender of this Warrant,
with the Form of Assignment attached hereto duly completed and signed, to the
Transfer Agent or to the Company at the office specified in or pursuant to
Section 3(b). Upon any such registration or transfer, a new warrant to purchase
Common Stock, in substantially the form of this Warrant (any such new warrant, a
"New Warrant"), evidencing the portion of this Warrant so transferred shall be
issued to the transferee and a New Warrant evidencing the remaining portion of
this Warrant not so transferred, if any, shall be issued to the transferring
Holder. The acceptance of the New Warrant by the transferee thereof shall be
deemed the acceptance of such transferee of all of the rights and obligations of
a holder of a Warrant.

                        (c) This Warrant is exchangeable, upon the surrender
hereof by the Holder to the office of the Company specified in or pursuant to
Section 3(b) for one or more New Warrants, evidencing in the aggregate the right
to purchase the number of Warrant Shares which may then be purchased hereunder.
Any such New Warrant will be dated the date of such exchange.

                  3. Duration, Exercise and Vesting of Warrants.

                        (a) This Warrant shall be exercisable by the registered
Holder on any business day before 8:00 P.M., New York City time, at any time and
from time to time on or after the date hereof to and including the Termination
Date. At 8:00 P.M., New York City time on the Termination Date, the portion of
this Warrant not exercised prior thereto shall be and become void and of no
value. Prior to the Termination Date, the Company may not call or otherwise
redeem this Warrant without the prior written consent of the Holder.

                        (b) Subject to Sections 2(b), 6 and 10, upon surrender
of this Warrant, with the Form of Election to Purchase attached hereto duly
completed and signed, to the Company at its address for notice set forth in
Section 13 and upon payment of the Exercise Price multiplied by the number of
Warrant Shares that the Holder intends to purchase hereunder, in the manner
provided hereunder, all as specified by the Holder in the Form of Election to
Purchase, the Company shall promptly (but in no event later than 3 business days
after the Date of Exercise (as defined herein)) issue or cause to be issued and
cause to be delivered to or upon the written order of the Holder and in such
name or names as the Holder may designate, a certificate for the Warrant Shares
issuable upon such exercise, free of restrictive legends except (i) either in
the event that a registration statement covering the resale of the Warrant
Shares and naming the Holder as a selling stockholder thereunder is not then
effective or the Warrant Shares are not freely transferable without volume
restrictions pursuant to Rule 144(k) promulgated under the Securities Act of
1933, as amended (the "Securities Act"), or (ii) if this Warrant shall have been
issued pursuant to a written agreement between the original Holder and the
Company, as required by such agreement. Any person so

                                   -2-                          Class A Warrant
<PAGE>   3
designated by the Holder to receive Warrant Shares shall be deemed to have
become holder of record of such Warrant Shares as of the Date of Exercise of
this Warrant.

                        A "Date of Exercise" means the date on which the Company
shall have received (i) this Warrant (or any New Warrant, as applicable), with
the Form of Election to Purchase attached hereto (or attached to such New
Warrant) appropriately completed and duly signed, and (ii) payment of the
Exercise Price for the number of Warrant Shares so indicated by the holder
hereof to be purchased.

                        (c) This Warrant shall be exercisable, either in its
entirety or, from time to time, for a portion of the number of Warrant Shares
which have vested pursuant to Section 3(d). If less than all of the Warrant
Shares which may be purchased under this Warrant are exercised at any time, the
Company shall issue or cause to be issued, at its expense, a New Warrant
evidencing the right to purchase the remaining number of Warrant Shares for
which no exercise has been evidenced by this Warrant.

                         (d)      (i) On the date hereof, 57,500 Warrant Shares
                                  shall vest on the date hereof;

                                  (ii) Upon each exercise by the Holder pursuant
                                  to Section 3(a) of the Class B Warrant of even
                                  date hereof, issued by the Company in the name
                                  of the Holder (the "Class B Warrant"), this
                                  Warrant shall vest with respect to 1/20th of
                                  the Warrant Shares so exercised under the
                                  Class B Warrant, provided, that no more than
                                  75,000 Warrant Shares shall be permitted to
                                  vest under this subsection 3(d)(ii);

                                  (iii) If, on or prior to the Expiration Date
                                  (as defined in the Class B Warrant), the
                                  Company has failed to deliver one or more Call
                                  Notices (as defined in the Class B Warrant)
                                  pursuant to Section 3(a) of the Class B
                                  Warrant for a minimum of 500,000 Warrant
                                  Shares (as defined in the Class B Warrant),
                                  then on the Expiration Date, this Warrant
                                  shall vest with respect to a number of Warrant
                                  Shares equal to the difference between (i)
                                  25,000 and (ii) 1/20th of the number of
                                  Warrant Shares called pursuant to Section 3(a)
                                  of the Redeemable Warrant; and

                                  (iv) If the Class B Warrant shall be canceled
                                  pursuant to Section 2(f) of the Registration
                                  Rights Agreement of even date herewith to
                                  which the Company and the original holder are
                                  parties, then, on the date of such
                                  cancellation, this Warrant shall vest with
                                  respect to 25,000 Warrant Shares.

                  4. Piggyback Registration Rights. During the Effectiveness
Period (as defined in the Registration Rights Agreement, of even date herewith,
between the Company and the original

                                     -3-                       Class A Warrant
<PAGE>   4
Holder), the Company may not file any registration statement with the Securities
and Exchange Commission (other than registration statements of the Company filed
on Form S-8 or Form S-4, each as promulgated under the Securities Act, pursuant
to which the Company is registering securities pursuant to a Company employee
benefit plan or pursuant to a merger, acquisition or similar transaction
including supplements thereto, but not additionally filed registration
statements in respect of such securities) at any time when there is not an
effective registration statement covering the resale of the Warrant Shares and
naming the Holder as a selling stockholder thereunder, unless the Company
provides the Holder with not less than 20 days notice of its intention to file
such registration statement and provides the Holder the option to include any or
all of the applicable Warrant Shares therein. The piggyback registration rights
granted to the Holder pursuant to this Section shall continue until all of the
Holder's Warrant Shares have been sold in accordance with an effective
registration statement or upon the expiration of the Effective Period. The
Company will pay all registration expenses in connection therewith.

                  5. [intentionally left blank]

                  6. Payment of Taxes. The Company will pay all documentary
stamp taxes attributable to the issuance of Warrant Shares upon the exercise of
this Warrant; provided, however, that the Company shall not be required to pay
any tax which may be payable in respect of any transfer involved in the
registration of any certificates for Warrant Shares or Warrants in a name other
than that of the Holder. The Holder shall be responsible for all other tax
liability that may arise as a result of holding or transferring this Warrant or
receiving Warrant Shares upon exercise hereof.

                  7. Replacement of Warrant. If this Warrant is mutilated, lost,
stolen or destroyed, the Company shall issue or cause to be issued in exchange
and substitution for and upon cancellation hereof, or in lieu of and
substitution for this Warrant, a New Warrant, but only upon receipt of evidence
reasonably satisfactory to the Company of such loss, theft or destruction and
indemnity, if requested, satisfactory to it. Applicants for a New Warrant under
such circumstances shall also comply with such other reasonable regulations and
procedures and pay such other reasonable charges as the Company may prescribe.

                  8. Reservation of Warrant Shares. The Company covenants that
it will at all times reserve and keep available out of the aggregate of its
authorized but unissued Common Stock, solely for the purpose of enabling it to
issue Warrant Shares upon exercise of this Warrant as herein provided, the
number of Warrant Shares which are then issuable and deliverable upon the
exercise of this entire Warrant, free from preemptive rights or any other actual
contingent purchase rights of persons other than the Holder (taking into account
the adjustments and restrictions of Section 9). The Company covenants that all
Warrant Shares that shall be so issuable and deliverable shall, upon issuance
and the payment of the applicable Exercise Price in accordance with the terms
hereof, be duly and validly authorized, issued and fully paid and nonassessable.

                                       -4-                      Class A Warrant
<PAGE>   5
                  9. Certain Adjustments.

                  (a) If the Company, at any time while this Warrant is
outstanding, (i) shall pay a stock dividend (except scheduled dividends paid on
outstanding preferred stock as of the date hereof which contain a stated
dividend rate) or otherwise make a distribution or distributions on shares of
its Common Stock or on any other class of capital stock payable in shares of
Common Stock, (ii) subdivide outstanding shares of Common Stock into a larger
number of shares, or (iii) combine outstanding shares of Common Stock into a
smaller number of shares, the Exercise Price shall be multiplied by a fraction
of which the numerator shall be the number of shares of Common Stock (excluding
treasury shares, if any) outstanding before such event and of which the
denominator shall be the number of shares of Common Stock (excluding treasury
shares, if any) outstanding after such event. Any adjustment made pursuant to
this Section shall become effective immediately after the record date for the
determination of stockholders entitled to receive such dividend or distribution
and shall become effective immediately after the effective date in the case of a
subdivision or combination, and shall apply to successive subdivisions and
combinations.

                        (b) In case of any reclassification of the Common Stock
or any compulsory share exchange pursuant to which the Common Stock is converted
into other securities, cash or property, then the Holder shall have the right
thereafter to exercise this Warrant only into the shares of stock and other
securities and property receivable upon or deemed to be held by holders of
Common Stock following such reclassification or share exchange, and the Holder
shall be entitled upon such exercise to receive such amount of securities or
property equal to the amount of Warrant Shares such Holder would have been
entitled to had such Holder exercised this Warrant immediately prior to such
reclassification or share exchange. The terms of any such reclassification or
share exchange shall include such terms so as to continue to give to the Holder
the right to receive the securities or property set forth in this Section 9(b)
upon any exercise following any such reclassification or share exchange.

                        (c) If the Company, at any time while this Warrant is
outstanding, shall distribute to all holders of Common Stock (and not to holders
of this Warrant) evidences of its indebtedness or assets or rights or warrants
to subscribe for or purchase any security (excluding those referred to in
Sections 9(a), (b) and (d)) and other than with respect to rights granted
pursuant to a stockholders rights plan adopted by the Company, then in each such
case the Exercise Price shall be determined by multiplying the Exercise Price in
effect immediately prior to the record date fixed for determination of
stockholders entitled to receive such distribution by a fraction of which the
denominator shall be the Exercise Price determined as of the record date
mentioned above, and of which the numerator shall be such Exercise Price on such
record date less the then fair market value at such record date of the portion
of such assets or evidence of indebtedness so distributed applicable to one
outstanding share of Common Stock as determined by the Company's independent
certified public accountants that regularly examines the financial statements of
the Company (an "Appraiser").

                                      -5-                      Class A Warrant
<PAGE>   6
                        (d) In case of the closing of any (1) merger or
consolidation of the Company with or into another Person, or (2) sale by the
Company of more than one-half of the assets of the Company (on a book value
basis) in one or a series of related transactions, or (3) tender or other offer
or exchange (whether by the Company or another Person) pursuant to which holders
of Common Stock are permitted to tender or exchange their shares for other
securities, stock, cash or property of the Company or another Person; then the
Holder shall have the right thereafter to (A) exercise this Warrant for the
shares of stock and other securities, cash and property receivable upon or
deemed to be held by holders of Common Stock following such merger,
consolidation or sale, and the Holder shall be entitled upon exercise of this
Warrant to receive such amount of securities, cash and property as the Common
Stock for which this Warrant could have been exercised immediately prior to such
merger, consolidation or sales would have been entitled, or (B) in the event of
an exchange or tender offer or other transaction contemplated by clause (3) of
this Section, tender or exchange this Warrant for such securities, stock, cash
and other property receivable upon or deemed to be held by holders of Common
Stock that have tendered or exchanged their shares of Common Stock following
such tender or exchange, and the Holder shall be entitled upon such exchange or
tender to receive such amount of securities, cash and property as the shares of
Common Stock for which this Warrant could have been exercised immediately prior
to such tender or exchange would have been entitled as would have been issued.
The terms of any such merger, sale, consolidation, tender or exchange shall
include such terms so as continue to give the Holder the right to receive the
securities, cash and property set forth in this Section upon any conversion or
redemption following such event. This provision shall similarly apply to
successive such events.

                        (e) For the purposes of this Section 9, the following
clauses shall also be applicable:

                              (i) Record Date. In case the Company shall take a
record of the holders of its Common Stock for the purpose of entitling them (A)
to receive a dividend or other distribution payable in Common Stock or in
securities convertible or exchangeable into shares of Common Stock, or (B) to
subscribe for or purchase Common Stock or securities convertible or exchangeable
into shares of Common Stock, then such record date shall be deemed to be the
date of the issue or sale of the shares of Common Stock deemed to have been
issued or sold upon the declaration of such dividend or the making of such other
distribution or the date of the granting of such right of subscription or
purchase, as the case may be.

                              (ii) Treasury Shares. The number of shares of
Common Stock outstanding at any given time shall not include shares owned or
held by or for the account of the Company, and the disposition of any such
shares shall be considered an issue or sale of Common Stock.

                        (f) All calculations under this Section 9 shall be made
to the nearest cent or the nearest 1/100th of a share, as the case may be.

                        (g) Whenever the Exercise Price is adjusted pursuant to
Section 9(c) above, the Holder, after receipt of the determination by the
Appraiser, shall have the right to select an additional appraiser (which shall
be a nationally recognized accounting firm), in which case the


                                      -6-                       Class A Warrant
<PAGE>   7
adjustment shall be equal to the average of the adjustments recommended by each
of the Appraiser and such appraiser. The Holder shall promptly mail or cause to
be mailed to the Company, a notice setting forth the Exercise Price after such
adjustment and setting forth a brief statement of the facts requiring such
adjustment. Such adjustment shall become effective immediately after the record
date mentioned above.

                        (h) If:

                                    (i)      the Company shall declare a
                                             dividend (or any other
                                             distribution) on its Common Stock;
                                             or

                                    (ii)     the Company shall declare a special
                                             nonrecurring cash dividend on or a
                                             redemption of its Common Stock; or

                                    (iii)    the Company shall authorize the
                                             granting to all holders of the
                                             Common Stock rights or warrants to
                                             subscribe for or purchase any
                                             shares of capital stock of any
                                             class or of any rights; or

                                    (iv)     the approval of any stockholders of
                                             the Company shall be required in
                                             connection with any
                                             reclassification of the Common
                                             Stock, any consolidation or merger
                                             to which the Company is a party,
                                             any sale or transfer of all or
                                             substantially all of the assets of
                                             the Company, or any compulsory
                                             share exchange whereby the Common
                                             Stock is converted into other
                                             securities, cash or property; or

                                    (v)      the Company shall authorize the
                                             voluntary dissolution, liquidation
                                             or winding up of the affairs of the
                                             Company,

then the Company shall cause to be mailed to each Holder at their last addresses
as they shall appear upon the Warrant Register, at least 30 calendar days prior
to the applicable record or effective date hereinafter specified, a notice
stating (x) the date on which a record is to be taken for the purpose of such
dividend, distribution, redemption, rights or warrants, or if a record is not to
be taken, the date as of which the holders of Common Stock of record to be
entitled to such dividend, distributions, redemption, rights or warrants are to
be determined or (y) the date on which such reclassification, consolidation,
merger, sale, transfer or share exchange is expected to become effective or
close, and the date as of which it is expected that holders of Common Stock of
record shall be entitled to exchange their shares of Common Stock for
securities, cash or other property deliverable upon such reclassification,
consolidation, merger, sale, transfer, share exchange, dissolution, liquidation
or winding up; provided, however, that the failure to mail such notice or any
defect therein or in the mailing thereof shall not affect the validity of the
corporate action required to be specified in such notice.


                                      -7-                      Class A Warrant
<PAGE>   8
                  10. Payment of Exercise Price. The Holder shall pay the
Exercise Price in one of the following manners:

                        (a) Cash Exercise. The Holder may deliver immediately
available funds; or

                        (b) Cashless Exercise. The Holder may surrender this
Warrant to the Company together with a notice of cashless exercise, in which
event the Company shall issue to the Holder the number of Warrant Shares
determined as follows:

                            X = Y [(A-B)/A]
         where:
                            X = the number of Warrant Shares to be issued
         to the Holder.

                            Y = the number of Warrant Shares with respect to
                            which this Warrant is being exercised.

                            A = the average of the closing sale prices of the
                            Common Stock for the five (5) trading days
                            immediately prior to (but not including) the Date of
                            Exercise.

                            B = the Exercise Price.

For purposes of Rule 144 promulgated under the Securities Act, it is intended,
understood and acknowledged that the Warrant Shares issued in a cashless
exercise transaction shall be deemed to have been acquired by the Holder, and
the holding period for the Warrant Shares shall be deemed to have been
commenced, on the issue date.

         11. Certain Exercise Restrictions. A Holder may not exercise this
Warrant to the extent such exercise would result in the Holder, together with
any affiliate thereof, beneficially owning (as determined in accordance with
Section 13(d) of the Securities Exchange Act of 1934, as amended and the rules
promulgated thereunder) in excess of 9.999% of the then issued and outstanding
shares of Common Stock, including shares of Common Stock issuable upon such
exercise and held by such Holder after application of this Section. Since the
Holder will not be obligated to report to the Company the number of shares of
Common Stock it may hold at the time of an exercise hereunder, unless the
exercise at issue would result in the issuance of shares of Common Stock in
excess of 9.999% of the then outstanding shares of Common Stock without regard
to any other shares which may be beneficially owned by the Holder or an
affiliate thereof, the Holder shall have the authority and obligation to
determine whether the restriction contained in this Section will limit any
particular exercise hereunder and to the extent that the Holder determines that
the limitation contained in this Section applies, the determination of which
portion of this Warrant is exercisable shall be the responsibility and
obligation of the Holder. If the Holder has delivered a Form of Election to
Purchase for a number of Warrant Shares that, without regard to any other shares
that the Holder or

                                      -8-                      Class A Warrant
<PAGE>   9
its affiliates may beneficially own, would result in the issuance in excess of
the permitted amount hereunder, the Company shall notify the Holder of this fact
and shall honor the exercise for the maximum portion of this Warrant permitted
to be exercised on such Date of Exercise in accordance with the periods
described herein and, at the option of the Holder, either keep the portion of
the Warrant tendered for exercise in excess of the permitted amount hereunder
for future exercises or return such excess portion of the Warrant to the Holder.
The provisions of this Section may be waived by a Holder (but only as to itself
and not to any other Holder) upon not less than 61 days prior notice to the
Company. Other Holders shall be unaffected by any such waiver.

                  12. Fractional Shares. The Company shall not be required to
issue or cause to be issued fractional Warrant Shares on the exercise of this
Warrant. The number of full Warrant Shares which shall be issuable upon the
exercise of this Warrant shall be computed on the basis of the aggregate number
of Warrant Shares purchasable on exercise of this Warrant so presented. If any
fraction of a Warrant Share would, except for the provisions of this Section, be
issuable on the exercise of this Warrant, the Company shall pay an amount in
cash equal to the Exercise Price multiplied by such fraction.

                  13. Notices. Any and all notices or other communications or
deliveries hereunder shall be in writing and shall be deemed given and effective
on the earliest of (i) the date of transmission, if such notice or communication
is delivered via facsimile at the facsimile telephone number specified in this
Section prior to 8:00 p.m. (New York City time) on a business day, (ii) the
business day after the date of transmission, if such notice or communication is
delivered via facsimile at the facsimile telephone number specified in this
Section later than 8:00 p.m. (New York City time) on any date and earlier than
11:59 p.m. (New York City time) on such date, (iii) the business day following
the date of mailing, if sent by nationally recognized overnight courier service,
or (iv) if sent other than by the methods set forth in (i)-(iii) of this
section, upon actual receipt by the party to whom such notice is required to be
given. The addresses for such communications shall be: (i) if to the Company, to
157 Technology Drive, Irvine, CA 92618, Attention: Chief Financial Officer, or
to Facsimile No. (949) 788-6706, or (ii) if to the Holder, to the Holder at the
address or facsimile number appearing on the Warrant Register or such other
address or facsimile number as the Holder may provide to the Company in
accordance with this Section.

                  14. Warrant Agent. The Company shall serve as warrant agent
under this Warrant. Upon thirty (30) days' notice to the Holder, the Company may
appoint a new warrant agent. Any corporation into which the Company or any new
warrant agent may be merged or any corporation resulting from any consolidation
to which the Company or any new warrant agent shall be a party or any
corporation to which the Company or any new warrant agent transfers
substantially all of its corporate trust or shareholders services business shall
be a successor warrant agent under this Warrant without any further act. Any
such successor warrant agent shall promptly cause notice of its succession as
warrant agent to be mailed (by first class mail, postage prepaid) to the Holder
at the Holder's last address as shown on the Warrant Register.


                                      -9-                      Class A Warrant
<PAGE>   10
                  15. Miscellaneous.

                        (a) This Warrant shall be binding on and inure to the
benefit of the parties hereto and their respective successors and assigns. This
Warrant may be amended only in writing signed by the Company and the Holder and
their successors and assigns.

                        (b) Subject to Section 15(a), above, nothing in this
Warrant shall be construed to give to any person or corporation other than the
Company and the Holder any legal or equitable right, remedy or cause under this
Warrant. This Warrant shall inure to the sole and exclusive benefit of the
Company and the Holder.

                        (c) The corporate laws of the State of Delaware shall
govern all issues concerning the relative rights of the Company and its
stockholders. All other questions concerning the construction, validity,
enforcement and interpretation of this Warrant shall be governed by and
construed and enforced in accordance with the internal laws of the State of New
York, without regard to the principles of conflicts of law thereof. The Company
and the Holder hereby irrevocably submit to the exclusive jurisdiction of the
state and federal courts sitting in the City of New York, borough of Manhattan,
for the adjudication of any dispute hereunder or in connection herewith or with
any transaction contemplated hereby or discussed herein, and hereby irrevocably
waives, and agrees not to assert in any suit, action or proceeding, any claim
that it is not personally subject to the jurisdiction of any such court, or that
such suit, action or proceeding is improper. Each of the Company and the Holder
hereby irrevocably waives personal service of process and consents to process
being served in any such suit, action or proceeding by receiving a copy thereof
sent to the Company at the address in effect for notices to it under this
instrument and agrees that such service shall constitute good and sufficient
service of process and notice thereof. Nothing contained herein shall be deemed
to limit in any way any right to serve process in any manner permitted by law.

                        (d) The headings herein are for convenience only, do not
constitute a part of this Warrant and shall not be deemed to limit or affect any
of the provisions hereof.

                        (e) In case any one or more of the provisions of this
Warrant shall be invalid or unenforceable in any respect, the validity and
enforceability of the remaining terms and provisions of this Warrant shall not
in any way be affected or impaired thereby and the parties will attempt in good
faith to agree upon a valid and enforceable provision which shall be a
commercially reasonable substitute therefor, and upon so agreeing, shall
incorporate such substitute provision in this Warrant.



                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK,
                             SIGNATURE PAGE FOLLOWS]


                                      -10-                     Class A Warrant
<PAGE>   11
                  IN WITNESS WHEREOF, the Company has caused this Warrant to be
duly executed by its authorized officer as of the date first indicated above.


                                    NEOTHERAPEUTICS, INC.

                                    By:         /s/Samuel Gulko
                                        ------------------------------------
                                    Name:       Samuel Gulko
                                    Title:      Chief Financial Officer
<PAGE>   12
                          FORM OF ELECTION TO PURCHASE

(To be executed by the Holder to exercise the right to purchase shares of Common
Stock under the foregoing Warrant)

To NeoTherapeutics, Inc.:

         In accordance with the Warrant enclosed with this Form of Election to
Purchase, the undersigned hereby irrevocably elects to purchase
shares of common stock, $.001 par value per share, of NeoTherapeutics, Inc. (the
"Common Stock") and , if such Holder is not utilizing the cashless exercise
provisions set forth in this Warrant, encloses herewith $         in cash,
certified or official bank check or checks, which sum represents the aggregate
Exercise Price (as defined in the Warrant) for the number of shares of Common
Stock to which this Form of Election to Purchase relates, together with any
applicable taxes payable by the undersigned pursuant to the Warrant.

         The undersigned requests that certificates for the shares of Common
Stock issuable upon this exercise be issued in the name of

                                           PLEASE INSERT SOCIAL SECURITY OR
                                           TAX IDENTIFICATION NUMBER

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

--------------------------------------------------------------------------------
                         (Please print name and address)


         If the number of shares of Common Stock issuable upon this exercise
shall not be all of the shares of Common Stock which the undersigned is entitled
to purchase in accordance with the enclosed Warrant, the undersigned requests
that a New Warrant (as defined in the Warrant) evidencing the right to purchase
the shares of Common Stock not issuable pursuant to the exercise evidenced
hereby be issued in the name of and delivered to:


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                         (Please print name and address)

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Dated:            ,                       Name of Holder:
      ------------------

                                          (Print)
                                                -------------------------------
                                           (By:)
                                                -------------------------------
                                           (Name:)
                                           (Title:)
                                           (Signature must conform in all
                                           respects to name of holder as
                                           specified on the face of the Warrant)

                                                                Class A Warrant
<PAGE>   13
                               FORM OF ASSIGNMENT

           [To be completed and signed only upon transfer of Warrant]

         FOR VALUE RECEIVED, the undersigned hereby sells, assigns and transfers
unto                  the right represented by the within Warrant to purchase
             shares of Common Stock of NeoTherapeutics, Inc. to which the within
Warrant relates and appoints                  attorney to transfer said right on
the books of NeoTherapeutics, Inc. with full power of substitution in the
premises.

Dated:

---------------, ----


                                      ---------------------------------------
                                      (Signature must conform in all respects to
                                      name of holder as specified on the face
                                      of the Warrant)


                                      ---------------------------------------
                                      Address of Transferee

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

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



In the presence of:


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                                                                Class A Warrant