<PAGE>   1


                                                                     EXHIBIT 4.6



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 B WARRANT

Warrant No. B-1                                            Dated: April 6, 2000


         NeoTherapeutics, Inc., a Delaware corporation (the "Company"), hereby
certifies that, for value received, Montrose Investments Ltd., or its registered
assigns (the "Holder"), is entitled, subject to the terms and conditions set
forth herein, to purchase from the Company up to a total of 2,000,000 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").
Certain terms used herein are defined in Exhibit A attached hereto:

                  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

                                                                 Class B Warrant
<PAGE>   2
statement or to the Company, the Company may require the transferor thereof to
provide to the 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. 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 its address for notice set forth in
Section 11. 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.

                        (b) This Warrant is exchangeable, upon the surrender
hereof by the Holder to the Company at its address for notice set forth in
Section 11 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 Redemption of Warrants.

                        (a) Company Call Option.

                   (i) Subject to the terms and conditions set forth herein,
prior to 2:30 p.m. (New York City time) on any Trading Day (as defined in
Exhibit A) during the period between the Effective Date (as defined in Exhibit
A) and the Trading Day immediately following the second year anniversary of the
Effective Date (the "Expiration Date"), the Company may deliver written notices
to the Holder (each, a "Call Notice" and the Trading Day a Call Notice is
delivered, a "Delivery Date"), of the Company's election to call, for a price of
$.0005 per Warrant Share, a portion of this Warrant as further described herein;
provided that such price shall be adjusted to reflect any adjustment in the
number of Warrant Shares issuable hereunder, so that the maximum aggregate
redemption price shall continue to be $1,000. Notwithstanding anything to the
contrary set forth in this Warrant: (1) a Call Notice may not apply to a number
of Warrant Shares in excess of 15% of the average trading volume of the Common
Stock for the two Trading Days immediately preceding the Delivery Date, (2) no
Call Notice may be delivered until the expiration of the Call Expiration Time
(as defined below) for the immediately preceding Call Notice, (3) a Call Notice
may indicate that if the Exercise Price (as defined herein) applicable to an
exercise of this Warrant pursuant to such Call Notice shall be lower than a
dollar amount designated by the Company in such Call Notice (such dollar amount,
a "Floor Price"), then, at the option of the

                                      -2-                       Class B Warrant
<PAGE>   3
Holder: (A) the Exercise Price shall, exclusively for the purpose of such Call
Notice, equal the Floor Price or (B) such Call Notice shall be null and void ab
initio, provided, that a Floor Price must be less than 90% of the Per Share
Market Value on the Trading Day preceding the Delivery Date and (4) no Call
Notice may be delivered unless the conditions set forth in Section 3(a)(iii)
have been either satisfied by the Company or waived by the Holder.

                  (ii) The portion of this Warrant subject to a Call Notice will
be canceled and of no further effect from and after 5:30 p.m. (New York City
time) on the Trading Day following Delivery Date (the "Call Expiration Time"),
unless between the Delivery Date and the Call Expiration Time the Holder
notifies the Company in writing that it will exercise this Warrant to acquire
the number of Warrant Shares subject to such Call Notice at the Exercise Price
per share set forth in Section 3(c). Such exercise shall be in accordance with
Section 3(b)(ii).

                  (iii) The right of the Company to deliver a Call Notice is
subject to the satisfaction or waiver by the Holder, at or before the applicable
Call Expiration Time, of each of the following conditions (and, if after
delivery thereof and on the applicable Exercise Date, any of the following
conditions shall cease to be met, such Call Notice, at the option of the Holder,
shall be null and void ab initio):

                           (a)      The representations and warranties of the
                                    Company contained in the Purchase Agreement
                                    shall be true and correct as of each of the
                                    applicable Delivery Date and Call Expiration
                                    Time, as though first made on and as of such
                                    Delivery Date and Call Expiration Time
                                    (other than representations and warranties
                                    which relate to a specific date (which shall
                                    not include representations and warranties
                                    relating to the "date hereof") which
                                    representations and warranties shall be true
                                    as of such specific date);

                           (b)      The Company shall have performed, satisfied
                                    and complied in all material respects with
                                    all covenants (including timely delivery of
                                    Warrant Shares in accordance with Section
                                    3(a)), agreements and conditions of the
                                    Transaction Documents (as defined in the
                                    Purchase Agreement) to be performed,
                                    satisfied or complied with by the Company at
                                    or prior to the applicable Delivery Date and
                                    Call Expiration Time;

                           (c)      The Underlying Shares Registration Statement
                                    (as defined in Exhibit A) shall be effective
                                    on the Delivery Date, not subject to any
                                    stop order or suspension;

                           (d)      No statute, rule, regulation, executive
                                    order, decree, ruling or injunction shall
                                    have been enacted, entered, promulgated or


                                      -3-                        Class B Warrant
<PAGE>   4
                                    endorsed by any court or governmental
                                    authority of competent jurisdiction and in
                                    force on the Delivery Date which prohibits
                                    the consummation of any of the transactions
                                    contemplated by the Transaction Documents;

                           (e)      Since the Closing Date (as defined in the
                                    Purchase Agreement), no event or series of
                                    events which reasonably would be expected to
                                    have or result in a Material Adverse Effect
                                    (as defined in the Purchase Agreement) and
                                    no Change of Control Transaction (as defined
                                    in Exhibit A) shall have occurred;

                           (f)      Since the Closing Date, trading in the
                                    Common Stock shall not have been suspended
                                    by the Securities and Exchange Commission
                                    for a period in excess of five consecutive
                                    Trading Days or ten Trading Days in the
                                    aggregate (which need not be consecutive
                                    Trading Days), except for any suspensions of
                                    trading of not more than one Trading Day
                                    solely to permit dissemination of material
                                    information regarding the Company;

                           (g)      On the Delivery Date, the Common Stock shall
                                    be trading on the Nasdaq Small Cap Market
                                    ("NASDAQ"), or on the Nasdaq National
                                    Market, New York Stock Exchange or American
                                    Stock Exchange (each, a "Subsequent
                                    Market");

                           (h)      No approval of the shareholders of the
                                    Company shall be required under the rules of
                                    the Nasdaq Stock Market or any other
                                    Subsequent Market on which the Common Stock
                                    is traded or listed for trading in order to
                                    issue the number of Warrant Shares indicated
                                    in the applicable Call Notice at the
                                    Exercise Price;

                           (i)      For the five Trading Days immediately
                                    preceding the applicable Delivery Date, the
                                    average daily trading volume of the Common
                                    Stock on the NASDAQ as reported by Bloomberg
                                    L.P., shall be at least 20,000 shares and
                                    the average of the Per Share Market Values
                                    (as defined in Exhibit A) for such five
                                    Trading Days shall be at least $5.00; and

                           (j)      The Call Notice at issue would not result in
                                    a violation of Section 3(e).

                           (b)      Exercise By Holder.


                                      -4-                        Class B Warrant
<PAGE>   5
                  (i) At any time on and after the Effective Date (and in the
case of an election to purchase which is not in response to a Call Notice, if
earlier, the 90th day after the date of this Warrant) and prior to 5:30 p.m.
(New York City time) on the Expiration Date, the Holder shall be entitled to
purchase all or a portion of the Warrant Shares which have not been previously
issued and with respect to which this Warrant has not been previously redeemed
or canceled in accordance with the terms hereof.

                  (ii) The Holder may purchase Warrant Shares hereunder by
delivering to the Company, at its address for notice set forth in Section 11, a
completed Form of Election to Purchase in the form attached hereto, together
with the payment of the Exercise Price multiplied by the number of Warrant
Shares indicated therein. An "Exercise Date" means the date of the delivery
(which may be made via facsimile) of the Form of Election to Purchase and
applicable Exercise Price.

                  (iii) After the end of the week in which the Company receives
one or more Forms of Election to Purchase and the applicable Exercise Price, the
Company shall promptly (but in no event later than three Trading Days following
the end of such week) 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 as required by the Purchase Agreement,
provided, that, if in any week the Company shall receive one or more Forms of
Election to Purchase for the purchase of in excess of 30,000 Warrant Shares, the
Company shall issue such certificate no later than the third Trading Day
following the date of the delivery of the applicable Form of Election to
Purchase which resulted in the purchase of in excess of 30,000 Warrant Shares.

                           (A)      If the Company fails to deliver to the
                                    Holder the certificate or certificates
                                    pursuant to this Section within the time
                                    specified in above, the Holder shall be
                                    entitled by written notice to the Company at
                                    any time on or before its receipt of such
                                    certificate or certificates thereafter, to
                                    rescind such exercise.

                           (B)      In addition to the rights set forth in (A)
                                    above, if the Company fails to deliver to
                                    the Holder such certificate or certificates
                                    pursuant to this Section within the time
                                    specified in above, and if after such time
                                    the Holder purchases (in an open market
                                    transaction or otherwise) Common Stock to
                                    deliver in satisfaction of a sale by such
                                    Holder of the Warrant Shares which the
                                    Holder anticipated receiving upon such
                                    exercise (a "Buy-In"), then the Company
                                    shall (1) pay in cash to the Holder the
                                    amount by which (x) the Holder's total
                                    purchase price (including brokerage
                                    commissions, if any) for the Common Stock so
                                    purchased exceeds (y) the product of (i) the
                                    aggregate number of Warrant Shares that such
                                    Holder anticipated receiving from the
                                    exercise at issue multiplied by (ii) the Per
                                    Share Market

                                      -5-                        Class B Warrant
<PAGE>   6
                                    Value on the Exercise Date and (2) at the
                                    option of the Holder, either rescind the
                                    exercise at issue or deliver to the Holder
                                    the number of Warrant Shares that would have
                                    been issued had the Company timely complied
                                    with its delivery requirements under this
                                    Section. For example, if the Holder
                                    purchases Common Stock having a total
                                    purchase price of $11,000 to cover a Buy-In
                                    with respect to an attempted exercise with
                                    respect to which the Per Share Market Value
                                    on the Exercise Date was a total of $10,000,
                                    the Company shall be required to pay the
                                    Holder $1,000. The Holder shall provide the
                                    Company written notice indicating the
                                    amounts payable to the Holder in respect of
                                    the Buy-In.

                           (c) Exercise Price.

                  The "Exercise Price" applicable to an exercise following a
Call Notice under Section 3(a) shall equal the lower of (i) $33.75(subject to
equitable adjustment for stock splits, reverse splits, combinations and other
similar events) and (ii) 97% of the Per Share Market Value on the Trading Day
immediately following the applicable Delivery Date. The Exercise Price
applicable to an exercise pursuant to Section 3(b)(i) that is not in response to
a Call Notice shall equal $33.75 (subject to equitable adjustment for stock
splits, reverse splits, combinations and other similar events). The Exercise
Price shall be subject to adjustment in accordance with Section 8.

                           (d) Redemption at Option of Company.

                  On and after the 6th month anniversary of the Effective Date,
the Company may redeem all or any portion of this Warrant which has not been
previously exercised and for which no Form of Election to Purchase shall been
received by delivery to the Holder of a notice of such redemption, together with
the redemption price equal to $.05 per Warrant Share to be redeemed, payable by
the third Trading Day following the delivery of such notice by the Company;
provided that the redemption price shall be adjusted to reflect any adjustment
in the number of Warrant Shares issuable hereunder, so that the maximum
aggregate redemption price shall continue to be $100,000. Interest shall accrue
on the unpaid portion of such redemption price at the rate of 10% per annum
beginning on such third Trading Day.

                           (e) Certain Exercise Restrictions.

                  (i) The Company may not issue Warrant Shares upon exercise of
this Warrant, in response to a Call Notice in excess of the product of (x) 50%
and (y) 19.9999% of the shares of Common Stock outstanding on the Closing Date,
less an amount equal to the aggregate number of shares of Common Stock issued
(A) upon conversion of the Company's 5% Subordinated Convertible Debentures
originally issued to the Holder, and (B) upon any exercise of this Warrant, in
response to a Call Notice unless the Company shall have obtained the approval of
the

                                      -6-                        Class B Warrant
<PAGE>   7
stockholders of the Company as required under the rules of the Nasdaq Stock
Market or such other exchange or trading facility on which the Common Stock is
traded or listed for trading for such issuance. In the event of any subdivision,
transfer or exchange of this Warrant, the limitation contained in this Section
3(e)(i) shall be appropriately adjusted to ensure that in no event shall the
Company issue, upon any exercise of this Warrant in response to a Call Notice,
in excess of the product of (x) 50% and (y) 19.999% of the shares of Common
Stock outstanding on the Closing Date, less an amount equal to the aggregate
number of shares of Common Stock issued (A) upon conversion of the Company's 5%
Subordinated Convertible Debentures originally issued to the Holder, and (B)
upon any exercise of this Warrant, in response to a Call Notice unless the
Company shall have obtained the approval of the stockholders of the Company as
required under the rules of the Nasdaq Stock Market or such other exchange or
trading facility on which the Common Stock is traded or listed for trading for
such issuance.

                  (ii) 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 (the "Exchange Act") and the rules
promulgated thereunder) in excess of 9.999% of the then issued and outstanding
shares of Common Stock, including shares 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 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.

                  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 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,

                                      -7-                        Class B Warrant
<PAGE>   8
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. 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.

                  6. 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.

                  7. 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 8). 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.

                  8. Certain Adjustments.

                        (a) 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

                                      -8-                        Class B Warrant
<PAGE>   9
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.

                        (b) 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.

                        (c) All calculations under this Section 8 shall be made
to the nearest cent or the nearest 1/100th of a share, as the case may be.

                        (d) 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

                                      -9-                        Class B Warrant
<PAGE>   10
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, 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.

                  9. Payment of Exercise Price. The Holder shall pay the
Exercise Price for Warrant Shares purchased hereunder by delivery of immediately
available funds.

                  10. 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.

                  11. 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.

                  12. 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

                                      -10-                       Class B Warrant
<PAGE>   11
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.

                  13. 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 13(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]



                                      -11-                       Class B Warrant
<PAGE>   12
                  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>   13
                          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:


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

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

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

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 B Warrant
<PAGE>   14
                               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:


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


                                                                 Class B Warrant
<PAGE>   15
                                                                       EXHIBIT A


         (i) "Business Day" means any day except Saturday, Sunday and any day
which shall be a federal legal holiday or a day on which banking institutions in
the State of New York and the State of California are authorized or required by
law or other governmental action to close.

         (ii) "Change of Control Transaction" means the occurrence of any of (i)
an acquisition after the date hereof by an individual or legal entity or "group"
(as described in Rule 13d-5(b)(1) promulgated under the Exchange Act) of
effective control (whether through legal or beneficial ownership of capital
stock of the Company, by contract or otherwise) of in excess of 33% of the
voting securities of the Company, (ii) a replacement at one time or over time of
more than one-half of the members of the Company's board of directors which is
not approved by a majority of those individuals who are members of the board of
directors on the date hereof (or by those individuals who are serving as members
of the board of directors on any date whose nomination to the board of directors
was approved by a majority of the members of the board of directors who are
members on the date hereof), (iii) the merger or consolidation of the Company
with or into another entity that is not wholly-owned by the Company upon the
completion of which the stockholders of the Company immediately before such
merger or consolidation own or control less than 2/3 of the voting securities of
the surviving entity or sale of 50% or more of the assets of the Company in one
or a series of related transactions, or (i) the execution by the Company of an
agreement to which the Company is a party or by which it is bound, providing for
any of the events set forth above in (i), (ii) or (iii).

         (iii) "Commission" means the Securities and Exchange Commission.

         (iv) "Effective Date" means the date the Underlying Shares Registration
Statement is declared effective by the Commission.

         (v) "Per Share Market Value" means on any particular date (a) the
closing bid price per share of Common Stock on such date on the NASDAQ or on
such Subsequent Market on which the shares of Common Stock are then listed or
quoted, or if there is no such price on such date, then the closing bid price on
the NASDAQ or on such Subsequent Market on the date nearest preceding such date,
or (b) if the shares of Common Stock are not then listed or quoted on the NASDAQ
or a Subsequent Market, the closing bid price for a share of Common Stock in the
over-the-counter market, as reported by the National Quotation Bureau
Incorporated or similar organization or agency succeeding to its functions of
reporting prices) at the close of business on such date, or (c) if the shares of
Common Stock are not then reported by the National Quotation Bureau Incorporated
(or similar organization or agency succeeding to its functions of reporting
prices), then the average of the "Pink Sheet" quotes for the relevant conversion
period, as determined in good faith by the Holder, or (d) if the shares of
Common Stock are not then publicly traded the fair market value of a share of
Common Stock as determined by an Appraiser selected in good faith by the Holders
of a majority in interest of the Warrants then outstanding.

         (vi) "Purchase Agreement" means the Convertible Debenture Purchase
Agreement dated as of the date hereof, to which the Company and the original
Holder hereof are parties.


                                                                 Class B Warrant
<PAGE>   16
         (vii) "Trading Day" means (a) a day on which the shares of Common Stock
are traded on the NASDAQ or on such Subsequent Market on which the shares of
Common Stock are then listed or quoted, or (b) if the shares of Common Stock are
not listed on the NASDAQ or a Subsequent Market, a day on which the shares of
Common Stock are traded in the over-the-counter market, as reported by the OTC
Bulletin Board, or (c) if the shares of Common Stock are not quoted on the OTC
Bulletin Board, a day on which the shares of Common Stock are quoted in the
over-the-counter market as reported by the National Quotation Bureau
Incorporated (or any similar organization or agency succeeding its functions of
reporting prices); provided, however, that in the event that the shares of
Common Stock are not listed or quoted as set forth in (a), (b) and (c) hereof,
then Trading Day shall mean a Business Day.

         (viii) "Underlying Shares Registration Statement" shall have the
meaning set forth in the Purchase Agreement.


                                                                 Class B Warrant