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                                                                   EXHIBIT 10.57
                                CREDIT AGREEMENT


         THIS AGREEMENT is entered into as of  March 24, 1997, by and between
NEXSTAR PHARMACEUTICALS, INC., ("NeXstar") a Delaware corporation, and NEXSTAR
PHARMACEUTICALS ITALIA, S.r.1., an Italian corporation, and NEXSTAR
PHARMACEUTIQUE SARL, a French corporation, ("Borrower"), and WELLS FARGO BANK
(COLORADO), NATIONAL ASSOCIATION ("Bank").  Unless otherwise designated, each
reference herein to "Borrower" shall mean each and every party collectively and
individually, defined above as a Borrower.


                                    RECITALS


         Borrower has requested from Bank the credit accommodation described
below, and Bank has agreed to provide said credit accommodation to Borrower on
the terms and conditions contained herein.

         NOW, THEREFORE, for valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Bank and Borrower hereby agree as
follows:


                                   ARTICLE I
                                   THE CREDIT


         SECTION 1.1.     LINE OF CREDIT.

         (a)     Line of Credit.  Subject to the terms and conditions of this
Agreement, Bank hereby agrees to make advances to Borrower from time to time up
to and including March 24, 1998, not to exceed at any time the aggregate
principal amount of Fifteen Million Dollars ($15,000,000.00) ("Line of
Credit"), the proceeds of which shall be used for working capital requirements.
Borrower's obligation to repay advances under the Line of Credit shall be
evidenced by a promissory note substantially in the form of Exhibit A attached
hereto ("Line of Credit Note"), all terms of which are incorporated herein by
this reference.

         Notwithstanding any provision to the contrary in this Agreement or the
Line of Credit Note, the joint and several liability of any Foreign Borrower
(as hereinafter defined), for principal under the Line of Credit Note shall be
limited to the greater of the aggregate outstanding advances made to or for the
benefit of such Foreign Borrower or the amount of the collateral provided to
Bank by such Foreign Borrower pursuant to this Agreement and the Loan Documents
(as hereinafter defined).  NeXstar shall be jointly and severally liable for
all indebtedness and obligations under the Line of Credit Note and the Loan
Documents.

         (b)     Limitation on Borrowings.  Outstanding borrowings under the
Line of Credit, to a maximum of the principal amount set forth above, shall not
at any time exceed an aggregate of one hundred percent (100%) of Borrower's
eligible accounts receivable.

         As an additional limitation, at no time may outstanding borrowings to
or for the benefit of an individual Borrower other than NeXstar (each, a
"Foreign Borrower"), exceed the country limits of such Foreign Borrower's
location as set forth in an Approved Insurance Policy (as hereinafter defined),
or may outstanding borrowings to or for the benefit of NeXstar exceed the
aggregate of the country limits, other than the country limits




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applicable to the Foreign Borrowers and the Country of Portugal, as set forth
in an Approved Insurance Policy, with the understanding that no account debtor
of a Foreign Borrower is located outside of the country in which such Foreign
Borrower is located and that no account debtor of NeXstar is located in a
country in which any Foreign Borrower is located.

         All the foregoing shall be determined by Bank upon receipt and review
of all collateral reports required hereunder and such other documents and
collateral information as Bank may from time to time require.  Borrower
acknowledges that said borrowing base was established by Bank with the
understanding that, among other items, the aggregate of all returns (except
replacement of expired  product which does not affect any account debtor's
obligation to pay an account), rebates, discounts, credits and allowances for
the immediately preceding three (3) months at all times shall be less than five
percent (5%) of Borrower's gross sales for said period excluding replacement of
expired product which does not affect any account debtor's obligation to pay an
account.  If such dilution of Borrower's accounts for the immediately preceding
three (3) months at any time exceeds five percent (5%)of Borrower's gross sales
for said period, or if there at any time exists any other matters, events,
conditions or contingencies which Bank reasonably believes may affect payment
of any portion of Borrower's accounts, Bank, in its sole discretion, may reduce
the foregoing advance rate against eligible accounts receivable to a percentage
appropriate to reflect such additional dilution and/or establish additional
reserves against Borrower's eligible accounts receivable.

         As used herein, "eligible accounts receivable" shall consist solely of
trade accounts with respect to debtors located outside of the United States
(such location to be determined by the location of such account debtor's chief
executive office) other than an obligation from an account debtor located in
Spain, Australia or Japan, created in the ordinary course of Borrower's
business, which accounts are insured under a policy of foreign credit insurance
(with Bank named as loss payee), in form, substance and issued by a party
acceptable to Bank in its sole and absolute discretion ("Approved Insurance
Policy"), upon which Borrower's right to receive payment is absolute and not
contingent upon the fulfillment of any condition whatsoever, and in which Bank
has a security interest, with such a perfected priority lien position as Bank
may require, and shall not include:

                 (i)      any account, which is past due more than (a) two
         hundred seventy  (270) days with respect to accounts from account
         debtors located in Greece, Saudi Arabia or Kuwait, (b) two hundred ten
         (210) days with respect to acounts from account debtors located in
         Italy and (c)  more than ninety (90) days past due with respect to all
         other such accounts, and in each case, with respect to which no
         extension for payment has been granted;

                 (ii)     that portion of any account for which there exists
         any right of setoff, defense or discount (except regular discounts
         allowed in the ordinary course of business to promote prompt payment)
         or for which any defense or counterclaim has been asserted;

                 (iii)    any account which represents an obligation of an
         account debtor located in a foreign country, except to the extent any
         such account, in Bank's determination, is (a) supported by a letter of
         credit in form substance and issued by a party acceptable to Bank in
         its sole and absolute discretion or, (b) insured under an Approved
         Insurance Policy, with the understanding that such account shall not
         be deemed insured to the extent of any deductible or risk retention;

                 (iv)     any account which arises from the sale or lease to or
         performance of services for, or represents an obligation of any
         Borrower or, an employee, affiliate, partner, member, parent or
         subsidiary of any Borrower;





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                 (v)      that portion of any account which represents interim
         or progress billings or retention rights on the part of the account
         debtor;

                 (vi)     that portion of any account from an account debtor
         which represents the amount by which Borrower's total accounts from
         said account debtor exceeds twenty-five percent (25%) of Borrower's
         total accounts;

                 (vii)    any account which is not payable in U.S. Dollars
         except to the extent such account is payable in U.S. Dollars under an
         Approved Insurance Policy;

                 (viii)   any portion of any account which is subject to any
         deduction or withholding on account of any tax imposed, levied,
         collected, withheld or assessed by or within the United States of
         America or any political subdivision in or of the United States of
         America, or any other jurisdiction from or to which a payment is made
         by or on behalf of Borrower or an account party or by any federation
         or organization of which the United States of America, or any such
         jurisdiction is a member at the time of payment;

                 (ix)     any account deemed ineligible by Bank when Bank, in
         its sole discretion, deems the creditworthiness or financial condition
         of the account debtor, or the industry unsatisfactory.

         (c)     Borrowing and Repayment.  Borrower may from time to time
during the term of the Line of Credit borrow, partially or wholly repay its
outstanding borrowings, and reborrow, subject to all of the limitations, terms
and conditions contained herein or in the Line of Credit Note; provided
however, that the total outstanding borrowings under the Line of Credit shall
not at any time exceed the maximum principal amount available thereunder, as
set forth above.

         SECTION 1.2.     INTEREST/FEES.

         (a)     Interest.  The outstanding principal balance of the Line of
Credit shall bear interest at the rate  set forth in the Line of Credit Note.

         (b)     Computation and Payment.  Interest shall be computed on the
basis of a 360-day year, actual days elapsed.  Interest shall be payable at the
times and place set forth in the Line of Credit Note.

         (c)     Commitment Fee.  Borrower shall pay to Bank a non-refundable
commitment fee for the Line of Credit equal to Thirty Seven Thousand Five
Hundred Dollars ($37,500.00), which fee shall be due and payable in full upon
execution of this agreement.

         (d)     Unused Commitment Fee.  Borrower shall pay to Bank a fee equal
to one eighth percent (1/8%) per annum (computed on the basis of a 360-day
year, actual days elapsed) on the average daily unused amount of the Line of
Credit, which fee shall be calculated on a monthly basis by Bank and shall be
due and payable by Borrower in arrears on the first business day of each month.

         SECTION 1.3.     COLLECTION OF PAYMENTS.  Borrower authorizes Bank to
make advances under the Line of Credit only into Borrower's demand deposit
account number 4439821356 with Bank, and to collect all interest and fees due
under the Line of Credit by charging said demand deposit account, or any other
demand deposit account maintained by Borrower with Bank, for the full amount
thereof.  Should there be





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insufficient funds in any such demand deposit account to pay all such sums when
due, the full amount of such deficiency shall be immediately due and payable by
Borrower.

         SECTION 1.4              CERTAIN TAXES.

         (a)     All payments made to or for the benefit of Bank pursuant to
any Loan Document will be made without setoff, counterclaim or deduction for
and free and clear of any Taxes, but excluding those Taxes imposed on income or
capital of Bank by the jurisdiction (or any political subdivision thereof)
under the laws of which Bank is organized or in which its principal place of
business or lending office is located.

         (b)     If any Borrower is required by any applicable law to withhold
any Taxes from any amounts payable to Bank hereunder or thereunder,
respectively, (i) the amounts so payable to Bank shall be increased to the
extent necessary to yield to Bank (after payment of all Taxes) the amounts
payable in the full amounts so to be paid, (ii) Borrower, as applicable, will
make such withholdings, and (iii) Borrower, as applicable, will pay the full
amount required to be withheld to the appropriate tax or other authority in
accordance with such applicable laws.  Whenever a Tax is paid by Borrower, as
promptly as possible thereafter, such Borrower will deliver to Bank an official
receipt showing payment of such Tax, together with such additional documentary
evidence as Bank from time to time may require.

         (c)     Borrower will pay any present or future Taxes that arise from
any payment made pursuant to any Loan Document or from the execution, delivery,
registration, performance or enforcement of any Loan Document.

         (d)     Borrower will indemnify Bank, and reimburse Bank promptly upon
demand, for the full amount of any Taxes (including, without limitation, any
Taxes imposed by any jurisdiction on amounts payable under this  Section) paid
by Bank and any liability (including, without limitation, penalties, interest
and expenses) arising therefrom or with respect thereto, regardless of whether
such Taxes were correctly and legally asserted.

         (e)     Without prejudice to the survival of any other agreement or
obligation of Borrower under this Agreement or any other Loan Document, the
agreements and obligations of Borrower contained in this Section shall survive
the payment in full of all amounts due under the Loan Documents.

"Tax" or "Taxes" shall mean any one or more taxes, levies, imposts, duties,
charges, fees, deductions, withholdings or restrictions or conditions of any
nature whatsoever now or hereafter imposed, levied, collected, withheld, or
assessed by any country or by any political subdivision or taxing authority
thereof or therein, including, without limitation, any present or future stamp
or documentary taxes or other excise or property taxes, charges or similar
levies.

         SECTION 1.5.     COLLATERAL.

         As security for all indebtedness of Borrower to Bank subject hereto,
Borrower hereby grants to Bank security interests of first priority in all
Borrower's trade accounts and other rights to payment now or hereafter owing by
an account debtor located outside of the United States, other than Spain,
Australia and Japan.





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         All of the foregoing shall be evidenced by and subject to the terms of
such security agreements, financing statements, deeds of trust and other
documents as Bank shall reasonably require, all in form and substance
satisfactory to Bank.  Borrower shall reimburse Bank immediately upon demand
for all costs and expenses incurred by Bank in connection with any of the
foregoing security, including without limitation, filing and recording fees and
costs of appraisals, audits and title insurance.


                                   ARTICLE II
                         REPRESENTATIONS AND WARRANTIES


         Borrower makes the following representations and warranties to Bank,
which representations and warranties shall survive the execution of this
Agreement and shall continue in full force and effect until the full and final
payment, and satisfaction and discharge, of all obligations of Borrower to Bank
subject to this Agreement.

         SECTION 2.1.     LEGAL STATUS.  Borrower is a corporation, duly
organized and existing and in good standing under the laws of the jurisdiction
of its incorporation, and is qualified or licensed to do business (and is in
good standing as a foreign corporation, if applicable) in all jurisdictions in
which such qualification or licensing is required or in which the failure to so
qualify or to be so licensed could have a material adverse effect on Borrower.

         SECTION 2.2.     AUTHORIZATION AND VALIDITY.  This Agreement, the Line
of Credit Note, and each other document, contract and instrument required
hereby or at any time hereafter delivered to Bank in connection herewith
(collectively, the "Loan Documents") have been duly authorized, and upon their
execution and delivery in accordance with the provisions hereof will constitute
legal, valid and binding agreements and obligations of Borrower or the party
which executes the same, enforceable in accordance with their respective terms.

         SECTION 2.3.     NO VIOLATION.  The execution, delivery and
performance by Borrower of each of the Loan Documents do not violate any
provision of any law or regulation, or contravene any provision of the Articles
of Incorporation or By-Laws or other organizational or governing documents of
Borrower, or result in any breach of or default under any contract, obligation,
indenture or other instrument to which Borrower is a party or by which Borrower
may be bound.

         SECTION 2.4.     LITIGATION.  There are no pending, or to the best of
Borrower's knowledge threatened, actions, claims, investigations, suits or
proceedings by or before any governmental authority, arbitrator, court or
administrative agency which could have a material adverse effect on the
financial condition or operation of Borrower other than those disclosed by
Borrower to Bank in writing prior to the date hereof.

         SECTION 2.5.     CORRECTNESS OF FINANCIAL STATEMENT.  The consolidated
financial statement of Borrower dated September 30, 1996, a true copy of which
has been delivered by Borrower to Bank prior to the date hereof, (a) is
complete and correct and presents fairly the financial condition of Borrower,
(b) discloses all liabilities of Borrower that are required to be reflected or
reserved against under generally accepted accounting principles, whether
liquidated or unliquidated, fixed or contingent, and (c) has been prepared in
accordance with generally accepted accounting principles consistently applied.
Since the date of such financial statement there has been no material adverse
change in the financial condition of Borrower, nor has Borrower mortgaged,
pledged, granted a security interest in or otherwise encumbered any of the
collateral required under this Agreement except in favor of Bank or as
otherwise permitted by Bank in writing.





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         SECTION 2.6.     INCOME TAX RETURNS.  Borrower has no knowledge of any
pending assessments or adjustments of its income tax payable with respect to
any year.

         SECTION 2.7.     NO SUBORDINATION.  There is no agreement, indenture,
contract or instrument to which Borrower is a party or by which Borrower may be
bound that requires the subordination in right of payment of any of Borrower's
obligations subject to this Agreement to any other obligation of Borrower.

         SECTION 2.8.     PERMITS, FRANCHISES.  Borrower possesses, and will
hereafter possess, all permits, consents, approvals, franchises and licenses
required and rights to all trademarks, trade names, patents, and fictitious
names, if any, necessary to enable it to conduct the business in which it is
now engaged in compliance with applicable law.

         SECTION 2.9.     ERISA.  Borrower is in compliance in all material
respects with all applicable provisions of the Employee Retirement Income
Security Act of 1974, as amended or recodified from time to time ("ERISA") or
similar laws or regulations which apply to Borrower; Borrower has not violated
any provision of any defined employee pension benefit plan (as defined in
ERISA) maintained or contributed to by Borrower (each, a "Plan"); no Reportable
Event as defined in ERISA has occurred and is continuing with respect to any
Plan initiated by Borrower; Borrower has met its minimum funding requirements
under ERISA with respect to each Plan; and each Plan will be able to fulfill
its benefit obligations as they come due in accordance with the Plan documents
and under generally accepted accounting principles.

         SECTION 2.10.    OTHER OBLIGATIONS.  Borrower is not in default on any
obligation for borrowed money, any purchase money obligation or any other
material lease, commitment, contract, instrument or obligation.  All premiums
under any Approved Insurance Policy have been fully paid and Bank is entitled
to the benefits as a loss payee under any such Approved Insurance Policy.

         SECTION 2.11.    ENVIRONMENTAL MATTERS.  Except as disclosed by
Borrower to Bank in writing prior to the date hereof, Borrower is in compliance
in all material respects with all applicable federal, state or governmental
environmental, hazardous waste, health and safety statutes, and any rules or
regulations adopted pursuant thereto, which govern or affect any of Borrower's
operations and/or properties, including without limitation, the Comprehensive
Environmental Response, Compensation and Liability Act of 1980, the Superfund
Amendments and Reauthorization Act of 1986, the Federal Resource Conservation
and Recovery Act of 1976, and the Federal Toxic Substances Control Act, as any
of the same may be amended, modified or supplemented from time to time.  None
of the operations of Borrower is the subject of any federal, state or
governmental investigation evaluating whether any remedial action involving a
material expenditure is needed to respond to a release of any toxic or
hazardous waste or substance into the environment.  Borrower has no material
contingent liability in connection with any release of any toxic or hazardous
waste or substance into the environment.

         SECTION 2.12     VALIDITY OF ACCOUNTS.  Each eligible account, upon
its creation, is a genuine obligation enforceable against the account debtor in
accordance with its terms, and represents an undisputed bona fide indebtedness
owing to Borrower, without defense, set off or counterclaim, free and clear of
all liens or claims other than Bank's, and no payment has been received with
respect to such eligible account.

         SECTION 2.13     SECURITY INTERESTS.  The Loan Documents create legal,
valid and enforceable security interests in and liens on all of the collateral
required under this Agreement and when all proper filings and actions required
to perfect such security 





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interests and to provide a continuing perfected security interest have been
made, the Loan Documents and such filings and actions will create a perfected
and continuing first priority security interest in favor of Bank upon all such
collateral required with respect to NeXstar, and in such other collateral as
the Bank may request, and enforceable against the Borrower and all third
parties.


                                  ARTICLE III
                                   CONDITIONS


         SECTION 3.1.     CONDITIONS OF INITIAL EXTENSION OF CREDIT.  The
obligation of Bank to extend any credit contemplated by this Agreement is
subject to the fulfillment to Bank's satisfaction of all of the following
conditions:

         (a)     Approval of Bank Counsel.  All legal matters incidental to the
extension of credit by Bank shall be satisfactory to Bank's counsel.

         (b)     Documentation.  Bank shall have received, in form and
substance satisfactory to Bank, each of the following, duly executed:

                 (i)      This Agreement and the Line of Credit Note.

                 (ii)     Continuing Security Agreements with respect to the
                          collateral required under this Agreement, executed by
                          each Borrower.

                 (iii)    Financing Statements for the United States 
                          jurisdiction.

                 (iv)     Evidence of the existence of all insurance policies
                          required under this Agreement, and as applicable,
                          showing Bank as additional insured and loss payee.

                 (v)      Opinion of local counsel of Borrower in form and
                          substance satisfactory to Bank, regarding
                          authorization, validity, enforceability, collateral
                          perfection and such other matters as may be requested
                          by Bank.

                 (vi)     Corporate resolutions or other evidence of due
                          authorization with respect to each Borrower.

                 (vi)     Such other documents as Bank may require under any
                          other Section of this Agreement.

         (c)     Financial Condition.  There shall have been no material
adverse change, as determined by Bank, in the financial condition or business
of Borrower, nor any material decline, as determined by Bank, in the market
value of any collateral required hereunder or a substantial or material portion
of the assets of Borrower.

         (d)     Insurance.  Borrower shall have delivered to Bank evidence of
insurance coverage on all Approved Insurance Policies, in form, substance,
amounts, covering risks





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and issued by companies satisfactory to Bank, and with loss payable
endorsements in favor of Bank.

         SECTION 3.2.     CONDITIONS OF EACH EXTENSION OF CREDIT.  The
obligation of Bank to make each extension of credit requested by Borrower
hereunder shall be subject to the fulfillment to Bank's satisfaction of each of
the following conditions:

         (a)     Compliance.  The representations and warranties contained
herein and in each of the other Loan Documents shall be true on and as of the
date of the signing of this Agreement and on the date of each extension of
credit by Bank pursuant hereto, with the same effect as though such
representations and warranties had been made on and as of each such date, and
on each such date, no Event of Default as defined herein, and no condition,
event or act which with the giving of notice or the passage of time or both
would constitute such an Event of Default, shall have occurred and be
continuing or shall exist.

         (b)     Documentation.  Bank shall have received all additional
documents which may be required in connection with such extension of credit.

         (c)     Audit.  Within thirty (30) days from the date of this
Agreement Bank shall have received a satisfactory audit of the books and
records of NeXstar Pharmaceuticals Italia, S.r.1., which shall be conducted by
Bank's internal auditors.


                                   ARTICLE IV
                             AFFIRMATIVE COVENANTS


         Borrower covenants that so long as Bank remains committed to extend
credit to Borrower pursuant hereto, or any liabilities (whether direct or
contingent, liquidated or unliquidated) of Borrower to Bank under any of the
Loan Documents remain outstanding, and until payment in full of all obligations
of Borrower subject hereto, Borrower shall, unless Bank otherwise consents in
writing:

         SECTION 4.1.     PUNCTUAL PAYMENTS.  Punctually pay all principal,
interest, fees or other liabilities due under any of the Loan Documents at the
times and place and in the manner specified therein, and immediately upon
demand by Bank, the amount by which the outstanding principal balance of the
Line of Credit at any time exceeds any limitation on borrowings applicable
thereto.

         SECTION 4.2.     ACCOUNTING RECORDS.  Maintain adequate books and
records on a consolidated basis in accordance with generally accepted
accounting principles consistently applied, and permit any representative of
Bank, at any reasonable time, to inspect, audit and examine such books and
records, to make copies of the same, and to inspect the properties of Borrower.

         SECTION 4.3.     FINANCIAL AND OTHER STATEMENTS.  Provide to Bank all
of the following, in form and detail satisfactory to Bank:

         (a)     not later than 100 days after and as of the end of each fiscal
year, an audited consolidated financial statement of  NeXstar, prepared by a
certified public accountant or firm acceptable to Bank (Bank acknowledges Ernst
& Young to be an acceptable firm), to include balance sheet, income statement
and applicable footnotes;

         (b)     not later than 50 days after and as of the end of each fiscal
quarter, a consolidated financial statement of NeXstar, prepared by NeXstar, to
reasonably include balance sheet, income statement and applicable footnotes;





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         (c)     not later than 15 days after and as of the end of each month,
a compliance certificate with respect to the continued effectiveness of
Approved Insurance Policies, a summary of foreign exchange exposure and
corresponding hedging contracts, a schedule of outstanding advances by each
individual Borrower and applicable country limit, a borrowing base certificate,
an aged listing of accounts receivable (by country and account debtor) and
accounts payable, and a reconciliation of accounts, and immediately upon each
request from Bank, a list of the names and addresses of all Borrower's account
debtors;

         (d)     not later than five (5) days after filing, a copy of each Form
10-Q and 10-K report filed by NeXstar with the Securities and Exchange
Commission pursuant to Sections 13 or 15(d) of the Securities Exchange Act of
1934 and Rules issued thereunder;

         (e)     contemporaneously with each annual and quarterly consolidated
financial statement of Borrower required hereby, a certificate of the president
or chief financial officer of NeXstar that said financial statements are
accurate and that there exists no Event of Default nor any condition, act or
event which with the giving of notice or the passage of time or both would
constitute an Event of Default;

         (f)     notification to Bank, of all of the countries in which account
debtors are  required to withhold taxes or the Borrower is required to collect
taxes from such account debtors and the rates of such taxes.  If, after the
date of this Agreement, additional countries require such collection or
withholding taxes, then, within five (5) days of notice thereof, provide Bank
with the name of the country and the rate of such taxes; and

         (g)     from time to time such other information as Bank may reasonably
request.

         SECTION 4.4.     COMPLIANCE.  Preserve and maintain all licenses,
permits, governmental approvals, rights, privileges and franchises necessary
for the conduct of its business; and comply with the provisions of all
documents pursuant to which Borrower is organized and/or which govern
Borrower's continued existence and with the requirements of all laws, rules,
regulations and orders of any governmental authority applicable to Borrower
and/or its business.

         SECTION 4.5.     INSURANCE.  Maintain and keep in force insurance of
the types and in amounts customarily carried in lines of business similar to
that of Borrower, including but not limited to fire, extended coverage, public
and product liability, flood, property damage and workers' compensation, with
all such insurance carried with companies and in amounts satisfactory to Bank,
and deliver to Bank from time to time at Bank's request schedules setting forth
all insurance then in effect.

         Maintain at all times one or more Approved Insurance Policies and not
amend the same without Bank's consent, with an aggregate coverage amount of at
least Fifteen Million Dollars ($15,000,000.00) and comply at all times with all
requirements thereunder, including without limitation the payment in full of
all premiums.  Borrower shall promptly file claims arising under such Approved
Insurance Policies, , and concurrently therewith, deliver copies of such claims
to Bank.  Additionally, Borrower shall promptly deliver to Bank copies of all
reports and other information as may be required under such Approved Insurance
Policies or by such insurers thereunder, and all correspondence to or from
insurers under Approved Insurance Policies.

         Borrower will promptly notify Bank of, and promptly settle, all
Disputes with account parties, at Borrower's expense and costs, including
attorneys' fees and other expenses.  However, if any Dispute is not settled by
Borrower during the Waiting Period (as such term is defined in an Approved
Insurance Policy) or within such shorter period as Bank may determine, in its
sole discretion, Bank may settle, compromise or litigate such





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dispute in Bank's or Borrower's name, upon such terms as Bank in its sole
discretion deems advisable and for Borrower's account and risk.

         "Dispute", as used in this Section, shall mean any dispute, deduction,
claim, offset, defense or counterclaim of any kind relating to an account
party, regardless of whether the same (i) is in an amount greater than, equal
to or less than the account concerned, (ii) is bona fide or not, or (iii)
arises by reason of an act of God, civil strife, war, currency restrictions,
foreign political restrictions or regulations or any other circumstance beyond
the control of Borrower or the applicable account party.

         SECTION 4.6.     FACILITIES.  Keep all properties useful or necessary
to Borrower's business in good repair and condition, and from time to time make
necessary repairs, renewals and replacements thereto so that such properties
shall be fully and efficiently preserved and maintained.

         SECTION 4.7.     TAXES AND OTHER LIABILITIES.  Pay and discharge when
due any and all indebtedness, obligations, assessments and Taxes, both real or
personal, including without limitation federal and state income taxes and state
and local property taxes and assessments, and any tax imposed, levied, withheld
or assessed with respect to payments made by or on behalf of account debtors or
Borrower, except such (a) as Borrower may in good faith contest or as which a
bona fide dispute may arise, and (b) for which Borrower has made provision, to
Bank's satisfaction, for eventual payment thereof in the event Borrower is
obligated to make such payment.

         SECTION 4.8.     LITIGATION.  Promptly give notice in writing to Bank
of any litigation pending or threatened against Borrower with a claim in excess
of $500,000.00.

         SECTION 4.9.     FINANCIAL CONDITION.  Maintain, on a consolidated
basis,  NeXstar's financial condition as follows using generally accepted
accounting principles consistently applied and used consistently with prior
practices (except to the extent modified by the definitions herein):

         (a)     At all times:

                 (i)  a Quick Ratio not at any time less than 1.40 to 1.0, with
                 "Quick Ratio" defined as the aggregate of unrestricted cash,
                 unrestricted marketable securities and receivables convertible
                 into cash divided by total current liabilities.

                 (ii)  maintain within the United States, unrestricted liquid
                 assets not subject to any liens, ( with liquid assets defined
                 as cash, cash equivalents and/or publicly traded/quoted
                 marketable securities accceptable to Bank) with an aggregate
                 fair market value not at any time less than Twenty Million
                 Dollars ($20,000,000.00).

         SECTION 4.10.    NOTICE TO BANK.  Promptly (but in no event more than
five (5) days after the occurrence of each such event or matter) give written
notice to Bank in reasonable detail of:  (a) the occurrence of any Event of
Default, or any condition, event or act which with the giving of notice or the
passage of time or both would constitute an Event of Default; (b) any change in
the name or the organizational structure of Borrower; (c) the occurrence and
nature of any Reportable Event or Prohibited Transaction, each as defined in
ERISA, or any funding deficiency with respect to any Plan; or (d) any
termination or cancellation of any insurance policy which Borrower is required
to maintain, or any uninsured or partially uninsured loss through liability or
property damage, or through fire, theft or any other cause affecting Borrower's
property in excess of an aggregate of $1,000,000.00.





                                       10
<PAGE>   11
         SECTION 4.11.    PERFECTION OF SECURITY INTERESTS/ATTORNEY OPINIONS.
Execute and deliver such documents and take such actions as Bank deems
necessary to create, perfect and continue the security interests of Bank
required under this Agreement.  Additionally, upon request of Bank from time to
time as Bank and Bank's counsel determine as necessary, Borrower shall provide
an opinion of Borrower's local country counsel, in form and substance
satisfactory to Bank, addressed to Bank, pertaining to  validity and
enforceability of, and any other matter regarding, any of the Loan Documents
relevant to Borrower domiciled in such country, or the perfection of any
collateral required under this Agreement.  All of the foregoing shall be at
Borrower's expense.

         SECTION 4.12.    FOREIGN CURRENCY HEDGING.  Establish and maintain
foreign exchange hedging on outstanding accounts of Borrower as Bank may
require.


                                   ARTICLE V
                               NEGATIVE COVENANTS

         Borrower further covenants that so long as Bank remains committed to
extend credit to Borrower pursuant hereto, or any liabilities (whether direct
or contingent, liquidated or unliquidated) of Borrower to Bank under any of the
Loan Documents remain outstanding, and until payment in full of all obligations
of Borrower subject hereto, Borrower will not without Bank's prior written
consent:

         SECTION 5.1.     USE OF FUNDS.  Use any of the proceeds of any credit
extended hereunder except for the purposes stated in Article I hereof.

         SECTION 5.2.     MERGER, CONSOLIDATION, TRANSFER OF ASSETS.  Merge
into or consolidate with any other entity; make any substantial change in the
nature of Borrower's business as conducted as of the date hereof; acquire all
or substantially all of the assets of any other entity which, in the aggregate,
exceed $5,000,000.00; sell, assign, transfer, pledge, hypothecate or grant a
security interest in any of the capital stock of any Borrower other than
NeXstar, nor sell, lease, transfer or otherwise dispose of all or a substantial
or material portion of Borrower's assets except in the ordinary course of its
business.

         SECTION 5.3.     GUARANTIES.  Guarantee or become liable in any way as
surety, endorser (other than as endorser of negotiable instruments for deposit
or collection in the ordinary course of business), accommodation endorser or
otherwise for, nor pledge or hypothecate any portion of the collateral required
under this Agreement as security for, any liabilities or obligations of any
other person or entity, except any of the foregoing in favor of Bank or as
previously disclosed in writing to Bank.

         SECTION 5.4.     LOANS, ADVANCES, INVESTMENTS.  Make any loans or
advances to or investments in any person or entity, except any of the foregoing
existing as of, and disclosed to Bank prior to the date hereof, and

         (a)     Investments  which comply, at all times, with Borrower's
                 existing Investment Policy, attached herto as Exhibit A and
                 incorporated herein;

         (b)     Stock, obligations or securities received from customers in
                 connection with debts created in the ordinary course of
                 business owing to the Borrower;

         (c)     Continued ownership by NeXstar of the existing capital stock
                 the Foreign Borrowers and NeXstar Farmaceutica Portugal, LDA,
                 EuroNex





                                       11
<PAGE>   12
                 Pharmaceuticals Limited, NeXstar Pharmaceuticals Limited
                 (U.K.), NeXstar Pharmaceuticals GmbH, NeXstar Farmaceutica,
                 S.A., NeXstar Pharmaceuticals Int'l B.V., NeXstar
                 Pharmaceuticals B.V. and NeXstar Pharmaceuticals Limited
                 (Ireland), NeXstar Pharmaceuticals Pty Limited (Australia)
                 (collectively, the "Subsidiaries");

         (d)     Endorsement of negotiable instruments for deposit or
                 collection or similar transactions in the ordinary course of
                 business;

         (e)     Subsidiaries may make or permit to remain outstanding advances
                 from such Subsidiaries to NeXstar;

         (f)     Loans or advances to Subsidiaries, employees, or entities or
                 persons related to Borrower in an aggregate amount for all
                 such loans and advances not exceeding $4,000,000.00, at any
                 one time.

         (g)     Cash investments in the ordinary course of business to any
                 person or entity other than a Subsidiary, in an aggregate
                 amount for all such investments not exceeding $5,000,000.00,
                 at any one time.


         SECTION 5.5.     PLEDGE OF ASSETS.  Mortgage, pledge, grant or permit
to exist a security interest in, or lien upon, all or any portion of the
collateral required under this Agreement.


                                   ARTICLE VI
                               EVENTS OF DEFAULT


         SECTION 6.1.     DEFAULT.  The occurrence of any of the following
shall constitute an "Event of Default" under this Agreement:

         (a)     Borrower shall fail to pay when due any principal, interest,
                 fees or other amounts payable under any of the Loan Documents.

         (b)     Any financial statement or certificate furnished to Bank in
                 connection with, or any representation or warranty made by
                 Borrower or any other party under this Agreement or any other
                 Loan Document shall prove to be incorrect, false or misleading
                 in any material respect when furnished or made.

         (c)     Any default in the performance of or compliance with any
                 obligation, agreement or other provision contained herein or
                 in any other Loan Document (other than those referred to in
                 subsections (a) and (b) above), and with respect to any such
                 default which by its nature can be cured, such default shall
                 continue for a period of twenty (20) days from its occurrence.

         (d)     Any default in the payment or performance of any obligation,
                 or any defined event of default, under the terms of any
                 contract or instrument (other than any of the Loan Documents)
                 pursuant to which Borrower has incurred debt or other
                 liability to Bank or to any other person or entity in excess
                 of $5,000,000.00.

         (e)     The filing of a notice of judgment lien against Borrower; or
                 the recording of any abstract of judgment against Borrower in
                 any county in which Borrower





                                       12
<PAGE>   13
                 has an interest in real property; or the service of a notice 
                 of levy and/or of a writ of attachment or execution, or
                 other like process, against the assets of Borrower; or the
                 entry of a judgment against Borrower; to the extent that any
                 of the above may result in an adverse financial impact on
                 Borrower in excess of $500,000.00.

         (f)     Borrower shall become insolvent, or shall suffer or consent to
                 or apply for the appointment of a receiver, trustee, custodian
                 or liquidator of itself or any of its property, or shall
                 generally fail to pay its debts as they become due, or shall
                 make a general assignment for the benefit of creditors;
                 Borrower shall file a voluntary petition in bankruptcy, or
                 seeking reorganization, in order to effect a plan or other
                 arrangement with creditors or any other relief under the
                 Bankruptcy Reform Act, Title 11 of the United States Code, as
                 amended or recodified from time to time ("Bankruptcy Code"),
                 or under any state or federal law granting relief to debtors,
                 whether now or hereafter in effect; or any involuntary
                 petition or proceeding pursuant to the Bankruptcy Code or any
                 other applicable state or federal law relating to bankruptcy,
                 reorganization or other relief for debtors is filed or
                 commenced against Borrower, or Borrower shall file an answer
                 admitting the jurisdiction of the court and the material
                 allegations of any involuntary petition; or Borrower shall be
                 adjudicated a bankrupt, or an order for relief shall be
                 entered against Borrower by any court of competent
                 jurisdiction under the Bankruptcy Code or any other applicable
                 state or federal law relating to bankruptcy, reorganization or
                 other relief for debtors.

         (g)     There shall exist or occur any event or condition which Bank
                 in good faith believes impairs, or is substantially likely to
                 impair, the prospect of payment or performance by Borrower of
                 its obligations under any of the Loan Documents.

         (h)     The dissolution or liquidation of Borrower; or Borrower, or
                 any of its directors, stockholders or members, shall take
                 action seeking to effect the dissolution or liquidation of
                 Borrower.

         SECTION 6.2.     REMEDIES.  Upon the occurrence of any Event of
Default:  (a) all indebtedness of Borrower under each of the Loan Documents,
any term thereof to the contrary notwithstanding, shall at Bank's option and
without notice become immediately due and payable without presentment, demand,
protest or notice of dishonor, all of which are hereby expressly waived by each
Borrower; (b) the obligation, if any, of Bank to extend any further credit
under any of the Loan Documents shall immediately cease and terminate; and (c)
Bank shall have all rights, powers and remedies available under each of the
Loan Documents, or accorded by law, including without limitation the right to
resort to any or all security for any credit accommodation from Bank subject
hereto and to exercise any or all of the rights of a beneficiary or secured
party pursuant to applicable law.  All rights, powers and remedies of Bank may
be exercised at any time by Bank and from time to time after the occurrence of
an Event of Default, are cumulative and not exclusive, and shall be in addition
to any other rights, powers or remedies provided by law or equity.


                                  ARTICLE VII
                                 MISCELLANEOUS


         SECTION 7.1.     NO WAIVER.  No delay, failure or discontinuance of
Bank in exercising any right, power or remedy under any of the Loan Documents
shall affect or





                                       13
<PAGE>   14
operate as a waiver of such right, power or remedy; nor shall any single or
partial exercise of any such right, power or remedy preclude, waive or
otherwise affect any other or further exercise thereof or the exercise of any
other right, power or remedy.  Any waiver, permit, consent or approval of any
kind by Bank of any breach of or default under any of the Loan Documents must
be in writing and shall be effective only to the extent set forth in such
writing.

         SECTION 7.2.     NOTICES.  All notices, requests and demands which any
party is required or may desire to give to any other party under any provision
of this Agreement must be in writing delivered to each party at the following
address:

         BORROWER:

                          NEXSTAR PHARMACEUTICALS, INC.
                          2860 Wilderness Place
                          Boulder, CO  80301
                          Attention:  Lauri R. Harker

                          With a copy to:

                          Vice President and General Counsel
                          At the address set forth above

         BANK:            WELLS FARGO BANK (COLORADO),
                          NATIONAL ASSOCIATION
                          633 17th Street, 3rd floor
                          Denver, CO 80202

or to such other address as any party may designate by written notice to all
other parties.  Each such notice, request and demand shall be deemed given or
made as follows:  (a) if sent by hand delivery, upon delivery; (b) if sent by
mail, upon the earlier of the date of receipt or three (3) days after deposit
in the U.S. mail, first class and postage prepaid; and (c) if sent by telecopy,
upon receipt.

         SECTION 7.3.     COSTS, EXPENSES AND ATTORNEYS' FEES.  Borrower shall
pay to Bank immediately upon demand the full amount of all payments, advances,
charges, costs and expenses, including reasonable attorneys' fees (to include
outside counsel fees and all allocated costs of Bank's in-house counsel),
expended or incurred by Bank in connection with (a) the negotiation and
preparation of this Agreement and the other Loan Documents, Bank's continued
administration hereof and thereof, and the preparation of any amendments and
waivers hereto and thereto, (b) the enforcement of Bank's rights and/or the
collection of any amounts which become due to Bank under any of the Loan
Documents, and (c) the prosecution or defense of any action in any way related
to any of the Loan Documents, including without limitation, any action for
declaratory relief, whether incurred at the trial or appellate level, in an
arbitration proceeding or otherwise, and including any of the foregoing
incurred in connection with any bankruptcy proceeding (including without
limitation, any adversary proceeding, contested matter or motion brought by
Bank or any other person) relating to any Borrower or any other person or
entity.

         SECTION 7.4.     SUCCESSORS, ASSIGNMENT.  This Agreement shall be
binding upon and inure to the benefit of the heirs, executors, administrators,
legal representatives, successors and assigns of the parties; provided however,
that Borrower may not assign or transfer its interest hereunder without Bank's
prior written consent. Bank reserves the right to sell, assign, transfer,
negotiate or grant participations in all or





                                       14
<PAGE>   15
any part of, or any interest in, Bank's rights and benefits under each of the
Loan Documents.  In connection therewith, Bank may disclose all documents and
information which Bank now has or may hereafter acquire relating to any credit
extended by Bank to Borrower, Borrower or its business, or any collateral
required hereunder.

         SECTION 7.5.     ENTIRE AGREEMENT; AMENDMENT.  This Agreement and the
other Loan Documents constitute the entire agreement between Borrower and Bank
with respect to any extension of credit by Bank subject hereto and supersede
all prior negotiations, communications, discussions and correspondence
concerning the subject matter hereof.  This Agreement may be amended or
modified only in writing signed by each party hereto.

         SECTION 7.6.     NO THIRD PARTY BENEFICIARIES.  This Agreement is made
and entered into for the sole protection and benefit of the parties hereto and
their respective permitted successors and assigns, and no other person or
entity shall be a third party beneficiary of, or have any direct or indirect
cause of action or claim in connection with, this Agreement or any other of the
Loan Documents to which it is not a party.

         SECTION 7.7.     TIME.  Time is of the essence of each and every
provision of this Agreement and each other of the Loan Documents.

         SECTION 7.8.     SEVERABILITY OF PROVISIONS.  If any provision of this
Agreement shall be prohibited by or invalid under applicable law, such
provision shall be ineffective only to the extent of such prohibition or
invalidity without invalidating the remainder of such provision or any
remaining provisions of this Agreement.

         SECTION 7.9.     COUNTERPARTS.  This Agreement and the other Loan
Documents may be executed in any number of counterparts, each of which when
executed and delivered shall be deemed to be an original, and all of which when
taken together shall constitute one and the same agreement, as the case may
be..

         SECTION 7.10.    GOVERNING LAW.  This Agreement shall be governed by
and construed in accordance with the laws of the State of Colorado.

         SECTION 7.11.    JURISDICTION AND SERVICE OF PROCESS, VENUE, IMMUNITY/
JUDGMENT CURRENCY.  Subject to the provisions of Section 7.13, any suit, action
or proceeding against any Borrower with respect to the Agreement may be brought
in (a) the courts of the State of Colorado, (b) the United States District
Court for the District of Colorado, or (c) the courts of the country of any
Borrower's incorporation, as Bank may elect in its sole discretion, and
Borrower hereby submits to any such suit, action, proceeding or judgment and
waives any other preferential jurisdiction by reason of domicile. Borrower
hereby agrees that service of all writs, processes and summonses in any suit,
action or proceeding brought in the State of Colorado may be made upon  NeXstar
Pharmeceuticals, Inc. and/or its successors, presently located at 2860
Wilderness Place, Boulder, CO 80301, U.S.A. (the "Process Agent").  Borrower
hereby irrevocably appoints the Process Agent its agent and true and lawful
attorney-in-fact while any of the Borrower's obligations under the Agreement
remain unsatisfied, in its name, place and stead only to accept such service of
any and all such writs, processes and summonses, and agrees that the failure of
the Process Agent to give any notice of any such service of process to the
Borrower shall not impair or affect the validity of such service or of any
judgment based thereon.  The Borrower hereby further irrevocably consents to
the service of process in any suit, action or proceeding in the above specified
courts by the mailing thereof by Bank by registered or certified mail, postage
prepaid, to the Borrower at the address specified in this Agreement. Nothing
herein shall in any way be deemed to limit the ability of Bank to serve any
writs, processes or summonses in any other manner, as may be permitted by
applicable law. Borrower irrevocably waives any objection which it may now





                                       15
<PAGE>   16
or hereafter have to the laying of the venue of any suit, action or proceeding
arising out of or relating to the Agreement brought in the courts of the State
of Colorado or of the United States District Court for the District of
Colorado, or the courts in the country of the  Borrower's incorporation, and
also irrevocably waives any claim that any such suit, action or proceeding
brought in any of those courts has been bought in an inconvenient form.

Notwithstanding any judgment rendered in a currency other than United States
Dollars, the Borrower shall not be relieved of any obligations with respect to
any amount owed by it to Bank under the Agreement except to the extent of the
amount in United Sates Dollars which Bank is able to acquire with such amount
of such currency on the Banking Day (a day when Bank is open for business in
Denver, Colorado, U.S.A.) following receipt of such amount by Bank.  If the
amount in United States Dollars so acquired is less than the amount initially
due to Bank, the  Borrower shall indemnify Bank by paying the difference
between such amounts in United States Dollars.  The payment of any additional
amount so required of the Borrower under this Section shall constitute an
independent obligation of the Borrowers, the enforcement of which obligation
may not be impeded by the Borrower.

         SECTION 7.12.    JOINT AND SEVERAL LIABILITY.  As used in this Section
7.12, the term "Joint Credit" shall mean the Line of Credit.

         (a)     Each Borrower has determined and represents to Bank that it is
in its best interests and in pursuance of its legitimate business purposes to
induce Bank to extend credit pursuant to this Agreement.  Each Borrower
acknowledges and represents that its business is related to the business of the
other Borrowers, the availability of the commitments provided for herein
benefits each Borrower, and advances and other credit extensions made hereunder
will inure to the benefit of Borrowers, individually and as a group.

         (b)     Each Borrower has determined and represents to Bank that it
has, and after giving effect to the transactions contemplated by this Agreement
will have, assets having a fair saleable value in excess of its debts (other
than inter-company debt), after giving effect to any rights of contribution or
subrogation which may be available to such Borrower, and each Borrower has, and
will have, access to adequate capital for the conduct of its business and the
ability to pay its debts as such debts mature.

         (c)     Each Borrower agrees that it is jointly and severally liable
to Bank for, and each Borrower agrees to pay to Bank when due the full amount
of, all indebtedness now existing or hereafter arising to Bank under or in
connection with the Joint Credit and all modifications, extensions and renewals
thereof, including without limitation all advances disbursed to any Borrower
under the Joint Credit, all interest which accrues thereon and all fees, costs
and expenses chargeable to any Borrower in connection therewith.

         (d)     The liability of each Borrower for the Joint Credit shall be
reinstated and revived and the rights of Bank shall continue if and to the
extent that for any reason any amount at any time paid on account of any of the
Joint Credit is rescinded or must otherwise be restored by Bank, whether as a
result of any proceedings in bankruptcy or reorganization or otherwise, all as
though such amount had not been paid.

         (e)     Each Borrower authorizes Bank, without notice to or demand on
such Borrower, and without affecting such Borrower's liability for the Joint
Credit, from time to time to:  (a) alter, compromise, extend, accelerate or
otherwise change the time for payment of, or otherwise change the terms of, the
liabilities and obligations of any other Borrower to Bank on account of any of
the Joint Credit; (b) take and hold security from any other Borrower for the
payment of any of the Joint Credit, and exchange, enforce, waive, subordinate
or release any such security; (c) apply such security and direct the order or
manner of sale thereof, including without limitation, a non-judicial sale
permitted by the





                                       16
<PAGE>   17
terms of the controlling security agreement or deed of trust, as Bank in its
discretion may determine; (d) release or substitute any one or more of the
endorsers or any guarantors of any of the Joint Credit, or any other party
obligated thereon; and (e) apply payments received by Bank from  any other
Borrower to indebtedness of such other Borrower to Bank other than the Joint
Credit.

         (f)     Each Borrower represents and warrants to Bank that it has
established adequate means of obtaining from any other Borrower on a continuing
basis financial and other information pertaining to such other Borrower's
financial condition, and each Borrower agrees to keep adequately informed from
such means of any facts, events or circumstances which might in any way affect
its risks hereunder  Each Borrower further agrees that Bank shall have no
obligation to disclose to it any information or material about any other
Borrower which is acquired by Bank in any manner.

         (g)     Each Borrower waives any right to require Bank to: (i) proceed
against any other Borrower or any other person; (ii) proceed against or exhaust
any security held from any other Borrower or any other person; (iii) pursue any
other remedy in Bank's power; (iv) apply payments received by Bank from any
other Borrower to any of the Joint Credit; or (v) make any presentments or
demands for performance, or give any notices of nonperformance, protests,
notices of protest or notices of dishonor in connection with any of the Joint
Credit.

         (h)     Each Borrower waives any defense to its liability for the
Joint Credit based upon or arising by reason of:  (i) any disability or other
defense of any other Borrower or any other person; (ii) the cessation or
limitation from any cause whatsoever, other than payment in full, of the
liability of any other Borrower for the Joint Credit; (iii) any lack of
authority of any officer, director, partner, agent or other person acting or
purporting to act on behalf of any other Borrower or any defect in the
formation of any other Borrower; (iv) the application by any other Borrower of
the proceeds of any of the Joint Credit for purposes other than the purposes
intended or understood by Bank or any Borrower; (v) any act or omission by Bank
which directly or indirectly results in or aids the discharge of any other
Borrower by operation of law or otherwise, or which in any way impairs or
suspends any rights or remedies of Bank against any other Borrower; (vi) any
impairment of the value of any interest in any security for any of the Joint
Credit, including without limitation, the failure to obtain or maintain
perfection or recordation of any interest in any such security, the release of
any such security without substitution, and/or the failure to preserve the
value of, or to comply with applicable law in disposing of, any such security;
or (vii) any modification of the obligations or liabilities of any other
Borrower for any of the Joint Credit, including without limitation the renewal,
extension, acceleration or other change in time for payment of, or other change
in the terms of, the indebtedness of any other Borrower for any of the Joint
Credit, including increase or decrease of the rate of interest thereon.  Until
the Joint Credit and all indebtedness of each Borrower to Bank arising under or
in connection with this Agreement shall have been paid in full, no Borrower
shall have any right of subrogation.  Each Borrower waives all rights and
defenses it may have arising out of (A) any election of remedies by Bank, even
though that election of remedies, such as a non-judicial foreclosure with
respect to any security for any of the Joint Credit, destroys its rights of
subrogation or its rights to proceed against any other Borrower for
reimbursement, or (B) any loss of rights it may suffer by reason of any rights,
powers or remedies of any other Borrower in connection with any anti-deficiency
laws or any other laws limiting, qualifying or discharging any Borrower's
indebtedness for any of the Joint Credit, whether by operation of law or
otherwise. Until the Joint Credit and all indebtedness of each Borrower to Bank
arising under or in connection with this Agreement shall have been paid in
full, each Borrower waives any right to enforce any remedy which Bank now has
or may hereafter have against any other Borrower or any other person, and
waives any benefit of, or any right to participate in, any security now or
hereafter held by Bank.





                                       17
<PAGE>   18
         (i)     If any of the waivers herein is determined to be contrary to
any applicable law or public policy, such waiver shall be effective only to the
extent permitted by law.

         (j)     It is the position of the Borrowers that each Borrower
benefits from the Joint Credit that have been made available by Bank under this
Agreement and from each extension of credit thereunder, regardless of whether
such credit is disbursed to a joint account of Borrowers or to or for the
account of any Borrower.

         SECTION 7.13.    ARBITRATION.

         (a)     Arbitration.  Upon the demand of any party, any Dispute shall
be resolved by binding arbitration (except as set forth in (e) below) in
accordance with the terms of this Agreement.  A  "Dispute," as used in this
Section, shall mean any action, dispute, claim or controversy of any kind,
whether in contract or tort, statutory or common law, legal or equitable, now
existing or hereafter arising under or in connection with, or in any way
pertaining to, any of the Loan Documents, or any past, present or future
extensions of credit and other activities, transactions or obligations of any
kind related directly or indirectly to any of the Loan Documents, including
without limitation, any of the foregoing arising in connection with the
exercise of any self-help, ancillary or other remedies pursuant to any of the
Loan Documents.  Any party may by summary proceedings bring an action in court
to compel arbitration of a Dispute.  Any party who fails or refuses to submit
to arbitration following a lawful demand by any other party shall bear all
costs and expenses incurred by such other party in compelling arbitration of
any Dispute.

         (b)     Governing Rules.  Arbitration proceedings shall be
administered by the American Arbitration Association ("AAA") or such other
administrator as the parties shall mutually agree upon in accordance with the
AAA Commercial Arbitration Rules.  All Disputes submitted to arbitration shall
be resolved in accordance with the Federal Arbitration Act (Title 9 of the
United States Code), notwithstanding any conflicting choice of law provision in
any of the Loan Documents.  The arbitration shall be conducted at a location in
Colorado selected by the AAA or other administrator.  If there is any
inconsistency between the terms hereof and any such rules, the terms and
procedures set forth herein shall control.  All statutes of limitation
applicable to any Dispute shall apply to any arbitration proceeding.  All
discovery activities shall be expressly limited to matters directly relevant to
the Dispute being arbitrated.  Judgment upon any award rendered in an
arbitration may be entered in any court having jurisdiction; provided however,
that nothing contained herein shall be deemed to be a waiver by any party that
is a bank of the protections afforded to it under 12 U.S.C. Section 91 or any
similar applicable state law.

         (c)     No Waiver; Provisional Remedies, Self-Help and Foreclosure.
No provision hereof shall limit the right of any party to exercise self-help
remedies such as setoff, foreclosure against or sale of any real or personal
property collateral or security, or to obtain provisional or ancillary
remedies, including without limitation injunctive relief, sequestration,
attachment, garnishment or the appointment of a receiver, from a court of
competent jurisdiction before, after or during the pendency of any arbitration
or other proceeding.  The exercise of any such remedy shall not waive the right
of any party to compel arbitration hereunder.

         (d)     Arbitrator Qualifications and Powers; Awards.  Arbitrators
must be active members of the Colorado State Bar or retired judges of the state
or federal judiciary of Colorado with expertise in the substantive law
applicable to the subject matter of the Dispute.  Arbitrators are empowered to
resolve Disputes by summary rulings in response to motions filed prior to the
final arbitration hearing.  Arbitrators (i) shall resolve all Disputes in
accordance with the substantive law of the state of Colorado, (ii) may grant
any remedy or relief that a court of the state of Colorado could order or grant
within the scope hereof





                                       18
<PAGE>   19
and such ancillary relief as is necessary to make effective any award, and
(iii) shall have the power to award recovery of all costs and fees, to impose
sanctions and to take such other actions as they deem necessary to the same
extent a judge could pursuant to the Federal Rules of Civil Procedure, the
Colorado Rules of Civil Procedure or other applicable law.  Any Dispute in
which the amount in controversy is $5,000,000 or less shall be decided by a
single arbitrator who shall not render an award of greater than $5,000,000
(including damages, costs, fees and expenses).  By submission to a single
arbitrator, each party expressly waives any right or claim to recover more than
$5,000,000.  Any Dispute in which the amount in controversy exceeds $5,000,000
shall be decided by majority vote of a panel of three arbitrators; provided
however, that all three arbitrators must actively participate in all hearings
and deliberations.

         (e)     Judicial Review.  Notwithstanding anything herein to the
contrary, in any arbitration in which the amount in controversy exceeds
$25,000,000, the arbitrators shall be required to make specific, written
findings of fact and conclusions of law.  In such arbitrations (i) the
arbitrators shall not have the power to make any award which is not supported
by substantial evidence or which is based on legal error, (ii) an award shall
not be binding upon the parties unless the findings of fact are supported by
substantial evidence and the conclusions of law are not erroneous under the
substantive law of the state of Colorado, and (iii) the parties shall have in
addition to the grounds referred to in the Federal Arbitration Act for
vacating, modifying or correcting an award the right to judicial review of (A)
whether the findings of fact rendered by the arbitrators are supported by
substantial evidence, and (B) whether the conclusions of law are erroneous
under the substantive law of the state of Colorado.  Judgment confirming an
award in such a proceeding may be entered only if a court determines the award
is supported by substantial evidence and not based on legal error under the
substantive law of the state of Colorado.

         (f)     Miscellaneous.  To the maximum extent practicable, the AAA,
the arbitrators and the parties shall take all action required to conclude any
arbitration proceeding within 180 days of the filing of the Dispute with the
AAA.  No arbitrator or other party to an arbitration proceeding may disclose
the existence, content or results thereof, except for disclosures of
information by a party required in the ordinary course of its business, by
applicable law or regulation, or to the extent necessary to exercise any
judicial review rights set forth herein.  If more than one agreement for
arbitration by or between the parties potentially applies to a Dispute, the
arbitration provision most directly related to the Loan Documents or the
subject matter of the Dispute shall control.  This arbitration provision shall
survive termination, amendment or expiration of any of the Loan Documents or
any relationship between the parties.





                                       19
<PAGE>   20
         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to
be executed as of the day and year first written above.

<TABLE>
<CAPTION>
NEXSTAR PHARMACEUTICALS, INC.                                     WELLS FARGO BANK (COLORADO),
<S>                                                               <C>
                                                                  NATIONAL ASSOCIATION
By:   /s/ PATRICK J. MAHAFFY                         
      -----------------------------------------
      Patrick J. Mahaffy                                          By: /s/ TRACEY A. HANSON                        
      President and Chief Executive Officer                           -------------------------------------
                                                                      Tracey A. Hanson
                                                                      Vice President


By:   /s/ MICHAEL E. HART                        
      -----------------------------------------
      Michael E. Hart
      Vice President, Chief Financial Officer


NEXSTAR PHARMACEUTICALS ITALIA, S.r.1.,
    an Italian corporation

By:   /s/ ANTONIO SPAGNA             
      -----------------------------------------
      Antonio Spagna
      Managing Director, General Manager

NEXSTAR PHARMACEUTIQUE SARL,
    a French corporation

By:   /s/ GERARD LAMPERTI                           
      -----------------------------------------
      Gerard  Lamperti
      Managing Director, General Manager
</TABLE>





                                       20