<PAGE>

                                                                 EXHIBIT 10.15b


                          AMENDMENT TO RIGHTS AGREEMENT
                         BETWEEN ARADIGM CORPORATION AND
                                BANKBOSTON, N.A.


        THIS AMENDMENT TO RIGHTS AGREEMENT (this "Amendment") is made as of
December 6, 2001, by and between ARADIGM CORPORATION, a California corporation
(the "Company"), and EQUISERVE TRUST COMPANY, N.A. (F/K/A FLEET NATIONAL BANK),
a national banking association, as rights agent (the "Rights Agent").

        WHEREAS, the Company is entering into a Securities Purchase Agreement
(the "Purchase Agreement") by and among the Company and the purchasers named
therein, pursuant to which the Company will sell shares of its Series A
Convertible Preferred Stock and warrants to purchase shares of its Common Stock
to New Enterprise Associates 10, Limited Partnership ("NEA") and the other
purchasers;

        WHEREAS, the Company and the Rights Agent are parties to that certain
Rights Agreement, dated as of August 31, 1998, as amended on October 22, 2001
(as so amended, the "Rights Agreement");

        WHEREAS, the Company desires to amend the Rights Agreement in connection
with the execution and delivery of the Purchase Agreement; and

        WHEREAS, the Board of Directors of the Company has approved this
Amendment and authorized its appropriate officers to execute and deliver the
same to the Rights Agent.

        NOW, THEREFORE, in accordance with the procedures for amendment of the
Rights Agreement set forth in Section 27 thereof, and in consideration of the
foregoing and the mutual agreements herein set forth, the parties hereby agree
as follows:

        1. Capitalized terms that are not otherwise defined herein shall have
the meanings ascribed to them in the Rights Agreement.

        2. The definition of "Acquiring Person" set forth in Section 1(a) of the
Rights Agreement is amended by adding the following sentence to the end of that
section:

                Notwithstanding the foregoing, none of New Enterprise Associates
        10, its Affiliates and Associates (collectively, "NEA") shall be deemed
        to be an "Acquiring Person" for the purposes of this Agreement;
        provided, that the foregoing exemption shall cease to apply if NEA
        becomes the Beneficial Owner of any additional Common Shares after the
        date hereof without the approval of a majority of the independent
        members of the Board of Directors of the Company other than in
        connection with the Securities Purchase Agreement dated as of December
        14, 2001 (the "Purchase Agreement") by and among the Company and the
        purchasers named therein and the exercise or conversion into Common
        Shares of any securities purchased thereunder.

        3. The definition of "Shares Acquisition Date" in Section l(n) of the
Rights Agreement is hereby deleted in its entirety and replaced with the
following:



                                       1.
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        "SHARES ACQUISITION DATE" shall mean the first date of public
        announcement by the Company or an Acquiring Person that an Acquiring
        Person has become such provided, however that, if such Person is
        determined not to have become an Acquiring Person pursuant to clause (y)
        of Subsection 1(a)(B) hereof or the last two sentences of Section 1(a)
        hereof, then no Shares Acquisition Date shall be deemed to have
        occurred.

        4. The Rights Agreement, as amended by this Amendment, shall remain in
full force and effect in accordance with its terms.

        5. All the covenants and provisions of this Amendment by or for the
benefit of the Company or the Rights Agent shall bind and inure to the benefit
of their respective successors and assigns hereunder.

        6. Nothing in this Amendment shall be construed to give to any Person
other than the Company, the Rights Agent and the registered holders of the Right
Certificates (and, prior to the Distribution Date, the Common Shares) any legal
or equitable right, remedy or claim under this Amendment; but this Amendment
shall be for the sole and exclusive benefit of the Company, the Rights Agent and
the registered holders of the Right Certificates (and, prior to the Distribution
Date, the Common Shares).

        7. If any term, provision, covenant or restriction of this Amendment is
held by a court of competent jurisdiction or other authority to be invalid, void
or unenforceable, the remainder of the terms, provisions, covenants and
restrictions of this Amendment shall remain in full force and effect and shall
in no way be affected, impaired or invalidated.

        8. This Amendment shall be deemed to be a contract made under the laws
of the State of California and for all purposes shall be governed by and
construed in accordance with the laws of such State applicable to contracts to
be made and performed entirely within such State.

        9. This Amendment may be executed in any number of counterparts and each
of such counterparts shall for all purposes be deemed to be an original, and all
such counterparts shall together constitute but one and the same instrument.

        10. The Company hereby certifies to the Rights Agent that this Amendment
is in compliance with Section 27 of the Rights Agreement.



                                       2.
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        IN WITNESS WHEREOF, the parties herein have caused this Amendment to be
duly executed and attested, all as of the date and year first above written.



                                            ARADIGM CORPORATION

                                            By: /s/ Thomas M. Speace
                                                -------------------------------

                                            Name: Thomas M. Speace
                                                  -----------------------------

                                            Title: Senior VP, Business
                                                   Development and Marketing
                                                   ----------------------------


Attest:

/s/ Michael Molkentin
-----------------------------------
Michael Molkentin
Acting Chief Financial Officer



                                            EQUISERVE TRUST COMPANY, N.A.

                                            By: /s/ Margaret Prentice
                                                -------------------------------

                                            Name: Margaret Prentice
                                                  -----------------------------

                                            Title: Managing Director
                                                   ----------------------------



                  SIGNATURE PAGE TO RIGHTS AGREEMENT AMENDMENT