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                                                                     EXHIBIT 4.6

                  FORM OF EXCHANGEABLE SHARE SUPPORT AGREEMENT

       MEMORANDUM OF AGREEMENT MADE AS OF THE   -  TH DAY OF   -  , 2001.

AMONG:

                  SHIRE PHARMACEUTICALS GROUP PLC, a company
                  registered in England under registry number
                  2883758 (hereinafter referred to as
                  "SHIRE");

                                    -- and --

                  3829359 CANADA INC., a corporation existing
                  under the laws of Canada (hereinafter
                  referred to as "CALLCO");

                                    -- and --

                  SHIRE ACQUISITION INC., a corporation
                  existing under the laws of Canada
                  (hereinafter referred to as "EXCHANGECO");

    WHEREAS pursuant to a merger agreement (the "MERGER AGREEMENT") dated as of
December 10, 2000 by and among Shire, ExchangeCo and BioChem Pharma Inc.
("BIOCHEM"), ExchangeCo has agreed to issue exchangeable shares (the
"EXCHANGEABLE SHARES") to certain holders of common shares of BioChem pursuant
to the plan of arrangement (the "ARRANGEMENT") contemplated by the Merger
Agreement;

    AND WHEREAS pursuant to the Merger Agreement, Shire and ExchangeCo have
agreed to execute an exchangeable share support agreement substantially in the
form of this agreement;

    NOW THEREFORE in consideration of the respective covenants and agreements
provided in this agreement and for other good and valuable consideration (the
receipt and sufficiency of which are hereby acknowledged), the parties hereto
covenant and agree as follows:

                                   ARTICLE 1
                         DEFINITIONS AND INTERPRETATION

1.1 DEFINED TERMS

    Each term denoted herein by initial capital letters and not otherwise
defined herein shall have the meaning ascribed thereto in the rights,
privileges, restrictions and conditions (collectively, the "SHARE PROVISIONS")
attaching to the Exchangeable Shares attached as Appendix 1 to the Plan of
Arrangement as set out in the Articles of Arrangement of BioChem, unless the
context requires otherwise.

1.2 INTERPRETATION NOT AFFECTED BY HEADINGS

    The division of this agreement into Articles, sections and other portions
and the insertion of headings are for convenience of reference only and shall
not affect the construction or interpretation of this agreement. Unless
otherwise indicated, all references to an "ARTICLE" or "SECTION" followed by a
number and/or a letter refer to the specified Article or section of this
agreement. The terms "THIS AGREEMENT", "HEREOF", "HEREIN" and "HEREUNDER" and
similar expressions refer to this agreement and not to any

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particular Article, section or other portion hereof and include any agreement or
instrument supplementary or ancillary hereto.

1.3 NUMBER, GENDER

    Words importing the singular number only shall include the plural and VICE
VERSA. Words importing any gender shall include all genders.

1.4 DATE FOR ANY ACTION

    If any date on which any action is required to be taken under this agreement
is not a Business Day, such action shall be required to be taken on the next
succeeding Business Day. For the purposes of this agreement, a "BUSINESS DAY"
means any day on which banks are not required or authorized to close in the City
of Montreal, Canada, the City of London, England and the City of New York,
U.S.A.

                                   ARTICLE 2
                       COVENANTS OF SHIRE AND EXCHANGECO

2.1 COVENANTS REGARDING EXCHANGEABLE SHARES

    So long as any Exchangeable Shares not owned by Shire or its Affiliates are
outstanding, Shire will:

    (a) not declare or pay any dividends on the Shire Ordinary Shares unless
       (i) ExchangeCo shall (w) simultaneously declare or pay, as the case may
       be, an equivalent dividend (as provided for in the Share Provisions and
       as determined by the Board of Directors of ExchangeCo as contemplated by
       Section 2.7(d) hereof) on the Exchangeable Shares (an "EQUIVALENT
       DIVIDEND") and (x) have sufficient money or other assets or authorized
       but unissued securities available to enable the due declaration and the
       due and punctual payment, in accordance with applicable law, of any
       Equivalent Dividend, or (ii) ExchangeCo shall (y) subdivide the
       Exchangeable Shares in lieu of a share dividend thereon (as provided for
       in the Share Provisions) (an "EQUIVALENT SHARE SUBDIVISION"), and
       (z) have sufficient authorized but unissued securities available to
       enable the Equivalent Share Subdivision.

    (b) advise ExchangeCo sufficiently in advance of the declaration by Shire of
       any dividend on Shire Ordinary Shares and take all such other actions as
       are reasonably necessary, in cooperation with ExchangeCo, to ensure that
       the respective declaration date, record date and payment date for a
       dividend on the Exchangeable Shares shall be the same as the declaration
       date, record date and payment date for the corresponding dividend on the
       Shire Ordinary Shares;

    (c) ensure that the record date for any dividend declared on Shire Ordinary
       Shares is not less than ten Business Days after the declaration date of
       such dividend;

    (d) take all such actions and do all such things as are reasonably necessary
       or desirable to enable and permit ExchangeCo, in accordance with
       applicable law, to pay and otherwise perform its obligations with respect
       to the satisfaction of the Liquidation Amount, the Retraction Price or
       the Redemption Price in respect of each issued and outstanding
       Exchangeable Share (other than Exchangeable Shares owned by Shire or its
       Affiliates) upon the liquidation, dissolution or winding-up of
       ExchangeCo, the delivery of a Retraction Request by a holder of
       Exchangeable Shares or a redemption of Exchangeable Shares by ExchangeCo,
       as the case may be, including without limitation all such actions and all
       such things as are necessary or desirable to enable and permit ExchangeCo
       to cause to be delivered Shire Ordinary Shares and/or Shire ADSs to the
       holders of Exchangeable Shares in accordance with the provisions of
       Article 5, 6 or 7, as the case may be, of the Share Provisions;

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    (e) take all such actions and do all such things as are reasonably necessary
       or desirable to enable and permit CallCo, in accordance with applicable
       law, to perform its obligations arising upon the exercise by CallCo of
       the Liquidation Call Right, the Retraction Call Right or the Redemption
       Call Right, including without limitation all such actions and all such
       things as are necessary or desirable to enable and permit CallCo to cause
       to be delivered Shire Ordinary Shares and/or Shire ADSs to the holders of
       Exchangeable Shares in accordance with the provisions of the Liquidation
       Call Right, the Retraction Call Right, the Redemption Call Right or the
       Shire Call Right, as the case may be;

    (f) take all such actions and do all such things as are reasonably necessary
       or desirable to enable and permit Shire and CallCo, in accordance with
       applicable law, to perform their respective obligations arising upon the
       exercise by Shire of the Shire Call Right, including without limitation,
       all such actions and all such things as are necessary or desirable to
       enable and permit Shire and CallCo to deliver or cause to be delivered
       Shire Ordinary Shares and/or Shire ADSs to holders of Exchangeable Shares
       in accordance with the provisions of the Shire Call Right; and

    (g) not exercise its vote as a shareholder to initiate the voluntary
       liquidation, dissolution or winding-up of ExchangeCo nor take any action
       or omit to take any action that is designed to result in the liquidation,
       dissolution or winding-up of ExchanceCo.

2.2 COVENANTS REGARDING EXCHANGECO AND CALLCO

    So long as any Exchangeable Shares not owned by Shire or its Affiliates are
outstanding, Shire will cause each of Callco and Exchangeco to keep its share
register outside of the United Kingdom.

2.3 SEGREGATION OF FUNDS

    Shire will cause ExchangeCo to deposit a sufficient amount of funds in a
separate account of ExchangeCo and segregate a sufficient amount of such other
assets and property as is necessary to enable ExchangeCo to pay dividends when
due and to pay or otherwise satisfy its respective obligations under Article 5,
6 or 7 of the Share Provisions, as applicable.

2.4 RESERVATION OF SHIRE ORDINARY SHARES

    Shire hereby represents, warrants and covenants in favour of ExchangeCo and
CallCo that Shire has reserved for issuance and will, at all times while any
Exchangeable Shares (other than Exchangeable Shares held by Shire or its
Affiliates) are outstanding, keep available, free from pre-emptive and other
rights, out of its authorized and unissued share capital such number of Shire
Ordinary Shares (or other shares or securities into which Shire Ordinary Shares
may be reclassified or changed as contemplated by Section 2.7 hereof) (a) as is
equal to the sum of (i) the number of Exchangeable Shares issued and outstanding
from time to time multiplied by three and (ii) the number of Exchangeable Shares
issuable upon the exercise of all rights to acquire Exchangeable Shares
outstanding from time to time multiplied by three, and (b) as are now and may
hereafter be required to enable and permit Shire to meet its obligations under
the Shire Call Right, under the Voting and Exchange Trust Agreement and under
any other security or commitment pursuant to which Shire may now or hereafter be
required to issue Shire Ordinary Shares, to enable and permit CallCo to meet its
obligations under each of the Liquidation Call Right, the Retraction Call Right
and the Redemption Call Right and to enable and permit ExchangeCo to meet its
respective obligations hereunder and under the Share Provisions.

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2.5 NOTIFICATION OF CERTAIN EVENTS

    In order to assist Shire to comply with its obligations hereunder and to
permit CallCo to exercise the Liquidation Call Right, the Retraction Call Right
and the Redemption Call Right, ExchangeCo will notify Shire and CallCo of each
of the following events at the time set forth below:

    (a) in the event of any determination by the Board of Directors of
       ExchangeCo to institute voluntary liquidation, dissolution or winding-up
       proceedings with respect to ExchangeCo or to effect any other
       distribution of the assets of ExchangeCo among its shareholders for the
       purpose of winding up its affairs, at least 60 days prior to the proposed
       effective date of such liquidation, dissolution, winding-up or other
       distribution;

    (b) promptly, upon the earlier of receipt by ExchangeCo of notice of and
       ExchangeCo otherwise becoming aware of any threatened or instituted
       claim, suit, petition or other proceedings with respect to the
       involuntary liquidation, dissolution or winding-up of ExchangeCo or to
       effect any other distribution of the assets of ExchangeCo among its
       shareholders for the purpose of winding up its affairs;

    (c) immediately, upon receipt by ExchangeCo of a Retraction Request;

    (d) on the same date on which notice of redemption is given to holders of
       Exchangeable Shares, upon the determination of a Redemption Date in
       accordance with the Share Provisions; and

    (e) as soon as practicable upon the issuance by ExchangeCo of any
       Exchangeable Shares or rights to acquire Exchangeable Shares (other than
       the issuance of Exchangeable Shares and rights to acquire Exchangeable
       Shares in exchange for outstanding BioChem Common Shares pursuant to the
       Arrangement).

2.6 DELIVERY OF SHIRE ORDINARY SHARES OR SHIRE ADSS TO EXCHANGECO AND CALLCO

    In furtherance of its obligations under Sections 2.1(d), (e) and
(f) hereof, upon notice from ExchangeCo or CallCo of any event that requires
ExchangeCo or CallCo to cause to be delivered Shire Ordinary Shares and/or Shire
ADSs to any holder of Exchangeable Shares, Shire shall, subject to all
applicable laws and regulatory or stock exchange requirements, forthwith issue
and deliver or cause to be delivered to ExchangeCo or CallCo the requisite
number of Shire Ordinary Shares and/or Shire ADSs to be received by, and issued
to or to the order of, the former holder of the surrendered Exchangeable Shares,
as ExchangeCo or CallCo shall direct. All such Shire Ordinary Shares and Shire
ADSs shall be duly authorized and validly issued as fully paid and
non-assessable and shall be free and clear of any lien, claim or encumbrance. In
consideration of the issuance and delivery of each such Shire Ordinary Share or
Shire ADS, ExchangeCo or CallCo, as the case may be, shall issue to Shire, or as
Shire shall direct, common shares of ExchangeCo or CallCo having equivalent
value.

2.7 QUALIFICATION OF SHIRE ORDINARY SHARES AND SHIRE ADSS

    If any Shire Ordinary Shares or Shire ADSs (or other shares or securities
into which Shire Ordinary Shares may be reclassified or changed as contemplated
by Section 2.7 hereof) to be issued and delivered hereunder require registration
or qualification with or approval of or the filing of any document, including
any prospectus or similar document or the taking of any proceeding with or the
obtaining of any order, ruling or consent from any governmental or regulatory
authority under any Canadian, United Kingdom or United States federal,
provincial or state securities or other law or regulation or pursuant to the
rules and regulations of any securities or other regulatory authority or the
fulfilment of any other United States, United Kingdom or Canadian legal
requirement before such shares (or such other shares or securities) may be
issued by Shire and delivered or cause to be delivered by Shire at the direction
of CallCo or ExchangeCo, if applicable, to the holder of surrendered
Exchangeable Shares or in order that such shares (or such other shares or
securities) may be freely traded thereafter (other than any restrictions of
general

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application on transfer by reason of a holder being a "CONTROL PERSON" for
purposes of Canadian provincial securities law or an "AFFILIATE" of Shire for
purposes of United States federal or state securities law or any United Kingdom
equivalent), Shire will in good faith expeditiously take all such reasonable
actions and do all such reasonable things as are necessary or desirable to cause
such Shire Ordinary Shares and Shire ADSs (or such other shares or securities)
to be and remain duly registered, qualified or approved under United States,
United Kingdom and/or Canadian law, as the case may be, do all such things as
are reasonably necessary or desirable to cause all Shire Ordinary Shares and
Shire ADSs (or such other shares or securities) to be delivered hereunder to be
listed, quoted or posted for trading on all stock exchanges and quotation
systems on which outstanding Shire Ordinary Shares or Shire ADSs (or such other
shares or securities) have been listed by Shire and remain listed and quoted or
posted for trading.

2.8 ECONOMIC EQUIVALENCE.

    So long as any Exchangeable Shares not owned by Shire or its Affiliates are
outstanding:

    (a) Shire will not without prior approval of ExchangeCo and the prior
       approval of the holders of the Exchangeable Shares given in accordance
       with Section 9.2 of the Share Provisions:

        (i) issue or distribute Shire Ordinary Shares (or securities
            exchangeable for or convertible into or carrying rights to acquire
            Shire Ordinary Shares) to the holders of all or substantially all of
            the then outstanding Shire Ordinary Shares by way of share dividend
            or other distribution, other than an issue of Shire Ordinary Shares
            (or securities exchangeable for or convertible into or carrying
            rights to acquire Shire Ordinary Shares) to holders of Shire
            Ordinary Shares who exercise an option to receive dividends in Shire
            Ordinary Shares (or securities exchangeable for or convertible into
            or carrying rights to acquire Shire Ordinary Shares) in lieu of
            receiving cash dividends; or

        (ii) issue or distribute rights, options or warrants to the holders of
             all or substantially all of the then outstanding Shire Ordinary
             Shares entitling them to subscribe for or to purchase Shire
             Ordinary Shares (or securities exchangeable for or convertible into
             or carrying rights to acquire Shire Ordinary Shares); or

       (iii) issue or distribute to the holders of all or substantially all of
             the then outstanding Shire Ordinary Shares (A) shares or securities
             of Shire of any class other than Shire Ordinary Shares (other than
             shares convertible into or exchangeable for or carrying rights to
             acquire Shire Ordinary Shares), (B) rights, options or warrants
             other than those referred to in Section 2.7(a)(ii) above,
             (C) evidences of indebtedness of Shire or (D) assets of Shire,

       unless the economic equivalent on a per share basis of such rights,
       options, securities, shares, evidences of indebtedness or other assets is
       issued or distributed simultaneously to holders of the Exchangeable
       Shares; provided that, for greater certainty, the above restrictions
       shall not apply to any securities issued or distributed by Shire in order
       to give effect to and to consummate the transactions contemplated by, and
       in accordance with, the Merger Agreement.

    (b) Shire will not without the prior approval of ExchangeCo and the prior
       approval of the holders of the Exchangeable Shares given in accordance
       with Section 9.2 of the Share Provisions:

        (i) subdivide, redivide or change the then outstanding Shire Ordinary
            Shares into a greater number of Shire Ordinary Shares; or

        (ii) reduce, combine, consolidate or change the then outstanding Shire
             Ordinary Shares into a lesser number of Shire Ordinary Shares; or

       (iii) reclassify or otherwise change Shire Ordinary Shares or effect an
             amalgamation, merger, reorganization or other transaction affecting
             Shire Ordinary Shares,

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       unless the same or an economically equivalent change shall simultaneously
       be made to, or in the rights of the holders of, the Exchangeable Shares.

    (c) Shire will ensure that the record date for any event referred to in
       Section 2.7(a) or 2.7(b) above, or (if no record date is applicable for
       such event) the effective date for any such event, is not less than five
       Business Days after the date on which such event is declared or announced
       by Shire (with contemporaneous notification thereof by Shire to
       ExchangeCo).

    (d) The Board of Directors of ExchangeCo shall determine, in good faith and
       in its sole discretion, economic equivalence for the purposes of any
       event referred to in Section 2.7(a) or 2.7(b) above and each such
       determination shall be conclusive and binding on Shire. In making each
       such determination, the following factors shall, without excluding other
       factors determined by the Board of Directors of ExchangeCo to be
       relevant, be considered by the Board of Directors of ExchangeCo:

        (i) in the case of any share dividend or other distribution payable in
            Shire Ordinary Shares, the number of such shares issued in
            proportion to the number of Shire Ordinary Shares previously
            outstanding;

        (ii) in the case of the issuance or distribution of any rights, options
             or warrants to subscribe for or purchase Shire Ordinary Shares (or
             securities exercisable or exchangeable for or convertible into or
             carrying rights to acquire Shire Ordinary Shares), the relationship
             between the exercise price of each such right, option or warrant
             and the Current Market Price of a Shire Ordinary Share;

       (iii) in the case of the issuance or distribution of any other form of
             property (including without limitation any shares or securities of
             Shire of any class other than Shire Ordinary Shares, any rights,
             options or warrants other than those referred to in
             Section 2.7(d)(ii) above, any evidences of indebtedness of Shire or
             any assets of Shire), the relationship between the fair market
             value (as determined by the Board of Directors of ExchangeCo in the
             manner above contemplated) of such property to be issued or
             distributed with respect to each outstanding Shire Ordinary Share
             and the Current Market Price of a Shire Ordinary Share;

        (iv) in the case of any subdivision, redivision or change of the then
             outstanding Shire Ordinary Shares into a greater number of Shire
             Ordinary Shares or the reduction, combination, consolidation or
             change of the then outstanding Shire Ordinary Shares into a lesser
             number of Shire Ordinary Shares or any amalgamation, merger,
             reorganization or other transaction affecting Shire Ordinary
             Shares, the effect thereof upon the then outstanding Shire Ordinary
             Shares; and

        (v) in all such cases, the general taxation consequences of the relevant
            event to holders of Exchangeable Shares to the extent that such
            consequences may differ from the taxation consequences to holders of
            Shire Ordinary Shares as a result of differences between taxation
            laws of Canada and the United Kingdom (except for any differing
            consequences arising as a result of differing marginal taxation
            rates and without regard to the individual circumstances of holders
            of Exchangeable Shares).

    (e) ExchangeCo agrees that, to the extent required, upon due notice from
       Shire, ExchangeCo will use its best efforts to take or cause to be taken
       such steps as may be necessary for the purposes of ensuring that
       appropriate dividends are paid or other distributions are made by
       ExchangeCo, or subdivisions, redivisions or changes are made to the
       Exchangeable Shares, in order to implement the required economic
       equivalent with respect to the Shire Ordinary Shares and Exchangeable
       Shares as provided for in this Section 2.7.

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2.9 TENDER OFFERS

    In the event that a tender offer, share exchange offer, issuer bid,
take-over bid or similar transaction with respect to the Shire Ordinary Shares
(an "OFFER") is proposed by Shire or is proposed to Shire or its shareholders
and is recommended by the Board of Directors of Shire, or is otherwise effected
or to be effected with the consent or approval of the Board of Directors of
Shire, and the Exchangeable Shares are not redeemed by ExchangeCo or purchased
by CallCo pursuant to the Redemption Call Right, Shire will use its reasonable
best efforts expeditiously and in good faith to take all such actions and do all
such things as are necessary or desirable to enable and permit holders of
Exchangeable Shares to participate in such Offer to the same extent and on an
economically equivalent basis as the holders of Shire Ordinary Shares, without
discrimination. Without limiting the generality of the foregoing, Shire will use
its reasonable best efforts expeditiously and in good faith to ensure that
holders of Exchangeable Shares may participate in all such Offers without being
required to retract Exchangeable Shares as against ExchangeCo (or, if so
required, to ensure that any such retraction, shall be effective only upon, and
shall be conditional upon, the closing of the Offer and only to the extent
necessary to tender or deposit to the Offer). Nothing herein shall affect the
rights of ExchangeCo to redeem (or CallCo to purchase pursuant to the Redemption
Call Right) Exchangeable Shares, as applicable, in the event of a Shire Control
Transaction.

2.10 OWNERSHIP OF OUTSTANDING SHARES

    Without the prior approval of ExchangeCo and the prior approval of the
holders of the Exchangeable Shares given in accordance with Section 9.2 of the
Share Provisions, Shire covenants and agrees in favour of ExchangeCo that, as
long as any outstanding Exchangeable Shares are owned by any person or entity
other than Shire or any of its Affiliates, Shire will be and remain the direct
or indirect beneficial owner of all issued and outstanding voting shares in the
capital of ExchangeCo and CallCo.

2.11 SHIRE AND AFFILIATES NOT TO VOTE EXCHANGEABLE SHARES

    Shire covenants and agrees that it will appoint and cause to be appointed
proxyholders with respect to all Exchangeable Shares held by it and its
Affiliates for the sole purpose of attending each meeting of holders of
Exchangeable Shares in order to be counted as part of the quorum for each such
meeting. Shire further covenants and agrees that it will not, and will cause its
Affiliates not to, exercise any voting rights which may be exercisable by
holders of Exchangeable Shares from time to time pursuant to the Share
Provisions or pursuant to the provisions of the CANADA BUSINESS CORPORATIONS ACT
(or any successor or other corporate statute by which ExchangeCo may in the
future be governed) with respect to any Exchangeable Shares held by it or by its
Affiliates in respect of any matter considered at any meeting of holders of
Exchangeable Shares.

2.12 STOCK EXCHANGE LISTING

    Shire covenants and agrees in favour of ExchangeCo that, as long as any
outstanding Exchangeable Shares are owned by any person or entity other than
Shire or any of its Affiliates, Shire will use its reasonable efforts (i) to
maintain a listing for such Exchangeable Shares on a Canadian stock exchange and
(ii) to ensure that ExchangeCo remains a "PUBLIC CORPORATION" within the meaning
of the INCOME TAX ACT (Canada).

2.13 EXTENSION OF COVENANTS

    If Shire, or any Affiliates of Shire, becomes the owner of Exchangeable
Shares, Shire's covenants set out in Article 2 shall not benefit the Corporation
in respect of such Exchangeable Shares.

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                                   ARTICLE 3
                                SHIRE SUCCESSORS

3.1 CERTAIN REQUIREMENTS IN RESPECT OF COMBINATION, ETC.

    Shire shall not consummate any transaction (whether by way of
reconstruction, reorganization, consolidation, merger, transfer, sale, lease or
otherwise) whereby all or substantially all of its undertaking, property and
assets would become the property of any other person or, in the case of a
merger, of the continuing corporation resulting therefrom unless:

    (a) such other person or continuing corporation (the "SHIRE SUCCESSOR") by
       operation of law, becomes, without more, bound by the terms and
       provisions of this Agreement or, if not so bound, executes, prior to or
       contemporaneously with the consummation of such transaction, an agreement
       supplemental hereto and such other instruments (if any) as are reasonably
       necessary or advisable to evidence the assumption by the Shire Successor
       of liability for all moneys payable and property deliverable hereunder
       and the covenant of such Shire Successor to pay and deliver or cause to
       be delivered the same and its agreement to observe and perform all the
       covenants and obligations of Shire under this Agreement; and

    (b) such transaction shall be upon such terms and conditions as
       substantially to preserve and not to impair in any material respect any
       of the rights, duties, powers and authorities of the other parties
       hereunder and the holders of the Exchangeable Shares.

3.2 VESTING OF POWERS IN SUCCESSOR

    Whenever the conditions of Section 3.1 have been duly observed and
performed, the parties, if required by Section 3.1, shall execute and deliver a
supplemental agreement hereto and thereupon Shire Successor shall possess and
from time to time may exercise each and every right and power of Shire under
this Agreement in the name of Shire or otherwise and any act or proceeding by
any provision of this Agreement required to be done or performed by the Board of
Directors of Shire or any officers of Shire may be done and performed with like
force and effect by the directors or officers of such Shire Successor.

3.3 WHOLLY-OWNED SUBSIDIARIES

    Nothing herein shall be construed as preventing the amalgamation or merger
of any wholly-owned direct or indirect subsidiary of Shire with or into Shire or
the winding-up, liquidation or dissolution of any wholly-owned subsidiary of
Shire provided that all of the assets of such subsidiary are transferred to
Shire or another wholly-owned direct or indirect subsidiary of Shire and any
such transactions are expressly permitted by this Article 3.

                                   ARTICLE 4
                                    GENERAL

4.1 TERM

    This Agreement shall come into force and be effective as of the date hereof
and shall terminate and be of no further force and effect at such time as no
Exchangeable Shares (or securities or rights convertible into or exchangeable
for or carrying rights to acquire Exchangeable Shares) are held by any person or
entity other than Shire and any of its Affiliates.

4.2 CHANGES IN CAPITAL OF SHIRE AND EXCHANGECO

    At all times after the occurrence of any event contemplated pursuant to
Sections 2.7 and 2.8 hereof or otherwise, as a result of which either Shire
Ordinary Shares or the Exchangeable Shares or both are in any

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way changed, this agreement shall forthwith be amended and modified as necessary
in order that it shall apply with full force and effect, MUTATIS MUTANDIS, to
all new securities into which Shire Ordinary Shares or the Exchangeable Shares
or both are so changed and the parties hereto shall execute and deliver an
agreement in writing giving effect to and evidencing such necessary amendments
and modifications.

4.3 SEVERABILITY

    If any provision of this Agreement is held to be invalid, illegal or
unenforceable, the validity, legality or enforceability of the remainder of this
Agreement shall not in any way be affected or impaired thereby and this
Agreement shall be carried out as nearly as possible in accordance with its
original terms and conditions.

4.4 AMENDMENTS, MODIFICATIONS

    This Agreement may not be amended or modified except by an agreement in
writing executed by ExchangeCo, CallCo and Shire and approved by the holders of
the Exchangeable Shares in accordance with Section 9.2 of the Share Provisions.

4.5 MINISTERIAL AMENDMENTS

    Notwithstanding the provisions of Section 4.4, the parties to this Agreement
may in writing at any time and from time to time, without the approval of the
holders of the Exchangeable Shares, amend or modify this Agreement for the
purposes of:

    (a) adding to the covenants of any or all parties provided that the Board of
       Directors of each of ExchangeCo, CallCo and Shire shall be of the good
       faith opinion that such additions will not be prejudicial to the rights
       or interests of the holders of the Exchangeable Shares;

    (b) making such amendments or modifications not inconsistent with this
       Agreement as may be necessary or desirable with respect to matters or
       questions which, in the good faith opinion of the Board of Directors of
       each of ExchangeCo, CallCo and Shire, it may be expedient to make,
       provided that each such Board of Directors shall be of the good faith
       opinion that such amendments or modifications will not be prejudicial to
       the rights or interests of the holders of the Exchangeable Shares; or

    (c) making such changes or corrections which, on the advice of counsel to
       ExchangeCo, CallCo and Shire, are required for the purpose of curing or
       correcting any ambiguity or defect or inconsistent provision or clerical
       omission or mistake or manifest error, provided that the Boards of
       Directors of each of ExchangeCo, CallCo and Shire shall be of the good
       faith opinion that such changes or corrections will not be prejudicial to
       the rights or interests of the holders of the Exchangeable Shares.

4.6 MEETING TO CONSIDER AMENDMENTS

    ExchangeCo, at the request of Shire, shall call a meeting or meetings of the
holders of the Exchangeable Shares for the purpose of considering any proposed
amendment or modification requiring approval pursuant to Section 4.4 hereof. Any
such meeting or meetings shall be called and held in accordance with the bylaws
of ExchangeCo, the Share Provisions and all applicable laws.

4.7 AMENDMENTS ONLY IN WRITING

    No amendment to or modification or waiver of any of the provisions of this
Agreement otherwise permitted hereunder shall be effective unless made in
writing and signed by all of the parties hereto.

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4.8 ENUREMENT

    This Agreement shall be binding upon and enure to the benefit of the parties
hereto and their respective successors and assigns.

4.9 NOTICES TO PARTIES

    All notices and other communications required or permitted to be delivered
to a party under this Agreement shall be in writing and shall be deemed to have
been properly delivered, given or received (a) upon receipt when delivered by
hand or (b) two business days after being sent by registered mail or by courier
or express delivery service or by facsimile, provided that in each case the
notice or communication is sent to the address or facsimile telephone number set
forth beneath the name of such party below:

    (a) if to ExchangeCo:

           Shire Acquisition Inc.

           c/o Shire Pharmaceuticals Group Plc

           East Anton Andover

           Hampshire, England

           England SP10 5RG

           Fax: 012 64 334 658

           Attention: Rolf Stahel

    (b) if to Shire or CallCo:

           Shire Pharmaceuticals Group Plc or 3829359 Canada Inc.

           c/o Shire Pharmaceuticals Group Plc

           East Anton Andover

           Hampshire, England

           England SP10 5RG

           Fax: 012 64 334 658

           Attention: Rolf Stahel

4.10 COUNTERPARTS

    This Agreement may be executed in counterparts, each of which shall be
deemed an original, and all of which taken together shall constitute one and the
same instrument.

4.11 JURISDICTION

    This Agreement shall be construed and enforced in accordance with the laws
of the Province of Quebec and the laws of Canada applicable therein.

    IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be duly
executed as of the date first above written.

                                            SHIRE PHARMACEUTICALS GROUP PLC

                                            By: ________________________________

                                            Name:

                                            Title:

                                            3829359 CANADA INC.

                                            By:_________________________________

                                            Name:

                                            Title:

                                            SHIRE ACQUISITION INC.

                                            By: ________________________________

                                            Name:

                                            Title:

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