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                                                                    Exhibit 4.13

THIS INSTRUMENT is made by way of deed on 6 June 2006

BY:

PROTHERICS PLC (No.02459087) whose registered office is at The Heath Business
and Technical Park, Runcorn, Cheshire WA7 4QF (the "COMPANY")

WHEREAS the Company has, pursuant to its Memorandum and Articles of Association
and by resolution of its board of directors created and authorised the issue of
a maximum nominal amount of E1,050,000 Unsecured Convertible Loan Notes 2026 to
be constituted as hereinafter provided and subject to, and with the benefit of,
the schedules hereto which shall be deemed to form part of this instrument.

BY THIS DEED THE COMPANY DECLARES AND COVENANTS AS FOLLOWS:

1.    DEFINITIONS AND INTERPRETATION

1.1   In this instrument and the schedules the following words and expressions
      shall have the following meanings, unless the context otherwise requires:

      "BUSINESS DAY" means a day (excluding Saturdays) on which banks generally
      are open In London for the transaction of normal banking business;

      "CONDITIONS" means the conditions of the Notes as set out in schedule 2;

      "DIRECTORS" means the board of directors for the time being of the
      Company;

      "NORTH AMERICAN PERSON" means:

      (a)   any individual who is a resident or individual of the United States;

      (b)   a corporation, partnership or other entity created or organised in
            or under the laws of the United States or any state thereof or an
            estate or trust the income of which is subject to United States
            federal income taxation regardless of its source; and

      (c)   any individual, corporation, partnership, trust or other entity
            resident In Canada,

      provided that the term "NORTH AMERICAN PERSON" shall not include A branch
      or agency of a United States bank or insurance company that is operating
      outside the United States for valid business reasons as a locally
      registered branch or agency engaged in the banking and insurance business
      and not solely for the purpose of investing in securities not registered
      under the United States Securities Act of 1933, as amended;

      "NOTES" means the E1,050,000 Unsecured Convertible Loan Notes 2006
      constituted by this instrument or, as the case may be, the principal
      amounts represented by them and for the time being issued and outstanding;

      "NOTEHOLDER" means a person whose name is entered in the Register as the
      holder of a Note;

      "ORDINARY SHARES" means ordinary shares of 2p each in the capital of the
      Company or any other ordinary shares of the Company into which such shares
      may be consolidated, sub-divided or converted and "ORDINARY SHARE CAPITAL"
      shall be interpreted accordingly;

      "REGISTER" means the register of holders of the Notes kept by or on behalf
      of the Company; and

      "UNITED STATES" means the United States of America.


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1.2   Subject as herein expressly defined any words and expressions defined in
      the Companies Act 1985 and the Companies Act 1989 shall have the meanings
      therein ascribed to them.

1.3   References to this "INSTRUMENT" or this "DEED" include, where the context
      so admits, the schedules hereto.

2.    AMOUNT OF THE NOTES

2.1   The aggregate nominal amount of the Notes constituted by this instrument
      is limited to E1,050,000.

2.2   The Notes will be issued in registered form in denominations of E1 in
      nominal amount or integral multiples thereof.

3.    STATUS OF THE NOTES

3.1   The Notes represent a direct and unsecured obligation of the Company for
      the due and punctual payment of the principal in respect of them and for
      the performance of all the obligations of the Company with respect to
      them.

3.2   The Notes when issued will rank pari passu equally and rateably without
      discrimination or preference as unsecured obligations of the Company and
      with all other unsecured indebtedness of the Company except to the extent
      provided by law.

3.3   The Notes shall be known as E1,050,000 Unsecured Convertible Loan Notes
      2026.

4.    CERTIFICATE FOR NOTES

4.1   Each Noteholder shall be entitled to a certificate stating the nominal
      amount of the Notes held by him. Each certificate shall bear a denoting
      number, and shall (subject as provided in this clause 4.1) be executed
      under the seal (or any securities seal) of the Company, shall be
      substantially in the form set out in schedule 1 and shall have endorsed on
      it conditions in the form or substantially in the form set out in schedule
      2. Where permitted by law, a certificate signed by one Director and the
      Secretary or by two Directors and expressed to be executed by the Company
      shall have the same effect as if executed under the seal. The Company
      shall not be bound to register joint holders of any Note. When a
      Noteholder has redeemed or transferred part only of his Notes the old
      certificate shall be cancelled and a new certificate for the balance of
      such Notes issued without charge.

4.2   The Directors may by resolution (either generally or in any particular
      case or cases) determine that the signatures required by clause 4.1 shall
      be affixed by means of some method or system of mechanical signature.

5.    COVENANTS BY THE COMPANY

      The Company HEREBY COVENANTS with the Noteholders and each of them to
      comply with the terms of the Notes and to observe and perform the
      conditions, which conditions shall be deemed to be incorporated in this
      instrument and shall be binding on the Company and the Noteholders and all
      persons claiming through or under them respectively.

6.    REGISTER OF NOTEHOLDERS

      The Company shall cause a register to be maintained in respect of the
      Notes.

7.    FOREIGN NOTEHOLDERS

      The Notes have not been and will not be registered under the United States
      Securities Act of 1933, as amended, nor under any of the relevant
      securities laws of any province or


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      territory of Canada or Australia. Accordingly, unless an exemption under
      such Act or laws is applicable, the Notes may not be offered, sold or
      delivered, directly or indirectly, in or into the United States, Canada or
      Australia or to or for the account or benefit of any North American person
      or resident of Canada or Australia.

8.    FURTHER NOTES

      The Company shall be entitled from time to time, by resolution of the
      board or of a duly authorised committee thereof to create and issue
      further unsecured convertible loan notes to be constituted by deed or
      instrument expressed to be supplemental hereto either so as to be
      identical in all respects and form a single series with the Notes or to
      carry such rights as the board may think fit.

9.    GOVERNING LAW

      This instrument (and any dispute, controversy, proceedings or claim of
      whatever nature arising out of or in any way relating to this instrument
      or the constitution of the Notes) shall be governed by and construed in
      accordance with English law. The Company hereby irrevocably submits to
      the non-exclusive jurisdiction of the High Court of Justice in London for
      the purpose of hearing and determining any dispute arising out of, or in
      connection with, this instrument and for the purpose of enforcement of any
      judgment against its assets.

IN WITNESS whereof this instrument has been executed as a deed and has been
delivered on the date which appears first on page 1.


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