<PAGE>

                                                                    Exhibit 4.22

                                                                           FINAL

                                   ----------

                                  RULES OF THE
                                 PROTHERICS PLC
                        2005 EXECUTIVE SHARE OPTION PLAN

                                   ----------

APPROVED BY SHAREHOLDERS OF THE COMPANY AT AN EXTRAORDINARY GENERAL MEETING HELD
ON 27 JANUARY 2005

APPROVED BY THE BOARD AT A MEETING HELD ON [________________]

UK APPROVED ADDENDUM APPROVED BY THE INLAND REVENUE ON 23 JUNE 2005 UNDER
REFERENCE 22911/PC

                                (DELOITTE LOGO)

                                4 Brindley Place
                                Birmingham B1 2HZ

                               Tel: 0121 632 6000


                                                                               1

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                                    CONTENTS

<TABLE>
<S>                                                                          <C>
1.  DEFINITIONS AND INTERPRETATION........................................     3
2.  GRANT OF OPTIONS......................................................     9
3.  LIMIT ON SHARE ISSUE..................................................    11
4.  RIGHTS OF EXERCISE AND LAPSE OF OPTIONS...............................    12
5.  TAKEOVER, RECONSTRUCTION AND WINDING-UP...............................    14
6.  MANNER OF EXERCISE....................................................    18
7.  ISSUE OR TRANSFER OF SHARES...........................................    19
8.  ADJUSTMENTS...........................................................    19
9.  ADMINISTRATION........................................................    20
10. ALTERATIONS...........................................................    21
11. LEGAL ENTITLEMENT.....................................................    23
12. GENERAL...............................................................    24
</TABLE>


                                                                               2

<PAGE>

                                  RULES OF THE

                                 PROTHERICS PLC
                        2005 EXECUTIVE SHARE OPTION PLAN

1.   DEFINITIONS AND INTERPRETATION

1.1  In this Plan, the following words and expressions shall have, where the
     context so admits, the meanings set forth below.

<TABLE>
<S>                              <C>
"APPROPRIATE PERIOD"             The meaning given by Paragraph 26(3) of
                                 Schedule 4 to ITEPA.

"ANNUAL REMUNERATION"            The higher of:

                                 (A)  the annual rate of the Participant's
                                      remuneration (exclusive of bonuses and
                                      commissions in the form of cash, Shares or
                                      other assets and of benefits-in-kind, from
                                      all Participating Companies at the Date of
                                      Grant); and

                                 (B)  the remuneration (exclusive of bonuses and
                                      commissions in the form of cash, Shares or
                                      other assets and of benefits-in-kind) paid
                                      or payable to the Participant by all
                                      Participating Companies in, or in respect
                                      of, the 12 months immediately preceding
                                      the Date of Grant.

"BOARD"                          The board of directors for the time being of
                                 the Company or a duly authorised committee
                                 thereof.

"COMMITTEE"                      Either:

                                 (A)  in relation to the grant of Options to
                                      executive directors of the Company, the
                                      remuneration committee; or

                                 (B)  in relation to the grant of Options to
                                      other directors and employees, such other
                                      duly
</TABLE>


                                                                               3

<PAGE>

<TABLE>
<S>                              <C>
                                      authorised committee of the Board as may
                                      be appointed from time to time.

"COMPANY"                        Protherics PLC registered in England and Wales
                                 under No. 02459087.

"CONTROL"                        The meaning given by Section 840 of the Taxes
                                 Act.

"DAILY OFFICIAL LIST"            The register of listed securities and the
                                 prices of transactions published by the London
                                 Stock Exchange.

"DATE OF GRANT"                  The date on which an Option is granted.

"DEALING DAY"                    Any day on which the London Stock Exchange is
                                 open for the transaction of business.

"ELIGIBLE EMPLOYEE"              Any person who at the Date of Grant is:

                                 (A)  an employee of a Participating Company,
                                      who is not a director, or

                                 (B)  an executive director of a Participating
                                      Company who devotes substantially the
                                      whole of his working time to the business
                                      of a Participating Company, and

                                 (C)  more than six months from his anticipated
                                      date of Retirement.

"EMPLOYEES' SHARE SCHEME"        The meaning given by Section 743 of the
                                 Companies Act 1985.

"EXECUTIVE SHARE OPTION PLAN"    A share option plan in which participation is
                                 discretionary (for the avoidance of doubt,
                                 excluding any Sharesave Plan).

"GRANT PERIOD"                   The period of 42 days commencing on the day
                                 after any of the following days:

                                 (A)  the day on which the Plan is adopted by
                                      the Company;
</TABLE>


                                                                               4

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<TABLE>
<S>                              <C>
                                 (B)  the day on which the UK Approved Addendum
                                      is approved by the Inland Revenue;

                                 (C)  the day on which the Company makes an
                                      announcement of its results for the last
                                      preceding financial year, half-year or
                                      other period;

                                 (D)  any day on which the Grantor resolves that
                                      exceptional circumstances exist which
                                      justify the grant of Options;

                                 (E)  any day on which any change to the
                                      legislation affecting Executive Share
                                      Option Plans is proposed or made;

                                 (F)  the date of commencement of an Eligible
                                      Employee's employment with a Participating
                                      Company provided that the Eligible
                                      Employee is not already employed by a
                                      Participating company, but only in respect
                                      of that Eligible Employee;

                                 PROVIDED THAT if by reason of primary or
                                 secondary legislation, regulation or government
                                 directive or by reason of any agreement to
                                 which the Company is or maybe a party, the
                                 Grantor is restricted from granting Options
                                 under the Plan during the period specified
                                 above the relevant Grant Period shall be 42
                                 days commencing on the day after the
                                 restriction is lifted.

"GRANTOR"                        The Committee (acting on behalf of the Company)
                                 or the Board or the Trustees acting on the
                                 recommendation of, or with the consent of, the
                                 Committee, as the case may be.

"GROUP MEMBER"                   A Participating Company or a body corporate
                                 which is
</TABLE>


                                                                               5

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<TABLE>
<S>                              <C>
                                 (within the meaning of Section 736 of the
                                 Companies Act 1985) the Company's holding
                                 company or a Subsidiary of the Company's
                                 holding company.

"ITEPA"                          The Income Tax (Earnings and Pensions) Act
                                 2003.

"LONDON STOCK EXCHANGE"          London Stock Exchange plc or any successor body
                                 carrying on the business of London Stock
                                 Exchange plc.

"MARKET VALUE"                   In relation to a Share on any day:

                                 (A)  if and so long as the Shares are listed on
                                      the London Stock Exchange, their closing
                                      middle market quotation (as derived from
                                      the Daily Official List) for the
                                      immediately preceding Dealing Day, or if
                                      the Grantor determines, the average of the
                                      closing middle market quotations over the
                                      three immediately preceding Dealing Days,
                                      or such other price over such period as
                                      may be agreed in writing with the Inland
                                      Revenue (provided that Options are granted
                                      within 30 days of the first day by
                                      reference to which the Market Value was
                                      calculated); or

                                 (B)  in any other case, their market value as
                                      determined in accordance with Part VIII of
                                      the Taxation of Chargeable Gains Act 1992
                                      or similar non-UK legislation.

"OPTION"                         A right to acquire Shares under the Plan which
                                 is either subsisting or is proposed to be
                                 granted.

"OPTION PERIOD"                  The period commencing on the Date of Grant and
                                 terminating on the latest date determined by
                                 reference to Rule 2.6.4.

"OPTION PRICE"                   The price per Share, as determined by the
                                 Grantor at the Date of Grant, at which an
                                 Eligible Employee may
</TABLE>


                                                                               6

<PAGE>

<TABLE>
<S>                              <C>
                                 acquire Shares upon the exercise of an Option
                                 granted to him being not less than the higher
                                 of

                                 (A)  the Market Value of a Share (on the Date
                                      of Grant); and

                                 (B)  if the Shares are to be subscribed, their
                                      nominal value,

                                 but subject to any adjustment pursuant to Rule
                                 8.

"PARTICIPANT"                    Any Eligible Employee to whom an Option has
                                 been granted, or (where the context so admits)
                                 the personal representative of any such person.

"PARTICIPATING COMPANY"          (A)  The Company; and

                                 (B)  any other company which is under the
                                      Control of the Company, and is a
                                      Subsidiary of the Company except one which
                                      the Grantor has designated shall not be a
                                      Participating Company.

"PERFORMANCE PERIOD"             The period of three years from the Date of
                                 Grant by reference to which the Grantor will
                                 determine whether any conditions imposed under
                                 Rule 2.3 have been fulfilled.

"PLAN"                           The Protherics PLC 2005 Executive Share Option
                                 Plan in its present form or as from time to
                                 time amended in accordance with the provisions
                                 hereof.

"RECOGNISED INVESTMENT           The meaning given by the Financial Services and
EXCHANGE"                        Markets Act 2000.

"RETIREMENT"                     Retirement on or after the date specified in
                                 the Participant's contract of employment.

"RULES"                          The rules of the Plan as amended from time to
                                 time.

"SHARE"                          A fully paid ordinary share in the capital of
                                 the Company.
</TABLE>


                                                                               7

<PAGE>

<TABLE>
<S>                              <C>
"SHARESAVE PLAN"                 A savings related share option plan approved
                                 under Schedule 3 to ITEPA.

"SUBSIDIARY"                     The meaning given by Section 736 of the
                                 Companies Act 1985.

"TAX LIABILITY"                  A liability to account for any tax, national
                                 insurance, social security or other levy in
                                 respect of an Option by the Company or any
                                 Participating Company ("the Relevant Company"),
                                 whether by reason of grant, exercise or
                                 otherwise, including for the avoidance of
                                 doubt:

                                      (A) any liability to pay secondary Class 1
                                      National Insurance Contributions for which
                                      an agreement or election has been entered
                                      into under paragraph 3 A or 3B of Schedule
                                      1 to the Social Security Contributions and
                                      Benefits Act 1992 ("National Insurance
                                      Election"); and

                                      (B) any liability arising after
                                      termination of a Participant's employment
                                      for whatever reason and which may arise or
                                      be incurred in any jurisdiction whatever,
                                      and by the law of the same jurisdiction
                                      may or shall be recovered from the person
                                      entitled to the Option,

                                 but subject to (A) above, not including any
                                 secondary Class 1 National Insurance
                                 Contributions.

"TAXES ACT"                      The Income and Corporation Taxes Act 1988.

"TREASURY SHARES"                Any shares bought and held by the Company in
                                 accordance with Section 162A(3) of the
                                 Companies Act 1985 (as amended).

"TRUSTEES"                       The trustee or trustees for the time being of
                                 any
</TABLE>


                                                                               8

<PAGE>

<TABLE>
<S>                              <C>
                                 employee benefit trust established for the
                                 benefit of all or substantially all of the
                                 Eligible Employees.

"UK APPROVED ADDENDUM"           That part of the Plan, comprising the UK
                                 Approved Addendum attached hereto, which has
                                 been approved by the UK Inland Revenue in
                                 accordance with Schedule 4 to ITEPA.
</TABLE>

1.2  Words and expressions not otherwise defined herein have the same meaning
     they have in the Taxes Act or ITEPA (as the case may be).

1.3  Where the context so admits or requires words importing the singular shall
     include the plural and vice versa and words importing the masculine shall
     include the feminine.

1.4  Reference in the Rules of the Plan to any statutory provisions are to those
     provisions as amended, extended or re-enacted from time to time, and shall
     include any regulations made thereunder. The Interpretation Act 1978 shall
     apply to these Rules on the same basis as if they were an Act of
     Parliament.

1.5  The headings in the Rules of the Plan are for the sake of convenience only
     and should be ignored when construing the Rules.

2.   GRANT OF OPTIONS

2.1  The Grantor may during a Grant Period grant Options at the Option Price to
     such Eligible Employees as it may in its absolute discretion determine.

2.2  When granting an Option, the Grantor may make its exercise conditional upon
     an Eligible Employee agreeing to enter into a National Insurance Election
     (or its overseas equivalent to the extent this is lawful).

2.3  The Grantor will retain the discretion not to attach performance
     conditions. However for options granted to an executive director of the
     Company, the Grantor must at the Date of Grant impose such condition or
     conditions on the exercise of an Option as it may determine. Such
     conditions:

     2.3.1 must be objective and stated in writing at the Date of Grant; and

     2.3.2 must not be waived, varied or amended by the Grantor unless in
          accordance with the terms of such conditions or where events happen
          which cause the Grantor, acting fairly and reasonably, to consider
          that a waived, varied or


                                                                               9

<PAGE>

          amended condition would be appropriate and that the waived, varied or
          amended condition would not be more or less difficult to satisfy than
          the condition first imposed.

2.4  The Grantor may from time to time set limits for the Market Value (measured
     at the relevant Date of Grant) of Shares which may be placed under option
     to any Eligible Employee in respect of any financial year of the Company,
     by reference to that Eligible Employee's Annual Remuneration PROVIDED THAT
     no Eligible Employee shall be granted Options which would, at the time they
     are granted, cause the aggregate Market Value of Shares which he may
     acquire, in pursuance of Options granted to him under the Plan in any
     financial year to exceed 200% of his Annual Remuneration other than in
     exceptional circumstances, at the discretion of the Grantor. If such limits
     have been set, they may not be exceeded without the prior approval of the
     Board provided that no account shall be taken of any Shares which may be
     acquired pursuant to any Option granted solely for the purpose of ensuring
     that a Participant is not materially disadvantaged by agreeing to enter
     into a National Insurance Election or its overseas equivalent to the extent
     this is lawful.

2.5  The grant of an Option or the delivery of any shares following its exercise
     shall be subject to obtaining any approval or consent required under any
     applicable laws, regulations of governmental authority and the requirements
     of the London Stock Exchange and any other Recognised Investment Exchange
     on which the Shares are traded.

2.6  The grant of an Option shall be evidenced by execution of a legally binding
     document on behalf of the Company which document may be in respect of an
     individual Option or any number of Options granted at the same time. As
     soon as practicable after the Date of Grant, the Grantor shall issue to
     each Participant a certificate in respect of the Option which may be under
     the autographic or facsimile signature of an officer of the Company and in
     such form as the Grantor may from time to time prescribe. Such certificate
     must state:

     2.6.1 the Option Price;

     2.6.2 the number of Shares over which the Option has been granted to the
          Participant;

     2.6.3 any condition or conditions imposed pursuant to Rule 2.3 on the
          exercise of the Option;


                                                                              10
<PAGE>

     2.6.4 the first date on which any part of the Option becomes capable of
          exercise and any subsequent dates on which any remaining part of the
          Option becomes capable of exercise;

     2.6.5 the Date of Grant; and

     2.6.6 the date on which the Option will lapse pursuant to Rule 4.5.1.

2.7  No payment by the Participant shall be required on the grant of an Option.

2.8  Subject to the rights of exercise by the Participant's personal
     representatives pursuant to Rule 4.2, every Option shall be personal to the
     Participant to whom it is granted and shall not be transferable or in any
     way alienable without the prior written agreement of the Grantor and such
     transfer shall be subject to such conditions as the Board may prescribe at
     that time.

2.9  A Participant may surrender his Option in whole or in part within the
     period of 30 days immediately following the Date of Grant and if an Option,
     or any part of an Option, is so surrendered, it shall be deemed for all
     purposes not to have been granted.

3.   LIMIT ON SHARE ISSUE

3.1  The number of Shares which may be allocated under the Plan on any day shall
     not, when added to the aggregate of the number of Shares which have been
     allocated during that and the previous nine years under the Plan and under
     any other Employees' Share Scheme (including a Sharesave plan) adopted by
     the Company or any other company when it is under the Company's Control,
     exceed such number as represents ten per cent of the ordinary share capital
     of the Company in issue immediately prior to that day.

3.2  In determining the above limit:

     3.2.1 any Shares allocated to the Trustees under the Plan and any other
          Employees' Share Scheme (including, for the purposes of Rule 3.1 only,
          a Sharesave plan) adopted by the Company shall be included;

     3.2.2 any Shares allocated in satisfaction of an Option pursuant to Rule
          7.7 shall be included;


                                                                              11

<PAGE>

     3.2.3 no account shall be taken of any Shares where the right to acquire
          such Shares was released or lapsed without being exercised, including
          pursuant to Rule 2.9 above; and

     3.2.4 no account shall be taken of any Shares where the right to acquire
          such Shares has been or is to be satisfied other than by the issue or
          allotment of any part of the share capital of the Company.

3.3  For the avoidance of doubt, references in this Rule 3 to the "allocation"
     of Shares shall mean, in the case of any share option plan, the placing of
     unissued Shares or Treasury Shares under option, and, in relation to other
     types of Employees' Share Schemes, shall mean the issue and allotment of
     Shares or Treasury Shares.

4.   RIGHTS OF EXERCISE AND LAPSE OF OPTIONS

4.1  An Option:

     4.1.1 save as provided in Rules 4.2, 4.3, and 5 below, shall not be
          exercised earlier than the third anniversary of the Date of Grant, or
          such other later or earlier date as is determined by the Grantor at
          the Date of Grant pursuant to Rule 2.6.4;

     4.1.2 save as provided in Rules 4.2, 4.3, and 5 below, may only be
          exercised by a Participant whilst he is a director or employee of a
          Group Member;

     4.1.3 may only be exercised if any conditions upon exercise (as waived,
          varied or amended) imposed pursuant to Rule 2.3 have been fulfilled to
          the satisfaction of the Grantor unless the Grantor, in its absolute
          discretion determines otherwise.

4.2  An Option may be exercised in the period of one year following the death of
     a Participant subject to Rule 4.1.3 unless the Grantor determines
     otherwise.

4.3  If a Participant ceases to hold office or employment with a Group Member as
     a result of:

     4.3.1 illness, injury or disability;

     4.3.2 retirement or early retirement;

     4.3.3 redundancy within the meaning or the Employment Rights Act 1996 (or
          applicable equivalent foreign legislation);


                                                                              12

<PAGE>

     4.3.4 the company which employs him ceasing to be a Group Member,

     4.3.5 the transfer or sale of the undertaking or part undertaking in which
          he is employed to a person who is not a Group Member, or

     4.3.6 or any other reason determined at the discretion of the Grantor,
          acting fairly and reasonably, within three months of the cessation,

     having regard to the extent that conditions imposed under Rule 2.3 have
     been met, a proportion of an Option may be exercised, from the date of
     cessation until six months thereafter, which proportion will reflect the
     period during which the Participant continued to hold office or employment
     during the Performance Period.

4.4  An Option cannot be exercised under Rule 4.3.6 prior to the Grantor
     exercising its discretion.

4.5  Options shall lapse upon the occurrence of the earliest of the following
     events:

     4.5.1 the tenth anniversary of the Date of Grant

     4.5.2 the expiry of any of the periods specified in Rules 4.2, 4.3 and 4.4
          (save that if at the time any of the applicable periods under Rules
          4.3 and 4.4 expire, time is running under the period in Rule 4.2, the
          Option shall not lapse by reason of this Rule 4.5.2 until the expiry
          of the period specified in Rule 4.2);

     4.5.3 the expiry of any of the periods specified in Rules 5.1, 5.3, 5.4 and
          5.5 save where an Option is released in consideration of the grant of
          a New Option (during one of the periods specified in Rules 5.1, 5.3 or
          5.4) pursuant to Rule 5.6);

     4.5.4 the Participant ceasing to hold an office or employment or giving or
          being given notice to terminate employment with a Group Member in any
          circumstances other than:

          4.5.4.1 where the cessation of office or employment arises on any of
               the grounds specified in Rules 4.2, or 4.3 provided that an
               Option shall not be regarded as having lapsed pursuant to this
               Rule 4.5.4.1 if the Grantor determines within three months of the
               Participant ceasing to hold his office or employment that the
               Participant ceased to hold the office or employment in accordance
               with Rule 4.3.6; or


                                                                              13

<PAGE>

          4.5.4.2 where the cessation of office or employment arises on any
               ground whatsoever during any of the periods specified in Rule 5
               save where an Option is released in consideration of the grant of
               a New Option (during one of the periods specified in Rules 5.1,
               5.3 or 5.4) pursuant to Rule 5.6;

     4.5.5 subject to Rule 5.5, the passing of an effective resolution, or the
          making of an order by the Court, for the winding-up of the Company;

     4.5.6 the Participant being deprived of the legal or beneficial ownership
          of the Option by operation of law, or doing or omitting to do anything
          which causes him to be so deprived or being declared bankrupt; and

     4.5.7 the Participant purporting to transfer or dispose of the Option or
          any rights in respect of it other than as permitted under Rule 2.8.

4.6  No Option may be granted, exercised, released or surrendered at a time when
     such grant, exercise, release or surrender would not be in accordance with
     the "Model Code on Directors' Dealings in Securities" issued by the UK
     Listing Authority as amended from time to time.

4.7  For the purpose of this Plan, no person shall be treated as ceasing to hold
     an office or employment with a Group Member by virtue of which that person
     is eligible to participate in the Plan until that person ceases to hold any
     office or employment with any Group Member.

4.8  For the purpose of this Plan, a woman on maternity leave will not cease to
     hold an office or employment with a Group Member until the earlier of the
     date on which she notifies her employer of her intention not to return or
     the date on which she ceases to have statutory or contractual rights to
     return to work.

4.9  If there is any conflict between any of the provisions of this rule 4 the
     provision which results in the shortest exercise period of the Option will
     prevail. However, the Grantor may permit an Option holder to exercise his
     Options within any applicable longer period set out in rules 4.2 and 4.3.

5.   TAKEOVER, RECONSTRUCTION AND WINDING-UP

5.1  Subject to Rules 5.3, 5.4 and 5.6 below, if any person obtains Control of
     the Company as a result of making, either:


                                                                              14

<PAGE>

     5.1.1 a general offer to acquire the whole of the issued ordinary share
          capital of the Company (which is either unconditional or is made on a
          condition such that if it is satisfied the person making the offer
          will have Control of the Company); or

     5.1.2 a general offer to acquire all the shares in the Company which are of
          the same class as the Shares, (in either case disregarding any shares
          already owned by it or by any company associated with it), an Option
          may, subject to Rule 5.10 be exercised within six months (or such
          earlier date as the Grantor may determine) of the earliest of:

     (a)  the date, being prior to the date on which the person making the offer
          under Rule 5.1.1 or 5.1.2 obtains Control of the Company, on which the
          Board resolves that, in its reasonable opinion, to do otherwise would
          result in a loss of a corporation tax deduction pursuant to Schedule
          23 of the Finance Act 2003; or

     (b)  the time when the person making the offer has obtained Control of the
          Company and any condition subject to which the offer is made has been
          satisfied.

     In each case, the Grantor shall notify Participants in writing as soon as
     possible and in any event with sufficient time to exercise their Options.
     Such exercise of Options shall be done in accordance with any procedure set
     down by the Grantor.

5.2  For the purpose of Rule 5.1 a person shall be deemed to have obtained
     Control of the Company if he and others acting in concert (as defined by
     the City Code on Take-overs and Mergers) with him have together obtained
     Control of it

5.3  If any person becomes bound or entitled to acquire Shares under Sections
     428 to 430F of the Companies Act 1985 subject to Rule 5.10 an Option may be
     exercised within a period of four weeks beginning with the date on which
     that person becomes so bound or entitled.

5.4  Subject to Rule 5.6, if under Section 425 of the Companies Act 1985 it is
     proposed that the Court sanctions a compromise or arrangement proposed for
     the purposes of or in connection with a plan for the reconstruction of the
     Company or its amalgamation with any other company or companies, the
     following apply:


                                                                              15

<PAGE>

     5.4.1 the Company shall give notice thereof to all Participants at the same
          time as it sends notices to members of the Company calling the meeting
          to consider such a compromise or arrangement;

     5.4.2 the Participant may then, subject to Rule 5.10 exercise the Option
          subject to the terms of this Rule 5.4 before the earlier of the expiry
          of six months from the date of such notice and the date on which the
          Court sanctions the compromise or arrangement;

     5.4.3 the exercise of an Option under this Rule 5.4 shall be conditional
          on:

          5.4.3.1 such compromise or arrangement being sanctioned by the Court;
               and

          5.4.3.2 the Participant agreeing to transfer or otherwise deal with
               any Shares issued to him in order that he is placed in the same
               position (so far as possible) as would have been the case if such
               Shares had been subject to such compromise or arrangement;

     5.4.4 the Option shall then lapse conditionally on such compromise or
          arrangement sanctioned by the Court becoming effective.

5.5  If notice is duly given of a resolution for the voluntary winding-up of the
     Company, the Company shall give notice thereof to all Participants. Subject
     to Rule 5.6, and subject to Rule 5.10 an Option may then be exercised until
     the resolution is duly passed or defeated or the meeting concluded or
     adjourned sine die provided that any such exercise of an Option pursuant to
     this Rule 5.5 shall be conditional upon the said resolution being duly
     passed. If such resolution is duly passed all Options shall, to the extent
     that they have not been exercised, lapse immediately.

5.6  If Options become exercisable pursuant to any of Rules 5.1, 5.3 or 5.4
     above (where this occurs as a result of a company obtaining Control in the
     case of Rules 5.1 and 5.4 or as a result of a company becoming bound or
     entitled in accordance with Rule 5.3), any Participant may at any time
     within the Appropriate Period, by agreement with the relevant company,
     release any Option which has not lapsed ("the Old Option") in consideration
     of the grant to him of an Option ("the New Option") which is equivalent to
     the Old Option but relates to shares in a different company (whether the
     company which has obtained Control of the Company itself or some other
     company).

5.7  For the purposes of Rule 5.6 the provisions of the Plan shall be construed
     as if:


                                                                              16

<PAGE>

     5.7.1 the New Option was an option granted under the Plan at the same time
          as the Old Option;

     5.7.2 except for the purpose of the definition of "Participating Company"
          in Rule 1 and the reference to "the Company" in Rule 10.2, the
          reference to Protherics PLC in the definition of "the Company" in Rule
          1 were a reference to the different company mentioned in Rule 5.6;

     5.7.3 subject to Rule 5.7.4 any conditions specified pursuant to Rule 2.3
          shall not apply; and

     5.7.4 where Rule 5.8 applies, any conditions specified pursuant to Rule 2.3
          shall apply in their original form unless the Grantor determines in
          accordance with Rule 2.3.2 that it would be appropriate for such
          conditions to be varied or waived in full or in part.

5.8  Rules 5.1, 5.3 and 5.4 above shall not apply where:

     5.8.1 the events form part of a scheme or arrangement whereby Control of
          the Company is obtained by another company ("the Acquiring Company");

     5.8.2 immediately after the Acquiring Company obtains Control, the issued
          equity share capital of the Acquiring Company is owned substantially
          by the same persons who were equity shareholders of the Company
          immediately prior to the Acquiring Company obtaining Control; and

     5.8.3 the Acquiring Company has agreed to grant new options in accordance
          with Rule 5.6 in consideration for the release of any Options which
          have not lapsed.

5.9  If the Company has been or will be affected by any demerger, dividend in
     specie, super dividend or other transaction which will adversely affect the
     current or future value of any Options, the Grantor may, acting fairly,
     reasonably and objectively, allow all such Options (but not some only) to
     be exercised conditionally on such event happening. The Grantor will
     specify the period of exercise of such Options. The Grantor will notify any
     Participant who is affected by this Rule.

5.10 Where rules 5.1, 5.3, 5.4 or 5.5 apply in deciding whether and to what
     extent Options will vest, the Grantor shall have regard as appropriate to
     the extent to which the Performance Period has elapsed and any conditions
     specified pursuant to Rule 2.3 have been met.


                                                                              17

<PAGE>

5.11 Where Rules 5.1, 5.3, 5.4 or 5.5 apply, Options shall lapse to the extent
     not already exercised following the expiry of any specified period.

6.   MANNER OF EXERCISE

6.1  An Option may be exercised, in whole or in part.

6.2  An Option may be exercised by the delivery to the Company Secretary (as
     agent for the Grantor), or his duly appointed agent, of an option
     certificate covering at least all the Shares over which the Option is then
     to be exercised, with the notice of exercise in the prescribed form duly
     completed and signed by the Participant (or by his duly authorised agent)
     together with a remittance for, or authorisation for the payment of, the
     total Option Price payable to the Company (as agent for the Trustees where
     the Trustees have agreed to satisfy the Option) in respect of the Shares
     over which the Option is to be exercised, unless the Grantor determines
     that a difference exercise procedure should apply.

6.3  If any conditions must be fulfilled before an Option may be exercised, the
     delivery of the certificate shall not be treated as effecting the exercise
     of an Option unless and until the Grantor is satisfied that the conditions
     have been fulfilled. The Grantor shall state whether the conditions have
     been fulfilled to its satisfaction as soon as practicable following the
     expiry of any performance period over which the fulfilment of conditions
     was to be measured or where a performance period is not relevant within 14
     days of receipt of the documentation referred to above.

6.4  The effective date of exercise shall be the later of the date of delivery
     of the notice of exercise: if appropriate, the date of payment; and the
     date that the Grantor states that the conditions imposed by Rule 2.3 have
     been fulfilled, if applicable. For the purposes of this Plan a notice of
     exercise shall be deemed to be delivered when it is received by the
     Company.

6.5  In the event that any Tax Liability becomes due on the exercise of an
     Option, the Participant will be deemed to have given irrevocable
     instructions to the Company's brokers (or any other person acceptable to
     the Company) for the sale of sufficient Shares acquired on the exercise of
     the Option to realise an amount equal to the Tax Liability and the payment
     of the Tax Liability to the Relevant Company, unless:

     6.5.1 the Relevant Company is able to deduct an amount equal to the whole
          of the Tax Liability from the Participant's net pay for the relevant
          pay period; or


                                                                              18

<PAGE>
     6.5.2 the Participant has paid to the Relevant Company an amount equal to
          the Tax Liability, or

     6.5.3 the Grantor determines otherwise.

7.   ISSUE OR TRANSFER OF SHARES

7.1  Subject to Rule 7.3 Shares to be issued pursuant to the exercise of an
     Option shall be allotted to the Participant (or his nominee) within 30 days
     following the date of effective exercise of the Option.

7.2  Subject to Rule 7.3, the Grantor shall procure the transfer of any Shares
     to be transferred to a Participant (or his nominee) pursuant to the
     exercise of an Option within 30 days following the date of effective
     exercise of the Option.

7.3  The allotment or transfer of any Shares under the Plan shall be subject to
     obtaining any such approval or consent as is mentioned in Rule 2.5 above.

7.4  Shares issued pursuant to the Plan will rank pari passu in all respects
     with the Shares then in issue, except that they shall not rank for any
     right attaching to Shares by reference to a record date preceding the date
     of exercise.

7.5  If Shares are transferred pursuant to the Plan the Participant shall not be
     entitled to any rights attaching to Shares by reference to a record date
     preceding the date of exercise.

7.6  If and so long as the Shares are listed on the London Stock Exchange, the
     Company shall apply for listing of any Shares issued pursuant to the Plan
     as soon as practicable after the allotment thereof.

7.7  The Grantor, in its discretion, may determine that, at any time that a
     Participant who exercises his Option shall not pay the Option Price, but
     shall instead receive an amount in Shares or in cash or a combination
     thereof equal to the amount by which the Market Value of the Shares on the
     date of exercise exceeds the Option Price. The Company shall return to the
     Participant any Option Price already paid in respect of the exercise of the
     Option.

8.   ADJUSTMENTS

8.1  The number of Shares over which an Option is granted, the conditions of
     exercise and the Option Price thereof (and where an Option has been
     exercised but no Shares have been allotted or transferred pursuant to such
     exercise, the number of Shares which may


                                                                              19

<PAGE>

     be so allotted or transferred and the price at which they may be acquired)
     shall be adjusted in such manner as the Grantor shall determine following
     any capitalisation issue, demerger, any offer or invitation made by way of
     rights, subdivision, consolidation, reduction, other variation in the share
     capital of the Company or any other exceptional event which in the
     reasonable opinion of the Grantor justifies such an adjustment, to the
     intent that (as nearly as may be without involving fractions of a Share)
     the aggregate Option Price payable in respect of an Option shall remain
     unchanged.

8.2  Apart from pursuant to this Rule 8.2, no adjustment under Rule 8.1 above
     may have the effect of reducing the Option Price to less than the nominal
     value of a Share. Where an Option subsists over both issued and unissued
     Shares any such adjustment may only be made if the reduction of the Option
     Price of Options over both issued and unissued Shares can be made to the
     same extent. Any adjustment made to the Option Price of Options over
     unissued Shares shall only be made if and to the extent that the Board
     shall be authorised to capitalise from the reserves of the Company a sum
     equal to the amount by which the nominal value of the Shares in respect of
     which the Option is exercisable exceeds the adjusted Option Price and to
     apply such sum in paying up such amount on such Shares so that on exercise
     of any Option in respect of which such a reduction shall have been made the
     Board shall capitalise such sum (if any) and apply the same in paying up
     such amount as aforesaid.

8.3  The Grantor may take such steps as it may consider necessary to notify
     Participants of any adjustment made under this Rule 8 and to call in,
     cancel, endorse, issue or reissue any certificate consequent upon such
     adjustment.

9.   ADMINISTRATION

9.1  Any notice or other communication under or in connection with the Plan may
     be given by personal delivery or by sending the same by electronic means or
     post, in the case of a company to its registered office, and in the case of
     an individual to his last known address, or, where he is a director or
     employee of a Group Member, either to his last known address or to the
     address of the place of business at which he performs the whole or
     substantially the whole of the duties of his office or employment, and
     where a notice or other communication is given by post, it shall be deemed
     to have been received 72 hours after it was put into the post properly
     addressed and stamped, and if by electronic means, when the sender receives
     electronic confirmation of delivery or if not available, 24 hours after
     sending the notice.


                                                                              20

<PAGE>

9.2  The Company may distribute to Participants copies of any notice or document
     normally sent by the Company to the holders of Shares.

9.3  In the case of partial exercise of an Option, the Grantor may in
     consequence call in, endorse, cancel and reissue, as it considers
     appropriate, any certificate for the balance of the Shares over which the
     Option was granted.

9.4  If any certificate shall be worn out, defaced or lost, it may be replaced
     on such evidence being provided as the Grantor may require.

9.5  The Company shall at all times keep available for allotment unissued Shares
     at least sufficient to satisfy all Options under which Shares may be
     subscribed or the Grantor shall procure that sufficient are available for
     transfer to satisfy all Options under which Shares may be acquired.

9.6  The Plan shall be administered by the Board. The Board shall have full
     authority, consistent with the Plan, to administer the Plan, including
     authority to interpret and construe any provision of the Plan, to amend the
     Plan to correct any errors or mistakes of procedure, and to adopt such
     regulations for administering the Plan and such forms of exercise as it may
     deem necessary or appropriate. Decisions of the Board shall be final and
     binding on all parties.

9.7  The costs of introducing and administering the Plan shall be borne by the
     Participating Companies.

10.  ALTERATIONS

10.1 Subject to Rules 10.2 and 10.4, the Board may at any time (but only with
     the prior consent of the Trustees if there are subsisting Options which
     they have agreed to satisfy or which will be affected by the alteration or
     addition) alter or add to all or any of the provisions of the Plan in any
     respect.

10.2 Subject to Rule 10.3, no alteration or addition to the material advantage
     of Participants or employees shall be made under Rule 10.1 to:

     10.2.1 the definition of "Eligible Employee";

     10.2.2 the limits in Rules 2 and 3;

     10.2.3 any rights attaching to the Options and the Shares;

     10.2.4 the rights of Participants under Rule 8; and


                                                                              21

<PAGE>

     10.2.5 the terms of this Rule 10.2,

     without the prior approval by ordinary resolution of the members of the
     Company in general meeting.

10.3 Rule 10.2 shall not apply to any minor alteration or addition which is to
     benefit the administration of the Plan, is necessary or desirable in order
     to obtain or maintain Inland Revenue approval of the UK Approved Addendum
     under Schedule 4 to ITEPA or any other enactment, or to take account of any
     change in legislation or to obtain or maintain favourable taxation,
     exchange control or regulatory treatment for the Company, or any Subsidiary
     of the Company or any Participant.

10.4 No alteration or addition shall be made under Rule 10.1 which would
     materially abrogate or adversely affect the subsisting rights of a
     Participant unless it is made:

     10.4.1 with the consent in writing of such number of Participants as hold
          Options under the Plan to acquire 75 per cent of the Shares which
          would be issued or transferred if all Options granted and subsisting
          under the Plan were exercised; or

     10.4.2 by a resolution at a meeting of Participants passed by not less than
          75 per cent of the Participants who attend and vote either in person
          or by proxy,

     and for the purpose of this Rule 10.4 the provisions of the Articles of
     Association of the Company relating to shareholder meetings shall apply
     mutatis mutandis.

10.5 Notwithstanding any other provision of the Plan other than Rule 10.1 the
     Grantor may at any time in respect of Options granted to Eligible Employees
     who are or who may become subject to taxation outside the United Kingdom on
     their remuneration amend or add to the provisions of the Plan and the terms
     of Options (whether by way of the establishment of further Plans to apply
     in overseas territories or otherwise) as it considers necessary or
     desirable to take account of or to mitigate or to comply with relevant
     overseas taxation, securities or exchange control laws, provided that:-

     10.5.1 the terms of Options granted to such Eligible Employees are not
          overall more favourable than the terms of Options granted to other
          Eligible Employees; and

     10.5.2 any Shares made available in respect of such Options shall be
          treated as counting against the limits contained in Rules 2.4 and Rule
          3.


                                                                              22

<PAGE>

10.6 As soon as reasonably practicable after making any alteration or addition
     under Rule 10.1, the Board shall give written notice thereof to any
     Participant materially affected thereby.

10.7 No alteration shall be made to the Plan if following the alteration the
     Plan would cease to be an Employees' Share Scheme.

10.8 No alteration to the Plan under this Rule 10 shall require the consent of
     any person unless expressly provided in the Rules.

11.  LEGAL ENTITLEMENT

11.1 Nothing in the Plan or in any instrument executed pursuant to it will
     confer on any person any right to continue in employment nor will it affect
     the right of any Group Member to terminate the employment of any person
     without liability at any time with or without cause, nor will it impose
     upon the Grantor or any other person any duty or liability whatsoever
     (whether in contract, tort or otherwise) in connection with:

     11.1.1 the lapsing of any Option pursuant to the Plan;

     11.1.2 the failure or refusal to exercise any discretion under the Plan;
          and/or

     11.1.3 a Participant ceasing to be a person who has a service relationship
          for any reason whatever.

11.2 Options shall not (except as may be required by taxation law) form part of
     the emoluments of individuals or count as wages or remuneration for pension
     or other purposes.

11.3 Nothing in the Plan shall be deemed to give any employee of any
     Participating Company any right to participate in the Plan.

11.4 Any person who ceases to have the status or relationship of an employee
     with any Group Member as a result of the termination of his employment for
     any reason and however that termination occurs, whether lawfully or
     otherwise, shall not be entitled and shall be deemed irrevocably to have
     waived any entitlement by way of damages for dismissal or by way of
     compensation for loss of office or employment or otherwise to any sum,
     damages or other benefits to compensate that person for the loss of
     alteration of any rights, benefits or expectations in relation to any
     Option, the Plan or any instrument executed pursuant to it.


                                                                              23

<PAGE>

11.5 The benefit of this Rule 11 is given to the Company for itself and as
     trustee and agent of each Group Member.

12.  GENERAL

12.1 The Plan shall terminate upon the tenth anniversary of its approval by the
     Company or at any earlier time by the passing of a resolution by the Board
     or an ordinary resolution of the Company in general meeting. Termination of
     the Plan shall be without prejudice to the subsisting rights of
     Participants.

12.2 By participating in the Plan, a Participant consents to the holding and
     processing of personal data provided by the Participant to the Company for
     all purposes relating to the operation of the Plan, including, but not
     limited to administering and maintaining Participant records, providing
     information to the Trustees, registrars, brokers, savings carrier or other
     third party administrators of the Plan, providing information to future
     purchasers of the Company or the business in which the Participant works
     and transferring information about the Participant to a country or
     territory outside the European Economic Area.

12.3 The Company and any Subsidiary of the Company may provide money to the
     Trustees or any other person to enable them or him to acquire Shares to be
     held for the purposes of the Plan, or enter into any guarantee or indemnity
     for those purposes, to the extent permitted by Section 153 of the Companies
     Act 1985. In addition, the Company may require any Subsidiary to enter into
     such other agreement or agreements as it shall deem necessary to oblige
     such Subsidiary to reimburse the Company for any other amounts paid by the
     Company hereunder, directly or indirectly in respect of such Subsidiary's
     employees.

12.4 These Rules shall be governed by and construed in accordance with the laws
     of England and Wales.


                                                                              24

<PAGE>

PROTHERICS PLC
2005 EXECUTIVE SHARE OPTION SCHEME

UK APPROVED ADDENDUM

1.   DEFINITIONS

1.1  The words and expressions used in this UK Approved Addendum which have
     capital letters have the meanings set out below, and words and expressions
     not otherwise defined have the same meaning they have in the Rules of the
     Plan to which this UK Approved Addendum is attached:

<TABLE>
<S>                              <C>
"ASSOCIATED COMPANY"             An associated company within the meaning of
                                 paragraph 35 of Schedule 4 to ITEPA.

"CLOSE COMPANY"                  A close company as defined in Section 414(1) of
                                 the Taxes Act as varied by Paragraph 9(4) of
                                 Schedule 4 to ITEPA.

"ELIGIBLE EMPLOYEE"              Any person who at the Date of Grant is:

                                 (A) an employee of a Participating Company, who
                                 is not a director; or

                                 (B) a full-time director of a Participating
                                 Company and in either case, not precluded by
                                 Paragraph 9 of Schedule 4 to ITEPA from
                                 participating in the Plan. For the purposes of
                                 the UK Approved Addendum, an Eligible Employee
                                 is a "full-time director" if he works for 25
                                 hours or more a week for a Participating
                                 Company.

"EXCESS SHARES"                  The aggregate number of Shares which, were they
                                 to be acquired by an Eligible Employee on the
                                 exercise of any option would cause the limit
                                 specified in Rule 2 of the UK Approved Addendum
                                 to be exceeded.

"MATERIAL INTEREST"              The meaning given by Paragraph 10 of Schedule 4
                                 to ITEPA.

"MARKET VALUE"                   The meaning given in the Rules of the Plan
                                 except that
</TABLE>


                                                                              25

<PAGE>

<TABLE>
<S>                              <C>
                                 section (B) shall be amended by the addition at
                                 the end of that section of the words "and
                                 agreed in advance with the Inland Revenue
                                 Shares Valuation.

"MEMBER OF A CONSORTIUM"         The meaning given by Paragraph 36(2) of
                                 Schedule 4 to ITEPA.

"SHARE"                          A fully paid ordinary share in the capital of
                                 the Company which satisfies the requirements of
                                 Paragraphs 16 to 20 of Schedule 4 to ITEPA.
</TABLE>

1.2  For the purposes of Paragraph 35 A of Schedule 4 to ITEPA the specified age
     shall be 55".

1.3  For the purposes of this UK Approved Addendum, the words "whether by reason
     of grant, exercise or otherwise" shall be deleted from the definition of
     "TAX LIABILITY" and substituted with "by reason of exercise".

2.   AMENDMENTS TO THE PLAN

     An Option may not be granted under this UK Approved Addendum before this UK
     Approved Addendum has been approved by the Inland Revenue under Schedule 4
     to ITEPA. The purpose of this UK Approved Addendum is to benefit Eligible
     Employees who are, or may become, resident in the United Kingdom. This UK
     Approved Addendum applies to any grant of Options specified as having been
     granted subject to its terms and conditions.

     For the purpose of Options granted under this UK Approved Addendum, all of
     the Rules of the Plan shall apply subject to the following amendments:

2.1  No Option shall be granted to an Eligible Employee at any time if it would
     result in:

     2.1.1 the aggregate Market Value of the Shares at the Date of Grant which
          he may acquire in pursuance of rights obtained under the Plan; and

     2.1.2 the aggregate market value (determined at the relevant Date of Grant)
          of shares which the Eligible Employee could acquire by the exercise of
          an option under any other Executive Share Option Plan approved by the
          Inland Revenue under Schedule 4 of ITEPA and established by the
          Company or any Associated Company and not exercised,


                                                                              26

<PAGE>

     (together, "Relevant Option Shares") to exceed L30,000 or such other limit
     contained from time to time in Paragraph 6(1) of Schedule 4 to ITEPA. If an
     Option is granted over Excess Shares, the Grantor shall forthwith notify
     the Eligible Employee of this fact. The Grantor may call in the option
     certificate for endorsement, replacement or cancellation (as appropriate).
     If an Option is granted over Excess Shares, such Option shall only take
     effect to the extent that the aggregate market value of all the Relevant
     Option Shares (as calculated above) does not cause the above limit to be
     exceeded.

2.2  Rule 2.2 of the Plan shall not apply for the purposes of Options granted
     under this UK Approved Addendum.

2.3  Rule 2.8 of the Plan shall be amended to read as follows: "Subject to the
     rights of exercise by the Participant's personal representatives pursuant
     to Rule 4.2 of the Plan, every Option shall be personal to the Participant
     to whom it is granted and shall not be transferable or in any way
     alienable."

2.4  An Option may be exercised pursuant to Rules 4.3 and 4.4 of the Plan from
     the date of cessation until six months thereafter unless the Grantor
     determines that the Option may be exercised within a period not exceeding
     42 months from the Date of Grant.

2.5  Rule 4.2 of the Plan shall be amended to exclude the words "unless the
     Grantor determines otherwise".

2.6  An Option may not be exercised at any time when a Participant has or has
     had within the preceding 12 months a Material Interest in a Close Company
     which is:

     2.6.1 the Company; or

     2.6.2 any company which has Control of the Company or is a Member of a
          Consortium which owns the Company.

2.7  No adjustment shall be made pursuant to Rule 8.1 of the Plan without the
     prior approval of the Inland Revenue (so long as the UK Approved Addendum
     is approved by the Inland Revenue).

2.8  If an alteration or addition is made by the Board under Rule 10.1 of the
     Plan to any key feature of the Plan at a time when the UK Approved Addendum
     is approved by the Inland Revenue under Schedule 4 to ITEPA, such
     alteration or addition shall not have effect until it has been approved by
     the Inland Revenue. For the purposes of this Rule 2.8 of the UK Approved
     Addendum a "key feature" is any provision of the UK


                                                                              27

<PAGE>

     Approved Addendum which is necessary to meet the requirements of Schedule 4
     to ITEPA.

2.9  Rule 5.6 of the Plan shall be amended as follows:

     2.9.1 The words "(for the purposes of Paragraph 27 of Schedule 4 to ITEPA)"
          shall be included after "... in consideration of the grant to him of
          an Option ("the New Option") which"; and

     2.9.2 the words "falling within Paragraph 16(b) or (c) of Schedule 4 to
          ITEPA)" shall be included after "... (whether the company which has
          obtained Control of the Company itself or some other company".

2.10 For the purposes of Rules 5.6 and 5.7 of the Plan the New Option shall not
     be regarded as equivalent to the Old Option unless the conditions set out
     in Paragraph 26(3) of Schedule 4 to ITEPA are satisfied.

2.11 For the purposes of Rule 6.2 of the Plan, any alternative procedure for the
     exercise of an Option granted under the UK Approved Addendum shall not take
     effect until such time as it has been agreed by the Inland Revenue (so long
     as the UK Approved Addendum is approved by the Inland Revenue).

2.12 No adjustment may be made in accordance with Rule 8 of the Plan:

     2.12.1 to the conditions of exercise of an Option granted under the UK
          Approved Addendum; or

     2.12.2 in the event of a demerger of the Company or other exceptional event
          that does not include the variation of the share capital of the
          Company.

2.13 Rule 7.7 of the Plan shall not apply to Options granted under the UK
     Approved Addendum.


                                                                              28

<PAGE>

                                 PROTHERICS PLC

               (Registered in England and Wales: Number 02459087)

Certificate No: [____]

                               PROTHERICS PLC 2005
                           EXECUTIVE SHARE OPTION PLAN
                              UK APPROVED ADDENDUM
                        APPROVED SHARE OPTION CERTIFICATE

THIS IS TO CERTIFY
That

Name
Of
Address

is the holder of an Option over [____] [Ordinary Shares] of [____] each in the
capital of the Company at an exercise price of L[____] per share in accordance
with the UK Approved Addendum and the Rules of the Protherics PLC 2005 Executive
Share Option Plan.

The Date of Grant of this Option is [date].

This Option is not transferable to any person and shall lapse if any attempt is
made to transfer, assign or charge it.

It shall in any event lapse on [tenth anniversary] to the extent that it has not
been exercised.

Exercise of this Option is subject to the conditions imposed by the Board as
attached to this Certificate.

This Option is an Approved Option for UK tax purposes. In order to qualify for
income tax relief upon exercise, this Option must be exercised:

     [ ]  at a time when the UK Addendum is approved by the Inland Revenue;

     [ ]  no later than ten years from the Date of Grant; and

     [ ]  no earlier than three years from the Date of Grant, unless the Option
          is exercised pursuant to Rules 4.3.1 or 4.3.3 and, if the retirement
          is on or after reaching the specified age (55), 4.3.2 and within six
          months from the date of cessation of office or employment

If you do not wish to accept this Option you may surrender it in writing to the
Company Secretary within 30 days of the Date of Grant

EXECUTED as a DEED by Protherics PLC acting by


------------------------------------   -----------------------------------------
           Director                               Director/Secretary]

THIS IS AN IMPORTANT DOCUMENT: PLEASE KEEP IT IN A SAFE PLACE.


                                                                              29

<PAGE>

                                 PROTHERICS PLC
                        2005 EXECUTIVE SHARE OPTION PLAN
                              UK APPROVED ADDENDUM

                           OPTION TERMS AND CONDITIONS

PERFORMANCE CONDITIONS

The exercise of this Option is subject to the following conditions):

[Insert performance conditions]

EXERCISE DATES

Subject to satisfaction of the Performance Condition(s), the Option may be
exercised on [Third anniversary of grant]

TAXATION

[It is a condition of the exercise of this Option that you satisfy any liability
for any PAYE and employees' class 1 national insurance contributions that may
arise in connection with the grant of the Option or its exercise, assignment or
release. You agree to enter into any arrangements required by the Company in
relation to such liability].


                                                                              30
<PAGE>

                                 PROTHERICS PLC
                        2005 EXECUTIVE SHARE OPTION PLAN
                      NOTICE OF EXERCISE - APPROVED OPTION

TO: The Company Secretary
    Protherics PLC
    The Heath Business and Technical Park
    Runcom
    WA7 4QF

I HEREBY exercise the Option evidenced by the Share Option Certificate attached
in respect of ______________________ Ordinary Shares of [__] each in the capital
of the Company.

1.   I enclose a cheque for L[__] being the aggregate Option Price in respect of
     those shares. OR

     I enclose completed Instructions to the Company's brokers in respect of the
     exercise of the Option and the sale of Shares to meet the aggregate Option
     Price in respect of those shares. (Delete as appropriate)(1)

2.   I enclose a cheque payable to [the Company] for L___ in respect of the
     estimated Tax Liability arising in connection with the exercise of my
     Option. If my Tax Liability is greater than the amount I have paid I
     authorise you to deduct any outstanding Tax Liability in relation to the
     Option from my salary. OR

     I authorise the Company or its duly appointed agent to sell such number of
     the Shares registered in my name as will enable it (after payment of all
     necessary selling expenses and commissions) to recover and retain for
     itself from the sale proceeds an amount equal to such Tax Liability and
     then account to me for any cash balance remaining and generally to sign any
     stock transfer form or other document or documents which may be required.
     (Delete as appropriate)(2)

3.   I understand that no Shares will be issued or transferred to me until ALL
     of my Tax Liability has been satisfied in full.(3)

4.   I request that you issue or transfer to me such number of [Ordinary Shares]
     and I agree to accept the same subject to the Memorandum and Articles of
     Association of the Company. I authorise you to place my name on the
     Register of Members in respect of the shares so issued or transferred to
     me.

5.   Please send the share certificate for the said shares, when ready, to me by
     post at my risk to the address below.


SIGNED:                                 DATE:
        -----------------------------         ----------------------------------
NAME IN FULL
             ------------------------
ADDRESS:
         ----------------------------

----------
(1)  You can choose whether you wish to provide your own funds to pay the Option
     Price or whether you wish to make use of the broker-assisted exercise
     method.

(2)  Where an approved option is exercised in circumstances where tax relief is
     not available, you must select one of these methods for payment of the Tax
     Liability.

(3)  This is only relevant if there is any liability to tax upon exercise of the
     approved option - see note (2) above.


                                                                              31

<PAGE>

                                 PROTHERICS PLC

               (Registered in England and Wales: Number 02459087)

Certificate No: [____]

                                 PROTHERICS PLC
                        2005 EXECUTIVE SHARE OPTION PLAN

                      Unapproved Share Option Certificate

THIS IS TO CERTIFY
That

Name
Of
Address

is the holder of an Option over [___] [Ordinary Shares] of [___] each in the
capital of the Company at an exercise price of L[___] per share in accordance
with the Rules of the Protherics PLC 2005 Executive Share Option Plan.

The Date of Grant of this Option is [date].

This Option is not transferable to any person and shall lapse if any attempt is
made to transfer, assign or charge it.

It shall in any event lapse on [tenth anniversary or any earlier date] to the
extent that it has not been exercised.

Exercise of this Option is subject to the conditions imposed by the Board as
attached to this Certificate

This Option is an Unapproved Option for UK tax purposes.

If you do not wish to accept this Option you may surrender it in writing to the
Company Secretary within 30 days of the Date of Grant.

EXECUTED as a DEED by Protherics PLC acting by


------------------------------------   -----------------------------------------
              Director                            Director/Secretary]

THIS IS AN IMPORTANT DOCUMENT: PLEASE KEEP IT IN A SAFE PLACE.


                                                                              32

<PAGE>

                                 PROTHERICS PLC
                        2005 EXECUTIVE SHARE OPTION PLAN

                           OPTION TERMS AND CONDITIONS

Unless a term is defined in these Option Terms and Conditions, the definitions
in Act of the Plan shall apply.

PERFORMANCE CONDITIONS

The exercise of this Option is subject to the following condition(s):

[Insert performance conditions]

EXERCISE DATES

Subject to satisfaction of the Performance Conditions, the Option may be
exercised on [Third anniversary of grant]

TAXATION

It is a condition of the exercise of this Option that you satisfy any liability
for PAYE and employees' class 1 national insurance contributions that may arise
in connection with the grant of the Option or its exercise, assignment or
release. You agree to enter into any arrangements required by the Company in
relation to such liability.

SATISFACTION OF OPTION

The Company reserves the right to determine that, upon exercise of any part of
this Option, you shall not pay the Option Price, but shall instead receive an
amount in Shares or in cash or a combination of cash and shares equal to the
amount by which the Market Value of the Shares on the date of exercise in
respect of which the Option is exercised exceeds the Option Price.


                                                                              33

<PAGE>

                              PROTHERICS PLC 2005
                          EXECUTIVE SHARE OPTION PLAN

                     NOTICE OF EXERCISE - UNAPPROVED OPTION

TO: The Company Secretary
    Protherics PLC
    The Heath Business and Technical Park
    Runcorn
    WA7 4QF

I HEREBY exercise the Option evidenced by the Share Option Certificate attached
in respect of ___________________________ Ordinary Shares of [_____] each in the
capital of the Company.

1.   I enclose a cheque for L[________________] being the aggregate Option Price
     in respect of those shares. OR

     I enclose completed Instructions to the Company's brokers in respect of the
     exercise of the Option and the sale of Shares to meet the aggregate Option
     Price in respect of those shares. (Delete as appropriate)(1)

2.   I enclose a cheque payable to [the Company] for L in respect of the
     estimated Tax Liability arising in connection with the exercise of my
     Option. If my Tax Liability is greater than the amount I have paid I
     authorise you to deduct any outstanding Tax Liability in relation to the
     Option from my salary. OR

     I authorise the Company or its duly appointed agent to sell such number of
     the Shares registered in my name as will enable it (after payment of all
     necessary selling expenses and commissions) to recover and retain for
     itself from the sale proceeds an amount equal to such Tax Liability and
     then account to me for any cash balance remaining and generally to sign any
     stock transfer form or other document or documents which may be required.
     (Delete as appropriate)(2)

3.   I understand that no Shares will be issued or transferred to me until ALL
     of my Tax Liability has been satisfied in full.

4.   I request that you issue or transfer to me such number of [Ordinary Shares]
     and I agree to accept the same subject to the Memorandum and Articles of
     Association of the Company. I authorise you to place my name on the
     Register of Members in respect of the shares so issued or transferred to
     me.

5.   Please send the share certificate for the said shares, when ready, to me by
     post at my risk to the address below.


SIGNED:                                 DATE:
        -----------------------------         ----------------------------------
NAME IN FULL
             ------------------------
ADDRESS:
         ----------------------------

----------
(1)  You can choose whether you wish to provide your own funds to pay the Option
     Price or whether you wish to make use of the broker-assisted exercise
     method.

(2)  You must choose one of these methods for satisfying the Tax Liability.


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