<PAGE>   1
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                 FORM 10-K/A

                ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF
                       THE SECURITIES EXCHANGE ACT OF 1934

                   For the fiscal year ended January 31, 1998

                         Commission file number: 1-8366

                         POLYDEX PHARMACEUTICALS LIMITED
             (Exact Name of Registrant as Specified in Its Charter)

           Commonwealth of the Bahamas                            None
         (State or Other Jurisdiction of                    (I.R.S. Employer
         Incorporation or Organization)                    Identification No.)

   421 Comstock Road, Toronto, Ontario, Canada                   M1L 2H5
    (Address of Principal Executive Offices)                   (Zip Code)

Registrant's telephone number, including area code  (416) 755-2231

Securities registered pursuant to Section 12(b) of the Act:

                                               Name of Each Exchange
         Title of Each Class                    on Which Registered
         -------------------                    -------------------
Common Shares, $.0167 Par Value                Boston Stock Exchange

Securities registered pursuant to Section 12(g) of the Act:  Same

Indicate by check mark whether the Registrant: (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
Registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.

Yes    X     No
    -------     -------

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of Registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K [ ]

The aggregate market value of the Registrant's voting stock held by
non-affiliates of the Registrant, computed by reference to the average bid and
ask prices of such stock as of March 31, 1998: $8,352,488.

The number of Common Shares outstanding as of March 31, 1998: 2,996,897.

                       Documents Incorporated By Reference

Portions of the Registrant's Annual Report to Shareholders for the fiscal year
ended January 31, 1998, are incorporated by reference into Part II.

Portions of the Registrant's definitive Proxy Statement for the Annual Meeting
of Shareholders to be held on June 19, 1998, are incorporated by reference into
Part III.



<PAGE>   2



                                     PART I

ITEM 1.  BUSINESS
         --------

Introduction
------------

         Polydex Pharmaceuticals Limited (the "Registrant") was incorporated
under the laws of the Commonwealth of the Bahamas on June 14, 1979 as Polydex
Chemicals Limited, and changed its name on March 28, 1984. The address of its
statutory office in the Bahamas is c/o Higgs & Johnson, 83 Shirley Street,
Nassau, Bahamas: telephone (242) 322-8571. The Registrant's current business is
conducted through two of its subsidiaries, Polydex Chemicals (Canada) Limited, a
wholly-owned Canadian corporation incorporated in 1969, which itself conducts
its business through its wholly-owned subsidiary, Dextran Products Limited
("Dextran Products") (incorporated in Ontario in 1966) and Chemdex, Inc.
("Chemdex"), a 90% owned Kansas corporation incorporated in 1987. On November
30, 1992, Chemdex acquired from Continental Grain Company 100% of the issued and
outstanding share capital of Veterinary Laboratories Inc. ("Vet Labs"), a Kansas
corporation, which previously had been wholly-owned by the Registrant. On
December 1, 1992, Vet Labs and Sparhawk Laboratories Inc. ("Sparhawk") entered
into a joint venture (the "Sparhawk Joint Venture") for the purpose of
manufacturing and selling veterinary pharmaceutical products. Sparhawk is an
affiliated company owned primarily by the management of the Sparhawk Joint
Venture. The Registrant controls the Sparhawk Joint Venture through its control
of the board of directors. On May 9, 1995, the Registrant acquired from its then
Chairman (now Vice-Chairman), Thomas C. Usher, a 90% interest in Novadex
International Inc. ("Novadex International"), a Bahamian corporation. The
Registrant acquired the remaining 10% interest in Novadex International from an
unaffiliated third person on July 14, 1997. The principal asset of Novadex
International is a patent, developed by Mr. Usher, for the use of Cellulose
Sulphate in a number of applications including the development of a new
contraceptive gel.

General
-------

         The current business of the Registrant is the manufacture and sale of
Dextran and several of its derivatives, including Iron Dextran and Dextran
Sulphate, veterinary pharmaceutical products and other specialty chemicals, and
cosmetic raw materials, with some related research and development.

         Dextran, a generic name applied to certain synthetic compounds formed
by bacterial growth on sucrose, is a polymer or giant molecule. The name Polydex
combines the words "polymer" and "dextran."




                                      -2-
<PAGE>   3


Description, Usage and Regulated Aspects of the Products
--------------------------------------------------------

         The operations of the Registrant are presently carried on through
Dextran Products and Vet Labs. These subsidiaries operate principally in one
industry: the manufacture of veterinary pharmaceutical products.

Iron Dextran
------------

A.  Description
    -----------

         Iron Dextran is a derivative of Dextran produced by complexing Iron
with Dextran. Iron Dextran is injected into most pigs at birth as a treatment
for anemia.

B.  Regulation and Usage
    --------------------

         Sales presently are being made by the Registrant in the following
countries, which have approved the use of Iron Dextran for animals, require no
approval, or accept the Canadian registration: Canada (registration number
R625), Denmark, France, Switzerland, Hong Kong, Germany, the Netherlands,
Finland, Ecuador, Thailand, Hungary, Malaysia, the Philippines, Japan, Brazil,
Korea, Spain, Sweden, Israel, New Zealand, Mexico, Costa Rica, and Australia. In
the United States, sale for veterinary use requires the approval of the U.S.
Food and Drug Administration (the "FDA"). Chemdex has FDA approval for
veterinary use of Iron Dextran in the United States. For classification
purposes, the Registrant treats these sales of the Iron Dextran raw materials as
sales of Iron Dextran.

Dextran Sulphate
----------------

A.  Description
    -----------

         Dextran Sulphate is a specialty chemical which finds use in research
applications of the pharmaceutical industry and other centers of chemical
research.

B.  Regulation and Usage
    --------------------

         The Dextran Sulphate manufactured by the Registrant is sold in
Australia, Switzerland, France, the Netherlands, New Zealand and the United
States, where it is used in limited quantities in the manufacture of film, as
well as analytical chemical applications. This usage requires no regulatory
approval.

Veterinary Products
-------------------

A.  Description
    -----------

         The Registrant manufactures tablets and boluses, internal and external
solutions, ointments, powders and sterile injectable products.


                                      -3-
<PAGE>   4
B.  Regulation and Usage
    --------------------
         The products are sold in the United States and are used by large
animal veterinarians and by farmers for the treatment of various diseases and
conditions that affect farm animals. The Vet Labs facility is regulated and
inspected by the FDA and the U.S. Drug Enforcement Agency. 


Sales, Distribution and Reliance Upon Foreign Countries
-------------------------------------------------------

Iron Dextran and Dextran Sulphate
---------------------------------

         The Registrant sells Iron Dextran on an exclusive basis in certain
countries and on a non-exclusive basis elsewhere. Dextran Sulphate is sold on a
non-exclusive basis throughout the world. For the fiscal year ended January 31,
1998, no single customer accounted for 10% or more of total sales.

         The Registrant has not changed its mode of distribution of Iron Dextran
or Dextran Sulphate during the past twelve fiscal years. The Registrant sells
its product primarily to independent distributors and wholesalers throughout the
world. Orders are forwarded to the Registrant's manufacturing facilities in
Toronto, Ontario, Canada where they are processed and shipped. The Canadian
Embassies and Consulates in various countries also assist the Registrant by
making available information regarding the Registrant and its products.

Veterinary Products
-------------------

         All of the sales of Vet Labs for the fiscal year ended January 31, 1998
were within the United States. Distribution is achieved through private label
buying groups who then distribute to their own distributors, and through full
service independent distributors who purchase products under Vet Labs' house
labels. Private label products accounted for approximately 79% of sales with
house label sales contributing approximately 16%. In addition, Vet Labs also
does "contract filling" for other industry companies. Four customers (all
private label buying groups) accounted for 61% of sales at Vet Labs, with
individual customer shares ranging from 3% to 17%. Management does not believe
that the loss of any one or more of these customers would have a material
adverse effect upon Vet Labs' results of operations.

Working Capital Requirements
----------------------------

         There are no special inventory requirements or credit terms extended to
customers that would have a material adverse effect upon the Registrant's
working capital.



                                      -4-
<PAGE>   5


Patents, Trademarks and Licenses
--------------------------------

Iron Dextran
------------

         Effective February 1, 1995, the Registrant entered into an agreement
with Novadex Inc., an affiliated company, whereby Novadex Inc. granted the
Registrant the exclusive worldwide license to use a certain process developed by
Novadex Inc. for producing Iron Dextran. This process allows the Registrant to
produce Iron Dextran at a lower cost than would otherwise be possible. The term
of the license agreement is 10 years. The Registrant pays a license fee based on
production volumes. Upon the expiration of the license, the technology relating
to the process described above will belong to the Registrant, with no further
obligation to make royalty payments to Novadex Inc.

         The technology in the field of Dextran and its derivatives is
undergoing continuous expansion and development. The manufacture of Dextran and
its derivatives may be achieved by different processes and variations (including
glycoside, which is in the public domain). Therefore, the Registrant does not
believe that the license agreement described above gives it any substantial
competitive advantage.

Dextran Sulphate
----------------

         This material was patented under U.S. patent number 4,855,410 in
August, 1989 and has been tested with other drugs for efficacy in controlling
the HIV virus. At this time research has been halted so that the Registrant can
focus its resources on projects relating to cystic fibrosis and Cellulose
Sulphate. Once these projects have been completed, the Registrant expects to
return its attention to Dextran Sulphate.

Veterinary Products
-------------------

         Vet Labs holds a New Animal Drug Application from the FDA for the
production of both 10% Bulk Iron Hydrogenated Dextran and 10% Injectable Iron
Hydrogenated Dextran.

Elastin and Collagen
--------------------

         These materials were patented under U.S. patent numbers 4,659,740 and
4,784,986 on April 21, 1987 and November 15, 1988, respectively. The patents
cover a process whereby the materials are modified in such a way as to penetrate
the skin and act as a hydrating agent.

Cellulose Sulphate
------------------

         During the fiscal year ended January 31, 1996, a patent for a new
method of manufacture of Cellulose Sulphate was purchased for $1 million. The
process was patented under U.S. patent number 5,378,828 in June of 1995. Prior
to development of the


                                      -5-
<PAGE>   6


patented process the manufacture of the compound required the use of dangerous
and environmentally sensitive chemicals. The new method is safer, and appears to
produce a more consistent product. This material appears to have applications in
film manufacture and capsule production and is presently being investigated in
conjunction with the Rush Institute of the University of Chicago as a potential
contraceptive which also has antiviral capabilities. With regard to the latter
application, the Registrant is looking to perform human clinical trials and to
this end most of the animal toxicology work necessary for the filing of an
Investigation New Drug (IND) has been completed. The IND will be filed when all
of the work is complete.

Cystic Fibrosis
---------------

         Effective April 1, 1994, the Registrant entered into a Research
Agreement (the "UBC Research Agreement") with an affiliated company and the
University of British Columbia ("UBC"). On April 1, 1996, the UBC Research
Agreement was amended and expanded to include a number of Canadian hospitals.
Under the terms of the UBC Research Agreement, the Registrant has agreed to
provide equipment and funding in return for continuing research on cystic
fibrosis to be carried out in connection with two patents issued in 1996. U.S.
patent number 5,441,938 is held jointly by UBC and the Registrant, whereas U.S.
patent number 5,514,665 is held by UBC and licensed to the Registrant. In
conjunction with the UBC Research Agreement, UBC granted the Registrant, through
a sub-licensing agreement with an affiliated company, an exclusive worldwide
license to manufacture, distribute and sell products derived or developed from
the research performed. The Registrant will pay a quarterly royalty, based on
sales.

Status of New Products or Industry Segments
-------------------------------------------

         There has been no public announcement of, and no information otherwise
has been made public about, a new product or industry segment that would require
the investment of a material amount of the assets of the Registrant or that
otherwise is material.

Suppliers and Sales
-------------------

Iron Dextran and Dextran Sulphate
---------------------------------

         With regard to its basic raw materials, the Registrant utilizes one
basic supplier for its sugar requirements and one basic supplier for its Iron.
Both of these materials, as well as others used by the Registrant, are readily
available from numerous suppliers at competitive prices in the market. The
Registrant has no long-term contracts with any of its suppliers.

         The Registrant is dependent upon a single source for a certain raw
material used in the production of Dextran Sulphate. Such supply was adequate in
fiscal 1998 and no shortages are anticipated in the near term. However, any
curtailment in



                                      -6-
<PAGE>   7


availability of such raw material could be accompanied by production or other
delays as well as increased raw material costs, with consequent adverse effect
on the Registrant's results of operations.

Veterinary Products
-------------------

         Raw materials are readily available from a variety of suppliers at
competitive prices in the market. The Registrant has no long-term contracts with
any of its suppliers.

Backlog and Seasonality
-----------------------

         The Registrant's backlog as at January 31, 1998 was approximately
$1,000,000, whereas backlog as at January 31, 1997 was approximately $700,000.
All of these orders are expected to be filled within the current fiscal year.
The Registrant's business is not seasonal to any material extent.

Competition
-----------

         The Registrant is the only Canadian manufacturer of Iron Dextran and,
as a result of its acquisition of Vet Labs, the Registrant is also the only
manufacturer in the United States. There exist several European sources of Iron
Dextran. However, the only other major supplier of Iron Dextran is located in
Denmark. Dextran Sulphate is also manufactured by several manufacturers in the
U.S. and Europe. With regard to Iron Dextran and Dextran Sulphate, the
Registrant competes on the basis of quality, service and price.

         The Registrant currently produces approximately 50 veterinary products
including analgesics, anti-diarrheals, topical antiseptics, nutritional
supplements, local and general anesthesia agents and euthanizing agents. Primary
market segments include beef and dairy cattle, swine, equine and to a small
extent, companion animals (dogs and cats). With the exception of Iron Dextran
and Nitrofurazone ointment, the product offering is generic or non-licensed (non
NADA). As such, all products are subject to numerous competitors. In addition to
competing on the basis of quality, service and price, the Registrant
differentiates itself from competitors through its ability to supply multiple
product dosage forms (i.e., injectables, boluses, tablets, liquids and powders)
and provide customers with technical and regulatory support and assistance from
in-house quality control and regulatory departments.

Research and Development
------------------------

         During the fiscal years ended January 31, 1998, 1997, and 1996, the
Registrant expended $184,901, $92,063 and $314,149, respectively, on research
and development relating primarily to cystic fibrosis and Cellulose Sulphate.



                                      -7-
<PAGE>   8


Environmental Compliance
------------------------

         The Registrant believes that it is in substantial compliance with all
existing applicable foreign, federal, state and local environmental laws and
does not anticipate that such compliance will have a material effect on its
future capital expenditures, earnings or competitive position.

Governmental Contracts
----------------------

         No portion of the Registrant's business is subject to renegotiation of
profits or termination of contracts or subcontracts at the election of the U.S.
Government.

Employees
---------

         As of March 31, 1998, the Registrant employed 79 employees, of whom 51
were engaged in production, 14 in quality control, 3 in research and
development, 6 in administration and 5 in marketing and sales activities. Of
such employees, 53 were employed by Vet Labs and 26 by Dextran Products. None of
the Registrant's employees are covered by collective bargaining agreements.
Management considers its relations with employees to be good.

Recent Developments -- New Products
-----------------------------------

Activated Collagen and Elastin
------------------------------

         Collodex, a modified collagen, has been formulated as a principal
ingredient of a cosmetic skin cream. During fiscal 1998, the Registrant engaged
several marketing companies for the promotion of this product. To date, efforts
by these companies have met with limited success. At the present time, minor
sales are being made to cosmetic manufacturers in the Pacific Rim with the
potential for increased sales in the future.

         Elastin, a material with similar applications, has been developed by
the Registrant. It has not been commercialized, however, and no sales are
expected to occur in the current fiscal year.

Cystic Fibrosis
---------------

         Cystic fibrosis is a genetic disease which causes a cascade of effects,
the most severe being a build up of mucus in the lungs. This mucus is difficult
to remove and also permits the colonization of bacteria which then cause
secondary infections and often death. Research relating to cystic fibrosis is
underway in collaboration with the University of British Columbia where in vitro
studies are being performed. This research has shown that a special form of
Dextran, Usherdex 4, is effective in preventing the colonization of bacteria in
the mouth and in stimulating the macrophages in the lungs to remove the bacteria
present and lessen secondary infections. The Registrant is in



                                      -8-
<PAGE>   9


preliminary discussions with certain companies about financing or forming an
alliance to further this research through clinical trials and to market,
however, the results of their discussions are indeterminable at this time.
Further animal work is being planned prior to the commencement of human clinical
trials.

Cellulose Sulphate
------------------

         Production of this product was halted in 1989 when the customer found a
substitute. However, interest in the industrial use of Cellulose Sulphate has
been revived and samples have been supplied, but it is difficult to predict if
sales will occur this year. As discussed above, research is also underway in the
United States to evaluate the use of this material as a contraceptive gel with
antiviral capabilities. The Registrant is currently in preliminary discussions
with certain companies to fund the further research necessary to commercialize
this Cellulose Sulphate product, however, the results of these discussions are
indeterminable at the present time.

Segmented Information
---------------------

         The information regarding the geographic distribution of revenue,
operating results and assets set forth in Note 14 to the Registrant's
Consolidated Financial Statements included in the Registrant's Annual Report to
Shareholders for the fiscal year ended January 31, 1998 is incorporated herein
by reference.

ITEM 2.  PROPERTIES
         ----------

         The Registrant's wholly-owned subsidiary, Polydex Chemicals (Canada)
Limited, maintains its executive and sales offices and its manufacturing plant
of approximately 30,000 square feet in Toronto, Ontario, Canada.

         The Registrant operates a fermentation plant in Toronto, Ontario,
Canada, having the capacity to produce both 10% and 20% Iron Dextran at the rate
of up to 10,000 litres a week (there are 1.057 quarts in one litre). Present
production is approximately 8,000 litres a week. Complexing of the Iron Dextran
takes place in Toronto, Ontario, Canada.

         Dextran Sulphate presently is manufactured at the Registrant's plant in
Toronto, Ontario, Canada where reactors and spray drying equipment are
available. The Registrant presently manufactures approximately 500 kilos of
Dextran Sulphate per quarter (there are 2.2 pounds in one kilo), and has the
capacity to manufacture 500 kilos per month simultaneously with the 10,000
litres per week of Iron Dextran.

         The Registrant has engaged the services of an engineering company to
prepare drawings in contemplation of the planned refurbishment of the Toronto
facility. These drawings are nearly complete and management expects to submit
them in connection with



                                      -9-
<PAGE>   10


its application for a building permit in the second quarter of 1998.

         Through its subsidiary Vet Labs, the Registrant manufactures tablets
and boluses, internal and external solutions, ointments, powders and injectable
products. The manufacturing facility is located on 8 acres of land in Lenexa,
Kansas. The plant is 55,000 square feet with separate production areas for each
of the above product groups. The plant has the capacity to manufacture over
200,000 boluses per day, 4,000 gallons of liquids per day, 1,500 pounds of
powder per day and 1,000 gallons of injectable products per day. The facility is
currently running at approximately 50% of capacity.

         Each of the properties described above is owned by the Registrant.
Management believes that the Registrant's facilities are adequate for its
present requirements. These facilities have additional capacity for expansion of
production of existing and new products. The Registrant considers its current
equipment to be in good condition and suitable for the operations involved.

ITEM 3.  LEGAL PROCEEDINGS
         -----------------

         On May 23, 1996, FMMG, Inc. ("FMMG") filed suit against the Registrant
in the United States District Court for the Southern District of Florida seeking
damages for the alleged breach of an option given by the Registrant in favor of
FMMG and another company with respect to 160,000 shares of common stock in
Novatek International, Inc. previously held by the Registrant. The Registrant
has challenged the jurisdiction of the U.S. District Court by a motion to
dismiss. Should the motion to dismiss be denied, the Registrant intends to
vigorously defend the action. Discovery on the merits has been stayed pending
resolution of the motion to dismiss; accordingly, it is not possible at this
point in time to accurately predict the likelihood of an unfavorable outcome or
the magnitude of any potential damages.

         There are no other material pending legal proceedings other than
ordinary routine litigation incidental to the business, to which the Registrant
or any of its subsidiaries is a party, or to which any of the their property is
subject.

ITEM 4.  SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS
         ---------------------------------------------------

         No matters were submitted to a vote of security holders, through the
solicitation of proxies or otherwise, during the Registrant's fourth quarter
ended January 31, 1998.

                                     PART II

ITEM 5.  MARKET FOR REGISTRANT'S COMMON EQUITY AND RELATED SHAREHOLDER 
         -------------------------------------------------------------
         MATTERS
         -------
   
         The information contained under the caption "Market for the Company's
Common Shares and Related Shareholder Matters" in


                                      -10-
<PAGE>   11


the Registrant's Annual Report to Shareholders for the fiscal year ended January
31, 1998 is incorporated herein by reference.

ITEM 6.  SELECTED FINANCIAL DATA
         -----------------------

         The information required under this item is included under the caption
"Financial Highlights" in the Registrant's Annual Report to Shareholders for the
fiscal year ended January 31, 1998 and is incorporated herein by reference.

ITEM 7.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND 
         ---------------------------------------------------------------
         RESULTS OF OPERATIONS
         ---------------------

         The information required under this item is included under the caption
"Management's Discussion and Analysis of Financial Condition and Results of
Operations" in the Registrant's Annual Report to Shareholders for the fiscal
year ended January 31, 1998 and is incorporated herein by reference.

ITEM 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK
         ----------------------------------------------------------

         Not applicable.

ITEM 8.  FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA
         -------------------------------------------

         The Registrant's Consolidated Financial Statements are included in the
Registrant's Annual Report to Shareholders for the fiscal year ended January 31,
1998 and are incorporated herein by reference. Supplementary financial
information is not required.

ITEM 9.  CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND 
         ---------------------------------------------------------------
         FINANCIAL DISCLOSURE
         --------------------

         Not applicable.


                                      -11-
<PAGE>   12
                                    PART III

ITEM 10.  DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT
          --------------------------------------------------

         The information required under this item is incorporated herein by
reference from the material contained under the captions "Board of Directors",
"Proposals","Executive Officers" and "Section 16(a) Beneficial Ownership
Reporting Compliance" in the Registrant's definitive proxy statement to be filed
with the Securities and Exchange Commission pursuant to Regulation 14A, not
later than 120 days after the end of the fiscal year.

ITEM 11.  EXECUTIVE COMPENSATION
          ----------------------

         The information required under this item is incorporated herein by
reference from the material contained under the captions "Board of Directors",
"Board Meetings and Committees", "Compensation of Executive Officers" and
"Company Stock Performance" in the Registrant's definitive proxy statement to be
filed with the Securities and Exchange Commission pursuant to Regulation 14A,
not later than 120 days after the end of the fiscal year.

ITEM 12.  SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
          --------------------------------------------------------------

         The information required under this item is incorporated herein by
reference from the material contained under the caption "Ownership of Voting
Securities" in the Registrant's definitive proxy statement to be filed with the
Securities and Exchange Commission pursuant to Regulation 14A, not later than
120 days after the end of the fiscal year.

ITEM 13.  CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS
          ----------------------------------------------

         The information required under this item is incorporated herein by
reference from the material contained under the caption "Transactions With the
Company" in the Registrant's definitive proxy statement to be filed with the
Securities and Exchange Commission pursuant to Regulation 14A, not later than
120 days after the end of the fiscal year.




                                      -12-
<PAGE>   13


                                     PART IV

ITEM 14.          EXHIBITS, FINANCIAL STATEMENT SCHEDULES, AND REPORTS ON
                  -------------------------------------------------------
                  FORM 8-K
                  --------

         (a)      The following documents are filed as a part of this Annual
                  Report on Form 10-K/A:

                  (1)      Financial Statements included in the Registrant's
                           Annual Report to Shareholders for the fiscal year
                           ended January 31, 1998 and incorporated by reference
                           from Exhibit 13 filed herewith

                           Auditors' Report to the Shareholders -- Ernst & Young
                             Chartered Accountants
                           Consolidated Balance Sheets
                           Consolidated Statements of Shareholders' Equity
                           Consolidated Statements of Operations
                           Consolidated Statements of Cash Flows
                           Notes to Consolidated Financial Statements

                  (2)      Financial Statement Schedules

                           Auditors' Report to Shareholders - KPMG Peat Marwick 
                           Thorne

                           All other schedules for which provision is made in
                  the applicable accounting regulation of the Securities and
                  Exchange Commission are not required under the related
                  instructions or are inapplicable, and therefore, have been
                  omitted.

                  (3)      Exhibits

                           3.1      Memorandum of Association of Polydex
                                    Pharmaceuticals Limited, as amended (filed
                                    as Exhibit 3.1 to the Annual Report on Form
                                    10-K filed April 30, 1997, and incorporated
                                    herein by reference)
                           3.2      Articles of Association of Polydex
                                    Pharmaceuticals Limited, as amended (filed
                                    as Exhibit 3.2 to the Quarterly Report on
                                    Form 10-Q filed September 9, 1997, and
                                    incorporated herein by reference)
                           10.1     Employment Agreement between Polydex
                                    Pharmaceuticals Limited and Thomas C. Usher
                                    dated December 22, 1993, as amended on
                                    November 1, 1996 (filed as Exhibit 10.1 to
                                    the Annual Report on Form 10-K filed April
                                    30, 1997, and incorporated herein by
                                    reference)
                           10.2     Employment Agreement between Polydex
                                    Pharmaceuticals Limited and George G. Usher
                                    dated December 22, 1993 (filed as Exhibit 
                                    10.2 to the Annual Report on



                                      -13-
<PAGE>   14


                                    Form 10-K filed April 30, 1997, and
                                    incorporated herein by reference)
                           10.3     Employment Agreement between Polydex
                                    Pharmaceuticals Limited and Natu Patel dated
                                    February 12, 1990 (filed as Exhibit 10.3 to
                                    the Annual Report on Form 10-K filed April
                                    30, 1997, and incorporated herein by
                                    reference)
                           10.4     Research Agreement among Dextran Products
                                    Limited, Canadian Microbiology Consortium,
                                    British Columbia's Children's Hospital and
                                    the University of British Columbia, dated
                                    April 1, 1996 (filed as Exhibit 10.4 to the
                                    Annual Report on Form 10-K filed April 30,
                                    1997, and incorporated herein by reference)
                           10.5     Joint Venture Agreement among Chemdex, Inc.,
                                    Veterinary Laboratories Inc. and Sparhawk
                                    Laboratories, Inc., dated December 1, 1992
                                    (filed as Exhibit 10.5 to the Annual Report
                                    on Form 10-K filed April 30, 1997, and
                                    incorporated herein by reference)
                           10.6     Manufacturing Agreement among Sparhawk
                                    Laboratories, Inc., Agri Laboratories, Ltd.
                                    and Veterinary Laboratories Inc., dated
                                    September 23, 1996 (filed as Exhibit 10.6 to
                                    the Annual Report on Form 10-K filed April
                                    30, 1997, and incorporated herein by
                                    reference)
                           10.7     Stock Sale and Purchase Agreement between
                                    Continental Grain Company and Polydex
                                    Pharmaceuticals Limited dated October 30,
                                    1992, as amended on November 22, 1996 (filed
                                    as Exhibit 10.8 to the Annual Report on Form
                                    10-K filed April 30, 1997, and incorporated
                                    herein by reference)
                           13       Annual Report to Shareholders for the fiscal
                                    year ended January 31, 1998 (only those
                                    portions incorporated herein by reference)
                           21       Subsidiaries of Polydex Pharmaceuticals
                                    Limited (filed as Exhibit 21 to the Annual
                                    Report on Form 10-K filed April 30, 1997,
                                    and incorporated herein by reference)
                           23       Consent of Ernst & Young Chartered
                                    Accountants
                           27       Financial Data Schedule



                                      -14-
<PAGE>   15


         (b)      Reports on Form 8-K

                  November 7, 1997 - Item 5. Other Events. On November 4, 1997,
                  the Registrant announced that it had ceased negotiations to
                  acquire privately held Del Crane Medical, Inc. and associated
                  companies. The Registrant reported the announcement on a Form
                  8-K filed November 7, 1997.



                                      -15-
<PAGE>   16


                                   SIGNATURES
                                   ----------


Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the Registrant has duly caused this Annual Report on Form 10-K/A to
be signed on its behalf by the undersigned, thereunto duly authorized.

Dated:  June 1, 1998

                                         POLYDEX PHARMACEUTICALS LIMITED


                                         By: /s/ George G. Usher
                                            ------------------------------------
                                            George G. Usher, President and
                                              Chief Executive Officer



<PAGE>   17


                      AUDITORS' REPORT TO THE SHAREHOLDERS


         We have audited the consolidated balance sheets of Polydex
Pharmaceuticals Limited as at January 31, 1996 and 1995 and the related
consolidated statements of operations, shareholders' equity and cash flows for
each of the years in the three-year period ended January 31, 1996. These
financial statements are the responsibility of the Company's management. Our
responsibility is to express an opinion on these financial statements based on
our audits.

         We conducted our audits in accordance with generally accepted auditing
standards. Those standards require that we plan and perform an audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.

         In our opinion, these consolidated financial statements present fairly,
in all material respects, the financial position of the Company as of January
31, 1996 and 1995, and the results of its operations and the changes in its
financial position for each of the years in the three-year period ended January
31, 1996, in accordance with accounting principles generally accepted in the
United States of America.

KPMG
Chartered Accountants
Toronto, Canada
April 30, 1996
<PAGE>   18


                                  EXHIBIT INDEX
                                  -------------

Exhibit Number                      Exhibit Description
--------------                      -------------------

         13                         Annual Report to Shareholders for the fiscal
                                    year ended January 31, 1998 (only those
                                    portions incorporated herein by reference)
         23                         Consent of Ernst & Young Chartered
                                    Accountants
         27                         Financial Data Schedule