<PAGE>

                                                                    EXHIBIT 10.4

                                                                  EXECUTION COPY

                        AMENDMENT TO EMPLOYMENT AGREEMENT

     This FIRST AMENDMENT TO EMPLOYMENT AGREEMENT (the "Amendment") is made this
9th day of July, 2007 between DEVIN J. ANDERSON (the "Executive") and POLYMEDICA
CORPORATION (the "Company").

                                    RECITALS

     R-1. The Executive and the Company entered into an Employment Agreement
dated February 13, 2006, which sets forth the terms of the Executive's
employment (the "Employment Agreement"); and

     R-2. The Company through the Compensation Committee of its Board of
Directors (the "Compensation Committee") has determined that it is in Company's
interest to modify certain terms of the Executive's employment, and the
Executive has agreed to those modifications.

     In consideration of the recitals set forth above, the mutual promises
contained in this Amendment and other good and valuable consideration, the
receipt and sufficiency of which are acknowledged by the parties, the Executive
and the Company agree as follows:

     1. Term. The parties hereby agree that the initial term of employment as
set forth in Section 1 of the Employment Agreement is hereby amended such that
the initial term shall continue in effect until March 31, 2010. All other
provisions within Section 1 of the Agreement shall remain in full force and
effect.

     2. Title. The parties hereby acknowledge that pursuant to Section 2(a) of
the Employment Agreement, the Executive's title has been modified from "General
Counsel and Secretary of the Company" to "Executive Vice President - General
Counsel and Secretary of the Company" and that the Executive shall report
directly to the President of the Company.


                                       1

<PAGE>

     3. Base Salary. The parties acknowledge that pursuant to Section 3(a) of
the Employment Agreement (providing for periodic increases in the Executive's
base salary), the Executive's base salary was increased to $275,000 per annum
effective April 1, 2007.

     4. Calculation of the Executive's Severance for Certain Terminations - Lump
Sum Payment of Severance.

          a.   The parties hereto agree that any severance payment payable to
               the Executive pursuant to Section 7(b)(ii)(C) of the Employment
               Agreement shall be equal to two times the sum of (x) the
               Executive's highest Base Salary during the period the Executive
               was employed by the Company and (y) 100% of Employee's target
               bonus, as established by the Compensation Committee, for that
               Fiscal Year in which the Executive was terminated without Cause
               or in which the Executive terminated his employment for Good
               Reason, and any severance payment payable to the Executive
               pursuant to Section 7(b)(v)(C) of the Employment Agreement shall
               be equal to two times the sum of (x) and (y) as set forth in this
               paragraph 4.

          b.   In connection with the severance payments set forth in paragraph
               4(a), above, the parties hereto agree that, notwithstanding
               anything to the contrary set forth in Sections 7(b)(ii)(C),
               7(b)(ii)(H), 7(b)(v)(C) and 7(b)(v)(H), in the event the
               Executive is deemed to be a "key employee" with the meaning of
               Code Section 416(i), such severance payments shall be paid to the
               Executive in a single lump sum payment on the first business day
               of the seventh month following the Termination Date, consistent
               with Sections 7(b)(ii)(H) and 7(b)(v)(H) therein, or such earlier
               date as may be in compliance with the terms of Code Section 409A
               or any successor statute, regulation and guidance


                                       2

<PAGE>

               thereto, provided that such earlier payment shall not increase
               the total financial obligation of the Company under the
               Agreement, as amended.

     5. Miscellaneous.

          a.   Any capitalized term not expressly defined in this Amendment
               shall have the meaning ascribed to it in the Employment
               Agreement.

          b.   Except as expressly modified by this Amendment, all terms of the
               Executive's Employment Agreement, dated February 13, 2006 shall
               remain in full force and effect.

                     [Remainder of Page Intentionally Blank]


                                       3

<PAGE>

     IN WITNESS WHEREOF, the Company has caused this Amendment to be executed by
its duly authorized officer and the Executive has executed this Amendment to
Employment Agreement as of the day and year first above written.

                                        POLYMEDICA CORPORATION

                                        /s/ Patrick T. Ryan
                                        ----------------------------------------
                                        Name:  Patrick T. Ryan
                                              ----------------------------------
                                        Title:  Chief Executive Officer
                                               ---------------------------------


                                        DEVIN J. ANDERSON

                                         /s/ Devin J. Anderson
                                        ----------------------------------------


                                        4