Exhibit 10.45
                            SHARE EXCHANGE AGREEMENT


         This Share Exchange  Agreement  (this  "Agreement") is made and entered
into as of the 15th day of September,  1998, by and between American  Physicians
Service Group, Inc., a Texas corporation ("APS") and Donald Columbus,  M.D. (the
"Shareholder").

                                R E C I T A L S:

         WHEREAS,  pursuant to that certain Agreement and Plan of Reorganization
(the "Merger  Agreement")  entered into by Shareholder of even date herewith and
the other  contracts and  agreements to which  Shareholder  was, or was to be, a
party as contemplated in the Merger Agreement (the Merger Agreement and all such
other contracts and agreements are  hereinafter  referred to collectively as the
"Acquisition Documents"),  Shareholder has acquired or will acquire Seventy Four
Thousand  Four  Hundred  Forty Eight  (74,448)  shares (the "PM  Shares") of the
$0.001 par value per share common  stock of Syntera  HealthCare  Corporation,  a
Texas  corporation  ("Syntera")  for a  consideration  of $5  per PM  Share  (in
aggregate, the "Exchange Value"); and

         WHEREAS,  APS has agreed,  on the terms and  subject to the  conditions
hereof, to exchange certain shares of its $0.10 par value per share common stock
("APS Common") for the PM Shares.

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         NOW,  THEREFORE,  in  consideration of the foregoing and other good and
valuable  consideration,  the  receipt  and  sufficiency  of  which  are  hereby
acknowledged, the parties hereto agree as follows:

         1.  CONDITIONS  TO EXCHANGE  RIGHT.  In addition to the other terms and
conditions  contained in this Agreement,  Shareholder  shall only be entitled to
exchange  the PM  Shares  for  shares  of APS  Common  if each of the  following
conditions has been satisfied:

                  (a) There shall not have been, on or before  September 1, 2000
(the  "Determination  Date"), any registered public offering of the common stock
of  Syntera,  or any other  transaction  or event  pursuant  to which  shares of
Syntera of the same class as the PM Shares shall have become publicly traded, at
a per share price of greater than $5; and

                  (b)  Shareholder  shall not be, on the date of the  closing of
any exchange of stock pursuant to this Agreement (the "Closing Date"), in breach
of, or default under,  this Agreement,  any of the Acquisition  Documents or any
other  contract or agreement  to which  Shareholder  and Syntera  and/or APS are
parties; and

                  (c) At the Closing Date,  Shareholder  has all requisite legal
capacity  and  authority  to engage  in the  transactions  contemplated  by this
Agreement,  is the owner of all the PM Shares, and the PM Shares are free of any
and all liens, claims or encumbrances of any kind whatsoever; and

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                  (d) At or before the Closing  Date,  Syntera  shall not be, or
have  been,  a party to any  merger,  consolidation  or similar  transaction  or
agreement with respect thereto,  pursuant to which (i) Syntera was not, or would
not be, the named  surviving  entity after such merger,  consolidation  or other
transaction and (ii) dissenting shareholders have a legal right of redemption or
appraisal.

         2.  EXCHANGE  NOTICE.   In  the  event  the  conditions   described  in
subsections (a) and (d) of Section 1 are satisfied as of the Determination  Date
and  Shareholder  elects to  exercise  its right to  exchange  its PM Shares for
shares of APS Common,  Shareholder  shall provide  written  notice  thereof (the
"Exchange  Notice") to APS,  which  Exchange  Notice must be received by APS not
later than the date (the  "Expiration  Date") which is ninety (90) calendar days
after the  Determination  Date. In the event (i) any of the conditions  required
for an exchange to be  permissible,  as described in subsections  (a) and (d) of
Section 1 above, fail to be satisfied on or prior to the Determination  Date, or
(ii) any of the conditions specified in subsections (b) or (c) of Section 1 fail
to be satisfied on the Closing  Date,  or (iii) APS fails to receive an Exchange
Notice from  Shareholder on or prior to the Expiration  Date;  then, in any such
case,  all of  Shareholder's  rights under this  Agreement  shall  automatically
terminate and be of no further force or effect whatsoever.

         3. SHARE  CONVERSION.  Shareholder's  right to  exchange  its PM Shares
hereunder shall apply as to all, but not less than all, of the PM Shares. In the
event  Shareholder  has  complied  with all of the  conditions  allowing  for an
exchange  pursuant  to this  Agreement,  the closing of any such  exchange  (the
"Closing")  shall occur at the offices of APS in Austin,  Texas, on such day and

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at such time as the parties hereto may mutually agree upon, or in the failure to
so agree, at 10:00 a.m. Austin,  Texas time on the first business day that falls
thirty  (30) days  after the later of (i) the  Expiration  Date,  or (ii) in the
event a Lock-Up Period (as hereinafter defined) is imposed pursuant to Section 4
hereof,  the day on which such Lock-Up  Period ends.  For purposes  hereof,  any
additional  shares of  Syntera  stock of any  class  which  Shareholder  obtains
pursuant  to  stock   dividends,   stock   splits,   reverse   stock  splits  or
recapitalizations  to which  Syntera or the PM Shares are subject after the date
this Agreement was originally  entered into as first written above shall also be
considered  to  be  included  in  the  PM  Shares;  however,  no  adjustment  or
modification  will  be  made to the  Exchange  Value  as a  result  of any  such
transaction.  At the  Closing,  Shareholder  shall be entitled  to receive  such
shares of APS Common as is  determined  by dividing  Three  Hundred  Seventy Two
Thousand Two Hundred  Forty  Dollars  ($372,240) by the average of the "bid" and
"ask" prices for APS Common as quoted by the National  Association of Securities
Dealers  Automated  Quotation System at the close of trading on each of the last
five (5) business days immediately preceding the Closing Date.

         At the Closing,  Shareholder shall tender its share  certificate(s) for
all of the PM Shares, duly endorsed in blank, to APS, and shall also provide APS
with an executed blank stock power, in form and substance reasonably  acceptable
to APS, wherein Shareholder  represents and warrants to APS (i) that Shareholder
has  all  necessary  legal  capacity,  power  and  authority  to  engage  in the
transactions  contemplated  hereby, and (ii) that Shareholder owns all interests
in and to the PM Shares and that the PM Shares are being transferred to APS free
and clear of all liens, claims or encumbrances of any kind whatsoever.

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         The shares of APS Common that Shareholder  receives in the exchange are
hereinafter  referred to as the "New APS  Shares." The parties  acknowledge  and
agree  that  Shareholder  shall  receive a whole  number of shares of APS Common
only,  and  that any  fractional  share  amounts  resulting  from the  foregoing
conversion  calculation  shall be rounded up or down, as the case may be, to the
next whole number of shares. APS shall be under no obligation to pay any cash or
other  amounts with respect to any  fractional  share  amounts,  or to issue any
fractional  share  amounts to  Shareholder.  At the Closing,  Shareholder  shall
either  receive  a share  certificate  for all its New APS  Shares  or,  if APS'
transfer agent is unable to produce such  certificate by the Closing Date,  will
receive  a copy of a  registered  letter  sent  from APS to the  transfer  agent
instructing  the  transfer  agent to  deliver  such  certificate  in the name of
Shareholder directly to Shareholder or Shareholder's designee.

         4. NEW APS SHARES TRANSFERABILITY. APS will have registered the New APS
Shares with the Securities and Exchange Commission,  and made such other filings
and taken such other steps as necessary,  so that  Shareholder  may  immediately
sell, or otherwise  convey,  the New APS Shares without  restriction  (except as
otherwise  provided  below).  Shareholder  agrees to cooperate  fully and in all
respects  with  APS in  connection  with  any such  registration,  whether  such
cooperation  is requested  before or after the  Determination  Date.  Failure of
Shareholder to cooperate fully, including without limitation, promptly providing
complete and accurate information to APS, in connection with the registration of
any APS Common shares,  whether such cooperation and/or information is requested
before or after the Determination  Date or before or after Shareholder  delivers
any Exchange Notice,  shall automatically  terminate  Shareholder's rights under
this Agreement.  Notwithstanding  anything contained herein to the contrary,  in

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the  event  that APS is in the  process,  either at the  Closing  Date or at the
Determination Date, of registering and/or selling any of its capital stock in or
pursuant to any underwritten  public  offering,  upon the written request of the
lead underwriter  involved therein,  Shareholder agrees, and shall then agree in
writing in form and substance reasonably acceptable to APS, to not sell, attempt
to sell, or solicit or accept any offers to sell or otherwise convey, any of the
New APS Shares for such period of time (not to exceed one hundred  eighty  (180)
days) as may be requested by such lead underwriter ( the "Lock-Up Period").

         5.       MISCELLANEOUS.

                  (a) FEES AND  EXPENSES.  Each party hereto  agrees to bear all
fees and expenses  (including  without  limitation all fees and expenses for its
legal counsel and any accountants or other  professional  advisors)  incurred in
connection with the transactions contemplated hereby.

                  (b) GOVERNING LAW AND VENUE.  This Agreement shall be governed
by, and  construed  and enforced in  accordance  with,  the laws of the State of
Texas  (except  the  laws  of  Texas  that  would  render  such  choice  of  law
ineffective).  Venue for any action  relating to this Agreement  shall be proper
only in Texas.

                  (c)    COUNTERPARTS.    This   Agreement   may   be   executed
simultaneously  in one or more  counterparts,  each of which  shall be deemed an
original,  and  all  of  which  together  shall  constitute  one  and  the  same
instrument.

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<PAGE>

                  (d)  INUREMENT.  This  Agreement  shall  be  binding  upon the
parties hereto and their respective heirs, legal representatives, successors and
permitted  assigns.  No party hereto may assign this Agreement,  or any of their
rights or obligations  hereunder,  without the express prior written  consent of
all parties hereto in each instance.

                  (e)  Notices.  Any notices  required or  permitted to be given
under this Agreement  shall be given in writing and shall be deemed received (a)
when  personally  delivered  to the  relevant  party at its address as set forth
below or (b) if sent by mail, on the third day following the date when deposited
in the United States mail, certified or registered mail, postage pre-paid to the
relevant party at its address indicated below:

                  APS:               American Physicians Service Group, Inc.
                                     1301 Capital of Texas Highway, Suite C-300
                                     Austin, Texas 78746-6550
                                     Attn: President

                  Shareholder:       Donald Columbus, M.D.
                                     2400 Highway 365, Suite 101
                                     Nederland, Texas 77627-6268

Any party may change its address for purposes of this Agreement by proper notice
to the other party.

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         IN WITNESS  WHEREOF,  the parties hereto have executed this  Agreement,
intending to be legally bound hereby, as of the date first above written.

APS:                                AMERICAN PHYSICIANS SERVICE GROUP, INC.

                                    By:           /s/ William H Hayes
                                                  -------------------     
                                    Printed Name:     William H Hayes           
                                                  -------------------
                                    Title:            Sr. VP Finance
                                                  -------------------
                                                       
SHAREHOLDER:

                                                  /s/ Donald G. Columbus, M.D.
                                                  ----------------------------

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