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                                                                    Exhibit 10.3

                         REGISTRATION RIGHTS AGREEMENT
                         -----------------------------

This Registration Rights Agreement ("Agreement") is made and entered into as of
the 5/th/ day of February, 2001, by and among Antares Pharma, Inc. (formerly
known as Medi-Ject Corporation), a Minnesota corporation (the "Company"), and
the investors listed on the signature page hereof, with the exception of Lombard
Odier & Cie, in which case this Agreement is made and entered into as of the
5/th/ day of March, 2001 (collectively, the "Investors").

                                   RECITALS

     A.   The Investors have subscribed to purchase shares of the Company's
common stock, $.01 par value (the "Common Stock") and warrants to purchase
shares of Common Stock (the "Warrants").

     B.   It is a condition to such purchase that the Company provide the
registration rights provided herein and the parties hereto desire to provide for
such rights on the terms and conditions contained herein.

     NOW, THEREFORE, in consideration of the premises and covenants contained
herein, the parties hereto agree as follows:

1.   Registration Rights.  The Company covenants and agrees as follows:
     -------------------

     1.1  Registration.  On or prior to June 3, 2001, the Company will file with
          ------------
the Securities and Exchange Commission (the "Commission") a registration
statement on Form S-3 (or, if the Company is ineligible to use Form S-3, then on
Form S-1) registering the resale of the shares of the Common Stock and the
shares of Common Stock underlying the Warrants (the "Registrable Stock") under
the Securities Act of 1933, as amended (the "Securities Act") and shall
thereafter take all necessary steps to qualify such resale under such state laws
as the holders of Registrable Stock may reasonably request. The costs and
expenses directly related to such registration pursuant to this section,
including but not limited to legal fees of the Company's counsel, audit fees,
printing expense, filing fees and fees and expenses relating to qualifications
under state securities or blue sky laws shall be borne entirely by the Company;
provided, however, that the persons for whose account the securities covered by
such registration are sold shall bear the brokerage fees and commissions
applicable to their shares and the fees and expenses of their own legal counsel
and other advisors.  The Company shall keep effective and maintain any
registration, qualification, notification or approval specified in this
paragraph for such period as may be necessary for the holders to dispose of such
securities (not to exceed two (2) years) and, from time to time shall amend or
supplement the prospectus or offering circular used in connection therewith to
the extent necessary in order to comply with applicable law.

     1.2  Registration--General Provisions.  In connection with the registration
          --------------------------------
of the Registrable Stock under the Securities Act, the Company will:
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          (a)  prepare and file with the Commission a registration statement
with respect to such securities and use its best efforts to cause such
registration statement to become effective as soon as possible after the date it
is filed and keep the prospectus which is a part of such registration statement
current until the earlier of the date on which: (i) all such shares of
Registrable Stock have been sold, or (ii) two (2) years after the date it is
declared effective by the Commission (the "Effectiveness Period"); provided,
however, that if at any time the Company shall obtain a written opinion of legal
counsel reasonably satisfactory to Investors to the effect that the Registrable
Shares may be publicly offered for sale in the United States by the Investors
without restriction as to manner of sale and amount of securities sold and
without registration under the Securities Act, the Company shall no longer by
obligated to file or maintain a registration statement with respect to the
Registrable Shares pursuant to this Agreement, unless at a later date, an
Investor delivers to the Company an opinion of counsel to such Investor, which
opinion is reasonably satisfactory in form and substance to counsel to the
Company, that registration is then required as a result of a change in
applicable law;

          (b)  prepare and file with the Commission such amendments to such
registration statement and supplements to the prospectus contained therein as
may be necessary to keep such registration statement effective for the
Effectiveness Period referred to in Section 1.2(a) above;

          (c)  at the request of Investors holding a majority of the Registrable
Stock, provide legal counsel for such Investors (referred to herein as
"Investor's Counsel") with reasonable opportunities to review and comment on,
and otherwise participate in, the preparation of such registration statement;

          (d)  furnish to the Investor of the securities being registered such
reasonable number of copies of the registration statement, preliminary
prospectus, final prospectus and such other documents as the Investor may
reasonably request in order to facilitate the public offering of such
securities;

          (e)  use its commercially reasonable efforts to register or qualify
the securities covered by such registration statement under such state
securities or blue sky laws of such jurisdictions as the Investor may reasonably
request in writing within 30 days following the original filing of such
registration statement, except that the Company shall not for any purpose be
required to execute a general consent to service of process (which shall not
include a "Uniform Consent to Service of Process" or other similar consent to
service of process which relates only to actions or proceedings arising out of
or in connection with the sale of securities, or out of a violation of the laws
of the jurisdiction requesting such consent) or to qualify to do business as a
foreign corporation in any jurisdiction wherein it is not so qualified;

          (f)  notify the Investor, promptly after it shall receive notice
thereof, of the time when such registration statement, or any post-effective
amendment thereto, has become effective or a supplement to any prospectus
forming a part of such registration statement has been filed with the
Commission;
<PAGE>

          (g)  notify the Investor promptly of any request by the Commission for
the amending or supplementing of such registration statement or prospectus or
for additional information;

          (h)  prepare and file with the Commission, promptly upon the request
of the Investor, any amendments or supplements to such registration statement or
prospectus which, in the opinion of Investor's Counsel, if any (and concurred in
by counsel for the Company), is required under the Securities Act or the rules
and regulations promulgated thereunder in connection with the distribution of
the shares of the Company's common stock by the Investor;

          (i)  prepare and promptly file with the Commission and promptly notify
the Investor of the filing of such amendment or supplement to such registration
statement or prospectus as may be necessary to correct any statements or
omissions if, at the time when a prospectus relating to such securities is
required to be delivered under the Securities Act, any event shall have occurred
as the result of which any such prospectus or any other prospectus as then in
effect would include an untrue statement of a material fact or omit to state any
material fact necessary to make the statements therein, in the light of the
circumstances in which they were made, not misleading;

          (j)  advise the Investor, and the Investor's Counsel, if any, promptly
after it shall receive notice or obtain knowledge thereof, of the issuance of
any stop order by the Commission suspending the effectiveness of such
registration statement or the initiation or threatening of any proceeding for
that purpose and promptly use its best efforts to prevent the issuance of any
stop order or to obtain its withdrawal if such stop order should be issued;

          (k)  at the request of the Investor, furnish on the effective date of
the registration statement: (i) opinions, dated such respective dates, of the
counsel representing the Company for the purposes of such registration and to
the Investor making such request, covering such matters as the Investor may
reasonably request, and (ii) letters, dated such respective dates, from the
independent certified public accountants of the Company, addressed to the
Investor, covering such matters as the Investor may reasonably request.

          (l)  Notwithstanding the foregoing, following the effectiveness of
such registration statement, the Company may, based upon the reasonable
determination of the Company's Board of Directors, suspend the effectiveness of
such registration statement for up to no longer than ninety (90) days in any
365-day period, as appropriate (a "Suspension Period"), by giving notice to the
Investor, if (i) the Company, with the advice of its counsel, shall have
determined that the Company may be required to disclose any material corporate
development; (ii) based upon advice from the Company's investment banker or
financial advisor, if the Company shall be involved in a pending or contemplated
financing or offering which could be adversely affected or (iii) in the good
faith judgment of the Board of Directors, the registration would impede, delay,
or otherwise interfere with any pending or contemplated material acquisition,
corporate reorganization or otherwise interfere with any pending or contemplated
material acquisition, corporate reorganization or other similar material
transaction involving the Company. The Company will use its best efforts to
minimize the length of any Suspension
<PAGE>

Period. Further, the Effectiveness Period referred to in Section 1.2(a) shall be
extended by the number of days such registration is subject to any Suspension
Period. The Investor agrees that, upon receipt of any notice from the Company of
a Suspension Period, it will not sell (subject to the limitations on the Company
set forth above) any Registrable Stock pursuant to such registration statement
until (x) the Investor is advised in writing by the Company that the use of the
applicable prospectus may be resumed, (y) the Investor has received copies of
any additional or supplemental or amended prospectus, if applicable, and (z) the
Investor has received copies of any additional or supplemental filings which are
incorporated or deemed to be incorporated by reference in such prospectus. Upon
notice by the Company to the Investors of any determination under subclauses (i)
or (iii) above, the Investors shall keep the fact and content of such notice
strictly confidential.

     1.3  Registration Expenses.  The Company shall pay all Registration
          ---------------------
Expenses (as defined below) in connection with the inclusion of shares of the
Company's common stock in any registration statement, or application to register
or qualify such shares under state securities laws, filed by the Company
hereunder, other than as set forth herein.  For purposes of this Agreement, the
term "Registration Expenses" means the filing fees payable to the Commission,
any state agency and the NASD and any securities exchange; the fees and expenses
of the Company's legal counsel and independent certified public accountants in
connection with the preparation and filing of the registration statement (and
all amendments and supplements thereto) with the Commission; and all expenses
relating to the printing of the registration statement, prospectuses and various
agreements executed in connection with the registration statement. Each Investor
will pay its proportionate share of any custodian fees or commission or
discounts or transfer taxes which may be payable to any broker and any other
expenses incurred by the Investor not expressly included herein.

     1.4  Indemnification. With respect to the registration of the resale of the
          ---------------
shares of Registrable Stock:

          (a)  To the extent permitted by law, the Company will indemnify and
hold harmless the Investors, the trustees, partners, officers and directors of
the Investors, any underwriter or broker for the Investors and each person, if
any, who controls the Investor or any underwriter, broker within the meaning of
the Securities Act or the Securities Exchange Act of 1934, as amended (the
"Exchange Act"), against any losses, claims, damages, or liabilities (joint or
several) to which they may become subject under the Securities Act, the Exchange
Act or other federal or state law, insofar as such losses, claims, damages or
liabilities (or actions in respect thereof) arise out of or are based upon any
of the following statements, omissions or violations (collectively a
"Violation") by the Company: (i) any untrue statement or alleged untrue
statement of a material fact contained in the Registration Statement, including
any preliminary prospectus or final prospectus contained therein or any
amendments or supplements thereto, (ii) the omission or alleged omission to
state therein a material fact required to be stated therein, or necessary to
make the statements therein not misleading, (iii) any violation or alleged
violation by the Company of the Securities Act, the Exchange Act, any state
securities law or any rule or regulation promulgated under the Securities Act,
the Exchange Act or any state securities law in connection with the offering
covered by the Registration Statement, or (iv) any failure of the
<PAGE>

Company to perform its material obligations under this Agreement; and the
Company will reimburse the Investor, trustee, partner, officer, director,
underwriter, broker, or controlling person for any legal or other expenses
reasonably incurred by them in connection with investigating or defending any
such loss, claim, damage, liability or action; provided, however, the Company
shall not be liable in any such case for any such loss, claim, damage, liability
or action to the extent that it is indirect, incidental, consequential, special,
or punitive or to the extent that it arises out of or is based upon a Violation
which occurs (a) in reliance upon and in conformity with written information
furnished to it expressly for use in connection with such registration by the
Investor, trustee, partner, officer, director, or controlling person of the
Investor, (b) by the Investors' failure to furnish the Company, upon request,
with information with respect to the Investors, any broker of an Investor, or
the Investors' intended method of distribution required to be stated in the
Registration Statement or necessary to make the statements therein in light of
the circumstance under which they were made not misleading, or (c) if the
Company shall sustain the burden of proving that the Investors or such broker
sold securities to the person alleging such Violations without sending or
giving, at or prior to the written confirmation of such sale, a copy of the
applicable prospectus, as then amended or supplemented (excluding any documents
incorporated by reference therein), if the Company had within a reasonable
period of time prior to such written confirmation furnished copies thereof to
such Investor or such broker, and such prospectus corrected such untrue
statement or alleged untrue statement or omission or alleged omission made in
such registration statement.

          (b)  To the extent permitted by law, each Investor will indemnify the
Company, each director, officer and controlling person of the Company and each
officer of the Company who signed the registration statement against all claims,
losses, damages and liabilities (or actions, proceedings or settlements, if such
settlements are effected with the written consent of the Investor, in respect
thereof) arising out of or based on any untrue statement (or alleged untrue
statement) of a material fact contained in any prospectus, offering circular or
other document in which the Investor's shares are included (including any
related registration statement, notification of the like) incident to any such
registration, qualification or compliance, or any omission (or alleged omission)
to state therein a material fact required to be stated therein or necessary to
make the statements therein not misleading in each case to the extent that any
such claim, loss, damage, liability or expense arises out of or is based on any
untrue statement or omission made in such registration statement, prospectus,
offering circular or other document in reliance upon and in conformity with
written information furnished to the Company by such Investor and stated to be
specifically for use therein, or any violation by the Investor of the Securities
Act or the Exchange Act or any rule or regulation thereunder applicable to the
Investor and relating to action or inaction required of the Investor in
connection with any such registration, qualification or compliance, provided,
however, that the Investor shall not be liable for any such untrue statement (or
alleged untrue statement) or omission (or alleged omission) of which the
Investor has delivered to the Company in writing a correction before the
occurrence of the transaction from which such loss was incurred and Investor
will reimburse the Company, each of its officers, directors, and each person
controlling the Company, each such underwriter and each person who controls any
such underwriter, for any legal and any other expenses reasonably incurred in
connection with investigating and defending or settling any such claim, loss,
damage, liability, action or proceeding.
<PAGE>

          (c)  Promptly after receipt by an indemnified party under this Section
of notice of the commencement of any action (including any governmental action),
such indemnified party shall, if a claim in respect thereof is to be made
against any indemnifying party under this Section, deliver to the indemnifying
party a written notice of the commencement thereof and the indemnifying party
shall have the right to participate in, and, to the extent the indemnifying
party so desires, jointly with any other indemnifying party similarly noticed,
to assume the defense thereof with counsel mutually satisfactory to the parties;
provided, however, that an indemnified party shall have the right to retain its
own counsel, with the reasonable fees and expenses to be paid by the
indemnifying party; and provided further, that if there is more than one
indemnified party, the indemnifying party shall pay for the reasonable fees and
expenses of one counsel for any and all indemnified parties to be mutually
agreed upon by such indemnified parties, unless representation of an indemnified
party by the counsel retained by the other indemnified parties would be
inappropriate due to actual or potential differing interests between such
indemnified parties. The failure to deliver written notice to the indemnifying
party within a reasonable time of the commencement of any such action, if
materially prejudicial to its ability to defend such action, shall relieve such
indemnifying party of any liability to the indemnified party under this Section,
but the omission so to deliver written notice to the indemnifying party will not
relieve it of any liability that it may have to any indemnified party other than
under this Section.

          (d)  If the indemnification provided for in this Section is held by a
court of competent jurisdiction to be unavailable to an indemnified party with
respect to any losses, claims, damages or liabilities referred to herein, the
indemnifying party, in lieu of indemnifying such indemnified party thereunder,
shall to the extent permitted by applicable law, contribute to the amount paid
or payable by such indemnified party as a result of such loss, claim, damage or
liability in such proportion as is appropriate to reflect the relative fault of
the indemnifying party on the one hand and of the indemnified party on the other
in connection with the Violation(s) that resulted in such loss, claim, damage or
liability, as well as any other relevant equitable considerations. The relative
fault of the indemnifying party and of the indemnified party shall be determined
by a court of law by reference to, among other things, whether the untrue or
alleged untrue statement of a material fact or the omission or alleged omission
to state a material fact relates to information supplied by the indemnifying
party or by the indemnified party and the parties' relative intent, knowledge,
access to information and opportunity to correct or prevent such statement or
omission. No person or entity guilty of fraudulent misrepresentation (within the
meaning of Section 11 of the Securities Act) shall be entitled to contribution
from any person or entity who shall not have been guilty of such fraudulent
misrepresentation.

2.   Covenants of the Investors.  Each Investor agrees that, for a period of 180
     --------------------------
days following the effective date of a registration statement of the Company
under the Securities Act, such Investor will not sell, offer to sell, grant any
option to purchase or otherwise transfer or dispose of any securities of the
Company held by such Investor except for shares of Common Stock included in such
registration pursuant to the terms of this Agreement.  Each Investor further
agrees that it will promptly notify the Company of any changes in the
information set forth in the Registration Statement regarding the Investor or
its plan of distribution.
<PAGE>

3.   Information Rights.  The Company hereby covenants and agrees as follows:
     ------------------

     3.1  Information Available.  So long as the registration statement covering
the resale of Registrable Stock owned by any Investor is effective, the Company
will furnish to such Investor the following items including any exhibits
thereto:

          (a)  as soon as practicable after available (but in the case of the
Company's Annual Report to Stockholders, within 90 days after the end of each
fiscal year of the Company), one copy of:

               (i)    its Annual Report to Stockholders (which shall contain
financial statements audited in accordance with generally accepted accounting
principles by a national firm of certified public accountants);

               (ii)   if not included in substance in the Annual Report to
Stockholders, its Annual Report on Form 10-K;

               (iii) its quarterly reports on Form 10-Q; and

               (iv)  a full copy of the particular registration statement
covering the Registrable Stock.

          (b)  upon the request of an Investor, a reasonable number of copies of
the Prospectus to supply to any other party requiring the Prospectus.

     3.2  Rule 144 Information.  For two years after the date of this Agreement,
          --------------------
the Company shall file all reports required to be filed by it under the
Securities Act, the Rules and Regulations and the Exchange Act and shall take
such further action to the extent required to enable the Investors to sell the
Registrable Stock pursuant to Rule 144 under the Securities Act.

4.   Miscellaneous.
     -------------

     4.1  Amendments.  Except as otherwise provided herein, the provisions of
          ----------
this Agreement may not be amended, modified or supplemented, and waivers or
consents to or departures from the provisions hereof may not be given or made
unless the Company has obtained the written consent of Investors holding a
majority of the Registrable Stock.

     4.2  Notices.  All notices and other communications provided for or
          -------
permitted hereunder shall be made by hand delivery, facsimile, overnight courier
or registered first-class mail to the address of the Investor and the Company as
set forth in the Company's records. All such notices and communications shall be
deemed to have been duly given:  when delivered, if by hand, overnight courier
or mail or when transmission is confirmed by the sending unit, if by facsimile.
<PAGE>

     4.3  Counterparts.  This Agreement may be executed in any number of
          ------------
counterparts and by the parties hereto in separate counterparts, each of which
when so executed shall be deemed to be an original and all of which taken
together shall constitute one and the same agreement.

     4.4  Headings.  The headings to this Agreement are for convenience of
          --------
reference only and shall not limit or otherwise affect the meaning hereof.

     4.5  Governing Law.  This Agreement shall be governed by and construed and
          -------------
enforced in accordance with the laws of the State of Minnesota without giving
effect to the principles of conflicts of law thereof.

     4.6  Severability.  In the event that any one or more of the provisions
          ------------
contained herein, or the application thereof in any circumstances, is held
invalid, illegal or unenforceable in any respect for any reason, the validity,
legality and enforceability of such provision in every other respect and of the
remaining provisions contained herein shall not be in any way impaired thereby,
it being intended that all of the rights and privileges of the Investors and the
Company shall be enforceable to the fullest extent permitted by law.

     4.7  Remedies.  The remedies provided for in this Agreement shall be
          --------
cumulative and in addition to all other remedies available, at law or in equity,
and nothing herein shall limit a holder's right to pursue actual damages for any
failure by the Company to comply with the terms of this Agreement.

     4.8  Consent to Jurisdiction.  In connection with any suite, claim, action
          -----------------------
or proceeding arising out of this Agreement, the parties hereby consent to the
in personam jurisdiction of the United States federal courts and states courts
located in the State of Delaware.  Each party agrees to service in the manner
set forth in Section 4.2 shall be valid and sufficient for all purposes; and
each party agrees, and irrevocably waives any objection based on forum non
conveniens or venue, to appear in any United States federal court or state court
located in the State of Delaware.

     4.9  Successors and Assigns.  This Agreement shall be binding upon and
          ----------------------
inure to the benefit of the parties hereto and their respective successors,
assigns, heirs and legal representatives.

                           [Signature page follows.]
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Registration Rights
Agreement to be executed by their duly authorized representatives as of the date
indicated above.

                            Antares Pharma, Inc.


                            By:   /s/ Franklin M. Pass, M.D.
                                  ----------------------------------------------
                            Its:  Chief Executive Officer


                            INVESTORS:

                            Aventic AG
                            bp Aventic Partners AG

                            By: /s/ Elvire M. Gazeau    /s/ Jean-Claude Rebelez
                                -----------------------------------------------
                            Its: Investment Manager         CFO
                                 ----------------------------------------------

                            Basellandschaftliche Kantonalbank


                            By: /s/ Meinrad Geering    /s/ Rolf Rudin
                                -----------------------------------------------


                            HCI Healthcare Investments Limited


                            By: /s/ C.A. Rowlandson
                                ------------------------------------------------
                                For and on behalf of Healthcare Advisers Limited
                                ------------------------------------------------
                            Its: Director
                                 -----------------------------------------------

                            Lombard Odier & Cie


                            By: /s/ Alexandre Meyer  /s/ Fernando Perez Diaz
                                ------------------------------------------------
                            Its: Vice President          Assistant Manager
                                ------------------------------------------------