JOINT FILING AGREEMENT

                                    EXHIBIT 1

                             JOINT FILING AGREEMENT

                  Each of the undersigned hereby acknowledges and agrees, in
compliance with the provisions of Rule 13d-1(k)(1) promulgated under the
Securities Exchange Act of 1934, as amended, that the Schedule 13D to which this
Agreement is attached as an Exhibit (the "Schedule 13D"), and any amendments
thereto, will be filed with the Securities and Exchange Commission jointly on
behalf of the undersigned. This Agreement may be executed in one or more
counterparts.

Dated:  December 16, 2004

                                PERSEUS-▇▇▇▇▇ BIOPHARMACEUTICAL FUND, LP

                                By:     Perseus-▇▇▇▇▇ Partners, LLC,
                                        General Partner

                                By:     SFM Participation, L.P.,
                                        Managing Member

                                By:     SFM AH LLC
                                        General Partner

                                By:     ▇▇▇▇▇ Fund Management LLC,
                                        Managing Member

                                By:     /s/ ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        -------------------------------------
                                        Name:  ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        Title: Assistant General Counsel


                                PERSEUS-▇▇▇▇▇ PARTNERS, LLC

                                By:     SFM Participation, L.P.
                                        Managing Member

                                By:     SFM AH LLC
                                        General Partner

                                By:     ▇▇▇▇▇ Fund Management LLC,
                                        Managing Member

                                By:     /s/ ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        -------------------------------------
                                        Name:  ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        Title: Assistant General Counsel


                                PERSEUS BIOTECH FUND PARTNERS, LLC

                                By:     Perseuspur, L.L.C.
                                        Managing Member

                                By:     /s/ ▇▇▇▇ ▇▇▇▇▇▇▇
                                        -------------------------------------
                                        Name:  ▇▇▇▇ ▇▇▇▇▇▇▇
                                        Title: Secretary and Treasurer


                                PERSEUSPUR, L.L.C.

                                By:    /s/ ▇▇▇▇ ▇▇▇▇▇▇▇
                                       -------------------------------------
                                        Name:   ▇▇▇▇ ▇▇▇▇▇▇▇
                                        Title:  Secretary and Treasurer



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CUSIP NO. ▇▇▇▇▇▇▇▇▇               SCHEDULE 13D              Page 18  of 18 Pages
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                                ▇▇. ▇▇▇▇▇ ▇. ▇▇▇▇▇

                                By:    /s/ ▇▇▇▇ ▇▇▇▇▇▇▇
                                       -------------------------------------
                                        Name:  ▇▇▇▇ ▇▇▇▇▇▇▇
                                        Title: Attorney-in-Fact


                                SFM PARTICIPATION, L.P.

                                By:     SFM AH LLC
                                        General Partner

                                By:     ▇▇▇▇▇ Fund Management LLC,
                                        Managing Member

                                By:     /s/ ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        -------------------------------------
                                        Name:  ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        Title: Assistant General Counsel


                                SFM AH LLC

                                By:     ▇▇▇▇▇ Fund Management LLC,
                                        Managing Member

                                By:     /s/ ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        -------------------------------------
                                        Name:  ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        Title: Assistant General Counsel


                                MR. ▇▇▇▇▇▇ ▇▇▇▇▇

                                By:    /s/ ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                       -------------------------------------
                                        Name:  ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        Title: Attorney-in-Fact


                                ▇▇▇▇▇ FUND MANAGEMENT LLC

                                By:    /s/ ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                       -------------------------------------
                                        Name:  ▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇
                                        Title: Assistant General Counsel