EXHIBIT 1 JOINT FILING AGREEMENT By this Agreement, the undersigned agree that this Statement on Schedule 13D being filed on or about this date, and any subsequent amendments thereto filed by any of us, with respect to the securities of NeurogesX, Inc. is being filed on behalf of each of us. February 22, 2010 MOSHE ARKIN /s/ Menachem Inbar ---------------------------- By: Menachem Inbar* Title: Attorney-in-fact M. ARKIN (1999) LTD. /s/ Menachem Inbar ---------------------------- By: Menachem Inbar** Title: Attorney-in-fact for Moshe Arkin, Chairman of M. Arkin (1999) Ltd. SPHERA FUNDS MANAGEMENT LTD. /s/ David Lieber ---------------------------- By: David Lieber Title: CEO ISRAEL MOR /s/ Israel Mor ---------------------------- By: Israel Mor
DORON BREEN /s/ Doron Breen ---------------------------- By: Doron Breen RON SENATOR /s/ Ron Senator ---------------------------- By: Ron Senator * Duly authorized under Special Power of Attorney appointing Menachem Inbar attorney-in-fact, dated August 12, 2009 by and on behalf of Moshe Arkin (incorporated herein by reference to Exhibit 2 to the Schedule 13G filed by Moshe Arkin, M. Arkin (1999) Ltd., Sphera Global Healthcare GP Ltd., Sphera Global Healthcare Management L.P., Sphera Global Healthcare Fund, and Sphera Global Healthcare Master Fund on August 13, 2009 (the "Original Schedule 13G)). ** Duly authorized under Special Power of Attorney appointing Menachem Inbar attorney-in-fact, dated August 12, 2009 by and on behalf of Moshe Arkin as Chairman M. Arkin (1999) Ltd. (incorporated herein by reference to Exhibit 3 to the Original Schedule 13G). 2