Apparatus for use in a drug mixing system including a vial adapter assembly(300) including a main body element(302) having a vial receiving portion (304) and a needle puncturable port(348), the main body element (302) including an axialhollow tubular portion (330) which is in fluid flow engagement with a bore(327) of a vial puncturing spike (322), and the mainbody element (302) further including a membrane support surface (332) thatsupports a first membrane (336) which is in fluidflow engagement with the vial puncturing spike (32) via the bore (327) and viaa recess (337) formed in an intermediate portion(328) of the main body element (302), characterized by a second membrane (236)supported by a membrane support member(240) and separated by a gap (238) from the first membrane (336).
