A drug container closure for mounting on an open-topped drug container to form a ready-to-use drug reconstitution assemblage for use with a needleless syringe, the open-topped drug container having a drug container rim defining a drug container opening, the drug container closure having a longitudinal centerline and comprising: (a) a tubular closure housing for securely mounting on the drug container rim, said closure housing including at least one inverted L-shaped track having an open-ended upright access leg, a horizontal priming leg and an upright activation leg, said activation leg having a proximal activation leg end and a distal activation leg end correspondingly adjacent and distal to said priming leg, each said inverted L-shaped track having: i) an one-way retaining snap member between said open-ended upright access leg and said horizontal priming leg, ii) an one-way primed snap member between said horizontal priming leg and said proximal activation leg end, and iii) an one-way activated snap member towards said distal activation leg end; (b) a drug container stopper securely mounted on said closure housing for sealing the drug container opening on securely mounting said closure housing on the drug container rim; and (c) a fluid transfer member having an integral needleless syringe connector and a puncturing cannula in flow communication therewith, said needleless syringe connector for attachment of the needleless syringe thereto, said puncturing cannula for puncturing said drug container stopper, said fluid transfer member being initially disposed along each said horizontal priming leg whereupon, on manual rotation of said fluid transfer member relative to said longitudinal centerline, said fluid transfer member is urged past each said one-way primed snap member to each said proximal activation leg end prior to being manually urged passed each said one-way activated snap member to each said distal activation leg end for puncturing said drug container stopper for flow communication with the drug container. (a) a tubular closure housing for securely mounting on the drug container rim, said closure housing including at least one inverted L-shaped track having an open-ended upright access leg, a horizontal priming leg and an upright activation leg, said activation leg having a proximal activation leg end and a distal activation leg end correspondingly adjacent and distal to said priming leg, each said inverted L-shaped track having: i) an one-way retaining snap member between said open-ended upright access leg and said horizontal priming leg, ii) an one-way primed snap member between said horizontal priming leg and said proximal activation leg end, and iii) an one-way activated snap member towards said distal activation leg end; i) an one-way retaining snap member between said open-ended upright access leg and said horizontal priming leg, ii) an one-way primed snap member between said horizontal priming leg and said proximal activation leg end, and iii) an one-way activated snap member towards said distal activation leg end; (b) a drug container stopper securely mounted on said closure housing for sealing the drug container opening on securely mounting said closure housing on the drug container rim; and (c) a fluid transfer member having an integral needleless syringe connector and a puncturing cannula in flow communication therewith, said needleless syringe connector for attachment of the needleless syringe thereto, said puncturing cannula for puncturing said drug container stopper, said fluid transfer member being initially disposed along each said horizontal priming leg whereupon, on manual rotation of said fluid transfer member relative to said longitudinal centerline, said fluid transfer member is urged past each said one-way primed snap member to each said proximal activation leg end prior to being manually urged passed each said one-way activated snap member to each said distal activation leg end for puncturing said drug container stopper for flow communication with the drug container.