A capping system and method of use for sealing injectable drugs within vials is disclosed. The system includes a closure assembly and a locking cap. The closure assembly includes a retainer member and a resilient stopper located within the retainer member. The retainer member is arranged to be disposed on the vial whereupon a gap results between the stopper and the vial. The retainer member is movable to close that gap. The locking cap is used to permanently seal the vial.