a drug mixing system including at least one receptacle port adaptor adapted to be inserted into a port of a fluid receptacle , at least one syringe adaptor adapted to be attached to a syringe and to the at least one receptacle port adaptor and at least one vial adaptor adapted for connection to a vial containing a drug and adapted for connection to the at least one syringe adaptor , the system being characterized in that at least one of the receptacle port adaptor , the at least one syringe adaptor and the at least one vial adaptor being vented to the atmosphere in a manner which prevents release to the atmosphere of possibly harmful contents of the vial in a liquid , solid or gaseous form .