Bung assembly for anti vacuum lock medical vials

A method of preventing vacuum lock during withdrawal of medicinal fluid by hypodermic syringe from a vial having a neck and an internal volume for retaining a medicinal solution that is dispensed to patients in aliquots by use of said hypodermic syringe, comprising the steps of:

• a) providing a vial having medicinal fluid carried in said volume, said vial including an elastomeric bladder in said volume, the change of volume of said bladder compensates for the change in volume of said medicinal fluid as it is withdrawn from said vial;
• b) providing a hypodermic syringe assembly including a tubular body, an injection needle and a plunger movable in said tubular body from a first, retracted position to a second, extended position to control the volume of fluid introduced into and dispensed from said hypodermic, said needle having a bore communicating with said tubular body;
• c) providing a vial stopper disposed in the neck of said vial and having annular depending fingers disposed at an inner end thereof to extend into the medicinal fluid volume of said vial to form an open-bottomed finger cavity, said fingers having a length selected to extend beyond the end of said hypodermic needle inserted through said stopper into said medicinal fluid volume so that said needle can access medicinal fluid in said finger cavity;
• d) inserting said hypodermic needle through said stopper into said medicinal fluid volume in said finger cavity with said plunger in said retracted position, said stopper fingers preventing said needle from puncturing said bladder, and
• e) withdrawing said medicinal fluid in said finger cavity without pre-pressurizing said vial, by moving said plunger from said retracted position to a preselected extended position defining a selected aliquot amount, said bladder changing in volume during said withdrawal of said aliquot to compensate for the volume of fluid aliquot withdrawn, thereby to prevent formation of vacuum lock and to prevent contamination of said medicinal fluid by introduction of external air containing contaminants.