Many drugs, such as sodium Pentothal as manufactured and sold by Abbott Laboratories and a wide variety of antibiotics as manufactured by other pharmaceutical companies, are stored in powdered lyophilized form and must be mixed with a liquid such as sterile water, glucose or normal saline immediately prior to use. This pre-use mixing is necessary as some medicaments lose their potency or strength when stored with a diluent over a long period of time.
The concept of mixing a wet diluent and a dry powder within the barrel of a syringe or vial has been known in the past. The developments in this area have ranged from the very complex to the very simple. Indicative of the very complex means is the Choski U.S. Pat. No. 4,243,080. In this patent, two plungers and a venting system are used. Manually removed closures separate the two components to be mixed. The Choski U.S. Pat. No. 4,243,080 also describes screw and pressure means which facilitate the mating of parts containing the medicaments to be mixed. Venting is provided to release the pressures built up by the mixing of medications. The complexity of operation increases the cost of manufacture and similarly increases the possibility of failure. It is these two problems that the present invention seeks to avoid. In contrast, the Kobel U.S. Pat. No. 4,048,999 and the Kobel U.S. Pat. No. 4,153,057 are representative of simpler means to combine two medicaments or combine a medicament with a diluent. In the Kobel '999 patent, the entire mixing system is described, while in the Kobel '057 patent, only the unique design of the stopper used in the U.S. '999 patent is disclosed. These two Kobel patents describe a stoppered stopper. Operation of the mixing system is effected by dislodging a small stopper within a bore of a main stopper. The small stopper, when dislodged from the bore of the main stopper, creates an open channel for passage of diluent into a powder. Proper dilution of powdered medicament such as with antibiotics administered intravenously requires the use of large, high volume syringes. The size of these syringes greatly increases the cost and difficulty of use by health care personnel. If the high volume syringe were replaced with a series of smaller syringes to decrease the difficulty of use, the exposure to a nonsterile environment would rapidly increase. The present invention overcomes these difficulties. Between the complexity of the Choski '080 patent and the simplicity of the Kobel '999 and '057 patents is the Tischlinger U.S. Pat. No. 4,059,112. While describing a means of using an additive syringe with a container, the '112 patent discloses only a frictional fit nozzle member with a container. This patent discloses force exerted on the liquid diluent rather than the powder medicament. The complexity of manufacture of this device reduces the ability to maintain a sterile environment. Careful packaging and shipping are also very critical to maintaining operability of the device disclosed in the '112 patent, as the integrity of the diaphragm holding the diluent in its storage chamber is critical to the successful operation of this device. Furthermore, as with the devices claimed in the Kobel '999 and '057 patents a large volume syringe would be required to obtain proper dilution. The presently disclosed invention overcomes these problems by placing powder in a chamber member and allowing for separation of the plunger mechanism from the diluent and medicament containers. In this manner, any chance of accidental activation is avoided. Additionally, a wide variety of solution concentrations are possible by the use of containers of diluent covering a broad range of volumes.