1. Field of the Invention
The present invention relates to a hypodermic syringe assembly, and more particularly concerns a hypodermic syringe suitable for prefilling including a needle shield assembly having cannula sealing features and features to help prevent accidental needle sticks.
2. Description of the Prior Art
Many injectable medications are packaged and distributed in the hypodermic syringe that will eventually be used to administer the medication to the patient. Prefilled syringes are available from pharmaceutical manufacturers, and syringes are frequently prefilled in hospital pharmacies. In both instances, the prefilled syringe is subject to a variety of environmental challenges during storage, shipping and/or handling before the medication is administered to the patient. Accordingly, the contents of the syringe must be sealed to preserve their sterility.
Articles such as hypodermic syringe tip caps are sometimes used to seal the distal tip of a prefilled hypodermic syringe. Syringes having a permanently attached needle cannula can be sealed with a resilient needle shield as taught in U.S. Pat. No. 3,865,236 to Rycroft. Rycroft teaches a needle shield of resilient rubber closed at one end and adapted to be positioned in surrounding relationship with respect to the needle so as to normally maintain the needle in a sealed atmosphere. The needle shield of Rycroft seals the cannula so that the prefilled medication is not in fluid communication with the environment.
Resilient rubber needle shields such as those taught by Rycroft are widely used and accepted. However, in recent years there has developed an increased concern regarding the transfer of disease and/or infection to syringe users and healthcare professionals who accidentally stick themselves with hypodermic needles while preparing, using or disposing of a hypodermic syringe products. Placing an excessive force on the tip of a syringe and needle assembly having a resilient rubber needle shield may cause the needle to penetrate the needle shield to expose the sharp injection point. Although reshielding is neither preferred nor recommended by many people, circumstances arise where it is necessary or convenient for the user to reshield the needle after injection. A resilient needle shield can present a potential problem if it is reshielded improperly so that the needle pierces the sidewall of the needle shield or the distal end of the needle shield and sticks the user. Syringe assemblies having rigid plastic needle shields avoid some of these problems but are generally not suitable for prefilled glass syringes because they do not have the ability to seal the needle cannula and because of their hardness and relative inelasticity may not effectively attach to the tip of a glass syringe barrel which in normal manufacturing has a much broader range of tolerances than a plastic syringe.
One way to retain the positive and desirable features of the resilient needle shield and to reduce the potential for accidental needle sticks is to provide a hard plastic protector or cover which can be installed over the needle assembly having a barrel with fixed needle cannula and a resilient needle shield in place such as an already prefilled hypodermic syringe assembly. U.S. Pat. No. 4,430,082 to Schwabacher teaches an inflexible hollow cylindrical sleeve which fits over an elastomeric protective needle cover. The cylindrical sleeve is provided with flexible gripping means which when depressed exerts pressure on the inner elastomeric protective cover thereby allowing the cover to be removed along with the protective cylindrical sleeve. Although the teachings of Schwabacher provide an improvement the device still has several shortcomings with respect to prevention of accidental needle stick. First, if the syringe is assembled by hand, there is still the potential of sticking during the assembly process before the rigid cover is applied. After the rigid cover is applied to the syringe assembly it can be removed leaving the needle covered only by the elastomeric protecting cover, effectively returning the device to its original state, before the rigid sleeve was installed, having all the shortcomings recited for syringe assemblies without rigid needle sleeves.
A similar device is taught by Ambrosio et al. in U.S. Pat. No. 4,317,446. Ambrosio et al. teach a plunger rod/protector which fits over a elastomeric needle sheath on a prefilled syringe having a fixed needle cannula. The plunger rod/protector of Ambrosio et al. does not engage the sheath and maintains its position on the syringe assembly by engaging the outer surface of the syringe barrel so that the plunger rod protector can be installed and removed from the distal end of the syringe without removing the elastomeric needle sheath. Ambrosio et al. has all of the disadvantages of Schwabacher in that the initial assembly may still be accomplished manually providing the opportunity for an accidental needle stick and the plunger rod protector may be removed leaving the needle covered only by the elastomeric needle sheath.
A further improvement is taught by Ambrose et al. in U.S. Pat. No. 4,636,201. Ambrose et al. teach a rigid sheath cover adapted to be placed over a rubber needle cover on a hypodermic syringe. The rigid sheath cover has a plurality of spaced cantilever like teeth projecting outwardly from the tubular body of the cover to form the open end. At least two of the teeth include a lip projecting inwardly toward the center of the opening formed by the teeth for ripping the needle cover after installation. Ambrose et al. still have an initial shortcoming in that the syringe having the rubber needle cover is already assembled. Manual assembly or use before installation of the rigid sheath cover provides all of the opportunity for accidental needle sticks as the original prior art syringe before rigid covers are installed. Also, because the rigid sheath is installed over the rubber needle cover there is an opportunity for the user to be stuck by the needle during the process of applying the rigid sheath to the needle assembly of Abrose et al. The rigid sheath cover of Ambrose et al. also provides an additional chance for accidental needle sticks because a needle can properly enter the open end of the rubber needle cover, at an angle, and pass through the cover and the space between the spaced teeth to stick the user. The only apparent advantage of Abrose et al. over the devices of Ambrosio et al. and Schwabacher is that after installation it appears that the rubber needle cover will remain within the rigid sheath. However, the spaced teeth of the Ambrose et al. sheath cover must be flexible enough to deform while passing over a soft rubber needle cover to the final assembled position. If the teeth are very rigid they may not flex enough to pass over the rubber needle cover or tear the cover in the process of assembly. Accordingly, the Ambrose et al. device must perform a balancing act between being flexible enough for proper installation yet strong enough to retain the rubber needle cover after assembly.
Shields for sealing the contents of a prefilled hypodermic syringe and protecting the needle from the environment have been addressed by the prior art. Improvements involving rigid covers and protectors which can be installed on a prefilled syringe having a resilient needle sheath have also been addressed by the prior art. However, there is still a need for a simple, straight forward, reliable, easily fabricated hypodermic syringe assembly having a needle shield assembly which retains the cannula sealing and cleanliness protecting features of the resilient needle sheath and incorporates a rigid shield to help prevent accidental needle sticks during all phases of the assembly and operation and disposal of the syringe.