1. Field of the Invention
The present invention generally relates to an apparatus for injecting drugs into a patient and, more specifically, to an automatic injection device that utilizes a flexible membrane assembly and a propellant to automatically inject a single dose of a drug into a patient when the propellant is ignited.
2. Background of the Invention
Presently available automatic injection systems are typically large and bulky devices requiring skill and training in order to properly operate the device. Accordingly, such devices are not amenable to applications for which rapid administration of either a single drug or a combination of different compounds in rapid succession is desirable. Such systems are commonly used for mass vaccinations and self-administration of medications--such as for injection of insulin in diabetic patients, epinephrine in anaphylactic shock, and antimigraine drugs (e.g., sumatriptan). Devices for self-administration typically require cleaning after each use. Automated injectors used for mass vaccinations, as in military applications, typically use the same injection head for all patients and often require a supply of compressed gas.
Automatic injection devices are also presently in use for parenteral administration of medications under field conditions, where injections with a syringe are either impractical, require undue attention or training, or are painful. Examples of such situation s are administration of chemical warfare antidotes (e.g., atropine) and treatment of anaphylactic shock (e.g., epinephrine). In both instances, drug administration must be rapid, simple and reliable and must minimize the possibility of human error on selection and administration of drug doses. One such automatic injection device used by the military comprises an elongate tube with a needle protruding from one end. The needle is rapidly and forcefully inserted into a muscle, resulting in the painful injection of a drug contained within the tube. Upon removal of the needle, however, the needle remains exposed and thus requires proper handling to prevent contact by and/or injury to other persons.
For mass vaccination programs, reduction of the delivery costs associated with immunizations presents a big opportunity to boost immunization coverage rates. One way to decrease costs is to reduce the number of trained personnel required to complete an immunization series. Frequently, patient compliance is a major factor limiting effectiveness of mass vaccination programs--children, parents, and health care providers are less willing to accept the increased numbers of separate injections. Thus, it is desirable to deliver as many vaccines as possible during a single, quick patient visit. Mixing of vaccines in one syringe is often contraindicated due to potential incompatibilities and a reduced potency of the mixed vaccines. However, vaccines are typically safe and effective when administered at the same time at different application sites, such as with a single, multiple-site injection. Therefore, there is a clear need to simultaneously inject several vaccines into a patient with each vaccine being delivered at a discrete injection site. Due to problems associated with typical needle injections, including transmission of disease between patients, hazards to health-care workers, and expensive handling and disposal procedures, a method and apparatus for injecting a patient without using needles or by utilizing retractable needles is desirable.
U.S. Pat. No. 5,167,625 to Jacobsen et al. discloses an implantable drug delivery system which includes a housing having a plurality of compartments, each of which includes a flexible drug containment sack. A cover is disposed over the compartment openings to prevent the inadvertent release of drug formulations contained in the sacks. Gas generating elements are disposed in the compartments and are responsive to an initiation signal for producing gas to force the sacks and drug formulations out of the housing. Such a device, however, is designed for internal use, requiring surgery for implantation.
A portable, hand-held injection device is disclosed in U.S. Pat. No. 5,616,132 to Newman, and includes a diaphragm mounted within a housing having a needle associated therewith that moves in response to movement of the diaphragm when pressurized gas is released into the housing. Each device, however, is a completely self-contained unit that would be relatively expensive to manufacture, and difficult, if not impossible, to reuse. Accordingly, such a device would be impractical for mass injection scenarios as previously discussed.
Thus, it would be advantageous to provide prefilled, interchangeable and disposable injection devices that are inexpensive, easy to use, and safe for both the patient and medical personnel. It would also be advantageous to provide a prefilled injection device that reduces the risk associated with cross-infection, improves compliance--especially in children--improves the effectiveness of vaccination programs, does not require special sharps handling for disposal, and is a self-contained unit that presents a single item with few contaminated components for disposal.