The present invention relates to an implantable medication dispensing device. More particularly, the invention is directed to a device for implantation into an animal or human for delivery of medicine to the animal or human at specific intervals over a long period of time.
Various implantable drug dispensers are known in the art. For example, U.S. Pat. No. 3,692,027 discloses an implantable, timed drug dispenser that dispenses the drug mechanically. The dispenser comprises a case and a circular medication storage wheel member which is rotatably mounted within the case, the wheel member having an outer peripheral face with a plurality of cavities formed therein. Each cavity contains a capsule of the desired medication and has an associated piston member which when moved radially outward in a timed sequence ejects its respective capsule through an aperture formed in the case. The wheel member driven by a battery powered clock mechanism. Since many moving parts are involved in the drug delivery, such a mechanical dispenser is generally sensitive to shock and therefore is not reliable.
U.S. Pat. No. 5,059,175, on the other hand, discloses an implantable drug dispenser which is electrically operated to actuate a plunger for dispensing the drug. The dispenser comprises a tubular housing having a plurality of elongated, drug containing vesicles formed therein. Disposed in each vesicle near the bottom thereof is a plunger adapted to be forced upwardly in the vesicle by gas pressure. The housing includes a bottom compartment in which is disposed a plurality of pyrotechnic gas generating beads each associated with a respective vesicle and responsive to heat resulting from an electrical signal applied to a heating element, thereby igniting and producing gas which forces a corresponding plunger upwardly in the respective vesicle. The plunger in turn forces the drug contained in the vesicle against a rupturable cover to rupture the cover and thereby push the drug out of the vesicle. Such a drug dispenser requires gas-tight vesicles and these are often prone to leakage. In addition, the ignition of the pyrotechnic gas generating beads produces heat as well as hot and high pressure gases that may induce high levels of stress, which in turn may lead to material breakage and an uncontrolled release of drug.