One of the current treatments for opiate addiction is to use opiate antagonists which generally have chemical structures similar to those of opiates. The treatment of opiate addiction requires the use of these drugs over an extended period of time. For several years, methadone, naltrexone, and buprenorphine have been used for the treatment of opiate dependent individuals. Sustained release preparations of these drugs will have an advantage over current dosage forms, which require dosing daily or three times a week. Thus, the development of a biodegradable delivery system of an opiate antagonist capable of maintaining a therapeutically useful plasma concentration is recognized as an important area of research. Sustained release microcapsules using biodegradable polymers have been developed for numerous therapeutic agents. However, the present microcapsule technology consisting of a single drug dispersed within a polymer matrix has several drawbacks. One of these drawbacks is the so called """"""""burst effect"""""""". This is due to the rapid release of the drug which becomes trapped within the surface of the polymer during the manufacturing process. Once this rapid release has stopped, the microcapsules are able to release the drug at a fairly constant rate, as is usually desirable. This """"""""burst effect"""""""" could be minimized by exploiting the phenomenon of phase separation between two immiscible polymers dissolved in a mutual solvent. The second polymer would provide a protective coating over the drug/polymer matrix. This one-step process would provide a consistent coating of even very small nanoparticles and would help to smooth out by lessening the """"""""burst effect"""""""". These double-walled microcapsules will be prepared using the following biodegradable polymer combinations: polylactide and polystyrene; polylactide and polylactide-co-glycolide (50:50); polylactide and polyglycolide; polystyrene and polylactide-co-glycolide (50:50); polyglycolide and polylactide-co-glycolide; polystyrene and polyglycolide. Following the preparations, buprenorphine microcapsules will be evaluated for particle size distribution, efficiency of encapsulation, yield of microcapsules, drug release kinetics and degradation kinetics. The surface morphology of the microcapsules will be evaluated by scanning electron microscope. The stability of microcapsules will be monitored up to one year at 0, 15, 20, 25, and 30 C.
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