The use of a non-biodegradable polymer system to provide a sustained release of the narcotic antagonist naloxone in rats is described. The kinetics of morphine analgesia (measured by the hot-plate test) in the presence of the naloxone implant, and the urinary excretion of radiolabeled naloxone were measured. The shift of the morphine dose-response curve to the right is expressed in terms of dose ratios, which were calculated from the ED50 values for morphine obtained 9 days before, and 1, 8, 15, 22 and 29 days after implantation of the polymer. Our experiments indicate that effective levels of antagonist were maintained for 3–4 weeks after implantation of a polymer system containing 16 mg of naloxone. After 29 days, more than 95 % of the absorbed drug had been released, with 16 % of the implanted radioactivity appearing in the urine. These results demonstrate the feasibility of using a sustained release form of a narcotic antagonist to block the effects of morphine.

Keywords:
Morphine analgesia, Naloxone implant, Non-biodegradable polymer, Sustained release
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© 1975 S. Karger AG, Basel
1975
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