Profiles of Activity in Rodents of Some Narcotic and Narcotic Antagonist Drugs

Abstract

THE narcotic analgesics and their antagonists form a series ranging from morphine, which is a powerful and highly addictive analgesic, to naloxone, which is a potent antagonist of morphine¹. One of the drugs between these extremes is pentazocine, which has both analgesic and antimorphine properties. In man, pentazocine is an effective analgesic drug; but, unlike the narcotic analgesics, it does not support morphine dependence and it precipitates abstinence effects in persons dependent on morphine². Unlike cyclazocine and nalorphine, pentazocine rarely causes hallucinations in man. These properties render pentazocine a useful analgesic of a new type; but tests in animals that show its profile of activity are not well developed. For example, pentazocine is poorly effective in antinociceptive tests based on mechanical pressure, in which morphine and other narcotic analgesics are active; whereas in the antinociceptive tests in animals in which pentazocine has proved effective^3–8, it cannot clearly be distinguished from other narcotic antagonists not useful as analgesics in man (cyclazocine, levallorphan and nalorphine) nor from antipyretic analgesics, such as aspirin and mefenamic acid. We describe here new tests in rodents that we have devised to indicate those features of the activity of pentazocine that are important for its clinical usefulness in man.