Propoxyphene falls into the opiate category. It is derived from methadone but, unlike methadone, is a mild narcotic. Most deaths are accidents that result from an individual's taking too much medication over too short a time. Propoxyphene has a narrow margin of safety, as not only does it cause respiratory depression as opiates usually do, but also acts as a local anesthetic with resultant cardiac toxicity. The minimum lethal dose of propoxyphene in adults is approximately 650 to 780 mg. Following ingestion, peak levels are reached in 1 to 2 h. Propoxyphene is rapidly metabolized to norpropoxyphene. In chronic users of propoxyphene, norpropoxyphene levels are always higher than propoxyphene, often by a factor of 2 or 3 times. In individuals who die of an acute overdose, the concentration of propoxyphene is higher than nor-propoxyphene, with the propoxypnene concentration 1 mg/L and higher. In some propxyphene related deaths, the individual presents with a lethal concentration of propoxyphene accompanied by a higher level of norpro-poxyphene, though not 2-3 times higher. This is the picture of either an individual who died of an acute overdose but survived long enough to metabolize a significant amount of the propoxyphene ingested to norpropoxyphene, or of a chronic user of propoxyphene who took an acute overdose.
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