Propoxyphene (PPX) is a mild narcotic analgesic found in various pharmaceutical preparations, usually as the hydrochloride or napsylate salt. PPX is a prescription narcotic analgesic structurally related to methadone, sold as Darvocet, Darvon, Dolene, Novrad. It is most often combined with aspirin, acetaminophen, caffeine or napsylate to treat mild to moderate pain.
Peak plasma concentrations of propoxyphene are achieved from 1 to 2 hours post dose. In the case of overdose, propoxyphene blood concentrations can reach significantly higher levels. In humans, propoxyphene is metabolized by N-demethylation to yield norpropoxyphene. Norpropoxyphene has a longer half-life (30 to 36 hours) than parent propoxyphene (6 to 12 hours). The accumulation of norpropoxyphene seen with repeated doses may be largely responsible for resultant toxicity.
In November 2010 the FDA concluded that PPX caused “serious toxicity to the heart, even when used at therapeutic doses.” Subsequently, the FDA requested that manufacturers discontinue production of the drug. Cardiac arrest has been reported with as little as 35mg. Moderate to highly toxic doses of PPX typically result in delusions, hallucinations, confusion, pulmonary edema and cardio toxicity. According to one report, abuse of PPX “differs from other narcotics in that abusers are observed to have grand mal seizures in the presence of normal EEG and brain scans,” specifically when consuming more than 1000mg per day. Recommended prescribed adult doses are 65mg (HCl) or 100mg (Napsylate) orally every four hours as needed.
Research indicates that given orally, PPX is “approximately one third as potent as orally administered codeine in depressing respiration” (Hardman et al). Additional research indicates that morphine addicts were able to prevent withdrawal syndrome more effectively with 800-1200mg of PPX, even though these dose sizes fall within the toxic level threshold.
The DrugCheck® Drug of Abuse Test yields a positive result when the concentration of Propoxyphene or Norpropoxyphene in urine exceeds 300 ng/mL.