Norpropoxyphene

Norpropoxyphene is a major metabolite of the opioid analgesic drug propoxyphene, and has been shown to be responsible for many of the adverse effects of this drug, including respiratory depression and seizures.

Pharmacology

Norpropoxyphene is formed in the body by the metabolism of propoxyphene by the liver enzyme CYP3A4. It is then excreted in the urine. The half-life of norpropoxyphene is much longer than that of propoxyphene, and it can accumulate in the body with repeated doses of propoxyphene, leading to higher blood levels and increased side effects.

Adverse effects

The most serious adverse effects of norpropoxyphene are respiratory depression and seizures. These effects are more likely to occur in patients who have taken high doses of propoxyphene, or who have impaired liver function which slows the metabolism of the drug. Other adverse effects can include dizziness, nausea, vomiting, and constipation.

Overdose

Overdose of propoxyphene can lead to high levels of norpropoxyphene in the body, which can be fatal. Symptoms of overdose can include severe drowsiness, slow or shallow breathing, slow heartbeat, coma, and death. Treatment of overdose involves supportive care, including breathing support and treatment of seizures. There is no specific antidote for propoxyphene or norpropoxyphene overdose.

See also

• Propoxyphene
• Opioid
• CYP3A4

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