Pethidine

Meperidine, also known as pethidine or by the brand name Demerol, is a synthetic opioid analgesic used for the relief of moderate to severe acute pain. It has historically been employed for postoperative pain and obstetric analgesia, but its use has declined due to safety concerns and the availability of safer alternatives.

Meperidine acts as a mu-opioid receptor agonist with some antimuscarinic activity. It has a relatively rapid onset after intramuscular or intravenous administration and a short duration of action, typically 2–4 hours. Unlike some other opioids, it forms the active metabolite normeperidine, which can accumulate in renal impairment and may provoke CNS excitation, tremors, seizures, and confusion.

Metabolism and safety considerations: Normeperidine and other metabolites are cleared by the kidneys, so caution is required in renal dysfunction and in the elderly. Meperidine crosses the placenta and is excreted in breast milk. Adverse effects include respiratory depression, nausea, vomiting, sedation, and constipation; it also has anticholinergic effects that can cause tachycardia and dry mouth.

Interactions and regulatory status: Significant interactions include monoamine oxidase inhibitors, which can lead to hyperthermia, agitation, and serotonin- or autonomic-related complications; concomitant use with other central nervous system depressants increases the risk of respiratory depression. Because of neurotoxic metabolite formation, guidelines discourage prolonged or high-dose use.

Meperidine is a controlled substance in many countries; in the United States it is a Schedule II narcotic. Its role in pain management has narrowed, and it is often reserved for brief analgesia when other opioids are unsuitable.