Pethidine (also known as Meperidine) is an opioid analgesic used to relieve moderate to severe pain. It acts on the central nervous system to reduce the perception of pain. Mechanism of Action Pethidine binds to μ-opioid receptors in the brain and spinal cord, leading to: • Inhibition of pain signal transmission • Reduction in pain perception • Sedative effects Pharmacokinetics • Absorption: Administered orally or by injection (IV/IM) • Distribution: Rapidly crosses the blood–brain barrier • Metabolism: Metabolized in the liver to an active metabolite (Normeperidine) • Elimination: Excreted through the kidneys Therapeutic Uses • Relief of acute pain • Postoperative pain management • Labor pain management • Treatment of post-anesthetic shivering Side Effects • Drowsiness and dizziness • Nausea and vomiting • Respiratory depression • Hypotension • Risk of drug dependence Normeperidine, the active metabolite, may cause: • Seizures • Hallucinations Contraindications and Warnings • Renal failure • Patients with seizure disorders (epilepsy) • Concurrent use with MAO inhibitors • Respiratory depression conditions Zaidoon abd alwahab Al-Mustaqbal University The First University in Iraq.