| Class |
Opioid (μ‑receptor agonist) |
| Indication |
Moderate to severe pain (post‑operative, acute, or inflammatory) in adults and children. Also used for severe cough (rare) and as part of anesthesia in some settings. |
| Typical adult dose |
25–100 mg IV/IM every 3–4 h (maximum 200 mg/day). For IV infusion, 100 mg over 10–30 min every 3–4 h. |
| Pediatric dose |
0.3–0.5 mg/kg IV/IM every 3–4 h (max 0.3–0.5 mg/kg/day). |
| Route of administration |
IV, IM, SC (injections). Oral formulations are available but not common in the U.S. |
| Mechanism |
Binds to μ‑opioid receptors in the central and peripheral nervous system, inhibiting ascending pain pathways, increasing pain threshold, and producing analgesia, sedation, and respiratory depression. |
| Metabolism |
Hepatic amidation to meperidine‑1‑hydrogen‑cysteine (MHC), then N‑demethylation to normeperidine (a neurotoxic metabolite). Excreted mainly by the kidneys. |
| Half‑life |
Meperidine: ~4 h; normeperidine: ~15–24 h. |
| Key safety concerns |
|
| • Normeperidine accumulation |
Especially in renal impairment; can cause seizures, myoclonus, delirium, and neurotoxicity. |
| • Respiratory depression |
Dose‑dependent; caution in elderly, patients with COPD, or concomitant CNS depressants. |
| • Serotonin syndrome |
When combined with serotonergic drugs (SSRIs, MAOIs, triptans, etc.). |
| • Seizures |
Rarely, especially with high doses or chronic use. |
| • Tolerance and dependence |
Potential for physical dependence and withdrawal if used >5–7 days. |
| • Drug interactions |
MAO inhibitors, SSRIs, SNRIs, duloxetine, tramadol, other opioids, alcohol, benzodiazepines, muscle relaxants, anticholinergics. |
| Contraindications |
Known hypersensitivity to meperidine or other opioids; uncontrolled seizures; severe respiratory depression; severe hepatic/renal dysfunction (risk of normeperidine accumulation). |
| Precautions |
Use lowest effective dose for shortest duration. Monitor for signs of neurotoxicity, especially in patients with renal disease. Avoid in patients on serotonergic drugs. |
| Common adverse events |
Nausea, vomiting, constipation, pruritus, dizziness, somnolence, hypotension, urinary retention. |
| Rare but serious |
Seizures, severe CNS depression, serotonin syndrome, hypersensitivity reactions, renal impairment exacerbation. |
| Discontinuation/withdrawal |
Taper gradually if used >5 days to avoid abrupt withdrawal. Monitor for symptoms: agitation, anxiety, tremor, sweating, nausea, diarrhea. |
| Alternative agents |
Morphine, hydromorphone, fentanyl, oxycodone, tramadol (if neuropathic pain), NSAIDs, acetaminophen, regional techniques. |
| Why it’s less used now |
1) Normeperidine risk → seizures and neurotoxicity. 2) Better alternatives with longer duration, fewer side effects. 3) Risk of dependence. 4) Regulatory warnings and black‑box label. |
| Special populations |
• Elderly: Increased sensitivity, risk of CNS depression. • Pregnancy: Category C; use only if benefits outweigh risks. • Pediatric: Dose adjustments for weight; monitor for neurotoxicity. • Renal impairment: Reduce dose, increase interval, or avoid. |
| Monitoring |
• Vitals (BP, HR, RR, O₂ sat). • Pain scores. • Mental status (alertness, confusion). • Urine output if renal dysfunction. • Electrolytes, especially if seizures suspected. |
| Patient counseling |
• Take exactly as prescribed. • Do not exceed prescribed dose. • Avoid alcohol and other sedatives. • Report dizziness, confusion, seizures, or breathing problems. • Store in a safe place out of reach of children/others. |