Meperidine
Demerol
Synthetic phenylpiperidine μ-opioid agonist (with κ and anticholinergic activity)
μ-opioid agonist ~1/10 morphine, plus κ-agonism (anti-shivering). Active metabolite normeperidine is renally cleared, proconvulsant, and neurotoxic.
Indications
- •Postop/neuraxial shivering (low dose — first-line)
- •Analgesia (limited modern use)
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Shivering | 12.5–25 mg IV | — |
| Analgesia (rarely) | 0.5–1 mg/kg IM/IV | — |
Pharmacokinetics
Onset ~5 min IV, duration 2–3 h. Hepatic; normeperidine t½ 15–30 h (longer in renal failure).
Hemodynamic effects
Tachycardia (atropine-like structure — unlike other opioids); mild myocardial depression.
Respiratory effects
Dose-dependent depression.
Side effects
- !Normeperidine accumulation → seizures (renal failure, high/repeated doses)
- !Tachycardia
- !N/V
- !Serotonin syndrome risk
Contraindications
- ×MAOI within 14 days (ABSOLUTE — fatal serotonin syndrome/hyperpyrexia)
- ×Renal failure
- ×Seizure disorder
- ×Chronic/PCA use
Reversal / antidote
Naloxone (does NOT reverse normeperidine-induced seizures)
Clinical pearls
- ★Best agent for postoperative shivering (κ effect) at low dose (12.5–25 mg).
- ★ABSOLUTE contraindication with MAOIs — serotonin syndrome can be fatal.
- ★Avoid in renal failure and for repeated/PCA dosing — normeperidine seizures.
Other drugs in Narcotics & Analgesics
- Fentanyl
μ-opioid receptor agonist. ~100× potency of morphine.
- Remifentanil
μ-opioid agonist. Ester linkage hydrolyzed by nonspecific tissue + plasma esterases — no organ-dependent clearance.
- Morphine
μ-opioid receptor agonist. Active metabolite morphine-6-glucuronide (M6G) is analgesic and renally cleared — accumulates in renal failure → prolonged sedation/respiratory depression. Causes histamine release.
- Hydromorphone
μ-opioid agonist ~5–7× more potent than morphine. No clinically significant active metabolites → safer than morphine in renal failure. Less histamine release.
- Sufentanil
Most potent opioid in common clinical use — ~1000× morphine, ~10× fentanyl. High lipid solubility.
- Alfentanil
μ-opioid agonist ~1/5–1/10 the potency of fentanyl but FASTEST onset of the family — low pKa means a high non-ionized fraction at physiologic pH.
- Methadone
μ-opioid agonist with NMDA-receptor antagonism (blunts tolerance + opioid-induced hyperalgesia) and monoamine reuptake inhibition. Very long, variable half-life.
- Nalbuphine
κ-receptor agonist + μ-receptor antagonist. Ceiling on respiratory depression. Reverses μ-mediated pruritus/respiratory depression while preserving some analgesia.
Browse all classes: /reference/drugs
Suggested reading
- •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
- •Miller's Anesthesia, 9e
- •FDA package insert
