Alfentanil
Alfenta
Synthetic short-acting μ-opioid agonist
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.
Indications
- •Blunting a brief intense stimulus (laryngoscopy, retrobulbar block, MAC)
- •Short procedures
Dosing
| Context | Adult | Pediatric |
|---|---|---|
| Bolus (blunt laryngoscopy) | 10–20 mcg/kg IV | — |
| Procedural analgesia | 5–10 mcg/kg IV | — |
| Infusion | 0.5–2 mcg/kg/min | — |
Pharmacokinetics
Onset ~1 min (fastest of the fentanyl family), duration 10–15 min. Hepatic CYP3A4.
Hemodynamic effects
Minimal; bradycardia.
Respiratory effects
Dose-dependent depression; chest wall rigidity.
Side effects
- !Respiratory depression
- !Bradycardia
- !Chest wall rigidity
- !N/V
Contraindications
- ×MAOI within 14 days (relative)
- ×Strong CYP3A4 inhibitors prolong effect
Reversal / antidote
Naloxone
Clinical pearls
- ★Fastest-onset opioid — ideal to cover a single brief predictable stimulus.
- ★CYP3A4 inhibitors (erythromycin, azoles) markedly prolong its effect.
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.
- Meperidine
μ-opioid agonist ~1/10 morphine, plus κ-agonism (anti-shivering). Active metabolite normeperidine is renally cleared, proconvulsant, and neurotoxic.
- Methadone
μ-opioid agonist with NMDA-receptor antagonism (blunts tolerance + opioid-induced hyperalgesia) and monoamine reuptake inhibition. Very long, variable half-life.
Suggested reading
- •Stoelting & Hines, Pharmacology & Physiology in Anesthetic Practice, 6e
- •Miller's Anesthesia, 9e
- •FDA package insert
