ALFENTA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ALFENTA (ALFENTA).
μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing cAMP production, leading to reduced neuronal excitability and pain transmission.
| Metabolism | Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive). |
| Excretion | Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces. |
| Half-life | Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment. |
| Protein binding | Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin. |
| Volume of Distribution | 0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly. |
| Bioavailability | Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration). |
| Onset of Action | Intravenous: 30–60 seconds; intramuscular: 5–15 minutes; intrathecal: 5–10 minutes. |
| Duration of Action | Intravenous: 30–60 minutes (analgesic); dose-dependent; prolonged with repeated doses due to accumulation. |
Intravenous: Initial dose 8-20 mcg/kg (0.5-1 min) then 0.5-3 mcg/kg/min or 3-5 mcg/kg q5-20min. For short procedures: 8-20 mcg/kg. For longer procedures: 50-75 mcg/kg followed by 0.5-3 mcg/kg/min.
| Dosage form | INJECTABLE |
| Renal impairment | No specific dose adjustment is recommended for renal impairment; however, alfentanil is primarily metabolized in the liver and its pharmacokinetics are not significantly altered in renal failure. |
| Liver impairment | In hepatic impairment (Child-Pugh class A, B, C): Reduce dose by 50% and titrate carefully due to prolonged elimination half-life. Consider lower initial doses and extended dosing intervals. |
| Pediatric use | Children (1-12 years): Induction of anesthesia: 10-20 mcg/kg IV; maintenance: 5-10 mcg/kg IV or infusion 0.5-1 mcg/kg/min. For neonates and infants: Dose individualization required; titrate to effect. |
| Geriatric use | Elderly patients (>65 years): Reduce initial dose by 30-50% and administer slowly. Due to decreased clearance and increased sensitivity, lower infusion rates (e.g., 0.3-0.5 mcg/kg/min) may be needed. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ALFENTA (ALFENTA).
| Breastfeeding | Alfentanil is excreted into human breast milk in low concentrations. The milk-to-plasma (M/P) ratio is approximately 0.3. Estimated infant dose is <1% of maternal weight-adjusted dose, which is considered clinically insignificant. However, due to potential for neonatal opioid effects, caution is advised; monitor infant for drowsiness, respiratory depression, and feeding difficulties. Consider alternative analgesics with established safety profiles, such as acetaminophen or ibuprofen, for lactation. |
| Teratogenic Risk | Alfentanil, a short-acting opioid analgesic, is classified as FDA Pregnancy Category C. No well-controlled studies in pregnant women exist. In animal studies, no teratogenic effects were observed at clinically relevant doses; however, high doses caused embryotoxicity and increased fetal mortality. Trimester-specific risks: First trimester - potential for minor malformations based on limited human data; second trimester - possible risk if used chronically; third trimester - prolonged use may lead to neonatal respiratory depression, withdrawal syndrome, or opioid dependence. Use only if benefits outweigh risks. |
■ FDA Black Box Warning
Risk of respiratory depression, particularly in elderly or debilitated patients. Concomitant use with benzodiazepines or other CNS depressants may cause profound sedation, respiratory depression, coma, and death.
| Serious Effects |
Hypersensitivity to alfentanil or any component; significant respiratory insufficiency; severe asthma; paralytic ileus; concurrent use of MAOIs (or within 14 days); acute or postoperative pain management in children (except for procedural sedation).
| Precautions | Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use. |
| Food/Dietary | No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption. |
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| Fetal Monitoring | Monitor maternal vital signs including heart rate, blood pressure, respiratory rate, and oxygen saturation continuously during administration. Assess level of consciousness and pain score. For fetus, perform continuous fetal heart rate monitoring if appropriate (e.g., in obstetrical settings). Monitor for signs of maternal respiratory depression or bradycardia. In prolonged use or near term, monitor neonate for respiratory depression, sedation, and withdrawal symptoms after delivery. |
| Fertility Effects | Human data are lacking. Animal studies have not reported adverse effects on fertility at clinically relevant doses. Opioid use may be associated with menstrual cycle irregularities or decreased libido due to hormonal alterations; however, specific effects of alfentanil on fertility have not been established. |
| Clinical Pearls | Alfentanil is a potent, rapid-onset, short-acting opioid analgesic used primarily for induction and maintenance of anesthesia. Due to its high protein binding (90%) and rapid redistribution, it has a shorter duration of action than fentanyl, making it suitable for brief, painful procedures. It undergoes hepatic metabolism via CYP3A4, so concomitant use with CYP3A4 inhibitors like ketoconazole or erythromycin can prolong its effects. Use caution in elderly or hypovolemic patients due to increased risk of hypotension. Naloxone reverses respiratory depression. Alfentanil is 5-10 times less potent than fentanyl. |
| Patient Advice | This medication is given only by a healthcare professional in a hospital or surgical setting. · You may feel drowsy, dizzy, or nauseated after receiving this drug. · Report any difficulty breathing or slow heart rate to your healthcare provider immediately. · Avoid alcohol and sedatives for 24 hours after administration, as they can increase side effects. · Do not drive or operate machinery until the effects have fully worn off. |