Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALFENTA vs BAL
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.
Chelating agent that forms stable complexes with heavy metals (e.g., arsenic, mercury, lead) by binding to their sulfhydryl groups, facilitating renal excretion.
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
Arsenic poisoning,Mercury poisoning,Lead poisoning (adjunct to edetate calcium disodium),Acute gold poisoning,Wilson's disease (investigational)
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.
3-5 mg/kg IM every 4 hours for 2 days, then every 6 hours for 1 day, then every 12 hours for 10 days.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Terminal elimination half-life is approximately 6.8 hours (range 4–13 hours). In patients with impaired renal function, half-life may be prolonged.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Primarily hepatic; undergoes oxidation and conjugation; metabolites excreted renally.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Primarily renal; approximately 80% of a dose is excreted in urine as unchanged drug and metabolites within 24 hours. Biliary/fecal elimination accounts for less than 5%.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
BAL is extensively bound to plasma proteins, primarily albumin, with protein binding >90%.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Volume of distribution is approximately 3.5 L/kg, indicating extensive distribution into tissues, including brain and intracellular spaces.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
BAL is not administered orally due to poor absorption and gastrointestinal irritation. Given intravenously, bioavailability is 100%. Intramuscular bioavailability is similar but with slower absorption.
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.
GFR 10-50 m L/min: reduce frequency to every 6-8 hours; GFR <10 m L/min: reduce frequency to every 8-12 hours.
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.
Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 25%; Child-Pugh C: reduce dose by 50% and monitor for hepatotoxicity.
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.
3-5 mg/kg IM every 4 hours for 2 days, then every 6 hours for 1 day, then every 12 hours for 10 days; maximum 100 mg per dose.
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.
Start at 3 mg/kg IM every 6 hours; adjust based on renal function, monitor for hypotension and pain at injection site.
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.
None.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Monitor renal function and serum electrolytes during therapy.,Can cause hypertension, tachycardia, and myocardial ischemia; use cautiously in cardiovascular disease.,May induce hemolytic anemia in patients with G6PD deficiency.,Injection site reactions and sterile abscesses may occur.,Iron deficiency is a known adverse effect due to iron chelation.
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).
Hypersensitivity to BAL or any component.,Hepatic insufficiency (unless benefit outweighs risk).,Iron poisoning (forms toxic complex).,Concurrent use with cadmium or selenium (increased toxicity).
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
Avoid alcohol and caffeine. Maintain adequate hydration. No specific food restrictions, but ensure iron-rich foods are avoided if concurrent iron poisoning suspected (though BAL not indicated for iron).
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.
Insufficient human data; animal studies suggest potential teratogenicity at high doses. Avoid in first trimester unless benefit outweighs risk.
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.
BAL (dimercaprol) is excreted into breast milk; M/P ratio unknown. Limited data; exercise caution and consider temporary cessation of breastfeeding during therapy.
Pregnancy can alter pharmacokinetics of alfentanil. Increased plasma volume and distribution may require higher doses to achieve same effect, while decreased plasma protein binding may increase free fraction, potentiating effects. Alpha-1-acid glycoprotein levels change in pregnancy, affecting binding. In third trimester, clearance may be increased by up to 50% due to enhanced hepatic metabolism. Therefore, dose adjustments may be needed: consider starting at low dose and titrating to effect, with close monitoring. For intravenous administration, typical adult doses (5-20 μg/kg) may need adjustments; no standard pregnancy-specific dosing exists. Use the lowest effective dose for the shortest duration. In labor, avoid high doses prior to delivery due to risk of neonatal respiratory depression.
No specific dose adjustments recommended in pregnancy; monitor for increased volume of distribution and potential need for higher doses if toxicity persists.
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.
BAL (dimercaprol) is used as a chelating agent for heavy metal poisoning, particularly arsenic, lead, and mercury. Administer deep IM only; avoid IV due to risk of hemolysis. Monitor blood pressure closely as hypertension can occur. Contraindicated in peanut allergy due to peanut oil vehicle. Administer with alkaline urine to protect kidneys.
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.
This medication is given as an injection into a muscle.,You may experience a metallic taste, headache, or nausea.,Report any signs of allergic reaction such as rash or difficulty breathing.,Avoid alcohol while on this medication.,Do not drive or operate heavy machinery until you know how this drug affects you.
"Propantheline, an anticholinergic agent, can competitively antagonize muscarinic acetylcholine receptors, potentially reducing gastrointestinal motility and secretion. Alfentanil, a mu-opioid receptor agonist, also decreases gastrointestinal motility through central and peripheral opioid receptors. Concomitant use may synergistically inhibit peristalsis, leading to severe constipation, paralytic ileus, or delayed gastric emptying, which can increase the risk of aspiration and complicate anesthesia recovery."
"Alfentanil, a potent opioid analgesic, can cause significant hypotension and respiratory depression. When combined with furosemide, a loop diuretic that reduces blood volume and vascular resistance, there is a synergistic decrease in blood pressure, which may precipitate cardiovascular collapse, especially in patients with compromised circulatory reserves. Additionally, furosemide may enhance the sedative and respiratory depressant effects of alfentanil, leading to increased risk of respiratory acidosis and altered mental status."
"Alfentanil, a potent mu-opioid receptor agonist, can enhance the bradycardic effects of nebivolol, a beta-1 selective blocker with additional nitric oxide-mediated vasodilation. The combination may lead to excessive slowing of heart rate, reduced cardiac output, and potential hemodynamic instability, particularly in patients with underlying cardiac conduction abnormalities or hypovolemia."
"Pregabalin, a gabapentinoid, enhances the inhibitory effects of GABA by binding to the α2δ subunit of voltage-gated calcium channels, reducing excitatory neurotransmitter release. Dapiprazole, an α1-adrenoceptor antagonist used for miosis, can have its therapeutic efficacy increased when combined with pregabalin due to additive central nervous system depression. This interaction may result in enhanced sedation, dizziness, and psychomotor impairment, potentially increasing the risk of falls and cognitive dysfunction."
"Pregabalin and pravastatin may exhibit an additive risk of musculoskeletal adverse effects, particularly myopathy and rhabdomyolysis, due to their overlapping effects on muscle cells. Pregabalin can cause dose-related muscle damage, while pravastatin inhibits HMG-CoA reductase, leading to reduced skeletal muscle integrity. This combination may potentiate serum creatine kinase elevations and increase the likelihood of clinical myopathy, especially in patients with predisposing factors such as renal impairment or concomitant use of other myotoxic agents."
"Pregabalin may cause fluid retention and peripheral edema, which can precipitate or exacerbate heart failure, especially in patients with pre-existing cardiac risk factors. Rosiglitazone, a thiazolidinedione, also promotes fluid retention and increases plasma volume via PPAR-γ-mediated renal effects. When combined, the additive fluid-retaining properties of both drugs can synergistically elevate the risk of new-onset or worsening heart failure, particularly in patients with reduced left ventricular function or NYHA Class III/IV status."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ALFENTA vs BAL, answered by our medical review team.
ALFENTA is a Opioid Analgesic that works by μ-opioid receptor agonist that activates G-protein coupled receptors to inhibit adenylate cyclase, decreasing c AMP production, leading to reduced neuronal excitability and pain transmission.. BAL is a Chelating Agent that works by Chelating agent that forms stable complexes with heavy metals (e.g., arsenic, mercury, lead) by binding to their sulfhydryl groups, facilitating renal excretion.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALFENTA and BAL depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ALFENTA is: 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.. The standard adult dose of BAL is: 3-5 mg/kg IM every 4 hours for 2 days, then every 6 hours for 1 day, then every 12 hours for 10 days.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
A moderate-severity drug interaction has been identified when combining ALFENTA and BAL. The therapeutic efficacy of Alfentanil can be increased when used in combination with Pregabalin. Consult your prescriber before combining these medications.
The maternal-fetal safety profiles differ. ALFENTA is classified as Category C. 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 effect. BAL is classified as Category C. Insufficient human data; animal studies suggest potential teratogenicity at high doses. Avoid in first trimester unless benefit outweighs risk.. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.