Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
AZASAN vs ALFENTA
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Azathioprine is a purine analog that inhibits purine synthesis, thereby interfering with DNA and RNA synthesis. It is metabolized to 6-mercaptopurine, which inhibits T-cell activation and proliferation, leading to immunosuppression.
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.
Renal transplant rejection prophylaxis,Rheumatoid arthritis,Off-label: inflammatory bowel disease (Crohn's disease, ulcerative colitis), lupus nephritis, autoimmune hepatitis, pemphigus vulgaris, myasthenia gravis, Behçet's disease, dermatomyositis, polymyositis
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
1-3 mg/kg/day orally once daily or divided twice daily; maximum dose 2.5 mg/kg/day for rheumatoid arthritis; usual dose 50-150 mg/day.
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.
Terminal elimination half-life of azathioprine is approximately 4.5 hours (range 2–6 h), while its active metabolite 6-mercaptopurine has a half-life of 0.5–2 hours. Clinical context: Renal impairment prolongs half-life.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Metabolized via xanthine oxidase and thiopurine methyltransferase (TPMT) to active and inactive metabolites. Co-administration with allopurinol inhibits xanthine oxidase, requiring dose reduction of azathioprine.
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Renal: 88% as 6-mercaptopurine and metabolites; biliary: <10%
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
30% bound to plasma proteins, primarily albumin.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
0.8–1.0 L/kg, indicating extensive distribution into tissues.
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Oral: 41–47% (azathioprine); 100% for IV administration.
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
GFR >50 m L/min: no adjustment; GFR 10-50 m L/min: 75% of normal dose; GFR <10 m L/min: 50% of normal dose.
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.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: contraindicated.
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.
2-3 mg/kg/day orally once daily; initial dose 1 mg/kg/day in divided doses; not recommended in children <1 year.
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.
Start at low end of dosing range (50 mg once daily); monitor renal function and adjust accordingly.
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.
Chronic immunosuppression increases the risk of malignancy, particularly lymphoma and skin cancer. Patients should be monitored for neoplasia. The drug should be used only if potential benefits outweigh risks.
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.
Hematologic toxicity (leukopenia, thrombocytopenia, anemia) - monitor blood counts. Hepatotoxicity. Increased infection risk. Hypersensitivity reactions. TPMT deficiency increases toxicity risk. Monitor for pancreatitis, especially in Crohn's patients. Avoid live vaccines. Photosensitivity and skin cancer risk.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Hypersensitivity to azathioprine or 6-mercaptopurine. Pregnancy (category D) unless potential benefit justifies risk. Lactation. Severe hepatic impairment. Myelosuppression or active infection. Concurrent use with allopurinol without dose adjustment.
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).
No significant food interactions. May be taken with food to reduce gastrointestinal upset. Avoid concurrent use with raw or undercooked meats to reduce risk of infection due to immunosuppression.
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
Azathioprine is FDA Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., atrial septal defect, limb defects) in case reports, but risk may be lower than with other immunosuppressants. Second and third trimesters: Risk of fetal growth restriction, preterm delivery, and neonatal immunosuppression. Avoid unless benefit outweighs 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.
Azathioprine is excreted into breast milk in small amounts; milk-to-plasma ratio approximately 0.1. Infant exposure is low, but theoretical risk of immunosuppression. Weigh benefits against risks; consider monitoring infant for leukopenia and infections.
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.
Increased clearance and reduced bioavailability during pregnancy may require dose increase to maintain therapeutic levels; monitor thiopurine metabolite levels (6-TGN, 6-MMP) and adjust accordingly. Often no change required if stable disease.
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.
Azasan (azathioprine) is a prodrug of 6-mercaptopurine. Screen for TPMT deficiency before initiation to avoid severe myelosuppression. Monitor CBC and liver function weekly for first month, then monthly. Corticosteroid-sparing agent in autoimmune conditions. Avoid live vaccines during therapy.
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.
Take exactly as prescribed; do not change dose without consulting your doctor.,Report any signs of infection, unusual bruising/bleeding, or fatigue immediately.,Avoid exposure to individuals with infections; maintain good hand hygiene.,Use effective contraception during treatment and for at least 3 months after stopping.,Do not receive live vaccines (e.g., MMR, varicella) while taking this medication.,Limit sun exposure; use sunscreen and protective clothing due to increased skin cancer risk.
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.
No interactions on record
"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."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about AZASAN vs ALFENTA, answered by our medical review team.
AZASAN is a Immunosuppressant that works by Azathioprine is a purine analog that inhibits purine synthesis, thereby interfering with DNA and RNA synthesis. It is metabolized to 6-mercaptopurine, which inhibits T-cell activation and proliferation, leading to immunosuppression.. 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.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between AZASAN and ALFENTA 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 AZASAN is: 1-3 mg/kg/day orally once daily or divided twice daily; maximum dose 2.5 mg/kg/day for rheumatoid arthritis; usual dose 50-150 mg/day.. 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.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between AZASAN and ALFENTA in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. AZASAN is classified as Category C. Azathioprine is FDA Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., atrial septal defect, limb defects) in case reports, but risk may be lower th. 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. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.