Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ALFENTA vs BACTRIM DS
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.
BACTRIM DS is a combination of sulfamethoxazole and trimethoprim. Sulfamethoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid (PABA), while trimethoprim inhibits dihydrofolate reductase, blocking reduction of dihydrofolate to tetrahydrofolate. This sequential blockade of folic acid synthesis leads to bactericidal action.
Induction and maintenance of anesthesia,Analgesic supplement during surgical procedures,Intravenous use for monitored anesthesia care (MAC)
FDA-approved: Urinary tract infections, acute otitis media, acute exacerbations of chronic bronchitis, traveler's diarrhea, shigellosis, Pneumocystis jirovecii pneumonia (PCP), toxoplasmosis,Off-label: Methicillin-resistant Staphylococcus aureus (MRSA) infections, Stenotrophomonas maltophilia infections, nocardiosis, Wegener's granulomatosis (as second-line therapy), inflammatory bowel disease
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.
One double-strength tablet (trimethoprim 160 mg-sulfamethoxazole 800 mg) orally every 12 hours.
Terminal elimination half-life: 90–111 minutes (1.5–1.85 hours); prolonged in hepatic impairment.
Sulfamethoxazole: 8-10 hours; Trimethoprim: 8-12 hours; prolonged in renal impairment (creatinine clearance <30 m L/min: up to 24-48 hours).
Hepatic via CYP3A4 to inactive metabolites; major metabolite is desmethylalfentanil (inactive).
Sulfamethoxazole is metabolized primarily by N-acetylation and glucuronidation; trimethoprim is metabolized by O-demethylation and N-oxidation. Both are eliminated renally via glomerular filtration and tubular secretion.
Primarily renal (urinary) elimination as metabolites; approximately 80% recovered in urine, 20% in feces.
Renal: 50-70% as sulfamethoxazole (unchanged and acetylated metabolite), 40-60% as trimethoprim (unchanged); biliary: <10% for both; fecal: <4%.
Approximately 92% bound, primarily to alpha-1 acid glycoprotein and albumin.
Sulfamethoxazole: 68% bound (albumin); Trimethoprim: 44% bound (albumin, alpha-1-acid glycoprotein).
0.5–1.0 L/kg; reflects moderate tissue distribution; higher Vd in neonates and elderly.
Sulfamethoxazole: 0.21 L/kg; Trimethoprim: 1.3-1.8 L/kg (wide distribution, higher in tissues than plasma).
Intravenous: 100%; intramuscular: approximately 90%; intrathecal: approximately 10% (due to systemic absorption following spinal administration).
Oral: >90% for both components; IV: 100%.
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.
Cr Cl >30 m L/min: No adjustment; Cr Cl 15-30 m L/min: 50% of usual dose every 12 hours; Cr Cl <15 m L/min: Not recommended.
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 Class A: No adjustment; Child-Pugh Class B: Use with caution, no specific dose recommendation; Child-Pugh Class C: Contraindicated.
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.
Based on trimethoprim component: 8 mg/kg/day of trimethoprim divided every 12 hours. For severe infections, up to 20 mg/kg/day of trimethoprim divided every 6 hours.
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.
Monitor renal function; adjust dose based on Cr Cl. Increased risk of hyperkalemia and folate deficiency; consider folate supplementation.
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.
BACTRIM DS carries a black box warning for severe hypersensitivity reactions including Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and fulminant hepatic necrosis. Also warns about fatal reactions such as agranulocytosis, aplastic anemia, and other blood dyscrasias. Additionally, use in pregnancy at term may cause kernicterus in the newborn.
Respiratory depression; abuse potential; hypotension; bradycardia; muscle rigidity; serotonin syndrome with concurrent serotonergic drugs; adrenal insufficiency; risk of withdrawal with prolonged use.
Hypersensitivity reactions: risk of SJS/TEN, especially in patients with HIV, folate deficiency, or genetic susceptibility (e.g., HLA-B*1502, HLA-A*3101). Discontinue at first sign of rash.,Hematologic toxicity: monitor CBCs; caution in patients with folate deficiency, renal impairment, or prolonged therapy.,Hepatic toxicity: can cause cholestatic jaundice, hepatic necrosis; avoid in hepatic impairment.,Renal toxicity: maintain adequate hydration to prevent crystalluria; adjust dose in renal impairment.,Hyperkalemia: risk with high-dose trimethoprim; monitor potassium, especially in patients with renal dysfunction or on potassium-sparing diuretics.,Hypoglycemia: risk in patients with renal impairment or malnutrition; caution with sulfonylureas.,Photosensitivity: avoid excessive sun exposure.,Pregnancy: avoid at term due to risk of kernicterus; use only if benefit outweighs risk.,Lactation: caution due to potential for kernicterus in infants with G6PD deficiency.
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 sulfamethoxazole, trimethoprim, or any component.,History of drug-induced immune thrombocytopenia with sulfonamides or trimethoprim.,Severe hepatic disease (e.g., acute hepatitis, cirrhosis with jaundice).,Severe renal impairment (Cr Cl <15 m L/min) unless dialysis is available.,Megaloblastic anemia due to folate deficiency.,Pregnancy at term and nursing mothers (due to risk of kernicterus).,Concurrent use with dofetilide (increased risk of arrhythmias).,Infants <2 months of age (sulfonamides can cause kernicterus).
No known interactions with food. However, grapefruit juice may increase alfentanil serum concentrations due to CYP3A4 inhibition; avoid concurrent consumption.
Avoid high-potassium foods (e.g., bananas, oranges, potatoes) as trimethoprim can increase serum potassium. Avoid alcohol, which may cause disulfiram-like reaction (flushing, nausea, tachycardia). No significant food-drug interactions beyond potassium and alcohol.
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.
First trimester: Folate antagonist; associated with neural tube defects, cardiovascular malformations, and cleft palate. Second trimester: Growth restriction, preterm birth. Third trimester: Kernicterus risk due to bilirubin displacement from albumin. Avoid during entire pregnancy.
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.
Breastfeeding safety: Both trimethoprim and sulfamethoxazole are excreted into breast milk; M/P ratio for trimethoprim ~1.25, sulfamethoxazole ~0.15. Caution in infants under 2 months or with G6PD deficiency; theoretical risk of kernicterus.
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 standard dose adjustment recommended; avoid use if possible. If necessary, ensure adequate folic acid intake; may need to increase dose due to increased clearance in pregnancy, but specific data lacking.
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.
Bactrim DS (sulfamethoxazole/trimethoprim) is contraindicated in G6PD deficiency due to risk of hemolytic anemia. Monitor for hyperkalemia, especially in elderly or those with renal impairment. Caution with warfarin (potentiates anticoagulation). Avoid in pregnancy (teratogenic) and lactation. Use with caution in folate deficiency; supplement folate if needed.
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.
Take with a full glass of water and stay well-hydrated to prevent crystalluria.,Avoid prolonged sun exposure; use sunscreen as this drug may cause photosensitivity.,Complete the full course even if you feel better to prevent antibiotic resistance.,Report any skin rash, sore throat, fever, or unusual bleeding immediately.,Do not take if you are pregnant, planning to become pregnant, or breastfeeding.,Inform your doctor if you have kidney disease, G6PD deficiency, or are on blood thinners.
"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."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ALFENTA vs BACTRIM DS, 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.. BACTRIM DS is a Sulfonamide Antibiotic Combination that works by BACTRIM DS is a combination of sulfamethoxazole and trimethoprim. Sulfamethoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid (PABA), while trimethoprim inhibits dihydrofolate reductase, blocking reduction of dihydrofolate to tetrahydrofolate. This sequential blockade of folic acid synthesis leads to bactericidal action.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ALFENTA and BACTRIM DS 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 BACTRIM DS is: One double-strength tablet (trimethoprim 160 mg-sulfamethoxazole 800 mg) orally every 12 hours.. 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 ALFENTA and BACTRIM DS 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. 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. BACTRIM DS is classified as Category C. First trimester: Folate antagonist; associated with neural tube defects, cardiovascular malformations, and cleft palate. Second trimester: Growth restriction, preterm birth. Third . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.