SULFA-TRIPLE #2
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SULFA-TRIPLE #2 (SULFA-TRIPLE #2).
The sulfonamides (sulfamethazine, sulfathiazole, sulfamerazine) act as competitive inhibitors of para-aminobenzoic acid (PABA) utilization in bacterial dihydrofolate synthesis, thereby inhibiting folic acid synthesis and bacterial growth.
| Metabolism | Hepatic metabolism via acetylation, glucuronidation, and oxidation; CYP450 involvement is minimal. |
| Excretion | Renal (approximately 70-80% as unchanged sulfonamides via glomerular filtration and tubular secretion); biliary/fecal (approximately 20-30% as metabolites). |
| Half-life | Sulfadiazine: 10-16 hours; Sulfamerazine: 15-24 hours; Sulfamethazine: 12-24 hours. The combined half-life is approximately 15-20 hours in patients with normal renal function, requiring dosing every 12-24 hours. |
| Protein binding | Sulfadiazine: 45-60% bound to albumin; Sulfamerazine: 56-70%; Sulfamethazine: 60-80%. Overall, approximately 50-70% bound to serum albumin. |
| Volume of Distribution | 0.3-0.5 L/kg for each component; total Vd approximately 0.4 L/kg, indicating distribution throughout total body water and tissues. |
| Bioavailability | Oral: 70-90% for each sulfonamide, with complete absorption from the gastrointestinal tract. |
| Onset of Action | Oral: 2-4 hours for therapeutic sulfonamide concentrations in blood; clinical effect typically seen within 24-48 hours. |
| Duration of Action | Oral: Approximately 12-24 hours following a single dose, supporting twice-daily dosing. Clinical effect persists for 1-2 days after discontinuation due to slow elimination of components. |
2 tablets orally every 4 hours initially, then 2 tablets every 6 hours thereafter. Each tablet contains 167 mg sulfadiazine, 167 mg sulfamerazine, and 167 mg sulfamethazine (total sulfonamide 500 mg per tablet).
| Dosage form | TABLET |
| Renal impairment | GFR 15-50 mL/min: administer every 8-12 hours; GFR <15 mL/min: contraindicated due to accumulation of sulfonamides. |
| Liver impairment | Child-Pugh Class B: use with caution and consider 50% dose reduction; Child-Pugh Class C: contraindicated due to risk of hepatotoxicity and impaired drug metabolism. |
| Pediatric use | For children ≥2 years: 1 tablet per 20 lbs (9 kg) body weight orally initially, then 1/2 tablet per 20 lbs every 6 hours. Maximum single dose 2 tablets. Not recommended for infants <2 months (risk of kernicterus). |
| Geriatric use | Start at lower end of dosing interval (every 8-12 hours) due to age-related decline in renal function. Monitor renal function and adjust based on GFR. Avoid in patients with GFR <30 mL/min. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SULFA-TRIPLE #2 (SULFA-TRIPLE #2).
| Breastfeeding | Sulfonamides are excreted into breast milk; M/P ratio approximately 0.5-0.8. Avoid in breastfeeding if infant is premature, ill, or G6PD-deficient due to risk of kernicterus and hemolysis. Use caution and monitor infant for jaundice, diarrhea, and rash. |
| Teratogenic Risk | First trimester: Avoid; sulfonamides are associated with teratogenic effects in animal studies (e.g., cleft palate) and possible neural tube defects in humans, though data are conflicting. Second and third trimesters: Risk of kernicterus in the neonate if administered near term due to displacement of bilirubin from albumin; avoid after 32 weeks gestation. Potential for hemolytic anemia in G6PD-deficient fetuses. |
■ FDA Black Box Warning
Not available (sulfonamides have boxed warnings for severe hypersensitivity reactions; specific warning for SULFA-TRIPLE #2 is not explicitly documented).
| Serious Effects |
Hypersensitivity to sulfonamides; porphyria; severe hepatic or renal impairment; pregnancy and lactation (relative); concurrent use with methenamine.
| Precautions | Risk of hypersensitivity reactions including Stevens-Johnson syndrome, hepatotoxicity, agranulocytosis, and blood dyscrasias; use with caution in renal or hepatic impairment; adequate fluid intake to prevent crystalluria. |
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| Fetal Monitoring | Monitor maternal CBC (especially for agranulocytosis, hemolytic anemia), renal function, and liver function. In fetus/neonate, monitor for signs of kernicterus (bilirubin levels, neurologic status) if exposure occurred near term. Consider G6PD testing in at-risk populations. |
| Fertility Effects | No specific data on human fertility impairment. In animal studies, high doses have shown reduced fertility; clinical significance unknown. |