TRIPLE SULFAS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TRIPLE SULFAS (TRIPLE SULFAS).
Competitive inhibition of dihydropteroate synthase, thereby blocking folate synthesis and bacterial DNA replication. Triple sulfas (sulfadiazine, sulfamerazine, sulfamethazine) act synergistically to inhibit folic acid synthesis.
| Metabolism | Primarily hepatic acetylation to inactive metabolites; also conjugation with glucuronic acid. Metabolites are renally excreted. Sulfamethazine is acetylated at a slower rate. |
| Excretion | Primarily renal; approximately 70-100% excreted unchanged in urine via glomerular filtration and tubular secretion. Minor biliary/fecal elimination (<5%) with enterohepatic circulation possible. |
| Half-life | Terminal elimination half-life ranges from 10-12 hours in adults with normal renal function. Prolonged in renal impairment (up to 24-48 hours) and neonates (40-120 hours). |
| Protein binding | Sulfamethazine: 60-80%; sulfamerazine: 70-80%; sulfadiazine: 20-50%. Primary binding proteins: albumin (weakly, with displacement interactions). |
| Volume of Distribution | 0.3-0.6 L/kg for individual sulfonamides; combined Vd approximately 0.4 L/kg, indicating distribution into total body water with some tissue binding. |
| Bioavailability | Oral: approximately 85-95% for the combination; well absorbed from GI tract. Intravenous: 100%. |
| Onset of Action | Oral: 1-2 hours for bacteriostatic effect; peak serum concentrations at 2-4 hours. Intravenous: immediate onset; peak at end of infusion. |
| Duration of Action | 6-12 hours; clinical effect lasts approximately 12 hours after oral dose. Use every 6 hours for continuous coverage. Longer duration in renal impairment. |
| Molecular Weight | 251.3 |
1 to 2 tablets (each containing sulfadiazine 167 mg, sulfamerazine 167 mg, sulfamethazine 167 mg) orally every 4 hours initially, then 2 tablets every 6 hours. Maximum daily dose: 6 grams of total sulfonamide.
| Dosage form | SUSPENSION |
| Renal impairment | GFR 30-50 mL/min: administer 75% of normal dose every 12 hours. GFR 10-29 mL/min: administer 50% of normal dose every 12-18 hours. GFR <10 mL/min: contraindicated. |
| Liver impairment | Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 25-50% and monitor for toxicity. Child-Pugh Class C: contraindicated. |
| Pediatric use | Children >2 months: initial loading dose of 75 mg/kg (based on total sulfonamide) orally, then 150 mg/kg/day divided every 6 hours. Maximum daily dose: 6 grams. |
| Geriatric use | Initiate at lower end of dosing range (e.g., 1 tablet every 6 hours) due to age-related renal impairment. Monitor renal function and adjust dose based on GFR. |
| 1st trimester | Contraindicated due to risk of kernicterus and teratogenic effects (folate antagonism, possible neural tube defects). Avoid use. |
| 2nd trimester | Use only if clearly needed; theoretical risk of kernicterus increases in third trimester. Consider alternative agents. |
| 3rd trimester | Contraindicated due to increased risk of kernicterus in the newborn. Avoid use, especially near term. |
Clinical note
Comprehensive clinical and safety monograph for TRIPLE SULFAS (TRIPLE SULFAS).
| Placental transfer | Sulfonamides readily cross the placenta, achieving fetal serum levels approximately 50-100% of maternal levels. Competition for bilirubin binding sites may increase risk of kernicterus. |
| Breastfeeding | Sulfonamides are excreted into breast milk in small amounts. In healthy term infants, risk is low, but in ill, premature, or hyperbilirubinemic infants, there is potential for kernicterus. Use only if benefit outweighs risk and monitor infant for jaundice. |
■ FDA Black Box Warning
Fatalities have occurred due to severe reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias. Do not use in patients with hypersensitivity to sulfonamides.
| Serious Effects |
Hypersensitivity to sulfonamidesPorphyriaSignificant hepatic or renal impairmentThird trimester of pregnancyNewborns (especially premature) and infants less than 2 months of age
| Precautions | Serious hypersensitivity reactions (e.g., Stevens-Johnson syndrome) may occur; discontinue at first sign of rash. Potential for blood dyscrasias, crystalluria with renal damage (ensure adequate hydration). Use caution in patients with renal or hepatic impairment, G6PD deficiency (risk of hemolytic anemia), and porphyria. May cause photosensitivity. |
| Food/Dietary | Avoid alcohol; may cause disulfiram-like reaction. No significant food interactions, but maintain high fluid intake to prevent crystalluria. |
Loading safety data…
| Lactation Rating | L3 (Moderately Safe, avoid in premature or jaundiced infants) |
| Teratogenic Risk | Sulfonamides cross the placenta. First trimester: association with neural tube defects, cardiovascular anomalies. Third trimester: risk of kernicterus in neonate due to bilirubin displacement from albumin; avoid near term. |
| Fetal Monitoring | Maternal: CBC, renal function, hepatic enzymes; fetal: ultrasound for anomalies, neonatal bilirubin monitoring if used near term. |
| Fertility Effects | No known significant impact on fertility in humans; animal studies show no adverse effects. |
| Clinical Pearls | Triple sulfas (sulfadiazine, sulfamethazine, sulfamerazine) are rarely used today due to resistance; efficacy limited to uncomplicated UTIs; ensure adequate hydration to prevent crystalluria; contraindicated in G6PD deficiency; avoid in infants <2 months due to risk of kernicterus. |
| Patient Advice | Take with a full glass of water and drink plenty of fluids throughout treatment. · Complete the full course even if symptoms improve. · Report rash, fever, sore throat, or unusual bleeding immediately. · Avoid sun exposure and use sunscreen; may cause photosensitivity. · Notify prescriber if pregnant, planning to become pregnant, or breastfeeding. · Do not use if allergic to sulfonamides or sulfa-containing drugs. |