GANTANOL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GANTANOL (GANTANOL).
Sulfamethoxazole is a sulfonamide that inhibits bacterial dihydropteroate synthase, preventing folate synthesis. Trimethoprim inhibits bacterial dihydrofolate reductase, blocking tetrahydrofolate production. The combination produces sequential blockade of folate metabolism, leading to bactericidal activity.
| Metabolism | Sulfamethoxazole is metabolized primarily by N-acetylation and glucuronidation. Trimethoprim undergoes O-demethylation and oxidative metabolism. Both are excreted renally. |
| Excretion | Renal: 70% as unchanged drug; hepatic metabolism: 20% (glucuronidation); fecal: 10%. |
| Half-life | Terminal elimination half-life: 8-12 hours in healthy adults; prolonged in renal impairment (up to 24-36 hours in CrCl <30 mL/min). |
| Protein binding | 85-90% primarily to albumin. |
| Volume of Distribution | 0.15-0.3 L/kg; indicates limited extravascular distribution, primarily confined to plasma and interstitial fluid. |
| Bioavailability | Oral: 90-95%; Intravenous: 100%. |
| Onset of Action | Oral: 1-2 hours; Intravenous: 15-30 minutes. |
| Duration of Action | 12-24 hours; clinical effect persists for the dosing interval due to active metabolites. |
| Molecular Weight | 253.28 |
800 mg orally every 12 hours for 5-7 days.
| Dosage form | TABLET |
| Renal impairment | CrCl 30-60 mL/min: 800 mg every 24 hours. CrCl 15-29 mL/min: 800 mg every 48 hours. CrCl <15 mL/min or hemodialysis: 800 mg every 48-72 hours. |
| Liver impairment | Child-Pugh Class A: no adjustment. Child-Pugh Class B: reduce dose by 50%. Child-Pugh Class C: use contraindicated. |
| Pediatric use | 15 mg/kg orally every 6 hours for children 2 months to 12 years; maximum 2 g/day. |
| Geriatric use | Use with caution; start at 400 mg every 12 hours due to age-related renal decline. Monitor for toxicity. |
| 1st trimester | Contraindicated due to risk of neural tube defects and other teratogenic effects; folate antagonism interferes with fetal development. Evidence from animal studies and limited human data suggests increased risk of malformations. |
| 2nd trimester | Avoid unless no alternative; may cause kernicterus in neonates if administered near term due to displacement of bilirubin from albumin. Risk of hemolytic anemia in G6PD-deficient fetuses. |
| 3rd trimester | Contraindicated in third trimester due to high risk of neonatal hyperbilirubinemia and kernicterus. Avoid after 32-34 weeks gestation. Alternative therapy strongly recommended. |
Clinical note
Comprehensive clinical and safety monograph for GANTANOL (GANTANOL).
| Placental transfer | Sulfamethoxazole crosses the placenta readily, achieving fetal serum concentrations approximately 50-100% of maternal levels. Competes with bilirubin for albumin binding sites, posing risk of kernicterus. |
| Breastfeeding |
■ FDA Black Box Warning
Fatal hypersensitivity reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, and hepatic necrosis have occurred. Also associated with fatal hematologic toxicities (e.g., agranulocytosis, aplastic anemia). Coadministration with methotrexate increases risk of megaloblastic anemia.
| Serious Effects |
Hypersensitivity to sulfonamides or any componentInfants < 2 months of age (except for treatment of congenital toxoplasmosis)Pregnancy at term (third trimester) or nursing mothers with infants at risk for kernicterusSevere hepatic or renal impairment (creatinine clearance < 15 mL/min)Known G6PD deficiencyPorphyria (may precipitate acute attack)
| Precautions | Hypersensitivity and skin reactions (discontinue at first sign of rash). Hemolysis in G6PD-deficient patients. Risk of hepatotoxicity, including cholestatic jaundice and hepatic necrosis. Photosensitivity. Severe renal and hepatic impairment. Use caution in elderly, folate-deficient patients, and those with megaloblastic anemia. Possible hyperkalemia with high-dose treatment in renal impairment. |
| Food/Dietary |
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| Gantanol (sulfamethoxazole) is excreted into breast milk in low concentrations, but may cause kernicterus in jaundiced or G6PD-deficient infants. Caution is advised, especially in preterm or ill infants. American Academy of Pediatrics considers sulfonamides compatible with breastfeeding in healthy term infants, but avoid if infant has hyperbilirubinemia or G6PD deficiency. |
| Lactation Rating | L3 (Moderately Safe) - Use with caution in healthy term infants; avoid in preterm, jaundiced, or G6PD-deficient infants. |
| Teratogenic Risk | First trimester: Sulfonamides cross the placenta; risk of kernicterus in neonates if used near term. Animal studies show cleft palate and other anomalies at high doses. Human data insufficient; avoid use in first trimester unless benefit outweighs risk. Second/third trimester: Risk of neonatal jaundice and hemolytic anemia in G6PD deficiency; contraindicated after 38 weeks or near delivery due to kernicterus risk. |
| Fetal Monitoring | Monitor complete blood count, renal function, liver enzymes, and bilirubin levels. Assess for fetal distress or preterm labor. In newborn, monitor for jaundice, anemia, and signs of kernicterus. |
| Fertility Effects | No significant adverse effects on fertility reported in animal studies or human data. Sulfonamides may rarely cause reversible oligospermia in males. |
| Avoid alcohol during and for 3 days after therapy. Limit high-potassium foods if using high doses. Take with food to reduce GI upset. |
| Clinical Pearls | Gantanol (sulfamethoxazole) is a sulfonamide antibiotic often used in combination with trimethoprim (co-trimoxazole). Monitor for hypersensitivity reactions, especially in HIV patients. Adjust dose in renal impairment (CrCl <30 mL/min avoid). Hydrate to prevent crystalluria. |
| Patient Advice | Take with a full glass of water to prevent kidney stones. · Complete full course even if feeling better. · Avoid prolonged sun exposure; use sunscreen. · Report rash, fever, or sore throat immediately. · Do not use if allergic to sulfa drugs. |