GANTANOL-DS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for GANTANOL-DS (GANTANOL-DS).
Sulfamethoxazole is a sulfonamide that inhibits bacterial dihydrofolate synthesis by competing with para-aminobenzoic acid, thereby blocking folate synthesis. Trimethoprim inhibits bacterial dihydrofolate reductase, converting dihydrofolate to tetrahydrofolate. This sequential blockade produces bactericidal activity.
| Metabolism | Sulfamethoxazole is metabolized primarily by N-acetylation and glucuronidation; trimethoprim is metabolized by oxidation and conjugation. Both undergo hepatic metabolism with involvement of CYP450 enzymes. |
| Excretion | Primarily renal (70-100%) as unchanged drug and inactive metabolites (sulfamethoxazole N4-acetyl and glucuronide conjugates); <5% biliary/fecal. |
| Half-life | 10-12 hours (sulfamethoxazole component); prolonged in renal impairment (up to 30 hours with CrCl <15 mL/min). |
| Protein binding | Sulfamethoxazole: 65-70% bound (primarily albumin); trimethoprim: 40-45% bound. |
| Volume of Distribution | 0.2-0.4 L/kg (sulfamethoxazole); 1.5-2.0 L/kg (trimethoprim, indicating extensive tissue penetration). |
| Bioavailability | Oral: 85-95% (sulfamethoxazole); 90-100% (trimethoprim). |
| Onset of Action | Oral: 1-2 hours (peak serum concentration); clinical effect within 24-48 hours for susceptible infections. |
| Duration of Action | 12-24 hours (dosing every 12 hours recommended); sustained with once-daily dosing for urinary tract infections. |
| Molecular Weight | 253.28 |
2 g (DS strength: 2 g sulfamethoxazole/400 mg trimethoprim) orally every 12 hours for 14-21 days for Pneumocystis jirovecii pneumonia.
| Dosage form | TABLET |
| Renal impairment | CrCl 15-30 mL/min: decrease dose by 50% (e.g., 1 g PO q12h); CrCl <15 mL/min: contraindicated unless hemodialysis; use with caution and monitor levels. |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B: reduce dose by 50% (e.g., 1 g PO q12h); Class C: avoid use or use with extreme caution. |
| Pediatric use | For PCP: 75-100 mg/kg/day of sulfamethoxazole (Bactrim component) divided every 6-8 hours, PO or IV. Weight-based: sulfamethoxazole 20 mg/kg/dose (max 2 g/dose) q8h. |
| Geriatric use | Start at lower end of dosing (e.g., 1 g DS PO q12h) due to age-related renal decline; monitor renal function and serum potassium; adjust per renal function. |
| 1st trimester | Avoid; sulfonamides cross placenta and may cause kernicterus in neonate; associated with congenital malformations in some studies. |
| 2nd trimester | Caution; risk of hemolytic anemia in G6PD-deficient fetus; use only if benefit outweighs risk. |
| 3rd trimester | Avoid near term; risk of kernicterus and hemolytic anemia in neonate due to bilirubin displacement. |
Clinical note
Comprehensive clinical and safety monograph for GANTANOL-DS (GANTANOL-DS).
| Placental transfer | High; crosses placenta readily, achieving fetal concentrations 50-90% of maternal levels. |
| Breastfeeding | Excreted into breast milk in low concentrations; risk of kernicterus in neonates, especially with G6PD deficiency or jaundice; avoid in nursing mothers of ill or premature infants. |
■ FDA Black Box Warning
Fatal hypersensitivity reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias have been reported.
| Serious Effects |
Hypersensitivity to sulfonamidesSevere hepatic or renal impairmentPorphyriaG6PD deficiency (relative, but absolute in hemolytic risk)Infants <2 months (except for congenital toxoplasmosis)Pregnancy at term or lactation (risk of kernicterus)
| Precautions | Hypersensitivity reactions, severe dermatologic reactions, hematologic toxicity, folate deficiency, glucose-6-phosphate dehydrogenase deficiency, renal/hepatic impairment, elderly patients, pregnancy (contraindicated at term), lactation, phototoxicity, hyperkalemia (high-dose trimethoprim). |
| Food/Dietary | Avoid high-potassium foods (bananas, oranges, potatoes) as TMP can increase potassium levels. Limit vitamin K-rich foods if on anticoagulants. |
Loading safety data…
| Lactation Rating |
| L3 - Moderately Safe (risk of kernicterus, especially in first month) |
| Teratogenic Risk | First trimester: Avoid due to risk of neural tube defects and congenital malformations. Second/Third trimester: Risk of kernicterus and hemolytic anemia in G6PD-deficient fetuses; avoid near term. |
| Fetal Monitoring | Monitor complete blood count, liver function tests, bilirubin, and G6PD status. Fetal ultrasound for anomalies if exposed in first trimester. Assess neonatal bilirubin after delivery. |
| Fertility Effects | No significant adverse effects on fertility reported in humans; animal studies show no impairment. |
| Clinical Pearls | GANTANOL-DS is a sulfamethoxazole/trimethoprim double-strength combination. Monitor renal function, CBC, and potassium levels. Avoid in G6PD deficiency. Use with caution in elderly and patients with folate deficiency. Maintain adequate hydration to prevent crystalluria. |
| Patient Advice | Take with a full glass of water and stay well hydrated. · Complete the entire course even if symptoms improve. · Avoid prolonged sun exposure; use sunscreen. · Report rash, fever, sore throat, or unusual bleeding. · If you have G6PD deficiency, inform your doctor. |