BACTRIM DS
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BACTRIM DS (BACTRIM DS).
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.
| Metabolism | 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. |
| Excretion | Renal: 50-70% as sulfamethoxazole (unchanged and acetylated metabolite), 40-60% as trimethoprim (unchanged); biliary: <10% for both; fecal: <4%. |
| Half-life | Sulfamethoxazole: 8-10 hours; Trimethoprim: 8-12 hours; prolonged in renal impairment (creatinine clearance <30 mL/min: up to 24-48 hours). |
| Protein binding | Sulfamethoxazole: 68% bound (albumin); Trimethoprim: 44% bound (albumin, alpha-1-acid glycoprotein). |
| Volume of Distribution | Sulfamethoxazole: 0.21 L/kg; Trimethoprim: 1.3-1.8 L/kg (wide distribution, higher in tissues than plasma). |
| Bioavailability | Oral: >90% for both components; IV: 100%. |
| Onset of Action | Oral: therapeutic effect within 1-2 days for urinary tract infections; IV: 30-60 minutes. |
| Duration of Action | 12-24 hours; typically dosed every 12 hours; clinical effect persists until drug concentrations fall below MIC. |
| Brand Substitutes | Cortina DS 800mg/160mg Tablet, Patrim DS 800mg/160mg Tablet, Colizole DS 800mg/160mg Tablet, Tabrol DS Tablet, Trisulfose DS 800mg/160mg Tablet |
One double-strength tablet (trimethoprim 160 mg-sulfamethoxazole 800 mg) orally every 12 hours.
| Dosage form | TABLET |
| Renal impairment | CrCl >30 mL/min: No adjustment; CrCl 15-30 mL/min: 50% of usual dose every 12 hours; CrCl <15 mL/min: Not recommended. |
| Liver impairment | Child-Pugh Class A: No adjustment; Child-Pugh Class B: Use with caution, no specific dose recommendation; Child-Pugh Class C: Contraindicated. |
| Pediatric use | 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. |
| Geriatric use | Monitor renal function; adjust dose based on CrCl. Increased risk of hyperkalemia and folate deficiency; consider folate supplementation. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BACTRIM DS (BACTRIM DS).
| Breastfeeding | 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. |
| Teratogenic Risk | 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. |
■ FDA Black Box Warning
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.
| Serious Effects |
["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 (CrCl <15 mL/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)."]
| Precautions | ["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."] |
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| Fetal Monitoring |
| Folic acid supplementation; folate levels. Fetal ultrasound for congenital anomalies. Newborn bilirubin and G6PD status. Maternal CBC, renal function, and periodic urinalysis. |
| Fertility Effects | Trimethoprim inhibits dihydrofolate reductase, potentially impairing spermatogenesis and ovulation. Reversible upon discontinuation. |
| Food/Dietary | 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. |
| Clinical Pearls | 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. |
| Patient Advice | 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. |