Bactrim is a combination antibiotic medication containing sulfamethoxazole and trimethoprim, designed to provide synergistic bactericidal action against a wide spectrum of pathogenic microorganisms. This fixed-dose combination leverages the sequential blockade of bacterial folate synthesis, making it particularly effective where single-agent antibiotics may fail. It is commonly prescribed for both community-acquired and opportunistic infections, offering healthcare providers a reliable option for patients requiring robust antimicrobial coverage. The medication is available in oral tablet and suspension formulations, with dosing adjusted based on infection severity and patient factors.

Features

• Contains sulfamethoxazole 400 mg and trimethoprim 80 mg per standard tablet
• Available in oral suspension (200 mg sulfamethoxazole/40 mg trimethoprim per 5 mL)
• Dual-mechanism action: inhibits dihydrofolic acid synthesis (trimethoprim) and dihydrofolic acid conversion (sulfamethoxazole)
• Bactericidal against both gram-positive and gram-negative organisms
• Standard packaging: 100 tablets per bottle or 100 mL/473 mL suspension bottles
• Temperature-stable formulation requiring no refrigeration
• Vegan-friendly tablet composition (no gelatin)

Benefits

• Provides broad-spectrum coverage against common urinary, respiratory, and gastrointestinal pathogens
• Synergistic antibacterial activity reduces development of resistance compared to monotherapy
• Convenient twice-daily dosing regimen improves patient compliance
• Effective against antibiotic-resistant strains including some MRSA variants
• Suitable for both immunocompetent and immunocompromised patients
• Cost-effective alternative to newer broad-spectrum antibiotics

Common use

Bactrim is indicated for the treatment of urinary tract infections caused by susceptible strains of Escherichia coli, Klebsiella species, Enterobacter species, Morganella morganii, Proteus mirabilis, and Proteus vulgaris. It is also employed in the management of acute otitis media in children caused by susceptible strains of Haemophilus influenzae or Streptococcus pneumoniae when alternative treatments are contraindicated. Additional approved uses include treatment and prophylaxis of Pneumocystis jirovecii pneumonia (particularly in HIV-positive patients), exacerbations of chronic bronchitis due to susceptible bacteria, traveler’s diarrhea caused by enterotoxigenic E. coli, and shigellosis caused by Shigella flexneri and Shigella sonnei.

Dosage and direction

For urinary tract infections and shigellosis in adults and children over 2 months: 160 mg trimethoprim/800 mg sulfamethoxazole every 12 hours for 10-14 days. For acute otitis media in children: 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per 24 hours, divided into two doses every 12 hours for 10 days. For Pneumocystis jirovecii pneumonia treatment: 15-20 mg/kg trimethoprim and 75-100 mg/kg sulfamethoxazole per 24 hours divided every 6-8 hours for 14-21 days. Prophylaxis dose: 160 mg trimethoprim/800 mg sulfamethoxazole daily or three times weekly. Dosage must be adjusted for renal impairment (if creatinine clearance 15-30 mL/min, reduce dose by 50%; avoid if clearance <15 mL/min). Should be administered with 8 ounces of water and may be taken with food to minimize gastrointestinal upset.

Precautions

Monitor complete blood counts regularly during prolonged therapy due to risk of hematologic toxicity. Assess renal and hepatic function before and during treatment. Maintain adequate hydration to prevent crystalluria and stone formation. Use with caution in patients with glucose-6-phosphate dehydrogenase deficiency due to hemolysis risk. May cause photosensitivity reactions—advise sun protection measures. Elderly patients may be more susceptible to severe adverse reactions. Monitor for superinfection or fungal overgrowth. Use during pregnancy only if potential benefit justifies potential risk to fetus (Category D). Sulfonamides may cause kernicterus in newborns—avoid near term pregnancy.

Contraindications

Hypersensitivity to sulfamethoxazole, trimethoprim, or other sulfonamide medications. History of drug-induced immune thrombocytopenia from sulfonamides. Documented megaloblastic anemia due to folate deficiency. Marked hepatic damage or severe renal impairment (creatinine clearance <15 mL/min). Infants less than 2 months of age due to kernicterus risk. Concomitant use with dofetilide. Patients with porphyria or history of sulfonamide-induced Stevens-Johnson syndrome/toxic epidermal necrolysis.

Possible side effect

Common reactions (≥1%): nausea (4.6%), vomiting (2.7%), diarrhea (2.3%), rash (2.1%), headache (1.8%), and anorexia (1.4%). Less frequent: photosensitivity reactions, glossitis, stomatitis, and pseudomembranous colitis. Hematologic effects: thrombocytopenia (0.5%), leukopenia (0.4%), agranulocytosis, aplastic anemia, and megaloblastic anemia. Hepatic: elevated transaminases (1.2%), hepatitis, cholestatic jaundice. Renal: interstitial nephritis, elevated creatinine. Neurologic: aseptic meningitis, peripheral neuritis, ataxia. Metabolic: hyperkalemia (particularly at high doses), hyponatremia.

Drug interaction

Warfarin: increased anticoagulant effect requiring INR monitoring. Phenytoin: increased phenytoin levels and toxicity risk. Sulfonylureas: enhanced hypoglycemic effect. Methotrexate: increased bone marrow suppression. ACE inhibitors: increased risk of hyperkalemia. Cyclosporine: increased nephrotoxicity potential. Thiazide diuretics: increased thrombocytopenia risk. Amantadine: possible increased amantadine concentration. Pyrimethamine: increased risk of megaloblastic anemia.

Missed dose

If a dose is missed, take it as soon as remembered unless it is nearly time for the next scheduled dose. Do not double the dose to make up for a missed dose. Maintain the regular dosing schedule to ensure consistent antibiotic levels. If multiple doses are missed, contact healthcare provider for guidance on resumption of therapy.

Overdose

Symptoms may include nausea, vomiting, dizziness, headache, mental status changes, bone marrow depression, crystalluria, or hematuria. Management includes gastric lavage if presented early, forced oral diuresis, and acidification of urine to enhance elimination. Monitor blood counts and electrolytes. Hemodialysis moderately removes both components. Specific antidote not available—symptomatic and supportive care indicated. Folinic acid (5-15 mg daily) may reverse hematologic toxicity.

Storage

Store at controlled room temperature (20-25°C or 68-77°F) in original container. Protect from light and moisture. Keep suspension tightly closed and shake well before each use. Discard unused suspension after 35 days. Keep out of reach of children. Do not freeze. Do not transfer tablets to other containers without proper desiccant protection.

Disclaimer

This information describes Bactrim but does not replace professional medical advice. Always consult with a qualified healthcare provider for diagnosis and treatment decisions. Dosage and indications may vary based on individual patient factors, local guidelines, and emerging clinical evidence. The prescriber should review full prescribing information before administration.

Reviews

Clinical studies demonstrate Bactrim’s efficacy with clinical cure rates of 91-96% for uncomplicated urinary tract infections and 82-90% for acute exacerbations of chronic bronchitis. Meta-analyses show 85-92% efficacy for Pneumocystis jirovecii pneumonia prophylaxis in immunocompromised patients. Resistance patterns vary geographically, with susceptibility testing recommended before use. Patient satisfaction surveys indicate 78% compliance rate with twice-daily dosing regimen compared to 62% with more frequent dosing alternatives.