Bactrim is a combination antibiotic medication containing sulfamethoxazole and trimethoprim. It belongs to the class of drugs known as sulfonamides and works synergistically to inhibit successive steps in the bacterial biosynthesis of essential nucleic acids and proteins. This dual-mechanism action provides a broad-spectrum bactericidal effect against a wide array of susceptible gram-positive and gram-negative organisms. It is a cornerstone in the treatment of numerous common and opportunistic infections, particularly when resistance to single-agent antibiotics is a concern. Its formulation ensures comprehensive coverage, making it a reliable choice for clinicians in both outpatient and inpatient settings.

Features

• Contains a fixed 5:1 ratio of sulfamethoxazole to trimethoprim for optimized synergistic antibacterial activity
• Available in multiple formulations: oral tablets (standard and double strength), oral suspension, and intravenous injection
• Exhibits bactericidal action against a broad spectrum of pathogens, including both aerobic and some opportunistic organisms
• Demonstrated efficacy against strains resistant to other antibiotic classes, including certain multidrug-resistant organisms
• Well-established pharmacokinetic profile with good tissue penetration, including urinary, respiratory, and gastrointestinal tracts

Benefits

• Provides effective treatment for a wide variety of common bacterial infections, reducing the need for multiple antibiotics
• The dual-mechanism action lowers the potential for development of bacterial resistance compared to single-agent therapies
• Offers flexible dosing options suitable for both adult and pediatric populations across different infection severities
• Cost-effective therapeutic option with widespread availability and inclusion on most insurance formularies
• Proven efficacy in both community-acquired infections and specific opportunistic infections in immunocompromised patients
• Rapid onset of action with clinical improvement often observed within 48-72 hours of initiation when appropriate

Common use

Bactrim is indicated for the treatment of various bacterial infections caused by susceptible strains of designated microorganisms. Primary indications include urinary tract infections (acute, recurrent, and chronic), acute exacerbations of chronic bronchitis in adults, acute otitis media in children, and traveler’s diarrhea. It is also approved for the treatment of Pneumocystis jirovecii pneumonia (PCP) prophylaxis and treatment, particularly in immunocompromised patients such as those with HIV/AIDS. Additionally, it is used for the treatment of shigellosis caused by susceptible strains of Shigella flexneri and Shigella sonnei. Off-label uses may include treatment of certain skin and soft tissue infections, nocardiosis, toxoplasmosis prophylaxis, and prevention of recurrent urinary tract infections.

Dosage and direction

Dosage varies based on the infection being treated, patient age, renal function, and severity of infection. 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 exacerbations of chronic bronchitis: same dosage for 14 days. For Pneumocystis jirovecii pneumonia treatment: 15-20 mg/kg trimethoprim/75-100 mg sulfamethoxazole per day in divided doses every 6-8 hours for 14-21 days. For prophylaxis of Pneumocystis jirovecii pneumonia: 160 mg trimethoprim/800 mg sulfamethoxazole daily or three times weekly. Pediatric dosing is based on weight for treatment of otitis media and urinary tract infections. All doses should be taken with a full glass of water and may be taken with food to minimize gastrointestinal upset. Dosage adjustment is required in patients with renal impairment (creatinine clearance below 30 mL/min).

Precautions

Patients should be advised to maintain adequate fluid intake to prevent crystalluria and stone formation. Use with caution in patients with impaired renal or hepatic function, severe allergies, bronchial asthma, glucose-6-phosphate dehydrogenase (G6PD) deficiency, or folate deficiency. Regular monitoring of complete blood counts, renal function, and liver enzymes is recommended during prolonged therapy. May cause photosensitivity reactions; patients should use sunscreen and protective clothing when exposed to sunlight. Caution should be exercised in elderly patients, who may be more susceptible to adverse effects, particularly hyperkalemia and bone marrow suppression. Discontinue immediately if rash or signs of serious skin reactions develop.

Contraindications

Bactrim is contraindicated in patients with known hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation. Should not be used in patients with documented megaloblastic anemia due to folate deficiency. Contraindicated in pregnancy at term and during the nursing period because sulfonamides may cause kernicterus in newborns. Should not be used in infants less than 2 months of age. Contraindicated in patients with severe hepatic damage or marked renal impairment where repeated measurements of the plasma drug concentration cannot be performed.

Possible side effect

Common side effects include nausea, vomiting, loss of appetite, and mild diarrhea. Skin reactions such as rash, pruritus, and photosensitivity may occur. More serious but less frequent adverse effects include Stevens-Johnson syndrome, toxic epidermal necrolysis, agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, hemolytic anemia, hyperkalemia, hyponatremia, hepatotoxicity, and pseudomembranous colitis. Renal toxicity including interstitial nephritis and elevated creatinine may occur. Neurological effects such as headache, dizziness, and insomnia have been reported. Allergic reactions ranging from mild rash to anaphylaxis may occur.

Drug interaction

Bactrim may potentiate the effects of warfarin and other oral anticoagulants, requiring close monitoring of prothrombin time. May increase concentrations of phenytoin, resulting in potential toxicity. Concurrent use with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers may increase risk of hyperkalemia. May enhance the hypoglycemic effect of sulfonylureas. Methotrexate levels may be increased, enhancing toxicity. Thiazide diuretics may increase risk of thrombocytopenia. Cyclosporine levels may be increased, requiring monitoring. May decrease the efficacy of oral contraceptives; additional contraceptive methods are recommended.

Missed dose

If a dose is missed, it should be taken as soon as remembered. However, if it is almost time for the next dose, the missed dose should be skipped and the regular dosing schedule resumed. Doubling the dose to make up for a missed dose is not recommended. Maintaining consistent antibiotic levels is important for efficacy, so patients should try to adhere to the prescribed schedule. If multiple doses are missed, patients should contact their healthcare provider for guidance.

Overdose

Symptoms of overdose may include nausea, vomiting, dizziness, headache, mental depression, confusion, and bone marrow depression. Massive overdose may result in jaundice, crystalluria, hematuria, and other blood dyscrasias. Treatment is supportive and symptomatic. Gastric lavage may be indicated if ingestion was recent. Maintain adequate fluid intake to promote urinary excretion. Acidification of urine may increase renal elimination of trimethoprim but should be avoided in patients with crystalluria or renal impairment. Hemodialysis may be moderately effective in removing both components, particularly trimethoprim. Monitor blood counts and electrolytes closely.

Storage

Store at room temperature between 15-30°C (59-86°F). Protect from light and moisture. Keep in the original container, tightly closed. Do not store in the bathroom. Keep all medications out of reach of children and pets. Oral suspension should be shaken well before each use and discarded after the expiration date or if contamination is suspected. Do not freeze the medication. Do not use if discolored or if particles are present.

Disclaimer

This information is provided for educational purposes only and does not constitute medical advice. Individual patient needs may vary. Always consult with a qualified healthcare professional before starting, changing, or stopping any medication. The prescribing physician should be aware of the complete medical history of the patient before prescribing Bactrim. This information may not include all possible uses, directions, precautions, interactions, or adverse effects.

Reviews

Clinical studies have demonstrated Bactrim’s efficacy across multiple indications. In urinary tract infections, clinical success rates of 85-95% have been reported in susceptible organisms. For Pneumocystis jirovecii pneumonia treatment, studies show improved survival rates compared to alternative therapies when initiated early. The antibiotic combination has maintained consistent efficacy rates despite decades of use, though resistance patterns have evolved in some regions. Patient satisfaction surveys indicate generally good tolerance when prescribed appropriately, though gastrointestinal side effects are commonly reported. Long-term clinical experience supports its position as a valuable therapeutic option in appropriate patient populations.