Bactrim: Potent Dual-Antibiotic Therapy for Bacterial Infections
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Bactrim is a combination antibiotic medication containing sulfamethoxazole and trimethoprim. This synergistic formulation is designed to combat a wide spectrum of susceptible bacterial strains by inhibiting successive steps in the biosynthesis of nucleic acids and proteins essential to many bacteria. It is a first-line and empiric choice for numerous common and opportunistic infections, valued in both outpatient and clinical settings for its broad efficacy and well-understood pharmacokinetic profile. Healthcare providers rely on Bactrim for its targeted action against pathogens responsible for urinary tract infections, acute otitis media, exacerbations of chronic bronchitis, and traveler’s diarrhea, among other conditions.
Features
- Dual-action antibiotic combining sulfamethoxazole (800 mg) and trimethoprim (160 mg) in a standard DS (double strength) tablet
- Available in multiple formulations: oral tablets, oral suspension, and intravenous solution
- Bactericidal activity through sequential blockade of bacterial folate synthesis
- Effective against both Gram-positive and Gram-negative organisms, including Staphylococcus aureus, Escherichia coli, Klebsiella species, Enterobacter species, Haemophilus influenzae, and others
- Standardized dosing allows for predictable serum concentrations and clinical response
Benefits
- Provides broad-spectrum coverage for common community-acquired and nosocomial infections
- Synergistic antibacterial effect enhances efficacy and reduces the potential for resistance development compared to single-agent therapy
- Well-established safety and tolerability profile with decades of clinical use and post-marketing surveillance
- Convenient twice-daily dosing regimen supports patient adherence and completion of therapy
- Cost-effective therapeutic option with widespread availability in generic formulations
- Proven efficacy in both immunocompetent and immunocompromised patient populations
Common use
Bactrim is indicated for the treatment of various bacterial infections caused by susceptible microorganisms. Its primary uses include urinary tract infections, including cystitis and pyelonephritis, particularly when caused by E. coli, Klebsiella-Enterobacter, Proteus mirabilis, Proteus vulgaris, and Proteus morganii. It is also employed for acute exacerbations of chronic bronchitis in adults when due to susceptible strains of Haemophilus influenzae or Streptococcus pneumoniae, and for acute otitis media in children caused by susceptible strains of H. influenzae or S. pneumoniae when in conjunction with adequate penicillin. Additionally, Bactrim is used for enteritis caused by susceptible strains of Shigella flexneri and Shigella sonnei, and for the treatment and prophylaxis of Pneumocystis jirovecii pneumonia in immunocompromised individuals.
Dosage and direction
Dosage must be individualized based on the type and severity of infection, renal function, and patient-specific factors. For urinary tract infections and shigellosis in adults and children, and for acute otitis media in children, the usual adult dosage is 1 DS tablet (800 mg sulfamethoxazole/160 mg trimethoprim) every 12 hours for 10 to 14 days. For children, the recommended dose is 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per 24 hours, administered in two divided 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 in equally divided doses every 6-8 hours for 14-21 days. For prophylaxis: 150 mg/m² trimethoprim and 750 mg/m² sulfamethoxazole daily in equally divided doses twice daily on 3 consecutive days per week. All doses should be taken with a full glass of water and patients should maintain adequate fluid intake to prevent crystalluria and stone formation.
Precautions
Bactrim should be used with caution in patients with impaired renal or hepatic function, severe allergy or bronchial asthma, glucose-6-phosphate dehydrogenase deficiency (may cause hemolysis), potential folate deficiency (e.g., elderly, chronic alcoholics, patients receiving anticonvulsant therapy, or those with malabsorption syndromes), and in those with history of drug-induced thrombocytopenia. Periodic CBCs are advisable during prolonged therapy. Use may lead to superinfection with nonsusceptible organisms, including fungi. Caution should be exercised when prescribing to elderly patients, as they may be more susceptible to severe adverse reactions. Photosensitivity reactions may occur; patients should avoid unnecessary sun exposure and use sunscreen.
Contraindications
Bactrim is contraindicated in patients with known hypersensitivity to trimethoprim, sulfonamides, or any component of the formulation; documented megaloblastic anemia due to folate deficiency; pregnancy at term and during the nursing period (due to risk of kernicterus in the newborn); infants less than 2 months of age; and in patients with marked hepatic damage or severe renal insufficiency when renal function cannot be monitored.
Possible side effect
Common adverse reactions include nausea, vomiting, anorexia, and abdominal pain. Dermatologic reactions such as rash, pruritus, and urticaria may occur. Less frequently, patients may experience headache, dizziness, insomnia, depression, or apathy. Hematologic effects can include thrombocytopenia, leukopenia, neutropenia, megaloblastic anemia, hemolytic anemia (especially in G6PD-deficient individuals), purpura, hypoprothrombinemia, and methemoglobinemia. Allergic reactions ranging from mild rash to Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported. Gastrointestinal manifestations such as glossitis, stomatitis, pancreatitis, and hepatitis may occur. Renal toxicity including interstitial nephritis and elevated BUN and serum creatinine has been observed.
Drug interaction
Bactrim may potentiate the effects of warfarin and other oral anticoagulants, requiring close monitoring of prothrombin time. It may enhance the hypoglycemic effect of sulfonylureas. Concurrent use with angiotensin-converting enzyme inhibitors may increase risk of hyperkalemia. Bactrim may increase concentrations of phenytoin, potentially leading to toxicity. Methotrexate levels may be increased, enhancing its toxic effects. Cyclosporine levels may be increased with concomitant use, increasing nephrotoxicity risk. Thiazide diuretics may increase risk of thrombocytopenia in elderly patients. Bactrim may interfere with the hepatic metabolism of drugs metabolized by CYP2C9, including numerous anticonvulsants and antidepressants.
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. Maintenance of consistent blood levels is important for efficacy, particularly in serious infections, so patients should be counseled on adherence.
Overdose
Symptoms of overdose may include nausea, vomiting, dizziness, headache, mental depression, confusion, bone marrow depression, crystalluria, and blood dyscrasias. In massive overdose, jaundice, liver necrosis, and acute renal failure may occur. Treatment is supportive and symptomatic. Gastric lavage may be indicated if performed soon after ingestion. Acidification of urine may increase renal elimination of trimethoprim but should be avoided in patients with crystalluria or renal impairment. Monitor CBC and appropriate blood chemistries, including electrolytes. Hemodialysis is moderately effective in eliminating both components, particularly trimethoprim.
Storage
Store at controlled room temperature 20°-25°C (68°-77°F). Protect from light and moisture. Keep container tightly closed. Do not freeze the oral suspension. Keep out of reach of children. Discard any unused portion after 14 days if using the oral suspension. 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. Bactrim is a prescription medication that should be used only under the supervision of a qualified healthcare provider. The prescribing physician should be consulted for diagnosis and treatment of medical conditions. Never disregard professional medical advice or delay in seeking it because of something you have read in this product information. Individual results may vary based on specific patient factors and bacterial susceptibility.
Reviews
Clinical studies and post-marketing surveillance over decades have established Bactrim as an effective and generally well-tolerated antibiotic for indicated uses. In clinical trials for urinary tract infections, Bactrim demonstrated bacteriological cure rates of approximately 85-95% in susceptible organisms. For acute exacerbations of chronic bronchitis, studies show clinical improvement in 80-90% of patients. Pediatric trials for acute otitis media show comparable efficacy to other antibiotics with similar spectrums. In immunocompromised patients, Bactrim remains the prophylactic agent of choice for Pneumocystis jirovecii pneumonia, with efficacy demonstrated in multiple large-scale studies. While side effects occur in a minority of patients, most are mild and reversible upon discontinuation. The drug’s extensive clinical history provides physicians with substantial real-world experience regarding its appropriate use and management of potential adverse effects.