Bactrim for treating bacterial infections including pneumonia and UTIs

Bactrim is an oral antibiotic containing sulfamethoxazole and trimethoprim designed to treat and prevent infections caused by susceptible bacteria. It works by blocking two key steps in bacterial folate synthesis, which bacteria need to grow, making it effective against a variety of bacterial and Pneumocystis jirovecii infections.

Bactrim is approved for use in adults and pediatric patients to treat or prevent bacterial infections proven or strongly suspected to be caused by susceptible bacteria including:

• Urinary tract infections caused by Escherichia coli, Klebsiella, Enterobacter, Morganella morganii, Proteus mirabilis, and Proteus vulgaris.
• Acute otitis media in pediatric patients from Streptococcus pneumoniae or Haemophilus influenzae, used when Bactrim is deemed advantageous over other antibiotics. Not for prophylactic or prolonged use in otitis media.
• Acute exacerbations of chronic bronchitis in adults caused by Streptococcus pneumoniae or Haemophilus influenzae when Bactrim offers an advantage over single agents.
• Enteritis due to Shigella flexneri or Shigella sonnei when antibacterial therapy is indicated.
• Treatment and prophylaxis of Pneumocystis jirovecii pneumonia in immunosuppressed individuals at increased risk.
• Treatment of traveler's diarrhea in adults caused by susceptible enterotoxigenic E. coli strains.

Sulfamethoxazole and Trimethoprim

Bactrim combines two antibiotics that interfere with bacterial folate synthesis. Sulfamethoxazole inhibits the production of dihydrofolic acid by competing with para-aminobenzoic acid (PABA), while trimethoprim blocks the conversion of dihydrofolic acid to tetrahydrofolic acid by reversibly inhibiting dihydrofolate reductase. This dual blockade prevents bacteria from producing nucleic acids and proteins needed for growth and survival.

Bactrim is administered orally. The double strength tablets each contain 800 mg sulfamethoxazole and 160 mg trimethoprim. Dosing regimens vary by infection type and patient factors. Dosage adjustments are necessary for patients with severely impaired renal function. For pediatric patients aged 2 months to 18 years, similar blood levels are achieved when dosed at 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per day divided every 12 hours.

It is recommended to use a single effective antibacterial agent for initial uncomplicated urinary tract infections rather than the combination.

• Known hypersensitivity to trimethoprim or sulfonamides.
• History of drug-induced immune thrombocytopenia with trimethoprim and/or sulfonamides.
• Documented folate-deficiency megaloblastic anemia.
• Pediatric patients under 2 months of age.
• Marked hepatic damage.
• Severe renal insufficiency when renal function status cannot be monitored.
• Concomitant administration with dofetilide.

• Serious hypersensitivity reactions: Bactrim can cause severe and sometimes fatal cutaneous reactions including Stevens-Johnson syndrome, toxic epidermal necrolysis, DRESS, and other systemic hypersensitivity reactions.
• Respiratory reactions: Cough, shortness of breath, pulmonary infiltrates, and respiratory failure requiring mechanical ventilation or ECMO have been reported.
• Circulatory shock: Can occur rapidly on re-exposure in sensitized patients; characterized by fever, hypotension, confusion needing IV fluids and vasopressors.
• Hemophagocytic lymphohistiocytosis (HLH): A rare life-threatening immune activation syndrome may occur; discontinue Bactrim and manage appropriately if suspected.
• Clostridioides difficile-associated diarrhea (CDAD): May range from mild to fatal colitis; consider in any patient developing diarrhea during or after antibiotic use.
• Pregnancy risks: Exposure during pregnancy may increase risks for neural tube defects and other congenital malformations; advise patients accordingly.
• Do not use for group A β-hemolytic streptococcal infections: Ineffective for eradication and prevention of rheumatic fever.
• Thrombocytopenia: May be immune-mediated and severe; usually reverses after stopping the drug.
• Avoid coadministration with dofetilide and leucovorin: Dofetilide is contraindicated; leucovorin reduces effectiveness in Pneumocystis jirovecii pneumonia treatment.

• Common: skin rash, fever, leukopenia, elevated liver enzymes (especially in AIDS patients).
• Serious: severe cutaneous adverse reactions, blood dyscrasias (agranulocytosis, aplastic anemia), hepatic necrosis, lung injury, anaphylaxis, circulatory shock.
• Hypoglycemia: rare, mostly in patients with renal or liver disease or malnutrition.

• Concomitant use with dofetilide is contraindicated due to risk of serious cardiac effects.
• Coadministration with leucovorin during Pneumocystis jirovecii pneumonia treatment should be avoided as it may cause treatment failure and increased mortality.
• Drugs that increase potassium levels may increase risk of hyperkalemia with trimethoprim.

Some studies suggest that Bactrim exposure during pregnancy may increase the risk of birth defects such as neural tube defects, cardiovascular malformations, urinary tract anomalies, oral clefts, and club foot. Patients should be informed of potential fetal risks if used during pregnancy.

Bactrim crosses the placental barrier and is excreted in human milk; caution is advised when administering to nursing mothers.