Sulfamethoxazole
Sulfamethoxazole is the sulfonamide component of Bactrim, a combination antibiotic with trimethoprim used for Urinary Tract Infections and Pneumocystis Pneumonia. Bactrim comes in two combination strengths: 400 mg plus 80 mg and 800 mg plus 160 mg.
Key points
- Life-threatening skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported with co-trimoxazole; if these occur, the medicine must never be restarted.
- Bactrim is contraindicated in the first trimester of pregnancy and should be avoided in the second and third trimesters unless clinically necessary, as both components cross the placenta.
- Beyond urinary tract infections and pneumocystis pneumonia, Bactrim is also listed for shigellosis, a bacterial bowel infection.
How does Sulfamethoxazole work?
In Bactrim, sulfamethoxazole interferes with a step in bacterial folate synthesis, and trimethoprim blocks the next step in the same pathway. Together they stop bacteria from producing the folate needed to grow and multiply. Antibiotics like co-trimoxazole will not work against viruses.