Sulfamethoxazole and Trimethoprim RLP Episode 026

Bactrim, a combination of trimethoprim and sulfamethoxazole, treats various bacterial infections by inhibiting bacterial folic acid production. While frequently prescribed for urinary tract infections and skin conditions like cellulitis, it serves as a primary drug of choice for PCP prophylaxis in immunocompromised patients. Clinical management requires distinguishing between sulfa and trimethoprim allergies, as reactions attributed to sulfa may actually stem from the trimethoprim component. Significant drug interactions include the inhibition of CYP2C9, which can dangerously elevate warfarin concentrations and INR levels, and the potential for trimethoprim to cause hyperkalemia or phenytoin toxicity. Patients should maintain high fluid intake to mitigate the risk of drug-induced kidney stones and monitor blood glucose levels closely, as the medication can exacerbate hypoglycemia, particularly when combined with sulfonylureas or reduced caloric intake during illness.