Sulfonamide antibiotics (sulfa drugs)
Sulfonamide antibiotics block bacteria from making folic acid, which they need to grow, and are often paired with trimethoprim to block a second step. Trimethoprim-sulfamethoxazole treats urinary tract infections, ear infections, bronchitis flares, traveler's diarrhea, and Pneumocystis pneumonia. Rash is common, and rare severe skin reactions, blood disorders, and high potassium can occur. People with a sulfa allergy avoid them, and they can strengthen the effect of warfarin.