Take orally with a full glass of water, with or without food. To minimize gastrointestinal upset, it can be taken with food. Ensure adequate fluid intake during treatment to prevent crystalluria.

Sulfamethoxazole competitively inhibits the incorporation of para-aminobenzoic acid (PABA) into dihydrofolic acid, an essential precursor in the synthesis of folic acid. Trimethoprim reversibly inhibits dihydrofolate reductase, an enzyme that catalyzes the reduction of dihydrofolate to tetrahydrofolate. The combination blocks two successive steps in the biosynthesis of nucleic acids and proteins essential for many bacteria.

• •Hypersensitivity to sulfamethoxazole, trimethoprim, or any excipients
• •Megaloblastic anemia due to folate deficiency
• •Severe renal impairment where plasma concentrations cannot be monitored
• •Severe hepatic impairment
• •Infants under 2 months of age
• •Pregnancy (especially near term)

Store in a cool, dry place, below 30°C. Protect from light and moisture. Keep out of reach of children.

Symptoms of acute overdose include nausea, vomiting, dizziness, headache, and mental depression. Chronic overdose may lead to bone marrow depression (megaloblastic anemia, leukopenia, thrombocytopenia) due to folate deficiency. Treatment involves gastric lavage or emesis, forced diuresis, and acidification of the urine to increase trimethoprim excretion. Leucovorin may be administered to counteract folate deficiency.

Pregnancy Category D. Co-trimoxazole should be avoided during pregnancy, especially in the first trimester (due to potential for neural tube defects) and near term (due to risk of kernicterus in neonates). Excreted in breast milk; generally not recommended for breastfeeding mothers, especially if the infant is premature, jaundiced, or G6PD deficient.