Adults

Typically 20 mL of 200 mg/40 mg per 5 mL suspension (equivalent to 800 mg SMX + 160 mg TMP) every 12 hours for 5-14 days for standard infections. Doses vary significantly for different indications and patient conditions.

Elderly

Same as adults, but caution advised with renal impairment; dosage adjustment may be necessary based on creatinine clearance.

Renal_impairment

Creatinine clearance 15-30 mL/min: half usual dose. Creatinine clearance <15 mL/min: not recommended.

Onset

Antibacterial effects observed within 1-3 hours.

Excretion

Primarily excreted by the kidneys through glomerular filtration and tubular secretion. A small amount is excreted in feces.

Half life

Trimethoprim: 8-10 hours; Sulfamethoxazole: 10-12 hours.

Absorption

Rapidly absorbed from the gastrointestinal tract. Peak plasma concentrations usually occur 1-4 hours after oral administration.

Metabolism

Both components are metabolized in the liver. Sulfamethoxazole primarily undergoes N4-acetylation and glucuronidation, while trimethoprim undergoes various oxidative and conjugative pathways.

Warfarin

Potentiates anticoagulant effect, increasing bleeding risk.

Phenytoin

Increases phenytoin levels.

Cyclosporine

May cause nephrotoxicity and reduce cyclosporine levels.

Methotrexate

Increases methotrexate levels, leading to increased toxicity (e.g., bone marrow suppression).

Diuretics (especially thiazides)

Increased risk of thrombocytopenia in elderly patients.