Kidney Transport in Man of Sulfamethoxazole and Trimethoprim

Evidence is presented to show that trimethoprim (TMP) is subjected to passive, nonionic tubular diffusion in the kidneys. With urinary pH values below 6.2 there is generally net tubular secretion, whereas there is net reabsorption above this point. The reabsorption of active sulfamethoxazole (SMZa) was only slightly influenced by the urinary pH. The urine concentration of SMZa remained the same for all degrees of renal impairment until 5 ml/min creatinine clearance. The urine concentrations of TMP were lowered more gradually with reductions in renal function. In nephrosis, TMP excretion was above that found with a corresponding renal function for a group of patients with other chronic renal diseases.