The effect of trimethoprim on serum creatinine.

The influence of trimethoprim on renal function has been investigated in two groups of volunteers, both without a history of either acute or chronic urinary tract disease. All had normal serum creatinine. They were treated with trimethoprim 200 mg bd for 14 days. In group A (median age 78 years), serum creatinine increased significantly from median 89 to 134 mumol/l (P less than 0.01) during the first week and returned to normal 1 week after termination of treatment to median 90 mumol/l (P less than 0.02). After 1 week's treatment in group B (median age 29 years), serum creatinine had increased significantly from median 87 to 107 mumol/l (P less than 0.05), remained stable in the second week and returned to the pre-treatment level 1 week after cessation of treatment: 87 mumol/l (P less than 0.05). The glomerular filtration rate determined by 51Cr-EDTA clearance did not change. There was a significant decrease in the 24-h endogenous creatinine clearance after 14 days' treatment from 111 to 87 ml/min/1.73 m2 (P less than 0.05). Our results are consistent with an age-independent reversible trimethoprim-induced inhibition of the tubular secretion of creatinine.