Cimetidine Improves the Accuracy of Creatinine Clearance as an Indicator for Glomerular Filtration Rate

BACKGROUND Although endogenous creatinine clearance is often used as an indicator for the glomerular filtration rate (GFR), it may result in an overestimation due to its tubular secretion. Since cimetidine is known to inhibit tubular secretion of creatinine, it may improve the accuracy of the creatinine clearance in measuring GFR. METHODS Creatinine clearance (Ccr) was compared with iothalamate clearance (C1oth) during oral administration of either placebo or cimetidine in 25 patients with varying degrees of renal dysfunction. RESULTS Cimetidine itself had no effect on C1oth but decreased Ccr, improving its validity, as measured by a significant decrease of Ccr/C1oth from 1.72 during placebo to 1.17 during cimetidine administration. The degree of overestimation measured by the Ccr was more pronounced in those with more severe renal dysfunction. A significant inverse correlation was noted between Ccr/C1oth and GFR. No apparent side effect due to cimetidine was noted. CONCLUSIONS These results suggest that cimetidine improves the accuracy of Ccr as an indicator for GFR in patients with varying degrees of renal dysfunction.