CIMETIDINE IMPROVES THE RELIABILITY OF CREATININE AS A MARKER OF GLOMERULAR-FILTRATION

To investigate whether the administration of cimetidine can improve the reliability of creatinine as a marker of GFR, we compared the creatinine clearance (C(Cr)) to the clearance of the true filtration markers Cr-51-EDTA (C(EDTA)) and inulin (C(In)), after oral ingestion of cimetidine in 10 healthy men and 29 patients with varying degrees of renal dysfunction. After administration of cimetidine for three to six days, serum creatinine level rose in all participants, while C(EDTA) and C(In) remained stable in a subgroup of 14 subjects in whom they were measured before as well as after the administration of cimetidine. The mean (+/- SD) ratios of Cc, to C(EDTA) (N = 39) and of C(Cr) to C(In) (N = 19) after ingestion of cimetidine were 1.02 +/- 0.13 and 1.01 +/- 0.13, respectively, and did not differ significantly from unity. This high degree of accuracy of the cimetidine-aided C(Cr) was present over the entire range of renal function in the study population. Our results also indicated an improved precision of the cimetidine-aided measurement of C(Cr), resulting in a variability that did not differ significantly from that of the measurement of C(EDTA) or C(In). We conclude that after oral administration of cimetidine, the creatinine clearance can be used as a reliable measure of GFR within a broad range of renal function.