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Abstract
Background. Determination of clearance of endogenous creatinine using its plasma and urinary concentration (standard clearance), Cockroft and Gault formula, or MDRD formula (estimated clearance) is commonly performed for assessment of glomerular filtration rate. Although the evaluation of renal function in this way is useful, it is biased with an error resulting from secretion of creatinine in tubules. This error can be reduced by determining the clearance after administration of cimetidine, which competitively blocks creatinine tubular transport. Methods. The study was performed in the group of 87 patients after renal transplantation. In this group, estimated clearance and creatinine clearance after cimetidine administration (1000 mg in 75 patients and then 1600 mg in 12 patients with plasma creatinine above 3 mg/dL) were determined. Results. Analysis of mean percentage differences between clearance values after cimetidine administration and estimated clearance shows increasing contribution of creatinine tubular secretion along with plasma creatinine increase in renal transplant recipients. A higher dose of cimetidine resulted in lower clearance values in renal transplant recipients with plasma creatinine above 3 mg/dL. Conclusions. Creatinine clearance after administration of 1000 mg cimetidine seems to be a useful measure of glomerular filtration rate in renal graft recipients with plasma creatinine concentration below 2.5 mg/L. Higher dose of cimetidine would be needed to effectively block tubular excretion at higher concentrations of creatinine. Establishing an efficient but safe dose of cimetidine for such patients needs further investigations. As we have noticed that creatinine clearance calculated according to MDRD formula was similar to the clearance after administration of cimetidine, we propose a strategy of one GFR measurement at baseline using 24h urine collection after cimetidine administration and follow-up with creatinine clearance calculated from MDRD formula during standard check-up visits.