Frits A. W. Kemperman

Cimetidine improves prediction of the glomerular filtration rate by the Cockcroft-Gault formula in renal transplant recipients.

Background. The glomerular filtration rate (GFR) can be predicted from plasma creatinine, age, gender, and body weight, using the formula of Cockcroft and Gault. Cimetidine improved the accuracy of GFR prediction in renal disease and also in diabetes mellitus type 2, due to inhibition of tubular creatinine secretion. We compared the accuracy and precision of GFR prediction from the Cockcroft-Gault formula without cimetidine (CG), with cimetidine (CGcim) and from the creatinine clearance without cimetidine in renal transplant recipients. Methods. CG and CGcim were calculated from plasma creatinine before and after 2400 mg of oral cimetidine during the 24 hr preceding the GFR measurement. The endogenous creatinine clearance was measured in 24 outpatients from a 24-hr urine collection (Ccr24) before cimetidine. GFR was measured as the urinary clearance of continuously infused 125I-iothalamate. Creatinine was determined with an automated enzymatic assay in plasma and with an alkaline picrate assay in urine. Results. GFR was 47.8±16.8 ml/min/1.73 m2 (mean±SD), Ccr24 was 71.8±23.1 ml/min/1.73 m2, CG was 62.2±15.2 ml/min/1.73 m2, and CGcim was 52.8±14.9 ml/min/1.73 m2. Ccr24 overestimated GFR in every patient by an average of 23.8 ml/min/1.73 m2 and CG by an average of 14.3 ml/min/1.73 m2, whereas CGcim overestimated GFR significantly less by an average 4.9 ml/min/1.73 m2 (P <0.001). The precision of CGcim was significantly better than that of Ccr24: the SD of the difference from GFR was 9.0 ml/min/1.73 m2 for CGcim and 14.5 ml/min/1.73 m2 for Ccr24 (P <0.05). Conclusion. CGcim is useful for GFR prediction in outpatient renal transplant recipients and has a far better accuracy and precision than Ccr24 and also a better accuracy than CG. We propose a strategy after kidney transplantation of one GFR measurement at baseline and follow-up with CGcim.

Estimation of the glomerular filtration rate in NIDDM patients from plasma creatinine concentration after cimetidine administration.

OBJECTIVE Glomerular filtration rate (GFR) can be estimated in patients with renal disease from plasma creatinine concentration, age, sex, and body weight according to the formula of Cockcroft and Gault. The hypothesis that this method can be improved when tubular secretion of creatinine is inhibited by cimetidine was studied in NIDDM patients. RESEARCH DESIGN AND METHODS In 30 outpatients with NIDDM and normo-(n = 10), micro- (n = 9), or macroalbuminuria (n = 11), GFR was measured as the urinary clearance during continuous infusion of 125I-labeled iothalamate. Plasma creatinine concentration was analyzed with an enzymatic assay before and after 800 mg t.i.d. oral cimetidine was given during a 24-h period. RESULTS Plasma creatinine rose in all patients after cimetidine administration and, as a consequence, the clearance calculated with the Cockcroft-Gault formula fell. The ratio of this formula and GFR decreased from 1.16 ± 0.20 to 0.97 ± 0.16 (means ± SD). This ratio tended to be smaller in the normo- (0.93) than in the micro- (0.98) and macroalbuminuric (1.00) groups. Also, 20 patients with a BMI < 30 kg/m2 had a smaller ratio than those with a BMI > 30 kg/m2 (0.92 vs. 1.07; P < 0.05). Bland and Altman analysis showed a difference of the Cockcroft-Gault formula and GFR of 12.0 ± 17.4 ml · min−1 · (1.73 m2)−1, which decreased to −3.8 ± 14.8 ml · min−1 · (1.73 m2)−1. The same analysis of 24-h creatinine clearance with urine collection and GFR showed larger standard deviations. CONCLUSIONS GFR can be estimated in an acceptable way from plasma creatinine concentration after cimetidine administration in outpatients with NIDDM. Despite a nonsignificant underestimation in normoalbuminuric and overestimation in overweighted patients, this method is superior to 24-h creatinine clearance with outpatient urine collection.