Time course of inulin and creatinine clearance in the interval between two haemodialysis treatments

Background. Urinary volume of haemodialysis patients with residual renal function increases during the interdialytic interval. The contribution of GFR to this change in water and solute excretion has not been quantified in detail. The creatinine clearance (Cl-c) as a determinant of the GFR may overestimate GFR caused by the tubular secretion of creatinine. Cimetidine has been used to inhibit the secretion of creatinine in non-dialysed patients. No data are available on its usefulness in haemodialysis patients. Methods. Two identical interdialytic intervals (DI) of 3 days (DI-1, DI-2) were investigated in 11 patients. The interval between DI-1 and DI-2 was 1 week. During DI-2 cimetidine 800 mg daily was administered. Each DI was divided in four urine-collection periods. Results. The water and solute excretion in DI-1 and DI-2 were similar. Urinary production increased from 0.37 +/- 0.30 ml/min to 0.66 +/- 0.33 ml/min (P < 0.05), inulin clearance (Cl-i) increased from 1.8 +/- 1.1 ml/min to 2.7 +/- 1.2 ml/min (P < 0.05), fractional sodium excretion from 9.0 +/- 5.7% to 14.5 +/- 9.0% (P < 0.05). In contrast to Cl-i the Cl-c showed no increase during the interdialytic interval both in DI-1 and DI-2. The overestimation of GFR by creatinine (Cl-c - Cl-i) decreased during DI-1 from 1.35 +/- 1.69 ml/min to 0.26 +/- 0.60 (P < 0.05) and during DI-2 from 1.01 +/- 1.33 ml/min to 0.10 +/- 0.67 (P < 0.01). The ratio Cl-c/Cl-i decreased during DI-1 from 1.78 +/- 0.53 to 1.09 +/- 0.19 (P < 0.01) and during DI-2 from 2.02 +/- 1.13 to 1.05 +/- 0.30 (P < 0.01). All parameters were not different between the comparable days of DI-1 and DI-2. Conclusion. We conclude that the urinary volume in the interdialytic interval is directly related to changes in GFR. During the interdialytic interval GFR increased and tubular secretion of creatinine decreased. The administration of cimetidine did not improve the accuracy of Cl-c as a measurement of GFR in end-stage renal failure.