TIME-COURSE OF INULIN AND CREATININE CLEARANCE IN THE INTERVAL BETWEEN 2 HEMODIALYSIS TREATMENTS

Background. Urinary volume of haemodialysis patients with residual ren al function increases during the interdialytic interval. The contribut ion of GFR to this change in water and solute excretion has not been q uantified in detail. The creatinine clearance (Cl-c) as a determinant of the GFR may overestimate GFR caused by the tubular secretion of cre atinine. Cimetidine has been used to inhibit the secretion of creatini ne in non-dialysed patients. No data are available on its usefulness i n haemodialysis patients. Methods. Two identical interdialytic interva ls (DI) of 3 days (DI-1, DI-2) were investigated in 11 patients. The i nterval between DI-1 and DI-2 was 1 week. During DI-2 cimetidine 800 m g daily was administered. Each DI was divided in four urine-collection periods. Results. The water and solute excretion in DI-1 and DI-2 wer e 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 sodiu m 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 t o 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 c hanges in GFR. During the interdialytic interval GFR increased and tub ular secretion of creatinine decreased. The administration of cimetidi ne did not improve the accuracy of Cl-c as a measurement of GFR in end -stage renal failure.