ASSESSMENT OF TOTAL-BODY WATER IN HEMODIALYSIS-PATIENTS BY A SINGLE ORAL DOSE OF ANTIPYRINE

Accurate determination of total body water in hemodialysis patients is important for calculation of the amount of fluid excess that should b e removed by ultrafiltration, and for dialysis prescribing by KT/V. In direct methods using 0.6 x body weight or pre and post serum urea conc entrations are inaccurate and determination by tritiated water space r equires the use of radioactivity. The authors measured the volume of d istribution for antipyrine that is distributed in body water, and comp ared it to tritiated water space in hemodialysis patients. Sixteen pat ients on hemodialysis were given 500 mg antipyrine and saliva samples were collected at fixed time points. Concentrations of antipyrine in s aliva were measured by high pressure liquid chromatography. Volume of distribution for antipyrine was calculated by pharmacokinetic methods. Fluid excess was determined as the difference between tritiated water space or volume of distribution for antipyrine and ideal total body w ater measured anthropometrically. Total body water as the volume of di stribution for antipyrine was 24.8 to 61.5 (mean 44.0+/-10.3) L, or 68 % of body weight, and tritiated water space 27.0 to 56.6 L (43.6+/-7.7 ), 67% of body weight. Volume of distribution for antipyrine correlate d well with tritiated water space (r = 0.997 and p = 0.001). Fluid exc ess calculated from tritiated water space was between 2.5 and 12.4 (6. 0+/-4.0) L, and from volume of distribution for antipyrine -0.7 to 13. 3 (5.7 +/- 5.1) L (r = 0.80, p = 0.001). The authors conclude that by using a single oral dose of antipyrine, one can simply and accurately measure total body water in hemodialysis patients.