A simple method for determination of antipyrine clearance

Antipyrine clearance (Cl(AP)) is widely used for assessment of microsomal liver function. The usual procedure involves collection of 4 to 7 samples of plasma or saliva obtained during 24 to 48 hr. To determine whether this procedure could be simplified it was compared with one based on a single sample (sCl(AP)) and an estimated volume of distribution (V(D)) in 142 persons. VD was estimated from body weight, in kilograms (BW), height, in centimeters (BH), age in years, and sex, or assumed to be 40 l. The agreement between values of Cl(AP and sCl(AP) increased with the time of the single sample and the two clearance estimates were nearly identical in all cases when the sample was taken after 18 hr. The method used for assessment of V(D) had only a small influence on the agreement. It is suggested that antipyrine clearance (in ml/min) is estimated as (formula: see text) where D is the dose of antipyrine (in mg), c(t) the concentration of antipyrine (in mg/t) at sampling time t (in min), t should be about 1440 min (24hr), and V(D) (in l) is calculated as 0.2363 X BW + 0.1962 X BH - 0.0272 X age - 10.26 (women) or 0.3625 X BW + 0.2239 X BH - 0.1387 X age - 14.47 (men). Little information is lost, however, if a fixed volume of 40 l is used. Then, if the dose is l gm, c(t) is expressed in milligrams per liter, and the sampling time is 24 hr, sCl(AP) = (3.28 - ln c(t)) X 28 ml/min.