Serial measurements of plasma half-lives and urinary excretion of antipyrine in low-birth-weight infants.

Abstract

Antipyrine has been used previously to estimate total body water in infants. In the present study, antipyrine spaces were determined early on the first day of life and again at the end of the fourth day in 22 early mild-fed low-birth-weight babies as part of a study of serial measurements of water balance. This report deals with findings arising from analysis of disappearance rates of antipyrine in plasma used for the determination of antipyrine space (total body water estimation). Urine excretion of antipyrine was measured from 24-hour urine outputs in 9 of these babies. The data showed that: (1) wide individual variants of plasma antipyrine half-life times occurred on both the first and fourth days of life; (2) plasma half-life times in the low-birth-weight infants were usually much longer than those of adults; (3) half-life times on the first day of life were significantly longer than on the fourth day of life; (4) urine excretion of unchanged antipyrine was a significant factor in the disappearance rate of antipyrine from the body with between 7 and 36% of the dose appearing in the urine (average 21%) within 96 h of the initial injection.