Urinary excretion of placentally transferred thiopentone by the human neonate.

The urinary excretion of thiopentone and its metabolite, pentobarbitone, was studied in 7 neonates whose mothers-had received thiopentone. During the urine collection period (range 39.3-63.8 h), a mean of 26.4 micrograms thiopentone was recovered, representing only a mean of 0.0066% of the maternal dose. This suggests that the elimination of thiopentone by the neonate occurs mainly by metabolism. The metabolite pentobarbitone could not be detected. Mean elimination half-life of thiopentone, calculated from sigma-minus plots, was 8.04 h which is similar to the value reported previously in adults. This contrasts with other barbiturates which show much longer half-lives in neonates than in adults.