[Pharmacokinetic data on phenobarbital. Study on the influence of gestational age and dysmaturity]

Blood levels of barbiturate after a single intramuscular injection of 10 mg of phenobarbiitone have been plotted against time in 15 neonates at term of whom five were normal and 10 were dysmature, and 15 pre-term infants between 32 and 34 wesks gestation, of whom 12 had a satisfactory weight and 3 were dysmature. The analysis of the experiments according to a mathematical model gave the following results. Half life of absorption +/- 1 S.D. 9.55 HR +/- 6.97 for the term neonates and 11.12 hr +/- 7.61 for the pre-term infants. The difference is not significant. Half life of elimination +/- 1 S.D. 118.06 hours +/- 64.79 for the neonates of term and 110.49 hr +/- 37.19 for the pre-term infants. The half life of elimination is much shorter in the pre-term dysmature infants 74.10 hrs +/- 40.12. The individual variations are important but the differences between the groups of neonates studied are not great. This permits re-grouping and calculation of a half life of elimination for the whole group of 114.28 hr +/- 28.05. The risk of over dosage and the large individual variation in the metabolism of phenobarbitone in the new born lead us to recommend checking the blood levels when giving repeated doses.