[Pharmacokinetics of injectable phenobarbital in the premature infant. Study of a new lyophilized form].

A lyophilized preparation of phenobarbital was studied in newborns without cerebral palsy. Plasma levels were determined using gas chromatograph fitted with thermo ionic probe after either an intra-muscular (IM) injection in premature infants or an intravenous (IV) injection over single dose of phenobarbital 10 mg/kg within 6 hours after birth. Five term babies were included in the study as controls and received an IM injection. The results showed rapid increase in plasma concentration after IM injection in 10 of 13 subjects with a peak concentration reached 60 minutes after injection. The mean ratio (maximal concentration/dose) was 1.25 and 1.10 for term infants and preterm infants respectively. In all cases, the drug was well tolerated. In 15 preterm infants (n: 7 IM and n: 8 IV) the plasma concentrations were followed over a period of 15 days. The disappearance curve was biphasic; it varied the first 7 days, then remained constant for the following week (apparent half life 106 hours).