SAFETY OF A HIGHER LOADING DOSE OF PHENOBARBITAL IN THE TERM NEWBORN

Abstract

The conventional loading dose of phenobarbital (PB) for newborns with hypoxic-ischemic convulsions, 20 mg/kg, often fails to control seizure activity. To determine the safety of a higher loading dose, 10 severely asphyxiated term newborns at a mean age of 2.7 hours (range 0.6 - 11.5) were given 30 mg/kg of PB intravenously over 15 minutes. Three of the infants received PB after the onset of convulsions, while 7 infants were similarly treated to prevent seizures. None of the 10 infants displayed any evidence of respiratory depression, hypotension, or bradycardia during or after receiving PB. Mean serum PB concentration 2 hours after loading was 30.0 ± 3.2 μg/ml and the apparent volume of distribution was 0.97 ± 0.18 L/kg. Calculated mean serum half-life was 148 hrs and steady-state clearance was 0.08 ml/min/kg. One of the 3 seizing infants responded to this dose. Despite serum PB concentrations of 36 and 28.3 μg/ml, the other two seizing infants required additional therapy. None of the 7 infants treated prophylactically developed clinical or electroencephalographic evidence of seizures.

We conclude that the higher PB loading dose can be administered to term infants without short term adverse effects on cardiorespiratory function. The results of our observations suggest the need for a controlled trial to assess the efficacy of PB to prevent seizures in asphyxiated term newborns.

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