Urinary excretion of phenobarbital and its metabolite p-hydroxyphenobarbital in convulsing and non-convulsing patients.

As part of an investigation of phenobarbital (PB) pharmacokinetics in patients with status epilepticus (SE), urinary excretion of PB and its main metabolite, hydroxyphenobarbital (HPB), was studied in patients who had an episode of SE, as well as in non-convulsing ones. Eleven in-patients were studied:(group 1) five patients (4 M + 1 F; 48 +/- 28 years old; 64 +/- 6 kg body weight; mean +/- SD) with convulsive status epilepticus, and (group 2) six patients (5 M + 1 F; 37 +/- 13 years old; 71 +/- 15 kg body weight) with epilepsy, seizure-free at the moment of PB administration and without established anti-epileptic therapy. All subjects received a single intravenous dose of PB (15 mg/kg) at a rate of 100 mg/min. PB and HPB concentrations were measured by high performance liquid chromatography with UV detection at 220 nm in urine samples collected throughout 24 h. The comparison of pharmacokinetic parameters of urinary excretion of PB and HPB showed a statistically significant difference in the values of recovery of HPB and total barbiturate (higher values in the patients with SE) in 24 h urine. Differences in the excretion of PB between the two groups of patients--higher values in the patients who had had an episode of SE, and in urine flow--slightly elevated volumes in the same group, failed to reach statistical significance, probably due to the small number of participants in the study.