The pharmacokinetics of phenobarbitone in fasting and non-fasting dogs

The pharmacokinetics of oral phenobarbitone was studied in 10 clinically healthy adult dogs. The drug was given once daily in tablet form, at a dose of 5 mg kg-1 of body mass. Serial venous blood samples (n = 9) were collected from each dog on Day 1 (the first day of drug dosing), on Day 22, and on Day 24 after continuous dosing. Trough serum concentrations were determined on Day 7, Day 14 and Day 21. The drug was administered to the dogs on an empty stomach, except on Day 24, when it was given with food, in order to assess the influence of food on its absorption. Drug serum concentrations were described by a one-compartmental open model with first order absorption and elimination. An average steady-state trough serum level of phenobarbitone of 52,96 +/- 8.40 mmol l-1 was achieved after 3 weeks of daily dosing. The mean elimination half-lives for Day 1 and Day 22 were 46.3 +/- 11.3 h and 29.3 +/- 4.6 h respectively. The area under the curve for Day 22 was 1,656.17 +/- 186.45 mumol h-1 l-1 and for Day 24 was 1,493.06 +/- 205.4 mumol h-1 l-1. The mean clearance value for Day 22 was 0.0133 +/- 0.0016 l h-1 kg-1. Side effects of polyphagia, polydipsia, sedation and ataxia were commonly observed in the first 2-9 d, but disappeared thereafter. It was concluded that a dose of 5 mg kg-1 would achieve an average serum concentration of 64.59 mumol l-1 in adult dogs.(ABSTRACT TRUNCATED AT 250 WORDS)