Pharmacokinetics of oral and compounded intravenous gabapentin in Duroc swine (Sus Scrofa).

ABSTRACT

The objective of this study was to determine the pharmacokinetics (PK) of oral (OS; 20 mg/kg) and compounded intravenous (IV; 5.5 mg/kg) gabapentin in 6 healthy, adult, Duroc pigs. Subjects were randomized to receive IV and OS gabapentin in a cross-over design, with at least 14 days of wash-out period between the two rounds of drug administrations. Blood samples were obtained before gabapentin administration and at various times up to 24 h, and harvested plasma was stored at -80°C until analysis. Concentration of gabapentin was quantified using a previously validated liquid chromatography/tandem mass spectrometry method, and compartment models were fitted to time-concentration data using non-linear mixed effect (population) analysis. A two-compartment model best fitted the data following IV administration. Typical values for volume of the central compartment and clearance and calculated volume of distribution at steady-state and terminal half-life were 170 ml/kg, 1.2 ml/(kg*min), and 594 ml/kg and 360 min, respectively. For the oral route, absorption half-life, estimated maximal plasma concentration and time to reach maximal plasma concentration were 58 min, 9155 ng/ml, and 194 min, respectively. Estimated oral bioavailability was 47%. Short-lived sedation (approximately 15 min) with sternal or lateral recumbency after IV administration was observed in all subjects without adverse clinical effects. Simulation based on the results of this study suggests that a first oral gabapentin dose of 15 mg/kg and subsequent doses of 8.5 mg/kg every 8 h would achieve and maintain plasma concentrations between 5 and 8 µg/ml in pigs.