Disposition of naltrexone after intravenous bolus administration in Wistar rats, low-alcohol-drinking rats and high-alcohol-drinking rats.

Reports have shown that interspecies differences in the metabolism and pharmacokinetics of naltrexone are a rule rather than exception. However, there is paucity of information on the disposition of naltrexone in selectively bred rat lines that reliably exhibit high and low voluntary alcohol consumption, and are often used to study alcohol-drinking behavior. We have characterized the pharmacokinetic profiles of naltrexone in selectively bred rat lines: high-alcohol-drinking (HAD-1) and low-alcohol-drinking (LAD-1) rats as well as the native Wistar strain. This study was carried out to establish a baseline pharmacokinetic profile of naltrexone in these rats prior to evaluating its pharmacokinetic profile in polymeric controlled-release formulations in our laboratory. The hypothesis is that alcohol-preferring and non-alcohol-preferring lines of rats should differ in the disposition of intravenously administered naltrexone. Naltrexone administration and blood collection were via the jugular vein. In a parallel experiment, naltrexone was administered via the jugular vein, but urine was collected using the Nalgene metabolic cage system. Data were analyzed by a noncompartmental approach. Results show a high clearance that is close to or higher than hepatic blood flow in all groups (Wistar > LAD-1 > HAD-1, but with a statistically significant difference only between Wistar and HAD-1). Volume of distribution (approximately 2.5-3 l/kg) and the half-life (approximately 1 h) were similar. Urinary elimination of naltrexone was small, but also showed differences between the rats: HAD-1 > LAD-1 > Wistar, but with a statistically significant difference only between HAD-1 and Wistar rats. This study has therefore established the baseline disposition characteristics of naltrexone in these strains of rats.