Clonidine plasma half-life is approximately 24 h in humans (Arndts, Doevendans, Kirsten, & Heintz, 1983) but less than 1 h in rats (Hui et al., 2007). Following intravenous administration of clonidine doses similar to those administered IP in the current study, clonidine is rapidly distributed throughout the rat brain (with peak levels within 2 min) and then rapidly eliminated from the brain (with a brain tissue half-life of approximately 30–50 min) (Conway & Jarrott, 1980). Consequently, clonidine was administered IP at 30 min before the start of alcohol access in the current study, consistent with the 30 min lead time for IP administration commonly used for other investigations of clonidine effects on rat behaviors (e.g., Shaham, Highfield, Delfs, Leung, & Stewart, 2000).
