Pharmacokinetics of Lofexidine Hydrochloride in Healthy Volunteers

The objective of this study was to characterize the clinical pharmacokinetic profile of lofexidine after oral delivery. A single dose, cross-over study and a multidose study using healthy volunteers were conducted for that purpose. In the single dose study the average time to maximum concentration was observed at approximately 3h for the single doses tested (1.2mg dose and 2.0mg). Area under the curve from time zero to infinity (AUC0−∞) demonstrated a degree of dose proportionality with a 1.72-fold increase as the dose increased by a factor of 1.67. Elimination rates and terminal half-lives were comparable between dose levels. The average elimination rates for the 1.2mg and the 2.0mg doses were 0.063 and 0.065h−1, respectively. In the multidose study, the average maximum concentration observed after the first dose of 0.4mg was 433 ng/L and ranged from 338 to 586 ng/L. This was slightly lower in proportion to the maximum concentration observed in the single dose study where Cmax was 1755 ng/L at the 1.2mg dose (normalized to 585 ng/L for 0.4mg dose) and for the 2.0mg dose (normalized to 559 ng/L for 0.4mg dose). The average time to maximum concentration (Tmax) was 3.33h which is comparable to values observed in the single dose study. The pharmacokinetic data indicate that lofexidine has a consistent profile. Steady state seems to be reached after 2 days on lofexidine, which is consistent with the lofexidine elimination half-life of approximately 11h. Evaluation of the Tmax, elimination rate, and terminal half-life are consistent across all dose levels studied, suggesting that changing the dose does not affect the absorption or elimination rates of lofexidine HCl. Thus, although preliminary due to the limited number of subjects, these findings are the first to document lofexidine clinical pharmacokinetic parameters in healthy volunteers using a highly sensitive liquid chromatography tandem mass spectrometric analysis. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:319–326, 2009