The Pharmacokinetics of the Enantiomers of Mexiletine in Humans

1. This study examined the pharmacokinetics of the enantiomers of mexiletine in five healthy subjects who were each given a single, 300 mg, oral dose of racemic mexiletine hydrochloride. 2. The time course of the concentration ratio between the R(−) and the S(+) enantiomers (R/S) in plasma showed a progressive decrease, with a mean ± S.D. ratio of 1.37±0.11 at 1 h and 0.64±0.11 at 48h. Similarly, the R/S ratios in urine were 1.38 ± 0.42 and 0.55 ± 0.12 at 1 h and 72 h, respectively. 3. The terminal elimination half-life of S(+)mexiletine was 11.0 + 3.80h, which was significantly greater (P