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Xenobiotica
the fate of foreign compounds in biological systems
Volume 19, 1989 - Issue 6
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Research Article

The Pharmacokinetics of the Enantiomers of Mexiletine in Humans

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Pages 677-682 | Received 09 Aug 1988, Accepted 27 Nov 1988, Published online: 22 Sep 2008
 

Abstract

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<0.05) than that of the R(-) enantiomer, 9.10±2.90h. S(+)Mexiletine also showed a significantly greater apparent volume of distribution (P<0.01) and renal clearance (P<0.05) than R(-)mexiletine. There was no significant difference in the apparent oral total drug clearance of the enantiomers.

4. The disposition of mexiletine enantiomers in man was stereoselective, and the differences observed between the enantiomers may be due largely to differences in their serum protein binding.

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