Serum concentrations of cis(Z)- and trans(E)-clopenthixol after administration of cis(Z)-clopenthixol and clopenthixol to human volunteers.

The serum concentrations of cis(Z)- and trans(E)-clopenthixol have been estimated in human volunteers by an HPLC-method after administration of a clopenthixol tablet, which contains the cis(Z)- and the trans(E)-isomers in the ratio 1/2, or a cis(Z)-clopenthixol tablet. The serum concentration curves obtained for the cis(Z)-isomer after administration of the two drug preparations were very similar, and thus independent of the presence of the trans(E)-isomer in one of the preparations. Likewise the biological half-lives and the areas under the serum concentration curves for cis(Z)-clopenthixol were similar after the two preparations. The biological half-life of cis(Z)-clopenthixol was as a mean 20 hours (12-29 hours) indicating that from a pharmacokinetic point of view a dosage interval of 24 hours is possible for most patients. The biological half-life of trans(E)-clopenthixol is found to be longer than that for cis(Z)-clopenthixol.