Pharmacokinetic studies in volunteers of intravenous and oral cis (Z)-flupentixol and intramuscular cis (Z)-flupentixol decanoate in viscoleo^®

Summary

Serum concentrations of cis (Z)-flupentixol have been estimated in three male human volunteers who received cis (Z)-flupentixol by intravenous infusion, flupentixol (cis (Z)/trans (E) mixture, 1:1) orally as single and repeated doses, and i. m. cis (Z)-flupentixol decanoate in Viscoleo^®. The intravenous data show that cis (Z)-flupentixol followed a multicompartment model, but it was not possible to fit the data to a two or three compartment model. The concentration curves after oral administration indicated relatively slow absorption with a peak concentration at 3–6 h, except for one case with peak at 1 h. The variation in the dosage interval after one daily oral administration was relatively limited (1.7–3.0 times), which indicates that 24 h is a reasonable dosage interval. Biological half-lives were estimated in different ways and showed some intra-individual variation; the half-life was of medium length (19–39 h). The serum concentrations after intramuscular injection of cis (Z)-flupentixol decanoate clearly demonstrated a depot effect, with a maximal concentration at 3–5 days after injection. The descending part of the serum curves allowed an approximate estimation of half-life of 3–8 days. This was not the elimination half-life, but in all probability the half-life of release of drug from the oil depot which was the rate-limiting step. From the areas under the serum concentration curves the fraction of orally administered cis (Z)-flupentixol available to the organism was calculated to be 55% (range 48–60%). The loss of drug might have been due to imcomplete absorption, but it is more likely that cis (Z)-flupentixol underwent first-pass metabolism in the gut wall and the liver. As the tablets contained about 50% cis (Z)-flupentixol, while the depot preparation contained 74% cis (Z)-flupentixol, the pharmacokinetically equivalent doses are: 10 mg tablet daily corresponds to 25 mg depot weekly. Calculation of systemic clearance gave values of 0.44–0.49 l/min, and an apparent volume of distribution was 12.5–17.2 l/kg.