A new gas chromatographic method was developed for the quantification of levamisole in human plasma and urine, using a nitrogen-phosphorus flame ionization detector. The adsorption of the drug onto glass was prevented by treating the glassware with a siliconizing agent. The sensitivity of the assay was 10 ng ml-1 and as low as 2 ng ml-1 can be detected in plasma. The urinary metabolite p-hydroxylevamisole was analysed by high performance liquid chromatography with ultraviolet detection. The sensitivity of this assay was 0.50 micrograms ml-1. Plasma and urinary concentrations of levamisole were determined in 10 healthy volunteers including seven men and three women following the administration of a single 150 mg dose of levamisole. Levamisole was rapidly absorbed (tmax 1.5 h), giving a peak plasma concentration of 716.7 +/- 217.5 ng ml-1. The plasma elimination half-life of levamisole was 5.6 +/- 2.5 h. Only 3.2 +/- 2.9 per cent of the oral dose was recovered as unchanged drug in the urine, suggesting the importance of clearance of levamisole by routes other than the kidney, and most probably by hepatic metabolism. The urinary concentrations of p-hydroxylevamisole were determined before and after hydrolysis of the urine samples with beta-glucuronidase, and the level of conjugation of the metabolite with glucuronic acid was then estimated. Cumulative recovery of the metabolite accounted for 1.6 +/- 1.1 per cent and 12.4 +/- 5.5 per cent of the oral dose of levamisole before and after hydrolysis, respectively, indicating that p-hydroxylation is a relatively important route of metabolism of levamisole, and that the p-hydroxylated metabolite is excreted mainly in conjugation with glucuronic acid. Except for the absorption rate of levamisole which is approximately twice as rapid in women as in men, there is no marked difference in the pharmacokinetics of levamisole between healthy men and women.

Zopiclone is a new sedative showing a rapid onset of hypnotic effect and a relatively short duration of action. The goal of this study was to assess the kinetic parameters of zopiclone and its interaction with trimipramine when administered concomitantly. Ten normal subjects each received doses of zopiclone (7.5 mg), trimipramine (50 mg), and zopiclone (7.5 mg) + trimipramine (50 mg) orally at 7-day intervals. The absorption of zopiclone was rapid, the observed plasma peak concentration and 95 per cent of all absorption occurring within one hour. The average elimination half-life was 3.8 +/- 0.2 h. The volunteers reported a bitter taste at an average of 24 min after zopiclone administration at which time concentrations in saliva were approximately 50 ng ml-1. Trimipramine decreased the relative bioavailability determined for zopiclone by 13.7 per cent, while zopiclone decreased the relative bioavailability of trimipramine by an average of 26.6 per cent, although neither of these changes was statistically significant (p greater than 0.05); there were no substantial changes in other kinetic parameters. It is concluded that zopiclone presents advantages over some other sedative drugs as it is rapidly absorbed and eliminated. When zopiclone is administered with trimipramine, the decrease in the relative bioavailability of trimipramine may be clinically significant.

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