A study of the pharmacokinetics of clozapine and its metabolites by the dynamics of its distribution in the oral fluid of healthy volunteers

Clozapine (CLZ) -related accidents or crimes are common in the world. Oral fluid drug detection is a convenient measure of dealing with things like that. There has not been any literature reported detailedly the representation rule of clozapine and its metabolites in oral fluid so far. The study aimed to describe the pharmacokinetics of CLZ and its metabolites N-desmethylclozapine and clozapine-N-oxide in human oral fluid after a single 12.5 mg oral dose of CLZ. Twenty-nine volunteers, including 20 males and 9 females, were recruited, and 2 mL oral fluid was collected from each participant at post-consumption time-points of prior (zero), 0.5, 1.5, 3, 5, 8, 12, 24, 36, 51, 82, and 130 h, respectively. Analytes of interest were extracted with solid-phase extraction and analyzed with liquid chromatography tandem mass spectrometry method. Pharmacokinetic parameters were calculated using the pharmacokinetic software DAS according to the non-compartment model. The maximum concentration, the time of maximum concentration, oral clearance, and the elimination half-life of clozapine were 16.57 ± 9.63 ng/mL, 4.53 ± 3.61 h, 57.65 ± 23.77 L/h and 53.58 ± 52.28 h, respectively. The maximum concentration, the time of maximum concentration, and the elimination half-life of the metabolite N-desmethylclozapine were 3.08 ± 1.19 ng/mL, 9.38 ± 9.33 h and 62.67 ± 82.57 h, respectively; of clozapine-N-oxide were 1.15 ± 0.36 ng/mL, 4.53 ± 2.19 h and 19.15 ± 23.11 h, respectively. It was the first study on the pharmacokinetics of CLZ and its metabolites in the oral fluid of Chinese healthy volunteers, and it provided a basis for the therapeutic drug monitoring and toxicological interpretation in clozapine-related cases.