Development of a simultaneous analytical method for clozapine and its metabolites in human plasma using liquid chromatography/electrospray ionization tandem mass spectrometry with linear range adjusted by in-source collision-induced dissociation.

Clozapine (CLZ) is a key drug in treatment-resistant schizophrenia. Therapeutic drug monitoring (TDM) of CLZ and its metabolites, N-desmethylclozapine and clozapine N-oxide, is required to monitor and manage the risks of side effects. Although quantification methods for TDM have been developed for CLZ and its metabolites, they were not sufficiently accurate for the quantification of CLZ owing to the upper limits of the calibration curves. An analytical method using high-performance liquid chromatography/electrospray ionization tandem mass spectrometry was developed and validated for the simultaneous measurement of CLZ and its metabolites in human plasma. To expand the concentration range of the calibration curves, we used a linear range shift technique using in-source collision-induced dissociation (CID). Using our approach, the linearity and quantitative range were improved compared to those reported by previous studies, and were sufficient for TDM in clinical practice. The intra- and inter-assay accuracy was 84.6%-114.8%, and the intra- and inter-assay precisions were ≤9.1% and ≤9.9%, respectively. Moreover, all samples from patients with treatment-resistant schizophrenia were successfully quantified. Therefore, our novel analytical method using in-source CID had the appropriate performance to measure the plasma concentrations of CLZ and its metabolites for TDM in clinical practice.

In Vitro Ravuconazole Susceptibility of Anthropophilic Dermatophyte Strains Isolated from Japanese Patients.

Ravuconazole (RVCZ) is a new human anti-fungal azole drug available in Japan since 2018 and is a broad-spectrum agent that exhibits excellent activity against dermatophytes. In the present study, the in vitro RVCZ susceptibility of clinical isolates of anthropophilic dermatophytes, including Trichophyton interdigitale strains with either low susceptibility to itraconazole (ITCZ) or resistance to terbinafine (TEBR), was investigated using the Clinical & Laboratory Standards Institute M38-A2 test. The MICs of RCVZ for 20 clinical isolates of T. interdigitale were < 0.03125-0.125 mg/L; for 4 clinical isolates of T. rubrum, < 0.03125-0.0625 mg/L; and for 20 clinical isolates of T. tonsurans, < 0.03125 mg/L. Similarly, the MICs of RCVZ for the T. interdigitale strains with either low susceptibility to ITCZ or resistance to TEBR were also < 0.03125 mg/L. To our knowledge, this is first study to investigate the in vitro RVCZ susceptibility of T. interdigitale strains with either low susceptibility to ITCZ or resistance to TEBR. Our results indicated that RVCZ was the most effective drug against these strains.