Mass spectrometric methods for evaluation of voriconazole avian pharmacokinetics and the inhibition of its cytochrome P450-induced metabolism

Abstract

Invasive fungal aspergillosis is a leading cause of morbidity and mortality in many species including avian species such as common ravens (Corvus corax). Methods were developed for mass spectral determination of voriconazole in raven plasma as a means of determining pharmacokinetics of this antifungal agent. Without further development, GC/MS/MS (gas chromatography-tandem quadrupole mass spectrometry) proved to be inferior to LC/MS/MS (liquid chromatography-tandem quadrupole mass spectrometry) for measurement of voriconazole levels in treated raven plasma owing to numerous heat-induced breakdown products despite protection of voriconazole functional groups with trimethylsilyl moieties. LC/MS/MS measurement revealed in multi-dosing experiments that the ravens were capable of rapid or ultrarapid metabolism of voriconazole. This accounted for the animals’ inability to raise the drug into the therapeutic range regardless of dosing regimen unless cytochrome P450 (CYP) inhibitors were included. Strategic selection of CYP inhibitors showed that of four selected compounds including cimetidine, enrofloxacin and omeprazole, only ciprofloxacin (Cipro) was able to maintain voriconazole levels in the therapeutic range until the end of the dosing period. The optimal method of administration involved maintenance doses of voriconazole at 6 mg/kg and ciprofloxacin at 20 mg/kg. Higher doses of voriconazole such as 18 mg/kg were also tenable without apparent induction of toxicity. Although most species employ CYP2C19 to metabolize voriconazole, it was necessary to speculate that voriconazole might be subject to metabolism by CYP1A2 in the ravens to explain the utility of ciprofloxacin, a previously unknown enzymatic route. Finally, despite its widespread catalog of CYP inhibitions including CYP1A2 and CYP2C19, cimetidine may be inadequate at enhancing voriconazole levels owing to its known effects on raising gastric pH, a result that may limit voriconazole solubility.

Keywords:

• Voriconazole
• LC/MS/MS
• aspergillosis
• raven
• veterinary antifungal agent

Acknowledgments

The authors declare that there were no conflicts of interest. Funding was provided by Wildlife World Zoo & Aquarium. The zoo was not involved in the study design, data analysis, interpretation, writing or publication of this manuscript.

Animal care

Institutional Animal Care and Use Committee of Wildlife World Zoo, Aquarium & Safari Park, La Paloma Animal Sanctuary, United States Fish & Wildlife Service, Region 2, and Arizona Game & Fish Department Wildlife Center approved the study and raven-specific procedures were performed in accordance with the ethical standards of the institution where the study was conducted.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Ethics of experimentation

All research reported in this paper has been conducted in an ethical and responsible manner. In addition, all mandatory laboratory health and safety procedures have been complied with in the course of conducting all experimental work reported in this paper.

Data availability statement

The author declares that reasonable requests for copies of original data will be reviewed and given appropriate responses.