In vitro studies for BCS classification of an antiviral agent, favipiravir. (COVID-19 dedicated issue.)

ABSTRACT

Favipiravir (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) is a purine nucleic acid analog, which is an antiviral agent used in the treatment of influenza. Since the recent outbreak caused by 2019-novel coronavirus (nCoV), there has been a seek for effective antiviral agents to be used in the treatment of coronavirus disease 2019 (COVID-19), and favipiravir has been one of the options which provides a broad-spectrum therapy. Herein, we studied the aqueous solubility and in vitro permeability characteristics of favipiravir in order to shed light on the BCS classification of this antiviral agent used in COVID-19 therapy. The in vitro solubility was assessed using saturated solution of favipiravir in four different aqueous media and the solubility values were evaluated during 72 h at 37..C. The solubility of favipiravir was between 4.48 to 8.5 mg/ml, which is 5.85 to 10.63 times of calculated solubility limit. Caco-2 cell monolayers were utilized for the permeability assessment, and the drug solutions in three different concentrations including the highest dose required for bioequivalence exemption of the immediate release dosage form were applied. The effect of efflux transporters on the permeability of favipiravir was also determined using a P-gp inhibitor, Verapamil HCl. According to the data obtained from the in vitro studies, favipiravir can be considered as a representative of class I compound.