Pulmonary delivery of favipiravir inhalation solution for COVID-19 treatment: in vitro characterization, stability, in vitro cytotoxicity, and antiviral activity using real time cell analysis

Abstract

Favipiravir, an RNA-dependent RNA polymerase (RdRp) inhibitor, is used to treat patients infected with influenza virus and most recently with SARS-CoV-2. However, poor accumulation of favipiravir in lung tissue following oral administration has required an alternative method of administration that directly targets the lungs. In this study, an inhalation solution of favipiravir at a concentration of 2 mg mL −1 was developed and characterized for the first time. The chemical stability of inhaled favipiravir solution in two different media, phosphate buffer saline (PBS) and normal saline (NS), was investigated under different conditions: 5 ± 3 °C, 25 ± 2 °C/60% RH ± 5% RH, and 40 ± 2 °C/75% RH ± 5% RH; in addition to constant light exposure. As a result, favipiravir solution in PBS revealed superior stability over 12 months at 5 ± 3 °C. Antiviral activity of favipiravir was assessed at the concentrations between 0.25 and 3 mg mL −1 with real time cell analyzer on Vero-E6 that were infected with SARS-CoV-2/B.1.36. The optimum concentration was found to be 2 mg mL −1 , where minimum toxicity and sufficient antiviral activity was observed. Furthermore, cell viability assay against Calu-3 lung epithelial cells confirmed the biocompatibility of favipiravir at concentrations up to 50 μM (7.855 mg mL −1 ). The in vitro aerodynamic profiles of the developed inhaled favipiravir formulation, when delivered with soft-mist inhaler indicated good lung targeting properties. These results suggest that favipiravir solution prepared with PBS could be considered as a suitable and promising inhalation formulation for pulmonary delivery in the treatment of patients with COVID-19.

Pulmonary Delivery of Favipiravir in Rats Reaches High Local Concentrations without Causing Oxidative Lung Injury or Systemic Side Effects

“…Moreover, soft-mist inhalers provide superiority with their easy use, patient-based dose setting and closed mouthpiece technology that prevents the spread out of contaminated aerosol droplets [60,63,64], making it advantageous for their use in the pulmonary infectious diseases. In our previous study performed to evaluate the in vitro antiviral activity of favipiravir, it was concluded that favipiravir at a dosage of 2 mg/mL effectively inhibits the SARS-CoV-2 virus [33]. The follow-up preclinical data support the claim of the study that the inhalation route provides higher lung accumulation compared to plasma.…”

“…Secondly, the translation from human inhalation dose to rat inhalation dose was scaled as mentioned by Nair and Jacob [32]. Moreover, we recently reported that favipiravir exerts antiviral activity at the concentrations between 0.25 and 3 mg/mL on Vero-E6 that were infected with SARS-CoV-2/B.1.36 [33]. Then, the dosage was prepared in the appropriate volume to fill the dead space in the device and to reach approximately 50% accumulation in the lungs [34].…”

Recent Advances in Inhaled Nanoformulations of Vaccines and Therapeutics Targeting Respiratory Viral Infections

“…reported that favipiravir inhalation solution in PBS buffer is stable for over a year when stored at the refrigerated condition [ 56 ]. The authors also found that nebulisation of 2 mg/mL favipiravir is optimal to achieve both antiviral and minimal toxicity in Vero-EG infected cells and Calu-3 lung epithelial cells, respectively [ 56 ]. A favipiravir solid lipid nanoparticle formulation for inhalation was developed with promising aerosolisation and antiviral properties [ 8 ].…”

A solvent-free HPLC method for the simultaneous determination of Favipiravir and its hydrolytic degradation product

“…Some adverse effects were noted with FPV such as diarrhea, changes in liver function parameters and hyperuricemia 7 . Accordingly, new dosage forms are being formulated for administration of FPV through lung inhalation 8 . Furthermore, there is an increasing need to formulate oral solution dosage forms suitable for children use 9 .…”