Medznat

Favipiravir is a pyrazine carboxamide derivative with a broad-spectrum antiviral action, mainly developed for influenza many years ago.

See All

Introduction

Favipiravir is a pyrazine carboxamide derivative with a broad-spectrum antiviral action, mainly developed for influenza many years ago.¹

The established in vitro activity of favipiravir against SARS-CoV-2 and early clinical experience has been found to be promising for the treatment of COVID-19.²

Pharmacological Class: Antiviral agent

Indications

COVID-19: Favipiravir has shown clinical improvements of up to 88% in COVID-19, with rapid reduction in viral load by 4 days and therefore holds a considerable potential for treating mild to moderate COVID-19 patients.³

Pharmachologic action

It offers a unique mechanism of action unlike other antiviral agents; it gets converted into an active phosphoribosylated form (favipiravir-RTP) in cells and identified as a substrate by viral RNA polymerase, thereby inhibiting RNA polymerase activity and preventing the replication of viral genome.^{3, 4}

Dosage

Dosage as per clinical study on COVID-19 patients: 1600 mg orally twice on Day 1 followed by 600 mg orally twice daily for Day 2-14.⁵

Pharmacokinetics

The bioavailability of favipiravir is almost complete at 97.6%. The mean Cmax for the recommended dosing schedule of favipiravir is 51.5 ug/mL. Favipiravir's metabolites are predominantly renally cleared. The apparent volume of distribution of favipiravir is 15 - 20 L. The elimination half-life of favipiravir is estimated to range from 2 to 5.5 hours.⁴

Contraindications

Contraindicated in

women known or suspected to be pregnant
patients with known hypersensitivity to any component of favipiravir

Drug interaction

Acyclovir –Favipiravir decrease the rate of excretion of acyclovir when combined with acyclovir
Aminophenazone: Favipiravir decreases its metabolism in the body when consumed together
Apomorphine: The metabolism of apomorphine is reduced when consumed with favipiravir
Benzylpenicillin, antibiotic for bacterial infections, shows reduced excretion when consumed with favipiravir
Chloroquine shows a decrease in its metabolism when combined with favipiravir

Side effects

Common

Reduced body weight
Nausea/vomiting
Reduced locomotive activity

Uncommon and rare:

Shock, anaphylaxis
Pneumonia
Hepatitis fulminant, hepatic dysfunction, jaundice
Toxic epidermal necrolysis (TEN), oculomucocutaneous syndrome (Stevens-Johnson syndrome)
Acute kidney injury
White blood cell count decreased, neutrophil count decreased, platelet count decreased
Neurological and psychiatric symptoms (consciousness disturbed, abnormal behavior, deliria, hallucination, delusion, convulsion, etc.)
Colitis haemorrhagic

Precautions

Favipiravir should not be used for treating bacterial infections
Should be used with caution in children as there is no data reporting its safety in children
Should be used with caution in patients with gout or a history of gout, and patients with hyperuricaemia as their blood uric acid level may increase, and symptoms may be aggravated
Should be used with caution in elderly patients as they have reduced physiological functions
Lactating women should be instructed to stop lactation while starting treatment with favipiravir

Clinical evidence

Favipiravir (FPV) controls the disease progression of COVID-19 by inhibiting the SARS-CoV-2: A recent open-label, nonrandomized, before-after controlled study compared the clinical outcomes between COVID-19 patients who were treated with FPV and those treated with Lopinavir (LPV)/ritonavir (RTV). In the FPV arm, COVID-19 patients who received oral FPV (1600 mg twice on Day 1 followed by 600 mg twice daily for Day 2-14) plus 5 million U interferon (IFN)-α twice daily by aerosol inhalation were included whereas the control arm included patients who were treated with LPV/RTV (400 mg/100 mg twice daily for Day 1-14) plus 5 million U interferon (IFN)-α twice daily by aerosol inhalation. The primary outcomes of the study were the changes in chest computed tomography (CT), viral clearance, and drug safety. As compared to the control arm, the FPV arm demonstrated shorter time for viral clearance (11 days vs. 4 days). In the FPV arm, the improvement in chest imaging was found to be significantly better than the control arm (91.43% vs. 62.22%). Also, the patients in the FPV arm experienced fewer adverse events compared to the patients in the control arm. Overall results showed promising outcomes of favipiravir in terms of disease progression and viral clearance in COVID-19 patients. ⁵

Important CT summaries from studies on Favipiravir

Russian Study basis which approved by Russian Ministry of Health:

No. of patients: 390 (Part 1- 60 and Final part 360)

It was observed that the median elimination time for the SARS CoV-2 was 4 days with Favipiravir compared to 9 days with standard therapy. With Favipiravir, Day 4 of treatment 65% of patients turned RT-PCR negative for SARS CoV-2, Day 10 of treatment, 90% of patients turned RT-PCR negative for SARS CoV-2 Favipiravir gr. 68% reached Fever resolution on day 3 vs Std. therapy on day 6 Overall reported efficacy of favipiravir is >80%.⁹

Observational Study from Japan

This study included 2141 In Mild to Moderate COVID-19 patients. The Favipiravir treatment was associated with a clinical improvement upto 74% by Day 7 and upto 88% by Day 14.¹⁰

Chinese Studies:

In a study conducted by Cai et al. 80 patients were enrolled and it was found that Favipiravir is associated with a significantly shorter viral (4 days) as compared to 11 days for LPV/RTV (Lopinavir/Ritonavir). It also showed significantly higher improvement in chest CT changes with Favipiravir (91.4%) compared to LPV/RTV (62.2 %). Favipiravir has better Safety profile than LPV/RTV stated the study results.¹¹

Chang Chen et al. conducted a study in which 236 moderate COVID-19 patients were enrolled and a superior clinical recovery rate (71.4%) at day 7 was observed with favipiravir than that of umifenovir (55.8%). Favipiravir had significantly shorter time to offer relief from fever and cough than umifenovir.¹²