Favilavir

Favilavir Uses, Dosage, Side Effects, Food Interaction and all others data.

Favilavir is approved for manufacture and sale in Japan as an influenza antiviral. It selectively inhibits the RNA polymerase of the influenza virus, an enzyme required for viral replication once human host cells are infected. COVID-19 also uses this enzyme to replicate and is classified into the same type of single-stranded RNA virus as influenza; hence, it is believed that Favilavir may be effective in treating COVID-19.Favilavir is only used when there is an outbreak of novel or re-emerging influenza virus infections in which other influenza antiviral drugs are either not effective or insufficiently effective. Its production and distribution is at the discretion of Japan’s Health, Labor and Welfare Ministry, so has never been distributed in the market and is not available at hospitals and pharmacies in Japan or overseas.Favilavir is a new antiviral drug against influenza. It is metabolized into favipiravir ribosyl triphosphate (favipiravir RTP) by an intracellular enzyme, and favipiravir RTP selectively inhibits RNA polymerase (RNA-dependent RNA polymerase) of the influenza virus, preventing replication of the influenza virus. It is a drug with a mechanism of action different from that of the existing influenza antiviral drugs and effective against all types and sub-types of human influenza A, B, and C viruses in vitro, showing a wide range of anti-viral activity against various influenza virus strains including avian and swine viruses.

Favilavir functions as a prodrug and undergoes ribosylation and phosphorylation intracellularly to become the active favipiravir-RTP. Favilavir-RTP binds to and inhibits RNA dependent RNA polymerase (RdRp), which ultimately prevents viral transcription and replication.

Favilavir
Uses
Dosage
Side Effect
Precautions
Interactions
Uses during Pregnancy
Uses during Breastfeeding
Accute Overdose
Food Interaction
Half Life
Volume of Distribution
Clearance
Interaction With other Medicine
Contradiction
Storage

Trade Name	Favilavir
Generic	Favipiravir
Favipiravir Other Names	Fapilavir, Favilavir, Favipiravir
Type
Formula	C₅H₄FN₃O₂
Weight	Average: 157.104 Monoisotopic: 157.028754544
Protein binding	Favipiravir is 54% plasma protein-bound. Of this fraction, 65% is bound to serum albumin and 6.5% is bound to ɑ1-acid glycoprotein.
Groups	Approved, Investigational
Therapeutic Class	Anti-viral drugs
Manufacturer
Available Country
Last Updated:	September 19, 2023 at 7:00 am

Uses

Treatment of novel or re-emerging pandemic influenza virus infections (limited to cases in which other influenza antiviral drugs are ineffective or not sufficiently effective).
This drug is only approved as an experimental drug and still a lot of studies is needed about it’s efficacy and also toxic reactions and use in children.

Favilavir is also used to associated treatment for these conditions: Treatment resistant Novel Influenza, Treatment resistant Reemerging Influenza

How Favilavir works

The mechanism of action of favipiravir is novel compared to existing influenza antivirals that primarily prevent entry and exit of the virus from cells. The active favipiravir-RTP selectively inhibits RNA polymerase and prevents replication of the viral genome. There are several hypotheses as to how favipiravir-RTP interacts with RNA dependent RNA polymerase (RdRp). Some studies have shown that when favipiravir-RTP is incorporated into a nascent RNA strand, it prevents RNA strand elongation and viral proliferation. Studies have also found that the presence of purine analogs can reduce favipiravir’s antiviral activity, suggesting competition between favipiravir-RTP and purine nucleosides for RdRp binding.

Although favipiravir was originally developed to treat influenza, the RdRp catalytic domain (favipiravir's primary target), is expected to be similar for other RNA viruses. This conserved RdRp catalytic domain contributes to favipiravir's broad-spectrum coverage.

Dosage

Favilavir dosage

The usual adult dosage is 1600 mg of Favilavir administered orally twice daily on Day 1, followed by 600 mg orally twice daily from Day 2 to Day 5 or as directed by physicians. The total treatment duration should be 5 days.

Side Effects

Most common side effects are Diarrhea and increase of blood uric acid levels.

Toxicity

Based on single-dose toxicity studies, the lethal dose for oral and intravenous favipiravir in mice is estimated to be >2000 mg/kg. In rats, the lethal dose for oral administration is >2000 mg/kg, while the lethal dose in dogs and monkeys is >1000 mg/kg. Symptoms of overdose appear to include but are not limited to reduced body weight, vomiting, and decreased locomotor activity.

In repeat-dose toxicity studies involving dogs, rats, and monkeys, notable findings after administration of oral favipiravir included: adverse effects on hematopoietic tissues such as decreased red blood cell (RBC) production, and increases in liver function parameters such as aspartate aminotransferase (AST), alkaline phosphatase (ALP), alanine aminotransferase (ALT) and total bilirubin, and increased vacuolization in hepatocytes. Testis toxicity was also noted.

Favilavir is known to be teratogenic; therefore, administration of favipiravir should be avoided in women if pregnancy is confirmed or suspected.

Toxicity information regarding favipiravir in humans is not readily available.

Precaution

Favilavir should not be given in pregnant women, requirement of the confirmation of non-pregnancy in women of childbearing potential before use, thorough contraception measures from the start of the treatment to 7 days after the end of the treatment. Caution should be taken for Hepatic and renal impaired patient or use Favilavir as per the direction of registered Physician

Interaction

In animal studies, decreased RBC production,and increases in liver function parameters such as AST, ALP, ALT and total bilirubin, and increased vacuolization in hepatocytes. Toxicity information regarding Favilavir in humans is not readily available.

Food Interaction

No interactions found.

Volume of Distribution

The apparent volume of distribution of favipiravir is 15 - 20 L.

Elimination Route

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.

Studies comparing the pharmacokinetic effects of multiple doses of favipiravir in healthy American and Japanese subjects are below:

Japanese subjects First Dose: Cmax = 36.24 ug/mL tmax = 0.5 hr AUC = 91.40 ugxhr/mL

American subjects First Dose: Cmax = 22.01 ug/mL tmax = 0.5 hr AUC = 44.11 ugxhr/mL

Japanese Subjects Final Dose: Cmax = 36.23 ug/mL Tmax = 0.5 hr AUC = 215.05 ugxhr/mL

American Subjects Final Dose: Cmax = 23.94 ug/mL Tmax = 0.6 hr AUC = 73.27 ugxhr/mL

When favipiravir was given as a single dose of 400 mg with food, the Cmax decreased. It appears that when favipiravir is given at a higher dose or in multiple doses, irreversible inhibition of aldehyde oxidase (AO) occurs and the effect of food on the Cmax is lessened.

Half Life

The elimination half-life of favipiravir is estimated to range from 2 to 5.5 hours.

Clearance

The recommended oral dosing regimen for favipiravir is as follows: Day 1: 1600 mg twice daily; Days 2-5: 600 mg twice daily.

The reported CL/F for favipiravir 1600 mg dosed once daily is 2.98 L/hr ±0.30 and the CL/F values for favipiravir 600 mg dosed twice daily on days 1-2 and once daily on days 3-7 were 6.72 L/hr ±1.68 on Day 1, and 2.89 L/hr ±0.91 on Day 7. There is currently no reported clearance data for favipiravir 1600 mg dosed twice daily.