Avigan (favipiravir) tablets from Japan's Fujifilm Corporation. Photo: AFP / Fujifilm

As the new coronavirus silently stormed through Wuhan and Shenzhen, doctors tried various existing drugs in search for a cure. Avigan, also known as favipiravir, was one of them.

Experimental treatment of 80 patients began in February. To be sure, it was a limited study and not a double-blinded placebo-controlled clinical trial.

On March 17, Chinese officials cautiously reported that favipiravir appeared to reduce the days needed for viral clearance, typically from 11 to four days. And 90% of patients had improved CT scans of their lungs. The trial was enlarged to 340 patients.

Favipiravir had been developed by a Fujifilm group company, Toyama Chemical, for treating influenza, which is caused by another type of coronavirus. Fujifilm’s brand name for the drug is Avigan.

There are hundreds of drugs and molecules that can kill the virus (SARS-CoV-2) that causes Covid-19. The problem is they can also damage human cells. How can you kill one and not damage the other?

Researchers at Toyama Chemical focused on how the coronavirus that causes influenza replicates itself and multiplies. If you can prevent exponential growth, you can keep the viral count low enough for the natural immune system to win.

The corona virus that causes influenza multiplies by replicating its single strand ribonucleic acid, again and again. If you can inhibit the RNA polymerase that allows this replication, you can prevent the influenza virus from overrunning the immune system.

And that is what Avigan appears to do. Reportedly the drug “does not inhibit RNA and DNA synthesis in mammalian cells and is not toxic to them.” 

Toyama Chemical, however, released a research paper in 2017 cautioning that the drug may affect the development of animal fetuses. South Korea has declined offers of free Avigan from Japan for this reason.

Japan approved Avigan in 2014 for the treatment of influenza “in emergency conditions only.” The US FDA completed Phase III clinical trial in 2015 for treating influenza.

As for trial treatment of Covid-19, China approved it on Mar 15, Italy on Mar 22 and Japan may follow within months. Fujifilm has started Phase III clinical trial and the drug has been administered in Tokyo hospitals.

In 2014, this drug for fighting influenza was also tried against the virus that causes Ebola in Africa. 

Reports from Guinea suggest that the drug is effective when Ebola virus count in the blood is “low-to-moderate” but not when the patient has “high levels of virus count.”

This report dovetails with reports from China: the drug was effective when Covid-19 was still in its early stages when the viral count was low, but not in advanced stages.

These reports follow the logic behind how the drug is suppose to work. It works to inhibit the exponential growth of the virus; once exponential growth has taken place, the drug is moot.

So here is the paradox: New drugs tend to get rushed out to treat the most severe cases where life and death lies in the balance. But that is exactly the condition under which Avigan does not work.