Flu drug favipiravir shows promise in reining in Covid-19

Further research will have to determine whether humans can tolerate a high dose of favipiravir, favipiravir -- a broad-spectrum antiviral drug used in Japan to treat influenza -- for four to five days.

"Because we administered the drug shortly before exposing the hamsters to the virus, we could establish that the medicine can also be used prophylactically, so in prevention," said Suzanne Kaptein from Rega Institute for Medical Research at Katholieke Universiteit Leuven (KU Leuven) in Belgium.

"If further research shows that the results are the same in humans, the drug could be used right after someone from a high-risk group has come into contact with an infected person. It may likely also be active during the early stages of the disease."

General preventive use is probably not an option, however, because it is not known whether long-term use, especially at a high dose, has side effects.

"In the hamsters, we detected hardly any side effects," said Leen Delang from KU Leuven.

The researchers used hamsters for the study as the rodents are particularly suitable for SARS-CoV-2 research because the virus replicates itself strongly in hamsters after infection. Moreover, hamsters develop a lung pathology similar to mild Covid-19 in humans. This is not the case with mice, for example.

For this study, published in the journal Proceedings of the National Academy of Sciences, the team gave the hamsters either hydroxychloroquine or favipiravir for four to five days.

They tested several doses of favipiravir. The hamsters were infected with the SARS-CoV-2 virus in two ways: by inserting a high dose of virus directly into their noses or by putting a healthy hamster in a cage with an infected hamster.

Drug treatment was started one hour before the direct infection or one day before the exposure to an infected hamster.

Four days after infection or exposure, the researchers measured how much of the virus was present in the hamsters.

Treatment with hydroxychloroquine had no impact: the virus levels did not decrease and the hamsters were still infectious.

"Despite the lack of clear evidence in animal models or clinical studies, many COVID-19 patients have already been treated with hydroxychloroquine," explained Joana Rocha-Pereira from KU Leuven.

"Based on these results and the results of other teams, we advise against further exploring the use of hydroxychloroquine as a treatment against Covid-19."

A high dose of favipiravir, however, had a potent effect. A few days after the infection, the virologists detected hardly any infectious virus particles in the hamsters that received this dose and that had been infected intranasally, said the study.

Moreover, hamsters that were in a cage with an infected hamster and had been given the drug did not develop an obvious infection.

Those that had not received the drug all became infected after having shared a cage with an infected hamster.

A low dose of the drug favipiravir did not have this outcome.