Vaccines don’t offer a solution for those already infected with SARS-CoV-2, which is why virologists at the Leuven Rega Institute are simultaneously searching for a drug that might inhibit the virus in COVID-19 patients. As part of their search, they’ve been analysing thousands of components of existing medicines for their effect against SARS-CoV-2.
Most recently, they noted promising results for favipiravir, a drug used in Japan against the flu virus. A high dose of favipiravir has been shown to have an inhibiting effect on viruses in hamsters infected with the SARS-CoV-2 virus.
During the study, test animals received a dose of favipiravir over the course of four to five days. The hamsters were infected with the SARS-CoV-2 virus shortly after the administration of the medicine. This was done either by administering the virus through the nose or by placing a healthy hamster in a cage with an infected hamster.
Four days after the infection, the researchers checked how much virus was left in the hamsters' bodies.
The hamsters that received a high dose of favipiravir and were infected through the nose showed almost no active virus a few days after the infection. Hamsters that received the drug and were in a cage with an infected hamster also showed no infectious virus in the lungs. That was not the case for the hamsters that had not been given the medicine.
‘A low dose of favipiravir did not have the same effect,’ says Professor Leen Delang. ‘It's the high dose that makes the difference. That’s important to know, because international clinical studies are being set up to test favipiravir in humans.’
The researchers are cautiously optimistic. ‘Because we gave the drug to the hamsters shortly before they became infected, we can conclude that it can be used to suppress an emerging infection. If further research shows that this is also the case in humans, the drug could be used, for example, shortly after someone from a risk group has been in contact with an infected person,’ says researcher Suzanne Kaptein. ‘It could therefore be used in the early stages of COVID-19. Generalised preventive use may not be an option, because we don’t yet know whether long-term use, especially at a high dose, will cause side effects.’
Virtually no side effects were observed in the hamsters. Moreover, favipiravir has been previously prescribed at high doses in Ebola patients. No toxicity was found at the time. Still, more research needs to be done on whether the drug can be well tolerated.
The researchers warn that it is not a wonder drug. Favipiravir has not been specifically developed for use against coronaviruses. At best, it has a moderate effect.
The study also emphasises the importance of in vivo research with small animals. ‘Our hamster model is particularly suited for examining which new or existing medicines should be investigated clinically,’ explains Professor Johan Neyts. ‘In the early days of the pandemic, no such model was available. At that point, the only option was to go immediately to the patients to see if a drug could help them. Testing drugs on hamsters provides crucial information. This way we can avoid losing valuable time and energy testing products that don't work.’