Japanese health authorities have found it difficult to reach a conclusion on the effectiveness of anti-viral drug Avigan in treating COVID-19 patients based on the results of clinical testing by its developer, government sources said Wednesday.

The latest assessment by the Pharmaceuticals and Medical Devices Agency will serve as key material for a health ministry review panel that will likely decide on Monday whether to approve the use of Avigan to treat COVID-19 in Japan.

Supplied photo shows tablets of the anti-influenza drug Avigan. (Photo courtesy of Fujifilm)(Kyodo)

Drugmaker Fujifilm Toyama Chemical Co., a unit of Fujifilm Holdings Corp., filed for COVID-19 approval in October. Avigan has already received approval as an influenza drug.

Some medical experts have opposed the use of Avigan, also known as favipiravir, in treating patients with COVID-19, the respiratory disease caused by the novel coronavirus.

Possible side effects include the worsening of liver function, but Fujifilm said no new safety concerns were identified. Pregnant women cannot use the drug as some animal studies have pointed to the possibility of fetal abnormalities.

Expectations have grown that Avigan would become the third treatment drug for COVID-19 in Japan, after the anti-viral medication remdesivir developed by U.S. firm Gilead Sciences Inc. and the steroid dexamethasone.

The assessment acknowledged that approving the use of Avigan as a COVID-19 drug would be "meaningful" at a time when there are limited treatment options available.

Japan has been battling a resurgence of coronavirus cases in recent weeks, forcing Prime Minister Yoshihide Suga to suspend nationwide a subsidy program to promote domestic travel, in a reversal of his earlier stance.

Tokyo confirmed more than 800 daily coronavirus cases Thursday, far higher than the previous record high of 678 reported a day earlier.

Nearly 3,000 coronavirus cases were reported by local authorities across the country on Wednesday, bringing the cumulative total to over 188,000 and the death toll to 2,768.

According to data gathered during clinical testing on 156 patients without severe COVID-19 symptoms, Fujifilm found those administered with Avigan showed improvement after 11.9 days, shorter than the 14.7 days for those in a placebo group.

One of the issues raised in the assessment report is the way the tests were performed. The doctors knew which patients received Avigan or a placebo, which the report argues prevented them from properly assessing symptoms, the sources said.

The government sources also said the criteria for determining whether symptoms had improved, based on body temperature and other data, lacked clarity.

"The clinical testing methodology was unconvincing for checking how symptoms had improved," one of the sources said.

In addition, medical experts said a lack of transparency regarding the development of Avigan raised concern, as detailed plans and the overall results of the tests had not been unveiled.

Fujifilm took longer than initially planned to complete its clinical study that began in March after facing difficulty in securing enough patients as the number of coronavirus cases was on a downward trend in Japan.

Former Prime Minister Shinzo Abe had expressed hope while he was in office that the drug would be approved in May and the government has decided to stockpile Avigan for 2 million people.

Fujifilm is aiming to market Avigan for COVID-19 treatment overseas, including in China.

Related coverage:

Coronavirus outbreak latest: Dec. 17, 2020

Tokyo's daily coronavirus cases top 800 for 1st time

Alaska health care worker has allergic reaction to COVID-19 vaccine