Avigan, a candidate drug for treating novel coronavirus infections, has not shown apparent efficacy in treating the respiratory disease in clinical trials so far, raising doubts about its approval by the end of this month as sought by the Japanese government, sources familiar with the matter said Tuesday.

Interim results of clinical tests of Avigan on COVID-19 patients reported to the health ministry did not provide clear evidence of the drug's effectiveness in reducing coronavirus growth, they said.

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

Japanese Prime Minister Shinzo Abe has said he is hoping for the approval of Avigan, developed by a Fujifilm Holdings Corp. subsidiary, by the end of May, although some medical experts have voiced concerns about rushing to approve the drug which is known to have potential side effects on the fetus when used by pregnant women.

The clinical trial data were reported by hospitals treating people showing mild or no symptoms. The Ministry of Health, Labor and Welfare has been expecting that the data, along with results of other trials involving thousands of coronavirus patients, will help lead to early approval, the sources said.

Fujifilm is also conducting clinical studies of the drug on COVID-19 patients.

"There are currently no data showing that Avigan has high efficacy," said Daisuke Tamura, an associate professor at Jichi Medical University specializing in pediatric infectious disease.

"It should be cautiously evaluated based on scientific evidence," he said.