Photo/Illutration The anti-influenza drug Avigan, generally known as favipiravir (Provided by Fujifilm Corp.)

A clinical trial for the anti-flu drug Avigan as treatment against COVID-19 is to be discontinued due to difficulties in assessing the drug's efficacy following the spread of the highly transmissible Omicron variant, the maker said.

Fujifilm Toyama Chemical Co., which manufactures the drug, said March 11 it has conducted the clinical trial on COVID-19 patients who have mild symptoms but are at high risk of becoming seriously ill in Japan.

However, the company said it will stop recruiting participants for the clinical trial at the end of the month as patients with the Omicron variant are less likely to develop serious symptoms.

Avigan attracted public attention in May 2020 after Shinzo Abe, the prime minister at the time, said he aimed to have the drug approved as a treatment for COVID-19 by the end of that month.

Avigan could have been authorized for that purpose if its safety and efficacy had been confirmed in a specified clinical trial held to gauge off-label use of a drug.

But the pharmaceutical firm could not obtain sufficient data to statistically prove the drug’s efficacy due to difficulties in recruiting participants for the trial following a drop in patient figures.

The company subsequently compiled the results of a separate clinical trial and submitted them to the health ministry in October 2020 in anticipation of gaining approval for use of the drug as a COVID-19 treatment.

But the ministry’s expert panel decided in December that year to continue discussing whether to give the green light, citing a lack of clear data on the drug’s efficacy.

The pharmaceutical firm then started a new clinical trial in April 2021 involving patients displaying mild symptoms.

Patients with the Omicron variant are less likely to become seriously ill, making it difficult to tell if a drug helped them recover or they were cured without medication in a clinical trial.

Fujifilm Toyama Chemical has also been struggling to recruit participants for the placebo-controlled trial since intravenous drugs and pills are now authorized to treat mild COVID-19 cases in Japan.

The pharmaceutical firm said it had not achieved its target of recruiting 316 participants for the trial as of March 14. The company added that it will consider whether to conduct another clinical trial under different conditions after examining the data it obtained in the trial that will end this month.

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