Atea Pharmaceuticals has announced that its drug, AT-527, failed to meet the primary goal of the international Phase II MOONSONG clinical trial in subjects with mild or moderate Covid-19 in the outpatient setting.

An oral direct-acting antiviral, AT-527 is being co-developed by Atea and Roche.

The randomised, multicentre, double-blind, placebo-controlled Phase II trial assessed the safety, antiviral activity and pharmacokinetics of twice-daily (BID) doses of 550mg and 1,100mg AT-527 in adult subjects with mild or moderate Covid-19 against placebo.

The change from baseline in measure of SARS-CoV-2 ribonucleic acid (RNA) as assessed by reverse transcription-polymerase chain reaction (RT-PCR) at particular intervals, was the trial’s primary goal.

Findings showed that AT-527 failed to meet the primary goal versus placebo in the overall trial population, which had two-thirds of subjects with mild symptoms at reduced risk.

A decline of viral load of nearly 0.5log₁₀ at day seven was reported in increased risk subjects with underlying health conditions when administered with BID 550mg and 1,100mg AT-527 against placebo.

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AT-527 was found to be safe and well-tolerated and the data was in line with prior trials.

Nearly 20% in the placebo arm and AT-527 550mg BID arm reported adverse event (AE) versus 27% in the AT-527 1100mg BID arm.

Furthermore, the most common AEs observed in the trial were gastrointestinal-related.

Atea Pharmaceuticals chief development officer Janet Hammond said: “Based on the totality of the results for AT-527 to date, the current level of understanding of the virus and the evolving Covid-19 environment, we are assessing the Phase III MORNINGSKY trial for modifications to ensure the best possible outcome for the programme.

“We, along with our partner Roche, are continuing to advance multiple studies in parallel to provide further clinical evidence, as well as outcome data to support AT-527 as an oral, potent, direct-acting antiviral treatment for Covid-19.”

Possible changes to the international Phase III MORNINGSKY trial, including its primary goal and subject population, will be analysed by Atea and Roche.

Results from this trial are anticipated in the second half of next year.

Earlier this year, Atea dosed the first subject in the Phase III trial of AT-527 in mild or moderate Covid-19 patients in an outpatient setting.