Merck & Co Inc said on Monday it has applied for US emergency use authorization for its tablet to treat mild-to-moderate patients of COVID-19, putting it on course to become the first oral antiviral medication for the disease.

Its authorization could help change clinical management of COVID-19 as the pill can be taken at home. The treatment, molnupiravir, could halve the chances of death or being hospitalized for those most at risk of contracting severe COVID-19, according to the drugmaker.

The interim efficacy data on the drug, which has been developed with Ridgeback Biotherapeutics, had heavily impacted the shares of COVID-19 vaccine makers when it was released last week.

Existing drugs from Gilead Sciences Inc's infused antiviral remdesivir and generic steroid dexamethasone are generally given only once a patient is hospitalized.

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Monoclonal antibody drugs from Regeneron Pharmaceuticals Inc and Eli Lilly have so far seen only limited use due to the difficulty in administering them.

In India, however, two drugmakers had last week sought to end late-stage trials of their generic versions of molnupiravir to treat moderate COVID-19, according to study documents.

A source with the Drug Controller General of India had said the pill has not shown "significant efficacy" against moderate cases, but was successful against mild cases.

Merck said its trials are based on US Food and Drug Administration definitions, which for moderate COVID-19 describe blood oxygen levels as no lower than 93% whereas the trials in India define moderate as blood oxygen levels between 90% and 93%.