Oct 28 (Reuters) - The U.S. government has agreed to pay $375 million to Eli Lilly and Co for 300,000 doses of its experimental COVID-19 antibody treatment, a drug similar to a treatment that U.S. President Donald Trump received.

Lilly will start delivering the doses within two months of receiving an emergency use authorization from the U.S. health regulator, the company said.

After that, the government has an option to buy an additional 650,000 vials for $812.5 million, the U.S. Department of Health and Human Services said in a statement.

Chief Executive Officer David Ricks said in statement on the company's website that the United States and other wealthy nations would pay $1,250 per dose for the drug.

The U.S. government said separately it would provide the treatment free to Americans.

Middle-income countries will get a steep discount, while the poorest nations will pay only marginal costs, Rick said, adding that the company plans to strike purchase deals with governments while supply is constrained.

While vaccines are seen critical to ending the pandemic, governments are increasingly looking at effective treatments to slow the spread of the virus and kick-start economic activity.

Lilly expects a modest financial return from the treatments by the end of 2021.

The U.S. government has also signed deals with AstraZeneca and Regeneron Pharmaceuticals for their antibody therapies, under Trump administration's Operation Warp Speed program aimed at speeding up COVID-19 treatments and vaccines.

The deal with Regeneron covers the cost of manufacturing, while the deal for AstraZeneca's antibody, which is yet to be tested in late-stage trials, also includes support for development.

Lilly submitted a request to the U.S. Food and Drug Administration earlier this month for emergency use authorization of the drug to treat mild to moderate COVID-19 patients.

The drug had a recent setback after it failed to show benefits in hospitalized patients, but has shown success in earlier use in patients.

In addition, Reuters reported that U.S. drug inspectors uncovered serious quality control problems at an Eli Lilly plant that was ramping up to make the therapy.

(Reporting by Manas Mishra in Bengaluru; Editing by Bernard Orr and Saumyadeb Chakrabarty)