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Sanofi, Regeneron cholesterol drug also effective in monthly doses

(Adds analyst comment in paragraph 5; updates shares)

Jan 9 (Reuters) - An experimental drug from Sanofi SA and Regeneron Pharmaceuticals was found to be effective in lowering "bad" cholesterol even when administered once every four weeks, instead of every two weeks.

The drug, alirocumab, belongs to an emerging class of injectable drugs that block a naturally occurring protein called PCSK9, which inhibits the liver from expelling "bad" LDL cholesterol.

These drugs, called PCSK9 inhibitors, are aimed at patients whose cholesterol levels do not fall enough despite the use of statins such as Pfizer Inc's Lipitor, and those who are unable to tolerate them.

Sanofi SA and Regeneron are in a fierce race with Pfizer and Amgen Inc to bring their PCSK9 inhibitor to the market, which is expected to be worth billions if these biotech drugs are also able to significantly reduce heart attacks and deaths as statins have.

Roth Capital's Joseph Pantginis said that by 2016, about 36 million patients across the United States and European Union are expected to be eligible for alirocumab and Amgen's evolocumab, which was also assessed using fortnightly and monthly doses.

Amgen, though, has a head start in getting marketing approval for evolocumab, having submitted an application with the U.S. Food and Drug Administration in August.

Hoping to close the gap, Sanofi and Regeneron paid BioMarin Pharmaceutical $67.5 million for a voucher that could speed up alirocumab's review process.

Alirocumab was tested in 803 high cholesterol patients with a moderate-to-high heart risk. It compared a 300 mg dose of the drug given every four weeks against a placebo, with over two-thirds of the patients also on statins.

A second study evaluated alirocumab in 233 high cholesterol patients with a high heart risk and/or a history of being unable to tolerate two or more statins. The trial compared a 150 mg dose of the drug given every four weeks against a placebo.

Early data from another trial suggested alirocumab could halve heart risk. A study also proved that the number of high-risk statin-intolerant patients able to get their "bad" cholesterol down using alirocumab was 10 times more than those on Merck & Co's Zetia.

Regeneron's stock was up 1.3 percent at $408.41 in morning trading on the Nasdaq on Friday. Sanofi's shares were down 3 percent in Paris.

(Reporting by Natalie Grover in Bengaluru and Leila Abboud in Paris; Editing by Savio D'Souza)