UPDATE 1-Somaxon: FDA denies approval for insomnia drug

* FDA denies approval for insomnia drug in present form

* FDA raises issues regarding efficacy data

* Shares drop 30 pct

Feb 26 (Reuters) - Somaxon Pharmaceuticals Inc (SOMX.O) said the U.S. health regulators denied approval for its experimental treatment for insomnia in the present form and raised several issues regarding the efficacy data of the drug.

In a complete response letter to the company, the U.S. Food and Drug Administration asked the company to address the possibility that the drug Silenor may prolong the cardiac QT interval -- a measure related to the heart's electrical cycle.

A prolonged QT interval can cause an abnormality in the heart's electrical system.

Somaxon said it plans to respond by submitting results from already completed trials that showed the drug, also known as doxepin, had no effect on QT interval prolongation when administered at 6 mg or 50 mg.

However, the FDA, which extended the review of the drug by three months last November, did not specifically request the company to conduct additional clinical trials. "As we continue to seek approval of Silenor, we will continue to take measures to conserve our cash and will evaluate financing alternatives available to us," Chief Executive Richard Pascoe said in a statement.

Somaxon shares dropped more than 30 percent to $1.49 after the bell from their Thursday's close of $2.14 on Nasdaq. (Reporting by Esha Dey in Bangalore; Editing by Himani Sarkar)