UPDATE 1-EU agency still probing safety of Novartis MS pill

* EU medicines agency to update on Gilenya safety in April

* Novartis says working with EMA to finalise drug label

* UK's NICE (Milan: NICE.MI - news) backs drug as cost-effective in about-turn (Combines news from EU medicines agency and Britain's NICE)

LONDON, March 16 (Reuters) - European regulators are still probing the safety of Novartis AG's multiple sclerosis pill Gilenya, one of the Swiss firm's top new drug hopes, delaying an expected update on the medicine until April.

The European Medicines Agency (EMA) initially aimed to give an update on the medicine by March 16 but a spokeswoman said on Friday that the review had not yet been finalised. As a result, an announcement is now due on April 19 or 20.

The delay leaves a question mark over the product, which has seen its prospects clouded by concern about serious heart problems.

But there was also good news for Gilenya as Britain's healthcare cost-effectiveness watchdog NICE, in an about-turn, decided it was ready to recommend its use on the state health service.

Gilenya, the first multiple sclerosis (MS) pill of its kind, is seen by analysts as a potential blockbuster with annual sales of $2 billion by 2015, according to consensus forecasts collected by Thomson Reuters Pharma.

However, that is down on the $2.2 billion seen at the end of 2011 as doctors have grown more cautious about the drug following reports of heart problems in some patients and the death of one person in the United States within 24 hours of starting treatment.

Those cases prompted the EMA to start its review in January, when it also advised doctors to continuously monitor patients for six hours after giving them a first dose. The U.S. Food and Drug Administration (FDA) is also looking into the drug.

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UPDATE 1-EU agency still probing safety of Novartis MS pill