UPDATE 1-EU agency backs Boehringer stroke prevention drug

* Pradaxa recommended for patients with atrial fibrillation

* Drug already sold in EU to prevent clots after surgery

(Adds details, background)

By Ben Hirschler

LONDON, April 15 (Reuters) - European regulators recommended Boehringer Ingelheim's drug Pradaxa for the prevention of stroke on Friday, confirming its leading position among a wave of new pills designed to stop blood clots.

The privately held drugmaker's medicine was approved for the same use in United States in October and it is already sold in Europe to prevent clots after hip and knee surgery.

The European Medicines Agency said it was now recommending Pradaxa for preventing strokes and systemic embolism among patients with atrial fibrillation, a type of irregular heartbeat most common among the elderly.

Recommendations from the agency's expert committee on new drugs are normally endorsed by the European Commission within a couple of months.

Warfarin has been the standard for preventing stroke in such patients since it was introduced in the mid 1950s.

But patients taking warfarin, which is sold by a number of generic drugmakers, must follow stringent diets and have frequent blood tests to make sure there is neither too little nor too much of the drug in their bloodstream. If too little, stroke prevention is reduced; if too much, they can be at high risk of bleeding, including brain haemorrhage.

With Pradaxa, patients do not have to adhere to special diets or have to undergo blood monitoring.

Industry analysts estimate the warfarin-replacement market at more than $10 billion a year and possibly up to $20 billion.

Pradaxa has won a head start as other drugmakers race to bring to market other rival blood clot preventers. They include Xarelto, from Bayer (BAYGn.DE) and Johnson & Johnson (JNJ.N), which has been awaiting U.S. approval for stroke prevention since January.

Bristol-Myers Squibb (BMY.N) and Pfizer (PFE.N) are conducting late-stage trials of their promising pill called apixaban.

In atrial fibrillation, part of the heart does not beat correctly and this can lead to blood clots forming, increasing the risk of stroke.

(Editing by Paul Sandle)