Doctors should exercise caution in using Boehringer Ingelheim's new stroke prevention pill Pradaxa, following 256 cases of fatal bleeding, but the benefits of the medicine still outweigh its risks, European regulators said on Friday.

Concern about the safety of Pradaxa has risen in recent weeks following the growing number of deaths. Of the total of 256 fatal bleedings worldwide as of November 6, there were 21 in the Europe Union.

Pradaxa is the first in a new class of medicines aimed at replacing the old and problematic drug warfarin. It is designed to prevent strokes in patients with atrial fibrillation, a form of irregular heartbeat common among the elderly.

As with all anti-blood-clotting treatments, it carries a risk of internal bleeding.

The European Medicines Agency said on Friday the efficacy of Pradaxa as demonstrated in clinical trials remained unchanged and recommended changes in use, agreed last month, should adequately manage the risk of bleeding.

The agency will continue to closely monitor this issue and the overall safety profile of Pradaxa, the watchdog said in a statement, following a monthly meeting of its committee of drugs experts.

The agency reiterated that Pradaxa should be used with caution and at lower doses in patients over 75 years and those with moderate kidney impairment. It is not recommended for those with severe kidney problems.

Unlisted German drugmaker Boehringer agreed with the agency last month to update information given to healthcare professionals across Europe advising that patients about to take Pradaxa should have their kidneys checked.

The additional checks and warnings surrounding the drug have further dimmed the safety profile of the first in a promising new class of oral anti-coagulation medicines.

Rival drugs include Xarelto, from Bayer and Johnson & Johnson, and Eliquis, from Bristol-Myers Squibb and Pfizer.

The London-based medicines agency said the increased number of deaths linked to Boehringer's pill has to be seen in the context of the rapidly increasing use of Pradaxa worldwide ... and also the increased awareness about the drug, a factor that is known to lead to higher than usual reporting of side effects.

(Reporting by Ben Hirschler; editing by Kate Kelland and Jane Merriman)