Doctors are being warned about the risk of uncontrollable bleeding in some patients on new anti-blood clotting drugs.

The head of the National Centre for Pharmacoeconomics at St James's Hospital in Dublin issued the warning about the drugs used to treat an irregular heartbeat and reduce the risk of stroke.

Dr Michael Barry said he was concerned that around 1,000 patients a month are being moved to these medicines, for which there is no immediate antidote for uncontrolled bleeding, a known risk.

He said new oral anticoagulants have a major bleeding rate of up to 3% a year and he is concerned that emergency departments could start to see more cases given the new trend.

The medicines are a major advance on the traditional drug Warfarin, which has been used since the mid 1950s.

However, Dr Barry said many of the 33,000 patients on Warfarin should not need to be switched.

Patients on the new drugs should not stop taking them, but should contact their doctor if they have any concerns.

Patients on the new anti-coagulants do not need regular blood monitoring at clinics unlike those on Warfarin.

They have lower rates of intracranial haemorrhage and there is a reduced potential for drug interactions.

A spokesperson for Boehringer Ingelheim, the makers of Pradaxa, one of the new drugs, said the efficacy and safety of it had been well-studied with real world evidence equating to over 1.3 million patient years to date.

The company said its product had been shown to significantly reduce the risk of strokes in patients with an irregular heartbeat compared to Warfarin.

The Irish Medicines Board said the new drugs are all licensed for use throughout the European Union and bleeding that may lead to serious or even fatal outcomes is a well recognised complication of all anticoagulant medicines.

It has received adverse reaction reports of bleeding which are known to be associated with the use of the drugs.

But it says these medicines offer an important health benefit and patients should not stop taking blood thinning medicines as that could increase the risk of a stroke.

The IMB said it will continue to monitor the experience with use of the drugs and will communicate any new information on the risk of bleeding, as necessary.

The Irish Heart Foundation said patients should remain on anti-coagulant medication to reduce the risk of stroke or other problems, but patients with any worries should talk with their doctor.

It said all patients should be aware of any significant bleeding or bleeding that goes on for longer than normal, such as a nose bleed, and should contact their doctor as the dose may need to be changed.

The other two major new blood thinning drugs are Xarelto, which is made by Bayer, and Eliquis by Bristol Myers Squibb.