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Stroke rate reduced to 2% by warfarin, say researchers

GPs should be ‘in no hurry' to switch patients from warfarin to newer anticoagulants say experts, after an analysis showed long-term use of the drug had led to a significant reduction in stroke rates.

In a study that supports restrictions planned by clinical commissioning groups on the use of newer anticoagulants, such as dabigatran, researchers found the rate of stroke was around 1.66% of patients per year on warfarin.

They attributed this to an improvement in the quality of anticoagulation services over the past two decades, and the inclusion of new data from more recent anticoagulant trials in their meta-analysis.

Experts said these data showed that switching to newer agents, such as dabigatran or rivaroxaban, could be premature, particularly because trials only showed non-inferiority with warfarin.

US researchers evaluated all high-quality randomised controlled trials that reported the safety and efficacy of warfarin in patients with non-valvular atrial fibrillation.

Across the eight trials included in the analysis, they found an annual event rate for stroke or non-central nervous system embolism of 1.66%, a rate of 0.76% for myocardial infarction and 3.83% for all-cause mortality.

There was a significantly higher incidence of stroke or non-CNS embolism in patients aged 75 years or older, and in women. Those with CHADS scores of two or more had a significantly greater risk of stroke or non-CNS embolism, compared with patients scoring below two.

Study leader Dr Shikhar Agarwal, a specialist in internal medicine at the Cleveland Clinic in Ohio, USA, said: ‘There has been a significant reduction in the stroke event rate with warfarin treatment during the past two decades.'

‘This reduction may be secondary to a considerable improvement in the quality of anticoagulation as reflected by a greater proportion of time spent in therapeutic anticoagulation.'

In an analysis of the trial by Professor Daniel Singer, professor of medicine at Massachusetts General Hospital, Boston, and Dr Alan Go, acting director of the Division of Research at Kaiser Permanente, Oakland, concluded that adherence might be worse with newer anticoagulants without regular monitoring.

They said: ‘Patients who are comfortable with warfarin therapy and whose time in the standard treatment range is above 75% should be in no hurry to switch.'

Dr Terry McCormack, a GPSI in cardiovascular medicine in Whitby, agreed with this analysis: ‘These new drugs should only be used if the patient cannot take warfarin for whatever reason. There is still some uncertainty with these newer treatments, and the costs are high.'

Arch Intern Med 2012, online 26 March


Event rate with warfarin (% per year)

Stroke or non-CNS embolism - 1.66%

Myocardial infarction – 0.76%

All-cause mortality – 3.83

Adverse vascular events* – 4.80

*Stroke/non-CNS embolism/myocardial infacrction and death

Source: Arch Intern Med 2012, online 26 March