A dramatic rise in the number of hemorrhagic strokes in the US during the 1990s may be linked to increased use of the anti-clotting drug warfarin.
A new study estimates the rate of such strokes increased fivefold across the decade, a period in which the distribution of warfarin also soared. Researchers say that the findings should make doctors more cautious about prescribing the medication to those elderly patients at high risk of hemorrhagic stroke.
Patients suffering from an irregular heart rhythm, also known as atrial fibrillation, commonly receive warfarin to prevent the formation of blood clots. This is because clots can sometimes form when blood is not pumped normally out of the heart and lingers there too long, explains Matthew Flaherty at the University of Cincinnati in Ohio, US.
Such clots can cause disability or death if they travel to the brain and block blood flow – an event called an ischemic stroke.
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However, excessive thinning of the blood by drugs such as warfarin can also increase the likelihood of blood vessels leaking. When this happens in the brain, the bleeding is referred to as a hemorrhagic stroke. Each year approximately 67,000 people in the US experience this type of stroke.
Going up
Flaherty and colleagues reviewed data from hospitals in the Cincinnati area in 1988, 1993 to 1994, and 1999 – including nearly 800 cases of brain haemorrhaging. They also noted which patients had taken warfarin.
The analysis revealed that the rate of hemorrhagic stroke associated with the drug increased from 0.8 cases per 100,000 people in 1988 to 4.4 per 100,000 in 1999. The rise in such cases was particularly striking among patients aged 80 years and above: this number leapt from 2.5 per 100,000 patients to 45.9 per 100,000 over the same time period.
Researchers note that the distribution of warfarin in the US quadrupled during the 1990s, roughly matching the increase in haemorrhagic stroke.
Although other smaller studies have linked warfarin to increased risk of bleeding in the brain, Flaherty says his report is the first to support this link in a population-scale analysis.
“Good medicine”
The team’s analysis of data from 1999 to 2004 is not yet complete, but the researchers extrapolate that the rate of hemorrhagic stroke will have further increased from 4.4 cases per 100,000 people to almost 6.0 per 100,000 during this time. “Warfarin use is still going up and so we think the incidence rate will go up,” Flaherty explains.
But he stresses that anti-clotting medicine can save lives: “Warfarin is good medicine and the message is not that it shouldn’t be used.”
The bottom line, he adds, is that “we need to study it more” and develop new, alternative medications that can prevent clotting in people with irregular heart rhythm without increasing their risk of stroke.
Flaherty also notes that before prescribing warfarin doctors should check for risk factors – such as high blood pressure and diabetes – that can put a patient at higher risk of brain bleeding. And he says that the new findings suggest that patients above 80 years of age are at particularly high risk for this complication.
Journal reference: Neurology (vol 68, p 116)
