What you need to know about risky blood thinners

A growing number of Canadians take powerful pills to thin their blood, to prevent clots and strokes. Doctors in this country write more than 7 million of these prescriptions each year. But with the benefit comes risk, according to a study just published in the Canadian Medical Association Journal (CMAJ). 

Blood thinners work by preventing clots in the brain that lead to strokes as well as clots in the legs and the lungs. But all clots aren't bad.  When you cut your skin, you need the blood to clot to stop the bleeding. When you fall and hit your head, you need to blood to clot to prevent a brain bleed. When it comes to blood thinners, too much of a good thing causes harm and for seniors it can even be fatal. The risk of a brain bleed following a relatively minor head injury increases dramatically in an older senior who takes blood thinners. In some studies, the chance of dying is as high as 50 per cent - far higher than the chance of dying among those who don't take blood thinners. 

The study in CMAJ - by researchers in Toronto  - looked at nearly 46,000 patients in Ontario age 65 and older who take a blood thinner called dabigatran etexilate - sold under the brand name Pradaxa. Between 2012 and 2014, 1,117 of the patients suffered a major episode of bleeding that necessitated being admitted to hospital or going to the ER. The risk of a bleed was significantly increased in patients who were taking dabigatran and one of two very popular medications called statins, which lower cholesterol. The drugs are simvastatin (sold under the brand name Zocor and generics), and lovastatin (sold under the brand name Mevacor and generics).

The researchers believe the two statin drugs interacted with the blood thinner to increase its potency - hence more bleeding. They concluded that patients who take dabigatran should consult with their doctor about not taking simvastatin or lovastatin.

Fortunately, simvastatin and lovastatin are just two of six statin drugs that lower cholesterol that are marketed in Canada. The other four are atorvastatin (sold under the brand name Lipitor plus generics), rosuvastatin (Crestor and generics), pravastatin (Pravachol and generics) and fluvastatin (Lescol and generics). The authors of the study in CMAJ say that the other four cholesterol-lowering drugs don't have the same interaction with dabigatran.  In the study, none of the four taken in combination with dabigatran caused excess bleeding. The bottom line is that any of the other four cholesterol-lowering medications may be taken safely in combination with dabigatran.

All blood thinners have a risk of bleeding.  According to a Canadian study, as recently as 2010, the vast majority of people who needed a blood thinner took a drug called coumadin - also known as Warfarin  Patients who took it got regular blood tests to monitor their blood to make certain it was thin, but not too thin.  

Then, newer blood thinners like dabigatran, apixiban and rivaroxaban arrived. At more than 2 million prescriptions a year, they're very popular because they're convenient to take. Unlike coumadin, you don`t need regular blood tests to monitor their effectiveness.  

The challenge is that you have little way of knowing if there`s an imminent risk of bleeding.  An antidote for coumadin is readily available.  A very expensive antidote for dabigatran is also available, and antidotes for the other two drugs are in development.  

Given the concerns, what should Canadians do?  Seniors who take a blood thinner - especially the new ones - need to be very careful. Remember that frail seniors are more likely than younger patients to fall and have a head injury or fracture their pelvis.  Many seniors who fall take blood thinners and are therefore at risk of a major bleeding episode. They usually end up in the ER where I've seen plenty of them. Since antidotes aren't widely available, preventing falls and being vigilant to the warning signs of a major bleed are crucial.  Ask your doctor if the medications you take could put you at increased risk.   

(Note: This is a print and audio version of Dr. Goldman's weekly House Doctor column which airs across Canada on local CBC stations. It does not air on on the program White Coat, Black Art).