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There seems to be an immediate increased risk of hip fracture when elderly patients start taking antihypertensive medications. (Joe Raedle/Getty)

Elderly people who start taking some blood pressure medications may face a higher risk of falling and breaking a hip, an Ontario study suggests.

When people who are elderly start taking drugs to control blood pressure, it can potentially cause a dizzy spell when blood pressure falls suddenly when standing. The effect occurs over a short time and may lead to falls, researchers say.

In this week's issue of the Archives of Internal Medicine, Dr. Richard Glazier of St. Michael's Hospital in Toronto and his co-authors estimated that elderly people with high blood pressure who started receiving an antihypertensive drug had a 43 per cent higher risk of having a hip fracture in the first 45 days after treatment compared with a control period. 

"To our knowledge, this is the first study to demonstrate an immediate increased risk of hip fracture on initiation of antihypertensive therapy in community-dwelling hypertensive elderly patients," the study's authors concluded.

They advised caution when starting antihypertensive drugs in the elderly. The average age of the people in the study was 81.

"Physicians need to be aware of the effect of drug therapies on fracture risk because it may have important implications for the elderly population and the health care system."

About 72 per cent of newly diagnosed hypertensive patients aged 60 and older take blood pressure medications, they noted.

During the 10-year study period, 1,463 hip fractures occurred.

For the study, researchers also used a prescription drug database of Ontario residents aged 66 and older who received a first prescription for five classes of blood pressure medications.

The trend towards hip fracture risk was found for most classes of antihypertensive drugs except for thiazide diuretics.

The associations were greatest for starting ACE inhibitors and beta blockers, the researchers said.

The study's authors said they weren’t able to estimate the risk for individual patients, such as how many people would have to receive treatment for one of them to experience a hip fracture.

There was also no information on the specific subclasses of the drugs or doses.

It's possible seniors took the medications at a younger age, or took samples of the drugs provided by the doctor, or that they were weren’t taking the drugs they were prescribed.

Patients may have also changed their behaviour at the same time that they started taking the antihypertensive drugs, such as increasing exercise levels, which also raises the risk for a hip fracture.

One of the study's authors is a consultant to several pharmaceutical companies.

The study was funded by the Ontario Ministry of Health and Long-Term Care and Canadian Institutes of Health Research.