People who take a combination of blood pressure drugs and certain painkillers are at increased risk for serious kidney problems that doctors should watch for, Canadian researchers say.

People who are prescribed a combination of blood pressure medications and non-steroidal anti-inflammatory drugs or NSAIDs are often at high risk of kidney injury, which is associated with about half of potentially preventable deaths in hospital.

For individuals, the risk of combining antihypertensive drugs with NSAIDs is low but worth being aware of, researchers say. (Justin Sullivan/Getty )

Researchers in Montreal and Italy designed a study to investigate the association between the drug combination and kidney failure for 487,372 users of blood pressure medications in the U.K., which they said has the world's largest computerized database of long-term health records from primary care.

"The use of a triple therapy combination was associated with an overall 31 per cent higher risk, which is driven by a nearly twofold increased risk in the first 30 days of use," epidemiology Prof. Samy Suissa of McGill University and his co-authors concluded in Tuesday's British Medical Journal.

The study looked at use different types of blood pressure medications, also called antihypertensives:

• Diuretics that help the body get rid of excess sodium and water.
• Angiotensin converting enzyme inhibitors or ACE inhibitors that help blood vessels relax.
• Angiotensin receptor blockers that help keep blood vessels open.

Given that NSAIDS are widely used and that estimated kidney injury rates are higher among those taking antihypertensives compared with the general population, Suissa's team said "increased vigilance may be warranted" when using the triple combination.

For individuals, antihypertensive drugs have cardiovascular benefits, and the risk is low but worth being aware of, they said.

The researchers used a strict definition of acute kidney injury, a journal editorial published with the study said.

Underestimated risk

Dorothea Nitsch and Laurie Tomlinson, of the London School of Hygiene and Tropical Medicine, said the study probably underestimated the risk of acute kidney injury associated with the drug combinations.

In part, that's because the researchers could not take use of over-the-counter NSAIDs into account and they could not tell when doctors detected increases in creatinine levels in the blood that signal the kidneys aren't working properly and stopped drugs before patients needed to be hospitalized, the editorial noted.

Nitsch and Tomlinson said the study highlights how observational data can improve understanding of the risks and benefits of taking drugs in the real world instead of the specific populations tested in clinical trials.

The study was funded by the Drug Safety and Effectiveness Network, the Canadian Institute of Health Research and the Canada Foundation for Innovation.

Several authors have received research grants or speaking fees from pharmaceutical companies that make blood pressure medications and pain relievers.