Patients with high blood pressure are increasingly being treated with powerful combinations of drugs.
And according to a new Canadian study, one in four patients are being prescribed unproven - and probably ineffective - combinations by their doctors.
"It's a good thing that there's more polytherapy," Karen Tu, a scientist at the Toronto-based Institute for Clinical Evaluative Sciences and co-author of the study, said in interview.
"[But] unfortunately, it appears that not all physicians are completely aware of the drug combinations that work best for their patients."
The research, published in today's edition of the Canadian Journal of Cardiology, sheds light on treatment for hypertension, a critical but rapidly changing field of medicine.
About five million Canadians are believed to have high blood pressure, a leading cause of heart disease and stroke.
While hypertension is principally a lifestyle disease, brought on by excess weight, inactivity, smoking and consuming too much salt or alcohol, many sufferers require medication.
The first-line treatment is diuretics. But in recent years it has become clear that most patients - probably two in three - need more than one drug to effectively bring their blood pressure down.
Dr. Tu said there are seven combinations of blood pressure medications that have proven effective:
Diuretics with any one of beta blockers, ACE inhibitors, angiotensin receptor blockers (ARBs) or calcium channel blockers;
Beta blockers with calcium channel blockers;
Calcium channel blockers with ACE inhibitors or ARBs.
But Dr. Tu said the research shows that about 27 per cent of prescriptions consist of other, unproven, combinations. For example, patients are prescribed ACE inhibitors with beta blockers, ACE inhibitors with ARBs, or ARBs with beta blockers.
"The clinical evidence for these other combinations is not there," she said.
The result, Dr. Tu said, is that patients' blood pressure will not be as well controlled as it could be if doctors followed the guidelines.
"It's not going to kill you, but it's not the most effective treatment either," she said.
The unproven combinations also tend to involve much more costly drugs, and that means a lot of money is being wasted on treatments that provide no additional benefit, the researcher added.
Practically speaking, it is difficult for patients to figure out themselves whether the combinations of drugs they are taking to treat their high blood pressure are good ones, Dr. Tu said. But she urged them to raise the issue with treating physicians.
The study involved 166,000 Ontario patients who were diagnosed with high blood pressure between 1994 and 2002.
Healthy adults should have a blood pressure of 120/80 millimetres of mercury (mmHg) or lower. A person is considered hypertensive with a blood pressure reading of 140/90 or higher, and usually requires treatment with prescription drugs.
Blood pressure is a measure of the force of the blood against the walls of blood vessels. It is expressed in two numbers: Systolic pressure, the upper number, is the pressure when the heart contracts; diastolic pressure, the lower number, is the pressure when the heart is relaxed.
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