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High-potency statins – Crestor, Lipitor and Zocor – significantly reduce cholesterol levels.JB Reed/Bloomberg

Patients taking powerful cholesterol-lowering drugs may be putting their kidneys at risk, according to the results of a landmark Canadian study.

The researchers focused on "high-potency" statins – Crestor, Lipitor and Zocor – which are well known for their ability to significantly reduce cholesterol levels.

The study found that patients prescribed the high-strength statins faced a 34-per-cent higher risk of being hospitalized for acute kidney injury, compared to those taking the low-potency versions of these and other statin medications.

"Our findings put into question the common approach of using higher and higher doses to push cholesterol levels lower and lower," said lead author Colin Dormuth, an epidemiologist and assistant professor at the University of British Columbia.

He noted that, for any individual patient, the risk remains relatively low. For instance, the study suggests one additional patient out of every 1,700 treated with high-potency statins for 120 days would end up in hospital with acute kidney injury – a condition that used to be called acute renal failure.

Yet the total number of affected patients could still be quite high, considering that these drugs are taken by millions of people worldwide. Furthermore, the study likely underestimates kidney injury because it includes only those patients who were hospitalized, Dormuth said. Others might have suffered kidney injury but were not hospitalized. "Our estimates are probably quite conservative."

The work was carried out by the Canadian Network for Observational Drug Effect Studies, or CNODES. The researchers combed through health databases from seven provinces, as well as databases in the United States and Britain, to pinpoint patients who had been prescribed statins between 1997 and 2008.

In total, they reviewed the medical records of more than 2 million patients to reach their conclusions, which were published Tuesday on the website of the British Medical Journal.

The study was not designed to investigate the long-term effects of these drugs on the kidneys. But Dormuth said that patients with acute kidney injury may require dialysis, a blood cleansing treatment. "Unfortunately, in some cases, there could be a permanent need for dialysis."

Kidney injury is a serious health concern, other members of the research team pointed out.

"The consequences of rapid loss of kidney function experienced in acute kidney injury can be profound and long-lasting," Dr. Matthew James, assistant professor at the University of Calgary, said in a statement.

The researchers said doctors and patients will have to weigh the risks and benefits of high-potency statins on a case-by-case basis.

Numerous randomized controlled trials have demonstrated that statins can extend the lives of patients who have already had a heart attack. "Statin treatment after heart attack is associated with a reduced chance of mortality, or death from any cause" said Dormuth. Statins help to reduce the risk of future heart attacks in these patients and, more importantly, that reduction in risk translates into a longer life.

However, the benefits are less clear-cut for other patients. In particular, the evidence is inconclusive when it comes to treating people who haven't had at least one prior heart attack.

"There are a number of meta-analyses of randomized trials in patients who don't have a history of occlusive vascular disease and some say that mortality is slightly reduced and some don't," said Dormuth.

That means "some patients may be exposed to unnecessary risk of kidney damage for small gains in life expectancy."

Dormuth added that patients should know what type of medication they are taking and discuss their treatment with their doctors.

High-potency statins include: Crestor (generic name rosuvastatin) at doses of 10 milligrams or higher; Lipitor (atorvastatin) at doses of 20 mg or higher; and Zocor (simvastatin) at doses of 40 mg or more. All other statins were considered low-potency.

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