The research found that when compared to low dose statin regimens, high potency versions of the pills were linked to slightly elevated rates of acute kidney injury.
The researchers, who are from institutions across Canada, estimate that for every 1,700 people who used high dose statins for 120 days, you would expect to see one more person hospitalized with kidney failure.
While that number may seem small, a drug safety expert who wasn't involved in the work noted that use of these drugs is common.
"Tens of millions of North Americans take these drugs, and so even side-effects that are relatively uncommon are important," said Dr. David Juurlink, a specialist in internal medicine and clinical pharmacology at Toronto's Sunnybrook Health Sciences Centre.
"The findings strongly suggest that high-dose statins can cause acute kidney injury.... Most clinicians don't generally perceive statins to be a potential cause of kidney injury. Hopefully this study will change that perception, and make us all a bit more careful of how we use these drugs."
The research was produced by the Canadian Network for Observational Drug Effect Studies, which is funded by Health Canada. The study was published in the journal BMJ.
Lead author Colin Dormuth said previous studies have shown hints that high potency statins may increase the risk of kidney failure, but the studies were not large enough to provide more than a signal of a potential problem. If the increased risk only shows up at a rate of one additional case per 1,700 people treated, a study would need to be very large to ensure that effect was real and not merely a chance observation.
So Dormuth and his colleagues pooled data on more than two million people who took statins, comparing those who took high potency formulations to those taking lower doses of the drugs. People included were aged 40 and older and started taking statins between the beginning of 1997 and April 30, 2008.
The data were drawn from databases from seven Canadian provinces as well as from Britain and the United States. About a third of the 2,067,639 people in the study were using high potency statins.
"We thought given that so many people use these medications that it was really important to try to determine if there was an association between statin potency and risk of acute kidney injury," said Dormuth, who is an epidemiologist with the University of British Columbia's Therapeutics Initiative. The program uses an evidence-based approach to drug therapy to try to balance the information sources funded by the pharmaceutical industry.
High potency statins were defined as 10 milligrams or more of rosuvastatin (sold under the brand name Crestor), 20 mg or more of atorvastatin (sold under the brand name Lipitor) and 40 mg or more of simvastatin (sold under the brand name Zocor). All other statins were considered to be low potency.
The kidney problems, when they occurred, seemed to materialize early in the treatment, generally within 120 days. But the risk of kidney injury associated with high potency statins remained elevated for at least two years, the study found.
An editorial on the issue that ran with the study said that despite the broad use of statin drugs, the science of finding the Goldilocks dosage — maximizing benefit while minimizing risk — was still evolving.
Still, Robert Fassett and Jeff Coombes, professors from the University of Queensland in Brisbane, Australia, said doctors should make note of the Canadian findings.
"The results of the current study indicate that clinicians should use low potency statins whenever possible to provide cardiovascular benefits without the increased risk of acute kidney injury," they wrote.
Dormuth said he and his colleagues are not suggesting there is no place for high potency statins. Rather, he suggested, people considering taking these drugs should talk with their doctors about their risk of heart disease and how it stacks up against the risk of taking these drugs.
"We're seeing patients younger and healthier getting the drugs," he said.
"This is where the 1,700 number needs to be put in context with other known harms, such as rhabdomyolysis (and) diabetes, and that needs to be weighed against the expected benefit. And the expected benefit of taking a statin is very small in younger, healthier people — particularly women."
Rhabdomyolysis is a potential side-effect of statin use. It is a condition where muscle tissue breaks down and is released into the blood stream, which can lead to kidney damage.