Statins are one of the most commonly prescribed drugs in Canada, taken over the long-term, and are used to lower cholesterol.
Using information from provincial health care databases, the study looked at Ontario adults 66 years and older who had continuous prescriptions for one of three statins (rosuvatstatin, fluvastatin and pravastatin) and received an additional prescription for one of two common antibiotics (clarithromycin or azithromycin) between June 2002 and March 2013.
It found that when adults are prescribed clarithromycin, or Biaxin XL, on top of their existing statin prescription, there's greater risk of getting admitted into hospital with acute kidney injury or hyperkalemia (high level of potassium in the blood stream) compared to those who were prescribed azithromycin, or Apo-Azithromycin.
Both clarithromycin and azithromycin are generally prescribed by doctors in the same way and for the same type of infections, according to Dr. Amit Garg, one of the study's senior authors. The study was conducted by doctors from the Lawson Health Research Institute in London, Ont., in conjunction with the Institute for Clinical Evaluative Sciences.
In an interview with CBC News, Garg said that there were 50,000 times when both clarithromycin and the statins looked at in the study were co-prescribed in Ontario over the past decade. Of these 50,000 times, there were "hundreds of cases" that showed serious adverse effects. He said for every 100 patients, at most there was one who was affected.
Absolute risk fairly low
The absolute risk, according to Garg, is still fairly low for a given patient — about one per cent.
“We can say it’s reassuring because it’s not much higher," he said, though Garg acknowledged the study didn't look at mild side effects, ones that don't require hospitalization.
However, "many people are co-prescribed these things, so at the population level you start to see hundreds of cases of severe toxicity,” he said.
What happens is clarithromycin blocks a certain enzyme that is needed to break down statin. Without that enzyme, there's increased levels of statin in the blood stream (statin toxicity), which causes those severe effects.
The other antibiotic, azithromycin, doesn't interfere with that enzyme.
"Some people stop taking statins because they’re concerned that it can produce harms,” said Garg. "This is an opportunity to improve their safety."
This new information is meant to help doctors become aware of the drug interaction between a statin and an antibiotic.
"To prevent toxicity, the use of azithromycin or another antibiotic that does not interact with statins can be considered," according to the study.