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Study finds common blood pressure pill and antibiotic when used together can cause serious side effects including kidney injury


The blood concentration of a common type of medication used by many patients to control high blood pressure may rise to dangerous levels when taken in conjunction with an antibiotic used to treat sinus infections and pneumonia.

In a new study, researchers at Lawson Health Research Institute (Lawson) and the Institute for Clinical Evaluative Sciences (ICES) found that when calcium channel blockers (such as amlodipine [Norvasc], nifedipine [Adalat], felodipine [Plendil], diltiazem [Cardizem] and verapamil [Isoptin]) are taken in conjunction with the antibiotic clarithromycin (Biaxin), it can result in hospitalization for dangerously low blood pressure and acute kidney injury. Some of these reactions are also fatal.

The study is being presented today at the American Society of Nephrology Renal Week in Atlanta, Georgia, with simultaneous publication online in JAMA.

Previous drug level studies in healthy volunteers have shown that plasma calcium channel blocker concentrations can rise up to 500 per cent when another drug is taken at the same time which interferes with calcium channel blocker metabolism (such as the antibiotic clarithromycin). The researchers wanted to see how often both drugs were being used together in Ontario, Canada, and what effect this was having on the public.

Ontario has almost 2 million adults over the age of 65 who have universal access to hospital care, physician services and prescription drug coverage. This allowed the researchers to track the medications they used and their outcomes. The researchers saw that calcium channel blockers and clarithromycin were co-prescribed to almost 100,000 patients in the last decade, with the practice continuing in recent years. A similar high rate of such co-prescriptions has been observed in other countries as well.

To put the risks into context, the researchers needed a ‘control’ group. For this they looked at patients taking calcium channel blockers who were co-prescribed azithromycin (Zithromax; Z-Pak). Azithromycin is an antibiotic just like clarithromycin, which is used in the same types of patients, by the same types of doctors, and for the same types of infections. But unlike clarithromycin, azithromycin does not interfere with calcium channel blocker metabolism.

The researchers found that taking a calcium channel blocker with clarithromycin (compared to taking it with azithromycin) almost doubled the 30-day risk of (1) being hospitalized with acute kidney injury; (2) being hospitalized with low blood pressure; and (3) dying.

“We conducted this study to raise awareness about the potential dangers of taking these medications together,” says Dr. Amit Garg, a researcher at Lawson and ICES, a kidney specialist at the London Health Sciences Centre (LHSC), and a Professor of Medicine and Epidemiology at Western University. “Drug prescribing references and regulatory agencies such as the U.S. Food and Drug Administration warn about the use of these drugs together, based on information from drug level studies. Our population-based study shows avoidable adverse drug events in real care, and should help convince any physicians and pharmacists who were uncertain about the dangers to now change their practice.”

“Calcium channel blocker-clarithromycin drug interactions and acute kidney injury” is available online in JAMA.

Lawson Health Research Institute. As the research institute of London Health Sciences Centre and St. Joseph's Healthcare London, and working in partnership with Western University, Lawson Health Research Institute is committed to furthering scientific knowledge to advance healthcare around the world. www.lawsonresearch.com

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.

This work was done by the new provincial ICES Kidney, Dialysis and Transplantation Research Program.

For more information please contact:

  • Julia Capaldi
  • Communications & Public Relations, Lawson Health Research Institute
  • [email protected]
  • (w) 519-685-8500 ext. 75616 or (c) 519-200-1115


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