Older people taking statins for high cholesterol should avoid taking the antibiotics clarithromycin or erythromycin at the same time because of potential kidney injury from an interaction, Canadian doctors say.

Each year, millions of people worldwide are prescribed statins to treat high cholesterol levels. The U.S. Food and Drug Administration has cautioned doctors and patients about a potential interaction between commonly prescribed statins and antibiotics that block a liver enzyme that may lead to higher concentrations of statins in the blood.

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Statins are frequently prescribed with antibiotics. (Mel Evans/Associated Press)

In Monday's online issue of the Annals of Internal Medicine, Dr. Amit Garg of the London Kidney Clinical Research Unit in Ontario and his co-authors measured the frequency of statin toxicity among statin users aged 65 and older who were also prescribed clarithromycin or erythromycin for bacterial infections such as pneumonia and bronchitis.

Those subjects were compared with statin users in the province prescribed another antibiotic, azithromycin, that does not block the liver enzyme the same way.

"Co-prescription of either clarithromycin or erythromycin with atorvastatin, simvastatin, or lovastatin was associated with an increased risk of hospital admission with rhabdomyolysis, acute kidney injury and all cause mortality," the study's authors concluded.

Rhabdomyolysis occurs when the body can't metabolize proteins released from the muscles and they enter the bloodstream.

Symptoms of rhabdomyolysis include muscle pain, weakness, tenderness, fever, dark urine, nausea, and vomiting. In severe cases, rhabdomyolysis can lead to kidney failure and be life-threatening, according to Health Canada.

"Given the frequency at which statins are prescribed (atorvastatin is currently the most commonly prescribed drug in Canada), and the high rate of co-prescription seen in our study and in other jurisdictions, this preventable drug-drug interaction remains clinically important," Garg's team said.

To prevent the interaction, the researchers suggested:

  • Stopping use of statins metabolized by the enzyme while the antibiotics are taken.
  • Using a statin that isn’t metabolized by CYP3A4 enzyme instead.
  • Choosing a different antibiotic when appropriate.

They also suggested that clinicians be aware of the most commonly observed drug interactions with statins, noting that free online drug interaction programs exist.

The researchers estimated 79 people need to be treated with both clarithromycin or erythromycin and the statins to cause acute kidney injury to one patient.

They estimate that 399 people need to be treated by the drug combination to cause one death, from any cause.  

Azithromycin is usually prescribed for a shorter time than the other antibiotics studied and it's possible that other factors such as duration of treatment were behind the differences observed.

The findings can only be generalized to older patients.