Antibiotics and Blood Pressure Drug Combos Dangerous to Older Adults

Some blood pressure drugs and antibiotics, when combined, could cause dangerously low blood pressure in older adults, according to the findings of a new study. 

Blood pressure medications known as calcium-channel blockers can cause hypotension when combined with E-Mycin and other erythromycin antibiotics, or when combined with Biaxin (clarithromycin).

According to the study, which was published online in the Canadian Medical Association Journal, doctors have been advised to first try the antibiotic Zithromax (azithromycin) if they have patients on calcium-channel blockers.

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Researchers from Toronto studied people 66-years of age and older who were given a calcium-channel blocker between April 1, 1994, and March 31, 2009 and found 7,100 patients who suffered hypotension while on a calcium –channel blocker like Norvasc, Plendil, Procardia, Adalat, Cardizem, Dilacor and Tiazac. Researchers found that the risk of hypotension increased six times when older patients on those drugs were given E-Mycin and similar antibiotics. Being given Biaxin increased the risk by a factor of four. Zithromax was not associated with an increased risk.

All three antibiotics tested are known as macrolide antibiotics, which are the most widely prescribed antibiotic class in the world. In 2008, 66 million prescriptions were filled for these antibiotics in the U.S. Researchers postulated that in the case of erythromycin and clarithromycin-based antibiotics, they inhibit an enzyme known as cytochrome P450 3A4, which helps metabolize calcium-channel blockers.

Calcium-channel blockers are very commonly prescribed long-term medications. Researchers said that it is probably not uncommon for someone on those blood pressure medications to be given a macrolide antibiotic.

They said the drops in blood pressure are likely rare, but severe, and would affect young patients as well as older ones. However, they said that older patients were of more concern because the drop in blood pressure could cause dizziness which could lead to falls, fractures and other injuries. Younger patients are likely to endure the blood pressure drops without injury.


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