Erythromycin, a commonly used antibiotic, was found to cause a significant increase in the risk of cardiac arrest when combined with drugs commonly taken for high blood pressure and infection.
An analysis of 1,476 sudden deaths in Tennessee revealed a five-fold increase in the risk of dying from a heart attack among people who had taken erythromycin in combination with other drugs. Researchers noted that taking erythromycin alone also doubled the risk of cardiac arrest.

The study, published in the New England Journal of Medicine, showed that other drugs slow down the breakdown of the antibiotic, which makes the drug more concentrated. At these high levels, salt is trapped inside resting heart muscles.

This extends the time in between heartbeats which can trigger an abnormal, potentially fatal rhythm.

Diltiazem (Cardizem), a drug taken to fight the chest pain of angina, reduce high blood pressure and to restore circulation to the fingers and toes in people with Raynaud’s Syndrome, is one of the drugs that should not be taken with erythromcyin.

Diltiazem is also sold under the brand names Tiazac and Dilacor.

Another drug is verapamil, which is used for heart and blood pressure problems, migraines, asthma, manic depression and panic attacks. It is sold under the brand names Calan and Isoptin.

Fungus-fighting drugs that contain nitromidazole, taken by people with HIV and AIDs, also affects the breakdown of erythromycin. Researchers also noted that grapefruit juice has a similar effect and could pose a risk.

SOURCE: New England Journal of Medicine, September 2004; Reuters Health, www.reuters.com,
September 8, 2004; USA Today, www.usatoday.com, September 9, 2004.