Z-Pack May Cause Fatal Irregular Heart Rhythyms

162017_132140396847214_292624_nOn March 12, 2013, the U.S. Food and Drug Administration (“FDA”) issued a formal Safety Announcement warning the public that azithromycin (Zithromax or Zmax), commonly referred to as “Z-pack,” can cause abnormal changes in the electrical activity of the heart that may lead to a potentially fatal irregular heart rhythm. Patients at particular risk for developing this condition include those with known risk factors such as existing QT interval prolongation, low blood levels of potassium or magnesium, a slower than normal heart rate, or use of certain drugs used to treat abnormal heart rhythms, or arrhythmias.

Z-pack is often prescribed by physicians because it is taken for only five days whereas other antibiotics are often taken for ten days.

The FDA advises that health care professionals should consider the risk of fatal heart rhythms with azithromycin when considering treatment options for patients who are already at risk for cardiovascular events. The FDA notes that the potential risk of QT prolongation with azithromycin should be placed in appropriate context when choosing an antibacterial drug. Alternative drugs in the macrolide class, or non-macrolides such as the fluoroquinolones, also have the potential for QT prolongation or other significant side effects that should be considered when choosing an antibacterial drug.

The FDA had previously released a statement on May 17, 2012 regarding a study published in the The New England Journal of Medicine that compared the risks of cardiovascular death in patients treated with the antibacterial drugs azithromycin, amoxicillin, ciprofloxacin (Cipro), and levofloxacin (Levaquin), or no antibacterial drug. The study reported an increase in cardiovascular deaths, and in the risk of death from any cause, in persons treated with a 5-day course of azithromycin (Zithromax) compared to persons treated with amoxicillin, ciprofloxacin, or no drug. The risks of cardiovascular death associated with levofloxacin treatment were similar to those associated with azithromycin treatment.


The study reported in The New England Journal of Medicine was conducted by researchers at Vanderbilt University who examined the medical records of thousands of Tennessee Medicaid patients for a period of over 14 years. The researchers found a significantly greater risk of death from heart disease in the first five days of using Z-pack when compared to use of another common antibiotic or no antibiotics at all, with people who have underlying heart problems appearing to be especially vulnerable.

The study included persons with 347,795 prescriptions for azithromycin, 1,348,672 prescriptions for amoxicillin, 264,626 prescriptions for ciprofloxacin, 193,906 prescriptions for levofloxacin, and 1,391,180 matched control periods with no study antibiotic treatment. Among patients who took azithromycin, there were 29 cardiovascular deaths during the 5-day course of treatment (85.2 per 1 million courses), of which 22 were sudden cardiac deaths (64.6 per 1 million courses). For the first 5 days of a course of amoxicillin therapy, there were 42 cardiovascular deaths (31.5 per 1 million courses) and 29 sudden cardiac deaths (21.8 per 1 million courses). There were 41 cardiovascular deaths (29.8 per 1 million periods) and 33 sudden cardiac deaths (24.0 per 1 million periods) among persons who did not take antibiotics for matched 5-day intervals.

The study found that when the researchers compared a 5-day course of azithromycin therapy with a matched period of no antibiotic treatment, azithromycin was associated with an increased risk of both cardiovascular death and death from any cause during that 5-day interval (the hazard ratio for cardiovascular death was 2.88 and the risk was increased for both sudden cardiac death and other cardiovascular deaths). It was also found that the risk of death from any cause was increased although there was no increased risk of death from noncardiovascular causes.

The study found that amoxicillin use was not associated with a significantly increased risk of death from cardiovascular or noncardiovascular causes or of death from any cause during either the first 5 or all 10 days of therapy.

The researchers concluded: “We found that a 5-day course of azithromycin was associated with a small absolute increase in the risk of cardiovascular death, which was most pronounced for patients in the highest decile of the baseline risk of cardiovascular disease. There was no increased risk of death from noncardiovascular causes among patients who took azithromycin, but there was an increase in the risk of death from any cause. The risk of cardiovascular death was significantly greater with azithromycin than with either amoxicillin or ciprofloxacin but did not differ significantly from the risk with levofloxacin.”

Source: The New England Journal of Medicine, May 17, 2012.

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This entry was posted on Thursday, March 14th, 2013 at 11:54 am. Both comments and pings are currently closed.


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