US regulators and pharmaceutical manufacturing giant Pfizer have announced new safety warnings regarding the popular antibiotic azithromycin, more commonly branded at Zithromax or Zmax, because of an elevated risk of potentially fatal arrhythmias.
The warning, issued on 12 March 2013, comes several months after FDA issued a preliminary safety warning regarding its safety in response to a study published in the New England Journal of Medicine (NEJM). That study showed the drug to be associated with a "small increase in cardiovascular deaths" over the course of a standard five-day Zmax treatment.
At the time (May 2012), FDA advised patients to continue taking their medications as directed, but for healthcare providers to exercise increased vigilance and to be aware of the potential for a prolonged QT interval and heart arrhythmias.
Shortly thereafter, FDA sent Pfizer an untitled letter regarding its presentation of drug risks after the company allegedly downplayed the QT prolongation risks factors associated with Zmax.
"The brochure prominently presents efficacy claims in large bolded font size and in colorful text and graphics surrounded by a significant amount of white space; in contrast, the risk information is placed in obscure locations, in block paragraph format, without the use of headers or other signals to alert readers to its significance," FDA explained. "The overall effect of this presentation undermines the communication of important risk information, minimizing the risks associated with Zmax, and misleadingly suggests that Zmax is safer than has been demonstrated."
Elevated Risks of Arrhythmia
Those same risks have now apparently been validated, with Pfizer updating its product labeling to include "additional information regarding a specific, rare heart rhythm abnormality in patients with risk factors such as 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."
FDA noted that while the risk factor is small-just one in 111,000 healthier patients and one in 4,100 high-risk patients would experience QT prolongation resulting in death-the effects are nevertheless severe enough and the patient pool large enough to warrant the labeling change and warning. The drug saw sales of more than $460 million 2011, according to data from IMS Health.
The risk factor is not unique to Zmax. FDA noted in its May 2012 warning that similar antibiotics, including clarithromycin and erythromycin, contain similar warnings. The drug is currently approved and indicated for the treatment of acute bacterial exacerbations of chronic pulmonary disease, acute bacterial sinusitis, community-acquired pneumonia, pharyngitis/tonsillitis, uncomplicated skin and skin structure infections, urethritis and cervicitis and genital ulcer disease.