Zithromax (Azithromycin) is a pharmacological blockbuster. The drug routinely brings in billions in revenue, due to the its efficacy against a wide variety of bacterial infections. However, the drug does carry the risk of two major complications: heart problems and autoimmune reactions.

Physicians refer to Zithromax as a broad-spectrum antibiotic. This means that the drug can interfere with bacterial growth across a wide range of different species of bacteria. This allows doctors to use Zithromax to treat a host of different diseases caused by bacterial infections. Everything from a sore throat to flesh-eating bacteria generally responds to treatment with Zithromax. This allows doctors to prescribe the drug without identifying an infection down to the species level, a time-consuming process that can translate to days without proper treatment. Additionally, Zithromax has a very different chemical structure from penicillin. This allows patients who are allergic to penicillin to take Zithromax without the risk of serious allergic reaction. These features have contributed to the drug’s success.

However, in 2012, a study in the prestigious New England Journal of Medicine (NEJM) discovered that patients taking Zithromax had an increased risk of fatal heart problems. It was known that other drugs in the Zithromax family, the macrolide antibiotics, had an increased risk of altering the heart rhythm, causing a chain of events that could lead to sudden cardiac arrest. Zithromax was believed to be free of this side effect, partially because the drug was created synthetically. Though Zithromax had a much-decreased risk of these problems, the widespread use meant that this relatively rare problem translated into serious problems for thousands of patients. In response to the NEJM study and their own post-market surveillance, the U.S. Food and Drug Administration issued an updated warning to the packaging of Zithromax to reflect the increased risk of Zithromax heart problems associated with the drug, particularly in those with existing heart problems.

In addition to heart problems, Zithromax has been linked to Stevens Johnson Syndrome, or SJS, a life-threatening autoimmune reaction. In autoimmune disease, the body’s internal immune system goes haywire and tries to attack the body’s own tissues, treating them as a foreign invading organism. In Zithromax SJS, the immune system locks onto the skin, causing a painful rash. This rash can escalate to sores and ulcers, and spread to the mucus membranes and the eyes. In the some cases, the damage can also spread to the internal organs. In the most deadly cases, SJS can escalate to an even more deadly form of the reaction called Toxic Epidermal Necrolysis or TEN. Once SJS reaches the TEN stage, patches of the skin die and slough off, leaving wounds very similar to burns.

A class-action lawsuit investigation has been launched to explore the possibility of legal action against the makers of Zithromax. Such a class action lawsuit could allege that drug manufacturers knew—or reasonably should have known—about the risk of heart problems and SJS allegedly linked to Zithromax. Similar class action lawsuits and other legal actions seek the cost of medical care and reimbursement for lost wages associated with illnesses caused by allegedly dangerous drugs.