Patients taking the antibiotic Zithromax may not expect to be suffering from a life-threatening skin condition within a few days. In rare instances, however, courses of Zithromax have led to cases of Stevens Johnson Syndrome and Toxic Epidermal Necrolysis, which can be life threatening.

Zithromax, made by Pfizer Inc., was first approved by the Food and Drug Administration (FDA) in 1991, as a treatment for:

• Respiratory infections, like bronchitis, pharyngitis and pneumonia
• Skin infections, like staphylococcus and streptococcus infections
• Genitourinary infections, like genital ulcer disease in men, or urethritis and cervicitis due to chlamydia or gonorrhea

For very young patients, Zithromax is also approved to treat acute otitis media, community acquired pneumonia, and pharyngitis or tonsillitis caused by streptococcus pyogenes.

Despite competition from generic versions, Zithromax sales remain brisk. Zithromax sales in the United States reached $435 million in 2012. Particularly popular are formulations of azithromycin in packs of three and five day courses branded as Z-Pak and a one-dose formulation called Zmax.

Yet despite its popularity, Zithromax is associated with a risk of developing two related and serious skin conditions known as Stevens Johnson Syndrome (SJS) and toxic epidermal necrolysis (TEN). Both conditions tend to require weeks of hospitalization and can be life-threatening.

One study documents the first known case of SJS associated with Zithromax. In October 2000, a five-year-old boy was suffering from eruptions and blisters on his skin and pain inside his mouth after having taken the antibiotic for three days.

After five days of treatment with acyclovir and cefazolin, his condition had only worsened. On admission to the hospital then, he was suffering from blisters, redness, oral ulcers, and conjunctivitis in both eyes.

With medication and topical treatment, his condition gradually improved. After nearly a month of treatment his doctors discontinued his medication.

The authors of the case study noted that this was the first report of SJS associated with Zithromax. They noted that azithromycin’s longer half-life, a measure of the time it remains active in the patient’s body, may have some connection to the risk of adverse effects.

Though cases of SJS and TEN are rare, when they do occur they are most often caused by drugs like Zithromax. Today, the labeling for Zithromax includes a warning stating that both SJS and TEN are possible adverse reactions.

The symptoms reported in the young boy’s 2000 case study are typical of SJS. The condition often first presents with cough, fever, and headache – symptoms similar to those of the flu.

The patient may also develop conjunctivitis or other eye symptoms. Then areas of rash with blisters begin to form on the skin. As the condition progresses, these blisters may coalesce and form large sheets of skin that peel away.

The amount of skin affected by these blisters is the main difference between SJS and TEN. It’s usually referred to as SJS if it affects less than 30 percent of body’s surface. If it affects more than 30 percent, it is then referred to as TEN. The two conditions are considered clinically similar, with some overlap between them.

The loss of skin leaves the patient at high risk for infection, organ failure, and possibly death. Treatment requires hospitalization with continuous management of symptoms. Patients typically get topical wound care and replacement of fluids and electrolytes.

As with the boy in the 2000 case study, treatment may go on for several weeks. Recovery sometimes takes several months and may still leave the patient with permanent damage.