Serious allergic reactions, including angioedema, anaphylaxis, and dermatologic
reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis have
been reported rarely in patients on azithromycin therapy using other formulations.
Although rare, fatalities have been reported. (See CONTRAINDICATIONS.) Despite
initially successful symptomatic treatment of the allergic symptoms, when symptomatic
therapy was discontinued, the allergic symptoms recurred soon thereafter in some
patients without further azithromycin exposure. These patients required
prolonged periods of observation and symptomatic treatment. The relationship of
these episodes to the long tissue half-life of azithromycin and subsequent exposure
to antigen has not been determined.
If an allergic reaction occurs, appropriate therapy should be instituted. Physicians
should be aware that reappearance of the allergic symptoms may occur when symptomatic
therapy is discontinued.
Pseudomembranous colitis has been reported with nearly all antibacterial agents and
may range in severity from mild to life-threatening. Therefore, it is important
to consider this diagnosis in patients who present with diarrhea subsequent to the
administration of antibacterial agents.
Treatment with antibacterial agents alters the normal flora of the colon and may
permit overgrowth of clostridia. Studies indicate that a toxin produced by Clostridium
difficile is a primary cause of "antibiotic-associated colitis."
After the diagnosis of pseudomembranous colitis has been established, therapeutic
measures should be initiated. Mild cases of pseudomembranous colitis usually respond
to discontinuation of the drug alone. In moderate to severe cases, consideration
should be given to management with fluids and electrolytes, protein supplementation,
and treatment with an antibacterial drug clinically effective against Clostridium
difficile colitis.