The most common side effects are:
- diarrhea or loose stools,
- abdominal pain, and
Other important side effects include:
- abnormal liver tests,
- allergic reactions,
- nervousness, and
- abnormal heart beats.
Antibiotics can alter the normal bacteria in the colon and encourage overgrowth of some bacteria such as Clostridium difficile, which causes inflammation of the colon (pseudomembranous colitis). Patients who develop signs of pseudomembranous colitis after starting azithromycin (diarrhea, fever, abdominal pain, and possibly shock) should contact their physician immediately.