Clarithromycin generally is well tolerated. Most adverse effects are mild and transient and usually resolve following discontinuance of the drug. The common adverse effect is GI effects such as diarrhea, nausea, vomiting, abnormal taste, dyspepsia, and abdominal discomfort. Other side effects included headache, anxiety, vertigo, insomnia, confusion, bad dreams, hallucination, and transient elevations of liver enzymes. Allergic reactions e.g., urticaria, rash, pruritus have been reported. Anaphylaxis and Stevens-Johnson Syndrome may occur rarely. Isolated cases of leukopenia and thrombocytopenia have been reported. Pseudomembranous colitis has been reported with nearly all antibacterial agents, including macrolides.