<p>Symptoms of toxicity include diarrhea, nausea, abnormal taste, dyspepsia, and abdominal discomfort. Transient hearing loss with high doses has been observed. Pseudomembraneous colitis has been reported with clarithromycin use. Allergic reactions ranging from urticaria and mild skin eruptions to rare cases of anaphylaxis and Stevens-Johnson syndrome have also occurred. Rare cases of severe hepatic dysfunctions also have been reported. Hepatic failure is usually reversible, but fatalities have been reported. Clarithromycin may also cause tooth decolouration which may be removed by dental cleaning. Fetal abnormalities, such as cardiovascular defects, cleft palate and fetal growth retardation, have been observed in animals. Clarithromycin may cause QT prolongation.</p>