It must not be used in patients with severe liver disease or who are taking any of the following medicines:  astemizole, terfenadine (commonly used to treat allergy symptoms - these medicines may be available without prescription);  dihydroergotamine, ergotamine, ergonovine, methylergonovine (used to treat migraine headache);  midazolam, triazolam (used to relieve anxiety or difficulty sleeping);  pimozide (used to treat mental illnesses);  cisapride (used to relieve certain stomach problems);  bepridil (used to treat angina);  St John ’ s wort (a herbal preparation used to treat depression).