Crixivan should not be used in patients who are taking any of the following medicines: • medicines that are broken down in the same way as Crixivan and are harmful at high levels in the blood; • amiodarone (used to correct irregular heartbeat); • terfenadine, astemizole (commonly used to treat allergy symptoms – these medicines may be available without a prescription); • cisapride (used to treat certain stomach problems); • alprazolam, triazolam, midazolam taken by mouth (used to treat anxiety or difficulty sleeping); • pimozide (used to treat mental illness); • ergot derivatives (used to treat migraine headache); • simvastatin, lovastatin (used to lower cholesterol in the blood); • rifampicin (used to treat tuberculosis); • St John ’ s wort (a herbal preparation used to treat depression).