2. Patients who have ever been treated with, or are currently receiving proton pump inhibitors (PPIs),histamine receptor (H2) blockers, or antacids are eligible (as long as they can go off PPIs and H2 blockers for three days prior to dosing, except for cimetidine, which must be discontinued for at least seven days prior to dosing; exclusion criteria 5 and 6). Also, patients should be able to go off PPI therapy for two weeks at the end active drug treatment.