4. Concomitant treatment with medicinal products that increase the pH (reduce acidity) of the upper gastrointestinal tract, including, but not limited to, proton-pump inhibitors (e.g. omeprazole), H2-antagonists (e.g. ranitidine) and antacids. Patients may be enrolled in the study after a wash-out period sufficient to terminate their effect (section 11.1.3.7).