A study to assess if pantoprazole affects the absorption of capecitabine in patients with breast and gastrointestinal cancers.

Proton pump inhibitors (PPIs) are very common medications used for managing gastritis and reflux. Patients on chemotherapy tend to have more problems with gastritis and reflux and approximately 20-55% patients on chemotherapy are reported to be on PPIs. Capecitabine is a tablet form of chemotherapy widely used to treat cancer and has to be absorbed in the gut to be effective. Recent studies have raised concerns that individuals on capecitabine who are also prescribed with PPIs may have poorer cancer survival outcomes compared to those who are not on PPIs. One suggestion is that changes in the pH of the stomach from PPI use, affects the dissolution of the tablet and decreases how much capecitabine enters the body.In late 2019, the NZ regulatory body MEDSAFE advised NZ oncologists that there may be a possible interaction between PPI drugs and capecitabine, but fell short of making any specific recommendations due to the paucity of good quality data. To address this very real and relevant concern, we plan to conduct a study that will help us determine whether pantoprazole, an approved PPI, affects capecitabine absorption. The study will be conducted in Auckland City Hospital and will involve 20 patients who are scheduled to receive capecitabine for their bowel or breast cancer treatment. The study will span the first 2 cycles (6 weeks) of their capecitabine treatment. Each participant will receive a short course of pantoprazole either before their first or second cycle of capecitabine (cross over design). Whether they receive pantoprazole before the first or second cycle will be randomly assigned (randomization). On the first day of both cycles of capecitabine, blood and urine samples will be collected over an 8 hour period. The samples will be analysed to determine how much capecitabine was absorbed and processed in each participant (pharmacokinetic study). This will allow us to compare if the short course of pantoprazole had any effects on capecitabine.