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

Interventions: Consented participants who are scheduled for capecitabine monotherapy for breast or gastrointestinal cancer will be randomly allocated to receive concomitant oral pantoprazole 40mg daily, 4 days prior to and on the first day (total 5 doses) of either the first (group A) or second (Group B) cycle of capecitabine. Pharmacokinetic blood and urine sampling for capecitabine will be performed over eight hours on both cycle1 day 1 and cycle 2 day 1 to determine if PK parameters are different with pantoprazole. Participants will be contacted by phone a day before their course of pantoprazole begins and will receive a daily text reminder on the subsequent 4 days. A medication diary will be kept. The washout period is 21 days (in between cycle 1 day 1 and cycle 2 day 1)
Primary outcome(s): Area Under the Curve AUC(0-8) of 5”DFUR (Blood and urine sample) [Cycle 1 Day 1: pre-dose, 0.25, 0,5, 1, 1.5, 2, 3, 4, 6, 8 hours post-ingestion of pantoprazole, Cycle 2 Day 1: pre-dose, 0.25, 0,5, 1, 1.5, 2, 3, 4, 6, 8 hours post-ingestion of pantoprazole];Area Under the Curve AUC(0-8) of 5-FU (blood and urine sample) [Cycle 1 Day 1: pre-dose, 0.25, 0,5, 1, 1.5, 2, 3, 4, 6, 8 hours post-ingestion of pantoprazole, Cycle 2 Day 1: pre-dose, 0.25, 0,5, 1, 1.5, 2, 3, 4, 6, 8 hours post-ingestion of pantoprazole]
Study Design: Purpose: Treatment; Allocation: Randomised controlled trial; Masking: Open (masking not used);Assignment: Crossover;Type of endpoint: Bio-equivalence