A secondary analysis of a phase III randomised trial was performed. The initial trial was comparing capecitabine and oxaplatin with or without lapatinib for treatment of advanced gastroesophageal cancer. Concurrent PPI use was identified by medication records.

Lower overall survival was found in patients who received PPIs concomitantly. A similar finding occurred in patients receiving capecitabine for colon cancer. The authors postulate that the elevated gastric pH levels achieved by the PPIs may affect the dissolution and absorption of the capecitabine and reduce its efficacy.

They suggest that the two medications should not be taken concurrently.