Lessons learned: use of 24-hour ambulatory esophageal and gastric pH monitoring and its implications for proton pump inhibitor use in cancer patients requiring oral oncologic therapies.

The proton pump inhibitors are widely prescribed for the symptomatic treatment of chronic epigastric pain and heartburn in cancer patients, but they carry the potential for drug-drug interactions (DDI) with oral antineoplastic agents. In this retrospective cohort study, we examine the utility of 24-hour esophageal and gastric ambulatory pH monitoring off- or on-proton pump inhibitors (PPI) therapy as a guide in safely prescribing of PPI for cancer patients. We analyzed data from 189 consecutive non-cancer patients with chronic PPI-refractory gastroesophageal reflux disease (GERD) 146 (75F/71M) 'off' and 39 (21F/18M) 'on' PPIs; 4 (2F/2M) had atrophic gastritis and were used as controls. There were 69 with pathologic esophageal acid reflux and 74 patients with normal esophageal acid exposure. The 24-hour % gastric pH <4 in these two groups that exhibited median values of 92% and 89%, respectively (NS). Gastric acidity was highest in non-PPI users (median 92.8%), less in PPI users (median 40.8%), and near absent (median 1.65%) in patients with atrophic gastritis (P < .005). In 39 patients who underwent 24-hour intragastric pH monitoring 'on' PPI, the best times to administer a drug that needs acidity for optimal bioavailability are 3 pm-6 pm and 3 am-6 am, and better with daily v. twice- daily PPI. We conclude that dual esophageal and gastric pH monitoring, identifies (a) the presence of pathologic esophageal acid reflux, justifying long-term PPI use; (b) the absence of pathologic esophageal reflux negating PPI use; (c) the presence of variable levels of PPI-induced gastric hypochlorhydria; (d) time-windows of gastric pH < 4 that would optimize other drug coadministration for maximal oncologic drug bioavailability.