To investigate the safety of C13-CAC and the relationship among C13-CAC breath test, gastric pH, and the improvement of symptoms by switching PPI in PPI resistant GERD patients

Inclusion Criteria:

• GERD patients who have been judged to require additional treatment to improve their symptoms by investigator or subinvestigator.

Exclusion Criteria:

• Patients suspected to have hypothyroidism or hyperparathyroidism.
• Patients with hypercalcemia
• Patients with a history of gastric or duodenal surgery.
• Patients who have received the eradication therapy of Helicobacter pylori within six months prior to participation of the study.
• Patients with a prior or current history of Zollinger-Ellison syndrome.
• Patients with a history of surgery or treatment affecting gastroesophageal reflux.
• Patients who have been diagnosed with acute upper gastrointestinal bleeding or active gastric or duodenal ulcer within 30 days prior to participation of the study.
• Patients with serious central nervous system disorders, cardiovascular disease, pulmonary disease, hepatic disease, renal disease, metabolic disease, gastrointestinal disorders, urinary disorders, endocrine disease, or blood dyspraxia.
• Patients scheduled for surgery requiring hospitalization or required surgery during the study period.
• Patients who have had either a prior or current history of chest pain due to heart disease or with chest pain suspected to have caused by heart disease within one year prior to participation of the study.