The purpose of this study is to evaluate the clinical utility of zastaprazan compared to proton pump inhibitors (PPIs) in patients receiving dual antiplatelet therapy (DAPT) including clopidogrel after percutaneous coronary intervention (PCI), by comparing their effects on platelet reactivity.

This study aims to evaluate the impact of zastaprazan on platelet reactivity when co-administered with clopidogrel and to identify differences in potential drug-drug interactions compared to conventional Proton Pump Inhibitors (PPIs). Through this, we intend to propose an optimal combination strategy that simultaneously addresses antiplatelet efficacy and gastrointestinal protection.

Notably, as rabeprazole is known to have a lower degree of CYP2C19 inhibition among PPIs, this study will specifically compare zastaprazan with rabeprazole to evaluate and confirm the comparative effects on platelet reactivity.

Inclusion Criteria:

1. Age 19 years or older at the time of providing informed consent.
2. Patients with Chronic Coronary Syndrome (CCS) who have undergone Percutaneous Coronary Intervention (PCI) and agreed to participate in the study.
3. Patients who are required to maintain dual antiplatelet therapy (DAPT) including clopidogrel for at least 6 months after PCI.
4. Patients who have voluntarily provided written informed consent to participate in this clinical study.

Exclusion Criteria:

1. History of hypersensitivity to P-CABs, PPIs, benzimidazoles, aspirin, clopidogrel, or any of the excipients in the study drugs.
2. History of or planned surgery that may affect gastric acid secretion, such as upper gastrointestinal resection, acid suppression surgery, or gastric mucosal resection. (However, patients who have undergone simple perforation repair of the stomach or duodenum, appendectomy, cholecystectomy, hysterectomy, or endoscopic/laparoscopic resection of benign tumors are eligible).
3. Diagnosis of Zollinger-Ellison syndrome or inflammatory diseases (e.g., pancreatitis, or inflammatory bowel diseases such as Crohn's disease or ulcerative colitis).
4. Currently receiving HIV protease inhibitors (atazanavir, nelfinavir) or rilpivirine-containing products.
5. Abnormal blood chemistry values within 4 weeks prior to screening: AST, ALT, ALP, or total bilirubin > 3 times the upper limit of normal (ULN). Estimated Glomerular Filtration Rate (eGFR) < 30 mL/min/1.73m², calculated using the IDMS-traceable MDRD equation.
6. Recent Medication Use: Use of medications expected to affect the study results, such as P2Y12 inhibitors (other than the prescribed clopidogrel), within 2 weeks prior to baseline.
7. Pregnant or lactating women, or women with a positive pregnancy test.
8. Patients with hereditary problems such as galactose intolerance, Lapp lactase deficiency, or glucose-galactose malabsorption.