palbociclib + rabeprazole

Palbociclib is an oral, selective, and reversible inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), developed by Pfizer for the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer. It works by blocking cell cycle progression from G1 to S phase, thereby suppressing DNA synthesis and cellular proliferation in retinoblastoma protein-proficient cancer cells[1][2][3][6][8]. Rabeprazole is a proton pump inhibitor used to treat gastrointestinal ulcers, gastroesophageal reflux disease (GERD), Helicobacter pylori eradication, and hypersecretory conditions such as Zollinger-Ellison syndrome. It inhibits the H+, K+-ATPase enzyme in gastric parietal cells, reducing gastric acid secretion[5]. When coadministered, rabeprazole significantly reduces the absorption of palbociclib due to increased gastric pH; this interaction can decrease palbociclib exposure by up to 80% under fasting conditions and up to 41% under fed conditions[1][4].

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