5PSQ-154 Co-administration of ribociclib/palbociclib and proton pump inhibitors (PPI): a real-world analysis in an Italian oncology centre

<h3>Background and Importance</h3> Ribociclib and palbociclib, CDK4/6 inhibitors, are often prescribed with aromatase inhibitors or fulvestrant to treat advanced/metastatic ER+ and HER2- breast cancer. Many patients concurrently take proton pump inhibitors (PPIs, ATC=A02BC) and/or antacids (ATC=A02A). PPIs can impact the absorption of drugs affected by pH, including ribociclib and palbociclib, both weak bases. Ribociclib, a CYP3A4 inhibitor and substrate, shares a metabolic pathway with omeprazole, also metabolised by CYP3A4. Ribociclib can prolong the QT interval, a risk potentially exacerbated by PPI use, especially in women. <h3>Aim and Objectives</h3> This study aims to analyse prescription patterns of ribociclib/palbociclib and PPIs/antacids among patients treated at an Italian oncology centre, focusing on potential drug interactions. <h3>Material and Methods</h3> Prescription data for ribociclib, palbociclib, PPIs, and antacids were collected from the prescription software, patient medical records, and interviews with patients at the hospital pharmacy from January to July 2024. Drug interactions were assessed using Terap, Micromedex, and drug leaflets. <h3>Results</h3> Data were analysed from 88 ribociclib patients (all female) and 12 palbociclib patients (two male), with median ages of 66 and 63, respectively. Among ribociclib patients, 26 (39%) used PPIs concurrently, and eight (9%) also took antacids. In the palbociclib cohort, nine (67%) were on PPIs, with one also using an antacid. Regarding specific PPI use, 44% (11/26) of ribociclib patients used omeprazole and 35% (9/26) pantoprazole. In the palbociclib group, 42% (5/12) used pantoprazole and 17% (2/12) omeprazole. Among ribociclib patients not using PPIs/antacids, 43% received a standard dose, compared to 38% of those on PPIs/antacids. One patient stopped ribociclib and omeprazole due to QT prolongation. <h3>Conclusion and Relevance</h3> This analysis highlights the need for clinician awareness of drug interactions in polytherapy, especially for patients on CDK4/6 inhibitors and PPIs. Competition for CYP enzymes can impact drug efficacy or toxicity risk. The intervention of hospital pharmacists was twofold: providing physician education on possible interactions and interviewing patients starting CDK4/6 therapy to identify potential interactions with chronic therapy, including medications not disclosed to their physician, which could interfere with efficacy and cause toxicity of the anti-tumour treatment. Real-world data stress the importance of medication reconciliation by hospital pharmacists to optimise patient care. <h3>References and/or Acknowledgements</h3> <h3>Conflict of Interest</h3> No conflict of interest