The Effect of Concomitant Administration of Proton Pump Inhibitors on the Pharmacokinetics of CDK4/6 Inhibitors in Rats: Implications for the Evaluation of Hepatic and Transporter-Mediated Drug-Drug Interactions.

Background and objectives: Numerous clinical concerns have been expressed regarding the potential worsening of cyclin-dependent kinase 4/6 inhibitor effects in breast cancer patients because of co-administration of proton pump inhibitors. Hence, this study evaluated the effects of proton pump inhibitors on the pharmacokinetics of palbociclib and ribociclib in terms of  cytochrome P450 (CYP) 3A4 and P-glycoprotein involvement.

Methods: The effects of omeprazole and rabeprazole on drug metabolism and efflux of these drugs were investigated using molecular docking, metabolic stability assay in rat liver microsomes, human recombinant CYP3A4 (rCYP3A4) enzymes, and Caco-2 cell monolayers, and in vivo pharmacokinetics with omeprazole and rabeprazole in (5 and 10 mg/kg) 30 min and 7 days before orally dosing palbociclib and ribociclib (10 mg/kg).

Results: Omeprazole and rabeprazole inhibited CYP3A4 enzyme activity in rCYP3A4 baculosomes with a 50-60% inhibition at 30 μM. Additionally, both omeprazole and rabeprazole (10 µm) significantly reduced the P-glycoprotein-mediated drug efflux of palbociclib and ribociclib. The 7-day pretreatment of omeprazole at a dose of 10 mg/kg resulted in 24% and 26% reductions in palbociclib's mean maximum plasma concentration) C_max and area under the plasma concentration-time curve (AUC_{0-24 h}), respectively. Palbociclib's pharmacokinetics were not significantly altered by the pretreatment with rabeprazole; however, ribociclib pharmacokinetics exhibited an 83.94% increase in AUC_{0-24 h}.

Conclusion: The findings indicate that long-term treatment with therapeutic doses of both omeprazole and rabeprazole can alter the pharmacokinetics of palbociclib and ribociclib. The co-administration of rabeprazole may alter the pharmacokinetics of palbociclib and ribociclib via CYP enzyme and P-glycoprotein inhibition.