Interaction Between Cyclosporine and Palbociclib in a Renal Transplant Patient: Case Report and Pharmacokinetic Perspective.

Solid organ transplant recipients have increased cancer risk due in part to chronic immunosuppression and opportunistic oncogenic viral infections. The management of drug interactions in transplant recipients being treated for cancer is important both to minimize the likelihood of drug-related toxicities and to optimize therapeutic outcomes. We present a case of a 41-year-old woman with a stable living-related kidney transplant maintained on an immunosuppressive regimen of cyclosporine, mycophenolate mofetil, and prednisone, who was subsequently diagnosed with a metastatic lobular breast carcinoma and papillary thyroid cancer and started palbociclib, a time-dependent CYP3A inhibitor. After initiation of palbociclib, cyclosporine trough and peak concentrations were increased by 159% and 81%, respectively, relative to the average cyclosporine concentrations pre-palbociclib. Using the Drug Interaction Probability Scale (DIPS), the interaction between palbociclib and cyclosporine was rated as "probable." Dose reductions of immunosuppressive agents that are CYP3A substrates are warranted if palbociclib is initiated, followed by close monitoring of blood concentrations. This report also highlights the challenges of coadministering a time-dependent inhibitor with a narrow therapeutic index drug that is metabolized by the same enzyme, particularly when the inhibitor is given in cycles with off-treatment periods.