Cytochrome P450 inhibition to decrease dosage and costs of venetoclax and ibrutinib: A proof-of-concept case study

The inhibition of cytochrome P450 (CYP) enzymes is the most frequent cause of drug-drug interactions. Many safe, inexpensive and widely available therapeutic drugs can inhibit CYP enzymes (e.g., azoles). Also, the specific potency of inhibition and the targeted CYP enzyme have been well described (e.g., itraconazole strongly inhibits CYP enzyme 3A4 and, in turn, CYP3A4 metabolizes venetoclax and ibrutinib). CYP enzyme inhibitors increase the plasma concentration of other drugs via shared metabolic pathways. We herein present the effects of inhibiting CYP enzymes with itraconazole-venetoclax for the treatment of refractory acute myeloid leukaemia, as well as itraconazole-ibrutinib to treat steroid-refractory acute graft vs. host disease in the same patient. Both of the patient's conditions responded completely. This appears to be a feasible strategy that decreases treatment costs by 75%. Previous Food and Drug Administration recommendations and clinical data support these subsequent dose reductions. Eleven months after the transplant, the patient remains in complete response and with no minimal residual disease. Another patient had been effectively treated before with CYP enzyme inhibition prior to venetoclax-itraconazole administration for orbital myeloid sarcoma. Thus, this case study furthers information on the CYP enzyme inhibition strategy when associated with another costly drug, ibrutinib. The CYP enzyme inhibition strategy could be applied to many more anticancer drugs (e.g., ruxolitinib and ponatinib) and facilitate the availability of expensive oncological treatments in low- and middle-income countries. Also, this strategy could be further generalized by using different CYP enzyme inhibitors with varied pharmacokinetic and pharmacodynamic properties (i.e., grapefruit, azoles and clarithromycin).