Ibrutinib is an inhibitor of Bruton’s tyrosine kinase (BTK). It forms a covalent bond with a cysteine residue in the active site of BTK, leading to its inhibition. BTK plays a role in signalling through the B-cell surface receptors which results in the activation of various pathways necessary for B-cell trafficking, chemotaxis, and adhesion. Ibrutinib has been shown to inhibit malignant B cell proliferation and survival in vivo as well as substrate adhesion and cell migration.
In patients with recurrent B-cell lymphoma > 90% occupancy of the BTK active site in peripheral blood mononuclear cells was observed up to 24 hours after ibrutinib doses of ≥ 2.5 mg/kg/day (≥ 175 mg/day for average weight of 70 kg).
It is metabolized to several metabolites primarily by cytochrome P450, CYP3A, and to a minor extent by CYP2D6. The active metabolite, PCI-45227, is a dihydrodiol metabolite with inhibitory activity towards BTK approximately 15 times lower than that of ibrutinib. The range of the mean metabolite to parent ratio for PCI-45227 at steady-state is 1 to 2.8.