Pharmacokinetics of oral neratinib during co-administration of ketoconazole in healthy subjects

center dot Neratinib is a potent, low-molecular-weight, orally administered, irreversible pan-ErbB (ErbB-1, -2, -4) receptor tyrosine kinase inhibitor that has shown anti-tumour activity in patients with advanced ErbB-2-positive breast cancer both with and without prior trastuzumab exposure. center dot Neratinib is in phase III development for the treatment of patients with ErbB-2-positive breast cancer. center dot Preclinical data suggest that neratinib is predominantly metabolized by CYP3A4. WHAT THIS STUDY ADDS center dot The pharmacokinetic profile of neratinib was evaluated in healthy subjects after a single oral administration of neratinib with and without the potent CYP3A4 inhibitor, ketoconazole. center dot Exposure to neratinib increased more than 3-fold during co-administration of ketoconazole, indicating that neratinib is a substrate of CYP3A and is susceptible to interactions with potent CYP3A inhibitors and, thus, dose adjustments may be needed if neratinib is administered with such compounds. AIM The primary objective was to evaluate the pharmacokinetics of a single dose of neratinib, a potent, low-molecular-weight, orally administered, irreversible pan-ErbB (ErbB-1, -2, -4) receptor tyrosine kinase inhibitor, during co-administration with ketoconazole, a potent CYP3A4 inhibitor. METHODS This was an open-label, randomized, two-period, crossover study. Fasting healthy adults received a single oral dose of neratinib 240 mg alone and with multiple oral doses of ketoconazole 400 mg. Blood samples were collected up to 72 h after each neratinib dose. Plasma concentration data were analyzed using a noncompartmental method. The least square geometric mean ratios [90% confidence interval (CI)] of C-max(neratinib+ketoconazole) : C-max(neratinib alone), and AUC(neratinib+ketoconazole) : AUC(neratinib alone) were assessed. RESULTS Twenty-four subjects were enrolled. Compared with neratinib administered alone, co-administration of ketoconazole increased neratinib C-max by 3.2-fold (90% CI: 2.4, 4.3) and AUC by 4.8-fold (3.6, 6.5). Median t(max) was 6.0 h with both regimens. Ketoconazole decreased mean apparent oral clearance of neratinib from 346 l h-1 to 87.1 l h-1 and increased mean elimination half-life from 11.7 h to 18.0 h. The incidence of adverse events was comparable between the two regimens (50% neratinib alone, 65% co-administration with ketoconazole). CONCLUSION Co-administration of neratinib with ketoconazole, a potent CYP3A inhibitor, increased neratinib C-max by 3.2-fold and AUC by 4.8-fold compared with administration of neratinib alone. These results indicate that neratinib is a substrate of CYP3A and is susceptible to interaction with potent CYP3A inhibitors and, thus, dose adjustments may be needed if neratinib is administered with such compounds.