The mass balance after administration of a single oral dose of 200 mg of neratinib was studied in six healthy subjects.
Absorption
Following oral administration of 240 mg neratinib, absorption was slow and peak plasma concentrations of neratinib occurred around 7 hours after administration. A single dose of 240 mg neratinib taken with food increased Cmax and AUC by approximately 17% and 13%, respectively, compared with administration in the fasting state. A single oral dose of 240 mg neratinib taken with a meal high in fat increased both Cmax and AUC by approximately 100%. In a mass balance study, the total recovery (urinary and fecal excretion) of intact neratinib and metabolites demonstrates that the fraction absorbed for neratinib is at least 10% and likely more than 20%. Moreover, model-based predictions suggested an overall absorbed fraction from the gut (fa) of 26%.
In vitro neratinib solubility is pH-dependent. Treatments that increase gastrointestinal pH may lower the absorption of neratinib, thus decreasing systemic exposure.
Distribution
Binding of neratinib to human plasma proteins, including covalent binding to human serum albumin (HSA), was greater than 98% and independent of the tested neratinib concentration. Neratinib bound predominantly to HSA and human alpha-1 acid glycoprotein (AAG). Binding of M6 main metabolite (M6) to human plasma proteins was greater than 99% and independent of the tested M6 concentrations.
In vitro studies demonstrated that neratinib is a substrate for P-glycoprotein (P-gp) (see sections 4.2, 4.3, 4.4 and 4.5) and BCRP. In vitro studies demonstrated that neratinib and its main metabolite M6 are not substrates of hepatic uptake transporters OATP1B1*1a and OATP1B3 at relevant clinical concentration.
Biotransformation
Neratinib is metabolised primarily in liver microsomes by CYP3A4 and to a lesser extent by flavin-containing monooxygenase (FMO).
Preliminary metabolite profiling in human plasma indicates that after oral administration, neratinib undergoes oxidative metabolism through CYP3A4. Circulating metabolites include neratinib pyridine N-oxide (M3), N-desmethyl neratinib (M6), neratinib dimethylamine N-oxide (M7) and traces of hydroxyl neratinib N-oxide and neratinib bis-N-oxide (M11). Neratinib represents the most prominent component in plasma and amongst circulating metabolites (M2, M3, M6, M7 and M11) none is above 8% of neratinib plus metabolite total exposure after oral administration of neratinib. The neratinib metabolites M3, M6, M7 and M11 were shown to have similar potencies to neratinib in either in vitro enzyme (binding assays) or cell based assays against cells expressing ERBB1, ERBB2 (HER2) and ERBB4.
Based on steady state exposures, neratinib provides the majority of pharmacological activity (73%), with 20% provided by exposure to M6, 6% provided by M3, and negligible contribution (<1%) from M7 and M11 AUC.
Elimination
Following single doses of neratinib, the mean apparent plasma half-life of neratinib was 17 hours in patients.
Excretion of neratinib is primarily via the faeces
Following the administration of a single radiolabelled dose of 240 mg neratinib oral solution, 95.5% and 0.96% of the administered dose was recovered in the faeces and urine, respectively.
The excretion was rapid and complete, with most of the dose recovered in faeces within 48 hours and 96.5% of total radioactivity recovered in excreta after 8 days.
Unchanged neratinib was the most abundant species in excreta accounting for 62.1% of total dose recovered in excreta. The most abundant metabolites in faeces were M6 (19.7% of administered dose), followed by M2, M3 and M7, all below 10% of administered dose.
Medicinal product interactions
Effect of CYP3A4/P-gp inducer on neratinib
Following concomitant administration of 240 mg neratinib with repeated doses of 600 mg rifampicin, a strong CYP3A4/P-gp inducer, neratinib exposures were significantly decreased by 76% and 87% for Cmax and AUC, respectively, compared with neratinib administration alone (see sections 4.3 and 4.5).
Effect of CYP3A4/P-gp inhibitor on neratinib
Co-administration of a single oral dose of 240 mg of neratinib in the presence of ketoconazole (400 mg once daily for 5 days), a strong CYP3A4/P-gp inhibitor, increased neratinib systemic exposure by 3.2- and 4.8-fold for Cmax and AUC, respectively, compared with neratinib administered alone.
Model-based predictions suggested that co-administration of a single oral dose of 240 mg of neratinib in the presence of fluconazole (200 mg once daily for 8 days), a moderate CYP3A4 inhibitor, increased neratinib systemic exposure by 1.3- and 1.7-fold for Cmax and AUC, compared with neratinib administered alone.
Model-based predictions suggested that co-administration of a single oral dose of 240 mg of neratinib in the presence of verapamil (120 mg twice daily for 8 days), a moderate CYP3A4/strong P-gp inhibitor, increased neratinib systemic exposure by 3.0- and 4.0-fold for Cmax and AUC, compared with neratinib administered alone (see sections 4.2, 4.4 and 4.5).
Effect of gastric pH modifiers on neratinib
Co-administration of lansoprazole or ranitidine (1x300 mg) with a 240 mg single dose of neratinib in healthy volunteers resulted in a decreased neratinib exposure by around 70% or 50%, respectively. The magnitude of ranitidine interaction on neratinib AUC was reduced by around 25%, by staggering the administration of ranitidine (2x150 mg) 2 hours after neratinib administration (see sections 4.2, 4.4 and 4.5).
Effect of other treatment on neratinib
There were no apparent clinically relevant drug-drug interactions observed for neratinib when administered concomitantly with capecitabine, paclitaxel, trastuzumab, vinorelbine, or antidiarrhoeals (loperamide) (see section 4.5).
Effect of neratinib on CYP substrates
Neratinib and metabolite M6 were not potent direct inhibitors of CYP1A2, 2A6, 2B6, 2C8, 2C9, 2D6, or 3A4 and no time-dependent inhibition is expected.
Neratinib did not induce CYP1A2, 2B6, 2C9, or 3A4.
Effect of neratinib on transporters
There was no clinically relevant inhibition of human BSEP efflux transporter activity in vitro, with a reported IC50 value of > 10 µM. Neratinib at 10 µM appeared to inhibit the BCRP efflux transporter which could be clinically relevant at intestinal level (see section 4.5).
In in vitro studies, neratinib was an inhibitor of P-glycoprotein (P-gp) efflux transporters, which was further confirmed in a clinical study. Multiple oral doses of neratinib 240 mg increased digoxin exposures (54 and 32% increase in Cmax and AUC, respectively) with no impact on its renal clearance level (see sections 4.4 and 4.5).
Neratinib produced no inhibitory activity towards the uptake transporters, OATP1B1*1a, OATP1B3, OAT1, OAT3 and OCT2, with reported IC50 values were > 10µM. Neratinib produced inhibitory activity in OCT1 uptake transporter, with an IC50 of 2.9 µM.
Special populations
Renal impairment
Pharmacokinetic studies in patients with renal impairment or undergoing dialysis have not been carried out. Population pharmacokinetic modelling revealed that creatinine clearance did not explain the variability between patients, hence, no dose modifications are recommended for patients with mild to moderate renal impairment (see sections 4.2 and 4.4).
Hepatic impairment
Neratinib is extensively metabolised in the liver. In subjects with severe pre-existing hepatic impairment (Child-Pugh Class C) without cancer, the clearance of neratinib was decreased by 36% and exposure to neratinib increased by about 3-fold as compared to healthy volunteers (see sections 4.2 and 4.3).