Absorption
Following the administration of a single 45 mg dose of dacomitinib tablets, the mean oral bioavailability of dacomitinib is 80% (range: 65% to 100%) compared to intravenous administration, with Cmax occurring 5 to 6 hours after oral dosing. Following dacomitinib 45 mg daily dosing, steady-state was reached within 14 days. Food does not alter bioavailability to a clinically meaningful extent. Dacomitinib is a substrate for the membrane transport proteins P-gp and BCRP. However, based on the oral bioavailability of 80%, these membrane transport proteins are unlikely to have any impact on dacomitinib absorption.
Distribution
Dacomitinib is extensively distributed throughout the body with a mean steady-state volume of distribution of 27 L/kg (patient of 70 kg) [coefficient of variation (CV%): 18%] following intravenous administration. In plasma, dacomitinib binds to albumin and α1-acid glycoprotein and the fraction unbound is approximately 2% in vitro and ex vivo in healthy volunteers.
Biotransformation
In humans, dacomitinib undergoes oxidation and glutathione conjugation as the major metabolic pathways. Following oral administration of a single 45-mg dose of [14C] dacomitinib, the most abundant circulating metabolite was O-desmethyl dacomitinib. This metabolite exhibited in vitro pharmacologic activity that was similar to that of dacomitinib in the in vitro biochemical assays. In faeces, dacomitinib, O-desmethyl dacomitinib, a cysteine conjugate of dacomitinib, and a mono-oxygenated metabolite of dacomitinib were the major drug-related components. In vitro studies indicated that CYP2D6 was the major CYP isozyme involved in the formation of O-desmethyl dacomitinib, while CYP3A4 contributed to the formation of other minor oxidative metabolites. O-desmethyl dacomitinib accounted for 16% of human plasma radioactivity and is formed mainly by CYP2D6 and to a lesser extent CYP2C9. The inhibition of CYP2D6 translated into approximately a 90% reduction in metabolite exposure and an approximate 37% increase in dacomitinib exposure.
Other information on drug-drug interactions
Effect of dacomitinib and O-desmethyl dacomitinib on CYP enzymes
In vitro, dacomitinib and its metabolite O-desmethyl dacomitinib have a low potential to inhibit the activities of CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, or CYP3A4/5 at clinically relevant concentrations. In vitro, dacomitinib has a low potential to induce CYP1A2, CYP2B6, or CYP3A4 at clinically relevant concentrations.
Effect of dacomitinib on drug transporters
In vitro, dacomitinib has a low potential to inhibit the activities of drug transporters P-gp (systemically), organic anion transporters (OAT)1 and OAT3, OCT2, organic anion transporting polypeptide (OATP)1B1, and OATP1B3, but may inhibit the activity of P-gp (in the GI tract), BCRP (systemically and GI tract), and OCT1 at clinically relevant concentrations.
Effect of dacomitinib on UGT Enzymes
In vitro, dacomitinib has a low potential to inhibit uridine-diphosphate glucuronosyltransferase (UGT)1A4, UGT1A6, UGT1A9, UGT2B7, and UGT2B15.
Elimination
The plasma half-life of dacomitinib ranges from 54 to 80 hours. Dacomitinib showed a clearance of 20.0 L/hr with an inter-individual variability of 32% (CV%). In 6 healthy male subjects given a single-oral dose of [14C] radiolabeled dacomitinib, a median of 82% of the total administered radioactivity was recovered in 552 hours; faeces (79% of dose) was the major route of excretion, with 3% of the dose recovered in urine, of which < 1% of the administered dose was unchanged dacomitinib.
Special populations
Age, race, gender, body weight
Based on population pharmacokinetic analyses, patient age, race (Asian and non-Asian), gender, and body weight do not have a clinically relevant effect on predicted steady-state exposure of dacomitinib. Approximately 90% of patients included in this analysis were Asian or White.
Hepatic impairment
In a dedicated hepatic impairment study, following a single-oral dose of 30 mg Vizimpro, dacomitinib exposure (AUCinf and Cmax) was unchanged in mild hepatic impairment (Child-Pugh class A; N=8) and decreased by 15% and 20%, respectively in moderate hepatic impairment (Child-Pugh class B; N=9) when compared to subjects with normal hepatic function (N=8). In a second dedicated hepatic impairment study, following a single-oral dose of 30 mg Vizimpro, dacomitinib exposure was unchanged for AUCinf and increased by 31% for Cmax in subjects with severe hepatic impairment (Child-Pugh class C; N=8), when compared to subjects with normal hepatic function (N=8). In addition, based on a population pharmacokinetic analysis using data from 1381 patients, that included 158 patients with mild hepatic impairment defined by National Cancer Institute (NCI) criteria [total bilirubin ≤ Upper Limit of Normal (ULN) and Aspartate Aminotransferase (AST) > ULN, or total bilirubin > 1.0 to 1.5 × ULN and any AST; N=158], mild hepatic impairment had no effect on the pharmacokinetics of dacomitinib. From the small number of patients in the moderate group [total bilirubin > 1.5 to 3 × ULN and any AST; N=5], there is no evidence for a change in dacomitinib pharmacokinetics.
Renal impairment
No clinical studies have been conducted in patients with impaired renal function. Based on population pharmacokinetic analyses, mild (60 mL/min ≤ CrCl < 90 mL/min; N=590) and moderate (30 mL/min ≤ CrCl < 60 mL/min; N=218) renal impairment, did not alter dacomitinib pharmacokinetics, relative to subjects with normal (CrCl ≥ 90 mL/min; N=567) renal function. Limited pharmacokinetic data are available in patients with severe renal impairment (CrCl < 30 mL/min) (N=4). The pharmacokinetics in patients requiring haemodialysis have not been studied.
Exposure response relationships
No clear relationship between dacomitinib exposure and efficacy could be characterised over the exposure range studied. Significant exposure-safety relationship was defined for Grade ≥ 3 rash/dermatitis acneiform, other skin toxicities, diarrhoea and Grade ≥ 1 stomatitis.