linoquinazoline. Afatinib is presented as the dimaleate salt, with the chemical name 2-butenamide, N-[4-[(3-chloro-4-fluorophenyl)amino]-7-[[(3S)-tetrahydro-3-furanyl]oxy]-6-quinazolinyl]-4-(dimethylamino)-,(2E)-, (2Z)-2-butenedioate (1:2). Its structural formula is:
Afatinib dimaleate is a white to brownish yellow powder, water soluble and hygroscopic, with an empirical formula of C32H33ClFN5O11, and a molecular weight of 718.1 g/mol.
GILOTRIF tablets for oral administration are available in 40 mg, 30 mg, or 20 mg of afatinib (equivalent to 59.12 mg, 44.34 mg, or 29.56 mg afatinib dimaleate, respectively). The inactive ingredients of GILOTRIF are the following: Tablet Core: lactose monohydrate, microcrystalline cellulose, crospovidone, colloidal silicon dioxide, magnesium stearate. Coating: hypromellose, polyethylene glycol, titanium dioxide, talc, polysorbate 80, FD&C Blue No. 2 (40 mg and 30 mg tablets only).
12 CLINICAL PHARMACOLOGY
12.1 Mechanism of Action
Afatinib covalently binds to the kinase domains of EGFR (ErbB1), HER2 (ErbB2), and HER4 (ErbB4) and irreversibly inhibits tyrosine kinase autophosphorylation, resulting in downregulation of ErbB signaling.
Afatinib demonstrated inhibition of autophosphorylation and in vitro proliferation of cell lines expressing wild-type EGFR or those expressing selected EGFR exon 19 deletion mutations or exon 21 L858R mutations, including some with a secondary T790M mutation, at afatinib concentrations achieved, at least transiently, in patients. In addition, afatinib inhibited in vitro proliferation of cell lines overexpressing HER2.
Treatment with afatinib resulted in inhibition of tumor growth in nude mice implanted with tumors either overexpressing wild type EGFR or HER2 or in an EGFR L858R/T790M double mutant model.
12.2 Pharmacodynamics
Cardiac Electrophysiology
The effect of multiple doses of GILOTRIF (50 mg once daily) on the QTc interval was eva luated in an open-label, single-arm study in patients with relapsed or refractory solid tumors. No large changes in the mean QTc interval (i.e., >20 ms) were detected in the study.
12.3 Pharmacokinetics
Absorption and Distribution
Following oral administration of GILOTRIF tablets, time to peak afatinib plasma concentrations (Tmax) is 2 to 5 hours. Maximum concentration (Cmax) and area under the concentration-time curve from time zero to infinity (AUC0-∞) values increased slightly more than dose proportional in the range of 20 to 50 mg. The geometric mean relative bioavailability of 20 mg GILOTRIF tablets was 92% as compared to an oral solution. In vitro binding of afatinib to human plasma proteins is approximately 95%.
A high-fat meal decreased Cmax by 50% and AUC0-∞ by 39% relative to the fasted condition [see Dosage and Administration (2.2)].
Metabolism and Elimination
Covalent adducts to proteins are the major circulating metabolites of afatinib and enzymatic metabolism of afatinib is minimal.
In humans, excretion of afatinib is primarily via the feces (85%) with 4% recovered in the urine following a single oral dose of [14C]-labeled afatinib solution. The parent compound accounted for 88% of the recovered dose.
The elimination half-life of afatinib is 37 hours after repeat dosing in cancer patients. Steady-state plasma concentrations are achieved within 8 days of repeat dosing of GILOTRIF resulting in an accumulation of 2.8-fold for |
