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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.
The effect of multiple doses of GILOTRIF (50 mg once daily) on the QTc interval was evaluated 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.
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].
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 AUC and 2.1-fold for Cmax.
Renal Impairment: The median trough afatinib plasma concentrations in patients with mild (CLcr 60-89 mL/min) and moderate (CLcr 30-59 mL/min) renal impairment were 27% and 85% higher than those in patients with normal renal function (CLcr ≥ 90 mL/min). GILOTRIF has not been studied in patients with severely impaired renal function (CLcr < 30 mL/min) [see Use In Specific Populations].
Hepatic Impairment: Afatinib is eliminated mainly by biliary/fecal excretion. Mild (Child Pugh A) or moderate (Child Pugh B) hepatic impairment had no influence on the afatinib exposure following a single dose of GILOTRIF. Subjects with severe (Child Pugh C) hepatic dysfunction have not been studied [see Use In Specific Populations].
Body Weight, Gender, Age, and Race: Based on the population pharmacokinetic analysis, weight, gender, age, and race do not have a clinically important effect on exposure of afatinib.
Effect of P-gp Inhibitors and Inducers on Afatinib: The effect of ritonavir dosing time relative to a single oral dose of GILOTRIF was evaluated in healthy subjects taking 40 mg of GILOTRIF alone as compared to those after ritonavir (200 mg twice daily for 3 days) co-administration at 6 hours after GILOTRIF administration. The relative bioavailability for AUC0-∞ and Cmax of afatinib was 119% and 104% when co-administered with ritonavir, and 111% and 105% when ritonavir was administered 6 hours after taking GILOTRIF. In another study, when ritonavir (200 mg twice daily for 3 days) was administered 1 hour before a 20 mg single dose of GILOTRIF, exposure to afatinib increased by 48% for AUC0-∞ and 39% for Cmax [see DRUG INTERACTIONS].
Pre-treatment with a potent inducer of P-gp, rifampicin (600 mg once daily for 7 days) decreased the plasma exposure to afatinib by 34% (AUC0-∞) and 22% (Cmax) [see DRUG INTERACTIONS].
P-glycoprotein (P-gp): Based on in vitro data, afatinib is a substrate and an inhibitor of P-gp.
Breast Cancer Resistance Protein (BCRP): Based on in vitro data, afatinib is a substrate and an inhibitor of the transporter BCRP.
Effect of CYP450 Enzyme Inducers and Inhibitors on Afatinib: In vitro data indicated that drug-drug interactions with GILOTRIF due to inhibition or induction of CYP450 enzymes by concomitant medications are unlikely. The metabolites formed by CYP450-dependent reactions were approximately 9% of the total metabolic turnover in sandwich-cultured human hepatocytes. In humans, enzyme-catalyzed metabolic reactions play a negligible role for the metabolism of afatinib. Approximately 2% of the afatinib dose was metabolized by FMO3; the CYP3A4-dependent N-demethylation was not detected.
Effect of Afatinib on CYP450 Enzymes: Afatinib is not an inhibitor or an inducer of CYP450 enzymes (CYP1A2, 2B6, 2C8, 2C9, 2C19, and 3A4) in cultured primary human hepatocytes. Therefore, afatinib is unlikely to affect the metabolism of other drugs that are substrates of CYP450 enzymes.
Non-small Cell Lung Cancer (NSCLC)
The efficacy and safety of GILOTRIF in the first-line treatment of 345 patients with EGFR mutation-positive, metastatic (Stage IV and Stage IIIb with pleural and/or pericardial effusion as classified by the American Joint Commission on Cancer [AJCC, 6th edition]) NSCLC were established in a randomized, multicenter, open-label trial (Study 1). Patients were randomized (2:1) to receive GILOTRIF 40 mg orally once daily (n=230) or up to 6 cycles of pemetrexed/cisplatin (n=115). Randomization was stratified according to EGFR mutation status (exon 19 deletion vs exon 21 L858R vs other) and race (Asian vs non-Asian). The major efficacy outcome was progression-free survival (PFS) as assessed by an independent review committee (IRC). Other efficacy outcomes included objective response rate (ORR) and overall survival (OS). EGFR mutation status was prospectively determined for screening and enrollment of patients by a clinical trial assay (CTA). Tumor samples from 264 patients (178 randomized to GILOTRIF and 86 patients randomized to chemotherapy) were tested retrospectively by the companion diagnostic therascreen® EGFR RGQ PCR Kit, which is FDA-approved for selection of patients for GILOTRIF treatment.
Among the patients randomized, 65% were female, the median age was 61 years, the baseline ECOG performance status was 0 (39%) or 1 (61%), 26% were Caucasian and 72% were Asian. The majority of the patients had a tumor sample with an EGFR mutation categorized by the CTA as either exon 19 deletion (49%) or exon 21 L858R substitution (40%), while the remaining 11% had other mutations.
A statistically significant improvement in PFS as determined by the IRC was demonstrated for patients randomized to GILOTRIF compared with those randomized to chemotherapy. See Table 3 and Figure 1. There was no statistically significant difference for overall survival between the treatment arms at the interim analysis conducted at 84% of the planned events for the final analysis.
Table 3: Efficacy Results of Study 1
|Number of Deaths or Progressions, N (%)||152 (66.1%)||69 (60.0%)|
|Median Progression-free Survival (months)||11.1||6.9|
|95% CI||(9.6, 13.6)||(5.4, 8.2)|
|HR (95% CI)||0.58 (0.43, 0.78)|
|Stratified Log-Rank Test P-value*||< 0.001|
|Number of Deaths, N (%)||116 (50.4%)||59 (51.2%)|
|Median Overall Survival (months)||28.1||28.2|
|95% CI||(24.6, 33.0)||(20.7, 33.2)|
|HR (95% CI)||0.91 (0.66, 1.25)|
|Stratified Log-Rank Test P-value*||0.55|
|Objective Response Rate (CR + PR)|
|N (%)||116 (50.4%)||22 (19.1%)|
|*Stratified by EGFR mutation status and race. CR=complete response; PR=partial response|
Figure 1 : Kaplan-Meier
Curve for PFS by Independent Review by Treatment Group
Subgroup analyses were conducted based on the stratification factor of EGFR mutation status (Del19, L858R, other) and mutation category (common [Del19, L858R] vs uncommon [other]). See Figure 2.
Figure 2 : Forest Plot of PFS and OS for Common
(Del19, L858R) and Uncommon (other) EGFR Mutation Categories
There were 26 GILOTRIF-treated patients in the “other” (uncommon) EGFR mutations subgroup with nine unique mutation patterns. None of these 26 patients achieved a complete response, while four achieved a partial response (see Table 4 below). No responses were seen in GILOTRIF-treated patients with the following mutations: T790M alone (n=2), deletion 19 and T790M (n=3), G719X and T790M (n=1), exon 20 insertion (n=6), and L861Q alone (n=3). There were 11 chemotherapy-treated patients in the “other” uncommon EGFR mutation subgroup; of these, four (36%) achieved a partial response.
Table 4 : Objective Tumor
Responses in GILOTRIF-Treated Patients Based on Investigator Assessment in the
“Other” (Uncommon) EGFR Mutation Subgroup
|EGFR Mutations||Number of GILOTRIF-Treated Patients||Number of Patients with Partial Responses||Duration of Response|
|L858R and T790M||5||1||6.9 months|
|L858R and S768I||2||1||12.4+ months|
|+ Censored observation|
Last reviewed on RxList: 12/4/2013
This monograph has been modified to include the generic and brand name in many instances.
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