Clinical Pharmacology for Bevyxxa
Mechanism Of Action
Betrixaban is an oral FXa inhibitor that selectively blocks the active site of FXa and does not require a cofactor (such as Anti-thrombin III) for activity. Betrixaban inhibits free FXa and prothrombinase activity. By directly inhibiting FXa, betrixaban decreases thrombin generation (TG). Betrixaban has no direct effect on platelet aggregation.
Pharmacodynamics
Inhibition of FXa by betrixaban results in an inhibition of thrombin generation at clinically relevant concentrations, and the maximum inhibition of thrombin generation coincides with the time of peak betrixaban concentrations.
Cardiac Electrophysiology
In a study that evaluated the effect of betrixaban on the QT interval, a concentration-dependent increase in the QTc interval was observed. Based on the observed concentration-QTc relationship a mean (upper 95% CI) QTc prolongation of 4 ms (5 ms) is predicted for 80 mg betrixaban and 13 ms (16 ms) for a 4.7-fold increase in exposure [see CLINICAL PHARMACOLOGY].
Pharmacokinetics
Within the anticipated therapeutic dose range a two-fold increase in dose resulted in a three-fold increase in exposure in the single ascending dose study. A two-fold increase in betrixaban exposure was observed after repeat dosing, and the time to steady-state is 6 days (without an initial loading dose).
Absorption
The oral bioavailability of betrixaban for an 80 mg dose is 34%, and peak concentrations occurred within 3 to 4 hours. Betrixaban is also a substrate of P-gp.
Effect Of Food
When administered with a low-fat (900 calories, 20% fat) or high-fat (900 calories, 60% fat) meal, C and AUC were reduced as compared to the fasting state by an average of 70% and 61% for low-fat and 50% and 48% for high-fat, respectively. The effect of food on betrixaban PK could be observed for up to 6 hours after meal intake.
Distribution
The apparent volume of distribution is 32 L/kg. In vitro plasma protein binding is 60%.
Elimination
The effective half-life of betrixaban is 19 to 27 hours.
Metabolism
Unchanged betrixaban is the predominant component found in human plasma. Two inactive major metabolites formed by CYP-independent hydrolysis comprise the other components in plasma, accounting for 15 to 18% of the circulating drug-related material. Less than 1% of the minor metabolites could be formed via metabolism by the following CYP enzymes: 1A1, 1A2, 2B6, 2C9, 2C19, 2D6, and 3A4.
Excretion
Following oral administration of radio-labeled betrixaban approximately 85% of the administered compound was recovered in the feces and 11% recovered in the urine. In a study of intravenous betrixaban a median value of 17.8% of the absorbed dose was observed as unchanged betrixaban in urine.
Specific Populations
Male And Female Patients
No clinically significant changes in betrixaban pharmacokinetics were observed between males and females.
Patients With Renal Impairment
In a dedicated renal impairment study mean AUC0-24 on day 8 was increased by 1.89, 2.27 and 2.63-fold in mild (eGFRMDRD ≥ 60 to < 90 mL/min/1.73 m²), moderate (eGFR MDRD ≥ 30 to < 60 mL/min/1.73 m²) and severe (eGFR MDRD ≥ 15 to < 30 mL/min/1.73 m²) renal impaired patients respectively compared to healthy volunteers [see Use In Specific Populations].
Patients With Hepatic Impairment
The safety and pharmacokinetics of single-dose BEVYXXA (80 mg) were evaluated in otherwise healthy subjects with varying degrees of hepatic impairment, i.e. normal, mild and moderate subjects. The maximum and total betrixaban exposure, as measured by Cmax and AUC0-∞, were approximately 60% and 30% higher, respectively, for subjects with mild hepatic impairment compared to subjects with normal hepatic function. Betrixaban Cmax and AUC0-∞ were approximately 119% and 57% higher, respectively, for subjects with moderate hepatic  impairment compared to subjects with normal hepatic function. Patients with severe hepatic impairment were not studied [see Use In Specific Populations].
Drug Interaction Studies
The effects of coadministered drugs on the pharmacokinetics of betrixaban exposure based on drug interaction studies are summarized in Figure 1.
Figure 1: Effect of Coadministered Drugs on the Pharmacokinetics of Betrixaban
Clinical Studies
The clinical evidence for the effectiveness of BEVYXXA is derived from the APEX clinical trial [NCT01583218]. APEX was a randomized, double-blind, multinational study comparing extended duration BEVYXXA (35 to 42 days) to short duration of enoxaparin (6 to 14 days) in the prevention of venous thromboembolic events (VTE) in hospitalized, acutely medically ill patients with risk factors for VTE.
Eligible patients included adults who were at least 40 years of age, hospitalized for an acute medical illness, at risk for VTE due to moderate or severe immobility, and had additional risk factors for VTE (described below). Expected duration of hospitalization was at least 3 days and patients were expected to be moderately or severely immobilized for at least 24 hours. The causes for hospitalization included heart failure, respiratory failure, infectious disease, rheumatic disease, or ischemic stroke. At study initiation eligible patients were required to have one of the following additional risk factors for VTE:
- ≥ 75 years of age,
- 60 through 74 years of age with D-dimer ≥ 2 ULN, or
- 40 through 59 years of age with D-dimer ≥ 2 ULN and a history of either VTE or cancer.
A total of 7,513 patients were randomized 1:1 to:
- BEVYXXA arm (BEVYXXA 160 mg orally on Day 1, then 80 mg once daily for 35 to 42 days AND enoxaparin subcutaneous placebo once daily for 6 to 14 days),
OR - Enoxaparin arm (enoxaparin 40 mg subcutaneously once daily for 6 to 14 days AND BEVYXXA placebo orally once daily for 35 to 42 days).
Patients with severe renal impairment (creatinine clearance ≥ 15 and < 30 mL/min) received reduced doses of study medications (BEVYXXA 80 mg loading dose, then 40 mg once daily or enoxaparin 20 mg once daily) along with corresponding placebo.
Patients taking a concomitant P-gp inhibitor received BEVYXXA 80 mg loading dose, then 40 mg once daily or enoxaparin 40 mg subcutaneously once daily for 6 to 14 days along with corresponding placebo.
Baseline characteristics were balanced between the treatment groups. The population was 55% female, 93% White, 2% Black, 0.2% Asian, and 5% others. The most prevalent acute medical illness at hospitalization was acutely decompensated heart failure (45%), followed by acute infection without septic shock (29%), acute respiratory failure (12%), acute ischemic stroke (11%) and acute rheumatic disorders (3%). The mean and median ages were 76.4 and 77 years, respectively, with 68% of patients ≥ 75 years of age, 97% were severely immobilized at study entry, and 62% had D-dimer ≥ 2 × ULN.
While the APEX Study was ongoing (after 35% enrollment), the study was amended to ensure enrollment of patients ≥ 75 years of age or with D-dimer values ≥ 2 × ULN. The APEX trial excluded patients whose condition required prolonged anticoagulation (e.g., concurrent VTE, atrial fibrillation, cardiac valve prosthesis), were at increased risk of bleeding, had liver dysfunction, were on dual antiplatelet therapy, or patients who had both severe renal insufficiency (CrCl 15-29 ml/min) and required the concomitant use of a P-gp inhibitor.
The efficacy of BEVYXXA was based upon the composite outcome of the occurrence of any of the following events up to Day 35 visit:
- Asymptomatic proximal Deep Vein Thrombosis (DVT) (detected by ultrasound),
- Symptomatic proximal or distal DVT,
- Non-fatal Pulmonary Embolism (PE), or
- VTE-related death.
Efficacy analyses were performed based on the modified Intent-to-Treat (mITT) population. The mITT population consisted of all patients who had taken at least one dose of study drug and who had follow-up assessment data on one or more primary or secondary efficacy outcome components. A total of 7,441 patients (N=3,721 for BEVYXXA and N=3,720 for enoxaparin) were included in the mITT population.
The efficacy results for the APEX trial are provided in Table 5 below.
Table 5: Efficacy Outcomes in APEX Trial (mITT Population)
| BEVYXXA N=3,721 n (%)* | Enoxaparin N=3,720 n (%) * | Relative Risk (95% CI) † |
| Composite Outcome | 165 (4.4) | 223 (6.0) | 0.75 (0.61, 0.91) |
| Asymptomatic Event | 133 (3.6) | 176 (4.7) | |
| Symptomatic DVT | 14 (0.4) | 22 (0.6) | |
| Non-fatal PE | 9 (0.2) | 18 (0.5) | |
| VTE-related Death | 13 (0.3) | 17 (0.5) | |
| Symptomatic Events ‡ | 35 (0.9) | 54 (1.5) | 0.64 (0.42, 0.98) |
*Percentages and event rates are based on the total number of patients and events included in each treatment group. †Relative Risk (BEVYXXA arm versus enoxaparin arm) is based on the Mantel-Haenszel test stratified by the dosing strata and D-dimer status from the local laboratory. The analyses are not adjusted for multiplicity. ‡Symptomatic events include symptomatic DVT, non-fatal PE or VTE-related death. |
For patients with D-dimer ≥ 2 ULN at baseline, the event rate is 5.7% in the BEVYXXA arm vs. 7.2% in the enoxaparin arm (relative risk = 0.79, 95% CI [0.63, 0.98]).
For patients with D-dimer ≥ 2 ULN at baseline or age ≥ 75 years, the event rate is 4.7% in the BEVYXXA arm vs. 6.0% in the enoxaparin arm (relative risk = 0.78, 95% CI [0.64, 0.96]).
Results for the primary efficacy analysis for subjects that were stratified at randomization to the 80 mg BEVYXXA dose group in the mITT population are shown in Table 6 below.
Patients who were randomized to receive 40 mg BEVYXXA (those with severe renal impairment or receiving P-gp inhibitors), had VTE rates similar to the enoxaparin arm (6 to 14 days followed by placebo) shown in Table 7 below.
Table 6: Efficacy Outcomes in APEX Trial (mITT Population) – Patients Stratified to 80 mg BEVYXXA Dose
| | | |
| BEVYXXA N=2,878 n (%) * | Enoxaparin N=2,926 n (%) * | Relative Risk (95% CI) † |
| Composite Outcome | 120 (4.2) | 180 (6.2) | 0.68 (0.55, 0.86) |
| Asymptomatic Event | 100 (3.5) | 146 (5.0) | |
| Symptomatic DVT | 11 (0.4) | 17 (0.6) | |
| Non-fatal PE | 4 (0.1) | 14 (0.5) | |
| VTE-related Death | 8 (0.3) | 12 (0.4) | |
| Symptomatic Events‡ | 22 (0.8) | 41 (1.4) | 0.55 (0.33, 0.92) |
* Percentages and event rates are based on the total number of patients and events included in each treatment group and stratified to 80 mg dose. † Relative Risk (BEVYXXA arm versus enoxaparin arm) is based on the Mantel-Haenszel test stratified by D-dimer status from the local laboratory. The analyses are not adjusted for multiplicity. ‡Symptomatic events include symptomatic DVT, non-fatal PE, or VTE-related death. |
Table 7: Efficacy Outcomes in APEX Trial (mITT Population) – Patients Stratified to 40 mg BEVYXXA Dose
| Severe Renal Impairment | Concomitant Use of P-gp Inhibitor |
BEVYXXA N=174 n (%) * | Enoxaparin N=149 n (%) * | Relative Risk (95% CI) † | BEVYXXA N=669 n (%) * | Enoxaparin N=645 n (%) * | Relative Risk (95% CI) † |
| Composite Outcome | 12 (6.9) | 10 (6.7) | 1.0 (0.45, 2.23) | 33 (4.9) | 33 (5.1) | 1.0 (0.63, 1.60) |
| Asymptomatic Event | 9 (5.2) | 7 (4.7) | | 24 (3.6) | 23 (3.6) | |
| Symptomatic DVT | 0 | 1 (0.7) | | 3 (0.4) | 4 (0.6) | |
| Non-fatal PE | 2 (1.1) | 2 (1.3) | | 3 (0.4) | 2 (0.3) | |
| VTE-related Death | 2 (1.1) | 0 | | 3 (0.4) | 5 (0.8) | |
| Symptomatic Events‡ | 4 (2.3) | 3 (2.0) | | 9 (1.3) | 10 (1.6) | |
*Percentages and event rates are based on the total number of patients and events included in each treatment group by dosing criteria. †Relative Risk (BEVYXXA arm versus enoxaparin arm) is based on the Mantel-Haenszel test stratified by D-dimer status from the local laboratory. The analyses are not adjusted for multiplicity. ‡Symptomatic events include symptomatic DVT, non-fatal PE, or VTE-related death. |