Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

13.2 Pharmacodynamics
Following twice weekly administration of 1 mg/m2 and 1.3 mg/m2 bortezomib doses, the maximum inhibition of 20S proteasome activity (relative to baseline) in whole blood was observed five minutes after drug administration. Comparable maximum inhibition of 20S proteasome activity was observed between 1 and 1.3 mg/m2 doses. Maximal inhibition ranged from 70% to 84% and from 73% to
83% for the 1 mg/m2 and 1.3 mg/m2 dose regimens, respectively.

Pharmacokinetic Properties

13.3 Pharmacokinetics
Following intravenous administration of 1 mg/m2 and 1.3 mg/m2 doses, the mean maximum plasma concentrations of bortezomib (Cmax) after the first dose (Day 1) were 57 and 112 ng/mL, respectively. When administered twice weekly, the mean maximum observed plasma concentrations ranged from 67 to 106 ng/mL for the 1 mg/m2 dose and 89 to 120 ng/mL for the 1.3 mg/m2 dose.

Following an intravenous bolus or subcutaneous injection of a 1.3 mg/m2 dose to patients with multiple myeloma, the total systemic exposure after repeat dose administration (AUClast) was equivalent for subcutaneous and intravenous administration. The AUClast geometric mean ratio (90% confidence interval) was 0.99 (0.80 to 1.23). The Cmax after subcutaneous administration (20.4 ng/mL) was lower than after intravenous administration (223 ng/mL) with repeat dose administration.

Distribution
The mean distribution volume of bortezomib ranged from approximately 498 to 1884 L/m2 following single- or repeat-dose administration of 1 mg/m2 or 1.3 mg/m2 to patients with multiple myeloma. The binding of bortezomib to human plasma proteins averaged 83% over the concentration range of 100 to 1000 ng/mL.
Elimination
The mean elimination half-life of bortezomib upon multiple dosing ranged from 40 to 193 hours after the 1 mg/m2 dose and 76 to 108 hours after the 1.3 mg/m2 dose. The mean total body clearances were 102 and 112 L/h following the first dose for doses of 1 mg/m2 and 1.3 mg/m2, respectively, and ranged from 15 to 32 L/h following subsequent doses for doses of 1 and 1.3 mg/m2, respectively.
Metabolism
Bortezomib is primarily oxidatively metabolized to several inactive metabolites in vitro via cytochrome P450 (CYP) enzymes 3A4, CYP2C19, and CYP1A2, and to a lesser extent by CYP2D6 and CYP2C9.

Excretion
The pathways of elimination of bortezomib have not been characterized in humans.
Specific Populations
No clinically significant differences in the pharmacokinetics of bortezomib were observed based on age, sex, or renal impairment (including patients administered VELCADE after dialysis). The effect of race on bortezomib pharmacokinetics is unknown.
Patients with Hepatic Impairment
Following administration of bortezomib doses ranging from 0.5 to 1.3 mg/m2, mild (total bilirubin ≤1x ULN and AST >ULN, or total bilirubin >1 to 1.5x ULN and any AST) hepatic impairment did not alter dose-normalized bortezomib AUC when compared to patients with normal hepatic function. Dose normalized mean bortezomib AUC increased by approximately 60% in patients with moderate (total 

bilirubin >1.5 to 3x ULN and any AST) or severe (total bilirubin >3x ULN and any AST) hepatic impairment. A lower starting dose is recommended in patients with moderate or severe hepatic impairment.
Renal Impairment:
A pharmacokinetic study was conducted in patients with various degrees of renal impairment who were classified according to their creatinine clearance values (CrCl) into the following groups: Normal (CrCl ≥60 mL/min/1.73 m2, N=12), Mild (CrCl=40-59 mL/min/1.73 m2, N=10), Moderate (CrCl=20-39 mL/min/1.73 m2, N=9), and Severe (CrCl < 20mL/min/1.73 m2, N=3). A group of dialysis patients who were dosed after dialysis was also included in the study (N=8). Patients were administered intravenous doses of 0.7 to 1.3 mg/ m2 of bortezomib twice weekly. Exposure of bortezomib (dose-normalized AUC and Cmax) was comparable among all the groups. [See Use in Specific Populations (10.6)]
Drug Interaction Studies
Clinical Studies
No clinically significant differences in bortezomib pharmacokinetics were observed when coadministered with dexamethasone (weak CYP3A4 inducer), omeprazole (strong CYP2C19 inhibitor), or melphalan in combination with prednisone.
In vitro studies indicate that bortezomib is a weak inhibitor of the cytochrome P450 (CYP) isozymes 1A2, 2C9, 2C19, 2D6 and 3A4. Based on the limited contribution (7%) of CYP2D6 to the metabolism of bortezomib, the CYP2D6 poor metaboliser phenotype is not expected to affect the overall disposition of bortezomib.
A drug-drug interaction study assessing the effect of ketoconazole, a potent CYP3A4 inhibitor, on the pharmacokinetics of bortezomib (injected intravenously), showed a mean bortezomib AUC increase of 35% (CI90% [1.032 to 1.772]) based on data from 12 patients.
Therefore, patients should be closely monitored when given bortezomib in combination with potent CYP3A4 inhibitors (e.g.
ketoconazole, ritonavir).
In a drug-drug interaction study assessing the effect of omeprazole, a potent CYP2C19 inhibitor, on the pharmacokinetics of bortezomib (injected intravenously), there was no significant effect on the pharmacokinetics of bortezomib based on data from 17 patients.
A drug-drug interaction study assessing the effect of rifampicin, a potent CYP3A4 inducer, on the pharmacokinetics of bortezomib (injected intravenously), showed a mean bortezomib AUC reduction of 45% based on data from 6 patients. Therefore, the concomitant use of bortezomib with strong CYP3A4 inducers (e.g., rifampicin, carbamazepine, phenytoin, phenobarbital and St. John’s Wort) is not recommended, as efficacy may be reduced.
In the same drug-drug interaction study assessing the effect of dexamethasone, a weaker CYP3A4 inducer, on the pharmacokinetics of bortezomib (injected intravenously), there was no significant effect on the pharmacokinetics of bortezomib based on data from 7 patients.

Strong CYP3A4 Inhibitor
Coadministration with ketoconazole (strong CYP3A4 inhibitor) increased bortezomib exposure by 35%.
Strong CYP3A4 Inducer
Coadministration with rifampin (strong CYP3A4 inducer) decreased bortezomib exposure by approximately 45%.

In Vitro Studies
Bortezomib may inhibit CYP2C19 activity and increase exposure to drugs that are substrates for this enzyme.