Clinical Pharmacology for Amvuttra
Mechanism Of Action
Vutrisiran is a double-stranded siRNA-GalNAc conjugate that causes degradation of mutant and wild-type TTR mRNA through RNA interference, which results in a reduction of serum TTR protein and TTR protein deposits in tissues.
Pharmacodynamics
In Study 1 [see Clinical Studies], following administration of the recommended AMVUTTRA dosage every 3 months to patients with hATTR amyloidosis, vutrisiran reduced mean serum TTR at steady state by 83%. Similar TTR reductions were observed regardless of Val30Met genotype status, weight, sex, age, or race.
Vutrisiran also reduced the mean steady state serum vitamin A by 62% over 9 months [see WARNINGS AND PRECAUTIONS].
Cardiac Electrophysiology
At a dose 12 times the recommended dosage of 25 mg once every three months, AMVUTTRA does not prolong the QT interval to any clinically relevant extent.
Pharmacokinetics
The pharmacokinetic (PK) properties of AMVUTTRA were evaluated following a single dose in healthy subjects and multiple doses in patients with hATTR amyloidosis, as summarized in Table 2.
Table 2: Pharmacokinetic Parameters of Vutrisiran
|
Vutrisiran |
| General Information |
| Dose Proportionality |
Vutrisiran Cmax showed dose proportional increase while AUClast and AUCinf were slightly more than dose proportional following single subcutaneous doses ranging from 5 to 300 mg (i.e., 0.2 to 12 times the recommended dose) |
| Accumulation |
No accumulation of vutrisiran was observed in plasma after repeated every 3 months dosage* |
| Absorption |
| Tmax [Median (Range)] |
4 (0.17, 12.0) hours† |
| Distribution |
| Estimated Vd/F (%RSE) |
10.1 (5.8) L‡ |
| Protein Binding |
80%§ |
| Organ Distribution |
Vutrisiran distributes primarily to the liver after subcutaneous dosing |
| Elimination |
| Half-Life [Median (Range)] |
5.2 (2.2, 6.4) hours† |
| Apparent Clearance [Median (Range)] |
21.4 (19.8, 30) L/hour‡ |
| Metabolism |
| Primary Pathway |
Vutrisiran is metabolized by endo- and exonucleases to short nucleotide fragments of varying sizes within the liver |
| Excretion |
| Primary Pathway |
The mean fraction of unchanged vutrisiran eliminated in urine was approximately 19.4% at the recommended dose of 25 mg. The mean renal clearance of vutrisiran ranged from 4.5 to 5.7 L/hour¶ |
AUCinf = area under the concentration-time curve from the time of dosing extrapolated to infinity; AUClast = area under the concentration-time curve from the time of dosing to the last measurable concentration; Cmax = maximum plasma concentration; CV = coefficient of variation; RSE = relative standard error; Tmax = time to maximum concentration; Vd/F = apparent volume of distribution
*After 25 mg every 3 months dosage in hATTR amyloidosis patients
†After 25 mg single dose in healthy subjects
‡Based on population PK model estimation
§Vutrisiran plasma protein binding was concentration-dependent and decreased with increasing vutrisiran concentrations (from 78% at 0.5 mcg/mL to 19% at 50 mcg/mL)
¶After single subcutaneous vutrisiran dose from 5 to 300 mg (i.e., 0.2 to 12 times the recommended dose) in healthy subjects |
Specific Populations
No clinically significant differences in the pharmacokinetics of vutrisiran were observed based on age, sex, race, mild and moderate renal impairment (eGFR≥30 to <90 mL/min/1.73 m²), or mild hepatic impairment (total bilirubin ≤1 x ULN and AST >1 x ULN, or total bilirubin >1.0 to 1.5 x ULN and any AST). Vutrisiran has not been studied in patients with severe renal impairment, end-stage renal disease, moderate or severe hepatic impairment, or in patients with prior liver transplant.
Drug Interaction Studies
No clinical drug-drug interaction studies have been performed with vutrisiran. In vitro studies suggest that vutrisiran is not a substrate or inhibitor of cytochrome P450 enzymes. Vutrisiran is not expected to cause drug-drug interactions by inducing CYP enzymes or modulating the activities of drug transporters.
Clinical Studies
The efficacy of AMVUTTRA was evaluated in a randomized, open-label clinical trial in adult patients with polyneuropathy caused by hATTR amyloidosis (Study 1; NCT03759379). Patients were randomized 3:1 to receive 25 mg of AMVUTTRA subcutaneously once every 3 months (N=122), or 0.3 mg/kg patisiran intravenously every 3 weeks (N=42) as a reference group. Ninety-seven percent of AMVUTTRA-treated patients and 93% of patisiran-treated patients completed at least 9 months of the assigned treatment.
Efficacy assessments were based on a comparison of the AMVUTTRA arm of Study 1 with an external placebo group in another study (NCT01960348) composed of a comparable population of adult patients with polyneuropathy caused by hATTR amyloidosis.
The primary efficacy endpoint was the change from baseline to Month 9 in modified Neuropathy Impairment Score +7 (mNIS+7). The mNIS+7 is an objective assessment of neuropathy and comprises the NIS and Modified +7 composite scores. In the version of the mNIS+7 used in the trial, the NIS objectively measures deficits in cranial nerve function, muscle strength, and reflexes, and the +7 assesses postural blood pressure, quantitative sensory testing, and peripheral nerve electrophysiology. The mNIS+7 has a total score range from 0 to 304 points, with higher scores representing a greater severity of disease.
The clinical meaningfulness of effects on the mNIS+7 was assessed by the change from baseline to Month 9 in Norfolk Quality of Life-Diabetic Neuropathy (QoL-DN) total score. The Norfolk QoL-DN scale is a patient-reported assessment that evaluates the subjective experience of neuropathy in the following domains: physical functioning/large fiber neuropathy, activities of daily living, symptoms, small fiber neuropathy, and autonomic neuropathy. The Norfolk QoL-DN has a total score range from -4 to 136, with higher scores representing greater impairment.
Additional endpoints were gait speed, as measured by the 10-meter walk test (10MWT), and modified body mass index (mBMI).
Treatment with AMVUTTRA in Study 1 resulted in statistically significant improvements in the mNIS+7, Norfolk QoL-DN total score, and 10-meter walk test at Month 9 compared to placebo in the external study (p<0.001) [Table 3, Figure 1, and Figure 3]. The distributions of changes in mNIS+7 and Norfolk QoL-DN total scores from baseline to Month 9 by percent of patients are shown in Figure 2 and Figure 4, respectively.
The change from baseline to Month 9 in modified body mass index nominally favored AMVUTTRA [Table 3].
Table 3: Clinical Efficacy Results (Comparison of AMVUTTRA Treatment in Study 1 to an External PlaceboControl*)
| Endpoint† |
Baseline, Mean (SD) |
Change from Baseline to Month 9, LS Mean (SEM) |
AMVUTTRA-Placebo* Treatment Difference, LS Mean (95% CI) |
p-value |
AMVUTTRA N=122
(Study 1) |
Placebo*
N=77 (NCT01960348) |
AMVUTTRA (Study 1) |
Placebo* (NCT01960348) |
| mNIS+7‡ |
60.6
(36.0) |
74.6
(37.0) |
-2.2
(1.4) |
14.8
(2.0) |
-17.0
(-21.8, -12.2) |
p<0.001 |
| Norfolk QoL-DN‡ |
47.1
(26.3) |
55.5
(24.3) |
-3.3
(1.7) |
12.9
(2.2) |
-16.2
(-21.7, -10.8) |
p<0.001 |
10-meter walk test
(m/sec)§ |
1.01
(0.39) |
0.79
(0.32) |
0
(0.02) |
-0.13
(0.03) |
0.13
(0.07, 0.19) |
p<0.001 |
| mBMI¶ |
1058
(234) |
990
(214) |
7.6
(7.9) |
-60.2
(10.1) |
67.8
(43.0, 92.6) |
p<0.001 |
CI = confidence interval; LS mean = least squares mean; mBMI = modified body mass index; mNIS = modified Neuropathy Impairment Score; QoL-DN = Quality of Life-Diabetic Neuropathy; SD = standard deviation; SEM = standard error of the mean
*External placebo group from another randomized controlled trial (NCT01960348)
†All endpoints analyzed using the analysis of covariance (ANCOVA) with multiple imputation (MI) method)
‡A lower number indicates less impairment/fewer symptoms §A higher number indicates less disability/less impairment
¶mBMI: nominal p-value; body mass index (BMI; kg/m²) multiplied by serum albumin (g/L). |
Figure 1: Change from Baseline in mNIS+7(Comparison of AMVUTTRA Treatment in Study 1 to an External Placebo Control*)
Figure 2: Histogram of mNIS+7 Change from Baseline at Month 9(Comparison of AMVUTTRA Treatment in Study 1 to an External Placebo Control*)
Figure 3: Change from Baseline in Norfolk QoL-DN Total Score(Comparison of AMVUTTRA Treatment in Study 1 to an External Placebo Control*)
Figure 4: Histogram of Norfolk QoL-DN Total Score Change from Baseline at Month 9(Comparison of AMVUTTRA Treatment in Study 1 to an External Placebo Control*)
Patients receiving AMVUTTRA in Study 1 experienced similar improvements relative to those in the external placebo group in mNIS+7 and Norfolk QoL-DN total score across all subgroups including age, sex, race, region, NIS score, Val30Met genotype status, and disease stage.