CLINICAL PHARMACOLOGY
Mechanism Of Action
Type 1 Gaucher disease is caused by a functional
deficiency of glucocerebrosidase, the enzyme that mediates the degradation of
the glycosphingolipid glucosylceramide.
Miglustat functions as a competitive and reversible
inhibitor of the enzyme glucosylceramide synthase, the initial enzyme in a
series of reactions which results in the synthesis of most glycosphingolipids.
Zavesca helps reduce the rate of glycosphingolipid
biosynthesis so that the amount of glycosphingolipid substrate is reduced to a
level which allows the residual activity of the deficient glucocerebrosidase
enzyme to be more effective (substrate reduction therapy). In vitro and in vivo
studies have shown that miglustat can reduce the synthesis of
glucosylceramide-based glycosphingolipids.
Pharmacokinetics
Absorption
After a 100 mg oral dose, the time to maximum observed
plasma concentration of miglustat (tmax) ranged from 2 to 2.5 hours in Gaucher
patients. Plasma concentrations show a biexponential decline, characterized by
a short distribution phase and a longer elimination phase. The effective
halflife of miglustat is approximately 6 to 7 hours, which predicts that
steady-state will be achieved by 1.5 to 2 days following the start of three
times daily dosing.
Miglustat, dosed at 50 and 100 mg three times daily in
Gaucher patients, exhibits dose-proportional pharmacokinetics. The
pharmacokinetics of miglustat were not altered after repeated dosing three
times daily for up to 12 months.
In healthy subjects, co-administration of Zavesca with
food results in a decrease in the rate of absorption of miglustat (maximum
plasma concentration [Cmax] was decreased by 36% and tmax delayed 2 h) but had
no statistically significant effect on the extent of absorption of miglustat
(area-under-theplasma- concentration time curve [AUC] was decreased by 14%).
The mean oral bioavailability of a 100-mg miglustat capsule is about 97%
relative to an oral solution administered under fasting conditions. The
pharmacokinetics of miglustat were similar between adult type 1 Gaucher disease
patients and healthy subjects after a single dose administration of miglustat
100 mg.
Distribution
Miglustat does not bind to plasma proteins. Mean apparent
volume of distribution of miglustat is 83-105 liters in Gaucher patients. At
steady state, the concentration of miglustat in cerebrospinal fluid of six
non-Gaucher patients was 31.4-67.2% of that in plasma, indicating that miglustat
crosses the blood brain barrier.
Metabolism And Excretion
The major route of excretion of miglustat is via kidney.
Following administration of a single dose of 100 mg 14C-miglustat to
healthy volunteers, 83% of the radioactivity was recovered in urine and 12% in
feces. In healthy subjects, 67% of the administered dose was excreted unchanged
in urine over 72 hours. The most abundant metabolite in urine was miglustat glucuronide
accounting for 5% of the dose. The terminal half-life of radioactivity in
plasma was 150 hours, suggesting the presence of one or more metabolites with a
prolonged half-life. The metabolite accounting for this observation has not
been identified, but may accumulate and reach concentrations exceeding those of
miglustat at steady state.
Specific Populations
Gender
There was no statistically significant gender difference
in miglustat pharmacokinetics, based on pooled data analysis.
Race
Ethnic differences in miglustat pharmacokinetics have not
been evaluated in Gaucher patients. However, apparent oral clearance of
miglustat in patients of Ashkenazi Jewish descent was not statistically
different to that in others (1 Asian and 15 Caucasians), based on a cross-study
analysis.
Hepatic Impairment
No studies have been performed to assess the
pharmacokinetics of miglustat in patients with hepatic impairment.
Renal Impairment
Limited data in non-Gaucher patients with impaired renal
function indicate that the apparent oral clearance (CL/F) of miglustat
decreases with decreasing renal function. While the number of subjects with
mild and moderate renal impairment was very small, the data suggest an
approximate decrease in the apparent oral clearance of 40% and 60%
respectively, in mild and moderate renal impairment, justifying the need to
decrease the dosing of miglustat in such patients dependent upon creatinine
clearance levels [see DOSAGE AND ADMINISTRATION].
Data in severe renal impairment are limited to two
patients with creatinine clearances in the range 18-29 mL/min and cannot be
extrapolated below this range. These data suggest a decrease in CL/F by at
least 70% in patients with severe renal impairment [see DOSAGE AND
ADMINISTRATION and Use In Specific Populations].
Drug Interaction Studies
Miglustat does not inhibit the metabolism of various
substrates of cytochrome P450 enzymes including, CYP1A2, CYP2A6, CYP2C9,
CYP2C19, CYP2D6, CYP2E1, CYP3A4 and CYP4A11 in vitro; consequently significant
interactions via inhibition of these enzymes are unlikely with drugs that are substrates
of cytochrome P450 enzymes.
Drug interaction between Zavesca (miglustat 100 mg orally
three times daily) and imiglucerase 7.5 or 15 U/kg/day was assessed in
imiglucerase-stabilized patients after one month of co-administration. There
was no significant effect of imiglucerase on the pharmacokinetics of miglustat,
with the coadministration of imiglucerase and miglustat resulting in a 22%
reduction in Cmax and a 14% reduction in the AUC for miglustat. While Zavesca
appeared to increase the clearance of imiglucerase by 70%, these results are
not conclusive because of the small number of subjects studied and because
patients took variable doses of imiglucerase [see DRUG INTERACTIONS].
Concomitant therapy with loperamide during clinical
trials did not appear to significantly alter the pharmacokinetics of miglustat.
Animal Toxicology And/Or Pharmacology
Histopathology findings in the absence of clinical signs
in the central nervous system of the monkey (brain, spine) that included
vascular mineralization, in addition to mineralization and necrosis of white matter
were observed at >750 mg/kg/day (4 times the human therapeutic systemic
exposure based on area-under-the-plasma-concentration curve [AUC] comparisons)
in a 52-week oral toxicity study using doses of 750 and 2000 mg/kg/d.
Vacuolization of white matter was observed in rats dosed orally by gavage at
≥ 180 mg/kg/d (6 times the human therapeutic exposure based on surface
area comparisons, mg/m²) in a 4-week study using doses of 180, 840, and 4200
mg/kg/d. Vacuolization can sometimes occur as an artifact of tissue processing.
Findings in dogs included tremor and absent corneal reflexes at 105 mg/kg/day
(10 times the human therapeutic systemic exposure, based on body surface area comparisons,
mg/m²) after a 4-week oral gavage toxicity study using doses of 35, 70, 105,
and 140 mg/kg/d. Ataxia, diminished/absent pupillary, palpebral, or patellar
reflexes were observed in a dog at ≥495 mg/kg/day (50 times the human
therapeutic systemic exposure based on body surface area comparisons, mg/m²),
in a 2-week oral gavage toxicity study using doses of 85, 165, 495, and 825 mg/kg/d.
Cataracts were observed in rats at ≥180 mg/kg/day
(4 times the human therapeutic systemic exposure, based on AUC) in a 52-week
oral gavage toxicity study using doses of 180, 420, 840, and 1680 mg/kg/d.
Gastrointestinal necrosis, inflammation, and hemorrhage
were observed in dogs at ≥ 85 mg/kg/day (9 times the human therapeutic
systemic exposure based on body surface area comparisons, mg/m²) after a 2-week
oral (capsule) toxicity study using doses of 85, 165, 495, and 825 mg/kg/d.
Similar GI toxicity occurred in rats at 1200 mg/kg/day (7 times the human
therapeutic systemic exposure, based on AUC) in a 26-week oral gavage toxicity
study using doses of 300, 600, and 1200 mg/kg/d. In monkeys, similar GI
toxicity occurred at ≥750 mg/kg/day (6 times the human therapeutic
systemic exposure based on AUC) following a 52-week oral gavage toxicity study
using doses of 750 and 2000 mg/kg/d.
Clinical Studies
The efficacy of Zavesca in type 1 Gaucher disease has
been investigated in two open-label, uncontrolled trials and one randomized,
open-label, active-controlled trial with enzyme replacement given as
imiglucerase. Patients who received Zavesca were treated with doses ranging
from 100 to 600 mg a day, although the majority of patients were maintained on
doses between 200 to 300 mg a day. Efficacy parameters included the evaluation
of liver and spleen organ volume, hemoglobin concentration, and platelet count.
A total of 80 patients were exposed to Zavesca during the three trials and
their extension period.
Open-Label Uncontrolled Monotherapy Trials
In Study 1, Zavesca was administered at a starting dose
of 100 mg three times daily for 12 months (dose range of 100 once-daily to 200
mg three times daily) to 28 adult patients with type 1 Gaucher disease, who
were unable to receive enzyme replacement therapy and who had not taken enzyme
replacement therapy in the preceding 6 months. Twenty-two patients completed
the trial. After 12 months of treatment, the results showed significant mean
percent reductions from baseline in liver volume of 12% and spleen volume of
19%, a non-significant increase from baseline in mean absolute hemoglobin concentration
of 0.26 g/dL and a mean absolute increase from baseline in platelet counts of 8
x 109/L (See Tables 3-6).
In Study 2, Zavesca was administered at a dose of 50 mg
three times daily for 6 months to 18 adult patients with type 1 Gaucher disease
who were unable to receive enzyme replacement therapy and who had not taken
enzyme replacement therapy in the preceding 6 months. Seventeen patients
completed the trial. After 6 months of treatment, the results showed
significant mean percent reductions from baseline in liver volume of 6% and
spleen volume of 5%. There was a non-significant mean absolute decrease from
baseline in hemoglobin concentration of 0.13 g/dL and a non-significant mean
absolute increase from baseline in platelet counts of 5 x 109/L (See
Tables 3-6).
Extension Period
Eighteen patients were enrolled in a 12-month extension
to Study 1. A subset of patients continuing in the extension had larger mean
baseline liver volumes, and lower mean baseline platelet counts and hemoglobin
concentrations than the original study population (See Tables 3-6). After a
total of 24 months of treatment, there were significant mean decreases from
baseline in liver and spleen organ volumes of 15% and 27%, respectively, and
significant mean absolute increases from baseline in hemoglobin concentration
and platelet count of 0.9 g/dL and 14 x 10 /L, respectively (See Tables 3-6).
Sixteen patients were enrolled in a 6-month extension to
Study 2. After a total of 12 months of treatment, there was a mean decrease
from baseline in spleen organ volume of 10%, whereas the mean percent decrease
in liver organ volume remained at 6%. There were no significant changes in hemoglobin
concentrations or platelet counts (See Tables 3-6).
Liver volume results from Studies 1 and 2 and their
extensions are summarized in Table 3:
Table 3: Liver Volume Changes in Two Open-Label
Uncontrolled Monotherapy Trials of Zavesca with Extension Period
|
n |
Liver Volume |
Absolute Mean (L) (2-sided 95% CI) |
Percent Mean (%) (2-sided 95% CI) |
Study 1 (starting dose Zavesca 100 mg three times daily) |
Baseline (Month 0) |
21 |
2.39 |
|
Month 12 Change from baseline |
|
-0.28
(-0.38, -0.18) |
-12.1%
(-16.4, 7.9) |
Study 1 Extension Phase |
Baseline (Month 0) |
12 |
2.54 |
|
Month 24 Change from baseline |
|
-0.36
(-0.48, -0.24) |
-14.5%
(-19.3, 9.7) |
Study 2 (Zavesca 50 mg three times daily) |
Baseline (Month 0) |
17 |
2.45 |
|
Month 6 Change from baseline |
|
-0.14
(-0.25, -0.03) |
-5.9%
(-9.9, -1.9) |
Study 2 Extension Phase |
Baseline (Month 0) |
13 |
2.35 |
|
Month 12 Change from baseline |
|
-0.17
(-0.3, -0.0) |
-6.2%
(-12.0, -0.5) |
Spleen volume results from Studies 1 and 2 and their
extensions are summarized in Table 4:
Table 4: Spleen Volume Changes in Two Open-Label Uncontrolled Monotherapy Trials of Zavesca with Extension Period
|
n |
Spleen Volume |
Absolute Mean (L) (2-sided 95% CI) |
Percent Mean (%) (2-sided 95% CI) |
Study 1 (starting dose Zavesca 100 mg three times daily) |
Baseline (Month 0) |
18 |
1.64 |
|
Month 12 Change from baseline |
|
-0.32
(-0.42, -0.22) |
-19.0%
(-23.7, -14.3) |
Study 1 Extension Phase |
Baseline (Month 0) |
10 |
1.56 |
|
Month 24 Change from baseline |
|
-0.42
(-0.53, -0.30) |
-26.4%
(-30.4, -22.4) |
Study 2 (Zavesca 50 mg three times daily) |
Baseline (Month 0) |
11 |
1.98 |
|
Month 6 Change from baseline |
|
-0.09
(-0.18, -0.01) |
-4.5%
(-8.2, -0.7) |
Study 2 Extension Phase |
Baseline (Month 0) |
9 |
1.98 |
|
Month 12 Change from baseline |
|
-0.23
(-0.46, 0.00) |
-10.1%
(-20.1, -0.1) |
Hemoglobin concentration results from Studies 1 and 2 and
their extensions are summarized in Table 5:
Table 5: Hemoglobin Concentration Changes in Two
Open-Label Uncontrolled Monotherapy Trials of Zavesca with Extension Period
|
n |
Hemoglobin Concentration |
Absolute Mean (g/dL) (2-sided 95% CI) |
Percent Mean (%) (2-sided 95% CI) |
Study 1 (starting dose Zavesca 100 mg three times daily) |
Baseline (Month 0) |
22 |
11.94 |
|
Month 12 Change from baseline |
|
0.26
(-0.05, 0.57) |
2.6%
(-0.5, 5.7) |
Study 1 Extension Phase |
Baseline (Month 0) |
13 |
11.03 |
|
Month 24 Change from baseline |
|
0.91
(0.30, 1.53) |
9.1%
(2.9, 15.2) |
Study 2 (Zavesca 50 mg three times daily) |
Baseline (Month 0) |
17 |
11.60 |
|
Month 6 Change from baseline |
|
-0.13
(-0.51, 0.24) |
-1.3%
(-4.4, 1.8) |
Study 2 Extension Phase |
Baseline (Month 0) |
13 |
11.94 |
|
Month 12 Change from baseline |
|
0.06
(-0.73, 0.85) |
1.2%
(-5.2, 7.7) |
Platelet count results from Studies 1 and 2 and their
extensions are summarized in Table 6:
Table 6: Platelet Count Changes in Two Open-Label
Uncontrolled Monotherapy Trials of Zavesca with Extension Period
|
n |
Platelet Count |
Absolute Mean (109/L) (2-sided 95% CI) |
Percent Mean (%) (2-sided 95% CI) |
Study 1 (starting dose Zavesca 100 mg three times daily) |
Baseline (Month 0) |
22 |
76.58 |
|
Month 12 Change from baseline |
|
8.28
(1.88, 14.69) |
16.0%
(-0.8, 32.8) |
Study 1 Extension Phase |
Baseline (Month 0) |
13 |
72.35 |
|
Month 24 Change from baseline |
|
13.58
(7.72, 19.43) |
26.1%
(14.7, 37.5) |
Study 2 (Zavesca 50 mg three times daily) |
Baseline (Month 0) |
17 |
116.47 |
|
Month 6 Change from baseline |
|
5.35
(-6.31, 17.02) |
2.0%
(-6.9, 10.8) |
Study 2 Extension Phase |
Baseline (Month 0) |
13 |
122.15 |
|
Month 12 Change from baseline |
|
14.0
(-3.4, 31.4) |
14.7%
(-1.4, 30.7) |
Open-Label Active-Controlled Trial
Study 3 was an open-label, randomized, active-controlled
study of 36 adult patients with type 1 Gaucher disease, who had been receiving
enzyme replacement therapy with imiglucerase for a minimum of 2 years prior to
study entry. Patients were randomized 1:1:1 to one of three treatment groups,
as follows:
- Zavesca 100 mg three times daily alone
- imiglucerase (patient's usual dose) alone
- Zavesca 100 mg three times daily and imiglucerase (usual
dose)
Patients were treated for 6 months, and 33 patients
completed the study. Because Zavesca is only indicated as monotherapy, the
results for the monotherapy arms are described below. At Month 6, the results
showed a decrease in mean percent change in liver volume in the Zavesca
treatment group compared to the imiglucerase alone group. There were no
significant differences between the groups for mean absolute changes in liver
and spleen volume and hemoglobin concentration. However, there was a
significant difference between the Zavesca alone and imiglucerase alone groups
in platelet counts at Month 6, with the Zavesca alone group having a mean absolute
decrease in platelet count of 21.6 x 109/L and the imiglucerase
alone group having a mean absolute increase in platelet count of 10.1 x 109/L
(See Tables 7-10).
Extension Period
Twenty-nine patients were enrolled in a 6-month extension
to Study 3. In the extension phase, all 29 patients had withdrawn from
imiglucerase and received open-label Zavesca 100 mg three times daily monotherapy.
At Month 12, the results showed non-significant decreases in platelet counts
from baseline in all the treatment groups (by original randomization). There
was a significant decrease in platelet counts from Month 6 to Month 12 in the
group originally randomized to treatment with imiglucerase, and a continued
decrease in platelet counts in the group originally randomized to Zavesca alone.
There were no significant changes in any treatment group for liver volume,
spleen volume, or hemoglobin concentration (See Tables 7-10).
Liver volume results from Study 3 and extension are
summarized in Table 7:
Table 7: Liver Volume Changes from Study 3 and Extension
Phase
|
Imiglucerase alone |
Zavesca alone |
Study 3 |
Month 0 |
n=11 |
n=10 |
Month 6 Change (L) |
1.81 |
1.58 |
Month 6 % Change |
0.04 |
-0.05 |
Adjusted mean Difference from Imiglucerase (95% CI) |
3.6% |
-2.9% |
|
-4.5%
(-13.2, 4.2) |
Extension Phase* |
n=10 |
n=8 |
Month 0 |
1.94 |
1.60 |
Month 12 Change (L) |
-0.05 |
-0.01 |
Month 12 % Change |
-0.7% |
-0.8% |
*All patients received Zavesca 100 mg three times daily
monotherapy from Month 6 to Month 12. |
Spleen volume results from Study 3 and extension are
summarized in Table 8:
Table 8: Spleen Volume Changes from Study 3 and Extension Phase
|
Imiglucerase alone |
Zavesca alone |
Study 3 |
n=8 |
n=7 |
Month 0 |
0.61 |
0.69 |
Month 6 Change (L) |
-0.02 |
-0.03 |
Month 6 % Change |
-2.1% |
-4.8% |
Adjusted % Difference from Imiglucerase (95% CI) |
|
-5.8%
(-22.1, 10.5) |
Extension Phase* |
n=7 |
n=6 |
Month 0 |
0.83 |
0.57 |
Month 12 Change (L) |
0.04 |
-0.05 |
Month 12 % Change |
1.5% |
-6.1% |
* All patients received Zavesca 100 mg three times daily
monotherapy from Month 6 to Month 12. |
Hemoglobin concentration results from Study 3 and
extension are summarized in Table 9:
Table 9: Hemoglobin Concentration Changes from Study 3
and Extension Phase
|
Imiglucerase alone |
Zavesca alone |
Study 3 |
n=12 |
n=10 |
Month 0 |
13.18 |
12.44 |
Month 6 Change (g/dL) |
-0.15 |
-0.31 |
Month 6 % Change |
-1.2% |
-2.4% |
Adjusted % Difference from Imiglucerase (95% CI) |
|
-1.9%
(-6.4, 2.6) |
Extension Phase* |
n=10 |
n=9 |
Month 0 |
13.39 |
12.46 |
Month 12 Change (g/dL) |
-0.48 |
-0.13 |
Month 12 % Change |
-3.1% |
-1.1% |
* All patients received Zavesca 100 mg three times daily
monotherapy from Month 6 to Month 12. |
Platelet count results from Study 3 and extension are
summarized in Table 10:
Table 10: Platelet Count Changes from Study 3 and
Extension Phase
|
Imiglucerase alone |
Zavesca alone |
Study 3 |
n=12 |
n=10 |
Month 0 |
165.75 |
170.55 |
Month 6 Change (109/L) |
15.29 |
-21.60 |
Month 6 % Change |
10.1% |
-9.6% |
Adjusted % Difference from Imiglucerase (95% CI) |
|
-17.1% (-32.9, -1.3) |
Extension Phase* |
n=10 |
n=9 |
Month 0 |
170.05 |
184.83 |
Month 12 Change (109/L) |
-3.75 |
-27.39 |
Month 12 % Change |
-3.2% |
-10.4% |
* All patients received Zavesca 100 mg three times daily
monotherapy from Month 6 to Month 12. |
Patients with platelet counts above 150 x 109/L
at baseline who were randomized to Zavesca treatment had significant decreases
in platelet counts at Month 12.