Mechanism of Action
Although the etiology of cognitive impairment in Alzheimer's disease (AD) is not fully understood, it has been reported that acetylcholine-producing neurons degenerate in the brains of patients with Alzheimer's disease.The degree of this cholinergic loss has been correlated with degree of cognitive impairment and density of amyloid plaques (a neuropathological hallmark of Alzheimer's disease).
Galantamine, a tertiary alkaloid, is a competitive and reversible inhibitor of acetylcholinesterase. While the precise mechanism of galantamine's action is unknown, it is postulated to exert its therapeutic effect by enhancing cholinergic function. This is accomplished by increasing the concentration of acetylcholine through reversible inhibition of its hydrolysis by cholinesterase. If this mechanism is correct, galantamine's effect may lessen as the disease process advances and fewer cholinergic neurons remain functionally intact. There is no evidence that galantamine alters the course of the underlying dementing process.
Pharmacokinetics
Galantamine is well absorbed with absolute oral bioavailability of about 90%.
It has a terminal elimination half-life of about 7 hours and pharmacokinetics
are linear over the range of 8-32 mg/day.
The maximum inhibition of acetylcholinesterase activity of about 40% was achieved
about one hour after a single oral dose of 8 mg galantamine in healthy male
subjects.
Absorption and Distribution
Galantamine is rapidly and completely absorbed with time to peak concentration
about 1 hour. Bioavailability of the tablet was the same as the bioavailability
of an oral solution. Food did not affect the AUC of galantamine but Cmax decreased
by 25% and Tmax was delayed by 1.5 hours. The mean volume of distribution of
galantamine is 175 L.
The plasma protein binding of galantamine is 18% at therapeutically relevant
concentrations. In whole blood, galantamine is mainly distributed to blood cells
(52.7%). The blood to plasma concentration ratio of galantamine is 1.2.
Metabolism and Elimination
Galantamine is metabolized by hepatic cytochrome P450 enzymes, glucuronidated,
and excreted unchanged in the urine. In vitro studies indicate that cytochrome
CYP2D6 and CYP3A4 were the major cytochrome P450 isoenzymes involved in the
metabolism of galantamine, and inhibitors of both pathways increase oral bioavailability
of galantamine modestly (see PRECAUTIONS: DRUG
INTERACTIONS). O-demethylation, mediated by CYP2D6 was greater in extensive
metabolizers of CYP2D6 than in poor metabolizers. In plasma from both poor and
extensive metabolizers, however, unchanged galantamine and its glucuronide accounted
for most of the sample radioactivity.
In studies of oral 3H-galantamine, unchanged galantamine and its
glucuronide, accounted for most plasma radioactivity in poor and extensive CYP2D6
metabolizers. Up to 8 hours post-dose, unchanged galantamine accounted for 39-77%
of the total radioactivity in the plasma, and galantamine glucuronide for 14-24%.
By 7 days, 93-99% of the radioactivity had been recovered, with about 95% in
urine and about 5% in the feces. Total urinary recovery of unchanged galantamine
accounted for, on average, 32% of the dose and that of galantamine glucuronide
for another 12% on average.
After i.v. or oral administration, about 20% of the dose was excreted as unchanged galantamine in the urine in 24 hours, representing a renal clearance of about 65 mL/min, about 20-25% of the total plasma clearance of about 300 mL/min.
RAZADYNE® ER 24 mg Extended-Release Capsules administered once daily under
fasting conditions are bioequivalent to RAZADYNE® Tablets 12 mg twice daily
with respect to AUC24h and Cmin. The Cmax and Tmax of the extended-release
capsules were lower and occurred later, respectively, compared with the immediate-release
tablets, with Cmax about 25% lower and median Tmax occurring about 4.5 – 5.0
hours after dosing. Dose-proportionality is observed for RAZADYNE® ER Extended-Release
Capsules over the dose range of 8 to 24 mg daily and steady state is achieved
within a week. There was no effect of age on the pharmacokinetics of RAZADYNE®
ER Extended-Release Capsules. CYP2D6 poor metabolizers had drug exposures that
were approximately 50% higher than for extensive metabolizers.
There are no appreciable differences in pharmacokinetic parameters when RAZADYNE® ER Extended-Release Capsules are given with food compared to when they are given in the fasted state.
Special Populations
CYP2D6 Poor Metabolizers
Approximately 7% of the normal population has a genetic variation that leads
to reduced levels of activity of CYP2D6 isozyme. Such individuals have been
referred to as poor metabolizers. After a single oral dose of 4 mg or 8 mg galantamine,
CYP2D6 poor metabolizers demonstrated a similar Cmax and about 35% AUC&inifn;
increase of unchanged galantamine compared to extensive metabolizers.
A total of 356 patients with Alzheimer's disease enrolled in two Phase 3 studies were genotyped with respect to CYP2D6 (n=210 hetero-extensive metabolizers, 126 homo-extensive metabolizers, and 20 poor metabolizers). Population pharmacokinetic analysis indicated that there was a 25% decrease in median clearance in poor metabolizers compared to extensive metabolizers. Dosage adjustment is not necessary in patients identified as poor metabolizers as the dose of drug is individually titrated to tolerability.
Hepatic Impairment
Following a single 4 mg dose of galantamine tablets, the pharmacokinetics of
galantamine in subjects with mild hepatic impairment (n=8; Child-Pugh score
of 5-6) were similar to those in healthy subjects. In patients with moderate
hepatic impairment (n=8; Child-Pugh score of 7-9), galantamine clearance was
decreased by about 25% compared to normal volunteers. Exposure would be expected
to increase further with increasing degree of hepatic impairment (see PRECAUTIONS
and DOSAGE AND ADMINISTRATION).
Renal Impairment
Following a single 8 mg dose of galantamine tablets, AUC increased by 37% and
67% in moderate and severely renal-impaired patients compared to normal volunteers
(see PRECAUTIONS and DOSAGE AND ADMINISTRATION).
Elderly
Data from clinical trials in patients with Alzheimer's disease indicate that
galantamine concentrations are 30-40% higher than in healthy young subjects.
Gender and Race
No specific pharmacokinetic study was conducted to investigate the effect of
gender and race on the disposition of RAZADYNE®, but a population pharmacokinetic
analysis indicates (n= 539 males and 550 females) that galantamine clearance
is about 20% lower in females than in males (explained by lower body weight
in females) and race (n=1029 White, 24 Black, 13 Asian and 23 other) did not
affect the clearance of RAZADYNE®.
Drug-Drug Interactions
(see also PRECAUTIONS: DRUG INTERACTIONS)
Multiple metabolic pathways and renal excretion are involved in the elimination
of galantamine so no single pathway appears predominant. Based on in vitro
studies, CYP2D6 and CYP3A4 were the major enzymes involved in the metabolism
of galantamine. CYP2D6 was involved in the formation of O-desmethyl-galantamine,
whereas CYP3A4 mediated the formation of galantamine-N-oxide. Galantamine is
also glucuronidated and excreted unchanged in urine.
Effect of Other Drugs on the Metabolism of RAZADYNE®
Drugs that are potent inhibitors for CYP2D6 or CYP3A4 may increase the AUC
of galantamine. Multiple dose pharmacokinetic studies demonstrated that the
AUC of galantamine increased 30% and 40%, respectively, during co-administration
of ketoconazole and paroxetine. As co-administered with erythromycin, another
CYP3A4 inhibitor, the galantamine AUC increased only 10%. Population PK analysis
with a database of 852 patients with Alzheimer's disease showed that the clearance
of galantamine was decreased about 25-33% by concurrent administration of amitriptyline
(n = 17), fluoxetine (n = 48), fluvoxamine (n = 14), and quinidine (n = 7),
known inhibitors of CYP2D6.
Concurrent administration of H2-antagonists demonstrated that ranitidine
did not affect the pharmacokinetics of galantamine, and cimetidine increased
the galantamine AUC by approximately 16%.
A multiple dose pharmacokinetic study with concurrent administration of memantine,
an N-methyl-D-aspartate (NMDA) receptor antagonist, demonstrated that co-administration
of memantine in a dose of 10 mg BID did not affect the pharmacokinetic profile
of galantamine (16 mg daily) at steady state.
Effect of RAZADYNE® on the Metabolism of Other Drugs
In vitro studies show that galantamine did not inhibit the metabolic
pathways catalyzed by CYP1A2, CYP2A6, CYP3A4, CYP4A, CYP2C, CYP2D6 and CYP2E1.
This indicated that the inhibitory potential of galantamine towards the major
forms of cytochrome P450 is very low. Multiple doses of galantamine (24 mg/day)
had no effect on the pharmacokinetics of digoxin and warfarin (R- and S- forms).
Galantamine had no effect on the increased prothrombin time induced by warfarin.
Clinical Trials
The effectiveness of RAZADYNE® ER/RAZADYNE® (galantamine hydrobromide)
as a treatment for Alzheimer's disease is demonstrated by the results of 5 randomized,
double-blind, placebo-controlled clinical investigations in patients with probable
Alzheimer's disease, 4 with the immediate-release tablet and 1 with the extended-release
capsule [diagnosed by NINCDS-ADRDA criteria, with Mini-Mental State Examination
scores that were ≥ 10 and ≤ 24]. Doses studied with the tablet formulation
were 8-32 mg/day given as twice daily doses. In 3 of the 4 studies with the
tablet, patients were started on a low dose of 8 mg, then titrated weekly by
8 mg/day to 24 or 32 mg as assigned. In the fourth study (USA 4-week Dose-Escalation
Fixed-Dose Study) dose escalation of 8 mg/day occurred over 4 week intervals.
The mean age of patients participating in these 4 RAZADYNE® trials was 75
years with a range of 41 to 100. Approximately 62% of patients were women and
38% were men. The racial distribution was White 94%, Black 3% and other races
3%. Two other studies examined a three times daily dosing regimen; these also
showed or suggested benefit but did not suggest an advantage over twice daily
dosing.
Study Outcome Measures
In each study, the primary effectiveness of RAZADYNE® was evaluated using a dual outcome assessment strategy as measured by the Alzheimer's Disease Assessment Scale (ADAS-cog) and the Clinician's Interview Based Impression of Change that required the use of caregiver information (CIBIC-plus).
The ability of RAZADYNE® to improve cognitive performance was assessed
with the cognitive sub-scale of the Alzheimer's Disease Assessment Scale (ADAS-cog),
a multi-item instrument that has been extensively validated in longitudinal
cohorts of Alzheimer's disease patients. The ADAS-cog examines selected aspects
of cognitive performance including elements of memory, orientation, attention,
reasoning, language and praxis. The ADAS-cog scoring range is from 0 to 70,
with higher scores indicating greater cognitive impairment. Elderly normal adults
may score as low as 0 or 1, but it is not unusual for non-demented adults to
score slightly higher.
The patients recruited as participants in each study using the tablet formulation
had mean scores on ADAS-cog of approximately 27 units, with a range from 5 to
69. Experience gained in longitudinal studies of ambulatory patients with mild
to moderate Alzheimer's disease suggests that they gain 6 to 12 units a year
on the ADAS-cog. Lesser degrees of change, however, are seen in patients with
very mild or very advanced disease because the ADAS-cog is not uniformly sensitive
to change over the course of the disease. The annualized rate of decline in
the placebo patients participating in RAZADYNE® trials was approximately
4.5 units per year.
The ability of RAZADYNE® to produce an overall clinical effect was assessed
using a Clinician's Interview Based Impression of Change that required the use
of caregiver information, the CIBIC-plus.The CIBIC-plus is not a single instrument
and is not a standardized instrument like the ADAS-cog. Clinical trials for
investigational drugs have used a variety of CIBIC formats, each different in
terms of depth and structure. As such, results from a CIBIC-plus reflect clinical
experience from the trial or trials in which it was used and cannot be compared
directly with the results of CIBIC-plus evaluations from other clinical trials.
The CIBIC-plus used in the trials was a semi-structured instrument based on
a comprehensive evaluation at baseline and subsequent time-points of 4 major
areas of patient function: general, cognitive, behavioral and activities of
daily living. It represents the assessment of a skilled clinician based on his/her
observation at an interview with the patient, in combination with information
supplied by a caregiver familiar with the behavior of the patient over the interval
rated. The CIBIC-plus is scored as a seven point categorical rating, ranging
from a score of 1, indicating “markedly improved,” to a score of 4, indicating
“no change” to a score of 7, indicating “marked worsening.” The CIBIC-plus has
not been systematically compared directly to assessments not using information
from caregivers (CIBIC) or other global methods.
Immediate-Release Tablets
U.S.Twenty-One Week Fixed-Dose Study
In a study of 21 weeks duration, 978 patients were randomized to doses of 8, 16, or 24 mg of RAZADYNE® per day, or to placebo, each given in 2 divided doses. Treatment was initiated at 8 mg/day for all patients randomized to RAZADYNE®, and increased by 8 mg/day every 4 weeks. Therefore, the maximum titration phase was 8 weeks and the minimum maintenance phase was 13 weeks (in patients randomized to 24 mg/day of RAZADYNE®).
Effects on the ADAS-cog
Figure 1 illustrates the time course for the change from baseline in ADAS-cog scores for all four dose groups over the 21 weeks of the study. At 21 weeks of treatment, the mean differences in the ADAS-cog change scores for the RAZADYNE®-treated patients compared to the patients on placebo were 1.7, 3.3, and 3.6 units for the 8, 16 and 24 mg/day treatments, respectively. The 16 mg/day and 24 mg/day treatments were statistically significantly superior to placebo and to the 8 mg/day treatment. There was no statistically significant difference between the 16 mg/day and 24 mg/day dose groups.
Figure 1: Time-Course of the Change From Baseline in ADAS-cog
Score for Patients Completing 21 Weeks (5 Months) of Treatment
Figure 2 illustrates the cumulative percentages of patients from each of the four treatment groups who had attained at least the measure of improvement in ADAS-cog score shown on the X-axis. Three change scores (10-point, 7-point and 4-point reductions) and no change in score from baseline have been identified for illustrative purposes, and the percent of patients in each group achieving that result is shown in the inset table.
The curves demonstrate that both patients assigned to galantamine and placebo have a wide range of responses, but that the RAZADYNE® groups are more likely to show the greater improvements.
Figure 2: Cumulative Percentage of Patients Completing 21
Weeks of Double-Blind Treatment With Specified Changes From Baseline in ADAS-cog
Scores. The Percentages of Randomized Patients Who Completed the Study Were:
Placebo 84%, 8 mg/day 77%, 16 mg/day 78% and 24 mg/day 78%.
| |
Change in ADAS-cog |
| Treatment |
-10 |
-7 |
-4 |
0 |
| Placebo |
3.6% |
7.6% |
19.6% |
41.8% |
| 8 mg/day |
5.9% |
13.9% |
25.7% |
46.5% |
| 16 mg/day |
7.2% |
15.9% |
35.6% |
65.4% |
| 24 mg/day |
10.4% |
22.3% |
37.0% |
64.9% |
Effects on the CIBIC-plus
Figure 3 is a histogram of the percentage distribution of CIBIC-plus scores
attained by patients assigned to each of the four treatment groups who completed
21 weeks of treatment. The RAZADYNE®-placebo differences for these groups
of patients in mean rating were 0.15, 0.41 and 0.44 units for the 8, 16 and
24 mg/day treatments, respectively. The 16 mg/day and 24 mg/day treatments were
statistically significantly superior to placebo. The differences vs. the 8 mg/day
treatment for the 16 and 24 mg/day treatments were 0.26 and 0.29, respectively.
There were no statistically significant differences between the 16 mg/day and
24 mg/day dose groups.
Figure 3: Distribution of CIBIC-plus Ratings at Week 21
U.S.Twenty-Six Week Fixed-Dose Study
In a study of 26 weeks duration, 636 patients were randomized to either a dose of 24 mg or 32 mg of RAZADYNE® (galantamine hydrobromide) per day, or to placebo, each given in two divided doses. The 26-week study was divided into a 3-week dose titration phase and a 23-week maintenance phase.
Effects on the ADAS-cog
Figure 4 illustrates the time course for the change from baseline in ADAS-cog scores for all three dose groups over the 26 weeks of the study. At 26 weeks of treatment, the mean differences in the ADAS-cog change scores for the RAZADYNE®- treated patients compared to the patients on placebo were 3.9 and 3.8 units for the 24 mg/day and 32 mg/day treatments, respectively. Both treatments were statistically significantly superior to placebo, but were not significantly different from each other.
Figure 4: Time-Course of the Change From Baseline in ADAS-cog
Score for Patients Completing 26 Weeks of Treatment
Figure 5 illustrates the cumulative percentages of patients from each of the three treatment groups who had attained at least the measure of improvement in ADAS-cog score shown on the X-axis. Three change scores (10-point, 7-point and 4-point reductions) and no change in score from baseline have been identified for illustrative purposes, and the percent of patients in each group achieving that result is shown in the inset table.
The curves demonstrate that both patients assigned to RAZADYNE® and placebo have a wide range of responses, but that the RAZADYNE® groups are more likely to show the greater improvements. A curve for an effective treatment would be shifted to the left of the curve for placebo, while an ineffective or deleterious treatment would be superimposed upon, or shifted to the right of the curve for placebo, respectively.
Figure 5: Cumulative Percentage of Patients Completing 26
Weeks of Double-Blind Treatment With Specified Changes From Baseline in ADAS-cog
Scores.The Percentages of Randomized Patients Who Completed the Study Were:
Placebo 81%, 24 mg/day 68%, and 32 mg/day 58%.
| |
Change in ADAS-cog |
| Treatment |
-10 |
-7 |
-4 |
0 |
| Placebo |
2.1% |
5.7% |
16.6% |
43.9% |
| 24 mg/day |
7.6% |
18.3% |
33.6% |
64.1% |
| 32 mg/day |
11.1% |
19.7% |
33.3% |
58.1% |
Effects on the CIBIC-plus
Figure 6 is a histogram of the percentage distribution of CIBIC-plus scores attained by patients assigned to each of the three treatment groups who completed 26 weeks of treatment. The mean RAZADYNE®-placebo differences for these groups of patients in the mean rating were 0.28 and 0.29 units for 24 and 32 mg/day of RAZADYNE®, respectively. The mean ratings for both groups were statistically significantly superior to placebo, but were not significantly different from each other.
Figure 6: Distribution of CIBIC-plus Ratings at Week 26
International Twenty-Six Week Fixed-Dose Study
In a study of 26 weeks duration identical in design to the USA 26-Week Fixed-Dose
Study, 653 patients were randomized to either a dose of 24 mg or 32 mg of RAZADYNE®
(galantamine hydrobromide) per day, or to placebo, each given in two divided
doses.The 26-week study was divided into a 3-week dose titration phase and a
23-week maintenance phase.
Effects on the ADAS-cog
Figure 7 illustrates the time course for the change from baseline in ADAS-cog scores for all three dose groups over the 26 weeks of the study. At 26 weeks of treatment, the mean differences in the ADAS-cog change scores for the RAZADYNE®- treated patients compared to the patients on placebo were 3.1 and 4.1 units for the 24 mg/day and 32 mg/day treatments, respectively. Both treatments were statistically significantly superior to placebo, but were not significantly different from each other.
Figure 7: Time-Course of the Change From Baseline in ADAS-cog
Score for Patients Completing 26 Weeks of Treatment
Figure 8 illustrates the cumulative percentages of patients from each of the three treatment groups who had attained at least the measure of improvement in ADAS-cog score shown on the X-axis. Three change scores (10-point, 7-point and 4-point reductions) and no change in score from baseline have been identified for illustrative purposes, and the percent of patients in each group achieving that result is shown in the inset table.
The curves demonstrate that both patients assigned to RAZADYNE® and placebo have a wide range of responses, but that the RAZADYNE® groups are more likely to show the greater improvements.
Figure 8: Cumulative Percentage of Patients Completing 26
Weeks of Double-Blind Treatment With Specified Changes From Baseline in ADAS-cog
Scores.The Percentages of Randomized Patients Who Completed the Study Were:
Placebo 87%, 24 mg/day 80%, and 32 mg/day 75%.
| |
Change in ADAS-cog |
| Treatment |
-10 |
-7 |
-4 |
0 |
| Placebo |
1.2% |
5.8% |
15.2% |
39.8% |
| 24 mg/day |
4.5% |
15.4% |
30.8% |
65.4% |
| 32 mg/day |
7.9% |
19.7% |
34.9% |
63.8% |
Effects on the CIBIC-plus
Figure 9 is a histogram of the percentage distribution of CIBIC-plus scores attained by patients assigned to each of the three treatment groups who completed 26 weeks of treatment. The mean RAZADYNE®-placebo differences for these groups of patients in the mean rating of change from baseline were 0.34 and 0.47 for 24 and 32 mg/day of RAZADYNE®, respectively.The mean ratings for the RAZADYNE® groups were statistically significantly superior to placebo, but were not significantly different from each other.
Figure 9: Distribution of CIBIC-plus Rating at Week 26
International Thirteen-Week Flexible-Dose Study
In a study of 13 weeks duration, 386 patients were randomized to either a flexible
dose of 24-32 mg/day of RAZADYNE® or to placebo, each given in two divided
doses. The 13-week study was divided into a 3-week dose titration phase and
a 10-week maintenance phase. The patients in the active treatment arm of the
study were maintained at either 24 mg/day or 32 mg/day at the discretion of
the investigator.
Effects on theADAS-cog
Figure 10 illustrates the time course for the change from baseline in ADAS-cog scores for both dose groups over the 13 weeks of the study. At 13 weeks of treatment, the mean difference in the ADAS-cog change scores for the treated patients compared to the patients on placebo was 1.9. RAZADYNE® at a dose of 24-32 mg/day was statistically significantly superior to placebo.
Figure 10: Time-Course of the Change From Baseline in ADAS-cog
Score for Patients Completing 13 Weeks of Treatment
Figure 11 illustrates the cumulative percentages of patients from each of the two treatment groups who had attained at least the measure of improvement in ADAS-cog score shown on the X-axis. Three change scores (10-point, 7-point and 4-point reductions) and no change in score from baseline have been identified for illustrative purposes, and the percent of patients in each group achieving that result is shown in the inset table.
The curves demonstrate that both patients assigned to RAZADYNE® and placebo have a wide range of responses, but that the RAZADYNE® group is more likely to show the greater improvement.
Figure 11: Cumulative Percentage of Patients Completing 13
Weeks of Double-Blind Treatment With Specified Changes from Baseline in ADAS-cog
Scores. The Percentages of Randomized Patients Who Completed the Study Were:
Placebo 90%, 24-32 mg/day 67%.
| |
Change in ADAS-cog |
| Treatment |
-10 |
-7 |
-4 |
0 |
| Placebo |
1.9% |
5.6% |
19.4% |
50.0% |
| 24 or 32 mg/day |
7.1% |
18.8% |
32.9% |
65.3% |
Effects on the CIBIC-plus
Figure 12 is a histogram of the percentage distribution of CIBIC-plus scores attained by patients assigned to each of the two treatment groups who completed 13 weeks of treatment. The mean RAZADYNE®-placebo differences for the group of patients in the mean rating of change from baseline were 0.37 units. The mean rating for the 24-32 mg/day group was statistically significantly superior to placebo.
Figure 12: Distribution of CIBIC-plus Ratings at Week 13
Age, Gender and Race: Patient's age, gender, or race did not
predict clinical outcome of treatment.
Extended-Release Capsules
The efficacy of RAZADYNE® ER Extended-Release Capsules was studied in a randomized, double-blind, placebo-controlled trial which was 6 months in duration, and had an initial 4-week dose-escalation phase. In this trial, patients were assigned to one of 3 treatment groups: RAZADYNE® ER in a flexible dose of 16 to 24 mg once daily; RAZADYNE® Tablets in a flexible dose of 8 to 12 mg twice daily; and placebo. The primary efficacy measures in this study were the ADAS-cog and CIBIC-plus. On the protocol-specified primary efficacy analysis at Month 6, a statistically significant improvement favoring RAZADYNE® ER over placebo was seen for the ADAS-cog, but not for the CIBIC-plus. RAZADYNE® ER showed a statistically significant improvement when compared with placebo on the Alzheimer's Disease Cooperative Study-Activities of Daily Living (ADCS-ADL) scale, a measure of function, and a secondary efficacy measure in this study. The effects of both RAZADYNE® ER Capsules and RAZADYNE®Tablets on the ADAS-cog, CIBIC-plus, and ADCS-ADL were similar in this study.
Last updated on RxList: 1/20/2009