CLINICAL PHARMACOLOGY
Mechanism Of Action
Although the precise mechanism of action of rivastigmine
is unknown, it is thought 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. The effect of rivastigmine may lessen as the disease process
advances and fewer cholinergic neurons remain functionally intact. There is no
evidence that rivastigmine alters the course of the underlying dementing
process.
Pharmacodynamics
After a 6-mg oral dose of rivastigmine in humans,
anticholinesterase activity is present in cerebrospinal fluid for about 10
hours, with a maximum inhibition of about 60% 5 hours after dosing.
In vitro and in vivo studies demonstrate that the
inhibition of cholinesterase by rivastigmine is not affected by the concomitant
administration of memantine, an N-methyl-D-aspartate receptor antagonist.
Pharmacokinetics
Absorption
After the initial application of EXELON PATCH, there is a
lag time of 0.5 to 1 hour in the absorption of rivastigmine. Concentrations
then rise slowly typically reaching a maximum after 8 hours, although maximum values
(Cmax) can also occur later (at 10 to 16 hours). After the peak, plasma
concentrations slowly decrease over the remainder of the 24-hour period of
application. At steady state, trough levels are approximately 60% to 80% of
peak levels.
EXELON PATCH 9.5 mg/24 hours gave exposure approximately
the same as that provided by an oral dose of 6 mg twice daily (i.e., 12
mg/day). Inter-subject variability in exposure was lower (43% to 49%) for the
EXELON PATCH formulation as compared with the oral formulations (73% to 103%).
Fluctuation (between Cmax and Cmin) is less for EXELON PATCH than for the oral
formulation of rivastigmine.
Figure 2 displays rivastigmine plasma concentrations over
24 hours for the 3 available patch strengths.
Figure 2: Rivastigmine Plasma Concentrations Following
Dermal 24-Hour Patch Application
Over a 24-hour dermal application, approximately 50% of
the drug content of the patch is released from the system.
Exposure (AUC∞) to rivastigmine (and metabolite
NAP266-90) was highest when the patch was applied to the upper back, chest, or
upper arm. Two other sites (abdomen and thigh) could be used if none of the 3
other sites is available, but the practitioner should be aware that the
rivastigmine plasma exposure associated with these sites was approximately 20%
to 30% lower.
There was no relevant accumulation of rivastigmine or the
metabolite NAP226-90 in plasma in patients with Alzheimer's disease with daily
dosing.
The pharmacokinetic profile of rivastigmine transdermal
patches was comparable in patients with Alzheimer's disease and in patients
with dementia associated with Parkinson's disease.
Distribution
Rivastigmine is weakly bound to plasma proteins
(approximately 40%) over the therapeutic range. It readily crosses the
blood-brain barrier, reaching CSF peak concentrations in 1.4 to 2.6 hours. It
has an apparent volume of distribution in the range of 1.8 to 2.7 L/kg.
Metabolism
Rivastigmine is extensively metabolized primarily via
cholinesterase-mediated hydrolysis to the decarbamylated metabolite NAP226-90.
In vitro, this metabolite shows minimal inhibition of acetylcholinesterase
( < 10%). Based on evidence from in vitro and animal studies, the major
cytochrome P450 isoenzymes are minimally involved in rivastigmine metabolism.
The metabolite-to-parent AUC∞ ratio was about 0.7
after EXELON PATCH application versus 3.5 after oral administration, indicating
that much less metabolism occurred after dermal treatment. Less NAP226-90 is
formed following patch application, presumably because of the lack of
presystemic (hepatic first pass) metabolism. Based on in vitro studies, no
unique metabolic routes were detected in human skin.
Elimination
Renal excretion of the metabolites is the major route of
elimination. Unchanged rivastigmine is found in trace amounts in the urine.
Following administration of 14C-rivastigmine, renal elimination was rapid and
essentially complete ( > 90%) within 24 hours. Less than 1% of the
administered dose is excreted in the feces. The apparent elimination half-life
in plasma is approximately 3 hours after patch removal. Renal clearance was
approximately 2.1 to 2.8 L/hr.
Age
Age had no impact on the exposure to rivastigmine in
Alzheimer's disease patients treated with EXELON PATCH.
Gender and Race
No specific pharmacokinetic study was conducted to
investigate the effect of gender and race on the disposition of EXELON PATCH. A
population pharmacokinetic analysis of oral rivastigmine indicated that neither
gender (n=277 males and 348 females) nor race (n=575 Caucasian, 34 Black, 4
Asian, and 12 Other) affected clearance of the drug. Similar results were seen
with analyses of pharmacokinetic data obtained after the administration of EXELON
PATCH.
Body Weight
A relationship between drug exposure at steady state
(rivastigmine and metabolite NAP226-90) and body weight was observed in
Alzheimer's dementia patients. Rivastigmine exposure is higher in subjects with
low body weight. Compared to a patient with a body weight of 65 kg, the
rivastigmine steady-state concentrations in a patient with a body weight of 35
kg would be approximately doubled, while for a patient with a body weight of 100
kg the concentrations would be approximately halved [see DOSAGE AND
ADMINISTRATION].
Renal Impairment
No study was conducted with EXELON PATCH in subjects with
renal impairment. Based on population analysis creatinine clearance did not
show any clear effect on steady state concentrations of rivastigmine or its
metabolite..
Hepatic Impairment
No pharmacokinetic study was conducted with EXELON PATCH
in subjects with hepatic impairment. Following a single 3-mg dose, mean oral
clearance of rivastigmine was 60% lower in hepatically impaired patients (n=10,
biopsy proven) than in healthy subjects (n=10). After multiple 6-mg twice a day
oral dosing, the mean clearance of rivastigmine was 65% lower in mild (n=7,
Child-Pugh score 5 to 6) and moderate (n=3, Child-Pugh score 7 to 9)
hepatically impaired patients (biopsy proven, liver cirrhosis) than in healthy
subjects (n=10). [see DOSAGE AND ADMINISTRATION, Specific Population].
Smoking
Following oral rivastigmine administration (up to 12
mg/day) with nicotine use, population pharmacokinetic analysis showed increased
oral clearance of rivastigmine by 23% (n=75 smokers and 549 nonsmokers).
Drug Interaction Studies
No specific interaction studies have been conducted with
EXELON PATCH. Information presented below is from studies with oral rivastigmine.
Effect of Rivastigmine on the Metabolism of Other
Drugs
Rivastigmine is primarily metabolized through hydrolysis
by esterases. Minimal metabolism occurs via the major cytochrome P450
isoenzymes. Based on in vitro studies, no pharmacokinetic drug interactions
with drugs metabolized by the following isoenzyme systems are expected: CYP1A2,
CYP2D6, CYP3A4/5, CYP2E1, CYP2C9, CYP2C8, CYP2C19, or CYP2B6.
No pharmacokinetic interaction was observed between
rivastigmine taken orally and digoxin, warfarin, diazepam or fluoxetine in
studies in healthy volunteers. The increase in prothrombin time induced by
warfarin is not affected by administration of rivastigmine.
Effect of Other Drugs on the Metabolism of
Rivastigmine
Drugs that induce or inhibit CYP450 metabolism are not
expected to alter the metabolism of rivastigmine.
Population pharmacokinetic analysis with a database of
625 patients showed that the pharmacokinetics of rivastigmine taken orally were
not influenced by commonly prescribed medications such as antacids (n=77), antihypertensives
(n=72), beta-blockers (n=42), calcium channel blockers (n=75), antidiabetics
(n=21), nonsteroidal anti-inflammatory drugs (n=79), estrogens (n=70),
salicylate analgesics (n=177), antianginals (n=35), and antihistamines (n=15).
Clinical Studies
The effectiveness of the EXELON PATCH in dementia of the
Alzheimer's type and dementia associated with Parkinson's disease was based on
the results of 3 controlled trials of EXELON PATCH in patients with Alzheimer's
disease (Studies 1, 2, and 3) (see below); 3 controlled trials of oral
rivastigmine in patients with dementia of the Alzheimer's type; and 1
controlled trial of oral rivastigmine in patients with dementia associated with
Parkinson's disease. See the prescribing information for oral rivastigmine for
details of the four studies of oral rivastigmine.
Mild to Moderate Alzheimer's Disease
International 24-Week Study of EXELON PATCH in
Dementia of the Alzheimer's Type (Study 1)
This study was a randomized double-blind, double dummy
clinical investigation in patients with Alzheimer's disease [diagnosed by
NINCDS-ADRDA and DSM-IV criteria, Mini-Mental Status Examination (MMSE) score ≥ 10
and &e;20] (Study 1). The mean age of patients participating in this trial
was 74 years with a range of 50 to 90 years. Approximately 67% of patients were
women, and 33% were men. The racial distribution was Caucasian 75%, Black 1%,
Asian 9%, and other races 15%.
The effectiveness of the EXELON PATCH was evaluated in
Study 1 using a dual outcome assessment strategy, evaluating for changes in
both cognitive performance and overall clinical effect.
The ability of the EXELON PATCH to improve cognitive
performance was assessed with the cognitive subscale 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 ability of the EXELON PATCH to produce an overall
clinical effect was assessed using the Alzheimer's Disease Cooperative
Study-Clinical Global Impression of Change (ADCS-CGIC). The ADCS-CGIC is a more
standardized form of the Clinician's Interview-Based Impression Of Change-Plus
(CIBIC-Plus) and is also scored as a 7-point categorical rating; scores range
from 1, indicating “markedly improved,” to 4, indicating “no change,” to 7,
indicating “marked worsening.”
In Study 1, 1195 patients were randomized to 1 of the
following 4 treatments: EXELON PATCH 9.5 mg/24 hours, EXELON PATCH 17.4 mg/24
hours, EXELON Capsules in a dose of 6 mg twice daily, or placebo. This 24-week
study was divided into a 16-week titration phase followed by an 8-week
maintenance phase. In the active treatment arms of this study, doses below the
target dose were permitted during the maintenance phase in the event of poor
tolerability.
Figure 3 illustrates the time course for the change from
baseline in ADAS-Cog scores for all 4 treatment groups over the 24-week study.
At 24 weeks, the mean differences in the ADAS-Cog change scores for the
EXELONtreated patients compared to the patients on placebo, were 1.8, 2.9, and
1.8 units for the EXELON PATCH 9.5 mg/24 hours, EXELON PATCH 17.4 mg/24 hours,
and EXELON Capsule 6 mg twice daily groups, respectively. The difference
between each of these groups and placebo was statistically significant.
Although a slight improvement was observed with the 17.4 mg/24 hours patch
compared to the 9.5 mg/24 hours patch on this outcome measure, no meaningful
difference between the two was seen on the global evaluation (see Figure 4).
Figure 3: Time Course of the Change from Baseline in
ADAS-Cog Score for Patients Observed at Each Time Point in Study 1
Figure 4 presents the distribution of patients' scores on
the ADCS-CGIC for all 4 treatment groups. At 24 weeks, the mean difference in
the ADCS-CGIC scores for the comparison of patients in each of the
EXELON-treated groups with the patients on placebo was 0.2 units. The
difference between each of these groups and placebo was statistically
significant.
Figure 4: Distribution of ADCS-CGIC Scores for
Patients Completing Study 1
International 48-Week Study of EXELON PATCH in Dementia
of the Alzheimer's Type (Study 2)
This study was a randomized double-blind clinical
investigation in patients with Alzheimer's disease [diagnosed by NINCDS-ADRDA
and DSM-IV criteria, Mini-Mental State Examination (MMSE) score ≥ 10 and
&e;24] (Study 2). The mean age of patients participating in this trial was
76 years with a range of 50 to 85 years. Approximately 65% of patients were
women and 35% were men. The racial distribution was approximately Caucasian
97%, Black 2%, Asian 0.5%, and other races 1%. Approximately 27% of the
patients were taking memantine throughout the entire duration of the study.
Alzheimer's disease patients who received 24 to 48 weeks
open-label treatment with EXELON PATCH 9.5 mg/24 hours and who demonstrated
functional and cognitive decline were randomized into treatment with either EXELON
PATCH 9.5 mg/24 hours or EXELON PATCH 13.3 mg/24 hours in a 48-week,
double-blind treatment phase. Functional decline was assessed by the
investigator and cognitive decline was defined as a decrease in the MMSE score
of ≥ 2 points from the previous visit or a decrease of ≥ 3 points
from baseline.
Study 2 was designed to compare the efficacy of EXELON
PATCH 13.3 mg/ 24 hours versus that of EXELON PATCH 9.5 mg/24 hours during the
48-week, double-blind treatment phase.
The ability of the EXELON PATCH 13.3 mg/24 hours to
improve cognitive performance over that provided by the EXELON PATCH 9.5 mg/24
hours was assessed by the cognitive subscale of the Alzheimer's Disease Assessment
Scale (ADAS-Cog) [see Clinical Studies, International 24-Week Study].
The ability of the EXELON PATCH 13.3 mg/24 hours to
improve overall function versus that provided by EXELON PATCH 9.5 mg/24 hours
was assessed by the instrumental subscale of the Alzheimer's Disease Cooperative
Study Activities of Daily Living (ADCS-IADL). The ADCS-IADL subscale is
composed of items 7 to 23 of the caregiver-based ADCS-ADL scale. The ADCS-IADL
assesses activities such as those necessary for communicating and interacting
with other people, maintaining a household, and conducting hobbies and
interests. A sum score is calculated by adding the scores of the individual
items and can range from 0 to 56, with higher scores indicating less
impairment.
Out of a total of 1584 patients enrolled in the initial
open-label phase of the study, 567 patients were classified as decliners and
were randomized into the 48-week double-blind treatment phase of the study. Two
hundred eightyseven (287) patients entered the 9.5 mg/24 hours EXELON PATCH
treatment group and 280 patients entered the 13.3 mg/24 hours EXELON PATCH
treatment group.
Figure 5 illustrates the time course for the mean change
from double-blind baseline in ADCS-IADL scores for each treatment group over
the course of the 48-week treatment phase of the study. Decline in the mean
ADCSIADL score from the double-blind baseline for the Intent to Treat–Last
Observation Carried Forward (ITT-LOCF) analysis was less at each timepoint in
the 13.3 mg/24 hour EXELON PATCH treatment group than in the 9.5 mg/24 hours
EXELON PATCH treatment group. The 13.3 mg/24 hours dose was statistically
significantly superior to the 9.5mg/24 hours dose at weeks 16, 24, 32, and 48
(primary endpoint).
Figure 6 illustrates the time course for the mean change
from double-blind baseline in ADAS-Cog scores for both treatment groups over
the 48-week treatment phase. The between-treatment group difference for EXELON PATCH
13.3 mg/24 hours versus EXELON PATCH 9.5 mg/24 hours was nominally
statistically significant at week 24 (p=0.027), but not at week 48 (p=0.227),
which was the primary endpoint.
Figure 5: Time Course of the Change from Double-Blind
Baseline in ADCS-IADL Score for Patients Observed at Each Time Point in Study 2
Figure 6: Time Course of the Change from Double-Blind
Baseline in ADAS-Cog Score for Patients Observed at Each Time Point in Study 2
Severe Alzheimer's Disease
24-Week United States Study with EXELON PATCH in
Severe Alzheimer's Disease (Study 3)
This was a 24-week randomized double-blind, clinical
investigation in patients with severe Alzheimer's disease [diagnosed by
NINCDS-ADRDA and DSM-IV criteria, Mini-Mental State Examination (MMSE) score
≥ 3 and &e;12]. The mean age of patients participating in this trial
was 78 years with a range of 51 to 96 years with 62% aged > 75 years.
Approximately 65% of patients were women and 35% were men. The racial
distribution was approximately Caucasian 87%, Black 7%, Asian 1%, and other
races 5%. Patients on a stable dose of memantine were permitted to enter the
study. Approximately 61% of the patients in each treatment group were taking memantine
throughout the entire duration of the study.
The study was designed to compare the efficacy of EXELON
PATCH 13.3 mg/ 24 hours versus that of EXELON PATCH 4.6 mg/24 hours during the
24-week double-blind treatment phase.
The ability of the 13.3 mg/24 hours EXELON PATCH to
improve cognitive performance versus that provided by the 4.6 mg/24 hours
EXELON PATCH was assessed with the Severe Impairment Battery (SIB) which uses a
validated 40-item scale developed for the evaluation of the severity of
cognitive dysfunction in more advanced AD patients. The domains assessed
included social interaction, memory, language, attention, orientation, praxis, visuospatial
ability, construction, and orienting to name. The SIB was scored from 0 to 100,
with higher scores reflecting higher levels of cognitive ability.
The ability of the 13.3 mg/ 24 hours EXELON PATCH to
improve overall function versus that provided by the 4.6 mg/24 hours EXELON
PATCH was assessed with the Alzheimer's Disease Cooperative Study-Activities of
Daily Living–Severe Impairment Version (ADCS-ADL-SIV) which is a
caregiver-based ADL scale composed of 19 items developed for use in clinical
studies of dementia. It is designed to assess the patient's performance of both
basic and instrumental activities of daily living such as those necessary for
personal care, communicating and interacting with other people, maintaining a
household, conducting hobbies and interests, and making judgments and
decisions. A sum score is calculated by adding the scores of the individual
items and can range from 0 to 54, with higher scores indicating less functional
impairment.
In this study, 716 patients were randomized into one of
the following treatments: EXELON PATCH 13.3 mg/24 hours or EXELON PATCH 4.6 mg/24
hours in a 1:1 ratio. This 24-week study was divided into an 8-week titration
phase followed by a 16-week maintenance phase. In the active treatment arms of
this study, temporary dose adjustments below the target dose were permitted
during the titration and maintenance phase in the event of poor tolerability.
Figure 7 illustrates the time course for the mean change
from baseline SIB scores for each treatment group over the course of the
24-week treatment phase of the study. Decline in the mean SIB score from the
baseline for the Modified Full Analysis Set (MFAS)-Last Observation Carried
Forward (LOCF) analysis was less at each timepoint in the 13.3 mg/24 hour
EXELON PATCH treatment group than in the 4.6 mg/24 hours EXELON PATCH treatment
group. The 13.3 mg/24 hours dose was statistically significantly superior to
the 4.6 mg/24 hours dose at weeks 16 and 24 (primary endpoint).
Figure 8 illustrates the time course for the mean change
from baseline in ADCS-ADL-SIV scores for each treatment group over the course
of the 24-week treatment phase of the study. Decline in the mean ADCS-ADLSIV score
from baseline for the MFAS-LOCF analysis was less at each timepoint in the 13.3
mg/24 hour EXELON PATCH treatment group than in the 4.6 mg/24 hours EXELON
PATCH treatment group. The 13.3 mg/24 hours dose was statistically
significantly superior to the 4.6 mg/24 hours dose at weeks 16 and 24 (primary endpoint).
Figure 7: Time Course of the Change from Baseline in
SIB Score for Patients Observed at Each Time Point (Modified Full Analysis
Set–LOCF)
Figure 8: Time Course of the Change from Baseline in
ADCS-ADL-SIV Score for Patients Observed at Each Time Point (Modified Full
Analysis Set–LOCF)