CLINICAL PHARMACOLOGY
Mechanism Of Action
The precise mechanism by which istradefylline exerts its
therapeutic effect in Parkinson disease is unknown. In in vitro studies and in in
vivo animal studies, istradefylline was demonstrated to be an adenosine A2A receptor
antagonist.
Pharmacodynamics
Cardiac Electrophysiology
The effect of NOURIANZ (40 mg or 160 mg [4 times the
maximum recommended dosage] once daily for 14 days) on the QTc interval was
evaluated in a randomized, placebo and moxifloxacincontrolled, multiple-dose,
blinded, parallel group study. There was no clinically significant prolongation
of QTc interval or relationship between changes in QTc and concentrations of
istradefylline.
Pharmacokinetics
Istradefylline exhibits dose-proportional
pharmacokinetics after multiple oral doses from 20 mg to 80 mg (2 times the
maximum recommended dosage). Steady-state was reached within 2 weeks of
once-daily dosing. The pharmacokinetics of istradefylline were similar in PD
patients and healthy subjects.
Absorption
The median time to reach the maximum concentration (Tmax)
for istradefylline was about 4 hours under fasted dosing conditions.
Effect Of Food
Istradefylline exposure, represented by the area under
the curve over time to infinity (AUCinf), increased 1.25-fold when NOURIANZ was
coadministered with a standard high-fat meal, compared with administration in a
fasted state. Istradefylline maximum plasma concentrations (Cmax) increased by
1.64-fold and Tmax was shortened by 1 hour when NOURIANZ was administered with
a high-fat meal. These differences in pharmacokinetic parameters are not
expected to be clinically significant [see DOSAGE AND ADMINISTRATION].
Distribution
The plasma protein binding of istradefylline was
approximately 98%. The apparent volume of distribution (Vd/F) of istradefylline
is approximately 557 liters.
Elimination
The total clearance of istradefylline is approximately
4.6 L/hour. The mean terminal half-life (t½) for istradefylline at
steady-state is approximately 83 hours.
Metabolism
In humans, istradefylline is exclusively eliminated via
metabolism. In vitro studies indicate that istradefylline is primarily
metabolized via CYP1A1 and CYP3A4, with minor contribution from CYP1A2, 2B6,
2C8, CYP2C9, CYP2C18, and 2D6. Six metabolites have been identified in human
plasma. These metabolites each account for less than 10% of the exposure of the
parent drug.
Excretion
Approximately 48% of a 40-mg oral dose of 14C-istradefylline
was eliminated in feces, and 39% in urine. Unchanged istradefylline was not
detected in urine.
Specific Populations
In patients with moderate hepatic impairment (Child-Pugh
B), the steady-state exposure (AUC0-24) of istradefylline is predicted to be
3.3-fold higher relative to healthy subjects, based on the estimated mean
terminal half-life [see Use In Specific Populations]. Based on
population pharmacokinetic analyses, no clinically relevant changes in the
pharmacokinetics of istradefylline were observed based on age, sex, weight, or
race. No clinically relevant changes in istradefylline exposure were observed
in patients with severe renal impairment (CrCL 15-29 mL/min) or mild hepatic
impairment. NOURIANZ has not been studied in patients with ESRD (CrCL < 15
mL/min), ESRD patients requiring hemodialysis, or severe hepatic impairment
(Child-Pugh C) [see Use In Specific Populations].
Steady-state systemic exposure to istradefylline (40 mg)
is 38% to 54% lower in tobacco smokers (who smoke 20 or more cigarettes per
day) when compared with non-smokers matched for age, gender, and body weight [see
Specific Populations].
Drug Interaction Studies
In Vitro Assessment Of Drug Interactions
Drug-Metabolizing Enzyme Inhibition
Istradefylline is a weak inhibitor of CYP3A4, but not an
inhibitor of CYP1A2, 2B6, 2C9, 2C19, or 2D6 in vitro.
Drug-Metabolizing Enzyme Induction
Istradefylline was a weak inducer of CYP3A4 but not an
inducer of CYP1A2 and 2B6 when tested in vitro. However, clinical drug-drug
interaction studies with a CYP3A4 substrate (i.e., midazolam) showed no
induction of CYP3A4.
Transporters
Istradefylline was not a substrate for drug transporters
P-gp, BCRP, OATP1B1, or OATP1B3 when tested in vitro. Istradefylline was a weak
inhibitor for P-gp, BCRP, OATP1B1, OATP1B3, OAT1, OCT2, MATE1, and MATE2-K, but
not an inhibitor of OAT3 when tested in vitro.
In Vivo Assessment Of Drug Interactions
Effect Of Other Drugs On Istradefylline
Strong CYP3A4 Inhibitors
Coadministration of ketoconazole (200 mg twice daily for
4 days) with a single dose of istradefylline (40 mg) increased the AUCinf of
istradefylline by 2.5-fold, but had no effect on Cmax [see DRUG INTERACTIONS].
Strong CYP3A4 Inducers
Coadministration of rifampin (600 mg daily for 20 days)
with a single dose of istradefylline (40 mg) reduced the Cmax and AUCinf of
istradefylline by 45% and 81% respectively, when compared with istradefylline
administered alone [see DRUG INTERACTIONS].
Effect Of Istradefylline On Other Drugs
CYP3A4 Substrates
Coadministration of istradefylline at higher than the
recommended doses (80 mg for 14 days) with a single dose of midazolam (10 mg)
increased midazolam AUCinf 2.4-fold, and Cmax by 1.6-fold, when compared with
midazolam administered alone. Coadministration of lower doses of istradefylline
(5 mg and 20 mg) with midazolam (7.5 mg) did not have these effects [see DRUG
INTERACTIONS].
Coadministration of istradefylline (40 mg daily for 17 days)
with a single dose of atorvastatin (40 mg) increased the Cmax and AUCinf of
atorvastatin by 1.5-fold, compared with atorvastatin alone [see DRUG
INTERACTIONS].
P-glycoprotein Substrates
Coadministration of istradefylline (40 mg daily for 21
days) with a single dose of digoxin (0.4 mg) increased the Cmax and AUCinf of
digoxin by 33% and 21%, respectively, when compared with digoxin alone [see DRUG
INTERACTIONS].
Carbidopa/Levodopa
Coadministration of istradefylline (80 mg [two times the
recommended maximum dosage] daily for 14 days) with a single dose of
carbidopa/levodopa (50/200 mg) did not affect the pharmacokinetics of
carbidopa/levodopa. Also, coadministration of istradefylline (20 mg or 40 mg
daily for 14 days) with carbidopa/levodopa (25/100 mg three times a day for 14
days) did not affect the systemic exposure of carbidopa/levodopa.
Animal Toxicology And/Or Pharmacology
Oral administration of istradefylline (0, 30, 100, or 320
mg/kg/day) to rats for two years resulted in an increase in the incidence and
severity of vascular mineralization in the brain (including in the caudate/putamen,
globus pallidus, thalamus, and nucleus accumbens) at all doses tested. The
vascular mineralization was composed of calcium and phosphorus and, at higher
doses, were reported to partially or completely occlude the blood vessels.
There was no evidence of neuronal degeneration, inflammation, or glial response
associated with the foci of mineralization.
Brain mineralization was not detected in mice
administered istradefylline (0, 25, 125, or 250 mg/kg/day) orally for two years
or in dogs administered istradefylline (0, 10, 30, or 100 mg/kg/day) orally for
52 weeks.
Clinical Studies
The efficacy of NOURIANZ for the adjunctive treatment to
levodopa/carbidopa in patients with Parkinson's disease experiencing “off”
episodes was shown in four randomized, multicenter, double-blind, 12-week,
placebo-controlled studies (Study 1, NCT00456586; Study 2, NCT00199407; Study
3, NCT00455507; and Study 4, NCT00955526). The studies enrolled patients with a
mean duration of Parkinson's disease of 9 years (range: 1 month to 37 years)
that were Hoehn and Yahr Stage II to IV, experiencing at least 2 hours (mean
approximately 6 hours) of “off” time per day, and were treated with levodopa
for at least one year, with stable dosage for at least 4 weeks before screening
(mean total daily dosage range: 416 to 785 mg). Patients continued levodopa
treatment with or without concomitant PD medications, including dopamine
agonists (85%), COMT inhibitors (38%), MAO-B inhibitors (40%), anticholinergics
(13%), and/or amantadine (33%), provided the medications were stable for at
least 4 weeks before screening and throughout the study period. The studies
excluded patients who had received a neurosurgical treatment for PD (e.g.,
pallidotomy, thalamotomy, deep brain stimulation).
The primary efficacy endpoint was the change from
baseline in the daily awake percentage of “off” time, or the change from
baseline in total daily “off” time, based on 24-hour diaries completed by
patients. A change from baseline in “on” time without troublesome dyskinesia
(i.e., “on” time without dyskinesia plus “on” time with non-troublesome
dyskinesia) was a secondary efficacy endpoint.
Study 1 was conducted in the U.S. and Canada, and Study 2
was conducted in the U.S. In these studies, patients were randomized to
once-daily treatment with NOURIANZ 20 mg, 40 mg, or placebo. Patients treated
with NOURIANZ 20 mg or NOURIANZ 40 mg once daily experienced a statistically
significant decrease from baseline in percentage of daily awake “off” time,
compared with patients on placebo, as summarized in Table 2.
Table 2: Studies 1 and 2: Change From Baseline in
Daily Awake OFF Time
|
Baseline |
Change from Baseline to Endpoint |
N |
(mean ± SD) % of awake “off” hours |
N |
(LSMD* vs. placebo), % awake “off” hours, (p-value) |
Study 1 |
Placebo |
66 |
37.2 ± 13.8 |
65 |
-- |
NOURIANZ 40 mg |
129 |
38.4 ± 16.2 |
126 |
- 6.78 (p=0.007) |
Study 2 |
Placebo |
113 |
38.7 ± 11.6 |
113 |
-- |
NOURIANZ 20 mg |
112 |
39.8 ± 14.0 |
112 |
-4.57 (p=0.025) |
* LSMD: Least squares mean difference; a negative value
indicates a greater reduction from baseline in Percentage Daily Awake “off”
time for NOURIANZ, relative to placebo. SD: Standard Deviation |
Compared with patients on placebo, patients treated with
NOURIANZ experienced an additional increase from baseline in “on” time without
troublesome dyskinesia of 0.96 hours (nominal p=0.026) in Study 1, and of 0.55
hours (nominal p=0.135) in Study 2.
Study 3 and Study 4 were conducted in Japan. In these
studies, patients were randomized equally to treatment with NOURIANZ 20 mg, 40
mg, or placebo. Patients treated with NOURIANZ 20 mg or NOURIANZ 40 mg once
daily experienced a statistically significant decrease from baseline in “off”
time compared with patients on placebo, as summarized in Table 3.
Table 3: Studies 3 and 4: Change From Baseline in
Daily OFF Time
|
Baseline |
Change from Baseline to Endpoint |
N |
(mean ± SD) hours |
N |
(LSMD* vs. placebo) hours ( p-value) |
Study 3 |
Placebo |
118 |
6.4 ± 2.7 |
118 |
-- |
NOURIANZ 20 mg |
115 |
6.8 ± 2.9 |
115 |
-0.65 (p=0.028) |
NOURIANZ 40 mg |
124 |
6.6 ± 2.5 |
124 |
-0.92 (p=0.002) |
Study 4 |
Placebo |
123 |
6.3 ± 2.5 |
123 |
-- |
NOURIANZ 20 mg |
120 |
6.6 ± 2.7 |
120 |
-0.76 (p=0.006) |
NOURIANZ 40 mg |
123 |
6.0 ± 2.5 |
123 |
-0.74 (p=0.008) |
* LSMD: Least squares mean difference; a negative value
indicates a greater reduction from baseline in “off” time for NOURIANZ,
relative to placebo.
SD: Standard Deviation |
In Study 3, compared with placebo, an additional increase
from baseline in “on” time without troublesome dyskinesia of 0.57 hours
(nominal p=0.085) and of 0.65 hours (nominal p=0.048), respectively, were
observed in patients treated with NOURIANZ 20 mg or NOURIANZ 40 mg. In Study 4,
the corresponding increases in “on” time without troublesome dyskinesia were
0.83 hours (nominal p=0.008) for NOURIANZ 20 mg and 0.81 hours (nominal p=0.008)
for NOURIANZ 40 mg.