CLINICAL PHARMACOLOGY
Mechanism Of Action
The mechanism(s) through which
modafinil promotes wakefulness is unknown. Modafinil has wake-promoting actions
similar to sympathomimetic agents including amphetamine and methylphenidate,
although the pharmacologic profile is not identical to that of the
sympathomimetic amines.
Modafinil-induced wakefulness
can be attenuated by the α1-adrenergic receptor antagonist, prazosin;
however, modafinil is inactive in other in vitro assay systems known to be
responsive to α-adrenergic agonists such as the rat vas deferens preparation.
Modafinil is not a direct-or
indirect-acting dopamine receptor agonist. However, in vitro, modafinil binds
to the dopamine transporter and inhibits dopamine reuptake. This activity has
been associated in vivo with increased extracellular dopamine levels in some
brain regions of animals. In genetically engineered mice lacking the dopamine
transporter (DAT), modafinil lacked wake-promoting activity, suggesting that
this activity was DAT-dependent. However, the wake-promoting effects of
modafinil, unlike those of amphetamine, were not antagonized by the dopamine
receptor antagonist haloperidol in rats. In addition, alpha-methyl-p-tyrosine,
a dopamine synthesis inhibitor, blocks the action of amphetamine, but does not
block locomotor activity induced by modafinil.
In the cat, equal
wakefulness-promoting doses of methylphenidate and amphetamine increased
neuronal activation throughout the brain. Modafinil at an equivalent
wakefulness-promoting dose selectively and prominently increased neuronal
activation in more discrete regions of the brain. The relationship of this
finding in cats to the effects of modafinil in humans is unknown.
In addition to its
wake-promoting effects and ability to increase locomotor activity in animals,
modafinil produces psychoactive and euphoric effects, alterations in mood,
perception, thinking, and feelings typical of other CNS stimulants in humans.
Modafinil has reinforcing properties, as evidenced by its self-administration
in monkeys previously trained to self-administer cocaine; modafinil was also
partially discriminated as stimulant-like.
The optical enantiomers of
modafinil have similar pharmacological actions in animals. Two major
metabolites of modafinil, modafinil acid and modafinil sulfone, do not appear
to contribute to the CNS-activating properties of modafinil.
Pharmacokinetics
Modafinil is a 1:1 racemic
compound, whose enantiomers have different pharmacokinetics (e.g., the half-life
of R-modafinil is approximately three times that of S-modafinil in adult
humans). The enantiomers do not interconvert. At steady state, total exposure
to R-modafinil is approximately three times that for S-modafinil. The trough
concentration (Cmin,ss) of circulating modafinil after once daily dosing
consists of 90% of R-modafinil and 10% of S-modafinil. The effective
elimination half-life of modafinil after multiple doses is about 15 hours. The
enantiomers of modafinil exhibit linear kinetics upon multiple dosing of
200-600 mg/day once daily in healthy volunteers. Apparent steady states of
total modafinil and R-modafinil are reached after 2-4 days of dosing.
Absorption
PROVIGIL is readily absorbed
after oral administration, with peak plasma concentrations occurring at 2-4
hours. The bioavailability of PROVIGIL tablets is approximately equal to that
of an aqueous suspension. The absolute oral bioavailability was not determined
due to the aqueous insolubility ( < 1 mg/mL) of modafinil, which precluded intravenous
administration. Food has no effect on overall PROVIGIL bioavailability;
however, time to reach peak concentration (tmax) may be delayed by
approximately one hour if taken with food.
Distribution
PROVIGIL has an apparent volume of distribution of
approximately 0.9 L/kg. In human plasma, in vitro, modafinil is moderately
bound to plasma protein (approximately 60%), mainly to albumin. The potential
for interactions of PROVIGIL with highly protein-bound drugs is considered to
be minimal.
Metabolism and Elimination
The major route of elimination is metabolism
(approximately 90%), primarily by the liver, with subsequent renal elimination
of the metabolites. Urine alkalinization has no effect on the elimination of
modafinil.
Metabolism occurs through hydrolytic deamidation,
S-oxidation, aromatic ring hydroxylation, and glucuronide conjugation. Less
than 10% of an administered dose is excreted as the parent compound. In a
clinical study using radiolabeled modafinil, a total of 81% of the administered
radioactivity was recovered in 11 days post-dose, predominantly in the urine
(80% vs. 1.0% in the feces). The largest fraction of the drug in urine was
modafinil acid, but at least six other metabolites were present in lower concentrations.
Only two metabolites reach appreciable concentrations in plasma, i.e.,
modafinil acid and modafinil sulfone. In preclinical models, modafinil acid,
modafinil sulfone, 2-[(diphenylmethyl)sulfonyl]acetic acid and 4-hydroxy
modafinil, were inactive or did not appear to mediate the arousal effects of
modafinil.
In adults, decreases in trough levels of modafinil have
sometimes been observed after multiple weeks of dosing, suggesting
auto-induction, but the magnitude of the decreases and the inconsistency of
their occurrence suggest that their clinical significance is minimal.
Significant accumulation of modafinil sulfone has been observed after multiple
doses due to its long elimination half-life of 40 hours. Auto-induction of
metabolizing enzymes, most importantly cytochrome P-450 CYP3A4, has also been
observed in vitro after incubation of primary cultures of human hepatocytes
with modafinil and in vivo after extended administration of modafinil at 400
mg/day.
Specific Populations
Age
A slight decrease (approximately 20%) in the oral
clearance (CL/F) of modafinil was observed in a single dose study at 200 mg in
12 subjects with a mean age of 63 years (range 53 – 72 years), but the change
was considered not likely to be clinically significant. In a multiple dose
study (300 mg/day) in 12 patients with a mean age of 82 years (range 67 – 87
years), the mean levels of modafinil in plasma were approximately two times
those historically obtained in matched younger subjects. Due to potential
effects from the multiple concomitant medications with which most of the
patients were being treated, the apparent difference in modafinil
pharmacokinetics may not be attributable solely to the effects of aging.
However, the results suggest that the clearance of modafinil may be reduced in
the elderly [see DOSAGE AND ADMINISTRATION and Use in Specific
Populations].
Gender
The pharmacokinetics of modafinil are not affected by
gender.
Race
The influence of race on the pharmacokinetics of
modafinil has not been studied.
Renal Impairment
In a single dose 200 mg modafinil study, severe chronic
renal failure (creatinine clearance ≤ 20 mL/min) did not significantly influence
the pharmacokinetics of modafinil, but exposure to modafinil acid (an inactive
metabolite) was increased 9-fold.
Hepatic Impairment
The pharmacokinetics and metabolism of modafinil were
examined in patients with cirrhosis of the liver (6 men and 3 women). Three
patients had stage B or B+ cirrhosis and 6 patients had stage C or C+ cirrhosis
(per the Child-Pugh score criteria). Clinically 8 of 9 patients were icteric
and all had ascites. In these patients, the oral clearance of modafinil was
decreased by about 60% and the steady state concentration was doubled compared
to normal patients [see DOSAGE AND ADMINISTRATION and Use in Specific
Populations].
Drug Interactions
In vitro data demonstrated that modafinil weakly induces
CYP1A2, CYP2B6, and possibly CYP3A activities in a concentration-related manner
and that CYP2C19 activity is reversibly inhibited by modafinil. In vitro data
also demonstrated that modafinil produced an apparent concentration-related
suppression of expression of CYP2C9 activity. Other CYP activities did not
appear to be affected by modafinil.
Potential Interactions with Drugs That Inhibit,
Induce, or Are Metabolized by Cytochrome P450 Isoenzymes and Other Hepatic
Enzymes
The existence of multiple pathways for modafinil
metabolism, as well as the fact that a non-CYP-related pathway is the most
rapid in metabolizing modafinil, suggest that there is a low probability of
substantive effects on the overall pharmacokinetic profile of PROVIGIL due to
CYP inhibition by concomitant medications. However, due to the partial
involvement of CYP3A enzymes in the metabolic elimination of modafinil, coadministration
of potent inducers of CYP3A4/5 (e.g., carbamazepine, phenobarbital, rifampin)
or inhibitors of CYP3A4/5 (e.g., ketoconazole, erythromycin) could alter the
plasma concentrations of modafinil.
The Potential of PROVIGIL to Alter the Metabolism of
Other Drugs by Enzyme Induction or Inhibition
- Drugs Metabolized by CYP3A4/5
- In vitro data demonstrated that modafinil is a weak
inducer of CYP3A activity in a concentration-related manner. Therefore, the
blood levels and effectiveness of drugs that are substrates for CYP3A enzymes
(e.g., steroidal contraceptives, cyclosporine, midazolam, and triazolam) may be
reduced after initiation of concomitant treatment with PROVIGIL[see DRUG
INTERACTIONS].
- Ethinyl Estradiol -Administration of modafinil to female
volunteers once daily at 200 mg/day for 7 days followed by 400 mg/day for 21
days resulted in a mean 11% decrease in mean Cmax and 18% decrease in mean AUC0-24
of ethinyl estradiol (EE2; 0.035 mg; administered orally with norgestimate).
There was no apparent change in the elimination rate of ethinyl estradiol.
- Triazolam -In the drug interaction study between PROVIGIL
and ethinyl estradiol (EE2), on the same days as those for the plasma sampling
for EE2 pharmacokinetics, a single dose of triazolam (0.125 mg) was also
administered. Mean Cmax and AUC0-∞ of triazolam were decreased by 42% and
59%, respectively, and its elimination half-life was decreased by approximately
an hour after the modafinil treatment.
- Cyclosporine -One case of an interaction between
modafinil and cyclosporine, a substrate of CYP3A4, has been reported in a 41
year old woman who had undergone an organ transplant. After one month of
administration of 200 mg/day of modafinil, cyclosporine blood levels were
decreased by 50%. The interaction was postulated to be due to the increased
metabolism of cyclosporine, since no other factor expected to affect the
disposition of the drug had changed.
- Midazolam -In a clinical study, concomitant
administration of armodafinil 250 mg resulted in a reduction in systemic
exposure to midazolam by 32% after a single oral dose (5 mg) and 17% after a
single intravenous dose (2 mg).
- Quetiapine -In a separate clinical study, concomitant
administration of armodafinil 250 mg with quetiapine (300 mg to 600 mg daily
doses) resulted in a reduction in the mean systemic exposure of quetiapine by
approximately 29%.
- Drugs Metabolized by CYP1A2
- In vitro data demonstrated that modafinil is a weak
inducer of CYP1A2 in a concentration-related manner. However, in a clinical
study with armodafinil using caffeine as a probe substrate, no significant
effect on CYP1A2 activity was observed.
- Drugs Metabolized by CYP2B6
- In vitro data demonstrated that modafinil is a weak
inducer of CYP2B6 activity in a concentration-related manner.
- Drugs Metabolized by CYP2C9
- In vitro data demonstrated that modafinil produced an
apparent concentration-related suppression of expression of CYP2C9 activity
suggesting that there is a potential for a metabolic interaction between
modafinil and the substrates of this enzyme (e.g., S-warfarin and phenytoin) [see
DRUG INTERACTIONS].
- Warfarin: Concomitant administration of modafinil with
warfarin did not produce significant changes in the pharmacokinetic profiles of
R-and S-warfarin. However, since only a single dose of warfarin was tested in
this study, an interaction cannot be ruled out [see DRUG INTERACTIONS].
- Drugs Metabolized by CYP2C19
- In vitro data demonstrated that modafinil is a reversible
inhibitor of CYP2C19 activity. CYP2C19 is also reversibly inhibited, with similar
potency, by a circulating metabolite, modafinil sulfone. Although the maximum
plasma concentrations of modafinil sulfone are much lower than those of parent
modafinil, the combined effect of both compounds could produce sustained
partial inhibition of the enzyme. Therefore, exposure to some drugs that are
substrates for CYP2C19 (e.g., phenytoin, diazepam, propranolol, omeprazole, and
clomipramine) may be increased when used concomitantly with PROVIGIL [see
DRUG INTERACTIONS].
- In a clinical study, concomitant administration of
armodafinil 400 mg resulted in a 40% increase in exposure to omeprazole after a
single oral dose (40 mg), as a result of moderate inhibition of CYP2C19
activity.
- Interactions with CNS Active Drugs
- Concomitant administration of modafinil with
methylphenidate or dextroamphetamine produced no significant alterations on the
pharmacokinetic profile of modafinil or either stimulant, even though the
absorption of modafinil was delayed for approximately one hour.
- Concomitant modafinil or clomipramine did not alter the
pharmacokinetic profile of either drug; however, one incident of increased
levels of clomipramine and its active metabolite desmethylclomipramine was
reported in a patient with narcolepsy during treatment with modafinil.
- CYP2C19 also provides an ancillary pathway for the
metabolism of certain tricyclic antidepressants (e.g., clomipramine and
desipramine) and selective serotonin reuptake inhibitors that are primarily
metabolized by CYP2D6. In tricyclic-treated patients deficient in CYP2D6 (i.e.,
those who are poor metabolizers of debrisoquine; 7-10% of the Caucasian
population; similar or lower in other populations), the amount of metabolism by
CYP2C19 may be substantially increased. PROVIGIL may cause elevation of the
levels of the tricyclics in this subset of patients [see DRUG INTERACTIONS].
- Concomitant administration of armodafinil with quetiapine
reduced the systemic exposure of quetiapine.
- Interaction with P-Glycoprotein
- An in vitro study demonstrated that armodafinil is a
substrate of P-glycoprotein. The impact of inhibition of P-glycoprotein is not
known.
Clinical Studies
Narcolepsy
The effectiveness of PROVIGIL in improving wakefulness in
adult patients with excessive sleepiness associated with narcolepsy was
established in two US 9-week, multi-center, placebo-controlled, parallel-group,
double-blind studies of outpatients who met the criteria for narcolepsy. A
total of 558 patients were randomized to receive PROVIGIL 200 or 400 mg/day, or
placebo. The criteria for narcolepsy include either: 1) recurrent daytime naps
or lapses into sleep that occur almost daily for at least three months, plus
sudden bilateral loss of postural muscle tone in association with intense
emotion (cataplexy); or 2) a complaint of excessive sleepiness or sudden muscle
weakness with associated features: sleep paralysis, hypnagogic hallucinations,
automatic behaviors, disrupted major sleep episode; and polysomnography
demonstrating one of the following: sleep latency less than 10 minutes or rapid
eye movement (REM) sleep latency less than 20 minutes. For entry into these
studies, all patients were required to have objectively documented excessive
daytime sleepiness, via a Multiple Sleep Latency Test (MSLT) with two or more
sleep onset REM periods and the absence of any other clinically significant
active medical or psychiatric disorder. The MSLT, an objective polysomnographic
assessment of the patient's ability to fall asleep in an unstimulating
environment, measured latency (in minutes) to sleep onset averaged over 4 test
sessions at 2-hour intervals. For each test session, the subject was told to
lie quietly and attempt to sleep. Each test session was terminated after 20
minutes if no sleep occurred or 15 minutes after sleep onset.
In both studies, the primary measures of effectiveness
were: 1) sleep latency, as assessed by the Maintenance of Wakefulness Test
(MWT); and 2) the change in the patient's overall disease status, as measured
by the Clinical Global Impression of Change (CGI-C). For a successful trial,
both measures had to show statistically significant improvement.
The MWT measures latency (in minutes) to sleep onset
averaged over 4 test sessions at 2 hour intervals following nocturnal
polysomnography. For each test session, the subject was asked to attempt to
remain awake without using extraordinary measures. Each test session was terminated
after 20 minutes if no sleep occurred or 10 minutes after sleep onset. The
CGI-C is a 7-point scale, centered at No Change, and ranging from Very Much
Worse to Very Much Improved. Patients were rated by evaluators who had no
access to any data about the patients other than a measure of their baseline
severity. Evaluators were not given any specific guidance about the criteria
they were to apply when rating patients.
Both studies demonstrated improvement in objective and
subjective measures of excessive daytime sleepiness for both the 200 mg and 400
mg doses compared to placebo. Patients treated with PROVIGIL showed a
statistically significantly enhanced ability to remain awake on the MWT at each
dose compared to placebo at final visit (Table 2). A statistically
significantly greater number of patients treated with PROVIGIL at each dose
showed improvement in overall clinical condition as rated by the CGI-C scale at
final visit (Table 3).
Nighttime sleep measured with polysomnography was not
affected by the use of PROVIGIL.
Obstructive Sleep Apnea (OSA)
The effectiveness of PROVIGIL in improving wakefulness in
patients with excessive sleepiness associated with OSA was established in two
multi-center, placebo-controlled clinical studies of patients who met the
criteria for OSA. The criteria include either: 1) excessive sleepiness or
insomnia, plus frequent episodes of impaired breathing during sleep, and
associated features such as loud snoring, morning headaches and dry mouth upon
awakening; or 2) excessive sleepiness or insomnia and polysomnography
demonstrating one of the following: more than five obstructive apneas, each
greater than 10 seconds in duration, per hour of sleep and one or more of the
following: frequent arousals from sleep associated with the apneas,
bradytachycardia, and arterial oxygen desaturation in association with the
apneas. In addition, for entry into these studies, all patients were required
to have excessive sleepiness as demonstrated by a score ≥ 10 on the
Epworth Sleepiness Scale (ESS), despite treatment with continuous positive
airway pressure (CPAP). Evidence that CPAP was effective in reducing episodes
of apnea/hypopnea was required along with documentation of CPAP use.
In the first study, a 12-week trial, a total of 327
patients with OSA were randomized to receive PROVIGIL 200 mg/day, PROVIGIL 400
mg/day, or matching placebo. The majority of patients (80%) were fully
compliant with CPAP, defined as CPAP use greater than 4 hours/night on > 70%
of nights. The remainder were partially CPAP compliant, defined as CPAP use
< 4 hours/night on > 30% of nights. CPAP use continued throughout the
study. The primary measures of effectiveness were 1) sleep latency, as assessed
by the Maintenance of Wakefulness Test (MWT) and 2) the change in the patient's
overall disease status, as measured by the Clinical Global Impression of Change
(CGI-C) at the final visit [see Clinical Studies for a description of
these measures].
Patients treated with PROVIGIL showed a statistically
significant improvement in the ability to remain awake compared to
placebo-treated patients as measured by the MWT at final visit (Table 2). A
statistically significant greater number of patients treated with PROVIGIL
showed improvement in overall clinical condition as rated by the CGI-C scale at
final visit (Table 3). The 200 mg and 400 mg doses of PROVIGIL produced
statistically significant effects of similar magnitude on the MWT, and also on
the CGI-C.
In the second study, a 4-week trial, 157 patients with OSA
were randomized to receive PROVIGIL 400 mg/day or placebo. Documentation of
regular CPAP use (at least 4 hours/night on 70% of nights) was required for all
patients. The primary measure of effectiveness was the change from baseline on
the ESS at final visit. The baseline ESS scores for the PROVIGIL and placebo
groups were 14.2 and 14.4, respectively. At week 4, the ESS was reduced by 4.6
in the PROVIGIL group and by 2.0 in the placebo group, a difference that was
statistically significant.
Nighttime sleep measured with polysomnography was not
affected by the use of PROVIGIL.
Shift Work Disorder (SWD)
The effectiveness of PROVIGIL in improving wakefulness in
patients with excessive sleepiness associated with SWD was demonstrated in a 12-week
placebo-controlled clinical trial. A total of 209 patients with chronic SWD
were randomized to receive PROVIGIL 200 mg/day or placebo. All patients met the
criteria for chronic SWD. The criteria include: 1) either, a) a primary complaint
of excessive sleepiness or insomnia which is temporally associated with a work
period (usually night work) that occurs during the habitual sleep phase, or b)
polysomnography and the MSLT demonstrate loss of a normal sleep-wake pattern
(i.e., disturbed chronobiological rhythmicity); and 2) no other medical or
mental disorder accounts for the symptoms, and 3) the symptoms do not meet
criteria for any other sleep disorder producing insomnia or excessive
sleepiness (e.g., time zone change [jet lag] syndrome).
It should be noted that not all patients with a complaint
of sleepiness who are also engaged in shift work meet the criteria for the
diagnosis of SWD. In the clinical trial, only patients who were symptomatic for
at least 3 months were enrolled.
Enrolled patients were also required to work a minimum of
5 night shifts per month, have excessive sleepiness at the time of their night
shifts (MSLT score < 6 minutes), and have daytime insomnia documented by a
daytime polysomnogram.
The primary measures of effectiveness were 1) sleep
latency, as assessed by the MSLT performed during a simulated night shift at
the final visit and 2) the change in the patient's overall disease status, as
measured by the CGI-C at the final visit [see Clinical Studies for a
description of these measures.].
Patients treated with PROVIGIL showed a statistically
significant prolongation in the time to sleep onset compared to placebo-treated
patients, as measured by the nighttime MSLT at final visit (Table 2). A statistically
significant greater number of patients treated with PROVIGIL showed improvement
in overall clinical condition as rated by the CGI-C scale at final visit (Table
3).
Daytime sleep measured with polysomnography was not
affected by the use of PROVIGIL.
Table 2: Average Baseline Sleep Latency and Change
from Baseline at Final Visit (MWT and MSLT in minutes)
Disorder |
Measure |
PROVIGIL 200 mg* |
PROVIGIL 400 mg* |
Placebo |
Baseline |
Change from Baseline |
Baseline |
Change from Baseline |
Baseline |
Change from Baseline |
Narcolepsy I |
MWT |
5.8 |
2.3 |
6.6 |
2.3 |
5.8 |
-0.7 |
Narcolepsy II |
MWT |
6.1 |
2.2 |
5.9 |
2.0 |
6.0 |
-0.7 |
OSA |
MWT |
13.1 |
1.6 |
13.6 |
1.5 |
13.8 |
-1.1 |
SWD |
MSLT |
2.1 |
1.7 |
- |
- |
2.0 |
0.3 |
*Significantly different than
placebo for all trials (p < 0.01 for all trials but SWD, which was p < 0.05) |
Table 3: Clinical Global
Impression of Change (CGI-C) (Percent of Patients Who Improved at Final Visit)
Disorder |
PROVIGIL 200 mg* |
PROVIGIL 400 mg* |
Placebo |
Narcolepsy I |
64% |
72% |
37% |
Narcolepsy II |
58% |
60% |
38% |
OSA |
61% |
68% |
37% |
SWD |
74% |
--- |
36% |
*Significantly different than
placebo for all trials (p < 0.01) |