Mechanism of Action

Entacapone is a selective and reversible inhibitor of COMT.

In mammals, COMT is distributed throughout various organs with the highest activities in the liver and kidney. COMT also occurs in the heart, lung, smooth and skeletal muscles, intestinal tract, reproductive organs, various glands, adipose tissue, skin, blood cells, and neuronal tissues, especially in glial cells. COMT catalyzes the transfer of the methyl group of S-adenosyl-L-methionine to the phenolic group of substrates that contain a catechol structure. Physiological substrates of COMT include dopa, catecholamines (dopamine, norepinephrine, and epinephrine) and their hydroxylated metabolites. The function of COMT is the elimination of biologically active catechols and some other hydroxylated metabolites. In the presence of a decarboxylase inhibitor, COMT becomes the major metabolizing enzyme for levodopa, catalyzing the metabolism to 3-methoxy-4-hydroxy-L-phenylalanine (3-OMD) in the brain and periphery.

The mechanism of action of entacapone is believed to be through its ability to inhibit COMT and alter the plasma pharmacokinetics of levodopa. When entacapone is given in conjunction with levodopa and an aromatic amino acid decarboxylase inhibitor, such as carbidopa, plasma levels of levodopa are greater and more sustained than after administration of levodopa and an aromatic amino acid decarboxylase inhibitor alone. It is believed that at a given frequency of levodopa administration, these more sustained plasma levels of levodopa result in more constant dopaminergic stimulation in the brain, leading to greater effects on the signs and symptoms of Parkinson's disease. The higher levodopa levels also lead to increased levodopa adverse effects, sometimes requiring a decrease in the dose of levodopa.

In animals, while entacapone enters the central nervous system (CNS) to a minimal extent, it has been shown to inhibit central COMT activity. In humans, entacapone inhibits the COMT enzyme in peripheral tissues. The effects of entacapone on central COMT activity in humans have not been studied.

Pharmacodynamics

Effect on the Pharmacokinetics of Levodopa and its Metabolites

When 200 mg entacapone is administered together with levodopa and carbidopa, it increases the area under the curve (AUC) of levodopa by approximately 35%, and the elimination half-life of levodopa is prolonged from 1.3 hours to 2.4 hours. In general, the average peak levodopa plasma concentration and the time of its occurrence (Tmax of 1 hour) are unaffected. The onset of effect occurs after the first administration and is maintained during long-term treatment. Studies in Parkinson's disease patients suggest that the maximal effect occurs with 200 mg entacapone. Plasma levels of 3-OMD are markedly and dose-dependently decreased by entacapone when given with levodopa and carbidopa.

Pharmacokinetics of Entacapone

Entacapone pharmacokinetics are linear over the dose range of 5 mg to 800 mg, and are independent of levodopa and carbidopa coadministration. The elimination of entacapone is biphasic, with an elimination half-life of 0.4 hour to 0.7 hour based on the β-phase and 2.4 hours based on the γ-phase. The γ-phase accounts for approximately 10% of the total AUC. The total body clearance after intravenous administration is 850 mL per min. After a single 200 mg dose of Comtan (entacapone), the Cmax is approximately 1.2 mcg per mL.

Clinical Studies

The effectiveness of Comtan (entacapone) as an adjunct to levodopa in the treatment of Parkinson's disease was established in three 24-week multicenter, randomized, double-blind, placebo-controlled studies in patients with Parkinson's disease. In two of these studies, patients had motor "fluctuations", characterized by documented periods of "On" (periods of relatively good functioning) and "Off" (periods of relatively poor functioning), despite optimum levodopa therapy. There was also a withdrawal period following 6 months of treatment. In the third study, patients were not required to have motor fluctuations. Prior to the controlled part of the studies, patients were stabilized on levodopa for 2 weeks to 4 weeks. Comtan has not been systematically evaluated in patients who have Parkinson's disease without motor fluctuations.

In the first two studies to be described, patients were randomized to receive placebo or entacapone 200 mg administered concomitantly with each dose of levodopa and carbidopa (up to 10 times daily, but averaging 4 doses to 6 doses per day). The formal double-blind portion of both studies was 6 months long. Patients recorded the time spent in the "On" and "Off" states in home diaries periodically throughout the duration of the study. In one study, conducted in the Nordic countries, the primary outcome measure was the total mean time spent in the "On" state during an 18-hour diary recorded day (6 AM to midnight). In the other study, the primary outcome measure was the proportion of awake time spent over 24 hours in the "On" state.

In addition to the primary outcome measure: the amount of time spent in the "Off" state, subparts of the Unified Parkinson's Disease Rating Scale (UPDRS) including mentation (Part I), activities of daily living (ADL) (Part II), motor function (Part III), complications of therapy (Part IV), and disease staging (Part V and VI) were assessed. Additional secondary endpoints included the investigator's and patient's global assessment of clinical condition, a 7-point subjective scale designed to assess global functioning in Parkinson's disease; and the change in daily levodopa and carbidopa dose.

In one of the studies, 171 patients were randomized in 16 centers in Finland, Norway, Sweden, and Denmark (Nordic study), all of whom received concomitant levodopa plus dopa-decarboxylase inhibitor (either levodopa and carbidopa or levodopa and benserazide). In the second study, 205 patients were randomized in 17 centers in North America (US and Canada); all patients received concomitant levodopa and carbidopa.

The following tables display the results of these two studies:

Effects on "On" time did not differ by age, sex, weight, disease severity at baseline, levodopa dose and concurrent treatment with dopamine agonists or selegiline.

Drugs Metabolized By Catechol-O-Methyltransferase (COMT)

When a single 400 mg dose of entacapone was given with intravenous isoprenaline (isoproterenol) and epinephrine without coadministered levodopa and dopa decarboxylase inhibitor, the overall mean maximal changes in heart rate during infusion were about 50% and 80% higher than with placebo, for isoprenaline and epinephrine, respectively.

Therefore, drugs known to be metabolized by COMT, such as isoproterenol, epinephrine, norepinephrine, dopamine, dobutamine, alpha-methyldopa, apomorphine, isoetherine, and bitolterol should be administered with caution in patients receiving entacapone regardless of the route of administration (including inhalation), as their interaction may result in increased heart rates, possible arrhythmias, and excessive changes in blood pressure.

Ventricular tachycardia was noted in one 32-year-old healthy male volunteer in an interaction study after epinephrine infusion and oral entacapone administration. Treatment with propranolol was required. A causal relationship to entacapone administration appears probable but cannot be attributed with certainty.

Falling Asleep During Activities of Daily Living and Somnolence

Patients with Parkinson's disease treated with Comtan, which increases plasma levodopa levels, or with levodopa have reported suddenly falling asleep without prior warning of sleepiness while engaged in ADL (including the operation of motor vehicles). Some of these episodes resulted in accidents. Although many of these patients reported somnolence while on Comtan, some did not perceive warning signs, such as excessive drowsiness, and believed that they were alert immediately prior to the event. Some of these events have been reported as late as one year after initiation of treatment.

The risk of somnolence was increased (Comtan 2% and placebo 0%) in controlled studies. It has been reported that falling asleep while engaged in ADL always occurs in a setting of preexisting somnolence, although patients may not give such a history. For this reason, prescribers should reassess patients for drowsiness or sleepiness especially since some of the events occur well after the start of treatment. Prescribers should also be aware that patients may not acknowledge drowsiness or sleepiness until directly questioned about drowsiness or sleepiness during specific activities. Patients should be advised to exercise caution while driving, operating machines, or working at heights during treatment with Comtan. Patients who have already experienced somnolence and/or an episode of sudden sleep onset should not participate in these activities during treatment with Comtan.

Before initiating treatment with Comtan, advise patients of the potential to develop drowsiness and specifically ask about factors that may increase this risk such as concomitant use of sedating medications and the presence of sleep disorders. If a patient develops daytime sleepiness or episodes of falling asleep during activities that require active participation (e.g., conversations, eating, etc.), Comtan should ordinarily be discontinued (see DOSAGE AND ADMINISTRATION for guidance on discontinuing Comtan). If the decision is made to continue Comtan, patients should be advised not to drive and to avoid other potentially dangerous activities. There is insufficient information to establish whether dose reduction will eliminate episodes of falling asleep while engaged in ADL.

Hypotension, Orthostatic Hypotension, and Syncope

Dopaminergic therapy in Parkinson's disease patients has been associated with orthostatic hypotension. Entacapone enhances levodopa bioavailability and, therefore, might be expected to increase the occurrence of orthostatic hypotension. In controlled studies, approximately 1.2% and 0.8% of 200 mg entacapone and placebo patients, respectively, reported at least one episode of syncope. Reports of syncope were generally more frequent in patients in both treatment groups who had an episode of documented hypotension.

Hallucinations and Psychotic-Like Behavior

Dopaminergic therapy in patients with Parkinson's disease has been associated with hallucinations. In clinical studies, hallucinations led to drug discontinuation and premature withdrawal in 0.8% and 0% of patients treated with 200 mg Comtan and placebo, respectively. Hallucinations led to hospitalization in 1.0% and 0.3% of patients in the 200 mg Comtan and placebo groups, respectively. Agitation occurred in 1% of patients treated with Comtan and 0% treated with placebo.

Postmarketing reports indicate that patients may experience new or worsening mental status and behavioral changes, which may be severe, including psychotic-like behavior during Comtan treatment or after starting or increasing the dose of Comtan. Other drugs prescribed to improve the symptoms of Parkinson's disease can have similar effects on thinking and behavior. Abnormal thinking and behavior can cause paranoid ideation, delusions, hallucinations, confusion, disorientation, aggressive behavior, agitation, and delirium. Psychotic-like behaviors were also observed during the clinical development of Comtan.

Patients with a major psychotic disorder should ordinarily not be treated with Comtan because of the risk of exacerbating psychosis. In addition, certain medications used to treat psychosis may exacerbate the symptoms of Parkinson's disease and may decrease the effectiveness of Comtan (see PRECAUTIONS).

Impulse Control and Compulsive Behaviors

Postmarketing reports suggest that patients treated with anti-Parkinson medications can experience intense urges to gamble, increased sexual urges, intense urges to spend money uncontrollably, and other intense urges. Patients may be unable to control these urges while taking one or more of the medications that are used for the treatment of Parkinson's disease and that increase central dopaminergic tone, including Comtan taken with levodopa and carbidopa. In some cases, although not all, these urges were reported to have stopped when the dose of anti-Parkinson medications was reduced or discontinued. Because patients may not recognize these behaviors as abnormal it is important for prescribers to specifically ask patients or their caregivers about the development of new or increased gambling urges, sexual urges, uncontrolled spending or other urges while being treated with entacapone. Physicians should consider dose reduction or stopping Comtan if a patient develops such urges while taking Comtan.

Diarrhea and Colitis

In clinical studies, diarrhea developed in 60 of 603 (10%) and 16 of 400 (4%) of patients treated with 200 mg Comtan and placebo, respectively. In patients treated with Comtan, diarrhea was generally mild to moderate in severity (8.6%) but was regarded as severe in 1.3%. Diarrhea resulted in withdrawal in 10 of 603 (1.7%) patients, 7 (1.2%) with mild and moderate diarrhea and 3 (0.5%) with severe diarrhea. Diarrhea generally resolved after discontinuation of Comtan. Two patients with diarrhea were hospitalized. Typically, diarrhea presents within 4 weeks to 12 weeks after entacapone is started, but it may appear as early as the first week and as late as many months after the initiation of treatment. Diarrhea may be associated with weight loss, dehydration, and hypokalemia.

Postmarketing experience has shown that diarrhea may be a sign of drug-induced microscopic colitis, primarily lymphocytic colitis. In these cases, diarrhea has usually been moderate to severe, watery, and non-bloody, at times associated with dehydration, abdominal pain, weight loss, and hypokalemia. In the majority of cases, diarrhea and other colitis-related symptoms resolved or significantly improved when Comtan treatment was stopped. In some patients with biopsy confirmed colitis, diarrhea had resolved or significantly improved after discontinuation of Comtan but recurred after retreatment with Comtan.

If prolonged diarrhea is suspected to be related to Comtan, the drug should be discontinued and appropriate medical therapy considered. If the cause of prolonged diarrhea remains unclear or continues after stopping entacapone, then further diagnostic investigations including colonoscopy and biopsies should be considered.

Dyskinesia

Comtan may potentiate the dopaminergic side effects of levodopa and may cause or exacerbate preexisting dyskinesia. Although decreasing the dose of levodopa may ameliorate this side effect, many patients in controlled studies continued to experience frequent dyskinesia despite a reduction in their dose of levodopa. The incidence of dyskinesia was 25% for treatment with Comtan and 15% for placebo. The incidence of study withdrawal for dyskinesia was 1.5% for 200 mg Comtan and 0.8% for placebo.

Other Events Reported With Dopaminergic Therapy

The events listed below are events associated with the use of drugs that increase dopaminergic activity:

Renal Toxicity

In a 1-year toxicity study, entacapone (plasma exposure 20 times that in humans receiving the maximum recommended daily dose of 1,600 mg) caused an increased incidence of nephrotoxicity in male rats that was characterized by regenerative tubules, thickening of basement membranes, infiltration of mononuclear cells, and tubular protein casts. These effects were not associated with changes in clinical chemistry parameters, and there is no established method for monitoring for the possible occurrence of these lesions in humans. Although this toxicity could represent a species-specific effect, there is not yet evidence that this is so.

Hepatic Impairment

Patients with hepatic impairment should be treated with caution. The AUC and Cmax of entacapone approximately doubled in patients with documented liver disease compared to controls (see CLINICAL PHARMACOLOGY, Pharmacokinetics of Entacapone and DOSAGE AND ADMINISTRATION).

Information for Patients

Instruct patients to take Comtan only as prescribed.

Inform patients that hallucinations and/or other psychotic-like behavior can occur.

Advise patients that they may develop postural (orthostatic) hypotension with or without symptoms such as dizziness, nausea, syncope, and sweating. Hypotension may occur more frequently during initial therapy. Accordingly, patients should be cautioned against rising rapidly after sitting or lying down, especially if they have been doing so for prolonged periods, and especially at the initiation of treatment with Comtan.

Advise patients that they should neither drive a car nor operate other complex machinery until they have gained sufficient experience on Comtan to gauge whether or not it affects their mental and/or motor performance adversely. Warn patients about the possibility of sudden onset of sleep during daily activities, in some cases without awareness or warning signs, when they are taking dopaminergic agents, including Comtan. Because of the possible additive sedative effects, caution should be used when patients are taking other CNS depressants in combination with Comtan.

Inform patients that nausea may occur, especially at the initiation of treatment with Comtan.

Inform patients that diarrhea may occur with Comtan and it may have a delayed onset. Sometimes prolonged diarrhea may be caused by colitis (inflammation of the large intestine). Patients with diarrhea should drink fluids to maintain adequate hydration and monitor for weight loss. If diarrhea associated with Comtan is prolonged, discontinuing the drug is expected to lead to resolution, if diarrhea continues after stopping entacapone, further diagnostic investigations may be needed.

Advise patients about the possibility of an increase in dyskinesia.

Tell patients that treatment with entacapone may cause a change in the color of their urine (a brownish orange discoloration) that is not clinically relevant. In controlled studies, 10% of patients treated with Comtan reported urine discoloration compared to 0% of placebo patients.

Although Comtan has not been shown to be teratogenic in animals, it is always given in conjunction with levodopa and carbidopa, which is known to cause visceral and skeletal malformations in rabbits. Accordingly, patients should be advised to notify their physicians if they become pregnant or intend to become pregnant during therapy (see PRECAUTIONS, Pregnancy).

Entacapone is excreted into maternal milk in rats. Because of the possibility that entacapone may be excreted into human maternal milk, advise patients to notify their physicians if they intend to breastfeed or are breastfeeding an infant.

Tell patients and family members to notify their healthcare practitioner if they notice that the patient develops unusual urges or behaviors.

Laboratory Tests

Comtan is a chelator of iron. The impact of entacapone on the body's iron stores is unknown; however, a tendency towards decreasing serum iron concentrations was noted in clinical studies. In a controlled clinical study, serum ferritin levels (as marker of iron deficiency and subclinical anemia) were not changed with entacapone compared to placebo after one year of treatment and there was no difference in rates of anemia or decreased hemoglobin levels.

Special Populations

Patients with hepatic impairment should be treated with caution (see INDICATIONS, DOSAGE AND ADMINISTRATION).

Drug Interactions

In vitro studies of human CYP enzymes showed that entacapone inhibited the CYP enzymes 1A2, 2A6, 2C9, 2C19, 2D6, 2E1 and 3A only at very high concentrations (IC50 from 200 microM to over 1,000 microM; an oral 200 mg dose achieves a highest level of approximately 5 microM in people); these enzymes would therefore not be expected to be inhibited in clinical use.

In an interaction study in healthy volunteers, entacapone did not significantly change the plasma levels of S-warfarin, while the AUC for R-warfarin increased on average by 18% [CI90 11% to 26%], and the international normalized ratio (INR) values increased on average by 13% [CI90 6% to 19%]. Nevertheless, cases of significantly increased INR in patients concomitantly using warfarin have been reported during the postapproval use of Comtan. Therefore, monitoring of INR is recommended when entacapone treatment is initiated or when the dose is increased for patients receiving warfarin.

Protein Binding

Entacapone is highly protein bound (98%). In vitro studies have shown no binding displacement between entacapone and other highly bound drugs, such as warfarin, salicylic acid, phenylbutazone, and diazepam.

Drugs Metabolized by Catechol-O-Methyltransferase (COMT)

See WARNINGS.

Hormone Levels

Levodopa is known to depress prolactin secretion and increase growth hormone levels. Treatment with entacapone coadministered with levodopa and dopa decarboxylase inhibitor does not change these effects.

Effect of Entacapone on the Metabolism of Other Drugs

See WARNINGS regarding concomitant use of Comtan and non-selective MAO inhibitors.

No interaction was noted with the MAO-B inhibitor selegiline in two multiple-dose interaction studies when entacapone was coadministered with a levodopa and dopa decarboxylase inhibitor (n = 29). More than 600 patients with Parkinson's disease in clinical studies have used selegiline in combination with entacapone and levodopa and dopa decarboxylase inhibitor.

As most entacapone excretion is via the bile, caution should be exercised when drugs known to interfere with biliary excretion, glucuronidation, and intestinal beta-glucuronidase are given concurrently with entacapone. These include probenecid, cholestyramine, and some antibiotics (e.g., erythromycin, rifampicin, ampicillin, and chloramphenicol).

No interaction with the tricyclic antidepressant imipramine was shown in a single-dose study with entacapone without coadministered levodopa and dopa-decarboxylase inhibitor.

Carcinogenesis

Two-year carcinogenicity studies of entacapone were conducted in mice and rats. In mice, no increase in tumors was observed at oral doses of 100, 200 and 400 mg/kg/day. At the highest dose tested, plasma exposures (AUC) were 4 times higher than that in humans at the maximum recommended daily dose (MRDD) of 1,600 mg. In rats administered oral doses of 20, 90, or 400 mg/kg/day, an increased incidence of renal tubular adenomas and carcinomas was observed in males at the highest dose tested. Plasma AUCs at the higher dose not associated with increased renal tumors (90 mg/kg/day) were approximately 5 times that in humans at the MRDD of entacapone.

The carcinogenic potential of entacapone administered in combination with levodopa and carbidopa has not been evaluated.

Mutagenesis

Entacapone was mutagenic and clastogenic in the in vitro mouse lymphoma tk assay in the presence and absence of metabolic activation, and was clastogenic in cultured human lymphocytes in the presence of metabolic activation. Entacapone, either alone or in combination with levodopa and carbidopa, was not clastogenic in the in vivo mouse micronucleus test or mutagenic in the bacterial reverse mutation assay (Ames test).

Impairment of Fertility

Entacapone did not impair fertility or general reproductive performance in rats treated with up to 700 mg/kg/day (plasma AUCs 28 times those in humans receiving the MRDD of 1,600 mg). Delayed mating, but no fertility impairment, was evident in female rats treated with 700 mg/kg/day of entacapone.

Pregnancy

In embryo-fetal development studies, entacapone was administered to pregnant animals throughout organogenesis at doses of up to 1,000 mg/kg/day in rats and 300 mg/kg/day in rabbits. Increased incidences of fetal variations were evident in litters from rats treated with the highest dose, in the absence of overt signs of maternal toxicity. The maternal plasma drug exposure (AUC) associated with this dose was approximately 34 times the estimated plasma exposure in humans receiving the maximum recommended daily dose (MRDD) of 1,600 mg. Increased frequencies of abortions, late and total resorptions, and decreased fetal weights were observed in the litters of rabbits treated with maternally toxic doses of 100 mg/kg/day (plasma AUCs 0.4 times those in humans receiving the MRDD) or greater. There was no evidence of teratogenicity in these studies.

However, when entacapone was administered to female rats prior to mating and during early gestation, an increased incidence of fetal eye anomalies (macrophthalmia, microphthalmia, anophthalmia) was observed in the litters of dams treated with doses of 160 mg/kg/day (plasma AUCs 7 times those in humans receiving the MRDD) or greater, in the absence of maternal toxicity. Administration of up to 700 mg/kg/day (plasma AUCs 28 times those in humans receiving the MRDD) to female rats during the latter part of gestation and throughout lactation produced no evidence of developmental impairment in the offspring.

Entacapone is always given concomitantly with levodopa and carbidopa, which is known to cause visceral and skeletal malformations in rabbits. The teratogenic potential of entacapone in combination with levodopa and carbidopa was not assessed in animals.

There is no experience from clinical studies regarding the use of Comtan in pregnant women. Therefore, Comtan should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Women

In animal studies, entacapone was excreted into maternal rat milk.

It is not known whether entacapone is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when entacapone is administered to a nursing woman.

Pediatric Use

Safety and effectiveness in pediatric patients have not been established.

Adverse Event Incidence in Controlled Clinical Studies

Table 4 lists treatment-emergent adverse events that occurred in at least 1% of patients treated with entacapone participating in the double-blind, placebo-controlled studies and that were numerically more common in the Comtan group, compared to placebo. In these studies, either Comtan or placebo was added to levodopa and carbidopa (or levodopa and benserazide).

Effects of Gender and Age on Adverse Reactions

No differences were noted in the rate of adverse events attributable to entacapone by age or gender.

Postmarketing Reports

The following spontaneous reports of adverse events temporally associated with Comtan have been identified since market introduction and are not listed in Table 4. Because these reactions are reported voluntarily from a population of unknown size, it is not always possible to reliably estimate their frequency or establish causal relationship to Comtan exposure.

Hepatitis with mainly cholestatic features has been reported.

To report SUSPECTED ADVERSE REACTIONS, contact Almatica Pharma LLC at 1-877-447-7979 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

Management of Overdose

Management of Comtan overdose is symptomatic; there is no known antidote to Comtan. Hospitalization is advised, and general supportive care is indicated. There is no experience with hemodialysis or hemoperfusion, but these procedures are unlikely to be of benefit, because Comtan is highly bound to plasma proteins. An immediate gastric lavage and repeated doses of charcoal over time may hasten the elimination of Comtan by decreasing its absorption and reabsorption from the gastrointestinal (GI) tract. The adequacy of the respiratory and circulatory systems should be carefully monitored and appropriate supportive measures employed. The possibility of drug interactions, especially with catechol-structured drugs, should be borne in mind.

Patients With Impaired Hepatic Function: Patients with hepatic impairment should be treated with caution. The AUC and Cmax of entacapone approximately doubled in patients with documented liver disease, compared to controls. However, these studies were conducted with single-dose entacapone without levodopa and dopa decarboxylase inhibitor coadministration, and therefore the effects of liver disease on the kinetics of chronically administered entacapone have not been evaluated (see CLINICAL PHARMACOLOGY, Pharmacokinetics of Entacapone).

Withdrawing Patients from Comtan: Rapid withdrawal or abrupt reduction in the Comtan dose could lead to emergence of signs and symptoms of Parkinson's disease (see CLINICAL PHARMACOLOGY, Clinical Studies), and may lead to hyperpyrexia and confusion, a symptom complex resembling NMS (see PRECAUTIONS, Other Events Reported With Dopaminergic Therapy). This syndrome should be considered in the differential diagnosis for any patient who develops a high fever or severe rigidity. If a decision is made to discontinue treatment with Comtan, patients should be monitored closely and other dopaminergic treatments should be adjusted as needed. Although tapering Comtan has not been systematically evaluated, it seems prudent to withdraw patients slowly if the decision to discontinue treatment is made.

Store at 25°C (77°F); excursions permitted to 15°C to 30°C (59°F to 86°F). [See USP Controlled Room Temperature.]