Comtan: Uses, Dosage & Side Effects
A COMT inhibitor used alongside levodopa to treat end-of-dose motor fluctuations in Parkinson's disease
Comtan (entacapone) is a prescription medication used as an adjunct to levodopa/carbidopa or levodopa/benserazide preparations in the treatment of Parkinson's disease. It belongs to a class of drugs known as catechol-O-methyltransferase (COMT) inhibitors. Entacapone works by blocking the COMT enzyme in peripheral tissues, which normally breaks down levodopa before it can reach the brain. By inhibiting this enzyme, Comtan extends the duration and effectiveness of each levodopa dose, helping to reduce the "wearing-off" motor fluctuations that many patients with Parkinson's disease experience. Comtan is always taken together with each dose of levodopa and should never be used as a standalone treatment for Parkinson's disease.
Quick Facts: Comtan
Key Takeaways
- Comtan (entacapone) is a COMT inhibitor that must always be taken together with levodopa/carbidopa or levodopa/benserazide – it has no anti-parkinsonian effect on its own.
- By inhibiting peripheral COMT, entacapone increases the bioavailability and duration of action of levodopa, reducing "wearing-off" motor fluctuations between doses.
- The standard dose is one 200 mg tablet taken with each levodopa dose, up to a maximum of 10 tablets (2,000 mg) per day, with the levodopa dose often needing reduction by 10–30%.
- Common side effects include dyskinesia, nausea, diarrhea, abdominal pain, and harmless reddish-brown discoloration of urine – dyskinesia and nausea can often be managed by reducing the levodopa dose.
- Comtan must never be stopped abruptly, as sudden withdrawal can trigger symptoms resembling neuroleptic malignant syndrome (NMS) with high fever, muscle rigidity, and altered consciousness.
What Is Comtan and What Is It Used For?
Comtan contains the active substance entacapone, a selective, reversible inhibitor of the catechol-O-methyltransferase (COMT) enzyme. This medication was specifically developed to address one of the most common challenges in the long-term management of Parkinson's disease: the gradual emergence of motor fluctuations, particularly the "wearing-off" phenomenon, in patients treated with levodopa. While levodopa remains the most effective medication for controlling the motor symptoms of Parkinson's disease, its therapeutic benefit tends to become less predictable over time, with patients experiencing increasingly shorter periods of good symptom control ("on" time) between doses.
To understand how Comtan works, it is helpful to understand the fate of levodopa after oral administration. When a patient takes a levodopa-containing medication, only a small fraction of the administered dose actually reaches the brain, where it is converted into dopamine – the neurotransmitter that is deficient in Parkinson's disease. The majority of levodopa is metabolized in the peripheral tissues (gut, liver, and other organs) before it can cross the blood-brain barrier. Two enzymes are primarily responsible for this peripheral metabolism: aromatic L-amino acid decarboxylase (AADC) and catechol-O-methyltransferase (COMT). Standard Parkinson's medications already contain an AADC inhibitor (either carbidopa or benserazide) to block the first pathway. Entacapone blocks the second pathway by inhibiting COMT.
The COMT enzyme converts levodopa to an inactive metabolite called 3-O-methyldopa (3-OMD). When COMT is inhibited by entacapone, less levodopa is converted to 3-OMD, and more levodopa remains available for absorption into the bloodstream and subsequent transport across the blood-brain barrier. This results in higher and more sustained plasma concentrations of levodopa, which translates into a longer duration of the therapeutic "on" state and reduced motor fluctuations. Importantly, entacapone acts only in the periphery and does not cross the blood-brain barrier to a significant extent, so it does not directly affect dopamine metabolism in the brain.
Clinical studies have demonstrated that adding entacapone to levodopa/AADC inhibitor therapy produces clinically meaningful improvements in patients with Parkinson's disease who experience wearing-off fluctuations. In pivotal phase III trials involving over 1,000 patients, entacapone significantly increased daily "on" time by approximately 1 to 1.5 hours while correspondingly reducing "off" time. These benefits were accompanied by improvements in motor function as measured by the Unified Parkinson's Disease Rating Scale (UPDRS) and in patients' overall quality of life. The clinical efficacy of entacapone has been confirmed in multiple randomized, double-blind, placebo-controlled trials and in large-scale observational studies in routine clinical practice.
Comtan was first approved by the European Medicines Agency (EMA) in 1998 and by the U.S. Food and Drug Administration (FDA) in 1999. It has since become one of the most widely prescribed adjunctive therapies for Parkinson's disease worldwide. Entacapone is also available in a combination tablet with levodopa and carbidopa (marketed as Stalevo), which simplifies the medication regimen for patients who require all three drugs. The Movement Disorder Society (MDS) and the National Institute for Health and Care Excellence (NICE) have included COMT inhibitors as recommended options for the management of motor fluctuations in their evidence-based guidelines for Parkinson's disease treatment.
Wearing-off is the term used to describe the return of Parkinson's symptoms before the next scheduled dose of levodopa. It occurs because the brain's ability to store dopamine decreases as the disease progresses, making patients increasingly dependent on a continuous supply of levodopa. Common wearing-off symptoms include tremor, stiffness, slowness of movement, difficulty walking, and non-motor symptoms such as anxiety and pain. Comtan helps by extending the time each levodopa dose remains effective, reducing the total daily "off" time.
What Should You Know Before Taking Comtan?
Contraindications
There are several important contraindications to Comtan use that must be carefully evaluated before starting treatment. The primary absolute contraindications include hypersensitivity (allergy) to entacapone or to any of the excipients in the formulation. Additional contraindications reflect the pharmacological mechanism of entacapone and the potential for serious adverse events in specific clinical situations.
Pheochromocytoma: Comtan is contraindicated in patients with pheochromocytoma, a rare tumor of the adrenal gland that produces excessive catecholamines. Because entacapone inhibits the metabolism of catecholamines by COMT, using Comtan in patients with pheochromocytoma could precipitate a hypertensive crisis with dangerously elevated blood pressure. Patients should be screened for pheochromocytoma before starting Comtan therapy if there is any clinical suspicion.
Severe hepatic impairment: Comtan is contraindicated in patients with severe liver disease. Entacapone is extensively metabolized by the liver, primarily through glucuronidation. In patients with significant hepatic dysfunction, the clearance of entacapone may be substantially reduced, leading to elevated plasma concentrations and increased risk of adverse effects. Patients with mild to moderate liver impairment should be monitored carefully, but severe hepatic impairment is an absolute contraindication.
History of neuroleptic malignant syndrome (NMS) or non-traumatic rhabdomyolysis: Patients with a history of NMS or rhabdomyolysis should not use Comtan. Both conditions have been reported in association with COMT inhibitor use, and a prior history significantly increases the risk of recurrence.
Concurrent use of non-selective MAO inhibitors: The combination of entacapone with non-selective monoamine oxidase (MAO) inhibitors (such as phenelzine or tranylcypromine) is contraindicated due to the risk of inhibiting the majority of pathways responsible for catecholamine metabolism. The selective MAO-B inhibitors selegiline and rasagiline can be used with Comtan, but the daily dose of selegiline should not exceed 10 mg.
Warnings and Precautions
Abrupt discontinuation of Comtan can cause symptoms resembling neuroleptic malignant syndrome (NMS), including high fever, severe muscle rigidity, altered consciousness, and elevated creatine kinase. If Comtan needs to be stopped, your doctor will gradually reduce the dose while adjusting other Parkinson's medications. Seek immediate medical attention if you develop unexplained high fever or muscle rigidity.
Several important precautions should be discussed with your healthcare provider before and during treatment with Comtan:
- Dyskinesia: Because Comtan increases the bioavailability of levodopa, it may intensify levodopa-related side effects, particularly dyskinesia (involuntary movements). This is the most common reason for dose adjustment when starting Comtan. Your doctor may need to reduce your levodopa dose by approximately 10–30% during the first days to weeks of Comtan treatment, especially if your pre-existing dyskinesia is moderate to severe.
- Diarrhea: Entacapone-associated diarrhea is a recognized adverse effect that typically develops 4 to 12 weeks after starting treatment. In most cases it is mild to moderate, but in some patients it may be severe enough to require discontinuation of the drug. If diarrhea develops during Comtan treatment, report it to your doctor. Adequate fluid and electrolyte replacement is important.
- Hepatic effects: Although rare, cases of hepatotoxicity have been reported with COMT inhibitors. Liver function tests should be checked before starting Comtan and periodically during treatment. Report any symptoms suggestive of liver problems (jaundice, dark urine, persistent fatigue, abdominal pain) to your doctor immediately.
- Impulse control disorders: Patients with Parkinson's disease treated with dopaminergic medications, including levodopa combined with COMT inhibitors, may develop impulse control disorders such as pathological gambling, increased libido, compulsive spending, or binge eating. If you or your family notice such behavioral changes, inform your doctor promptly.
- Orthostatic hypotension: Comtan may worsen orthostatic hypotension (a drop in blood pressure when standing up), particularly during the initial period of treatment. Use caution when standing up from a sitting or lying position, especially at the beginning of treatment or when doses are adjusted.
Pregnancy and Breastfeeding
Comtan should not be used during pregnancy unless the potential benefit to the mother clearly outweighs the potential risk to the fetus. Animal reproductive toxicity studies have shown that entacapone, administered at doses significantly higher than the human therapeutic dose, can cause some developmental toxicity including increased embryofetal lethality and delayed skeletal development. However, there is very limited clinical experience with entacapone use in pregnant women, and the relevance of these animal findings to humans is uncertain. If you are pregnant, planning to become pregnant, or discover that you are pregnant while taking Comtan, consult your neurologist immediately to discuss the risks and benefits of continuing treatment.
It is not known whether entacapone is excreted in human breast milk. In animal studies, entacapone was found in the milk of lactating rats. Because a risk to the breastfed infant cannot be excluded, breastfeeding is generally not recommended during Comtan treatment. The decision to breastfeed during treatment should be made in consultation with your doctor, considering the benefit of breastfeeding to the infant and the benefit of Comtan treatment to the mother.
Driving and Operating Machinery
Comtan, in combination with levodopa, may cause somnolence (excessive sleepiness) and episodes of sudden onset of sleep. Patients have reported falling asleep without warning during daily activities, including driving. If you experience excessive daytime sleepiness or episodes of sudden sleep onset, you should refrain from driving and operating machinery and contact your doctor. Patients who have experienced somnolence or an episode of sudden sleep onset should not drive or operate machines until such recurring episodes and somnolence have resolved.
How Does Comtan Interact with Other Drugs?
Understanding the drug interactions of Comtan is essential for safe and effective use. Because entacapone inhibits COMT, an enzyme involved in the metabolism of catecholamines and other catechol-structured compounds, it has the potential to interact with several classes of medications. Unlike many traditional medications, entacapone is metabolized primarily by glucuronidation rather than by cytochrome P450 (CYP) enzymes, which limits the range of its pharmacokinetic interactions but does not eliminate them entirely.
The most clinically significant interactions involve drugs that affect catecholamine metabolism or catechol-structured compounds. Your healthcare provider should be aware of all medications you are taking, including prescription drugs, over-the-counter medicines, herbal supplements, and vitamins, before starting Comtan therapy.
| Drug / Class | Interaction Type | Clinical Significance | Recommendation |
|---|---|---|---|
| Non-selective MAO inhibitors (phenelzine, tranylcypromine) | Pharmacodynamic – excessive catecholamine inhibition | Major – Contraindicated | Do not use together. Risk of hypertensive crisis. |
| Iron preparations (ferrous sulfate, iron supplements) | Pharmacokinetic – chelation in GI tract | Moderate | Separate administration by at least 2–3 hours. |
| Warfarin (coumarin anticoagulants) | Pharmacokinetic – potential displacement from protein binding | Moderate | Monitor INR closely when starting or stopping Comtan. |
| Catecholamines (epinephrine, norepinephrine, dobutamine, isoprenaline) | Pharmacodynamic – prolonged catecholamine action | Moderate | Use with caution. Monitor heart rate and blood pressure. |
| Selective MAO-B inhibitors (selegiline, rasagiline) | Pharmacodynamic – additive dopaminergic effect | Low – Generally safe | Can be used together. Selegiline max 10 mg/day. |
| Apomorphine | Pharmacodynamic – potentiated effect | Moderate | May need dose reduction of one or both drugs. |
| Tricyclic antidepressants (imipramine, desipramine) | Pharmacokinetic – both are catechol-structured or affect catecholamines | Low – Theoretical | Use with monitoring. No dose adjustment usually needed. |
Major Interactions
The most critical drug interaction involves non-selective monoamine oxidase (MAO) inhibitors. Both COMT and MAO are involved in the metabolism of catecholamines (dopamine, norepinephrine, and epinephrine). Simultaneous inhibition of both enzymes could lead to dangerously elevated levels of these catecholamines, potentially causing severe hypertension, cardiac arrhythmias, and other serious cardiovascular events. For this reason, the combination of entacapone with non-selective MAO inhibitors such as phenelzine and tranylcypromine is absolutely contraindicated. If a patient requires both a COMT inhibitor and an MAO inhibitor, a washout period of at least 14 days is recommended between discontinuation of the MAO inhibitor and initiation of entacapone.
The interaction with iron preparations is also clinically important. Entacapone can form chelates with iron in the gastrointestinal tract, reducing the absorption of both entacapone and iron. Patients who need iron supplementation should take their iron preparations at least 2 to 3 hours apart from Comtan. This is particularly relevant for patients with Parkinson's disease, as anemia and iron deficiency are relatively common comorbidities in this population.
Minor Interactions
The interaction with warfarin and other coumarin anticoagulants is based on the theoretical potential for entacapone to displace warfarin from plasma protein binding sites, as entacapone is highly protein-bound (approximately 98%). While clinically significant changes in INR have been reported only rarely, monitoring of INR is recommended when Comtan is started, stopped, or when the dose is changed in patients taking warfarin. This precaution applies to all coumarin-type anticoagulants.
Entacapone does not significantly inhibit or induce cytochrome P450 enzymes at therapeutic doses, so interactions mediated through CYP enzyme pathways are not expected. This means that most common medications, including antihypertensives, statins, proton pump inhibitors, and many other drug classes, can generally be used safely alongside Comtan without dose adjustment. However, because entacapone enhances levodopa bioavailability, the most frequent "interaction" in clinical practice is the need to reduce the levodopa dose when starting Comtan to avoid excessive dopaminergic stimulation.
When starting Comtan, your doctor may reduce your levodopa dose by 10–30%, particularly if you are already experiencing dyskinesia or nausea. This is not technically a drug interaction but rather a pharmacokinetic consequence of improved levodopa bioavailability. The degree of dose reduction needed varies between patients and should be guided by clinical response and tolerability.
What Is the Correct Dosage of Comtan?
Comtan should always be used exactly as prescribed by your doctor. The dosing of Comtan is uniquely straightforward: the same dose is taken with every levodopa administration, without the need for dose titration. However, the total daily dose depends on how many times per day you take levodopa. Understanding the correct dosing regimen is essential for optimal benefit and to avoid unnecessary side effects.
Adults
| Parameter | Recommendation | Notes |
|---|---|---|
| Standard dose | 200 mg (1 tablet) with each levodopa dose | Always taken simultaneously with levodopa |
| Maximum daily dose | 2,000 mg (10 tablets) | Corresponds to 10 levodopa doses per day |
| Levodopa adjustment | Reduce levodopa by 10–30% | Especially if dyskinesia or nausea present |
| Administration | Oral, with or without food | Swallow whole; do not crush or chew |
Comtan is taken as one 200 mg film-coated tablet with each dose of levodopa/carbidopa or levodopa/benserazide. It can be taken with or without food. Each tablet should be swallowed whole with a glass of water. The tablet should not be crushed, broken, or chewed. The onset of action is rapid, with the effect on levodopa pharmacokinetics apparent from the first dose.
When Comtan is added to existing levodopa therapy, the enhanced bioavailability of levodopa may cause or worsen dyskinesia and other dopaminergic side effects. In clinical trials, approximately 60–70% of patients starting Comtan required a reduction in their levodopa dose. The average reduction was approximately 10–30% of the previous daily levodopa dose. Your doctor will determine the appropriate levodopa dose reduction based on your individual clinical response. This adjustment is typically made during the first few days to weeks of Comtan treatment.
Children and Adolescents
The safety and efficacy of Comtan in children and adolescents under 18 years of age have not been established. Parkinson's disease is extremely rare in this age group, and there are no clinical data to support the use of entacapone in pediatric patients. Comtan should not be used in children or adolescents.
Elderly Patients
No dose adjustment of Comtan is required for elderly patients solely on the basis of age. The majority of patients with Parkinson's disease are elderly, and clinical trials included a representative population of older adults. The safety and efficacy profile of entacapone was consistent across age groups. However, elderly patients may be more susceptible to orthostatic hypotension, somnolence, and confusion, so careful monitoring is recommended, particularly during the initiation of treatment or dose adjustments.
Missed Dose
If you forget to take a Comtan tablet with a levodopa dose, simply take the next Comtan tablet with your next scheduled levodopa dose. Do not take a double dose to make up for a missed dose. Missing an occasional dose of Comtan is unlikely to cause significant problems, but regular omission will reduce the benefit of treatment. If you frequently forget to take your Comtan, discuss this with your doctor, who may consider prescribing a combination tablet containing levodopa, carbidopa, and entacapone (Stalevo) to simplify your medication regimen.
Overdose
There is limited clinical experience with entacapone overdose. The highest single doses of entacapone administered in clinical studies were 800 mg, resulting in increased plasma levels but no additional clinical benefit. In the event of overdose, supportive and symptomatic treatment is recommended. Hospitalization may be warranted for observation and monitoring. The theoretical risk in overdose is related to enhanced dopaminergic stimulation from increased levodopa bioavailability, which could manifest as severe dyskinesia, nausea, vomiting, and cardiovascular disturbances. Due to entacapone's high protein binding, dialysis is unlikely to be effective for removal.
Comtan has no anti-parkinsonian effect when taken alone. It must always be administered together with a levodopa/carbidopa or levodopa/benserazide preparation. Taking Comtan without levodopa provides no therapeutic benefit and should be avoided. If your levodopa is temporarily discontinued for any reason, Comtan should also be stopped – but only under medical supervision to avoid withdrawal effects.
What Are the Side Effects of Comtan?
Like all medicines, Comtan can cause side effects, although not everybody gets them. The side effect profile of Comtan reflects both the direct effects of entacapone itself and the indirect consequences of enhanced levodopa activity. Understanding which side effects are related to the increased dopaminergic effect (and therefore manageable through levodopa dose reduction) versus those that are intrinsic to entacapone is important for optimal clinical management.
The following frequency categories are used in accordance with international medical convention based on clinical trial data and post-marketing surveillance:
Very Common
Affects more than 1 in 10 patients
- Dyskinesia (involuntary movements) – most common side effect, related to increased levodopa effect; usually manageable by reducing levodopa dose
- Nausea – also related to enhanced dopaminergic stimulation; often improves with levodopa dose reduction
- Urine discoloration – harmless reddish-brown coloring caused by entacapone metabolites; not a sign of blood in urine
Common
Affects 1 to 10 in 100 patients
- Diarrhea – may develop 4–12 weeks after starting; usually mild but can be severe in some cases
- Abdominal pain
- Dry mouth
- Constipation
- Vomiting
- Worsening of Parkinson's symptoms during dose adjustments
- Dizziness
- Fatigue and somnolence (excessive sleepiness)
- Insomnia
- Hallucinations
- Increased sweating
- Fall (related to orthostatic hypotension or motor symptoms)
Uncommon
Affects 1 to 10 in 1,000 patients
- Confusion
- Vivid dreams or nightmares
- Orthostatic hypotension (drop in blood pressure when standing)
- Chest pain (angina pectoris)
- Skin rash or urticaria
- Elevated liver enzymes
Rare
Affects 1 to 10 in 10,000 patients
- Neuroleptic malignant syndrome (NMS)-like symptoms – typically associated with abrupt dose reduction or discontinuation
- Rhabdomyolysis (muscle breakdown)
- Hepatotoxicity (liver damage)
- Agranulocytosis (severe reduction in white blood cells)
- Impulse control disorders (pathological gambling, increased libido, compulsive behavior)
Not Known
Frequency cannot be estimated from available data
- Hepatitis with cholestatic features
- Colitis (inflammation of the colon, in cases of severe persistent diarrhea)
- Dopamine dysregulation syndrome (addictive use of dopaminergic medications)
The most important distinction to understand is that many of Comtan's most common side effects (dyskinesia, nausea, vomiting, hallucinations) are not caused directly by entacapone but rather by the increased availability of levodopa in the brain. These dopaminergic side effects can almost always be managed by reducing the dose of levodopa. In clinical trials, levodopa dose reductions of 10–30% were sufficient to control these symptoms in the majority of patients while still maintaining the beneficial effects of Comtan on wearing-off.
Diarrhea is the most common side effect attributed directly to entacapone rather than to enhanced dopaminergic stimulation. It typically appears several weeks after initiating treatment, can range from mild to severe, and in most cases resolves upon discontinuation of Comtan. In clinical trials, approximately 2–4% of patients discontinued entacapone due to diarrhea. The mechanism behind entacapone-induced diarrhea is not fully understood but may involve altered gut motility or local effects in the gastrointestinal tract.
The reddish-brown discoloration of urine caused by entacapone and its metabolites is entirely harmless and should not be mistaken for hematuria (blood in the urine). This effect occurs in most patients and is not a reason to discontinue treatment. Patients should be informed about this expected change to avoid unnecessary concern.
Contact your doctor immediately or seek emergency care if you experience: unexplained high fever with muscle stiffness and altered consciousness (possible NMS), dark urine with yellowing of the skin or eyes (possible liver problems), severe persistent diarrhea with signs of dehydration, or any severe allergic reaction with difficulty breathing, swelling of the face or throat, or widespread rash.
How Should You Store Comtan?
Proper storage of Comtan is important to maintain the quality and efficacy of the medication throughout its shelf life. Entacapone film-coated tablets should be stored at room temperature, not exceeding 25°C (77°F). The tablets should be kept in the original package to protect them from moisture, as entacapone is sensitive to humidity. Do not store Comtan in the bathroom or other areas with high humidity.
The film-coated tablets should be stored in their blister packaging until you are ready to take them. Do not remove tablets from the blister pack in advance to store in a pill organizer for extended periods, as this may expose them to moisture and light that could affect their stability. However, short-term use of a daily pill organizer (for the current day's doses) is generally acceptable.
Do not use Comtan after the expiry date stated on the carton and blister pack. The expiry date refers to the last day of that month. Do not dispose of medications via household waste or wastewater. Ask your pharmacist how to dispose of medicines you no longer need. These measures help to protect the environment and prevent accidental ingestion by others.
Keep Comtan out of the sight and reach of children. Children are particularly vulnerable to the effects of dopaminergic medications, and accidental ingestion could be dangerous. If you suspect a child has accidentally taken Comtan, contact your local poison control center or seek emergency medical attention immediately.
What Does Comtan Contain?
The active substance in Comtan is entacapone. Each film-coated tablet contains 200 mg of entacapone. Entacapone is a nitrocatechol-type compound that selectively and reversibly inhibits the COMT enzyme. It appears as a brownish-orange, oval-shaped film-coated tablet.
The tablet core contains the following inactive ingredients (excipients): microcrystalline cellulose, mannitol (E421), croscarmellose sodium, hydrogenated vegetable oil, and magnesium stearate. These excipients serve various pharmaceutical functions including acting as fillers, binders, disintegrants, and lubricants to ensure consistent tablet quality and reliable drug release.
The film coating contains hypromellose, polysorbate 80, glycerol 85%, sucrose, magnesium stearate, iron oxide yellow (E172), iron oxide red (E172), and titanium dioxide (E171). The iron oxide pigments are responsible for the characteristic brownish-orange color of the tablet. The film coating serves to protect the tablet core, improve swallowability, and mask the taste of the active ingredient.
Comtan contains sucrose. If you have been told by your doctor that you have an intolerance to some sugars, contact your doctor before taking this medicinal product. The amount of sucrose per tablet is small and is unlikely to cause problems for most patients with sugar intolerance, but it should be discussed with your healthcare provider if you have hereditary fructose intolerance, glucose-galactose malabsorption, or sucrase-isomaltase insufficiency.
Frequently Asked Questions About Comtan
Comtan (entacapone) is used as an adjunctive treatment for Parkinson's disease in patients who are already taking levodopa/carbidopa or levodopa/benserazide and are experiencing "wearing-off" motor fluctuations. It works by inhibiting the COMT enzyme, which extends the duration and effectiveness of each levodopa dose, resulting in more stable symptom control and reduced "off" time. Comtan is never used alone – it must always be taken together with a levodopa preparation.
When you take levodopa, the enzyme COMT converts a significant portion of it to an inactive metabolite (3-O-methyldopa) before it can reach the brain. Comtan blocks COMT in the peripheral tissues, preventing this breakdown. As a result, more levodopa reaches the bloodstream and crosses the blood-brain barrier, where it is converted to dopamine. This means each levodopa dose lasts longer and works more effectively, reducing the time you spend in the "off" state.
The most common side effects are dyskinesia (involuntary movements), nausea, and harmless reddish-brown discoloration of urine. Dyskinesia and nausea are typically related to the increased levodopa effect and can usually be managed by reducing the levodopa dose by 10–30%. Diarrhea is also a common side effect that may appear several weeks after starting treatment. Other common effects include abdominal pain, dizziness, and fatigue. Most side effects are mild to moderate and often resolve with dose adjustment.
No, you should never stop taking Comtan suddenly without your doctor's guidance. Abrupt discontinuation can trigger symptoms resembling neuroleptic malignant syndrome (NMS), which includes high fever, severe muscle rigidity, altered consciousness, and elevated creatine kinase. If Comtan needs to be discontinued, your doctor will gradually reduce the dose while adjusting your levodopa and other Parkinson's medications to maintain stable symptom control.
Comtan and its metabolites naturally produce a reddish-brown pigment that is excreted in the urine. This discoloration is entirely harmless and is not a sign of blood in the urine or any kidney or bladder problem. It occurs in most patients taking entacapone and does not require any medical attention or change in treatment. The color change is simply a characteristic of how the drug is processed and eliminated by the body.
Comtan should not be used during pregnancy unless the potential benefit to the mother clearly outweighs the risk to the fetus. Animal studies have shown some reproductive toxicity at high doses. There is very limited data on the use of entacapone in pregnant women. If you are pregnant or planning to become pregnant, discuss alternative treatment options with your neurologist. Breastfeeding is also not recommended during Comtan treatment, as it is not known whether entacapone passes into breast milk.
References
- European Medicines Agency (EMA). Comtan (entacapone) – Summary of Product Characteristics. Last updated 2024. Available from: EMA website.
- U.S. Food and Drug Administration (FDA). Comtan (entacapone) Prescribing Information. Revised 2023. Available from: FDA DailyMed.
- Fox SH, Katzenschlager R, Lim SY, et al. International Parkinson and Movement Disorder Society Evidence-Based Medicine Review: Update on Treatments for the Motor Symptoms of Parkinson's Disease. Movement Disorders. 2018;33(8):1248–1266. doi:10.1002/mds.27372
- National Institute for Health and Care Excellence (NICE). Parkinson's disease in adults: diagnosis and management. NICE Guideline NG71. Last updated 2024.
- Stocchi F, Rascol O, Kieburtz K, et al. Initiating levodopa/carbidopa therapy with and without entacapone in early Parkinson disease: the STRIDE-PD study. Annals of Neurology. 2010;68(1):18–27. doi:10.1002/ana.22060
- Brooks DJ, Sagar H; UK-Irish Entacapone Study Group. Entacapone is beneficial in both fluctuating and non-fluctuating patients with Parkinson's disease: a randomised, placebo-controlled, double blind, six month study. Journal of Neurology, Neurosurgery & Psychiatry. 2003;74(8):1071–1079.
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List, 2023. Geneva: WHO; 2023.
- Poewe W, Antonini A, Zijlmans JC, et al. Levodopa in the treatment of Parkinson's disease: an old drug still going strong. Clinical Interventions in Aging. 2010;5:229–238.
- Ferreira JJ, Lees A, Rocha JF, et al. Opicapone as an adjunct to levodopa in patients with Parkinson's disease and end-of-dose motor fluctuations: a randomised, double-blind, controlled trial. The Lancet Neurology. 2016;15(2):154–165.
- British National Formulary (BNF). Entacapone. Available from: NICE BNF. Accessed December 2025.
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