Carbidopa / Entacapone / Levodopa

Carbidopa, levodopa, and entacapone tablets are approved for the treatment of Parkinson's disease in adults. The combination can be used in two specific ways:

• As a convenient single-tablet replacement for patients already taking carbidopa/levodopa and entacapone as separate pills — substituting at equivalent strengths of each component
• To add entacapone for patients currently on carbidopa/levodopa alone who are experiencing end-of-dose "wearing-off" symptoms, provided they are taking 600 mg or less of levodopa daily and have not had dyskinesias (uncontrolled involuntary movements)

Parkinson's disease is caused by a loss of dopamine in a part of the brain called the corpus striatum. Dopamine itself can't be given as a medicine because it can't cross from the bloodstream into the brain. Levodopa can cross that barrier and is converted into dopamine once inside the brain, relieving Parkinson's symptoms. Carbidopa prevents levodopa from being broken down in the body before it reaches the brain, so more levodopa gets through. Entacapone blocks a second enzyme called COMT that would otherwise break down levodopa by a different route — keeping levodopa active longer and making the medication's effect more sustained and consistent.

These tablets are taken by mouth, one tablet at each dosing interval — tablets must never be split or broken. Your prescriber will carefully adjust the dose and frequency to find what works best for you. High-protein meals can compete with levodopa for absorption and may reduce how well the medication works, so it's worth discussing meal timing with your care team.

• Only one tablet is taken at each dosing interval
• The maximum number of tablets per day depends on the strength — your prescriber will set the limit appropriate for you
• Vitamin B6 levels should be checked before starting treatment and monitored periodically; supplement if levels are low
• Never stop taking or sharply reduce the dose without your doctor's guidance — a slow taper is required

The most common side effects — those reported at least 3% more often than with placebo — include:

• Dyskinesia (uncontrolled involuntary movements)
• Nausea
• Diarrhea
• Abdominal pain
• Vomiting
• Dry mouth
• Urine discoloration (may appear darker or reddish-brown — this is harmless but can be alarming)
• Dizziness and hyperkinesia (increased, exaggerated movements)

More serious reactions that require prompt medical attention include suddenly falling asleep without warning, fainting, hallucinations, uncontrollable compulsive behaviors, high fever with muscle rigidity (especially after stopping the medication), severe diarrhea, or muscle pain with dark urine.

• Sudden sleep episodes: This medication can cause you to fall asleep abruptly during everyday activities — even while driving — sometimes without feeling drowsy first. Do not drive or operate heavy machinery if this happens, and tell your doctor immediately.
• Low blood pressure and fainting: Dizziness on standing (orthostatic hypotension) and fainting are possible, especially early in treatment or when the dose changes.
• Do not stop abruptly: Suddenly stopping or sharply cutting the dose can trigger a life-threatening reaction similar to neuroleptic malignant syndrome — high fever, severe muscle rigidity, confusion, and rapid heart rate. Always taper slowly under medical supervision.
• Mental health effects: Hallucinations, depression with suicidal thoughts, and new compulsive behaviors (gambling, excessive spending, increased sexual urges) have all been reported. Caregivers and prescribers should watch for these changes.
• Diarrhea and colitis: Prolonged or severe diarrhea may signal drug-induced microscopic colitis (bowel inflammation) and should be reported to your doctor promptly.
• Vitamin B6 deficiency and seizures: This medication can lower vitamin B6 levels. In rare cases, severe deficiency has caused seizures that only resolved after vitamin B6 was given. Get your levels checked before and during treatment.

This medication can interact with several drugs and substances — always give your prescriber and pharmacist a full list of everything you take:

• Nonselective MAO inhibitors (e.g., phenelzine, tranylcypromine) — must be stopped at least 2 weeks before starting; the combination is contraindicated due to risk of dangerous adrenergic reactions
• Drugs broken down by COMT (e.g., epinephrine, norepinephrine, dopamine, dobutamine, isoproterenol) — entacapone can raise their levels, potentially causing rapid heart rate, irregular heartbeat, or dangerous blood pressure swings
• Blood pressure medications — may need dose adjustment, as this drug can further lower blood pressure
• Tricyclic antidepressants — reported to cause high blood pressure and dyskinesia when combined with carbidopa/levodopa
• Dopamine blockers (e.g., metoclopramide, risperidone, phenothiazines, butyrophenones) — can blunt the effectiveness of levodopa
• Iron supplements or multivitamins with iron — can bind to components and reduce absorption; take with caution and spacing if possible
• Warfarin — entacapone raises warfarin exposure; INR (blood clotting level) should be monitored when starting this medication
• Phenytoin, papaverine, and isoniazid — may reduce the benefit of levodopa and require dose adjustment

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do not take this medication if you have narrow-angle glaucoma — it is contraindicated
• Do not take if you are currently on nonselective MAO inhibitors; these must be stopped at least 2 weeks beforehand
• Pregnancy: Animal studies show risk of fetal malformations; discuss risks and benefits carefully with your doctor before use during pregnancy
• Breastfeeding: Levodopa has been detected in human milk; this medication may also reduce milk production by lowering prolactin. Discuss with your doctor before breastfeeding
• Children: Safety and effectiveness in pediatric patients have not been established
• Older adults: Adults 65 and older participated in clinical studies without overall differences in safety, but greater sensitivity cannot be ruled out; use with appropriate monitoring
• Liver disease or biliary obstruction: Use with extra caution; entacapone is primarily cleared through bile, so liver problems significantly affect how the drug behaves
• History of peptic ulcer: Levodopa may increase the risk of upper gastrointestinal bleeding in people with a prior ulcer history
• History of psychosis or depression: Use with caution; this medication can worsen hallucinations, agitation, and suicidal thinking

Taking too much of this medication can cause symptoms of excessive dopamine stimulation — including confusion, agitation, low blood pressure, rapid heart rate, and irregular heartbeats. Severe overdose may also lead to serious muscle breakdown (rhabdomyolysis) or temporary kidney problems. If an overdose is suspected, seek emergency care right away; treatment includes supportive care, monitoring of heart rhythm and organ function, and may involve gastric lavage (stomach pumping) and activated charcoal to limit further absorption.

After swallowing a tablet, levodopa and entacapone are absorbed quickly — levodopa peaks in the blood within about 1 to 2 hours, and entacapone even faster (under an hour). Carbidopa is absorbed a bit more slowly, reaching peak levels in roughly 2.5 to 3.5 hours. Levodopa has a short half-life of about 1.7 hours, meaning it leaves the body relatively quickly — which is one reason doses are needed several times a day. Entacapone clears even faster (half-life under 1 hour), and carbidopa takes 1.5 to 2 hours on average. Because half-lives are short, these ingredients do not build up significantly in the body with repeated doses.

High-protein meals can interfere with how much levodopa is absorbed, because large amino acids (from protein) compete with levodopa for the same transport pathway in the gut. Entacapone is almost entirely processed by the liver and cleared mainly through the bile and feces, so patients with liver disease or biliary obstruction need extra monitoring. Renal (kidney) impairment does not meaningfully affect entacapone clearance.

Store at 25°C (77°F); excursions permitted to 15°C to 30°C (59°F to 86°F) .