Entacapone is a medication used for the treatment of Parkinson's disease. It is often used in combination with levodopa/carbidopa to enhance the therapeutic effect of levodopa by inhibiting the COMT enzyme.

I. Common Side Effects and Manifestations

1. Musculoskeletal System-Related Side Effects

(1) Dyskinesia is the most common adverse reaction, with an incidence of 25%, characterized by involuntary choreiform movements.

(2) In addition, patients may experience hyperkinesia (10%) or hypokinesia (9%).

(3) These reactions are usually associated with elevated plasma concentrations of levodopa.

2. Gastrointestinal Side Effects

(1) Diarrhea occurs in 10% of patients, typically 4–12 weeks after treatment initiation, and may be accompanied by weight loss and dehydration.

(2) Nausea (14%), abdominal pain (8%), vomiting (4%), and dry mouth (3%) are also relatively common.

(3) Some patients with prolonged diarrhea may develop drug-induced microscopic colitis.

3. Urinary and Skin Reactions

(1) Approximately 10% of patients experience urine discoloration (brownish-orange), which is a normal phenomenon related to drug metabolites and has no clinical significance.

(2) Hyperhidrosis (2%) and purpura (2%) have been occasionally reported.

4. Neurological and Psychiatric Symptoms

(1) Dizziness (8%), taste disturbance (1%), somnolence (2%), and anxiety (2%) may occur.

(2) Hallucinations (incidence approximately 1%) and confusional behavior may develop in a small number of patients.

II. Serious Adverse Reactions and Precautions

1. Sudden Daytime Sleep Episodes

(1) Some patients may fall asleep suddenly during daily activities (e.g., driving) without warning signs.

(2) This phenomenon can occur at any time after the start of treatment and poses a serious threat to patient safety.

2. Impulse Control Disorders

(1) Patients may develop intense, uncontrollable impulsive behaviors, including pathological gambling, hypersexuality, compulsive shopping, etc.

(2) Patients may be unaware of abnormal behaviors, requiring close observation by family members.

3. Cardiovascular Reactions

(1) Orthostatic hypotension may cause dizziness and syncope (incidence approximately 1.2%).

(2) Concomitant use with adrenergic drugs may induce tachycardia and severe blood pressure fluctuations.

4. Withdrawal Syndrome

Abrupt discontinuation or rapid dose reduction may cause symptoms such as hyperthermia, muscle rigidity, and altered consciousness, similar to neuroleptic malignant syndrome. Dose reduction must be gradual under medical supervision.

III. Methods for Alleviating Side Effects

1. Dose Adjustment Strategies

(1) When dyskinesia occurs, the levodopa dose usually needs to be reduced by approximately 25%.

(2) Clinical studies show that more than 58% of patients taking a daily levodopa dose exceeding 800 mg require dose reduction.

(3) All dose adjustments must be performed under the guidance of a physician.

2. Management of Gastrointestinal Symptoms

(1) For diarrhea: maintain hydration and monitor in mild cases; seek medical evaluation promptly if it persists, worsens, or requires discontinuation.

(2) Nausea mostly occurs early in treatment and can be relieved by taking the medication with meals.

3. Precautions for Discontinuation

(1) If treatment needs to be stopped, dose reduction must be gradual under medical supervision, with close monitoring of symptom changes and adjustment of other dopaminergic medications as needed.

(2) Abrupt withdrawal may lead to symptom rebound and severe complications.

For further relevant information, please refer to the prescribing information for Entacapone.