trihexyphenidyl

Action and Spectrum

Actions and spectrum: 

trihexyphenidyl is an anticholinergic drug that is used to treat tremors, rigidity, and other symptoms associated with Parkinson’s disease. It acts by blocking the action of acetylcholine, a neurotransmitter in the brain that is involved in muscle movements. trihexyphenidyl is also used to treat drug-induced extrapyramidal symptoms, dystonia, and other movement disorders. 

trihexyphenidyl has a broad spectrum of action on the central nervous system. It can affect various brain regions involved in movement control, including the basal ganglia, thalamus, and cerebral cortex. Its primary action is to reduce the activity of the cholinergic neurons in these regions, which in turn reduces muscle spasms and tremors. Additionally, it can also have sedative and antihistamine effects. 

Drug Interaction

Adverse Reaction

Frequency defined 

>10% 

Rash 

Anticholinergic side effects (30-50%) 

<1% 

Hallucination 

Paralytic ileus 

Suppurative parotitis 

Black Box Warning

Contraindication / Caution

Contraindication/Caution: 

Contraindication: 

• Hypersensitivity to trihexyphenidyl or any component of the formulation. 
• Narrow-angle glaucoma. 
• Obstructive uropathy. 
• Obstructive disease of the gastrointestinal tract. 
• Paralytic ileus. 
• Toxic megacolon. 
• Myasthenia gravis. 
• Severe ulcerative colitis. 
• Patients who are being treated with or have recently (within 21 days) received an MAO inhibitor.

Caution: 

trihexyphenidyl is a medication that should be used in glaucoma with caution, obstructive disease of the gastrointestinal or genitourinary tract, prostatic hypertrophy, or myasthenia gravis. Patients with a history of cardiac arrhythmias, hypertension, hepatic or renal impairment, and elderly patients with dementia-related psychosis or Parkinson’s disease should also use the medication with caution. Additionally, trihexyphenidyl should be used with caution in patients who have a history of drug abuse or addiction, as it can be abused or lead to dependence.  

Comorbidities: 

• Glaucoma 
• Prostatic hypertrophy 
• Urinary bladder neck obstruction 
• Cardiovascular disease 
• Hypertension 
• Tachycardia 
• Myasthenia gravis 
• Paralytic ileus 
• Hepatic or renal impairment 
• Hyperthyroidism 
• Coronary artery disease 
• Congestive heart failure 

Pregnancy / Lactation

Pregnancy consideration: pregnancy category C 

Lactation: safety and efficacy not established  

Pregnancy category: 

• Category A: Satisfactory and well-controlled studies show no risk to the fetus in the first or later trimester. 
• Category B: There is no evidence of risk to the fetus found in animal reproduction studies and there are not enough studies on pregnant women. 
• Category C: Adverse effects on the fetus found with evidence in animal reproduction studies and no adequate evidence for an effect in humans, care must be taken for potential risks in pregnant women. 
• Category D: There is adequate data available with sufficient evidence of human fetal risk from various platforms, but despite potential risks may be used only in emergency cases for potential benefits. 
• Category X: Drugs listed in this category outweigh risks over benefits These category drugs should be prohibited for pregnant women. 
• Category N: There is no data available for the drug under this category. 

Pharmacology

Pharmacology: 

trihexyphenidyl is an anticholinergic drug that exerts its pharmacological effect by blocking the action of acetylcholine, a neurotransmitter that is involved in many bodily functions. Specifically, trihexyphenidyl blocks the action of acetylcholine in the central nervous system, thereby decreasing the activity of the cholinergic system. This results in a decrease in the symptoms of Parkinson’s disease, including tremors, rigidity, and bradykinesia. 

trihexyphenidyl acts primarily on muscarinic receptors, which are a type of receptor that is activated by acetylcholine. By blocking these receptors, trihexyphenidyl decreases the activity of the cholinergic system, which is overactive in Parkinson’s disease. Additionally, trihexyphenidyl has some dopaminergic activity, which may also contribute to its therapeutic effects in Parkinson’s disease.  

Pharmacodynamics: 

trihexyphenidyl is an anticholinergic medication that acts as an antagonist of acetylcholine at muscarinic receptors. It acts by blocking the action of acetylcholine in the central nervous system and reducing cholinergic activity. This results in a decrease in tremors, rigidity, and other symptoms associated with Parkinson’s disease. 

trihexyphenidyl also has antihistaminic, antiserotonergic, and local anesthetic properties. Its antihistaminic activity is thought to be responsible for the drug’s sedative effects, while its antiserotonergic activity may contribute to its antipsychotic effects. 

The pharmacodynamics of trihexyphenidyl is dose-dependent, and higher doses can cause more significant anticholinergic side effects, including dry mouth, constipation, blurred vision, urinary retention, confusion, and cognitive impairment.  

Pharmacokinetics: 

Absorption 

trihexyphenidyl is well absorbed after oral administration, with a bioavailability of 5-33% due to first-pass metabolism. 

Distribution 

trihexyphenidyl is widely distributed throughout the body, with a reported volume of distribution of 1.5-4.5 L/kg. 

Metabolism 

trihexyphenidyl undergoes extensive first-pass metabolism in the liver, with less than 1% of the drug being excreted unchanged in the urine. It is metabolized primarily by the cytochrome P450 enzyme system, specifically the CYP2D6 isoenzyme. 

Elimination and excretion 

trihexyphenidyl and its metabolites are eliminated mainly in the urine, with a small amount excreted in feces. The elimination half-life is approximately 3-8 hours. 

Special populations: There is limited information on the pharmacokinetics of trihexyphenidyl in special populations such as elderly patients, patients with hepatic impairment, or patients with renal impairment. 

Adminstartion

Administration: 

trihexyphenidyl is available in different forms, like tablets, capsules, and elixirs. The medication can be administered orally with or without food. The dosage and administration schedule of trihexyphenidyl may vary depending on the patient’s age, medical condition, and response to treatment.

The drug should be taken exactly as prescribed by the healthcare provider. For the treatment of Parkinson’s disease, the initial dose of trihexyphenidyl is usually 1 mg twice a day, which can be gradually increased up to a maximum of 6 mg daily. The maximum daily dose for adults is 15 mg.

In children, the dose is based on their weight and medical condition. For the treatment of drug-induced extrapyramidal symptoms, the recommended dose is usually 1 mg twice or three times a day. The dose can be increased up to 6 mg per day in divided doses. 

Patient Information Leaflet

Patient information leaflet 

Generic Name: trihexyphenidyl 

Pronounced: [ try-hex-ee-FEH-nih-dill]  

Why do we use trihexyphenidyl? 

trihexyphenidyl is an anticholinergic drug that is used for the treatment of Parkinson’s disease and drug-induced extrapyramidal symptoms (EPS), such as those caused by antipsychotic medications.

It is also used to treat certain movement disorders such as tremors, spasticity, and dystonia. Additionally, it can be used as an adjunctive treatment for the management of drooling and sweating in patients with certain neurological disorders.