Trihexyphenidyl hydrochloride for Parkinson’s disease
Fact-checked by What is trihexyphenidyl hydrochloride for Parkinson’s disease?
Trihexyphenidyl hydrochloride is an approved oral therapy that can help manage the symptoms of Parkinson’s disease. It is often used alongside levodopa.
The motor and nonmotor symptoms of Parkinson’s arise when the nerve cells that produce dopamine, a chemical messenger in the brain (also called a neurotransmitter), gradually die.
Dopamine works alongside other neurotransmitters, including acetylcholine, to help control movement and other brain functions. Researchers believe that an imbalance between dopamine and acetylcholine — with acetylcholine becoming relatively overactive as dopamine is lost — contributes to Parkinson’s symptoms.
Trihexyphenidyl’s mechanism of action is not entirely understood, but it appears to act as an anticholinergic, which blocks the effects of acetylcholine. This may help restore the balance between acetylcholine and available dopamine signaling, helping ease symptoms.
Lederle Laboratories initially developed trihexyphenidyl and marketed it under the brand name Artane. Now, only generic trihexyphenidyl is available in the U.S., including oral tablets and liquid solutions. The medication is also used to treat other conditions that cause Parkinson’s-like symptoms, known as parkinsonism, and to control movement problems caused by certain antipsychotic medications.Â
Therapy snapshot
| Brand name | Available as a generic medication only |
| Chemical name | Trihexyphenidyl hydrochloride |
| Usage | Used to ease symptoms of Parkinson’s disease |
| Administration | Oral tablets or liquid solution |
Who with Parkinson’s disease can take trihexyphenidyl hydrochloride?
Trihexyphenidyl has been used to treat Parkinson’s since the late 1940s and is approved in the U.S. to treat all types of parkinsonism.
The prescribing information states that trihexyphenidyl is contraindicated, meaning it should not be used, in people with:
- allergies to the medication or its ingredients
- narrow-angle glaucoma, a type of eye disease that involves increased pressure inside the eye
It should also be used with caution in people with:
- obstructive gastrointestinal or genitourinary disease
- possible prostate enlargementÂ
How is trihexyphenidyl hydrochloride administered in Parkinson’s disease?
Trihexyphenidyl is available as tablets or a liquid solution, both taken by mouth.Â
Most patients start at a low daily dosage of trihexyphenidyl, adjusting as needed over several days to achieve symptom control. For people with Parkinson’s, the optimal dose range is often between 6 and 10 mg daily, though doses up to 12 to 15 mg/day may be needed for some people. Full daily doses may be split into multiple smaller doses throughout the day.
Because of potential levodopa-trihexyphenidyl drug interactions, the doses of both medications may require adjustment when they are used together. Trihexyphenidyl can also increase the sedative effects of alcohol and other substances that depress the central nervous system, so care is needed if they are combined.
Trihexyphenidyl hydrochloride in Parkinson’s disease clinical trials
Several early clinical studies of trihexyphenidyl have helped demonstrate its potential efficacy. These include three early studies from the 1940s and 1950s:
- One study examined 117 people with Parkinson’s disease who received trihexyphenidyl. Of these, 76.1% reported at least some improvement, either reductions in symptom severity or improved comfort and well-being. No participants showed worsening of symptoms or overall health.
- A second study included 69 people with Parkinson’s disease. Of these, 77% reported improvement with trihexyphenidyl.
- The third study involved 411 people with Parkinson’s disease who received trihexyphenidyl for up to five years. About 73% reported an easing of symptoms.Â
Since then, additional studies and clinical experience have suggested that trihexyphenidyl can help manage Parkinson’s symptoms, particularly in younger people whose main symptom is tremor.
Trihexyphenidyl hydrochloride side effects
The most common side effects of trihexyphenidyl include:
- dry mouth
- blurry vision
- mild nausea
- nervousness
- dizziness
These tend to ease or disappear entirely with continued treatment or with careful adjustment of the dose or dosing schedule.
Trihexyphenidyl may trigger or worsen glaucoma. For people with narrow-angle glaucoma, the medication could worsen the condition and cause blindness. Because of this, an eye exam called a gonioscopy is recommended before starting treatment with trihexyphenidyl. Regular monitoring of eye pressure is also advised.Â
Close monitoring is also recommended for people with liver, kidney, or heart disease.
Some individuals may experience psychological or behavioral disturbances while taking trihexyphenidyl. This is a particular risk for people with a history of unusual reactions to other drugs and those with arteriosclerosis, a medical condition in which the arteries become thickened and hardened.
Treatment discontinuation, especially if it is abrupt, can cause serious side effects or an exacerbation of Parkinson’s symptoms, and should always be done under medical supervision.
Parkinson's News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
