Trihexyphenidyl Side Effects

Some side effects of trihexyphenidyl may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to trihexyphenidyl: oral capsule extended release, oral elixir, oral tablet

Along with its needed effects, trihexyphenidyl may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking trihexyphenidyl:

Rare
  • Abdominal or stomach cramps or pain
  • bloating
  • constipation
  • delusions of persecution, mistrust, suspiciousness, or combativeness
  • excessive dryness of the mouth
  • false beliefs that cannot be changed by facts
  • loss of appetite
  • nausea or vomiting
  • seeing, hearing, or feeling things that are not there
  • skin rash
  • stomach pain
  • swollen, painful, or tender lymph glands on the side of the face or neck
Incidence not known
  • Anxiety
  • blurred vision
  • change in vision
  • decrease in frequency of urination
  • decrease in urine volume
  • difficult urination
  • difficulty in passing urine (dribbling)
  • disturbed behavior
  • dry mouth
  • enlarged pupils
  • eye pain
  • fast, pounding, or irregular heartbeat or pulse
  • hyperventilation
  • irritability
  • loss of vision
  • mental confusion
  • nervousness
  • painful urination
  • restlessness
  • shaking
  • shortness of breath
  • trouble sleeping

Some side effects of trihexyphenidyl may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common
  • Dizziness
  • mild nausea
  • nervousness
Incidence not known
  • Drowsiness
  • weakness

For Healthcare Professionals

Applies to trihexyphenidyl: oral elixir, oral tablet

General

Most adverse effects of trihexyphenidyl are extensions of its pharmacologic activity and are anticholinergic in nature. Between 30% and 50% of all patients experience minor side effects (dry mouth, nausea, blurred vision, dizziness, nervousness). Elderly patients and those with underlying organic brain disease tend to be the most susceptible, especially to the central effects.

Gastrointestinal

Gastrointestinal side effects have included dry mouth, difficulty swallowing, anorexia, constipation, nausea, and vomiting. A reduction in dosage will sometimes help alleviate these problems. Paralytic ileus may develop, particularly in patients on concomitant phenothiazine or tricyclic antidepressant therapy, and may occasionally be fatal. Upon withdrawal of medication, nausea and vomiting may occur due to a cholinergic rebound.

Nervous system

Bucco-linguo-masticatory dyskinesias and chorea have been reported mostly in elderly patients being treated for Parkinson's disease with various anticholinergic agents, including trihexyphenidyl.

Nervous system side effects have included depression, anxiety, listlessness, drowsiness, numbness of fingers and dyskinesia. Chorea has been reported at higher dosages (>=15 mg/day). Trihexyphenidyl may also aggravate symptoms of tardive dyskinesia or elicit previously suppressed symptoms. Sleepwalking has been attributed to drugs or combination of drugs with anticholinergic activity.

Cognitive deficits, such as impairment of recent and short-term memory and inability to concentrate, may occur with clinical doses of anticholinergic agents and may be dose-related.

Psychiatric

Psychiatric side effects have included toxic psychosis which manifested as confusion, disorientation, agitation, excitation, memory impairment, delusions and hallucinations (usually visual, but may be auditory or tactile or all three), at toxic and therapeutic dosages (2% to 4%, up to 19% in elderly patients). Psychiatric deterioration and psychotic flare-ups have also been reported following withdrawal of therapy. Symptoms include delusions, hallucinations, aggression or violent behavior, and suicidal tendencies. In high dosages, trihexyphenidyl may sometimes produce euphorigenic effects. For this reason, it can be a drug of abuse.

Toxic psychosis, when present, tends to occur quickly, generally within several days to a week of initiating trihexyphenidyl therapy or within hours after an acute overdose. However, occasionally the onset may be delayed by months. Symptoms generally resolve spontaneously within a few days after the discontinuation of medication.

Ocular

Ocular side effects have included blurred vision, mydriasis, and cycloplegia. Trihexyphenidyl may also cause angle-closure glaucoma, which has rarely led to blindness.

Cardiovascular

Cardiovascular side effects have included tachycardia, although an isolated case of bradycardia has also been described. Orthostatic hypotension has been reported during withdrawal syndromes following discontinuation of long-term trihexyphenidyl therapy.

Genitourinary

Genitourinary side effects have included urinary retention and dysuria.

Metabolic

Metabolic side effects have included alterations in thermal homeostasis as a result of trihexyphenidyl's inhibition of the body's sweating mechanism. Heat stroke, hyperthermia, and fever have occurred with anticholinergic agents, most commonly in patients on concomitant neuroleptic or tricyclic antidepressant therapy.

Other

Anticholinergic poisoning syndrome may persist for more than a week's duration following trihexyphenidyl overdose. Most patients with anticholinergic intoxication require only supportive therapy of vital functions and/or discontinuation of medications. However, severely agitated, delirious, or comatose patients may be treated with physostigmine salicylate, an acetylcholinesterase inhibitor with both central and peripheral effects.

Anticholinergic intoxication may present with central and peripheral symptoms including those listed above, in addition to warm and dry skin, EKG abnormalities, insomnia, twitching or jerking movements, pantomime activity with nonexistent objects, hyperactivity, hyperreflexia, respiratory arrest, delirium, convulsions, shock and coma.

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