Trihexyphenidyl

Registered South African indications:

• Parkinsonism

Contraindications 

• Hypersensitivity to the active ingredient or any of its excipients

Cautions

• Pregnancy
• Breastfeeding
• Renal impairment 
• Hepatic impairment 
• Elderly
• Hypertension
• Cardiovascular disorders 
• Tardive dyskinesia
• Glaucoma
• Obstructive disease of the gastrointestinal or genitourinary tracts
• Suspected prostatic hypertrophy
• Myasthenia gravis
• Abrupt withdrawal 
• May impair ability to drive or operate machinery 

Forms avail. in SA and covered in this monograph: tab

Postencephalitic, arteriosclerotic and idiopathic Parkinsonism 
- Adjunctive or monotherapy

• Oral (tab): Initial: 1-2mg/day; Then titrate by 2mg at intervals of 3-5 days; Maintenance: 6-10mg/day, in 3-4 divided doses; Max: 12-15mg/24hrs 

Drug-induced extrapyramidal disorders

• Oral (tab): Initial: 1mg/day; Maintenance: 5-15mg/day, in 3-4 divided doses

Therapy should be of minimal duration and discontinued after symptoms have subsided for a reasonable period of time

When trihexyphenidyl is used concomitantly with levodopa the maintenance dose of each may need to be reduced

See additional prescribing points

Not established for use in children

Pregnancy

• FDA Pregnancy Category Not Rated (NR)

Breastfeeding 

• Caution; not recommended

Renal Impairment 

• Caution; no dose adjustment recommended

Hepatic Impairment

• Caution; no dose adjustment recommended

Elderly

• Caution; no dose adjustment recommended 

Central Nervous System Disorders

• Nervousness
• Restlessness
• Confusion
• Agitation
• Delusions
• Hallucinations
• Insomnia
• Euphoria
• Dizziness
• Immediate and short-term memory impairment
• Worsening of myasthenia gravis

Cardiovascular Disorders

• Tachycardia

Respiratory Disorders

• Decreased bronchial secretions

Gastrointestinal Disorders

• Dry mouth
• Constipation 
• Nausea and vomiting 

Genitourinary Disorders

• Urinary retention
• Difficulty in micturition

Endocrine and Metabolic Disorders

• Thirst 

Skin and Subcutaneous Tissue Disorders

• Skin flushing 
• Rashes
• Dry skin

Immune, Blood and Lymphatic System Disorders

• Hypersensitivity 
• Fever 

Sensory Disorders

• Blurred vision
• Loss of accommodation
• Photophobia
• Increased intraocular pressure

• Phenothiazines
• Clozapine
• Antihistamines
• Disopyramide
• Nefopam
• Amantadine
• Tricyclic antidepressants
• Monoamine oxidase inhibitors
• Metoclopramide
• Domperidone
• Levodopa
• Parasympathomimetics

• Gonioscopic evaluation
• Intraocular pressure 

Trihexyphenidyl causes anticholinergic side effects, potentially including cognitive slowing.

There is some evidence that it is not as effective for choreiform movements, which it may in fact exacerbate, and may be more effective in tardive dystonias

Trihexyphenidyl is a selective M1 muscarinic acetylcholine receptor antagonist. It is able to discriminate between the M1 (cortical or neuronal) and the peripheral muscarinic subtypes (cardiac and glandular). Trihexyphenidyl partially blocks cholinergic activity in the central nervous system, which is responsible for the symptoms of Parkinson's disease. It is also thought to increase the availability of dopamine, a brain chemical that is critical in the initiation and smooth control of voluntary muscle movement.

Tablet 2mg

• Benzhexol (Pharmacare)