trihexyphenidyl

General Information

Trihexyphenidyl (brand Artane; generics) is an anticholinergic antiparkinson agent used for parkinsonism and commonly used in psychiatric care for antipsychotic-induced Parkinsonism and acute Dystonia (label/clinical).

Labeling states anticholinergics do not alleviate TD and may aggravate TD, even though parkinsonism and TD can coexist in patients receiving chronic antipsychotics (label).

Anticholinergic adverse effects (constipation, urinary retention, blurred vision, confusion) are often the limiting factor, particularly in older adults and in patients with cognitive vulnerability (label/clinical).

For antipsychotic-induced parkinsonism, reviews emphasize assessing whether antipsychotic dose reduction or switching is feasible before relying on chronic anticholinergic therapy (Wisidagama 2021/clinical).

The trihexyphenidyl compare view, evidence feed, and print page support EPS counseling and regimen review.

Trihexyphenidyl is often used as a targeted symptomatic agent rather than a chronic default. When possible, reducing the causative antipsychotic exposure and limiting anticholinergic burden are emphasized, particularly in older adults (clinical).

Mechanism of Action

Refer to the Glossary entry on Neurotransmitters for background on receptor systems involved in serious mental illness.

Antimuscarinic (anticholinergic) agent that reduces cholinergic tone in basal ganglia and can improve parkinsonism symptoms (mechanism/class).

• Antimuscarinic (anticholinergic) antiparkinson agent.

Metabolism and Pharmacokinetics

• Contemporary labels for older anticholinergics may not provide detailed pharmacokinetic parameters; practical dosing is guided by clinical response and adverse effects (label/clinical).

Dosing and Administration

• Parkinsonism: labeling describes starting at 1 mg on day 1, then increasing by 2 mg increments at intervals of 3–5 days toward a typical daily total of 6–10 mg/day (label).
• Antipsychotic-induced extrapyramidal reactions: dosing is individualized; labeling notes typical total daily dosing ranges between 5–15 mg/day, with some patients controlled on lower doses (label/clinical).
• Dividing the total daily dose across meals can improve tolerability; high daily totals may be split with a bedtime dose as well (label/clinical).

Monitoring & Labs

• Anticholinergic adverse-effect monitoring (bowel function, urinary retention, blurry vision, dry mouth, tachycardia) (label/clinical).
• Mental status monitoring (confusion/delirium), especially in older adults or when anticholinergic burden is high (clinical).
• Screen for glaucoma risk and urinary obstruction symptoms when relevant (label/clinical).

If trihexyphenidyl is continued beyond acute symptom control, periodic reassessment of ongoing need helps avoid long-term anticholinergic burden that can worsen cognition and constipation (clinical).

Adverse Effects

Interactions

• Additive anticholinergic burden occurs with TCAs, first-generation antihistamines, many antipsychotics (notably clozapine), and other anticholinergic agents; regimen review is often higher yield than adding more anticholinergic therapy (clinical).
• Alcohol and sedatives can worsen dizziness and falls risk in the setting of anticholinergic load (clinical).
• Anticholinergics can counteract cholinesterase inhibitors; co-use is generally avoided when dementia medications are present (clinical).

Other Useful Information

• For antipsychotic-induced parkinsonism, reviews emphasize first evaluating dose reduction or antipsychotic switching feasibility, then using symptomatic agents when needed (Wisidagama 2021/clinical).
• Anticholinergic burden has been associated with worse cognitive performance in schizophrenia-spectrum populations; minimizing unnecessary exposure is a common goal (Georgiou 2021/clinical).
• Anticholinergics can reduce EPS symptoms but can worsen constipation and cognition; periodic reassessment and taper attempts are often considered once symptoms stabilize, especially in older adults and polypharmacy settings (clinical).
• Acute Dystonia management commonly uses anticholinergic treatment; follow-up often focuses on preventing recurrence and ensuring the primary antipsychotic regimen is adjusted appropriately (Raja 1998/clinical).

References

1. Trihexyphenidyl hydrochloride tablets prescribing information — DailyMed (2023)
2. Recognition AND Management OF Antipsychotic Induced Parkinsonism IN Older Adults A Narrative Review — Medicines (2021)
3. Managing Antipsychotic Induced Acute AND Tardive Dystonia — Drug Safety (1998)
4. Anticholinergic Burden and Cognitive Performance in Patients With Schizophrenia A Systematic Literature Review — Frontiers in Psychiatry (2021)
5. AGNP Consensus Guidelines for Therapeutic Drug Monitoring in Neuropsychopharmacology — Pharmacopsychiatry (2018)