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Library / Pharmacology / Autonomics / Anticholinergics / Benztropine & Trihexyphenidyl

Benztropine & Trihexyphenidyl

Key Board Facts Grid

Target Receptors

Central M1 muscarinic antagonist

BBB Penetration

Tertiary amines; cross the BBB

Primary Indication

Drug-induced parkinsonism, acute dystonia, tremor/rigidity

First-Line Antidote

Supportive; treat anticholinergic toxidrome with physostigmine if needed

Mechanism of Action

  • Competitive M1 antagonism in the basal ganglia.
  • Restores dopamine/acetylcholine balance reduced by D2 receptor blockade.
  • Improves tremor and rigidity; does not treat tardive dyskinesia.

Adverse Effects & Toxicities

  • Anticholinergic toxidrome: dry mouth, constipation, urinary retention, blurred vision, tachycardia, delirium.
  • Worsens or masks tardive dyskinesia rather than treating it.
  • Contraindications: narrow-angle glaucoma, urinary retention, GI obstruction.

DO / OMM Board Pearl

Craniosacral and basal ganglia motor tracking. Reduces relative cholinergic excess from D2 blockade. Best for acute dystonia and parkinsonian tremor, not tardive dyskinesia.