trihexyphenidyl (Artane, Trihexy)

Introduction

Tradename: Artane.

Indications

• adjunctive treatment of all forms of parkinsonism including antipsychotic-induced extrapyramidal reactions
• anticholinergic agents are the drugs of choice in Parkinson's disease patients presenting primarily with tremor
• NOT for tardive dyskinesia

Contraindications

Caution:

• use with caution in warm weather & during exercise
• elderly patients with atherosclerosis may be more susceptible to adverse effects
• cardiac arrhythmias
• hypertension
• benign prostatic hypertrophy

pregnancy category = c

safety in lactation = ?

Dosage

• start 1-2 mg/day divided TID
• increase as needed by 2 mg increments every 3-5 days
• maintenance dose: 6-10 mg QD divided TID
• a 4th daily dose if needed should be at bedtime
• max 15 mg/day

Tabs: 2 & 5 mg.

Elixir: 2 mg/5 mL.

Pharmacokinetics

• rapidly absorbed from the GI system following oral administration
• onset of action is with 1 hour
• duration of action is 6-12 hours

elimination via liver

elimination via kidney

Adverse effects

• common (> 10%)
  • constipation
  • decreased sweating
  • dry mouth, nose, throat or skin
• less common (1-10%)
  • decreased flow of breast milk, difficulty swallowing, photosensitivity
• uncommon (< 1%)
  • rash, confusion, increased intraocular pain, orthostatic hypotension, bloating, difficulty urinating, blurred vision, drowsiness, headache, loss of memory, nausea/vomiting, weakness, tiredness, ventricular fibrillation, tachycardia, palpitations, ataxia
• other
  • confusion in older patients
  • urinary retention in men
  • closed-angle glaucoma
  • mydriasis
  • nervousness
  • paralytic ileus
  • visual hallucinations

• drug adverse effects of parasympatholytics

Drug interactions

• concurrent administration of other anticholinergic agents may increase risk of adverse effects
• increased psychedelic experience: in combination with cannabinoids, barbiturates, opiates, alcohol

• drug interaction(s) of parasympatholytic with parasympathomimetic

Mechanism of action

• antimuscarinic activity
• direct spasmolytic activity on smooth muscle
• mechanism of antiparkinsonian effects is unknown, but may result from central cholinergic inhibition
• little effect on hypokinesia or rigidity

More general terms

• pharmacologic agents for treatment of Parkinson's disease
• parasympatholytic (anticholinergic, antimuscarinic agent)