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Oxybutynin

Class
  • Anticholinergic
    • Muscarinic Antagonist
Indications
Administration/Absorption
  • Oral
    • Rapidly absorbed from gastrointestinal tract
Dosage

Distribution
  • 91-93% protein bound
  • VOD 193 L
Mechanism
  • competitively antagonizes the M1, M2, and M3 subtypes of the muscarinic acetylcholine receptor
    • exerts a direct antispasmodic effect on smooth muscle
    • inhibits the muscarinic action of acetylcholine on smooth muscle
  • No blocking effects occur at skeletal neuromuscular junctions or autonomic ganglia (antinicotinic effects)
  • By inhibiting particularily the M1 and M2 receptors of the bladder, detrusor activity is markedly decreased
Excretion
  • metabolized primarily by the cytochrome P450 enzyme systems
    • particularly CYP3A4
    • found mostly in the liver and gut wall
  • Extensively metabolized by the liver, with less than 0.1% of the administered dose excreted unchanged in the urine
Side effects
  • dry mouth
    • over a quarter of patients who begin oxybutynin treatment may have to stop because of dry mouth
  • difficulty in urination
  • constipation
  • blurred vision
  • drowsiness and dizziness
  • Calcium defects
    • An intake of calcium of 800 to 1000 mg is suggested
Interactions

Contraindications
  • untreated angle closure glaucoma
  • untreated narrow anterior chamber angles
  • partial or complete obstruction of the gastrointestinal tract
  • hiatal hernia
  • gastroesophageal reflux disease
  • paralytic ileus
  • intestinal atony of the elderly or debilitated patient
  • toxic megacolon complicating ulcerative colitis
  • severe colitis
  • myasthenia gravis
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