Oxybutynin
Class
Anticholinergic
Muscarinic Antagonist
Indications
frequent urination
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