Urinary tract antispasmodics

Urinary tract antispasmodics

Urinary tract antispasmodics help decrease urinary tract muscle spasms. They include darifenacin, flavoxate, oxybutynin, solifenacin, tolterodine, and trospium.

Pharmacokinetics

Flavoxate, oxybutynin, tolterodine, darifenacin, and solifenacin are most often administered orally and are rapidly absorbed. Trospium is administered orally but is poorly absorbed. Oxybutynin is also available as a dermal patch. These drugs are all widely distributed, metabolized in the liver, and excreted in urine. Urinary tract antispasmodics also cross the placenta and are excreted in breast milk.

Pharmacodynamics

Urinary tract antispasmodics relieve smooth muscle spasms by inhibiting parasympathetic activity, which causes the detrusor and urinary muscles to relax. Flavoxate and oxybutynin also exhibit many anticholinergic effects.

Pharmacotherapeutics

Urinary tract antispasmodics are used for patients with overactive bladders who have symptoms of urinary frequency, urgency, or incontinence.

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How oxybutynin works

When acetylcholine is released within the bladder, it attaches to receptors on the surface of smooth muscle in the bladder, stimulating bladder contractions. Oxybutynin suppresses these involuntary contractions by blocking the release of acetylcholine. This anticholinergic effect is what makes oxybutynin useful in the treatment of overactive bladder.

Urgent symptoms

Trospium is also indicated for patients with overactive bladders who have symptoms of urge urinary incontinence, and oxybutynin acts as an antispasmodic for uninhibited or reflex neurogenic bladder. 

Drug interactions

Urinary tract antispasmodics have few drug interactions:

• Use with anticholinergic agents may increase dry mouth, constipation, and other anticholinergic effects. 
• Urinary tract antispasmodics may decrease the effectiveness of phenothiazines and haloperidol.
• Trospium may interfere with the elimination of certain drugs excreted through the kidneys (such as digoxin, metformin, and vancomycin), resulting in increased blood levels of these drugs