Urinary tract antispasmodics

Urinary tract antispasmodics

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

Pharmacokinetics

Flavoxate, oxybutynin, tolterodine, darifenacin, and solifenacin are most often administered orally and are rapidly absorbed. Tro-spium is administered orally but is poorly absorbed. Oxybutynin is also available as a dermal patch. These drugs are all widely dis-tributed, 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 in-hibiting 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 in-continence.

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. (See How oxybutynin works.)

Drug interactions

Urinary tract antispasmodics have few drug interactions:

§    Use with anticholinergic agents may increase dry mouth, consti-pation, and other anticholinergic effects. (See Adverse reactionsto urinary tract antispasmodics.)

§    Urinary tract antispasmodics may decrease the effectiveness of phenothiazines and haloperidol.

§    Trospium may interfere with the elimination of certain drugs ex-creted through the kidneys (such as digoxin, metformin, and van-comycin), resulting in increased blood levels of these drugs.