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Am Fam Physician. 2004;70(12):2351-2352

Synopsis

Oxytrol is a new transdermal patch form of the drug oxybutynin, which has long been used for urinary incontinence. Oxybutynin, via an anticholinergic effect, relaxes the detrusor muscle of the bladder. The transdermal form of the drug was developed to address the side effect of dry mouth. The patch avoids first-pass metabolism in the liver, reducing the active metabolite N-desethyloxybutynin, the main cause of dry mouth.

NameStarting dosageDose formApproximate monthly cost*
Transdermal oxybutynin (Oxytrol)1 patch topically, alternating sites every 3 to 4 daysTransdermal patch, 3.9 mg per day$107†

Safety

Oxtybutynin should not be used in patients with urinary retention, gastric retention, or uncontrolled angle-closure glaucoma.1 Because oxybutynin is metabolized in the liver and excreted via the kidney, patients with renal or hepatic impairment may experience a more pronounced response to the drug. The FDA pregnancy rating for this drug is category B.

Tolerability

Dry mouth is the most common complaint with the oral anticholinergic drugs oxybutynin and tolterodine. The incidence of dry mouth is reported as roughly 10 percent in the package labeling.1 In one study, the transdermal form of oxybutynin caused dry mouth in fewer patients than the immediate-release oral form (30 versus 94 percent, P <.001, number needed to treat=1.8).2 The transdermal formulation of oxybutynin has not been compared with the extended-release oral formulation. Another study compared transdermal oxybutynin with extended-release oral tolterodine, and found a similar rate of dry mouth (4.1 versus 7.3 percent).3 The difference in the rate of dry mouth between studies (4.1 percent versus 10 percent versus 38 percent) may be due to differences in definition, population, and measurement. Other anticholinergic side effects such as constipation and somnolence are reduced slightly with the patch as compared with oral therapy.1,3 Skin irritation and itching occurs in 10 to 20 percent of patients, and about one in 10 patients will stop using the patch due to these symptoms. Patch adhesion is good, with less than 1 percent partially or totally detaching.1,3

Effectiveness

Few studies have evaluated the effectiveness of transdermal oxybutynin. It has been compared with immediate-release oral oxybutynin and extended-release tolterodine, but only in previously treated patients. In 74 patients, mostly women, who previously responded to oral oxybutynin, the transdermal form produced a similar decrease in the number of episodes of incontinence to oral oxybutynin (7.3 to 7.4 episodes per day while on placebo and 2.4 to 2.6 episodes per day while on treatment).2 When compared with long-acting tolterodine (Detrol LA) in both urge and mixed incontinence, transdermal oxybutynin and tolterodine produced a similar modest decrease in the number of incontinence episodes from 7 to 9 episodes per day to 5 to 7 episodes per day (P <0.05 compared with placebo).3 Neither study reported the number of patients who were completely continent or a decline in the frequency of nighttime micturition. Older studies with the oral form showed more impressive results, but it is not clear whether that was due to different populations used or different dosing.4,5

Price

Transdermal oxybutynin will cost patients approximately $100 per month, similar to the cost of the extended-release forms of oxybutynin and tolterodine, and much more than the generic version of immediate-release oxybutynin ($15 to 30 per month).

Simplicity

The transdermal patch is applied to the abdomen, buttock, or hip, rotating sites every 3 to 4 days.

Bottom Line

The transdermal patch of oxybutynin is no more effective than the short- or long-acting oral form. The patch costs more, but causes less dry mouth. Skin reactions will cause about 10 percent of patients to stop using it.

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