The US Food and Drug Administration (FDA) has approved the first skin patch for treating overactive bladder, according to product maker Watson Pharmaceuticals Inc.

The patch, called Oxytrol, is intended to avoid some of the side effects -- such as dry mouth and constipation--associated with other medications. The standard drugs taken for the disorder are Pharmacia Corp.'s Detrol LA and Johnson & Johnson's Ditropan XL.

The FDA last year rejected Watson's application for the skin patch, which has the same active ingredient as Ditropan, and asked for additional clinical trial data.

Trials showed that the patch, placed on the abdomen, hip or buttock, relieved symptoms of overactive bladder for up to four days, with side effects similar to placebo.

Side effects can be avoided because the patch, which delivers the drug continuously through the skin to the bloodstream, bypasses the liver and the gastrointestinal system. Skin irritation was the most common side effect attributed to the patch itself.

Peggy Eisenhaur, a spokeswoman for Watson, said the translucent patch will be launched commercially in the second quarter. "Because it's a patch product, there are still some packaging and labeling particulars," she said.

Watson has estimated sales of the drug at $40 million to $50 million this year, and eventual peak sales at more than $200 million a year, the spokeswoman said.

According to Watson, an estimated 33 million Americans have an overactive bladder. As the "baby boomers" reach retirement age, that number is expected to rise.

Oxytrol is not advised for people who have urinary retention, gastric retention, a type of glaucoma or hypersensitivity to oxybutynin, the product's active ingredient.