Which medication works by relaxing bladder muscles to alleviate urge incontinence?

The medication that works by relaxing bladder muscles to alleviate urge incontinence is indeed Oxybutynin. This drug belongs to a class of medications known as anticholinergics, which reduce the activity of the bladder by blocking the action of acetylcholine on the bladder's muscarinic receptors. By doing so, Oxybutynin helps decrease involuntary contractions of the bladder, which is a primary contributor to urge incontinence. With reduced bladder muscle contractions, patients often experience an improvement in symptoms related to urgency and frequency of urination.

Mirabegron, another medication for overactive bladder, functions differently as it is a beta-3 adrenergic agonist. While it can also assist in treating urge incontinence, it does so by promoting relaxation of the bladder during storage phase without the anticholinergic side effects. Therefore, for this particular question focused on the mechanism of muscle relaxation specifically related to bladder function, Oxybutynin is the accurate choice.