Oxybutynin and the overactive bladder.

Oxybutynin is a tertiary amine, which undergoes an extensive first-pass metabolism. It has an active metabolite, N-desethyl oxybutynin, and the effect of oral oxybutynin is to a large extent exerted by this metabolite. Oxybutynin has both an antimuscarinic and a direct muscle relaxant effect, and, in addition, local anesthetic actions. Most probably, oral oxybutynin exerts its effects on the overactive bladder (OAB) by an antimuscarinic action. Several studies have shown that oral oxybutynin is effective in controlling OAB. Admininistred intravesically, it can increase bladder capacity and produce clinical improvement both in patients with hypereflexia and in other types of OAB with few side effects. Adverse effects related to the antimuscarinic activity occur frequently and can necessitate treatment discontinuation in up to 25% of patients, depending on the dosage. A controlled-release preparation has recently been introduced. Oxybutynin has a well-documented efficacy in the treatment of detrusor overactivity, and is a drug of first choice in patients with this disorder.