Oxybutynin and the overactive bladder

Oxybutynin is a tertiary amine, which undergoes an extensive first-pass met abolism. It has an active metabolite, N-desethyl oxybutynin, and the effect of oral oxybutynin is to a large extent exerted by this metabolite. Oxybut ynin has both an antimuscarinic and a direct muscle relaxant effect, and, i n addition, local anesthetic actions. Most probably, oral oxybutynin exerts its effects on the overactive bladder (OAB) by an antimuscarinic action. S everal studies have shown that oral oxybutynin is effective in controlling OAB. Admininistred intravesically, it can increase bladder capacity and pro duce clinical improvement both in patients with hypereflexia and in other t ypes of OAB with few side effects. Adverse effects related to the antimusca rinic activity occur frequently and can necessitate treatment discontinuati on 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.