Oxybutynin. A review of its pharmacodynamic and pharmacokinetic properties, and its therapeutic use in detrusor instability.

Abstract

Oxybutynin possesses anticholinergic and spasmolytic properties, which together form the basis for its use as a therapeutic option in patients with overactive detrusor function--either idiopathic detrusor instability (DI) or detrusor hyperreflexia. Of the symptoms of detrusor overactivity, urge incontinence is often the most distressing to the patient. Urge incontinence and other subjective parameters (urinary frequency, urgency) improve in tandem with objective (cystometric) measures (maximum detrusor pressure during filling, volume at first desire to void, maximum bladder capacity) in ambulatory, including elderly, patients treated with oxybutynin. However, on the basis of results of limited investigations, the drug appears ineffective in elderly institutionalised individuals. Relative to other anticholinergic drugs, oxybutynin appears at least as effective as propantheline and similar in efficacy to propiverine in small trials, although these results are not definitive. Further investigation of intravesical oxybutynin may lead to this route becoming an option in patients with pre-existing catheters. Adverse effects--dry mouth, constipation, blurred vision--related to the anticholinergic activity of oxybutynin occur frequently and can be sufficiently troublesome to necessitate treatment discontinuation in up to 25% of patients, depending on the dosage. Increases in residual urine volume suggesting urinary retention (undesirable in patients with idiopathic DI), also can develop in some oxybutynin recipients. In summary, oxybutynin is one of the few drugs proven to be beneficial in some patients with overactive detrusor function. Despite the occurrence of unwanted anticholinergic effects in many patients, and apparent lack of efficacy in the elderly institutionalised population, oxybutynin should be considered for the drug of first choice in patients with detrusor overactivity, including the elderly ambulatory population, when pharmacological therapy is indicated.