Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
5 mg tablets
Indication: detrusor over activity
Although there is little evidence of efficacy from controlled clinical trials, oxybutynin has been marketed overseas for many years and has been available in Australia through the Special Access Scheme. It inhibits the muscarinicactions of acetylcholine and has antispasmodic effects on smooth muscle. The drug can be considered for the treatment of conditions such as urge incontinence1,where there is detrusor instability which has failed to respond to behavioural interventions.
There is extensive first pass metabolism so the oral bioavailability is only6%.The drug is rapidly eliminated with a half-life of less than 2 hours.
Oxybutynin therapy can begin with a dose of 2.5-5mg twice a day, gradually increasing as necessary to control symptoms.2 The drug is more effective than placebo, but may not have a significant advantage over other anticholinergic drugs such as propantheline.
The usefulness of the drug may be limited by its atropine-like adverse effects. Elderly patients in particular may be prone to constipation, urinary retention, blurred vision, dry mouth and dizziness. A low dose is recommended for the elderly.
- Millard RJ. Uropharmacology in the management of incontinence. Aust Prescr 1992;15:66-9.
- Bent AE. Etiology and management of detrusor instability and mixed incontinence. Obstet Gynecol 1989;16:853-68.