A comparison of newer drug treatments for urinary incontinence
Oxybutynin is often considered to be the “gold standard” drug in the treatment of patients with an unstable bladder. It is both clinically effective and cost-effective, but its use is often limited by adverse effects. However, it is still usual for this drug to be the first-line treatment for this condition. The newer drugs are often advertised as more effective and better tolerated than oxybutynin, but questions still remain over which of these newer agents should be the second-line drug of choice in patients unable to tolerate the adverse effects of oxybutynin.
Principles of treatment
The principles of treatment take into account the physiology of the bladder.
The wall of the bladder comprises circular and longitudinal smooth muscle which is called detrusor muscle. When the detrusor muscle relaxes, urine is stored, and when it contracts, micturition occurs. The bladder can normally hold between 300ml and 600ml of urine.
The bladder has somatic, parasympathetic and sympathetic innervation. The pudendal nerve is the somatic component and innervates the external urethral sphincter. Parasympathetic nerve fibres innervate the detrusor muscle, via cholinergic receptors, and originate from the second, third and fourth segments of the spinal cord. Parasympathetic stimulation of the detrusor muscleresults in contraction of the bladder, leading to micturition.
An unstable detrusor (or unstable bladder) is characterised by involuntary contractions during the filling phase, while the patient is attempting to inhibit micturition, leading to a desire to void, urgency or urge incontinence.
Various drugs are currently available for the treatment of patients with an overactive or unstable bladder. The majority are antimuscarinic drugs and produce inevitable unwanted effects which must be balanced against the perceived benefits. The usual adverse effects of antimuscarinic drugs are dry mouth, constipation, difficulty in visual accommodation and somnolence. Therefore, these drugs should be avoided in patients with obstructive uropathy, bowel obstruction, ulcerative colitis, narrow angle glaucoma or myasthenia gravis.
Oxybutynin has been the most frequently prescribed drug for urinary incontinence. It has antimuscarinic, antispasmodic and local anaesthetic properties, although not all of these properties are seen at therapeutic dose levels. Oxybutynin has a relatively short half-life of two to four hours and some patients find it useful to cover specific events such as a night out, rather than take the drug on a continual basis.
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Citation: Hospital Pharmacist URI: 10975338
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