Chapter 30: Overactive Bladder – Pharmacologic Management

Overactive Bladder – Pharmacologic Management condition significantly increases morbidity, especially in the older population, and can lead to depression, social isolation, and physical risks like falls. The pathophysiology involves complex control mechanisms across the central nervous system (CNS), peripheral nervous system (PNS), and lower urinary tract (LUT), where detrusor muscle contraction is predominantly mediated by acetylcholine activation of the M3 muscarinic receptor subtype. Diagnostic efforts focus on ruling out underlying pathologies such as infection or obstruction, utilizing tools like detailed patient interviews and daily bladder diaries. Management begins with first-line behavioral therapies, including bladder training and pelvic floor muscle exercises. Pharmacologic intervention primarily relies on two classes: anticholinergic/antimuscarinic drugs (like oxybutynin or tolterodine), which antagonize muscarinic receptors to reduce contractions, and the newer beta-3 adrenoceptor agonist, mirabegron, which promotes detrusor relaxation during the filling phase. While anticholinergics are effective, they are limited by adverse effects like dry mouth, constipation, and cognitive impairment, particularly in older adults. Mirabegron offers similar efficacy but with a lower risk of anticholinergic side effects. For refractory cases that fail two or more initial drug therapies, third-line interventions include intra-detrusor injections of OnabotulinumtoxinA (Botox), which causes temporary flaccid paralysis of the bladder muscle. Other treatments discussed include Serotonin Norepinephrine Reuptake Inhibitors (SNRIs) for stress incontinence, alpha-adrenergic antagonists for men with OAB secondary to bladder outlet obstruction (BOO) from Benign Prostatic Hyperplasia (BPH), and topical estrogens for postmenopausal women. Ongoing assessment using symptom and quality-of-life inventories is essential to guide successful treatment and ensure adherence, as adverse effects often lead to medication discontinuation.