Darifenacin

• Overactive Bladder
• Urinary Incontinence
• Urinary Urgency
• Bladder Control Problems

Darifenacin is a muscarinic receptor antagonist (anticholinergic) used for the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency, and frequency. This medication selectively targets M3 receptors in the bladder, potentially offering efficacy with reduced cognitive side effects compared to less selective agents.

Mechanism of Action

Darifenacin is a selective antagonist of the M3 muscarinic acetylcholine receptor subtype. While five muscarinic receptor subtypes exist (M1-M5), the M3 subtype is primarily responsible for bladder smooth muscle contraction. By selectively blocking M3 receptors in the detrusor muscle, darifenacin reduces involuntary bladder contractions without significantly affecting M1 receptors in the brain (associated with cognitive function) or M2 receptors in the heart. This selectivity may translate to fewer cognitive side effects compared to non-selective antimuscarinics, particularly important for elderly patients. The medication also has some affinity for M1 and M5 receptors but minimal effect on M2 and M4 receptors.

Available Formulations

Darifenacin is available as extended-release tablets in 7.5 mg and 15 mg strengths. The tablets should be swallowed whole with liquid and should not be crushed, divided, or chewed. The medication can be taken with or without food. The extended-release formulation allows for once-daily dosing.

Medical Uses

Darifenacin is FDA-approved for the treatment of overactive bladder (OAB) with symptoms of urge urinary incontinence, urgency, and urinary frequency. These symptoms occur when the bladder muscle contracts involuntarily during bladder filling. Clinical trials demonstrated significant reductions in incontinence episodes, urgency episodes, micturition frequency, and improvement in quality of life measures compared to placebo.

Dosing Guidelines

The recommended starting dose is 7.5 mg once daily. Based on individual response, the dose may be increased to 15 mg once daily as early as 2 weeks after starting treatment. The medication should be taken at the same time each day. For patients with moderate hepatic impairment (Child-Pugh B) or those taking potent CYP3A4 inhibitors, the daily dose should not exceed 7.5 mg. The medication is not recommended for patients with severe hepatic impairment.

Important Safety Information

Darifenacin is contraindicated in patients with urinary retention, gastric retention, uncontrolled narrow-angle glaucoma, and in patients with known hypersensitivity to the drug. As with all anticholinergics, the medication should be used with caution in patients with clinically significant bladder outflow obstruction (risk of urinary retention), gastrointestinal obstructive disorders, decreased GI motility, controlled narrow-angle glaucoma, myasthenia gravis, and severe constipation or ulcerative colitis. Central nervous system effects including somnolence and dizziness have been reported.

Drug Interactions

Darifenacin is metabolized by CYP3A4 and CYP2D6. Potent CYP3A4 inhibitors (ketoconazole, itraconazole, ritonavir, nelfinavir, clarithromycin, nefazodone) increase darifenacin exposure; the daily dose should not exceed 7.5 mg. CYP2D6 inhibitors may also increase exposure. Darifenacin is a moderate CYP2D6 inhibitor; caution is advised with CYP2D6 substrates having narrow therapeutic indices. Concomitant use with other anticholinergics may increase anticholinergic effects.

Special Populations

There are no adequate studies of darifenacin in pregnant women; use during pregnancy only if clearly needed. It is unknown whether darifenacin is excreted in human breast milk; caution is advised during breastfeeding. Safety and efficacy have not been established in pediatric patients. Elderly patients do not require dose adjustment but may be more sensitive to anticholinergic effects. The medication is not recommended for patients with severe hepatic impairment; dose should not exceed 7.5 mg in moderate hepatic impairment. No dose adjustment is required for renal impairment.