Darifenacin is a competitive muscarinic receptor antagonist (anticholinergic) with selective affinity for the M3 receptor subtype. It is indicated for the treatment of overactive bladder (OAB) with symptoms of urge urinary incontinence, urgency, and frequency. The 7.5mg strength is the recommended starting dose, offering a favorable balance between efficacy and tolerability, particularly in the Indian population where anticholinergic side effects are a significant concern.
Adult: The recommended starting dose is 7.5 mg once daily. Based on individual response and tolerability, the dose may be increased to 15 mg once daily after a minimum of 2 weeks.
Note: Administer orally once daily with liquid. May be taken with or without food. The tablet should be swallowed whole; do not chew, divide, or crush.
Darifenacin functions as a competitive antagonist at muscarinic acetylcholine receptors, specifically demonstrating high selectivity and potency for the M3 receptor subtype. In the bladder detrusor muscle, M3 receptors are primarily responsible for mediating contraction. By blocking these receptors, darifenacin inhibits involuntary detrusor contractions, increases bladder capacity, reduces the frequency of micturition, and diminishes urgency.
Pregnancy: Category C: Animal studies have shown adverse effects (reduced fetal weight, increased resorptions). There are no adequate and well-controlled studies in pregnant women. Use only if the potential benefit justifies the potential risk to the fetus.
Driving: May cause blurred vision, dizziness, and somnolence. Patients should be cautioned about operating machinery or driving until they are certain darifenacin does not affect them adversely.
| Ketoconazole, Itraconazole, Voriconazole, Posaconazole | Potent CYP3A4 inhibitors increase darifenacin plasma concentrations. Dose should not exceed 7.5 mg daily. | Major |
| Clarithromycin, Telithromycin | Potent CYP3A4 inhibitors increase darifenacin plasma concentrations. Dose should not exceed 7.5 mg daily. | Major |
| Ritonavir, Nelfinavir | Potent CYP3A4 inhibitors increase darifenacin plasma concentrations. Dose should not exceed 7.5 mg daily. | Major |
| Fluconazole | Moderate CYP3A4 inhibitor; monitor for increased anticholinergic side effects. | Moderate |
| Other anticholinergic drugs (e.g., oxybutynin, tolterodine, tricyclic antidepressants, first-gen antihistamines) | Additive anticholinergic effects (dry mouth, constipation, blurred vision, cognitive impairment). | Moderate |
| Digoxin | Darifenacin may increase digoxin levels. Monitor digoxin levels when initiating or stopping darifenacin. | Moderate |
| Warfarin | No significant pharmacokinetic interaction observed, but monitor INR as a precaution. | Minor |
| Oral Contraceptives (Ethinyl Estradiol/Levonorgestrel) | No clinically significant interaction. | Minor |