Darifenacin (Enablex?, Novartis) is a medication used to treat urinary incontinence.
Darifenacin works by blocking the M3 muscarinic acetylcholine receptor, which is primarily responsible for bladder muscle contractions. It thereby decreases the urgency to urinate. It should not be used in people with urinary retention.
It is not known whether this selectivity for the M3 receptor translates into any clinical advantage when treating symptoms of overactive bladder syndrome.
Indication
For the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency and frequency.
Pharmacology
Darifenacin is a competitive muscarinic receptor antagonist. In vitro studies using human recombinant muscarinic receptor subtypes show that darifenacin has greater affinity for the M3 receptor than for the other known muscarinic receptors (9 and 12-fold greater affinity for M3 compared to M1 and M5, respectively, and 59-fold greater affinity for M3 compared to both M2 and M4). Muscarinic receptors play an important role in several major cholinergically mediated functions, including contractions of the urinary bladder smooth muscle and stimulation of salivary secretion. Adverse drug effects such as dry mouth, constipation and abnormal vision may be mediated through effects on M3 receptors in these organs.
Toxicity
Overdosage can potentially result in severe central anticholinergic effects.
Affected Organisms
Humans and other mammals
Biotransformation
Hepatic. Primarily mediated by the cytochrome P450 enzymes CYP2D6 and CYP3A4.
Absorption
The mean oral bioavailability at steady state is estimated to be 15% and 19% for 7.5 mg and 15 mg tablets, respectively.
Half Life
The elimination half-life of darifenacin following chronic dosing is approximately 13-19 hours.
Protein Binding
Darifenacin is approximately 98% bound to plasma proteins (primarily to alpha-1-acid-glycoprotein).
2-[(3S)-1-Ethylpyrrolidin-3-yl]-2,2-diphenylacetamide in which one of the hydrogens at the 2-position of the ethyl group is substituted by a 2,3-dihydro-1-benzofuran-5-yl group. It is a selective antagonist for the M3 muscarinic acetylcholine receptor, which is primarily responsible for bladder muscle contractions, and is used as the hydrobromide salt in the management of urinary incontinence.
