Mechanism of action of Oxybutynin?
**Core Concept**
Oxybutynin is an antimuscarinic medication used to treat overactive bladder symptoms. Its mechanism of action involves the blockade of muscarinic acetylcholine receptors in the bladder, which are responsible for detrusor muscle contraction.
**Why the Correct Answer is Right**
Oxybutynin is a tertiary amine antimuscarinic agent that selectively blocks M3 muscarinic receptors in the bladder, leading to a reduction in detrusor muscle contractions and an increase in bladder capacity. This blockade also results in decreased bladder muscle contractions and reduced urgency. The M3 receptors are responsible for the contraction of smooth muscle in the bladder, and by blocking these receptors, oxybutynin effectively reduces bladder contractions and alleviates symptoms of overactive bladder.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as oxybutynin does not work through adrenergic receptor blockade. Adrenergic receptors are involved in the sympathetic nervous system, which is not directly related to the mechanism of action of oxybutynin.
**Option B:** This option is incorrect as oxybutynin does not increase bladder contractions. Instead, it reduces detrusor muscle contractions, leading to an increase in bladder capacity.
**Option C:** This option is incorrect as oxybutynin does not work through direct relaxation of the detrusor muscle. Its mechanism of action involves the blockade of muscarinic receptors, which indirectly leads to relaxation of the detrusor muscle.
**Clinical Pearl / High-Yield Fact**
It's essential to note that oxybutynin can have significant anticholinergic side effects, such as dry mouth, constipation, and blurred vision, due to its blockade of muscarinic receptors in various parts of the body. This is a critical consideration when prescribing oxybutynin for patients with overactive bladder.
**Correct Answer: D. Antimuscarinic blockade of M3 receptors in the bladder.**