**Core Concept**
Detrusor instability, also known as overactive bladder, is a condition characterized by involuntary contractions of the detrusor muscle in the bladder, leading to urinary frequency, urgency, and incontinence. Effective management involves pharmacological interventions that target the underlying pathophysiology.

**Why the Correct Answer is Right**
The detrusor muscle is a smooth muscle layer in the bladder wall that plays a crucial role in urine storage and release. In detrusor instability, the detrusor muscle contracts abnormally, leading to symptoms of urinary urgency and frequency. Drugs used to treat detrusor instability typically target the muscarinic acetylcholine receptors, which are involved in the parasympathetic innervation of the bladder. These drugs include antimuscarinic agents such as oxybutynin, tolterodine, and solifenacin, which relax the detrusor muscle and reduce bladder contractions.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as oxybutynin is a commonly used antimuscarinic agent for treating detrusor instability.
* **Option B:** This option is incorrect as tolterodine is another antimuscarinic agent used to manage detrusor instability.
* **Option C:** This option is incorrect as solifenacin is a third-line antimuscarinic agent used for treating overactive bladder.

**Clinical Pearl / High-Yield Fact**
Antimuscarinic agents can cause dry mouth, constipation, and blurred vision as side effects due to their anticholinergic effects. It is essential to monitor these side effects closely when prescribing these medications.

**Correct Answer: D.**