A 60 yrs old male comes to casualty with acute retention of urine since 12 hrs. On examination there was distended bladder. His wife gives a history of taking some drug by the patient since 2 days as he is suffering from depression. The most likely drug is:

**Core Concept**
Anticholinergic side effects of certain medications can lead to urinary retention, particularly in the elderly. This is due to the blockade of muscarinic acetylcholine receptors in the bladder, which normally regulate bladder contraction and relaxation.

**Why the Correct Answer is Right**
Amitriptyline is a tricyclic antidepressant (TCA) that has significant anticholinergic properties. It can cause urinary retention by blocking the muscarinic receptors in the bladder, leading to an inability to contract and empty the bladder. This is a well-known side effect of TCAs, especially in older adults. Amitriptyline's anticholinergic effects can also cause other symptoms such as dry mouth, constipation, and blurred vision.

**Why Each Wrong Option is Incorrect**
**Option A:** Chlorpromazine (CPZ) is a first-generation antipsychotic with some anticholinergic effects, but it is not as potent as amitriptyline in causing urinary retention.

**Option C:** Haloperidol is a first-generation antipsychotic with minimal anticholinergic effects, making it an unlikely cause of urinary retention.

**Option D:** Pimozide is another first-generation antipsychotic with minimal anticholinergic effects, similar to haloperidol.

**Clinical Pearl / High-Yield Fact**
When considering urinary retention in an elderly patient on medication, always ask about anticholinergic medications such as TCAs, antihistamines, and antipsychotics, as these can cause significant bladder dysfunction.

**✓ Correct Answer: B. Amitriptyline**

✓ Correct Answer: B. Amitriptyline