**Question:** Polychromatic lustre is seen in:

A. Aminophylline
B. Nitroglycerin
C. Thiazide diuretics
D. Calcium channel blockers

**Correct Answer:** A. Aminophylline

**Core Concept:**
The term "polychromatic lustre" refers to the characteristic appearance of certain drugs when viewed under specific lighting conditions. In the context of this question, we are discussing the appearance of drugs when examined under ultraviolet (UV) light. This phenomenon is not directly related to the pharmacological properties of the drugs but rather a visual characteristic.

**Why the Correct Answer is Right:**
Aminophylline is a xanthine derivative used as a bronchodilator and phosphodiesterase inhibitor. When viewed under UV light, aminophylline exhibits a striking polychromatic lustre due to the presence of certain chromophores within its molecular structure that absorb UV light. This characteristic is not shared by the other options.

**Why Each Wrong Option is Incorrect:**
B. Nitroglycerin: Nitroglycerin is a vasodilator and is primarily responsible for lowering blood pressure. It does not possess a polychromatic lustre under UV light due to the absence of chromophores that absorb UV light.

C. Thiazide diuretics: Thiazide diuretics are employed for treating hypertension and edema. They exhibit no polychromatic lustre under UV light due to the lack of specific chromophores in their molecular structure that absorb UV light.

D. Calcium channel blockers: Calcium channel blockers are used to treat hypertension, angina, and other cardiovascular conditions. Similar to the other options, these drugs do not display a polychromatic lustre under UV light due to the absence of chromophores that absorb UV light.

**Clinical Pearl:**
It is essential for medical students and practicing physicians to be familiar with the visual characteristics of drugs, as it can serve as a quick reference for identification during clinical practice. However, the primary focus should be on understanding the pharmacology and therapeutic uses of these drugs rather than their UV light appearance.