## Core Concept
Nitroglycerine, also known as glyceryl trinitrate (GTN), is a vasodilator used primarily for the treatment of angina pectoris. It works by releasing nitric oxide (NO) in the body, which then relaxes vascular smooth muscle, leading to vasodilation. This effect reduces the preload on the heart, thereby decreasing myocardial oxygen demand.

## Why the Correct Answer is Right
The correct answer, , involves understanding the pharmacokinetics and pharmacodynamics of nitroglycerine. Nitroglycerine is highly lipophilic and undergoes extensive first-pass metabolism when taken orally, which significantly reduces its bioavailability. However, this characteristic also makes it suitable for sublingual administration, where it can be absorbed directly into the systemic circulation, bypassing the liver initially.

## Why Each Wrong Option is Incorrect
- **Option A:** Sublingual administration is a common route for nitroglycerine, allowing for rapid absorption and effect. This route is specifically used for acute angina relief.
- **Option B:** Intravenous administration is used in certain clinical settings, such as in the intensive care unit for patients with severe angina or acute myocardial infarction, where close monitoring and control of blood pressure are required.
- **Option C:** Transdermal patches are another method of administering nitroglycerine, providing a steady release of the drug through the skin into the systemic circulation. They are used for long-term prevention of angina.

## Why Option D is Incorrect
- **Option D:** Oral administration is not typically used for nitroglycerine due to its extensive first-pass metabolism, which results in low bioavailability. This makes oral administration less effective for immediate relief of angina symptoms.

## Clinical Pearl / High-Yield Fact
A key point to remember is that nitroglycerine's effectiveness can be significantly reduced by the development of tolerance, especially with long-acting formulations like transdermal patches. To avoid tolerance, a nitrate-free interval of 8-12 hours per day is often recommended when using long-acting nitrate formulations.

## Correct Answer: D. Oral.