## Core Concept
The loading dose of a drug is a higher dose given initially to rapidly achieve therapeutic plasma concentrations. Aminophylline, a non-selective phosphodiesterase inhibitor and adenosine receptor antagonist, is used in the treatment of asthma and COPD. Its loading dose is crucial for quickly attaining effective levels.

## Why the Correct Answer is Right
The correct loading dose of aminophylline is **5-6 mg/kg**. This dose is calculated based on the drug's volume of distribution and is administered over 20-30 minutes to avoid rapid changes in plasma concentration that could lead to toxicity. The goal is to achieve therapeutic levels promptly, which for aminophylline, is typically in the range of 20-40 mcg/mL.

## Why Each Wrong Option is Incorrect
- **Option A:** This dose seems too low for a loading dose of aminophylline, which requires a significant initial amount to quickly reach therapeutic levels.
- **Option B:** Similarly, this option appears to be an inadequate dose for rapidly achieving the desired plasma concentration of aminophylline.
- **Option D:** This option suggests a much higher dose than typically recommended for aminophylline, which could increase the risk of adverse effects without providing additional therapeutic benefit.

## Clinical Pearl / High-Yield Fact
A key point to remember is that aminophylline has a narrow therapeutic index, meaning the difference between an effective dose and a toxic dose is small. Therefore, monitoring plasma levels after administering a loading dose is crucial to ensure therapeutic levels are achieved without causing toxicity.

## Correct Answer: C. 5-6 mg/kg.