## **Core Concept**
Salbutamol, also known as albuterol, is a short-acting β2 adrenergic receptor agonist (SABA) widely used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease (COPD). Its primary mechanism of action involves the stimulation of β2 receptors in the lungs, leading to bronchodilation. However, like all medications, it can cause side effects, some of which are dose-related.

## **Why the Correct Answer is Right**
The most common dose-related side effect of salbutamol is **tachycardia** (or palpitations), which occurs due to the drug's effect on β1 receptors in the heart, although it is more selective for β2 receptors. At therapeutic doses, salbutamol can cause some degree of β1 receptor stimulation, leading to increased heart rate and force of contraction. This effect is more pronounced with higher doses.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Tremors can occur due to β2 receptor stimulation in skeletal muscle and are a known side effect of salbutamol but are not typically considered the most common dose-related side effect.
- **Option B:** Hypokalemia can occur due to the increased cellular uptake of potassium ions, but it's not usually described as a dose-related side effect in the same immediate context as cardiovascular effects.
- **Option C:** Muscle cramps are not commonly highlighted as a primary dose-related side effect of salbutamol.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while salbutamol is selective for β2 receptors, at higher doses, its selectivity is reduced, leading to more pronounced β1 effects, such as tachycardia. This is a critical consideration in patients with cardiovascular disease.

## **Correct Answer:** D. Tachycardia.