Dose response curves of salbutamol for bronchodilation and tachycardia are widely separated on dose axis. This information suggested that sulbutamol is
**Core Concept**
Salbutamol is a short-acting β2 adrenergic receptor agonist (SABA) used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease (COPD). The dose response curves for bronchodilation and tachycardia are determined by the drug's affinity and efficacy at the β2 adrenergic receptor.
**Why the Correct Answer is Right**
The widely separated dose response curves for bronchodilation and tachycardia suggest that salbutamol has a high β2 adrenergic receptor selectivity, also known as β2 selectivity. This means that salbutamol has a higher affinity for the β2 adrenergic receptor, which is responsible for bronchodilation, compared to the β1 adrenergic receptor, which is responsible for tachycardia. As a result, a higher dose of salbutamol is required to produce significant tachycardia, whereas bronchodilation is achieved at lower doses.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the widely separated dose response curves do not indicate a lack of β2 selectivity, but rather a high degree of selectivity.
**Option B:** This option is incorrect because the dose response curves are not widely separated due to a difference in the drug's pharmacokinetics, but rather due to its pharmacodynamics.
**Option C:** This option is incorrect because the dose response curves are not widely separated due to a difference in the drug's efficacy, but rather due to its selectivity for the β2 adrenergic receptor.
**Clinical Pearl / High-Yield Fact**
The β2 selectivity of salbutamol is a key factor in its therapeutic profile, allowing for effective bronchodilation with minimal cardiac side effects. This is an important consideration in the treatment of patients with asthma and COPD, where the goal is to achieve bronchodilation with minimal cardiovascular complications.
**Correct Answer: B. Salbutamol is a β2 selective agonist.**