Which of the following best characterizes the action of short-acting beta-2 agonists?

Short-acting beta-2 agonists (SABAs) are primarily used for quick relief of bronchospasm associated with conditions like asthma and chronic obstructive pulmonary disease (COPD). These medications work by stimulating beta-2 adrenergic receptors in the airways, resulting in the relaxation of bronchial smooth muscles.

The key characteristic of SABAs is their immediate onset of action, typically within minutes. This makes them particularly effective for rapid relief of acute symptoms such as wheezing and shortness of breath. However, their effects are short-lived, often lasting a few hours, which is why they are used as rescue medications rather than for long-term control of asthma or COPD symptoms.

In contrast to the other options, which suggest prolonged effects or gradual onset, the correct characterization emphasizes the immediacy of action and the limited duration of relief provided by SABAs. This acute response is what sets them apart from long-acting beta-2 agonists, which are designed for sustained control over more extended periods.