When successful, beta2 agonists produce relief almost immediately and may continue doing so for as long as 6 hours; in acute exacerbations, the duration of effect is often less than 6 hours. Short-acting beta2 agonists (e.g., albuterol, terbutaline) can be delivered either by inhalation or orally. Generally, the inhaled form of delivery is preferred because it is less likely to produce side effects than oral preparations. Injectable beta2 agonists, such as epinephrine (Epipen), are rarely used except in severe circumstances.
The inhaled anticholinergics presently are limited to ipratropium bromide (Atrovent). This medication does not modify reactions to allergens, nor does it prevent exercise-induced bronchospasm. Ipratropium bromide can be used as an alternative for patients intolerant to beta2 agonists, but it is not the drug of choice for quick relief of asthma symptoms. It is the drug of choice for relieving bronchospasm caused by beta-blocker medications.