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Short-acting beta-agonists (SABAs) are a class of prescription drugs used to quickly relieve shortness of breath and wheezing in people with asthma. SABAs work by relaxing the smooth muscles of the the airways leading to the lungs that become narrow (constrict) during an asthma attack—allowing air to flow more freely and alleviating spasms. They're used as needed to treat acute symptoms and, as such, are known as rescue medications. Most often SABAs are taken via an inhaler, although some are available in pill or syrup form or by injection.
SABAs are considered the frontline defense for acute asthma symptoms. They are most often inhaled via a metered-dose inhaler (using a pressurized canister) or as a dry powder that you simply breathe in, but are also available as tablets, syrups, nebulized solutions, injectable solutions, and even intravenous solutions.
SABAs are one of several classes of drugs known as bronchodilators because they dilate (open) the airways known as the bronchi and bronchioles.
When used as a rescue medication, a SABA can relieve dyspnea (shortness of breath) and wheezing within minutes. After one or two puffs, the drug will remain active for around four to six hours and can be used from three to six times a day depending on the formulation.
Two SABAs are approved by the U.S. Food and Drug Administration (FDA) for the treatment of acute asthma symptoms:
The FDA has approved one medication that combines a SABA and an inhaled corticosteroid (ICS) for the treatment of acute asthma symptoms and prevention of future asthma attacks:
Certain older-generation SABAs have been discontinued by their manufacturers or pulled from the market due to safety concerns, among them Alupent (metaproterenol), Maxair (pirbuterol), and Bricanyl (terbutaline).
SABAs, along with closely related long-acting beta-agonists (LABAs), belong to a class of drugs known as beta2 (β2)-adrenergic receptor agonists. By definition, agonists are drugs that bind to a cell receptor to trigger a specific reaction.
The receptor in this case is the beta2-adrenergic receptor, which relaxes smooth muscles. Smooth muscles are those in the walls of hollow organs that contract and relax involuntarily to, among other things, move food through the intestines, regulate blood pressure and circulation, or—as is relevant to asthma—open and close airways in the lungs.
The receptors are considered adrenergic because they respond to the hormone epinephrine (adrenaline) that helps regulate smooth muscle function. By mimicking epinephrine, beta-agonists can bind to adrenergic receptors and trigger a chain reaction in which calcium is quickly released from channels within smooth muscles, causing them to relax.
When applied to the lungs, this effect will cause the bronchi and bronchioles to quickly dilate, allowing more air to enter. It also alleviates bronchospasms that cause chest tightness and coughing during an asthma attack.
Although SABAs and LABAs have similar mechanisms of action, they differ by their half-life (the time it takes to clear 50% of the drug from the body). As per their name, SABAs have a short half-life (around three to six hours), while LABAs have a half-life closer to 36 hours.
How SABAs are used to treat asthma depends on the frequency or severity of symptoms:
SABAs are frequently used off-label to treat respiratory distress in people with severe lower respiratory infections, although their usefulness in this respect is unproven.
Albuterol is sometimes used off-label as a tocolytic (a drug that suppresses contractions to prevent or delay preterm birth). Depending on the severity of the contractions, the drug may be given intravenously or by mouth.
There are few absolute contraindications to SABAs other than a known allergy to the drug or an inactive ingredient in the formulation. If you are allergic to albuterol, you should not use levalbuterol (or vice versa).
SABAs are known to affect pulse rate, blood pressure, blood sugar, and thyroid hormone production and, on rare occasions, induce seizures. While not contraindicated for use, SABAs should be used with caution in people who have:
Results from animal studies show that use of albuterol or levalbuterol in pregnancy has the potential to be harmful to developing fetuses, but no well-controlled trials in humans have been conducted.
Based on the statistical risk, the drugs are unlikely to pose any harm. Even so, before taking them it is important to tell your healthcare provider if you are pregnant, planning to get pregnant, or breastfeeding, so that you can weigh the benefits and risks of use.
The recommended dosage of albuterol and levalbuterol varies according to the formulation as well as the age of the person who will be taking it. Among the approved formulations:
Tablets and syrups are prescribed used less often but may be appropriate for children and adults who can't tolerate or properly use inhaled medications.
| Recommend Dosages by Formulation | ||
|---|---|---|
| Drug | Adults | Children 4 Years and Over |
| Albuterol | MDI or DPI: 2 puffs every 4-6 hours as needed Nebulizer: 3-4 doses/day IR tablets: 2-4 mg taken 3-4 times/day ER tablets: 4-8 mg every 12 hours Syrup: 2-4 mg taken 3-4 times/day (max. 32 mg/day) | MDI or DPI: 2 puffs every 4-6 hours as needed Nebulizer: 3-4 doses/day IR tablets: not used ER tablets: not used Syrup: 2-24 mg/day (taken in 3-4 divided doses) |
| Levalbuterol | MDI: 1-2 puffs every 4-6 hours Nebulizer: 3-4 doses every 6-8 hours | MDI: 1-2 puffs every 4-6 hours Nebulizer: 3 doses taken 3 times/day |
| Airsupra | MDI: 2 puffs as needed up to 12 puffs/day | Not approved for people younger than 18 years of age |
SABAs should never be used in excess of the recommended dose. Overuse can lead to premature drug tolerance and treatment failure.
Of the three inhaled formulations, MDIs need to be primed before use if not recently used. This involves shaking and spraying the inhaler away from your face in two short bursts to clear the aerosol valve. (DPIs and nebulizers can be used as needed.)
The various inhalers also need to be regularly cleaned to avoid clogging and insufficient dosing:
The medications can be safely stored at room temperature (ideally between 68 and 77 degrees F). Keep the drug in its original packaging away from direct sunlight and where children cannot see or reach it.
Do not use a SABA after its expiration date.
The side effects of the various SABA formulations are largely the same. However, because inhaled SABAs are delivered straight to the lungs and therefore do not affect other organs in the body, they tend to have milder and shorter-lasting side effects than oral or intravenous SABAs.
On rare occasions, SABAs can cause paradoxical bronchospasm—meaning breathing symptoms get worse rather than better. Why this happens is unclear, but it seems to occur most often in people with allergic asthma who have severely inflamed airways.
SABA-induced paradoxical bronchospasm should always be considered a medical emergency.
Allergies to SABAs are rare but can occur. Call 911 or seek emergency care if you develop hives or rash, difficulty breathing, abnormal heartbeats, confusion, or the swelling of the face, throat, tongue, or throat. These are signs of a potentially life-threatening, whole-body allergy known as anaphylaxis.
Routine monitoring of heart function, blood glucose, or thyroid function is recommended for anyone in an at-risk group who takes albuterol. The treatment may need to be stopped if symptoms worsen or diagnostic test results fall well outside of the acceptable range of values.
Because of their effect on heart rhythms, never use more of an SABA than prescribed. On rare occasions overuse of albuterol or levalbuterol has caused myocardial infarction (heart attack) or stroke.
Beta2-agonists are known to interact with certain classes of drugs. In some cases, the interaction may increase the activity of a drug (raising the risk of side effects). In others, it may decrease the blood concentration of a drug (reducing its effectiveness).
Among the drugs that may interact with SABAs are:
To avoid interactions, let your healthcare provider know about any and all drugs you are taking, whether they are prescription, over-the-counter, herbal, or recreational.
Though rescue inhalers like albuterol and levalbuterol are safe and effective for relieving acute asthma symptoms, it is important not to overuse them. Some people will do out so of panic if the drug is "not working fast enough," while others will overuse SABAs to avoid having to take other longer-acting drugs. Both of these are signs that your condition is not being well controlled.
As a rule of thumb, if you need to use a rescue inhaler more than twice weekly, your asthma is being poorly controlled. By speaking with your healthcare provider and being honest about your inhaler use, you should be better able to find the right combination of drugs to control your asthma symptoms.
16 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
By Pat Bass, MD
Dr. Bass is a board-certified internist, pediatrician, and a Fellow of the American Academy of Pediatrics and the American College of Physicians.
