Short-Acting Beta Agonists (SABAs) for Asthma

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 as known as rescue medications. Most often SABAs are taken via an inhaler, although some are available in pill or syrup form or by injection.

What They Are

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 is breathed directly into you simply breathe in) but are also available as tablets, syrups, nebulized solutions, injectable solutions, and even intravenous solutions.

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:

• Albuterol, also known as salbutamol and marketed under the brand names ProAir, Proventil, Ventolin, and others
• Levalbuterol, marketed under the brand name Xopenex and others

Certain older-generations 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)

How SABAs Work

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.

Indications for Use

How SABAs are used to treat asthma depends on the frequency or severity of symptoms:

• Mild intermittent asthma: SABAs are often used on their own as needed.
• Persistent asthma: SABAs typically are used to relieve acute symptoms; inhaled LABAs and/or corticosteroids are also taken on a regular (typically daily) basis to provide long-term control.
• Exercise-induced asthma: SABAs can be taken five to 30 minutes before physical activity to reduce the risk of an attack.
• Asthma emergency: Albuterol is sometimes delivered intravenously (into a vein) by emergency department personnel.

Off-Label Uses

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.

Precautions and Contraindications

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:

• Coronary artery disease (CAD)
• Cardiac arrhythmias
• Uncontrolled hypertension
• Diabetes
• Convulsive disorders, including epilepsy
• Hyperthyroidism

Albuterol and levalbuterol are classified as Pregnancy Category C drugs, which means in animal studies the medications have shown 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 doctor if you are pregnant, planning to get pregnant, or breastfeeding so that you can weigh the benefits and risks of use.

Dosage

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:

• Albuterol is available as a metered-dose inhaler (MDI), dry powder inhaler (DPI), nebulized solution, immediate-release (IR) tablet, extended-release (ER) tablet, syrup, and intravenous solution.
• Levalbuterol is available as an MDI or nebulized solution.

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.

How to Take and Store

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:

• Metered-dose inhalers, which deliver the medications using an aerosolized propellant, should be cleaned once weekly by removing the canister and running water through the mouthpiece for 30 to 60 seconds. The canister should never be submerged in water.
• Dry powder inhalers, which have no propellant and are breath-activated, simply need to be wiped off between use. The unit should never be washed or submerged in water.
• Nebulizers, which deliver the medications using an inhaled mist, should be cleaned after every use and disinfected once weekly with either a steam sterilizer, an approved disinfecting solution, or a complete dishwasher cycle.

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.

Side Effects

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.

When to Call 911

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.

Warnings and Interactions

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:

• Anti-arrhythmia drugs like Multaq (dronedarone) or digoxin
• Antifungals like Diflucan (fluconazole), Noxafil (posaconazole), or ketoconazole
• Anti-malaria drugs like chloroquine or piperaquine
• Antipsychotics like Orap (pimozide), Mellaril (thioridazine), Serentil (mesoridazine), amisulpride, or ziprasidone
• Beta-blockers like Inderal (propranolol) or Lopressor (metoprolol)
• HIV protease inhibitors like Viracept (nelfinavir) or Fortovase (saquinavir)
• Monoamine oxidase inhibitor (MAOI) antidepressants like Parnate (tranylcypromine) or Marplan (isocarboxazid)
• Potassium-sparing diuretics like Aldactone (spironolactone) or Inspra (eplerenone)

A Word From Verywell

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 doctor and being honest about your inhaler use, you should be better able to find the right combination of drugs to control your asthma symptoms.