How Do Beta2 Agonists Work?

Beta2 agonists are bronchodilators that ease breathing difficulties caused by bronchial conditions such as bronchospasm, chronic obstructive pulmonary disease (COPD), and asthma. Beta2 agonists relax bronchial smooth muscles and inhibit hypersensitivity reactions in the bronchial passage.

Beta2 agonists, also known as long-acting beta2 agonists (LABAs), enhance the activity of beta2 adrenergic receptors, which are protein particles on cell membranes. Beta2 receptors activate intracellular activity when stimulated by epinephrine, a natural hormone in the body.

Beta2 receptors are abundant in airway smooth muscles and are also present in many other parts of the body including the heart, uterine and skeletal muscles, mucous glands, and many types of immune cells such as mast cells, eosinophils, and lymphocytes.

When stimulated by beta2 agonists, beta2 receptors stimulate adenyl cyclase, an enzyme involved in the regulation of smooth muscle function. Adenyl cyclase increases the intracellular levels of cyclic adenosine monophosphate (cAMP), a substance important for downstream signaling within the cell.

An increase in cAMP levels relaxes the bronchial smooth muscles and dilates the airway. Adenyl cyclase also inhibits the release of inflammatory substances from mast cells that are part of the first-line immune defense which play a prime role in initiating immediate hypersensitivity reactions common in asthma attacks.

Beta2 agonists may also be combined with other types of medications that include:

• Corticosteroids: Corticosteroids are potent anti-inflammatory agents that work on many types of immune cells to control inflammation. 
• Respiratory anticholinergics: Respiratory anticholinergics relax bronchial muscles by blocking the activity of acetylcholine, a neurotransmitter that nerve endings secrete to make muscles contract. Anticholinergics also reduce mucus secretion in the respiratory passage and improve lung function.

Beta2 agonists are available in various strengths and formulations that include:

• Oral inhalations in the form of powders, aerosolized tiny particles or droplets, and solutions nebulized into a fine mist. Many types of inhalation devices such as metered dose inhalers and nebulizers are available on prescription.
• Tablets
• Syrups
• Intravenous (IV) injections

Beta2 agonists are used in the treatment of the following conditions:

FDA-approved:

• Bronchospasm, including
  • Bronchospasm in patients with reversible obstructive airway disease
  • Acute or severe bronchospasm
  • Prevention of exercise-induced bronchospasm
• Long term maintenance treatment of chronic obstructive pulmonary diseases including:
  • Chronic bronchitis
  • Emphysema
• Prevention and maintenance treatment of asthma, an inflammatory bronchial condition
• Prevention of exercise-induced asthma

Off-Label:

• Preterm labor

Orphan designation:

• Prevention of paralysis caused by spinal cord injury

Side effects of beta2 agonists may include the following:

• Tremor
• Nervousness
• Insomnia
• Tachycardia (rapid heartbeat)
• Viral infection
• Headache
• Generalized pain
• Back pain
• Arthralgia (joint pain)
• Chest pain
• Chest infection
• Rhinitis (inflammation of the nasal passage)
• Pharyngitis (throat inflammation)
• Nasopharyngitis (inflammation of nose and throat)
• Sinusitis (inflammation of the sinuses)
• Bronchitis (inflammation of bronchial passage)
• Paradoxical bronchospasm
• Upper/lower respiratory tract infection
• Lung disorder
• Dyspnea (shortness of breath)
• Onset or exacerbation of asthma
• Pulmonary edema
• Pneumonia
• Nausea
• Vomiting
• Diarrhea
• Fever
• Dizziness
• Cough
• Otitis media (middle ear inflammation)
• Allergic reactions such as:
  • Rash
  • Urticaria (hives)
  • Contact dermatitis
  • Photodermatitis (light sensitive dermatitis)
  • Angioedema (swelling in the tissue under the skin or mucous membranes)
  • Oropharyngeal edema (swelling of mouth and throat)
  • Anaphylaxis (severe allergic reaction)
• Bruising
• Nasal edema
• Nasal congestion
• Epistaxis (nosebleed)
• Increased appetite
• Dry mouth
• Dryness and irritation in the throat
• Dysphonia (hoarseness)
• Bad taste in the mouth
• Dysgeusia (taste disorder)
• Oral/oropharyngeal candidiasis (Candida infection)
• Oropharyngeal pain (mouth and throat pain)
• Tooth abscess
• Belching and flatulence
• Dyspepsia (indigestion)
• Epigastric (upper abdominal) pain
• Abdominal pain
• Heartburn
• Gastroesophageal reflux disease (GERD)
• Gastroenteritis (inflammation of the gastrointestinal tract)
• Constipation
• Hypertension (high blood pressure)
• Hypotension (low blood pressure)
• Chest tightness and discomfort
• Musculoskeletal chest pain
• Angina pectoris (chest pain due to coronary heart disease)
• Palpitation
• Pounding heartbeat
• Abnormal ECG readings
• Cardiac arrhythmias (irregular heartbeat)
• Atrial fibrillation (irregular and rapid heart rate with the atria out of synchronization with the ventricles)
• Supraventricular tachycardia (rapid heart rate beginning above the ventricles)
• Ventricular and supraventricular extrasystoles (extra heartbeats)
• Myocardial ischemia (reduced blood flow to heart muscles)
• Myocardial infarction (heart attack)
• Increased fetal heart rate
• Urinary tract infection
• Dysuria (painful urination)
• Urinary retention
• Increased diaphoresis (sweating)
• Chills
• Hyperactivity
• Restlessness
• Trembling
• Anxiety
• Agitation
• Depression
• Abnormal behavior
• Lymphadenopathy (swollen lymph nodes)
• Ocular pruritus (eye itching)
• Conjunctivitis (inflammation of the conjunctiva, the membrane on the whites of the eyes and the inner surface of eyelids)
• Keratitis (inflammation of the cornea)
• Cataracts
• Blurred vision
• Increased intraocular pressure
• Glaucoma (a progressive disease that damages the optic nerve)
• Flu syndrome
• Leg cramps
• Spasms
• Pain in extremities
• Neck pain
• Migraine
• Central nervous system stimulation
• Paresthesia (prickling sensation)
• Peripheral edema
• Articular rheumatism (rheumatism in joints)
• Muscular stiffness and rigidity
• Muscle cramps
• Myositis (muscle inflammation)
• Asthenia (weakness)
• Lightheadedness
• Syncope (fainting)
• Drowsiness
• Sleep disturbance
• Vertigo
• Fatigue
• Fall
• Contusion
• Hyperglycemia (increased blood glucose levels)
• Hypoglycemia in some babies born to women who received beta2 agonists during labor
• Transient hypokalemia (low potassium levels in the blood)
• Metabolic acidosis (acid buildup in the body) 
• Sign and symptoms of systemic glucocorticoid steroid effects (e.g., hypofunctional adrenal gland)

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of beta2 agonist drugs include:

• AccuNeb
• albuterol
• Anoro Ellipta
• arformoterol
• Bevespi Aerosphere
• Breo Ellipta
• Brethine
• Breztri
• Brovana
• budesonide/formoterol/glycopyrrolate inhaled
• formoterol
• glycopyrrolate inhaled/formoterol
• levalbuterol
• metaproterenol
• olodaterol inhaled
• Perforomist
• ProAir Digihaler
• Proair HFA
• ProAir RespiClick
• Proventil HFA
• salmeterol
• Serevent Diskus
• Striverdi Respimat
• terbutaline
• Trelegy Ellipta
• umeclidinium bromide/vilanterol inhaled
• umeclidinium bromide/vilanterol inhaled/fluticasone furoate inhaled
• Ventolin HFA
• Ventolin Injection
• Ventolin Nebules PF
• Ventolin Oral Liquid
• Ventolin Respirator Solution
• vilanterol/fluticasone furoate inhaled
• Xopenex
• Xopenex HFA