Bronchodilators

Mechanism of Action

The mechanism of action of bronchodilators involves targeting the beta-2 receptors, a G-protein–coupled receptor found in the lung airways. Activation of these receptors causes relaxation of the airway smooth muscle, resulting in improved airflow for a limited duration. However, prolonged and consistent use of beta-2 agonists can lead to receptor downregulation, reducing drug efficacy and necessitating higher doses to achieve the same bronchodilatory effect.

Bronchodilators are primarily metabolized in the gastrointestinal tract by cytochrome P450 enzymes. Approximately 80% to 100% of the drug is excreted in the urine, whereas less than 20% is eliminated in feces. Short-acting bronchodilators typically have a half-life of 3 to 6 hours, whereas long-acting bronchodilators have a half-life ranging from 18 to 24 hours.[16] Please see StatPearls' companion resource, "Asthma Medications," for more information. 

Anticholinergic drugs target receptors of the parasympathetic nervous system in the airways and inhibit their activity. As the parasympathetic nervous system is responsible for increased bronchial secretions and airway constriction, reversing these effects should provide bronchodilation and reduced secretions. The anticholinergic drugs predominantly target the M3 receptor.[17] 

Revefenacin is considered an innovative inhaled muscarinic antagonist due to its classification within a novel chemical category of inhaled muscarinic antagonists, differentiating it from established agents such as glycopyrrolate, tiotropium bromide, and umeclidinium bromide. In contrast to the existing LAMAs, which are categorized as quaternary ammonium compounds, revefenacin is classified as a tertiary amine. This structural distinction may facilitate enhanced selectivity for pulmonary tissues while potentially minimizing systemic adverse effects.[18]

Pharmacokinetics

Absorption: Inhaled bronchodilators such as albuterol, formoterol, salmeterol, ipratropium, and tiotropium are formulated to provide localized pulmonary action with minimal systemic absorption. Albuterol is quickly absorbed through the bronchial mucosa, producing an onset of action within minutes. Formoterol, which is moderately hydrophilic, also has a rapid onset of action, whereas salmeterol's lipophilic side chain results in a slower onset due to membrane binding. Both ipratropium and tiotropium are quaternary ammonium compounds with poor systemic absorption, which contributes to their safety profile.

Distribution: The distribution of formoterol and salmeterol is influenced by their lipophilicity. Salmeterol, in particular, exhibits high membrane affinity and prolonged receptor occupancy. Both agents selectively target bronchial smooth muscle, with minimal distribution to extrapulmonary tissues. Ipratropium has limited systemic distribution due to its hydrophilic nature and inability to cross the blood–brain barrier. Tiotropium demonstrates sustained pulmonary receptor occupancy, supporting its 24-hour bronchodilatory effect with minimal central nervous system involvement.

Metabolism: Albuterol is primarily metabolized through phase II sulfation by sulfotransferase enzymes (eg, SULT1A3), producing inactive sulfate conjugates. Salmeterol and indacaterol undergo extensive hepatic metabolism via cytochrome P450 3A4 (CYP3A4). Ipratropium is minimally metabolized and largely excreted unchanged, whereas tiotropium undergoes slow hepatic biotransformation and nonenzymatic hydrolysis.

Excretion: Albuterol and ipratropium are primarily excreted unchanged in the urine. Formoterol is eliminated via both renal and fecal pathways, whereas salmeterol and indacaterol are predominantly excreted in the feces via biliary routes. Tiotropium is mainly excreted renally, and its prolonged terminal half-life supports once-daily dosing.

Administration

Available Dosage Forms and Strengths

Inhaled bronchodilators are available in various delivery forms, including metered-dose inhalers (MDIs), dry powder inhalers (DPIs), soft mist inhalers (eg, Respimat), nebulizer solutions, and capsules for oral inhalation. SABAs, such as albuterol and levalbuterol, are typically administered via MDI or nebulization, delivering 90 µg to 108 µg per actuation or 2.5 mg per nebulized dose every 4 to 6 hours as needed. LABAs, including formoterol, salmeterol, arformoterol, olodaterol, and indacaterol, are generally administered once or twice daily, depending on the formulation, with strengths ranging from 12 µg to 50 µg per inhalation.

Muscarinic antagonists are similarly categorized into short-acting (eg, ipratropium) and long-acting agents (eg, tiotropium, glycopyrrolate, aclidinium, and umeclidinium), with dosing frequencies ranging from 4 times daily (QID) to once daily. Combination inhalers incorporate agents from both classes, such as formoterol/glycopyrrolate or umeclidinium/vilanterol, and are typically administered once or twice daily according to product-specific labeling.

The administration of bronchodilators is primarily achieved through inhalation devices, which deliver the medication directly to the bronchioles in the lungs. These devices vary in shape and size, but the critical factor is to maximize the amount of drug that reaches the bronchioles. Despite optimal technique, the systemic bioavailability of inhaled bronchodilators remains low. The best way to achieve maximum bioavailability is for the patient to exhale fully, position the inhaler in the mouth, and take a full inhalation. After the patient has inhaled completely, a 10-second pause in breathing is recommended to allow the medicine to dissipate into the lung space. This should be followed by a slow exhalation to resume normal breathing.[19]

Failure to follow proper inhalation techniques can prevent patients from receiving the full therapeutic benefit of inhaled medications. Short-acting bronchodilators typically produce effects within seconds to minutes and provide clinical relief for approximately 4 hours. These medications are often referred to as emergency or rescue inhalers due to their immediate impact on bronchodilation. In contrast, long-acting bronchodilators have a slower onset of action and are not suitable for use in emergency settings.[20]

Dosages

Short-acting beta-2 agonists: Albuterol is typically administered at a dose of 90 µg per actuation via an MDI, with 2 inhalations every 4 to 6 hours as needed. Alternatively, it may be administered as 2.5 mg via nebulization up to 4 times daily. Levalbuterol, the (R)-enantiomer of albuterol, is administered at 45 µg per actuation via an MDI or a nebulizer at dosages of 0.31 mg, 0.63 mg, or 1.25 mg every 6 to 8 hours, depending on the symptom severity. Compared to racemic albuterol, levalbuterol may produce fewer systemic adverse effects due to its selective (R)-albuterol isomer composition.

Long-acting beta-2 agonists: LABAs are used in combination with ICS for maintenance therapy in asthma and COPD. Salmeterol is administered at 50 µg twice daily via a DPI. Formoterol is available in 12 µg doses via a DPI or 20 µg doses via a nebulizer, both administered twice daily. Arformoterol, the (R)-enantiomer of formoterol, is administered at a dose of 15 µg via nebulizer twice daily. Indacaterol (75-150 µg DPI), olodaterol (5 µg via a soft mist inhaler), and vilanterol (25 µg DPI, only in combination products) are administered once daily for the treatment of COPD.

Short-acting muscarinic antagonists: SAMAs are primarily used in the treatment of COPD and in combination products for asthma. Ipratropium is administered as 17 µg per actuation via MDI, typically 2 inhalations 4 times daily (maximum 12 inhalations per day), or 500 µg via nebulizer every 6 to 8 hours. This may be combined with SABAs for additive bronchodilation, especially in acute exacerbations.

Long-acting muscarinic antagonists: LAMAs are indicated for long-term bronchodilation in COPD and, in some cases, asthma. Tiotropium is available as an 18 µg capsule for DPI, administered once daily, or as a soft mist inhaler at 2.5 µg per actuation, with 2 inhalations once daily (total dose: 5 µg). Other LAMAs include glycopyrrolate (15.6-25 µg DPI twice daily or 25 µg via nebulizer), aclidinium (400 µg DPI twice daily), and umeclidinium (62.5 µg DPI once daily), with specific delivery based on device type and formulation. Dosage for all medications should be individualized based on clinical status, patient age, and institutional guidelines.

Specific Patient Populations

Hepatic impairment: Bronchodilators are generally well tolerated in patients with hepatic dysfunction. However, LABAs such as formoterol, arformoterol, indacaterol, and vilanterol are metabolized in the liver via CYP3A4 and should be used with caution in severe hepatic impairment. In contrast, SAMAs and LAMAs, such as ipratropium and tiotropium, undergo minimal hepatic metabolism.

Renal impairment: LAMAs such as tiotropium, glycopyrrolate, and aclidinium are primarily excreted via the kidneys. In patients with chronic kidney disease stage 3 or worse (estimated glomerular filtration rate <60 mL/min/1.73 m²), drug accumulation may increase the risk of anticholinergic adverse effects such as urinary retention and xerostomia. Therefore, the 2023 American Geriatrics Society Beers Criteria recommends exercising caution when using anticholinergic agents in this population. SABAs and LABAs generally do not require renal dosage adjustment; however, levalbuterol may be better tolerated due to its selective (R)-enantiomer formulation.

Pregnancy considerations: According to the American College of Obstetricians and Gynecologists, albuterol is the preferred bronchodilator for symptom relief during pregnancy. If controller therapy is necessary, combination treatment with an ICS and a LABA (eg, fluticasone/salmeterol) is acceptable when ICS alone is insufficient to control symptoms. Salmeterol and formoterol have more extensive safety data. Tiotropium and ipratropium have shown no teratogenic effects in animal models; however, human data remain limited. The primary goal is to maintain adequate maternal oxygenation, which outweighs the potential risks of the drug.[21] 

Breastfeeding considerations: Most inhaled bronchodilators, including albuterol, levalbuterol, salmeterol, formoterol, ipratropium, tiotropium, and revefenacin, have minimal systemic absorption and are considered compatible with breastfeeding. However, a risk-benefit evaluation is recommended. During prolonged use, clinicians should monitor for signs of decreased lactation.[22][23][24][25] 

Pediatric patients: According to the NHLBI, SABAs are the first-line treatment for rescue therapy in all pediatric age groups. LABAs should never be used as monotherapy in asthma and must be combined with an ICS. According to the 2020 NHLBI guidelines, a combination of ICS/LABA in a fixed-dose inhaler is preferred to ensure adherence. Tiotropium is approved by the FDA as an add-on maintenance therapy in children aged 6 or older with severe asthma. Ipratropium may be used in emergency settings in combination with albuterol for the treatment of moderate-to-severe exacerbations.[26][11] 

Older patients: Inhaled beta-2 agonists may lead to tachycardia, tremors, and hypokalemia, particularly in frail older adults or those with cardiovascular conditions. Although the 2023 American Geriatrics Society Beers Criteria advise caution with systemic beta-2 agonists, inhaled preparations are acceptable with appropriate monitoring. LAMAs effectively manage COPD but may exacerbate benign prostatic hyperplasia, narrow-angle glaucoma, or cognitive impairment due to anticholinergic effects. Clinicians should use the lowest effective dose and periodically reassess urinary and cognitive function to optimize safety and outcomes.[27]

Adverse Effects

The adverse effects of bronchodilators primarily result from sympathetic nervous system activation. Common adverse effects include tremors, nervousness, sudden and noticeable heart palpitations, and muscle cramps. More severe effects include sudden constriction of the bronchial airways, paradoxical bronchospasm, hypokalemia, and in rare cases, myocardial infarction. Patients with comorbid conditions should consult their primary care provider before use. Patients should talk to their primary care physician if they have any comorbidities.[28] Anticholinergic agents may cause dry mouth, urinary retention, tachycardia, constipation, and gastrointestinal discomfort. Older adults are particularly vulnerable to anticholinergic-related complications, such as acute delirium, and therefore require careful monitoring during treatment. Please see StatPearls' companion resource, "Asthma Medications," for more information.

Drug-Drug Interactions

Beta-2 agonists: Beta-2 agonists may exhibit antagonistic effects when used with nonselective beta-blockers, such as propranolol, potentially leading to bronchospasm and reduced bronchodilation. If beta-blocker use is essential, a cardioselective beta-1 blocker, such as atenolol, may be used with caution.

Co-administration with monoamine oxidase inhibitors (eg, phenelzine) or tricyclic antidepressants (eg, amitriptyline) can potentiate the risk of cardiovascular adverse effects, such as tachycardia and hypertension. A minimum 14-day washout period is recommended before initiating a beta-agonist. Concomitant use with loop or thiazide diuretics may lead to additive hypokalemia, especially in patients susceptible to electrolyte disturbances; therefore, regular monitoring of serum potassium is advised.

Beta-2 agonists may also reduce serum digoxin levels, potentially decreasing its therapeutic efficacy; monitoring of digoxin concentrations is recommended when clinically indicated. LABAs may exhibit elevated plasma concentrations and an increased risk of QT prolongation or cardiac arrhythmias when co-administered with potent CYP3A4 inhibitors, such as ketoconazole or ritonavir. Such combinations should be avoided. When used concurrently with other QT-prolonging agents (eg, macrolide antibiotics and antipsychotics), there is an additive risk of ventricular arrhythmias, and electrocardiogram (ECG) monitoring may be necessary.

Muscarinic antagonists: SAMAs may cause additive anticholinergic adverse effects, such as dry mouth, blurred vision, and urinary retention, when used in combination with other anticholinergic agents, including first-generation antihistamines or tricyclic antidepressants. When ipratropium is combined with oral solid potassium chloride formulations, the risk of gastrointestinal ulceration or strictures may increase due to reduced gastrointestinal motility. Therefore, a liquid potassium formulation is preferred in such cases. Additionally, concurrent use with clozapine may exacerbate anticholinergic toxicity, which may lead to paralytic ileus or severe constipation, especially in vulnerable patients.

LAMAs also exhibit additive systemic anticholinergic effects when co-administered with other anticholinergic medications such as oxybutynin or benztropine, especially in older adults. Thus, caution is advised when using this combination. Furthermore, LAMAs may worsen urinary retention when used with agents that impair bladder emptying (eg, opioids or alpha-adrenergic agonists). Patients should be regularly assessed for urologic symptoms to ensure safe and effective use.

Contraindications

Bronchodilators are contraindicated in patients with a known hypersensitivity to the drug or any of its components; therefore, healthcare providers should not prescribe them to these patients. Such hypersensitivity reactions may manifest as severe allergic responses, potentially leading to hemodynamic instability or loss of a patent airway. Clinicians should exercise caution in patients with ischemic heart disease, cardiac arrhythmias, or hypokalemia, as bronchodilators may exacerbate these conditions.[1] Additional caution is warranted during labor and delivery due to potential uterine relaxation effects, and in geriatric patients who may be more susceptible to adverse reactions. In cases of very high dosing, patients with renal impairment also require close monitoring.[29]

Box Warnings

Asthma-related death with long-acting beta-2 agonists monotherapy: LABAs, such as salmeterol, carry a box warning due to an increased risk of asthma-related death when used as monotherapy without ICS. This risk has been observed clinically where LABAs are used without the anti-inflammatory protection provided by ICS, resulting in an increased incidence of severe asthma exacerbations and asthma-related deaths. In contrast, when LABAs are administered as part of a fixed-dose combination with ICS, the incidence of severe asthma-related outcomes, such as hospitalization, intubation, or death, does not appear to be significantly higher than with ICS monotherapy.

The use of any LABAs alone in the treatment of asthma is contraindicated. LABAs should only be prescribed as add-on therapy for patients who remain symptomatic despite appropriate ICS use. Initiating LABA treatment in individuals whose asthma is adequately controlled with low- or medium-dose ICS alone is not recommended. Inappropriate monotherapy with LABAs can obscure underlying airway inflammation, delay appropriate treatment, and significantly increase the risk of severe, potentially life-threatening asthma events.

In pediatric and adolescent populations, LABA monotherapy has been associated with a higher incidence of asthma-related hospitalizations. For these patients, if LABA therapy is indicated, it should be administered as part of a fixed-dose combination with ICS to enhance treatment adherence and reduce the risk of adverse outcomes. When separate inhalers are used, it is critical for clinicians to ensure consistent and concurrent administration of both ICS and LABA. If adherence cannot be confidently maintained, a combination inhaler is strongly preferred to minimize the dangers associated with LABA monotherapy.

The boxed warning for asthma medications containing LABAs was first introduced due to early concerns about increased asthma-related deaths, intubations, and hospitalizations, particularly when LABAs were used without ICS. In response to these safety concerns, the FDA mandated large-scale, randomized, double-blinded trials to compare the safety and efficacy of fixed-dose ICS-LABA combination therapies with ICS monotherapy.

The trials consistently met their predefined safety objectives, showing no significant increase in the risk of asthma-related deaths, intubations, or hospitalizations when ICS–LABA combinations were used compared to ICS alone. Moreover, the combination therapy significantly reduced the frequency of asthma exacerbations requiring systemic corticosteroids. Based on this robust and consistent evidence, the FDA removed the boxed warning for ICS–LABA combination products in December 2017, affirming their safety and therapeutic benefit when used appropriately in asthma management.

Although some uncertainties persist, particularly in patients with life-threatening asthma or regarding pediatric trial margins, the overall benefit-risk profile strongly supports the continued use of LABAs only in combination with ICS. Thus, LABAs should never be used as monotherapy in asthma management.[30]

Monitoring

Clinicians should provide clear instructions on the correct dosage and administration techniques for bronchodilators to ensure therapeutic effectiveness and minimize risks. Patients must be educated on recognizing severe adverse effects of bronchodilators, including paradoxical bronchospasm, hypersensitivity reactions, hypertension, hypotension, cardiac arrest, hypokalemia, and hyperglycemia. Anticholinergics have been associated with dry mouth, constipation, urinary retention, and delirium. If a patient experiences any of these symptoms or unusual discomfort after taking the medication, they should seek emergency medical attention promptly. In particular, chronic use of SABAs can lead to downregulation of beta-2 receptors. Continuous stimulation of receptors causes desensitization and internalization, reducing the number of active receptors on airway smooth muscle. This results in a reduced bronchodilator response, requiring higher doses to achieve the same effect. Over time, this diminished efficacy may contribute to decreased symptom control and increased incidence of adverse effects.[28]

Asthma severity should be monitored using validated tools such as the Asthma Control Test.[31] The 6-minute walk test can be a practical indicator of functional capacity and exercise tolerance.[32] Serial spirometry and peak expiratory flow monitoring are also essential assessment tools. Additionally, fractional exhaled nitric oxide is a biomarker of eosinophilic airway inflammation, which can help determine the patient's response to steroids.[33]

Toxicity

Signs and Symptoms of Overdose

Overdose of inhaled beta-2 agonists (both SABA and LABA), including albuterol, levalbuterol, salmeterol, and formoterol, may result in excessive beta-2-adrenergic stimulation. Clinical manifestations include tachycardia, palpitations, chest pain, anxiety, tremor, headache, dizziness, hypokalemia, QTc prolongation, arrhythmias, lactic acidosis, and, in rare cases, seizures.

Overdose of muscarinic antagonists (both SAMAs and LAMAs), including ipratropium, tiotropium, and glycopyrrolate, may present with anticholinergic effects. These may include dry mouth, blurred vision, urinary retention, constipation, tachycardia, and, particularly in older adults, possible confusion or hallucinations at high doses. In the event of suspected overdose, immediate evaluation in an emergency setting is essential. Clinical assessment should include vital sign monitoring and laboratory testing, particularly electrolyte panels, to detect and correct any abnormalities.[34]

Management of Overdose

In the event of a bronchodilator overdose, the first step is to discontinue the offending agent immediately and initiate supportive care. Continuous ECG monitoring and frequent assessment of vital signs are essential. Most patients can be treated with close observation, symptomatic treatment, and supportive care. Intravenous fluids should be administered as needed to maintain hemodynamic stability.

In the event of a beta-2-agonist overdose, clinicians should monitor and correct serum potassium levels to prevent complications. If the patient develops severe tachyarrhythmia, the cautious use of cardioselective beta-blockers may be warranted. In critical cases involving respiratory compromise, intubation may be required to secure the airway. Seizures should be managed with benzodiazepines as appropriate. For anticholinergic overdose, symptomatic treatment, such as ensuring adequate hydration and addressing urinary retention or constipation, should be provided to patients, and physostigmine should be considered in cases of severe toxicity.[35]

Enhancing Healthcare Team Outcomes

Bronchodilators are commonly prescribed by a range of healthcare professionals, including nurse practitioners, physician assistants, family medicine physicians, internists, emergency medicine clinicians, and other qualified providers. Advanced practice providers and primary care physicians typically initiate bronchodilator therapy based on the patient’s clinical presentation, ensuring that treatment aligns with current guidelines. Pulmonologists further tailor and optimize long-term treatment for patients with moderate-to-severe airway diseases such as asthma and COPD. In acute care settings, critical care physicians oversee the management of acute exacerbations and bronchodilator overdose, including the titration and administration of appropriate agents in case of emergencies. Nurses play an essential role in reinforcing patient education, teaching correct inhaler techniques, and monitoring for therapeutic efficacy and adverse effects. Pharmacists contribute by reviewing and prescribing medication regimens for potential drug-drug interactions, ensuring proper dosing, and counseling patients on adherence and proper storage.

All members of the healthcare team who prescribe or manage bronchodilator therapy must provide thorough education on the potential adverse effects, which can include anticholinergic symptoms as well as cardiac symptoms. Patients should also be advised on recognizing early warning signs and knowing when to seek follow-up care. When prescribed and administered correctly, bronchodilators are generally safe and can significantly improve respiratory symptoms and quality of life for asthma patients. An interprofessional team-based approach, emphasizing clear communication and coordination among healthcare providers, is critical to reducing potential adverse effects, minimizing complications, maximizing treatment effectiveness, and ultimately improving patient outcomes related to bronchodilator therapy in obstructive lung disease.