Respiratory Pharmacology Foundations

Respiratory pharmacotherapy is built around a limited number of drug classes that are used differently depending on the disease being treated. The same bronchodilator may serve as rescue therapy in one setting and scheduled maintenance therapy in another, while anti-inflammatory treatment that is essential in asthma may have a narrower role in COPD. Rational prescribing therefore requires understanding both the pharmacology of the drug class and the disease-specific reason for using it (Global Initiative for Asthma [GINA], 2025; Global Initiative for Chronic Obstructive Lung Disease [GOLD], 2026).

Beta2-Adrenergic Agonists

Beta2-adrenergic agonists relax airway smooth muscle by stimulating beta2 receptors and increasing intracellular cyclic adenosine monophosphate (cAMP). They are classified primarily by duration of action.

Short-Acting Beta2 Agonists

Short-acting beta2 agonists (SABAs), including albuterol and levalbuterol, have a rapid onset and are used for acute bronchodilation. In asthma, contemporary GINA guidance no longer supports SABA-only treatment because bronchodilation without anti-inflammatory therapy leaves the underlying airway inflammation untreated and is associated with greater exacerbation risk. In COPD, a SABA remains an appropriate rescue medication for intermittent breakthrough symptoms and is also used during exacerbations (GINA, 2025; GOLD, 2026).

Long-Acting Beta2 Agonists

Long-acting beta2 agonists (LABAs) provide sustained bronchodilation. Examples include formoterol, salmeterol, arformoterol, olodaterol, indacaterol, and vilanterol. Formoterol has a sufficiently rapid onset to function as a reliever when it is combined with an inhaled corticosteroid in appropriate asthma regimens. LABA monotherapy should not be used for asthma because it does not treat airway inflammation; LABAs are paired with an inhaled corticosteroid. In COPD, LABAs are central maintenance bronchodilators and may be used with a long-acting muscarinic antagonist (LAMA) (GINA, 2025; GOLD, 2026).

Class adverse effects reflect beta-adrenergic stimulation and can include tremor, palpitations, tachycardia, nervousness, and hypokalemia. Cardiovascular effects become more clinically relevant with higher doses, frequent rescue use, or substantial comorbidity (F.A. Davis Company, 2021).

Antimuscarinic Bronchodilators

Antimuscarinic agents block muscarinic receptors in the airways, reducing vagally mediated bronchoconstriction. Short-acting muscarinic antagonists (SAMAs) include ipratropium. Long-acting muscarinic antagonists (LAMAs) include tiotropium, umeclidinium, glycopyrrolate, aclidinium, and revefenacin.

The role of this class differs markedly between asthma and COPD. LAMA therapy is a central component of COPD maintenance treatment and is often paired with a LABA. In asthma, LAMA therapy is generally an add-on option for patients whose asthma remains uncontrolled despite appropriate inhaled corticosteroid-containing treatment (GINA, 2025; GOLD, 2026).

Adverse effects are primarily anticholinergic. Dry mouth is common. Urinary retention and worsening of narrow-angle glaucoma are important considerations in susceptible patients. Correct inhaler technique also matters because medication deposited in the eyes can worsen ocular symptoms.

Inhaled Corticosteroids

Inhaled corticosteroids (ICSs) reduce airway inflammation and are foundational controller medications in asthma. Regular ICS-containing treatment reduces severe exacerbations, hospitalization, and asthma-related death. Current GINA treatment strategies ensure that patients receive ICS exposure even when symptoms are infrequent, either through as-needed ICS-formoterol or another regimen that pairs symptom treatment with anti-inflammatory therapy (GINA, 2025).

The COPD role is different. ICS is not routine monotherapy for COPD. GOLD uses exacerbation history, blood eosinophil count, asthma history, and adverse-effect risk to determine when adding ICS to long-acting bronchodilation is appropriate. When ICS is indicated in COPD, it is generally incorporated into triple therapy with LABA/LAMA rather than used alone (GOLD, 2026).

Local adverse effects include dysphonia and oropharyngeal candidiasis. Patients should use proper inhaler technique and rinse the mouth after doses when appropriate. Higher cumulative corticosteroid exposure increases the importance of monitoring systemic effects.

Systemic Corticosteroids

Systemic corticosteroids are primarily used for acute exacerbations rather than routine maintenance. They suppress airway inflammation more broadly than inhaled therapy but carry substantially greater systemic toxicity. Repeated or prolonged courses increase risks including hyperglycemia, hypertension, mood and sleep effects, infection, osteoporosis, adrenal suppression, and other corticosteroid complications. Contemporary asthma guidance reserves maintenance oral corticosteroids for exceptional circumstances because safer controller strategies and biologic therapies are preferred when available (GINA, 2025).

Leukotriene Modifiers

Leukotriene receptor antagonists (LTRAs), particularly montelukast, reduce leukotriene-mediated bronchoconstriction and inflammation. They are less effective than inhaled corticosteroids for preventing asthma exacerbations and are generally an alternative or add-on rather than preferred first-line controller therapy. Montelukast carries an important neuropsychiatric safety warning, so the expected benefit should justify its use and patients should be counseled about potential behavioral, mood, and sleep changes (GINA, 2025).

Leukotriene modifiers do not have an established routine role in COPD. COPD airway inflammation differs from asthma, and therapies should not be transferred between the two diseases simply because both produce airflow limitation (Wietholter & Whetsel, 2026).

Methylxanthines

Theophylline has bronchodilator and other respiratory effects but has a narrow therapeutic index, substantial drug-interaction potential, and serious dose-related toxicity. Nausea, vomiting, tremor, insomnia, tachyarrhythmias, and seizures can occur with excessive concentrations. Contemporary guidance gives theophylline a very limited role because inhaled therapies are generally more effective and safer (GINA, 2025; Wietholter & Whetsel, 2026).

Because theophylline exposure is affected by drug interactions, diet, illness, and smoking status, use requires medication reconciliation and therapeutic-drug monitoring when clinically indicated. Tobacco smoking increases theophylline clearance; a major reduction or cessation of smoking can therefore increase theophylline exposure if the dose is not reassessed. The course materials also emphasize checking serum concentrations during titration and when interacting medications are added or removed. These requirements further limit theophylline’s role compared with safer inhaled therapies (F.A. Davis Company, 2021).

Phosphodiesterase-4 Inhibition

Roflumilast is an oral phosphodiesterase-4 inhibitor used in selected patients with COPD. It is not a bronchodilator and does not provide rapid symptom relief. Its role is reduction of exacerbation risk in a specific COPD phenotype, particularly patients with chronic bronchitis, severe airflow obstruction, and a substantial exacerbation history despite appropriate inhaled therapy. Adverse effects include gastrointestinal symptoms, weight loss, headache, and insomnia; psychiatric effects are also clinically important (GOLD, 2026; Wietholter & Whetsel, 2026).

Oxygen Therapy

Oxygen is a respiratory therapy with specific indications rather than a treatment for dyspnea alone. In acute illness, oxygen is titrated to the patient’s physiologic need and clinical context. During a COPD exacerbation with acute respiratory failure, oxygen delivery may be combined with high-flow systems or noninvasive ventilation when indicated (GOLD, 2026).

Long-term oxygen therapy has a narrower role in stable COPD. GOLD recommends against routine long-term oxygen for stable patients with only moderate resting or exercise-induced desaturation. Survival benefit is associated with severe chronic resting hypoxemia, including a PaO2 of 55 mmHg or lower, or below 60 mmHg when cor pulmonale or secondary polycythemia is present (GOLD, 2026).

Asthma exacerbations may also require supplemental oxygen when hypoxemia is present, but oxygen does not replace bronchodilation, corticosteroid therapy, or assessment of exacerbation severity. The clinical question is therefore not whether a patient feels short of breath, but whether oxygenation is impaired and what underlying process is producing that impairment.

Inhaler Devices and Drug Delivery

Medication selection and device selection cannot be separated. Metered-dose inhalers, dry-powder inhalers, soft-mist inhalers, and nebulized formulations require different inspiratory flow, coordination, dexterity, and cognitive skills. An otherwise appropriate medication can fail clinically when the patient cannot use the delivery system correctly.

Device selection should account for inspiratory capacity, hand strength and coordination, cognition, vision, patient preference, portability, cost, and medication availability. Spacers or valved holding chambers can improve delivery from pressurized metered-dose inhalers in appropriate patients. Nebulized therapy may be useful when inhaler technique or inspiratory flow is inadequate, but nebulization does not make an ineffective drug more effective (GINA, 2025; GOLD, 2026).

Inhaler technique should be taught, demonstrated, and reassessed. Apparent treatment failure should prompt evaluation of adherence and device technique before unnecessary pharmacologic escalation.

High-Yield Distinctions

  • Beta2 agonists provide bronchodilation; they do not replace anti-inflammatory therapy in asthma.
  • LABA monotherapy is inappropriate in asthma but LABAs are central maintenance bronchodilators in COPD.
  • LAMA therapy is foundational in COPD and an add-on option in selected asthma patients.
  • ICS therapy is foundational in asthma but selective in COPD.
  • Systemic corticosteroids are useful for exacerbations but carry substantially greater toxicity than inhaled therapy.
  • Montelukast is less effective than ICS for asthma exacerbation prevention and carries a neuropsychiatric warning.
  • Theophylline has a narrow therapeutic index and limited contemporary use.
  • Theophylline exposure changes with important drug interactions and smoking status; serum monitoring and dose reassessment may be necessary.
  • Roflumilast reduces exacerbation risk in selected COPD patients but is not a rescue bronchodilator.
  • Long-term oxygen therapy is reserved for qualifying chronic hypoxemia rather than dyspnea alone.
  • Before escalating inhaled therapy, reassess diagnosis, adherence, device selection, and inhaler technique.

Content last reviewed:

References

F.A. Davis Company. (2021). Drugs affecting the respiratory system [PowerPoint slides].

Global Initiative for Asthma. (2025). Asthma management and prevention for adults, adolescents and children 6–11 years: A summary guide for healthcare providers. https://ginasthma.org/wp-content/uploads/2025/06/GINA-Summary-Guide-2025-WEB_FINAL-WMS.pdf

Global Initiative for Chronic Obstructive Lung Disease. (2026). Pocket guide to COPD diagnosis, management, and prevention: A guide for health care professionals (2026 ed.). https://goldcopd.org

Wietholter, J. P., & Whetsel, T. R. (2026). Chronic obstructive pulmonary disease. In M. A. Chisholm-Burns, P. M. Malone, J. M. Kolesar, K. C. Lee, P. B. Bookstaver, & K. R. Matthias (Eds.), Pharmacotherapy principles & practice (7th ed.). McGraw Hill.

Wilken, L. A., & Eades, A. L. (2026). Asthma. In M. A. Chisholm-Burns, P. M. Malone, J. M. Kolesar, K. C. Lee, P. B. Bookstaver, & K. R. Matthias (Eds.), Pharmacotherapy principles & practice (7th ed.). McGraw Hill.