Respiratory Medications Overview
A clinical reference covering the major drug classes used in respiratory therapy — mechanisms, indications, and key clinical considerations.
Role of Pharmacology in Respiratory Therapy
Respiratory therapists administer and monitor a wide range of inhaled and systemic medications. A strong foundation in respiratory pharmacology enables RTs to anticipate drug effects, recognize adverse reactions, educate patients on proper inhaler technique, and coordinate care with the prescribing team.
Inhaled drug delivery offers several advantages over systemic routes: rapid onset of action at the target organ, lower systemic drug concentrations reducing side effects, and direct delivery to the airways. However, effective inhaled delivery requires correct technique and appropriate device selection for each patient.
Drug Classes Overview
Short-Acting Beta-2 Agonists (SABAs)
Examples: Albuterol (salbutamol), levalbuterol
Mechanism: Stimulate beta-2 adrenergic receptors in bronchial smooth muscle, causing bronchodilation via increased intracellular cAMP.
- Acute bronchospasm (asthma, COPD exacerbation)
- Pre-procedure bronchodilation
- Exercise-induced bronchoconstriction
Onset: 5–15 minutes | Duration: 4–6 hours
Most commonly administered via MDI with spacer or nebulizer. Tachycardia and tremor are common side effects. Hypokalemia can occur with high doses.
Long-Acting Beta-2 Agonists (LABAs)
Examples: Salmeterol, formoterol, indacaterol
Mechanism: Same receptor mechanism as SABAs but with longer bronchial smooth muscle binding duration.
- Maintenance therapy for asthma (combined with ICS)
- Maintenance therapy for COPD
- NOT for acute rescue use
Onset: Formoterol: 1–3 min | Salmeterol: 15–30 min | Duration: 12–24 hours
LABAs should never be used as monotherapy in asthma — must be combined with inhaled corticosteroids due to safety evidence.
Short-Acting Anticholinergics (SAMAs)
Examples: Ipratropium bromide
Mechanism: Block muscarinic receptors in bronchial smooth muscle, reducing vagally-mediated bronchoconstriction and secretion production.
- COPD exacerbations (often combined with albuterol)
- Acute bronchospasm unresponsive to SABA alone
- Rhinorrhea
Onset: 15–30 minutes | Duration: 4–6 hours
Particularly effective in COPD. Fewer cardiovascular side effects than beta-2 agonists. Avoid eye contact (pupil dilation).
Long-Acting Anticholinergics (LAMAs)
Examples: Tiotropium, umeclidinium, aclidinium
Mechanism: Same as SAMAs but with prolonged receptor binding providing sustained bronchodilation and reduced mucus secretion.
- COPD maintenance therapy (first-line)
- Reducing exacerbation frequency
Onset: 30 minutes | Duration: 24 hours (tiotropium)
Tiotropium (Spiriva) is one of the most widely prescribed COPD maintenance medications. Available in HandiHaler and Respimat formulations.
Inhaled Corticosteroids (ICS)
Examples: Fluticasone, budesonide, beclomethasone, mometasone
Mechanism: Bind glucocorticoid receptors, suppressing inflammatory mediator release (cytokines, leukotrienes), reducing airway inflammation and hyperresponsiveness.
- Persistent asthma (all severities)
- COPD with frequent exacerbations
- Combined with LABAs in ICS/LABA fixed-dose inhalers
Onset: Hours to days for full effect | Duration: Dosed 1–2 times daily
Rinse mouth after use to prevent oral candidiasis. Systemic absorption is low but chronic use can affect adrenal function at high doses.
Systemic Corticosteroids
Examples: Prednisone, methylprednisolone, dexamethasone
Mechanism: Broad anti-inflammatory effect through nuclear receptor binding, suppressing multiple inflammatory pathways.
- Acute asthma exacerbations
- AECOPD
- Severe allergic reactions
- COVID-19 pneumonia (dexamethasone)
Onset: IV: 1–4 hours | Oral: several hours | Duration: Variable — course typically 3–7 days
Dexamethasone evidence for COVID-19 ARDS significantly reduced mortality (RECOVERY trial). Short courses generally well tolerated; long-term use carries significant side effect profile.
Mucolytics and Mucoactive Agents
Examples: N-acetylcysteine (NAC), dornase alfa (Pulmozyme), hypertonic saline
Mechanism: Break disulfide bonds in mucus (NAC), cleave extracellular DNA in CF mucus (dornase alfa), or draw water into airways (hypertonic saline) to reduce viscosity.
- Cystic fibrosis
- Chronic bronchitis
- Airway clearance support in bronchiectasis
Onset: Variable | Duration: Per protocol
Dornase alfa is specific to CF. Hypertonic saline is widely used for airway clearance and may trigger bronchospasm — always pretreat with bronchodilator.
Surfactant Replacement
Examples: Beractant (Survanta), calfactant (Infasurf), poractant alfa (Curosurf)
Mechanism: Replace endogenous surfactant to reduce alveolar surface tension, prevent atelectasis, and improve lung compliance in surfactant-deficient states.
- Neonatal respiratory distress syndrome (RDS)
- Meconium aspiration syndrome
- Some cases of ARDS (investigational)
Onset: Rapid (minutes) | Duration: Single or multiple doses per protocol
Administered via endotracheal tube directly into the lungs. Neonatal respiratory therapy specialty area. Requires repositioning of neonate during administration.
Inhaler Device Types
Metered-Dose Inhaler (MDI)
Most common inhaler device. Requires coordination. Always use with a valved holding chamber (spacer) for patients who struggle with coordination, pediatrics, and during acute illness.
Dry Powder Inhaler (DPI)
Breath-actuated — does not require coordination. Requires a minimum inspiratory flow rate. Not appropriate for patients with very severe airflow obstruction during acute exacerbation.
Small-Volume Nebulizer (SVN)
Does not require coordination or minimum inspiratory effort. Preferred for acute settings, intubated patients, and those who cannot use other devices. Longer administration time.
Soft Mist Inhaler (SMI)
Produces a slow-moving aerosol that improves lung deposition. Less flow-dependent than DPIs. Tiotropium Respimat is a well-known example.
Frequently Asked Questions
Why must LABAs be combined with ICS in asthma?
LABA monotherapy in asthma was associated with increased asthma-related death in clinical trials. ICS controls the underlying airway inflammation that LABAs do not address. In COPD, LABAs without ICS are acceptable and often first-line.
What is the difference between a nebulizer and an MDI?
Both deliver inhaled medication but by different mechanisms. Nebulizers convert liquid drug into an aerosol continuously, requiring no patient effort or coordination. MDIs require coordination of actuation with inhalation and generate higher particle velocities.
When is IV bronchodilator therapy used instead of inhaled?
IV magnesium sulfate is used in severe acute asthma unresponsive to initial bronchodilators. IV methylxanthines (aminophylline) are rarely used today due to narrow therapeutic index and limited efficacy compared to beta-2 agonists.
What is the Haldane effect in the context of albuterol?
Albuterol can cause a transient decrease in PaO₂ through pulmonary vasodilation, increasing perfusion to already poorly ventilated areas (worsening V/Q mismatch). This is typically mild and self-limiting, and SpO₂ monitoring during treatment is standard practice.
Summary
- SABAs (albuterol) are first-line for acute bronchospasm in asthma and COPD.
- Anticholinergics are particularly effective in COPD — SAMAs for acute care, LAMAs for maintenance.
- ICS control airway inflammation but must always be combined with LABAs in asthma.
- Systemic steroids are essential in acute exacerbations; short courses are generally safe.
- Device selection and proper inhaler technique significantly affect drug efficacy.
- Dornase alfa and hypertonic saline target mucus clearance in CF and bronchiectasis.
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