25.1 Adrenergics and Anticholinergics

Adrenergic and Anticholinergic Drugs in Respiratory Care

Adrenergic and anticholinergic drugs are two major classes of bronchodilators used to treat lower respiratory disorders. They target different receptor systems in the airways, but both ultimately relax airway smooth muscle and improve airflow. Understanding how they differ in mechanism, onset, and side effect profile is essential for safe administration and effective patient teaching.

Mechanisms of Action

Adrenergic drugs (sympathomimetics) stimulate adrenergic receptors in the respiratory system. The ones you'll see most often are β2-agonists, because β2 receptors are concentrated on bronchial smooth muscle.

When a β2-agonist binds to those receptors, it relaxes the smooth muscle surrounding the airways, producing bronchodilation. It also increases mucociliary clearance, helping move mucus out of the lungs.

β2-agonists fall into two categories:

• Short-acting (SABAs) like albuterol: rapid onset (within minutes), used as rescue inhalers for acute bronchospasm
• Long-acting (LABAs) like salmeterol and formoterol: slower onset, duration of ~12 hours, used for maintenance therapy (never as a rescue inhaler)

Anticholinergic drugs (parasympatholytics) work on the other side of the equation. They block muscarinic receptors (primarily M3) on airway smooth muscle. Normally, acetylcholine binds to these receptors and causes bronchoconstriction and mucus secretion. By blocking that signal, anticholinergics produce bronchodilation and reduce mucus production.

• Short-acting (SAMA): ipratropium (Atrovent), onset ~15 minutes
• Long-acting (LAMA): tiotropium (Spiriva), dosed once daily for maintenance

Indications

Side Effects

The side effects of each class follow logically from their mechanism.

Adrenergic drugs stimulate the sympathetic nervous system, so their side effects look like a "fight or flight" response:

• Tachycardia and palpitations (β1 stimulation of the heart, even though these drugs are β2-selective)
• Tremor, especially in the hands
• Hypokalemia with prolonged use (β2 stimulation drives potassium into cells)
• Hyperglycemia (sympathetic stimulation promotes glycogenolysis)
• Nervousness, restlessness

Anticholinergic drugs block parasympathetic activity, so their side effects reflect reduced "rest and digest" functions:

• Dry mouth (most common complaint with inhaled forms)
• Constipation
• Urinary retention (use caution in patients with BPH)
• Blurred vision (avoid spraying ipratropium near the eyes)
• In severe toxicity: confusion, hallucinations, elevated heart rate

Drug Interactions

Adrenergic drugs:

• Beta-blockers (propranolol, metoprolol): antagonize the bronchodilating effect. Non-selective beta-blockers are especially problematic because they block β2 receptors in the lungs.
• MAO inhibitors: inhibit the breakdown of catecholamines, increasing the risk of hypertensive crisis when combined with adrenergics.
• Other sympathomimetics: additive cardiovascular effects (tachycardia, hypertension).

Anticholinergic drugs:

• Other anticholinergic medications (antihistamines like diphenhydramine, tricyclic antidepressants, some antipsychotics): additive anticholinergic effects, increasing the risk of toxicity.
• Use caution in patients already on multiple medications with anticholinergic properties, particularly older adults.

Nursing Considerations

Before administration:

1. Assess respiratory rate, rhythm, depth, and effort.
2. Auscultate lung sounds bilaterally, noting wheezing, crackles, or diminished breath sounds as a baseline.
3. Check heart rate and blood pressure. Hold the dose and notify the provider if the heart rate is significantly elevated (facility protocol varies, but generally >120 bpm warrants a call).
4. Review the medication list for interacting drugs (beta-blockers, MAOIs, other anticholinergics).

During and after administration:

1. Verify the correct drug, dose, and route. SABAs are PRN; LABAs and LAMAs are scheduled. Mixing these up matters.
2. If a patient uses both a SABA and an anticholinergic, administer the SABA first to open the airways, then the anticholinergic.
3. If the patient also uses an inhaled corticosteroid, the bronchodilator should be given first (opens airways so the steroid can reach deeper tissue).
4. Reassess lung sounds and respiratory effort after treatment to evaluate effectiveness.
5. Monitor heart rate and blood pressure, especially after adrenergic drugs.
6. With prolonged adrenergic drug use, monitor serum potassium levels for hypokalemia.
7. Watch for signs of anticholinergic toxicity in patients on anticholinergic inhalers, particularly older adults: confusion, agitation, urinary retention.

Patient Education

Inhaler and nebulizer technique:

• Teach and have the patient return-demonstrate proper inhaler technique. Poor technique is one of the most common reasons respiratory medications don't work well. For MDIs (metered-dose inhalers), this includes shaking the canister, exhaling fully before activating, inhaling slowly and deeply, and holding the breath for about 10 seconds.
• Spacer devices improve drug delivery with MDIs and should be recommended when appropriate.
• Patients using inhaled corticosteroids (often prescribed alongside bronchodilators) should rinse their mouth after each use to prevent oral thrush. This doesn't apply to bronchodilators alone, but since patients often use both, reinforce the habit.

Recognizing problems:

• Teach patients to recognize signs that their condition is worsening: increased rescue inhaler use (more than 2 days/week suggests uncontrolled asthma), worsening shortness of breath, or decreased peak flow readings.
• Advise patients to report tachycardia, significant tremor, chest pain, or signs of allergic reaction promptly.
• For anticholinergic inhalers, patients should report difficulty urinating, severe constipation, or vision changes.

Lifestyle and follow-up:

• Smoking cessation is the single most important intervention for COPD patients. Provide resources and referrals.
• Encourage avoidance of known triggers: secondhand smoke, air pollution, cold air, allergens.
• Regular follow-up visits allow providers to assess inhaler technique, adjust medications, and monitor lung function with spirometry.
• A symptom diary tracking medication use, symptoms, and potential triggers helps both the patient and provider identify patterns and adjust the treatment plan.