====== Asthma ======

Asthma is a chronic inflammatory airway disease characterized by:

  * Reversible airflow obstruction
  * Airway hyperresponsiveness
  * Chronic airway inflammation

It is driven by immune-mediated and inflammatory pathways.

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===== Pathophysiology =====

Core mechanisms:

  * Th2-mediated inflammation
  * Eosinophilic airway infiltration
  * Mast cell activation
  * Leukotriene production
  * Airway smooth muscle hyperreactivity

Key mediators:

  * Histamine
  * Leukotrienes (LTC4, LTD4, LTE4)
  * IL-4, IL-5, IL-13

See:
  * [[allergy:immunology:type_i_hypersensitivity|Type I Hypersensitivity]]
  * [[respiratory:drug_classes:leukotriene_modifiers|Leukotriene Pathway]]

Result:

  * Bronchoconstriction
  * Mucus hypersecretion
  * Airway edema
  * Chronic airway remodeling (untreated disease)

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===== Clinical Features =====

  * Episodic wheezing
  * Shortness of breath
  * Chest tightness
  * Cough (often nocturnal)
  * Reversible obstruction on spirometry

Diagnosis supported by:
  * ↓ FEV1/FVC
  * Improvement after bronchodilator

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===== Acute Exacerbation =====

Mechanism:
  Acute bronchospasm + airway inflammation.

First-line treatment:
  * [[autonomics:adrenergic_agonists:albuterol|Albuterol]] (SABA)

Severe exacerbation:
  * Systemic Corticosteroids --> [[endocrine:drugs:prednisone]]
  * Oxygen
  * Consider epinephrine in severe cases

Steroids reduce inflammation but do NOT provide immediate bronchodilation.

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===== Chronic Management (Stepwise Overview) =====

==== Step 1 – Intermittent Asthma ====

  * As-needed low-dose ICS-formoterol
  OR
  * SABA PRN (less preferred in modern guidelines)

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==== Step 2 – Mild Persistent ====

  * Daily low-dose [[endocrine:drug_classes:corticosteroids|Inhaled Corticosteroid]]
  OR
  * As-needed ICS-formoterol

Consider:
  * [[respiratory:drugs:montelukast|Montelukast]] (alternative)

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==== Step 3–4 – Moderate Persistent ====

  * Low or medium-dose ICS + LABA
  * SMART therapy (ICS-formoterol maintenance and reliever)

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==== Step 5–6 – Severe Asthma ====

  * High-dose ICS + LABA
  * Add-on therapies:
      - [[respiratory:drugs:montelukast|Leukotriene modifiers]]
      - Anti-IgE (omalizumab)
      - Anti-IL-5 biologics
  * Consider systemic corticosteroids

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===== Medication Classes Used in Asthma =====

Bronchodilators:
  * [[autonomics:adrenergic_agonists:albuterol|Short-Acting Beta Agonists (SABA)]]
  * Long-Acting Beta Agonists (LABA)

Anti-inflammatory:
  * [[endocrine:drug_classes:corticosteroids|Inhaled Corticosteroids]]
  * [[respiratory:drug_classes:leukotriene_modifiers|Leukotriene Modifiers]]
  * Biologic agents (severe disease)

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===== Aspirin-Exacerbated Respiratory Disease (AERD) =====

Mechanism:
  COX inhibition → shunting toward leukotriene pathway → bronchospasm.

Often responds well to:
  * [[respiratory:drugs:montelukast|Montelukast]]
  * [[respiratory:drugs:zileuton|Zileuton]]

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===== Complications =====

  * Status asthmaticus
  * Airway remodeling
  * Frequent hospitalizations
  * Respiratory failure (severe cases)

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===== High-Yield Pearls =====

  * Asthma is primarily an inflammatory disease, not just bronchospasm.
  * Inhaled corticosteroids are foundational therapy.
  * Leukotrienes are potent bronchoconstrictors.
  * SABA overuse increases mortality risk.
  * Steroids treat inflammation, beta-agonists treat bronchospasm.
  * Always assess control before escalating therapy.

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===== Related Pages =====

  * [[respiratory:drug_classes:leukotriene_modifiers|Leukotriene Modifiers]]
  * [[endocrine:drug_classes:corticosteroids|Corticosteroids]]
  * [[allergy:histamine|Histamine & Antihistamines]]
  * [[allergy:immunology:type_i_hypersensitivity|Type I Hypersensitivity]]