Focus: Histamine signaling and pharmacologic control of allergic symptoms, with clinical links for common disease presentations (rhinitis, urticaria, anaphylaxis, asthma overlap).

Drug Classes • Clinical Use • Mechanisms • Learning Tools

• H1 Antihistamines — 1st Generation (Sedating)
• H1 Antihistamines — 2nd Generation (Non-sedating)

• H2 Blockers (Cimetidine, Famotidine, etc.)

• Mast Cell Stabilizers (Cromolyn, etc.)

• Leukotriene Modifiers (Montelukast, Zileuton)

• Corticosteroids (intranasal, inhaled, systemic)

• Epinephrine & Anaphylaxis Protocol
• Biologics (Anti-IgE, Anti-IL5, Anti-IL4/13)

Use this section when you’re starting from the patient presentation.

• Allergic Rhinitis → Treatment & Stepwise Therapy

(intranasal steroid first-line; add antihistamine based on symptoms)

• Urticaria / Pruritus → Treatment Approach

(scheduled 2nd-gen H1 blockers; escalate; chronic urticaria options)

• Angioedema → Histamine vs Bradykinin Angioedema

(distinguish allergic vs ACEi/HAE)

• Anaphylaxis → Emergency Algorithm

(IM epinephrine first-line; adjuncts second)

• Asthma overlap / AERD → Allergic Asthma + Leukotrienes

Use this section when you’re starting from physiology/pathophysiology.

• Histamine Physiology (Synthesis, Storage, Release)
• Histamine Receptors (H1–H4) & G-Protein Signaling
• Type I Hypersensitivity (IgE → Mast Cell → Early/Late Phase)
• Hypersensitivity Types I–IV (Drug Rash Mapping)
• Eicosanoids, Leukotrienes, Prostaglandins (Inflammation Link)

• Quiz: Histamine & Antihistamines
• Case Bank (Rhinitis, Urticaria, Anaphylaxis)
• One-Page Algorithms (High Yield)
• Crossword Puzzle
• Crossword Answers

• Board pearl: 1st-gen H1 blockers cross the BBB → sedation + anticholinergic toxicity (esp. elderly).
• Clinical pearl: Angioedema without hives raises concern for bradykinin-mediated etiologies (ACEi/HAE).