drugs used for allergy
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"allergic rhinitis" AND "antihistamine" AND treatment
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Drugs Used for Allergy
Allergic conditions span a spectrum from mild rhinitis and urticaria to life-threatening anaphylaxis. The drug classes used reflect this range.
1. Antihistamines (H1 Blockers)
The cornerstone of allergy pharmacotherapy. They competitively block H1 receptors, reducing itching, sneezing, rhinorrhea, and urticaria.
First-Generation (Sedating)
| Drug | Notes |
|---|---|
| Diphenhydramine (Benadryl) | Also used for anaphylaxis (adjunct) |
| Chlorpheniramine | Common in OTC cold/allergy combos |
| Promethazine | Also antiemetic; caution in children |
| Hydroxyzine | Used for urticaria and anxiety |
Drawbacks: CNS sedation, anticholinergic effects (dry mouth, urinary retention, blurred vision). Avoid in elderly (increased fall risk) and in competitive athletes.
Second-Generation (Non-Sedating) - Preferred
| Drug | Notes |
|---|---|
| Loratadine (Claritin) | Pregnancy category B; minimal sedation |
| Cetirizine (Zyrtec) | Slight sedation possible; pregnancy category B |
| Levocetirizine (Xyzal) | Active enantiomer of cetirizine |
| Fexofenadine (Allegra) | Truly non-sedating; no CNS penetration |
| Desloratadine | Active metabolite of loratadine |
| Azelastine | Available as intranasal spray (allergic rhinitis) |
A 2024 systematic review (PMID: 39028636) confirmed fexofenadine has negligible brain penetration, making it the least sedating option.
For allergic conjunctivitis, topical antihistamine-decongestant combinations (e.g., naphazoline/pheniramine - Naphcon-A) are used, though rebound vasodilation can occur with prolonged use. - Textbook of Family Medicine 9e
2. Corticosteroids
Intranasal Corticosteroids (INCS) - First-line for Moderate-Severe Allergic Rhinitis
| Drug | Brand |
|---|---|
| Fluticasone propionate | Flonase |
| Fluticasone furoate | Veramyst |
| Budesonide | Rhinocort (preferred in pregnancy) |
| Triamcinolone | Nasacort |
| Beclomethasone | Beconase AQ |
| Mometasone | Nasonex |
INCS are the most effective single agents for allergic rhinitis - indicated for inflammatory conditions including allergic and nonallergic rhinitis. - K.J. Lee's Essential Otolaryngology
Caution: In patients taking ritonavir, fluticasone propionate should be avoided (risk of systemic corticosteroid effects and adrenal suppression). Safer alternatives are budesonide, triamcinolone, and flunisolide. - Cummings Otolaryngology
Systemic Corticosteroids
- Used for severe acute allergic reactions, generalized allergic contact dermatitis (prednisone 40-60 mg/day, tapering), and as second-line therapy in anaphylaxis.
- Hydrocortisone 250-500 mg IV or methylprednisolone 80-125 mg IV are used in anaphylaxis management. - Tintinalli's Emergency Medicine
Inhaled Corticosteroids (ICS)
Used for allergic asthma - beclomethasone, budesonide, fluticasone, ciclesonide, triamcinolone.
3. Decongestants
Used as adjuncts for nasal congestion associated with allergic rhinitis.
| Drug | Route | Notes |
|---|---|---|
| Pseudoephedrine | Oral | Banned in competitive athletes |
| Oxymetazoline | Intranasal | Short-term only (rebound rhinitis if >3 days) |
| Xylometazoline | Intranasal | Same as above |
| Phenylephrine | Oral/intranasal | Less effective orally |
4. Leukotriene Receptor Antagonists (LTRAs)
| Drug | Mechanism |
|---|---|
| Montelukast | CysLT1 receptor antagonist; oral |
| Zafirlukast | CysLT1 receptor antagonist |
| Zileuton | 5-Lipoxygenase inhibitor (blocks leukotriene synthesis) |
Used for allergic rhinitis and asthma; montelukast is especially common in children with mild asthma. A 2026 meta-analysis (PMID: 41170705) found combined montelukast-antihistamine is more effective than montelukast alone for allergic rhinitis.
Key adverse effect: Montelukast carries a boxed warning for serious neuropsychiatric effects - agitation, depression, sleep disturbances, suicidal ideation. Rare: eosinophilic granulomatosis with polyangiitis (Churg-Strauss). Zafirlukast and zileuton require periodic liver enzyme monitoring. - Lippincott Illustrated Reviews Pharmacology
5. Mast Cell Stabilizers
| Drug | Route | Use |
|---|---|---|
| Cromolyn sodium | Intranasal, nebulized, ophthalmic | Allergic rhinitis, asthma (prophylaxis), mastocytosis |
| Nedocromil | Inhaled, ophthalmic | Asthma, allergic conjunctivitis |
Cromolyn inhibits mast cell degranulation and histamine release. It is prophylactic only - not useful for acute attacks. Requires dosing 3-4 times daily, which limits adherence. - Lippincott Illustrated Reviews Pharmacology
6. Epinephrine (Adrenaline) - For Anaphylaxis
First-line and life-saving. Mechanism:
- α1-receptor: reduces mucosal edema, treats hypotension
- β1-receptor: increases heart rate and myocardial contractility
- β2-receptor: bronchodilation and limits further mediator release
| Route | Adult Dose |
|---|---|
| IM (thigh preferred) | 0.3-0.5 mg of 1:1000 solution; repeat every 5-10 min |
| IV bolus (refractory) | 100 mcg over 5-10 min |
| IV infusion | Start 1 mcg/min, titrate |
| Auto-injector | EpiPen 0.3 mg (adult), EpiPen Jr 0.15 mg (child <30 kg) |
Patients on beta-blockers may have a limited response to epinephrine (risk of unopposed alpha-stimulation causing severe hypertension). - Tintinalli's Emergency Medicine; Dermatology 2-Volume Set 5e
7. Biologics / Monoclonal Antibodies
For severe allergic disease refractory to conventional therapy.
| Drug | Target | Use |
|---|---|---|
| Omalizumab (Xolair) | Anti-IgE | Severe allergic asthma, chronic urticaria |
| Mepolizumab (Nucala) | Anti-IL-5 | Severe eosinophilic asthma |
| Benralizumab (Fasenra) | Anti-IL-5Rα | Severe eosinophilic asthma |
| Reslizumab (Cinqair) | Anti-IL-5 | Severe eosinophilic asthma (IV) |
| Dupilumab (Dupixent) | Anti-IL-4/IL-13 | Severe asthma, atopic dermatitis |
Omalizumab binds free IgE, reducing IgE binding to mast cells/basophils and limiting allergic mediator release. These agents are administered subcutaneously (except reslizumab, which is IV). Rare but serious adverse effects include anaphylaxis, arthralgias, fever, rash, and increased infection risk. - Lippincott Illustrated Reviews Pharmacology
8. Other Agents
| Drug | Use |
|---|---|
| Ipratropium (intranasal) | Residual rhinorrhea in allergic rhinitis; anticholinergic |
| Albuterol/Salbutamol | Bronchospasm in allergic asthma/anaphylaxis |
| Theophylline | Rarely used; narrow therapeutic index; bronchodilator for asthma |
| H2 blockers (ranitidine, cimetidine) | Adjunct in anaphylaxis (second-line) |
| Immunotherapy (allergen-specific) | Long-term desensitization for allergic rhinitis, venom allergy |
Quick Reference: Drug by Condition
| Condition | First-Line | Add-on / Alternatives |
|---|---|---|
| Mild allergic rhinitis | Oral 2nd-gen antihistamine | Decongestant |
| Moderate-severe allergic rhinitis | Intranasal corticosteroid | INCS + antihistamine |
| Allergic asthma | ICS ± LABA | LTRA, omalizumab (severe) |
| Urticaria | 2nd-gen antihistamine | Omalizumab, cyclosporine |
| Anaphylaxis | Epinephrine IM | Corticosteroids, H1/H2 blockers (adjunct) |
| Allergic conjunctivitis | Topical antihistamine | Mast cell stabilizers |
| Atopic dermatitis | Topical corticosteroids | Dupilumab (moderate-severe) |
Sources: Cummings Otolaryngology; Tintinalli's Emergency Medicine; Lippincott Illustrated Reviews Pharmacology; Dermatology 2-Volume Set 5e; K.J. Lee's Essential Otolaryngology; Murray & Nadel's Respiratory Medicine
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