Pharmacotherapy of Allergic Rhinitis, Cough, and Cold

Vocabulary practice flashcards covering drug classes, brand and generic names, mechanisms of action, adverse effects, contraindications, and clinical pearls for allergic rhinitis, common cold, and cough pharmacology.

Allergic Rhinitis

Inflammation of the mucous membranes of the nose characterized by symptoms such as sneezing, nasal congestion, watery rhinorrhea, itchy nose and eyes, and nonproductive cough.

Histamine

An endogenous chemical mediator primarily synthesized and stored in mast cells and basophils within the skin, GI tract, and respiratory tract; it also functions as a central neurotransmitter and is found in insect stings and venoms.

$\text{H}\_1$ Antihistamines

A drug class that acts as competitive antagonists at $\text{H}\_1$ receptors to block the effects of histamine in bronchial smooth muscle, large blood vessels, the GI tract, and the uterus; more effective when administered preventatively before allergen exposure.

First-Generation Antihistamines (1st Gen)

Lipophilic H-1 antagonists that readily cross the blood-brain barrier into the central nervous system, producing pronounced sedation, psychomotor impairment, and anticholinergic adverse effects

Second-Generation $\text{H}\_1$ Antihistamines

Peripheral-selective $\text{H}\_1$ antagonists containing polar chemical groups that limit penetration into the central nervous system, resulting in significantly less drowsiness and fewer adverse anticholinergic effects.

Diphenhydramine (Benadryl)

A first-generation $\text{H}\_1$ antihistamine indicated for allergic conditions, motion sickness, insomnia, and cough suppression; carries a risk of paradoxical hyperactivity in some pediatric patients.

Hydroxyzine (Vistaril, Atarax)

A prescription first-generation $\text{H}\_1$ antihistamine used as a somnifacient and to treat allergic and inflammatory conditions and pruritus.

Meclizine (Antivert)

A first-generation $\text{H}\_1$ antihistamine with central anticholinergic activity, primarily indicated for the prevention and treatment of motion sickness and vertigo.

Chlorpheniramine (Aller-Chlor, Chlor-Phen)

An over-the-counter first-generation $\text{H}\_1$ antihistamine used to relieve allergy symptoms, notable for having an established historical record of safe use during pregnancy.

Cetirizine (Zyrtec)

An OTC 2nd generation H-1 antihistamine that possesses the highest relative potential for producing sedation and drowsiness among the second-generation class.

Fexofenadine (Allegra)

A nonsedating second-generation $\text{H}\_1$ antihistamine with minimal drowsiness potential, recommended for patients working in safety-critical occupations requiring constant wakefulness.

Loratadine (Claritin)

An over-the-counter nonsedating second-generation $\text{H}\_1$ antihistamine with low sedation potential, commonly chosen when daytime alertness is required.

Relative Drowsiness Ranking of Second-Generation Antihistamines

The comparative spectrum of sedative potential among second-generation agents, ordered from greatest to least: Cetirizine > Levocetirizine > Fexofenadine > Loratadine.

Antihistamine Anticholinergic Adverse Effects

Side effects resulting from off-target antagonism of cholinergic muscarinic receptors by $\text{H}\_1$ antihistamines, including dry mouth, urinary retention, blurred vision, constipation, and sinus tachycardia.

Adverse effects of $\alpha$-Adrenergic Antihistamines

Off-target blockade of this specific type of receptor manifest as hypotension, dizziness, and reflex tachycardia

Antihistamine Serotonin Receptor Antagonism

Off-target blockade of central serotonin receptors by certain antihistamines (such as cyproheptadine), which leads to increased appetite and potential weight gain.

Intranasal Corticosteroids

The first-line drug class for persistent or moderate-to-severe allergic rhinitis that suppresses local inflammation to treat rhinorrhea, sneezing, itching, and especially nasal congestion; may require several days of continuous use to achieve maximum benefit.

Fluticasone (Flonase)

A widely used intranasal corticosteroid available over the counter, serving as a first-line therapy for moderate-to-severe allergic rhinitis and nasal congestion.

Mometasone (Nasonex)

An intranasal corticosteroid indicated as a first-line treatment for the prophylaxis and management of nasal symptoms associated with allergic rhinitis.

$\alpha$-Adrenergic Agonists (Decongestants)

Sympathomimetic drugs that stimulate $\alpha\_1$ adrenoceptors on vascular smooth muscle to induce local vasoconstriction in the nasal mucosa, reducing mucosal blood flow, swelling, and airway resistance.

Oxymetazoline (Afrin)

A topical intranasal $\alpha$-adrenergic agonist decongestant that should not be used for more than $3\text{ consecutive days}$ due to the high risk of causing rebound nasal congestion.

Rhinitis Medicamentosa

Severe rebound nasal congestion, inflammation, and mucosal hypertrophy caused by the overuse of topical intranasal decongestants for longer than $3\text{ days}$.

Pseudoephedrine (Sudafed)

An oral systemic decongestant that stimulates both $\alpha$ and $\beta$ adrenoceptors with high oral bioavailability ($\sim 90\%$); adverse effects include insomnia, elevated blood pressure, palpitations, and arrhythmias.

Combat Methamphetamine Epidemic Act of 2005

Federal legislation regulating over-the-counter sales of pseudoephedrine by imposing daily and monthly purchase quantity limits, requiring storage behind the pharmacy counter, and mandating photo identification logbooks.

Oral Phenylephrine

A direct $\alpha\_1$-adrenergic agonist decongestant characterized by very low oral bioavailability ($\sim 38\%$), rendering currently available over-the-counter oral formulations largely ineffective.

Intranasal Phenylephrine

A direct $\alpha\_1$-adrenergic agonist topical decongestant spray that provides rapid local vasoconstriction to alleviate mucosal swelling; use must not exceed $3\text{ consecutive days}$ to avoid rebound congestion (rhinitis medicamentosa).

Adrenoreceptors ($\alpha$ and $\beta$ Subtypes)

Receptor families mediating sympathetic responses: $\alpha\_1$ mediates vasoconstriction, increased blood pressure, and mydriasis; $\alpha\_2$ inhibits neurotransmitter release; $\beta\_1$ mediates tachycardia, increased contractility, and renin release; $\beta\_2$ mediates vasodilation and bronchodilation.

Cromolyn Sodium (NasalCrom)

An over-the-counter intranasal mast cell stabilizer that prevents antigen-triggered degranulation and histamine release; requires $3\text{ to }7\text{ days}$ for initial clinical effect and up to $2\text{ to }4\text{ weeks}$ of regular use for maximal benefit.

Strategic Treatment Approaches for Allergic Rhinitis

Three evidence-based approaches to optimize therapeutic efficacy:

1. Advance Initiation: Starting treatment in advance prior to known allergen exposure (e.g., seasonal triggers or animal dander).

2. Regular Maintenance: Administering therapies consistently on a scheduled basis rather than 'as needed' (PRN).

3. Combination Regimens: Combining complementary drug classes (such as an oral antihistamine plus an intranasal corticosteroid) for superior symptom relief.

Guaifenesin

A protussive expectorant that thins and loosens phlegm and bronchial secretions to facilitate mucociliary clearance, rendering a nonproductive cough more productive.

Codeine

A centrally acting weak opioid antitussive that decreases the sensitivity of medullary cough centers; contraindicated in children younger than $12\text{ years}$ and avoided in adolescents aged $12\text{ to }18\text{ years}$ who have compromised respiratory function.

Dextromethorphan

A synthetic morphine derivative without analgesic properties at antitussive doses that acts directly on the medullary cough center to suppress cough; contraindicated within $14\text{ days}$ of monoamine oxidase inhibitor (MAOI) use.

Benzonatate (Tessalon Perles)

A prescription peripheral antitussive that anesthetizes stretch receptors located in the respiratory passages, lungs, and pleura; accidental ingestion in young children can be fatal.

Camphor and Menthol (Vicks) / (Vapor Rub)

Topical antitussives that stimulates sensory nerve endings in the nasal mucosa

-Provides local anesthetic sensation and perception of improved airflow

-Toxic and potentially fatal if ingested orally

Intranasal Zinc Safety Warning

An FDA warning issued against zinc-containing nasal sprays, gels, and swabs due to the risk of inducing irreversible anosmia (permanent loss of the sense of smell).

Saline Nasal Preparations

A non-pharmacologic option consisting of isotonic or hypertonic sodium chloride solutions used to moisten mucosal membranes, clean crusts, and clear nasal secretions; nasal irrigation systems must utilize sterile or distilled water to avoid lethal CNS infections.

Non-Pharmacologic Modalities for Cold and Cough Management

Supportive physical interventions and home remedies used to manage upper respiratory symptoms without medication:

1. Honey: Natural demulcent that coats and soothes irritated throat tissue; strictly contraindicated in pediatric patients younger than $1\text{ year}$ due to infantile botulism risk.

2. Humidifiers and Steam: Adds moisture to ambient air to loosen thickened secretions and ease mucosal dryness.

3. Breathe Right Nasal Strips: External adhesive devices applied to the nasal bridge that mechanically widen nasal passages to reduce airflow resistance.

4. Infant Bulb Syringe: Manually aspirates and extracts stubborn mucous secretions to clear obstructed airways in young pediatric patients.

Allergen Immunotherapy

A preventative treatment regimen consisting of repeated subcutaneous injections of patient-specific allergens in gradually increasing doses, indicated for refractory, moderate-to-severe allergic rhinitis.

Antitussives

Cough suppressant drugs which control, prevent, or eliminate a cough by reducing the sensitivity of the cough reflex. Thye can act centrally in the brainstem or peripherally in the airways.

Clinical use: Dry, non-productive coughs (common cold) where there is no mucus to clear or cough so severe that it causes exhaustion or prevents sleep.

Protussives

Cough Enhancing drugs that make a cough more effective by helping to mobilize, thin, or clear mucus and secretions from the respiratory tract. Further subcategorized into expectorants, mucolytics, and mucokinetics.

Clinical use: Productive coughs or chronic conditions involving thick mucus buildup.