ce CONTINUING EDUCATION
Antihistamines can also be used as topical agents through nasal preparations. These agents include azelastine and olopatadine. Below is a further classification of antihistamines in terms of their activity and adverse effect profile:
Class (specific drug entities)
Properties
Alkylamines (brompheniramine, chlorphe- niramine, dexbrompheniramine, dexchlor- pheniramine, pheniramine, triprolidine)
Moderately sedating; strong anticholinergic effects; higher risk of paradoxical CNS stimulation than with other classes
Ethanolamines (diphenhydramine, doxyl- amine)
Highly sedating; strong anticholinergic effects; large doses cause seizures and arrhythmias
Ethylenediamines (pyrilamine, thonzylamine) Weak CNS effects; increased GI effects
Highly sedating; strong anticholinergic effects; block alpha-adrenergic receptors; more likely to cause hypotension; akathisia and dystonic reactions may occur
Phenothiazines (promethazine)
Piperidines (fexofenadine, loratadine)
Nonsedating
Piperazines (cetirizine, chlorcyclizine, hy- droxyzine, levocetirizine, meclizine)
Minimally to moderately sedating
Decongestants Congestion is a common allergic rhinitis symp- tom controllable with systemic decongestants or with short-term use of topical nasal decongestants. These agents were discussed earlier in the cold section. Cromolyn Sodium Cromolyn is a mast cell stabilizer indicated for prevent- ing and treating the symptoms of allergic rhinitis. The agent is thought to work by blocking the influx of calcium into mast cells, which results in the prevention of mediator release. It is approved for use in patients 2 years of age or older and treatment is more effective if started before symptoms begin. It may take 3-7 days for the initial clinical benefit to become apparent and 2-4 weeks of continued therapy to achieve maximal therapeutic benefit. Sneezing is the most common adverse effect reported with intranasal cromolyn. Other possible side effects include nasal stinging and burning.
Young Children (< 2 years of age) • Minimally sedating antihistamines are available in liquid formulations. Cetirizine and fexofenadine are approved for children > 6 months of age • Sedating antihistamines should be avoided in young children due to the paradoxical agitation risk • Cromolyn sodium nasal spray is another great option as it is available without prescription and has essentially no adverse effects because it is not absorbed systemically • Severe symptoms • Changing to glucocorticoid nasal spray is the next step for children with severe symptoms not respon- sive to above measures • Mometasone furoate, fluticasone furoate, and triam- cinolone acetonide are approved by the FDA for use in children > 2 years CLINICAL APPROACH TO SPECIFIC PATIENT GROUPS WITH ALLERGIC RHINITIS
Older children and adults • Mild or episodic symptoms
• A second-generation oral antihistamine can be administered regularly or as needed (ideally two to five hours before an exposure for cetirizine and fexofenadine, while loratadine peaks eight hours after administration)
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