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Although second-generation antihistamines are preferred, patient preference should drive selection of therapy.
Second-Generation Antihistamines Are Preferred
As spring progresses into summer, almost every weather report includes a brief discussion of the pollen count alongside the predictions of sun, wind (which exacerbates allergies), or rain (which lessens allergies). Although intranasal corticosteroids (INCS) are first-line agents for seasonal allergic rhinitis,1-3 many patients prefer antihistamines because they provide relief quickly and effectively, have few adverse effects, and are accessible at reasonable prices. Many patients consult with pharmacy staff when they need relief from symptoms that wax and wane.
Usually, patients will find relief in the OTC aisle. Occasionally, some patients may need to step up to prescription antihistamines, INCS, or leukotriene-receptor antagonists (LTRAs).1,2 Although the antihistamines are generally safe and effective, pharmacy staff still need to remember a few key points.
Behind the Sneezing and Sniffling: Histamine
Since the early 1900s, researchers have known that histamine, a biogenic monoamine and neurotransmitter, is the culprit in most seasonal allergies.4 Researchers have also identified the H1 receptor, which is considered ubiquitous throughout the body, as the most likely cause of allergy symptoms (sneezing, itching, watery eyes, fatigue, and sinus swelling).5
The H1-receptor antagonists are grouped into first-generation and sec-ond-generation drugs.6 The first-generation drugs (brompheniramine, chlorpheniramine, dimenhydrinate, diphenhydramine, doxylamine, and hydroxyzine) tend to have more profound anticholinergic effects and can create psychomotor impairment, whereas the second-generation H1-receptor antagonists are less anticholinergic. The second-generation antihistamines are more selective for peripheral H1 receptors; adverse effects such as drowsiness, dry mouth, constipation, blurred vision, and urinary retention are less likely, but still possible.6 Patients older than age 65 should generally avoid the first-generation antihistamines.7
Guidelines are Available
The most recently updated guideline is the American Academy of Allergy, Asthma and Immunology/American College of Allergy, Asthma and Immunology 2020 Joint Task Force Practice Parameter (TFPP) recommendations for the treatment of allergic rhinitis and nonallergic rhinitis in adolescents aged 12 and older and adults. Table 12 summarizes their recommendations for allergic rhinitis. These guidelines recommend against LTRAs for initial treatment of allergic rhinitis.
The 2015 American Academy of Otolaryngology-Head and Neck Surgery Foundation guidelines address patients aged 2 and older who suffer from allergic rhinitis.1 They recommend intranasal steroids and oral antihistamines as first-line treatment. Similar to the TFPP recommendations, this guideline recommends against LTRAs as first-line treatment.1
Monotherapy is Good, But Sometimes Ineffective
Patients often use INCS, the recommended first-line treatment, for days before experiencing relief, but oral antihistamines usually suppress histamine within hours. INCS and antihistamines can be used concurrently if patients still have symptoms after taking antihistamines. Combining LTRAs with antihistamines may provide added benefit for patients with comorbid asthma.1,2
If patients’ main symptoms are sneezing and itching, a second-generation antihistamine is usually a good choice.2 Table 23,8-14 lists available options. All the second-generation antihistamines are similarly effective.15 Some patients prefer nasal antihistamines, and when that is the case, pharmacists should review the directions with the patient because many patients use these incorrectly.
Diminishing Response is Common
Many people adopt a favorite antihistamine and use it exclusively. Although little is written on the topic, many if not most patients experience “antihistamine tolerance,” or diminished effectiveness.16 It can occur after as few as 7 days of antihistamine use but is usually associated with prolonged use. Taking a break for 3 to 14 days or using a different antihistamine can restore response to the original antihistamine.
Conclusion
Recommending antihistamines for seasonal allergy usually boils down to recommending the second-generation nonsedating antihistamines over the first-generation antihistamines to start treatment. Because the antihistamines have similar efficacy and safety profiles, price, availability, and patient preference should drive selection. Patients whose symptoms are unresponsive or severe need to see a prescriber.
References
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About the Author
Jeannette Y. Wick, MBA, RPh, FASCP, is the director of pharmacy professional development in the Department of Pharmacy Practice at the University of Connecticut School of Pharmacy in Storrs.