Main Issue August 2011

Understanding the Role and Use of Antihistamines

Antihistamines represent a common baseline approach for many dermatologic conditions. But their benefits often vary depending upon their use.

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Antihistamines are known to quell inflammation and are common over-the-counter remedies for several dermatologic conditions. But like many other agents, antihistamines are most effective under a particular set of circumstances. Given the number of antihistamines available—from prescription to over-the-counter (OTC), sedating to non-sedating— choosing the agent that will provide the best results while carrying the least risk for adverse events is essential. Adverse events associated with antihistamines tend not to be severe, but it is nonetheless important to minimize them in younger patients.

When and How

Antihistamines are commonly used to treat several dermatologic conditions, according to Wynnis Tom, MD, Assistant Clinical Professor in the Departments of Pediatrics and Medicine (Dermatology) at the University of California, San Diego. These include urticaria (hives), atopic dermatitis (AD), facial eczema due to nasal allergies/hay fever, as well as bug bites. However, Dr. Tom observes that in pediatric patients, antihistamines should be chosen so as to minimize potential adverse events, such as drowsiness, which could interfere with school or activities. “For most skin conditions, non-sedating antihistamines (cetirizine (Zyrtec, McNeil), loratadine (Claritin, Merck/MSD), etc.) are better for the daytime so that patients are not drowsy,” she notes. However, these OTC agents do not appear to be very helpful for eczema/atopic dermatitis, Dr. Tom continues. “Nonsedating antihistamines are mainly only helpful in the facial area if there is a lot of itch and scratching/rubbing due to allergies or hay fever,” she says.

In most other cases of eczema, sedating antihistamines are more effective. “I do prescribe sedating antihistamines in the daytime but at lower amounts so that I try to minimize sleepiness,” explains Dr. Tom. Oral diphenhydramine hydrochloride (Benadryl, McNeil-PPC) is likely the most prominent OTC sedating antihistamine, but if a patient does not appear to be responding to it, Dr. Tom recommends choosing a prescription oral agent, such as hydroxyzine hydrochloride, that may provide longer-lasting relief.

Importantly, some antihistamines tend not to be effective for a given condition or in pediatric patients. For example, once-a-day antihistamines, such as Allegra (fexofenadine and pseudoephedrine, Sanofi Aventis), are not known to provide any relief for eczema. In addition, says Dr. Tom, “topical antihistamines, such as diphenhydramine hydrochloride cream (Benadryl, McNeil-PPC), don't appear to provide relief or benefit for rashes or bug bites.” In fact, some people can be allergic to Benadryl cream and get a rash from its use, she adds. For primary relief of itch, Dr. Tom says “Other topical possibilities include Sarna, which contains menthol, camphor, and in some forms, pramoxine (Stiefel) and topical steroids.” With topical steroids, exercise caution in pediatric patients to minimize any risks for adverse events.

Antihistamines have other potential uses in pediatric settings, according to Dr. Tom. “For those prone to bug bites, it is helpful to schedule them to take a daily non-sedating antihistamine for several weeks to months at times when they are likely to be in contact with bugs: the summer months, when camping, etc.,” she says. Taking antihistamines before being bitten decreases the rate and extent of reaction to the bites, according to Dr. Tom.

Striking the Right Note

Dr. Tom says antihistamines can provide symptomatic relief for the certain rashes. However, given the range of options available, it is incumbent upon physicians to learn about the differences between agents and decide which sedating or non-sedating option is appropriate, depending on the condition.

Take-Home Tips.

Antihistamines can provide symptomatic relief for certain rashes. However, given the range of options available, it is incumbent upon physicians to learn about the differences between agents and decide which sedating or non-sedating option is appropriate, depending on the condition. Antihistamines should be chosen so as to minimize potential adverse events, such as drowsiness, which could interfere with school or activities. Non-sedating antihistamines may be useful for facial eczema related to allergies. In most other cases of eczema, sedating antihistamines are more effective.

Available Antihistamines

Non-sedating Antihistamines
Fexofenadine (least-sedating)
Loratadine
Desloratadine
Cetirizine
Levocetirizine

Sedating Antihistamines
Diphenhydramine
Chlorpheniramine
Clemastine
Cyproheptadine
Hydroxyzine

www.fpnotebook.com/ent/Pharm/SdtngAnthstmn.htm

Research Trends: Antihistamines

Elucidating the Role of Antihistamines in Urticarial Flares
New research suggests that antihistamines play an integral role in the treatment of urticaria related to food allergies.1 Researchers note that the first step of treatment is to determine the cause and triggering factors, which can be difficult. Once this is determined, oral non-sedating H1 antihistamines are currently the recommended first-line treatment for urticarial flares in atopic dermatitis in young children with food allergy. If needed, the dosage of antihistamines may be doubled, although evidence is lacking for this. Alternative treatment should be reserved as add-on therapy for unresponsive patients, the researchers note.

Antihistamines Beneficial For Rare Condition of Infancy?
A recent study in Pediatric Dermatology has found that topical antihistamines may be useful in treating raised linear bands of infancy, a newly recognized but rarely reported entity.2 Some cases of raised linear bands have been associated with dermatographism, and it has been postulated that the bands may be related to an increase in collagen deposition and fibrosis from increased mast cell mediators.

New Publication Probes Mechanisms and Effects of Antihistamines in AD
A publication in July in Advanced Experimental Medical Biology explores the role of histamine in atopic dermatitis, as well as the efficacy of antihistamines in its treatment.3 The researchers observe that antihistamines are believed to share a common anti-pruritic effect and therefore are prescribed to the vast majority of AD patients suffering from itch. However, they note further that the level of evidence in support of the benefits of antihistamine treatment is somewhat low. The article assesses the benefit of antihistamines in the treatment of AD by examining precisely their mechanisms and specific effects.

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