Medication Summary
Because solar urticaria involves IgE-mediated mast cell degranulation with consequent histamine release, the first line of treatment for this disease consists of long-acting, nonsedating H1-receptor blockers. Often, such agents achieve a protective factor of 10 or more. The H2-receptor antagonist ranitidine and others may aid in treatment when an H1 blocker is not effective on its own.
Antimalarial agents can treat certain photosensitive eruptions, including those of solar urticaria, but their efficacy is unpredictable.
Patients with solar urticaria that is resistant to treatment with antihistamines have experienced promising results with injections of omalizumab. [17, 18, 19]
Antihistamines, 2nd Generation
Class Summary
The extent to which antihistamines are useful against solar urticaria depends on the severity of the disease itself. For example, someone who gets hives after just a few seconds of sun exposure is unlikely to benefit from antihistamine monotherapy, while a patient requiring 10 minutes or more of exposure would show more benefit. Antihistamines seem to block wheal response and minimize pruritus, but they do not entirely eliminate an erythematous reaction. This should be explained to the patient.
Cetirizine (Zyrtec)
Cetirizine forms a complex with histamine for H1-receptor sites in the blood vessels, gastrointestinal (GI) tract, and respiratory tract.
Fexofenadine (Allegra)
Fexofenadine competes with histamine for H1 receptors in the GI tract, blood vessels, and respiratory tract, reducing hypersensitivity reactions. The drug does not sedate.
Loratadine (Claritin, Alavert)
Loratadine selectively inhibits peripheral H1 receptors.
Desloratadine (Clarinex)
Desloratadine is a long-acting tricyclic histamine antagonist selective for H1 receptors. It relieves nasal congestion and systemic effects of seasonal allergy. The drug is a major metabolite of loratadine, which, after ingestion, is metabolized extensively to active metabolite 3-hydroxydesloratadine.
Antimalarials
Class Summary
Antimalarials are used to treat certain photosensitive eruptions, including solar urticaria, but their efficacy is unpredictable.
Hydroxychloroquine (Plaquenil)
Hydroxychloroquine inhibits chemotaxis of eosinophils and the locomotion of neutrophils. It impairs complement-dependent antigen-antibody reactions. Hydroxychloroquine sulfate 200 mg is equivalent to 155 mg hydroxychloroquine base and 250 mg chloroquine phosphate.
Histamine H2-Receptor Antagonists
Class Summary
These agents are usually given in addition to H1 blockers.
Ranitidine (Zantac)
Ranitidine is an H2 antagonist that, when combined with the H1 type, may be useful in treating allergic reactions that do not respond to H1 antagonists alone.
Famotidine (Pepcid)
Famotidine competitively inhibits histamine at the H2 receptors in gastric parietal cells, reducing gastric acid secretion, gastric volume, and hydrogen concentrations.
Nizatidine (Axid, Axid AR)
This agent competitively inhibits histamine at the H2 receptor of the gastric parietal cells, resulting in reduced gastric acid secretion, gastric volume, and reduced hydrogen concentrations.
Cimetidine (Tagamet HB 200)
This agent inhibits histamine at H2 receptors of gastric parietal cells, which results in reduced gastric acid secretion, gastric volume, and hydrogen concentrations.
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Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria.jpg).
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Solar urticaria. Courtesy of DermNet New Zealand (http://www.dermnetnz.org/assets/Uploads/reactions/solar-urticaria1.jpg).
