A patient who has chronic allergies takes loratadine (Claritin) and develops a severe reaction to bee stings. The patient asks the nurse why the antihistamine did not prevent the reaction. What will the nurse say?
a. "Allergy symptoms that are severe are caused by mediators other than histamine."
b. "H1 blockers do not prevent the release of histamine from mast cells and basophils."
c. "Second-generation H1 blockers contain less active drug and do not work in severe reactions."
d. "Severe allergic reactions occur through actions on muscarinic receptors."
ANS: A
Severe allergic reactions with symptoms of anaphylaxis are caused by mediators other than histamine, so the benefits of antihistamines are limited. H1 blockers do not block the release of histamine, but this is not why they are not effective in anaphylaxis. Second-generation agents are as effective as first-generation agents in allergic reactions mediated by histamine; neither is effective for treating anaphylaxis.
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