Master the board step 3

Master the Boards: USMLE Step 3
hemodynamic instability. The onset of the wheals and hives is usually within
30 minutes and lasts for < 24 hours. Itching is prominent.
The most common causes are:
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Medications (aspirin, NSAIDs, morphine, codeine, penicillins, phenytoin,
and quinolones)
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Insect bites
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Foods (peanuts, shellfish, tomatoes, and strawberries)
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Emotions (occasionally)
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Contact with latex (in any form)
Chronic urticaria is associated with:
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Pressure on the skin: Pressure on the skin resulting in localized urticaria is
also known as dermatographism.
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Cold
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Vibration
Treat urticaria with the following:
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H1 antihistamines: Severe, acute urticaria is treated with older medications,
such as diphenhydramine (Benadryl), hydroxyzine (Atarax), or cyproheptadine.
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For life-threatening reactions, add systemic steroids.
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Chronic therapy: Treat with newer, nonsedating antihistamines, such as
loratadine, desloratadine, fexofenadine, or cetirizine.
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Desensitization is the answer when the trigger cannot be avoided. An
example of this is a bee sting in a person who is a farmer. Beta blocker medications
must be stopped prior to desensitization, because they inhibit the
epinephrine that may be used if there is an anaphylactic reaction.
Morbilliform Rash
Morbilliform rash is a milder version of a hypersensitivity reaction than urticaria.
This is the “typical” type of drug reaction and is usually secondary to
medications to which the patient is allergic, such as penicillin, sulfa, allopurinol,
or phenytoin. The rash resembles measles; it is a generalized maculopapular
eruption that blanches with pressure. The reaction can appear a few days
after the exposure and may begin even after the medication has been stopped.
Morbilliform rash is lymphocyte mediated and is treated with antihistamines.
Steroids are rarely necessary.
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