Injecting Antihistamines: The Benefits and Proper Administration

Q: We are are in the process of training our staff to administer injections and our nurse mentioned administering Benadryl in a vial as an injection. It seems to make perfect sense that you would give someone with a compromised airway an injection if possible rather than a pill to swallow, but I haven’t heard of anyone doing this in a backcountry setting.  I would love to hear any thoughts on this you may have.

Although I would agree that one should not give a pill or liquid to someone with a swollen airway, anaphylaxis can occur without airway involvement. More importantly, however, I don’t believe that training to inject an antihistamine is necessary or worthwhile.  The treatment for anaphylaxis is epinephrine, period.  If you had nothing else, that would be okay.  Except for hives, antihistamines do little for the acute symptoms.  In fact, no one has clearly demonstrated that they are even necessary.  We use them in the hope that they will decrease the likelihood of a biphasic or rebound reaction.

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2 Responses to “Injecting Antihistamines: The Benefits and Proper Administration”

  1. Dana

    ADMIN: I am not sure you know what anaphylaxis is. You may want to rethink your answer after reading almost any material on the histamine reaction your body has to an allergen which causes anaphylaxis.

  2. Look again

    Dana,

    No. Just no. Read deeper into the literature. There is no evidence that oral antihistamines prevent an anaphylaxis from progressing if it has already begun (though they may prevent anaphylaxis if taken before exposure to the allergen), and if there’s any data on injected antihistamines, I haven’t seen it.

    From one review article:
    “During anaphylaxis, a number of inflammatory mediators are released from mast cells and basophils. Histamine plays a pivotal role in acute allergic inflammation, which is a complex network of events that involve redundant mediators and signals, including tryptase, mast cell carboxypeptidase, platelet-activating factor, prostaglandins, leukotrienes and cytokines. In a systemic response, however, there may be sufficient redundancy and amplification such that reactions do not respond to a single mediator antagonist.” (Sheikh A, Ten Broek V, Brown SG, Simons FE. H1-antihistamines for the treatment of anaphylaxis: Cochrane systematic review. Allergy. 2007
    Aug;62(8):830-7.)

    Meaning that taking care of just histamine probably won’t do it. Epinephrine covers it. Delayed injection of epinephrine is associated with fatal anaphylaxis (see various articles, or read a review).

    A decent review article is:
    Simons FE. First-aid treatment of anaphylaxis to food: focus on epinephrine. J Allergy Clin Immunol. 2004 May;113(5):837-44.
    (Abstract here, if you can’t access the entire article: http://www.ncbi.nlm.nih.gov/pubmed/15131564 )

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