Selecting a Treatment Regimen H1 and H2 Antihistamines
ÎAntihistamines are considered supportive therapy and do not replace epinephrine. Antihistamines are second line drugs that can be given after epinephrine administration since they may be useful for control of cutaneous and cardiovascular manifestations.
ÎDiphenhydramine, an H1 antagonist, may be given intramuscularly or by slow intravenous infusion in a dose of 25 to 50 mg in adults, and 1 mg/kg up to 50 mg in children. Indirect evidence supports the parenteral administration of diphenhdramine or hydroxyzine. Oral diphenhydramine as well as other oral first or second generation H1 antihistamines can also be used. There is no direct outcome data regarding the effectiveness of any antihistamine in anaphylaxis.
ÎAn H2 antagonist added to the H1 antagonist may be helpful in the management of anaphylaxis.
Comment: Parenteral ranitidine can be considered in a dose of 1 mg/kg in adults and 12.5 to 50 mg in children. Since time to maximum serum concentration (Cmax) is approximately the same for intravenous and intramuscular administration, either route can be considered. If intravenous administration is chosen, the drug should be infused over 10 to 15 minutes. It may also be diluted in 5% dextrose to a volume of 20 mL and injected over 5 minutes.
Corticosteriods
ÎGlucocorticosteroids have not been shown to be effective for the acute treatment of anaphylaxis but could, theoretically, prevent protracted anaphylaxis.
Comment: There is no conclusive evidence that the administration of corticosteroids prevents a biphasic response.
Other Proposed Therapies for Anaphylaxis
ÎSeveral other therapeutic agents have been proposed for use in anaphylaxis. However, there is no high quality evidence that supports these agents, and existing data are too limited for consensus opinions to be reached.
ÎLeukotriene modifiers: At this time there are no data documenting the efficacy of leukotriene modifiers in the treatment of anaphylaxis or in its prevention.
In addition, at this time, the only available route of
administration is oral and therefore the onset of action of such agents in anaphylaxis would not be optimal.
> Tranexamic acid has been used to treat anaphylactic episodes associated with disseminated intravascular coagulation. However, it is not available in the United States.
ÎIn case reports, methylene blue inhibition of nitric oxide synthesis has been reported to be helpful in the treatment of hypotension occurring during anaphylaxis. There are no controlled studies, however, involving the use of this agent in anaphylaxis.
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