International guidelines are conflicting on the use of antihistamines in anaphylaxis

No randomised controlled clinical trials or observational studies exist to inform us: a Cochrane review recently failed to identify any randomised controlled clinical trials evaluating antihistamines in acute anaphylaxis6; only one prospective trial was identified but was excluded as it lacked a control group and did not study patients with anaphylaxis.7 Our own PubMed search also did not identify any randomised controlled clinical trials or observational or cohort studies examining the appropriateness of antihistamines in anaphylaxis.

Unsurprisingly, a recent comparison of important international guidelines found conflicting advice about antihistamines,3 reflecting the uncertainty in international clinical practice: a US guideline recommends the use of diphenhydramine as second line treatment in anaphylaxis8; evidence for this recommendation is graded as “expert opinion/extrapolated from higher order evidence.”9 An Australian guideline advises against the use of antihistamines in anaphylaxis (except in special circumstances).10 The Resuscitation Council of the United Kingdom still recommends chlorphenamine as second line treatment after initial resuscitation, grading evidence to support its use as …