CRD Summary: The review concluded that data supporting the use of premedication in patients with a history of allergic reactions was lacking. Given the limited evidence base this seemed reasonable, however, the conclusion that routine premedication should be abandoned may be somewhat strong given that the absence of evidence was not evidence of lack of effectiveness.

[Five trials assessed H1 antihistamines (hydroxyzine, clemastine, chlorpheniramine, dimenhydrinate), five trials assessed corticosteroids (betamethasone, dexamethasone, methylprednisolone, prednisolone) and one trial assessed an H1-H1 combination (clemastine-cimetidine). ]

CRD Commentary: The review addressed a clear question that was defined in terms of the participants, intervention, outcomes and study design. Several relevant electronic databases were searched without language restriction, reducing the risk of language bias. Procedures to extract data and assess validity were likely to have minimised reviewer error and bias, but similar methods were not reported for the selection of studies. Variation in the dose, type and administration of the premedication and contrast media, and the outcomes assessed, suggested that pooling estimates was not appropriate. In addition, as acknowledged by the authors, selecting outcomes with the most pronounced treatment effect may have led to an overestimation of the efficacy of the premedication. Given the diversity between the studies, multiple treatment elements and the questionable quality of the primary studies, there did not appear to be sufficient evidence to determine the efficacy of pharmacological prevention of serious reactions to iodinated contrast media. The authors’ conclusion that data supporting the use of premedication in patients with a history of allergic reactions were lacking seems reasonable, however, the conclusion that routine premedication should be abandoned may have been somewhat strong given that absence of evidence was not the evidence of a lack of effectiveness.