Broad systematic review to examine evidence for an intervention across different conditions

What is it about?

Following the paradigm of evidence-based medicine, systematic reviews of medical literature (such as Cochrane reviews) have tended to focus on tightly formulated research questions. This has advantages of ensuring methodological rigour and that the review findings are directly applicable to the specific condition/patients. However, the downside is that other literature that could potentially be relevant and informative is often ignored altogether. One particular example is adverse drug effects, which could be rare but serious. Systematic reviews of literature for a single condition (indication) often lack statistical power to assess and quantify the risk of such adverse effects . Nevertheless, many drugs can be used to treat several conditions, and if the adverse effects are associated with how the drug works (i.e. are caused by the same mechanism), then there is no reason why evidence on adverse effects from studies of related conditions should be ignored. This is where a "multiple indication review", i.e. a systematic review of an intervention across several related conditions may be useful. This paper surveyed the literature to identify previous examples of multiple indication reviews, and discuss methodological approaches and challenges associated with conducting such reviews. Examples provided in this paper include the use of adjuvant chemotherapy after surgery vs. surgery alone for treating different types of cancer, and use of antibiotics to prevent infection for different types of surgery.

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Why is it important?

Focusing on a narrowly defined question (e.g. a specific drug for a specific condition) when undertaking a systematic review has its advantages and remains a suitable approach for many review topics. Nevertheless, this approach can result in evidence being evaluated in silos and may lead to ignorance of useful information. The consequence is that decisions are informed by evidence that has been evaluated and presented in a fragmented way. Multiple indication reviews address this issue by taking a "panoramic"view of all relevant literature to test a scientific hypothesis. The concept of multiple indication reviews can be easily extended from medical treatments to other context, for example, for public health interventions sharing the same mechanism(s) but implemented and evaluated in different contexts such as different populations and settings, or even to address different but related problems.

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