Description of studies
We identified a total of 212 publications through electronic searches and hand-searching. We excluded 174 duplicates among databases, clearly irrelevant publications or non-clinical studies. Thirty eight publications were retrieved for further assessment. Of these, we excluded 33 which are listed under ’Characteristics of excluded studies’ with reasons for exclusion. Accordingly, five trials fulfilled our inclusion criteria and were included. For a summary of the search see Figure 1.