Enriched enrolment: definition and effects of enrichment and dose in trials of pregabalin and gabapentin in neuropathic pain. A systematic review

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT Enriched enrolment (the exclusion of non-responders or specific inclusion of responders) is believed to add both to trial sensitivity and to the measured effect of an intervention. Enriched enrolment lacks specific definition, and the extent of any differences between results with non-enriched recruitment and enriched enrolment is not known. Enriched enrolment is thought to have influenced neuropathic pain trials. WHAT THIS STUDY ADDS The paper suggests definitions for complete and partial enriched enrolment, and applies those definitions to trials of pregabalin and gabapentin in neuropathic pain. The effect of enrichment was small, and especially in pregabalin trials with the best data, no difference was found between partial enrichment and no enrichment. The effects of complete enrichment are unknown. AIMS Enriched enrolment study designs have been suggested to be useful for proof of concept when only a proportion of the diseased population responds to a treatment intervention. We aim to investigate whether this really is the case in trials of pregabalin and gabapentin in neuropathic pain.