Summary measures of number needed to treat: How much clinical guidance do they provide in neuropathic pain?

BACKGROUND: Several systematic reviews of randomized controlled trials (RCTs) of drugs to treat neuropathic pain have reported summary estimates of efficacy - specifically, the number needed to treat (NNT). AIMS: To examine whether summary NNTs for drugs to treat neuropathic pain provide useful guidance for clinical decision making. METHODS: We examined the methods used to pool data across RCTs in systematic reviews - in particular, the extent of heterogeneity of agents (and dosages), neuropathic pain syndromes, and outcome measures. RESULTS: Published summary estimates of NNTs of drugs to treat neuropathic pain embody substantial heterogeneity, in that they reflect a pooling of data across agents with different mechanisms of action, across patients with different neuropathic pain syndromes, and/or across different outcome measures. CONCLUSIONS: Summary NNT estimates may have limited clinical relevance, due to problems of heterogeneity. The most that can be extracted from systematic reviews published to date is the identity of drugs that have demonstrated efficacy for specific types of neuropathic pain, and the strength of such evidence.