Web forums are proposed as a new complementary source of knowledge to spontaneous reports by patients and healthcare professionals due to underreporting of adverse drug reactions (ADRs). Some authors suggest that signal detection could be a convenient method for gathering mentions of ADRs in patients' posts. Signal detection methods were proposed to mine pharmacovigilance databases, but little is known about their applicability to web forums. We describe a method implementing several traditional decision rules on signal detection with baclofen applied to a set of more than 6 million posts. We then cross-validated four unexpected signals applying a logistic regression method. Most adverse effects (AEs) described in the summary of product characteristics of baclofen were detected by signal detection methods. Some unexpected AEs were too. Therefore, web forums are confirmed as a complementary resource for improving current knowledge in pharmacovigilance by detecting unexpected adverse drug reactions.
Keywords: Adverse drug reaction; Baclofen; Forums; Logistic regression; Signal detection; Social media.