Pharmacovigilance may be better known as the science of drug safety.

Its activities aim to detect, monitor, assess and evaluate undesirable medical events which are suspected or proved to be related to taking a particular medicinal product. This article will provide a brief lay introduction to the concepts of expected versus unexpected responses to medicines intended for human use.

Classification According To The Product Life Cycle: When Is A Response Considered Expected Or Unexpected?

Before a pharmaceutical product Pharmacovigilance course has been placed onto the market, it must successfully pass through a series of clinical trial phases. During this period, the current investigator’s brochure is used as the reference document against which all responses will be considered. At this stage, should a clinical trial participant or patient experience a medical event which does not correspond to those already detailed within the risk information in the brochure, the event will be classed as unexpected. It could be that the risk information was not required; or it may not have been available. Another possibility is that an event arises which presents a more specific risk than those described in the brochure. A case of cerebral thromboemobilsm would be more specific than cerebral vascular accident; if only the latter were described in the brochure then the former would be deemed unexpected. Finally, another possibility would be that the nature of the response is more severe than those contained within the brochure. If the brochure described elevated liver enzymes but a case arose involving hepatic necrosis, then this would be deemed unexpected due to higher severity.

After the product has passed satisfactorily through the clinical trial phases, it may be that the reference document changes. Once it has launched onto the market, it is possible that it could still be the investigators brochure. However, it is also common for the reference document to now be the standard product information. Examples could be any packaging inserts or the summary of product characteristics. If an event presents which is not precisely consistent with whichever reference document applies, it will be classed as unexpected. This includes again instances of escalated severity or greater specificity.