In contrast to RCTs, individual cases or case series do not provide a comparison with a control group and are unable to produce reliable risk estimates. In spite of their limitations, astute clinical observations are still fundamental to the description of new disease entities and the raising of new hypotheses concerning disease causation, including the effects of medical interventions. Case reports still represent a firstline modality to detect new adverse reactions once a drug is marketed.7 Spontaneous surveillance systems such as the International Drug Monitoring Program of the World Health Organization (WHO) capitalise on the collection and periodical analysis of spontaneous reports of suspected adverse drug reactions.8 All physicians are expected to take an active part in promoting the safety of medical interventions and to contribute by reporting any suspected adverse events they observe in association with drug use.9 Such a collection of reported adverse events may be explored to raise signals (Box 10.1) to be validated by more formal study designs, that is, studies providing estimates of incidence rates and quantifying risks.10,11 Spontaneous reporting should be seen as an early warning system for possible unknown adverse events and may be prone to all sorts of bias.12 Case reports may be more effective in revealing unusual or rare acute adverse events. In general, however, they do not reliably detect adverse drug reactions that occur widely separated in time from the original use of the drug or represent an increased risk of an adverse event that occurs commonly in populations not exposed to the drug.
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