Underreporting of suspected adverse drug reactions to newly marketed ("black triangle") drugs in general practice: observational study

Abstract

The Drug Safety Research Unit performs observational cohort studies (prescription event monitoring) on selected newly marketed drugs in general practice. All patients in England who have been dispensed selected new drugs are identified for these studies by the Prescription Pricing Authority. Questionnaires (“green forms”) are subsequently sent to prescribers asking about clinical events, suspected adverse drug reactions, and events reported to the Committee on Safety of Medicines as suspected adverse reactions. For the 10 drugs we examined (acarbose, risperidone, fluvastatin, tramadol, gabapentin, famciclovir, lansoprazole, zolpidem, venlafaxine, and losartan) median exposure was 46 435 (interquartile range 24 524 to 55 735) patient months. Events recorded by general practitioners as suspected adverse reactions, and those stated as having been reported to the Committee on Safety of Medicines, were classified as serious or non-serious, using the definition published in the British National Formulary.2 We determined whether the event was listed (“labelled”) in the summary of product characteristics at the time of the study; events not listed were classified as unlabelled. Reports stating “non-specific side effects” or intolerance were not classified. By calculating a risk ratio, using non-serious labelled events as the reference group, we determined the likelihood of each category of adverse reaction being reported to the Committee on Safety of Medicines.