UNDER-REPORTING OF ADVERSE DRUG-REACTIONS - ESTIMATE BASED ON A SPONTANEOUS REPORTING SCHEME AND A SENTINEL SYSTEM

Objective: Spontaneous reporting is the most common method used in pha rmacovigilance and the best one to generate signals on new or rare adv erse drug reactions (ADRs). Under-reporting is a major drawback of thi s system. The objective of this study was to quantify the extent of un der-reporting in general practice and to assess the factors which infl uence it. Method's: Details of ADRs collected through a short intensiv e survey were compared with primary care spontaneous reports received by the Castilla y Leon Regional Pharmacovigilance Centre during a 12-m onth reference period. The survey was undertaken by a random sample of 146 general practitioners (GPs), providing care to 149487 people. The pharmacovigilance centre received reports concerning the whole region al population (2.5 million) covered by primary health care. The under- reporting coefficient (U) was estimated as the ratio between the numbe r of effects observed by physicians in the survey and those spontaneou sly reported to the pharmacovigilance centre. Results: The overall und er-reporting rate was 1144 [95% confidence interval (CI): 928-1409]. U nder-reporting was greater for psychiatric (2119; 945-4752) and gastro intestinal (1946; 1424-2659) disorders. Severe effects were more repor ted (U = 605; 151-2431) than moderate (863; 473-1575) and mild (1209; 973-1503) ones. The under-reporting rate was lower for drugs recently marketed (706; 406-1230) and slightly lower for unlabelled effects (10 31; 641-1657). Conclusion: The under-reporting rate of ADRs is conside rable, though not homogeneous for the different cases. This should be taken into account when comparing adverse effects (AEs) for different drugs. Underreporting seems to be positively selective, as it involves mainly the less severe and better-known effects, preserving the value of spontaneous reporting for signal detection.