Under-reporting of serious adverse drug reactions in Sweden

Adverse drug reactions (ADR) constitute a major problem, both from a medical point of view and as an economical burden. Spontaneous reporting of ADRs is one of the methods for post marketing surveillance of drug safety. Under-reporting can also provide an important obstacle to rapid and relevant signal detection.

To investigate the rate of under-reporting serious ADRs of selected ICD 10 diagnoses.

In order to investigate the under-reporting rate we investigated at five hospitals within the county of Norrbotten in Sweden the total number of diagnosed cases during a period of 5 years (1996-2000) with the following diagnoses: cerebral haemorrhage (I 61.0-I 61.9), pulmonary embolism (I 26.0 and I 26.9), embolism or thrombosis (I 74.0-I 74.9), phlebititis, thrombophlebitits or venous thrombosis (I 80.0-I 80.3, I 80.8 and I 80.9) and portal vein thrombosis and other thrombosis or emboli (I 82.0-I 82.3, I 82.8 and I 82.9). The identity of these patients was obtained through a database search. The patients' case records were then scrutinized by a specially trained nurse and the drugs used at the time of the event were noted. An assessment of the possibility of an ADR was performed using standard WHO causality criteria. Later, database search in the Swedish ADR registry was performed in order to investigate whether these suspected ADRs had been reported to the national authority in Sweden or not.

In total 1349 case records were found and scrutinized. Of these, 107 patients had received drugs that could have been a probable or possible cause to the diagnoses. Of these 92 cases had not been reported and only 15 patients were found in the database, giving an overall under-reporting rate of all ADRs of 86%. The most commonly occurring diagnoses were cerebral haemorrhage followed by venous thrombosis, 545 and 468 respectively. Among those cases that should have been reported according to the existing rules for spontaneous reporting of suspected ADRs the most frequently occurring diagnosis was cerebral haemorrhage (I 61.0) in connection to treatment with anticoagulants.

The rate of spontaneous ADR reporting is very low, also for serious and fatal reactions.