Classification of ADRs: a proposal for harmonization and differentiation based on the experience of the Comprehensive Hospital Drug Monitoring Bern/St. Gallen, 1974-1993.

The present paper deals with the classification of adverse drug reactions (ADRs) according to today's largely accepted pathomechanisms. The classification system applied, relies primarily on the proposals of Rawlins and Thomson with type A ('augmented') and B ('bizarre') reactions. In the database of the Comprehensive Hospital Drug Monitoring (CHDM) Bern/St. Gallen on 48,005 consecutively hospitalized patients, ADRs had been attributed to 10 different pathomechanisms. These permit a versatile new system, easily adaptable to expanding knowledge. If we look at the 12,785 ADRs registered in the CHDM Bern/St. Gallen from 1974 to 1993, 76% were of type A, 13% of type B, and 11% of a pathomechanism not yet defined (type X). The main subgroups were A1 'not specified' in type A, Ba allergic/immunological and Bpa pseudoallergic/anaphylactoid in type B. Dose-related (A2) and drug-related reactions (A4, intolerance in a restricted sense), drug-to-drug interactions (A5), rebound/withdrawal effects (A6) and secondary reactions (A7) represented smaller subgroups. Patient-related reactions (A3, 'idiosyncrasy' in the strict sense) were not assessed. Today's algorithms for ADRs mainly rely on pharmacological, i.e. type A reactions. For most of the type B reactions adaptations including the experience of allergists, clinical immunologists and infectious disease specialists should be respected.