Aims To explore drug exposure, frequency of adverse drug reactions (ADRs), types of ADRs, predisposing risk factors and ADR-related excess hospital stay in medical inpatients. Methods Structured data regarding patient characteristics, 'events' (symptoms, laboratory results), diagnoses (ICD10) and drug therapy were collected using a computer-supported data entry system and an interface for data retrieval from electronic patient records. ADR data were collected by 'event monitoring' to minimize possible bias by the drug monitor. The causality of each event was assessed in relation to disease(s) and drug therapy. Results The analysis included 4331 (100%) hospitalizations. The median observation period was 8 days. The median number of different drugs administered per patient and day was 6 and varied between 4 (Q 1 ) and 9 (Q 3 ) different drugs in 50% of all hospital days. In 41% of all hospitalizations at least one disease-unrelated event could be possibly attributed to drug therapy. Clinically relevant ADRs occurred in 11% of all hospitalizations. In 3.3% of all hospitalizations ADRs were the cause of hospital admission. The incidence of possibly ADR-related deaths was 1.4‰. Factors predisposing for clinically relevant ADRs were female gender and polypharmacy. ADR-related excess hospital stay accounted for 8.6% of hospital days. Conclusions These data demonstrate the feasibility of the developed 'event monitoring' system for quantitative analysis of ADRs in medical inpatients. With increasing numbers of recorded patients the pharmacoepidemiological database provides a valuable tool to study specific questions regarding drug efficacy and safety in hospitalized patients.

Studies on the epidemiology of common adverse cutaneous drug reactions have rarely been reported, since they can only be successfully conducted in clinics of internal medicine employing consultant dermatologists and having a comprehensive or intensive system of monitoring. Between 1974 and 1993, the adverse skin reactions occurring in divisions of general internal medicine of three different hospitals were monitored by a computerized comprehensive system. The "drug-monitoring patient" was defined as the recipient of at least one drug during hospitalization. The relationship of the skin reactions to drug causality in these patients had to be either definite (proven by re-exposure) or probable (drug relation greater than that of nondrug causality). The skin reactions were classified into four diagnostic groups. Maculopapular exanthema, urticaria, and vasculitis were the three main groups. The fourth group comprised cases of nonhomogeneous but clinically well-defined special exanthema. For selected drugs and years of observation, special emphasis was placed on the study of time patterns (reaction time, exposure time). A total of 1317 definite or probable drug-induced skin reactions occurred during the hospitalization of 48,005 consecutively admitted "drug-monitoring patients": 1201 cases of maculopapular exanthema, 78 cases of urticaria, 18 cases of cutaneous vasculitis, and 20 cases of special exanthema (five of erythema multiforme minor, six of fixed eruption, one of photosensitivity reaction, and eight of acneiform eruption). The main drugs involved did not differ for the three main types of skin reactions, penicillins ranking in the first place, followed by sulfonamides--most often combined with trimethoprim--and in the third place nonsteroidal anti-inflammatory drugs. The reaction time (time from last drug exposure to first skin manifestation) for urticaria showed a relevant proportion of the acute type (within 1 h) and most of the subacute type (1-24 h). For maculopapular exanthema, the subacute or, rarely, the latent type (1-8 days, exceptionally more than 8 days) predominated. For aminopenicillins, the rate of occurrence of skin reactions increased with increasing exposure time up to 12 days, and then markedly diminished. Possibly due to the tendency to withdraw suspected drugs even in the case of minor (e.g., maculopapular) skin reactions, no severe events such as erythema multiforme major/Stevens-Johnson syndrome or toxic epidermal necrolysis occurred.

The patients with a lethal outcome were presented under the eight pharmacologic-therapeutic classes of drugs and the classification proposed by NS Irey. This is based on long histopathologic experience and helps to identify preventable risks.

These results suggest that paracetamol co-administration at a dosage of 2000-2500 mg/day for 3 days has no clinically relevant effects on the anticoagulant effects of phenprocoumon.

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.