42 CHAPTER 2.1 cases (n = 149). The two appraisers reassessed and discussed all discrepancies and reached a consensus without consulting a third expert. Overall, the PPV of the ADR trigger tool was 41.8%. The PPV varied considerably across triggers. The PPV related to the triggers fall (28.2%) and delirium (23.0%) were the lowest, whereas the mean number of drugs associated with these triggers was highest with a large range (fall: mean 3.1, min-max 1–8; delirium: mean 2.3, minmax 1–6). Although numbers were relatively small, the PPVs related to the triggers hypokalaemia (100%), supratherapeutic INR (100%) and vomiting/diarrhoea (88.9%) were highest (Table 2). Drugs related to ADRs More than half of the 941 trigger-drug combinations detected by the ADR trigger tool were associated with three drug classes: diuretics (25.4%), agents acting on the renin-angiotensin system (16.7%) and psychotropic agents (12.2%). The top three drug classes most frequently associated with the 393 ADRs were diuretics (35.4%), agents acting on the renin-angiotensin system (13.5%) and analgesics (11.2%), covering 60% of all drugs that caused an ADR. ADR recognition by usual care Usual care recognised 51.8% (481/929) of the trigger-drug combinations detected by the trigger tool and for which a causality classification could be determined. 42.3% (393/929) were considered ADRs with at least possible causality, of which 83.5% (328/393) were recognised by usual care according to information in the admission and discharge letters (Table 3). 16.5% (65/393) of ADRs were not recognised by usual care, of which 93.9% (n = 61) had a causal relationship considered to be possible. The majority of these possible ADRs not recognised by usual care were related to the top three most common events (fall, n = 29; delirium, n = 13; renal insufficiency, n = 10). Three probable ADRs were not recognised (furosemide – hyponatraemia; fentanyl – constipation; fentanyl – delirium) and one certain ADR was not recognised by usual care (bumetanide – renal insufficiency/dehydration). Recognition by usual care increased to 97.1% (135/139) when only ADRs considered to be probable or certain ADRs were included (Table 3). In 75.6% of possible, probable or certain ADRs and in 85.6% of probable or certain ADRs, the suspected drug was discontinued, or the dosage was reduced by usual care. The top three most frequently discontinued drugs related to ADRs were thiazides, opioids and high-ceiling diuretics. Table 3 provides a detailed overview of the number of ADRs per trigger and their associated drug classes in relation to their recognition by usual care. ADRs were stratified for a causal relationship considered to be possible, probable or certain and for those considered to be probable or certain.