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Huge variation in drug-drug interactions among hospitalised elderly patients

As a patient group, the elderly are most at risk of drug-drug interactions yet little is known about the prevalence of such interactions among those who are hospitalised.

A drug-drug interaction (DDI) describes the ability of one drug to modify the actions and/or effects of another when administered simultaneously. The elderly are considered to be at a higher risk than other patient groups because they tend to be prescribed more drugs and ageing itself, is an independent risk factor for DDIs. Although evidence indicates that elderly patients are more frequently admitted to hospital because of DDIs, the prevalence of these interactions among older people once hospitalised is largely unknown. Consequently, a team from the Federal University of Rio Grande do Sul, Brazil, set out to systematically review the actual and potential DDI prevalence in hospitalised elderly patients reported in observational studies and the particular range of drugs responsible for these interactions. The researchers defined the elderly as those aged 60 years and they excluded studies which focused solely on a particular class of drugs or from a narrow disease population. The main outcome of interest was the prevalence of actual or potential DDIs which was determined as a percentage of patients that presented with at least one DDI during their hospital stay, among the total number of patients studied.

Although the initial literature search identified 2409 studies, after review only 34 were included in the final analysis which involved a total of 9577 patients. Among studies undertaken in geriatric units, the prevalence of DDIs ranged from 80.5 to 90.5%. In contrast, in studies performed in other hospital units, the prevalence ranged from 8.3 to 100%. The mean number of drugs per patient ranged from 2 to 23.9 whereas the number of DDIs per patient ranged from 1.2 to 30.6. The class of drugs most commonly involved in DDIs were potassium -paring diuretics, angiotensin-converting enzyme inhibitors, anticoagulants, cardiac glycosides and antithrombotic agents. In terms of drug combinations, the results suggested that clopidogrel and omeprazole were associated with significantly higher major adverse cardiac events. The authors were unable to account for the wide range in prevalence rates but speculated that this was most likely due to the variation in the number of drugs per patient, differences in health status, complexity or care and differences in the software used to extract the DDI information.

Mello de Oliveira L et al. Prevalence of drug interactions in hospitalised elderly patients: a systematic review. Eur J Hosp Pharm 2021;28:4-9