Introduction

Hospital admissions and emergency department (ED) visits due to problems related to pharmacotherapy remain a major healthcare concern, despite efforts to improve medication prescribing and use in the last decades [1,2]. Two recent systematic reviews on drug-related readmissions to hospital report an average prevalence of 15% and 21%, of which at least a third seem preventable [3,4]. There is large variation between studies due to heterogeneity in definitions and methods [3,4]. In this study, a drug-related readmission or drug-related ED visit is defined as an unplanned hospital visit where a drug-related problem (DRP) is either the main cause or a significantly contributing cause (i.e., without the DRP, the visit would not have taken place). DRPs are defined as ‘undesirable patient experiences that involve drug therapy and that actually or potentially interfere with desired patient outcomes’ [5]. These can involve not only adverse drug reactions to prescribed medication, but also problems such as inappropriate prescribing and non-compliance. The literature on risk factors associated with drug-related visits is extensive, but also characterised by heterogeneity. Common positively associated factors are age, functional disability or dependent living situation, previous hospital visits, length of previous hospital stay, number of medications in use and multimorbidity (e.g., high Charlson Comorbidity Index score [6]) [1,3,7–9]. There is little agreement between studies regarding specific diseases related to drug-related visits. Commonly associated drug classes are cardiovascular drugs, antibiotics, corticosteroids, opioids and psychotropic drugs [1,3,9]. Studies often fail to report the degree of preventability and the causes of visits. A better understanding of preventable drug-related visits is essential for developing targeted interventions to minimise drug-related harm.
One of the interventions proposed to prevent hospital visits in older patients is conducting a medication review [10]. In a recent multicentre randomised controlled trial (MedBridge) in Sweden, aiming to study the effects of comprehensive medication reviews with or without post-discharge follow-up, a total of 2,637 hospitalised patients aged ≥ 65 years was included [11]. Patients were excluded if they were admitted for less than 24 hours, had undergone a medication review by a clinical pharmacist within the preceding month, did not reside in the hospital county or were receiving palliative treatment. The trial interventions did not affect drug-related readmissions or all-cause readmissions within 12 months after discharge. Drug-related ED visits were not a study outcome, but all-cause ED visits were increased in one of the intervention groups compared with in usual care [11]. It is unclear whether drug-related revisits could have been prevented or whether these visits were caused by the trial interventions. There was a large variation in the trial population, with 2,055 (78%) patients experiencing no drug-related readmission. It is important to target patients at risk of drug-related readmission and to understand the underlying preventability and causes of drug-related revisits. In this study, we therefore aimed to: 1) identify older patients’ risk factors for drug-related readmissions and 2) assess the preventability of older patients’ drug-related revisits (admissions and ED visits).