Abstract
Purpose
Although the prevalence of drug–drug interactions (DDIs) in elderly outpatients is high, many potential DDIs do not have any actual clinical effect, and data on the occurrence of DDI-related adverse drug reactions (ADRs) in elderly outpatients are scarce. This study aimed to determine the incidence and characteristics of DDI-related ADRs among elderly outpatients as well as the factors associated with these reactions.
Methods
A prospective cohort study was conducted between 1 November 2010 and 31 November 2011 in the primary public health system of the Ourinhos micro-region, Brazil. Patients aged ≥60 years with at least one potential DDI were eligible for inclusion. Causality, severity, and preventability of the DDI-related ADRs were assessed independently by four clinicians using validated methods; data were analysed using descriptive analysis and multiple logistic regression.
Results
A total of 433 patients completed the study. The incidence of DDI-related ADRs was 6 % (n = 30). Warfarin was the most commonly involved drug (37 % cases), followed by acetylsalicylic acid (17 %), digoxin (17 %), and spironolactone (17 %). Gastrointestinal bleeding occurred in 37 % of the DDI-related ADR cases, followed by hyperkalemia (17 %) and myopathy (13 %). The multiple logistic regression showed that age ≥80 years [odds ratio (OR) 4.4; 95 % confidence interval (CI) 3.0–6.1, p < 0.01], a Charlson comorbidity index ≥4 (OR 1.3; 95 % CI 1.1–1.8, p < 0.01), consumption of five or more drugs (OR 2.7; 95 % CI 1.9–3.1, p < 0.01), and the use of warfarin (OR 1.7; 95 % CI1.1–1.9, p < 0.01) were associated with the occurrence of DDI-related ADRs. With regard to severity, approximately 37 % of the DDI-related ADRs detected in our cohort necessitated hospital admission. All DDI-related ADRs could have been avoided (87 % were ameliorable and 13 % were preventable). The incidence of ADRs not related to DDIs was 10 % (n = 44).
Conclusions
The incidence of DDI-related ADRs in elderly outpatients is high; most events presented important clinical consequences and were preventable or ameliorable.
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Acknowledgments
We acknowledge the clinical pharmacists and physicians involved in the study. This study was supported by Fundação de Apoio ao Desenvolvimento Científico (FADEC).
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Obreli-Neto, P.R., Nobili, A., de Oliveira Baldoni, A. et al. Adverse drug reactions caused by drug–drug interactions in elderly outpatients: a prospective cohort study. Eur J Clin Pharmacol 68, 1667–1676 (2012). https://doi.org/10.1007/s00228-012-1309-3
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DOI: https://doi.org/10.1007/s00228-012-1309-3