Incidence and Predictors of Adverse Drug Reactions Caused by Drug-Drug Interactions in Elderly Outpatients: A Prospective Cohort Study

Abstract

Purpose. The primary objective of this study was to investigate the incidence of drug-drug interactions (DDIs) related to adverse drug reactions (ADRs) in elderly outpatients who attended public primary healthcare units in a southeastern region of Brazil. The secondary objective was to investigate the possible predictors of DDI-related ADRs. Methods. A prospective cohort study was conducted between November 1, 2010, and November 31, 2011, in the primary public healthcare system in the Ourinhos micro-region in Brazil. Patients who were at least 60 years old, with at least one potential DDI, were eligible for inclusion in the study. Eligible patients were assessed by clinical pharmacists for DDI-related ADRs for 4 months. The causality of DDI-related ADRs was assessed independently by four clinicians using three decisional algorithms. The incidence of DDI-related ADRs during the study period was calculated. Logistic regression analysis was used to study DDI-related ADR predictors. Results. A total of 433 patients completed the study. The incidence of DDI-related ADRs was 6.5%. A multivariate analysis indicated that the adjusted odds ratios (ORs) rose from 0.91 (95% confidence interval [CI] = 0.75-1.12, p = 0.06) in patients aged 65-69 years to 4.40 (95% CI = 3.00-6.12, p < 0.01) in patients aged 80 years or older. Patients who presented two to three diagnosed diseases presented lower adjusted ORs (OR = 0.93 [95% CI = 0.68-1.18, p = 0.08]) than patients who presented six or more diseases (OR = 1.12 [95% CI = 1.02-2.01, p < 0.01]). Elderly patients who took five or more drugs had a significantly higher risk of DDI-related ADRs (OR = 2.72 [95% CI = 1.92-3.12, p < 0.01]) than patients who took three to four drugs (OR = 0.93 [95% CI = 0.74-1.11, p = 0.06]). No significant difference was found with regard to sex (OR = 1.08 [95% CI 0.48-2.02, p = 0.44]). Conclusion. The incidence of DDI-related ADRs in elderly outpatients was significant, and most of the events presented important clinical consequences. Because clinicians still have difficulty managing this problem, highlighting the factors that increase the risk of DDI-related ADRs is essential. Polypharmacy was found to be a significant predictor of DDI-related ADRs in our sample.
 
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Drug-drug interactions and adverse drug reactions in polypharmacy among older adults: an integrative review

“…Of the 47 records resulting from the search strategies, 24 (51.1%) full-text articles were retrieved for review concerning ADR 11 - 18 , 20 , 24 - 25 , 28 - 29 , 34 - 36 , 38 - 40 , 46 , 51 - 52 , 54 , 56 ) , 14 (29.8%) DDI 21 - 23 , 27 , 30 - 33 , 41 , 43 - 45 , 49 , 53 and nine (19.1%) are related to both DDI and ADR 19 , 26 , 37 , 42 , 47 - 48 , 50 , 55 , 57 , according to Figures 2 and 3.…”

Polypharmacy and potential drug–drug interactions in emergency department patients in the Caribbean

“…The prevalence of DDI was estimated from studies from similar (low-and-middle-income country) settings as in Trinidad. It is not clear whether prescribing and health-seeking behaviours would have been similar in these populations, but we considered these setting the best approximation to what was likely to be found in our study [ 3 , 11 ].…”

“…Al-Olah in Saudi Arabia further concluded that 83% of the adverse drug effects seen in Emergency Department patients were avoidable [ 2 ]. While the demographics of some of these countries, such as Brazil, may be similar to that seen in the West Indies, it is unclear whether health behaviour and prescribing are comparable [ 1 , 3 ].…”

“…Polypharmacy has been identified as the single most important risk factor for DDI [ 3 ]. There is no universally agreed definition of polypharmacy, but many researchers describe it as the concurrent use of 5 or more medications [ 4 ].…”

Analysis of drug interactions at the end of life

“…Previous research has shown that patients at the end of life are taking, on average, five medications, the number increasing as death approaches2 with symptom-specific medication accounting for 49% 3. The number of different medications taken is the strongest risk factor for symptomatic DDIs 4 5. For example, a recent study in regional Australia of patients being admitted to a palliative care centre showed that over one-fifth were still taking a lipid-lowering medication 6.…”