Short-Term Risk of Unintentional Poisoning After New Initiation of Central Nervous System Medications in Swedish Older Adults: A Register-Based Case-Crossover Study

Introduction Medications acting on the central nervous system (CNS) are common causes of medication-related unintentional poisoning. Little is known about the short-term effects of CNS medications on unintentional poisoning. Objective This study aims to determine the short-term association between newly prescribed CNS drugs and unintentional poisoning. Methods We conducted a register-based case-crossover study of 9354 patients (age ≥ 50 years) with first-time hospitalization for unintentional poisoning in Sweden between 1 July, 2006 and 30 September, 2018. Newly initiated CNS medication was identified based on dispensations from the Swedish Prescribed Drug Register during 28 days prior to the unintentional poisoning event and compared with dispensations during an equally long control period. Conditional logistic regression was used to estimate the odds ratio and 95% confidence intervals. Results After a newly initiated CNS treatment, we found an increased risk of unintentional poisoning during the following 2 weeks with an odds ratio (95%) being 2.52 (1.98–3.21) and 1.47 (1.08–2.00) for the first and second week, respectively. The risk was elevated in all sub-groups but to a different degree with odds ratio ranges of 1.73–2.47 by age, 1.91–2.21 by sex, 1.40–2.30 by Charlson Comorbidity Index, 2.00–2.07 by neuropsychiatric comorbidity, and 1.63–2.82 by number of other medications. Conclusions The risk of unintentional poisoning doubles in 2 weeks following a new initiation of CNS drugs and the risk is increased across a range of population groups. Clinicians should carefully monitor signs of poisoning after such initiation among not only multimorbid older adults but also those with less comorbidity and polypharmacy.