Factors associated with seizure in tramadol overdose: a 12-year retrospective study in Hong Kong

Abstract

<h2>Background</h2><p>Early identification of patients at risk of seizure after acute tramadol overdose is crucial. Yet, current evidence has been inconclusive regarding the factors associated with the seizure. There is a lack of study on the Chinese population and the value of electrocardiogram (ECG) in risk prognostication has not been fully evaluated.</p><h2>Objectives</h2><p>We aimed 1) to characterise the clinical presentations of isolated tramadol overdose in Hong Kong; 2) to study the frequency of seizure in such overdose and the factors associated with it using multivariable analysis; and 3) to explore the association between individual ECG parameters and seizure.</p><h2>Methods</h2><p>This was a retrospective observational study on consecutive patients reported to the Hong Kong Poison Information Centre for tramadol overdose from 1 January 2008 to 30 November 2020. Duplicate cases or patients with an overdose of other co-ingestants were excluded. Univariate and multivariable logistic regression was performed to identify factors significantly associated with seizures in general and seizures that occurred after emergency department (ED) arrival.</p><h2>Results</h2><p>We identified 93 patients, including 54 women and 39 men, with a median age of 38 years during the study period. The majority was Chinese (90%) and only five patients had a history of seizure. The seizure occurred in 23 patients. Multivariable analysis showed that sinus tachycardia > 100 beats/min was significantly associated with a higher seizure risk (OR 27.95, 95% CI 2.22–351.84, <em>p</em> = 0.010) and age per 10 years increase was associated with a lower risk (OR 0.61; 95% CI 0.39–0.96, <em>p</em> = 0.033). No reliable predictors of seizure after ED arrival were identified. Many patients had ECG features consistent with sodium channel blockade but none of them was predictive of seizure.</p><h2>Conclusions</h2><p>A younger age and sinus tachycardia > 100 beats/min were associated with a higher seizure risk after tramadol overdose but no reliable predictors of seizure after ED arrival were identified. Individual ECG parameters were not predictive of seizure.</p>