Tramadol overdose as a cause of serotonin syndrome: a case series

Tramadol overdose impairs consciousness and may induce ECG changes and convulsions. These effects may be opioid and/or serotonin related. This study describes clinical manifestations, electrophysiological and hemodynamic findings, and the frequency of potential serotonin syndrome in tramadol overdose in a case series. It also focuses on potential factors by which convulsions could be predicted.

This is a prospective observational case series. All cases admitted with suspected tramadol overdose from September 1, 2006 to August 31, 2007 were included.

Tramadol overdose accounted for 1.2% of all poisonings (n = 158), of which 65% were tramadol only. It was predominantly male (63%). Mean (SD) age was 22.6 (7.4) years. Among these cases, 24 (15%) experienced seizure and in 10 (6%) cases creatine phosphokinase increased. Death occurred in one patient. Seizure occurred more frequently in patients with tramadol use only [odds ratio 3.0, 95% confidence interval 1.1, 8.4] and mydriasis (odds ratio 8.9, 95% confidence interval 1.9, 42.4) on admission. Eight cases were treated for potential serotonin syndrome. Concurrent intoxication with central nervous system depressants, age, alleged dose, consciousness level, respiratory rate, history of drug abuse, and naloxone administration was not associated with the occurrence of seizures.

In tramadol overdose, mydriasis or tachycardia appears to indicate a higher risk for seizure. Management may need to be focused on both mu-opioid agonism and potential mild serotonin syndrome.