This study examines the relation between seizure and plasma
tramadol concentration in patients with
tramadol poisoning, as a novel centrally acting
analgesic used for the treatment of mild to severe
pain. All patients admitted with a history of
tramadol overdose accompanied by unconsciousness or
seizures referred to Baharloo Hospital
Poison Center, Tehran, Iran from March 2008 to March 2009 were included. Demographic information, clinical findings, and blood
tramadol concentrations were studied. There were 401 patients with a history of
tramadol overdose; 121 (30.2%) with a history of seizure and 14 (3.5%) with a history of unconsciousness were included. Most of overdoses involved men (83%). The mean age was 22.9 years (range, 14-50 years). Intentional overdose was the most common mode of
poisoning (51.9%). The mean dose ingested was 1,511 mg (SD, 1,353; range, 200-7,000). Mean back-extrapolated
tramadol blood concentrations were 3,843 ng/mL (3,715; 269-20,049). Back-extrapolated blood concentrations were correlated with dose (r = 0.313; P < 0.001) as well as blood concentration levels (r = 0.801; P < 0.001). Seizure was significantly correlated to higher reported dose (P < 0.001) and
tramadol only to overdose (P < 0.001). However, it was neither related to higher
tramadol blood concentrations, nor related to time elapsed, age, sex, history of addiction, and observed Glasgow Coma Scale of patients. Most patients experienced just one seizure (76%). The
tramadol-induced seizure is dose dependent. Although higher doses of
tramadol was related to higher blood concentration, blood
tramadol concentrations was not associated with seizure.