Risks of flumazenil in mixed benzodiazepine-tricyclic antidepressant overdose: report of a preliminary study in the dog.

This preliminary study evaluates the cardiac and neurological risks associated with the sudden antagonism of benzodiazepine (BZD)--induced sedation in dogs intoxicated with tricyclic anti-depressants (TCA). Twelve dogs were anesthetized with midazolam and ventilated with room air. EEG, ECG, and arterial pressure were continuously recorded. An infusion of amitriptyline (6 dogs) or clomipramine (6 dogs) 1 mg/kg. min was maintained until signs of cardiotoxicity (QRS prolongation, hypotension or arrhythmias) occurred. The effects of a bolus of flumazenil 0.2 mg/kg were then observed until 120 minutes. In amitriptyline poisoning, BZD reversal was associated with development of convulsions in 3 dogs, with severe arrhythmias in 4 and with one death. In clomipramine intoxication, 2 dogs developed sudden fatal arrhythmias. These results show that BZD reversal may unmask the convulsant properties and increase the severity of arrhythmias induced by TCA.