Influence on the electrocardiogram of rats by antidepressants

The influence of lofepramine on the heart has been studied in anaesthetized rats. Lofepramine and other antidepressants were infused i.v. during 4 h at a rate of 0.5 mg/kg/min for lofepramine (equimolar concentrations for the other antidepressants). ECG and survival time were recorded. It was shown that lofepramine in contrast to the other antidepressants tested did not influence the PQ- and QRS-times at all. The other antidepressants tested increased the PQ-time 20-170% and the QRS-time 40-130%. Only the rats in the lofepramine group survived the whole experiment. The occurrence of multiple arrhythmias was low in this study and the difference between the groups was not striking. In further 13 rats the plasma level of desipramine, the main metabolite of lofepramine, after 200 min of lofepramine and 100-135 min of desipramine infusion was measured. The levels of desipramine at that time were found approximately comparable after infusion of the two different substances.