Amiodarone, a class III antidysrhythmic agent, blocks Na+, Ca2+, and K+ channels as well as the beta-adrenergic receptor. Despite increased use of amiodarone for wide-complex tachycardia, its efficacy in the treatment of dysrhythmias induced by tricyclic antidepressants has not been tested. We investigated the effect of amiodarone and amitriptyline in a mouse lethality model.
The LD50 of amitriptyline obtained from reference sources was confirmed by giving 100 mg/kg to 40 mice by intraperitoneal (IP) injection. The safety of the treatment dose of amiodarone was confirmed by giving 50 mg/kg by IP injection to 10 mice. One hundred and nine mice were randomized to receive pretreatment with 50 mg/kg amiodarone (n=55) or an equal volume of saline or water as a volume control (n=54). Thirty minutes after pretreatment or control injection, the mice received amitriptyline, 100 mg/kg. Outcome was defined as death or survival 3 h after amitriptyline injection.
In our confirmation of the LD50 of amitriptyline, 25/40 mice died (62.5%). None of the 10 mice that received only amiodarone died. In the control + amitriptyline arm, 36/54 (66.7%) died, compared with 39/55 (70.9%) in the amiodarone+amitriptyline arm (X2, p=0.663). Power analysis demonstrated a 90% chance of finding a 28% difference.
Pretreatment with amiodarone does not appear to significantly alter the lethality of amitriptyline poisoning in mice. Given the inability to monitor cardiac activity in this model, further investigation in a larger animal is required.