A 40-year-old man is brought by his friends to you. Apparently, he has ingested some unknown medication. Patient is disoriented. His temperature is 103°F, BP 120/85, pulse 100/min, and respirations 221min. The skin is flushed and dry. Has dilated pupils and muscle twitching. ECG reveals prolonged QRS complexes. Hepatic transaminases are normal, and ABG shows a normal pH. These findings are most likely due to intoxication by which of the following substances?

This patient's clinical picture is consistent with intoxication with tricyclic antidepressants such as amitriptyline and imipramine. Toxic effects 'are mediated by peripheral anticholinergic activity and "quinidine-like" action. The anticholinergic effects include mydriasis, tachycardia, impaired sweating with flushed skin. dry mouth, constipation, and muscle twitching. Quinidine-like effects (due to block of sodium channels in. the heart) result in cardiac arrhythmias, especially ventricular tachyarrhythrnias, In this setting, prolongation of the QRS complex is particularly important in the diagnosis. QRS width is, in fact. an even more faithful parameter of drug toxicity than serum drug levels. In severe intoxication, patients will develop seizures, severe hypotension, and coma.