Anticholinergic Toxidrome

A patient who is agitated, tachycardic, flushed and hyperthermic after taking an unknown medication may look like they have a primary psychiatric crisis or a sympathomimetic overdose. The clues that redirect the assessment are markedly dilated pupils, dry skin, reduced bowel activity, urinary retention and delirium. Antimuscarinic blockade explains the whole pattern: secretions and smooth-muscle activity fall, pupils cannot constrict, vagal slowing of the heart is lost, and central receptor blockade disrupts cognition. The immediate danger is not only delirium. Some agents, especially diphenhydramine and tricyclic antidepressants, also block cardiac fast sodium channels. Obtain the ECG early; it helps determine both the level of cardiac risk and whether physostigmine could cause harm. In Canada, consult the regional poison centre before considering physostigmine because the antidote may require Special Access Programme authorization or may not be stocked locally.