Rivastigmine to Prevent Recurrence of Antimuscarinic Delirium

Antimuscarinic delirium (AMD) is a common and dangerous toxicology condition caused by poisoning by medications and other chemicals that block muscarinic receptors. Physostigmine is effective in reversing AMD but has a short duration of action, and patient commonly experience recurrence of AMD after initial control with physostigmine. Recent case reports and small observational studies suggest that rivastigmine, which has a longer duration of action than physostigmine, might be useful in the treatment of AMD. In order to investigate the effectiveness of rivastigmine in preventing recurrence of AMD after initial control with physostigmine, the investigators propose a randomized, placebo-controlled clinical trial of rivastigmine for AMD. The investigators hypothesize that patients treated with rivastigmine after initial control of AMD with physostigmine will experience less recurrence of antimuscarinic delirium than those treated with placebo.

Inclusion Criteria: * 10 years of age or older * Diagnosis of antimuscarinic delirium by history and physical examination, in the opinion of the treating attending toxicologist. * Treatment with physostigmine according to the local standard of care is planned or has been administered by the treating attending toxicologist and is acceptable to the patient's primary attending physician and surrogate decision maker. * Antimuscarinic delirium is reasonably controlled after initial physostigmine treatment, as determined by treating toxicologist on bedside physical examination. (Patients may begin the screening and enrollment process prior to physostigmine administration, but will not undergo final initiation of study treatment until after response to physostigmine has been confirmed). Exclusion Criteria: * Age less than 10 years at time of enrollment * Surrogate decision maker not available to provide informed consent for enrollment. * Patient is pregnant or a ward of the state. * Inability to safely tolerate oral medication, in the judgement of the treating attending physician. * Evidence of significant risk for serious cardiac or neurologic sequelae of antimuscarinic poisoning: a. Any known or suspected seizure activity prior to enrollment b. QRS duration \>100 milliseconds on EKG at enrollment c. Any ventricular dysrhythmia prior to enrollment d. Respiratory failure of any etiology requiring endotracheal intubation e. Any hypotension at enrollment: i. Adults: systolic blood pressure (SBP) \