Timing and frequency of physostigmine redosing for antimuscarinic toxicity

Abstract

We sought to determine how frequently antimuscarinic-poisoned patients receiving physostigmine receive multiple doses of physostigmine, the length of time between physostigmine doses, and what impact multiple doses of physostigmine have on the disposition and total length of hospital stay. We performed a retrospective chart review of patients given physostigmine for likely antimuscarinic toxicity. A total of 45 patients met inclusion criteria. We abstracted patient demographics, vital signs, physical exam findings, electrocardiograms, the timing and dose of physostigmine, the implicated antimuscarinic agents, and disposition from the hospital. We counted the number of patients who required multiple physostigmine doses and calculated the time to repeat dosing. Fourteen of the 45 patients (31%) given physostigmine for antimuscarinic toxicity received multiple doses: nine patients (20%) received two doses, three patients (6.6%) received three doses, and two patients (4.4%) received four doses. Less than 5.5 h elapsed between sequential physostigmine doses, and less than 6.5 h elapsed between the first and last dose. Forty-five percent of patients receiving one dose of physostigmine were discharged from the emergency department (ED) and 36% of patients receiving more than one dose of physostigmine were discharged from the ED. Whether admitted or discharged, there was no statistically significant difference in the length of hospital stay between patients receiving one or multiple doses of physostigmine. Repeated physostigmine administration is not frequently needed in medication-induced antimuscarinic toxicity. Patients are not likely to require further physostigmine redosing more than 6.5 h from their first dose.

Fig. 1

Selection of participants

Fig. 2

Time (h) between physostigmine doses when more than one dose of physostigmine given. Small vertical line indicates interval between first and second dose, n = 4; triangle indicates interval between second and third dose, n = 5; inverted triangle indicates interval between third and fourth dose, n = 2

Fig. 3

Time (h) between first and last dose of physostigmine when more than one dose of physostigmine given. Small vertical line indicates first to second (max = 2 doses), n = 9; triangle indicates first to third (max = 3 doses), n = 3; filled circle indicates first to fourth (max = 4 doses), n = 2

Fig. 4

Time (days) to discharge from first dose of physostigmine. Unfilled circle indicates one dose given, admitted, n = 16; inverted triangle indicates one dose given, discharged, n = 14; filled circle indicates one dose given, admitted, n = 9; filled inverted triangle indicates more than one dose given, discharged, n = 5