When administering physostigmine, atropine should be present at the bedside with airway equipment readily available as cholinergic effects may develop (specifically bronchospasm, bronchorrhea, or bradycardia). Dosing of physostigmine in adult patients is 1 to 2 mg via slow intravenous (IV) push, in aliquots of 0.2 to 0.3 mg each, over 5 minutes; pediatric dosing is 20 mcg/kg to maximum 0.5 mg. Onset of effects can be expected within minutes of administration.3 Since the duration of physostigmine is less than that of many anticholinergic drugs, recurrence of anticholinergic effects should be anticipated.
Historically, physostigmine was included in the “coma cocktail,” along with thiamine, dextrose, and naloxone for treating undifferentiated patients with altered level of consciousness. Concern for its ubiquitous use arose following reports of asystole in two patients who presented with tricyclic antidepressant (TCA) overdose, although these patients actually had more complicated multidrug overdoses.4 Nevertheless, an ECG should be performed in all patients for whom physostigmine is being considered, and it should not be administered (or perhaps only extremely cautiously) if the ECG demonstrates a QRS complex duration >100 ms.3 Relative contraindications include reactive airways disease, peripheral vascular disease, or intestinal or bladder-outlet obstruction.
Prolongation of the QRS interval is not always indicative of TCA ingestion as certain other antimuscarinic drugs, such as diphenhydramine, may cause sodium-channel blockade. Based on extrapolation from TCA literature,5 if the QRS >100 ms, a bolus of 1 to 2 mEq/kg sodium bicarbonate should be given with monitoring of the QRS interval for narrowing.
Case conclusion
The clinicians at the bedside felt that the infant’s presentation was consistent with anticholinergic toxicity. Physostigmine was administered by slow IV push for a total dose of 1.5 mg. The patient had immediate improvement of symptoms, including decreased skin redness, decreased agitation, and improved vital signs (BP, 118/80 mm Hg and HR, 160 beats/minute). He was admitted to the pediatric intensive care unit for monitoring and was subsequently discharged home with complete symptom resolution 2 days later.