Dosage / Administration

Adult: 1-2 mg intravenous (IV). Re-dose in 10-15 minutes as needed.

Pediatric: 0.02 mg/kg (0.5 mg/dose maximum). Re-dose in 10-15 minutes as needed.

Pregnancy category C. Lactation safety has not been established.

• Physostigmine may cause bradycardia and vomiting. Have atropine and an antiemetic ready by the bedside.
• Put the patient on a monitor before administering the medication.
• Medication should be administered slowly over at least 5 minutes.

Indications
Physostigmine is a tertiary amine that serves as a diagnostic tool and treatment for anticholinergic toxicity, such as an antihistamine overdose and Jimson weed abuse.

Common anticholinergic signs / symptoms include mydriasis, dry skin, tachycardia, delirium, hyperthermia, and urinary retention.

Hypersalivation, nausea / vomiting, diaphoresis, abdominal cramps, seizure, and cardiac arrhythmia are some of the common expected adverse effects from physostigmine. See below for adverse events listed by system for more details.

Safety guidelines: Put the patient on a monitor, and have atropine and an antiemetic by the bedside prior to administering physostigmine.

Mandatory restrictions: Physostigmine should not be used in the setting of tricyclic antidepressant overdose.

Contraindications
Do not administer to patients taking cyclic antidepressants or phenothiazines.

Other contraindications include:

• Gastrointestinal or genitourinary obstruction.
• Reactive airway disease.
• Peripheral vascular disease.
• Cardiac conduction diseases such as atrioventricular block and intraventricular conduction defects.

Monitoring
While administering physostigmine, the patient should be on a cardiac monitor. Keep atropine by the bedside.

Adverse Effects

• Central nervous system: agitation
• Cardiac: bradycardia, hypotension, cardiac arrest
• Gastrointestinal: vomiting, diarrhea

Adverse effects of cholinergic syndrome induced by physostigmine include:

• Abdominal cramps.
• Arrhythmia.
• Agitation.
• Bradycardia.
• Cardiac arrest.
• Diaphoresis.
• Diarrhea.
• Emesis.
• Hypersalivation.
• Nightmares.
• Restless sleep.

Toxicity
Atropine can be used for physostigmine toxicity.

Physostigmine can cause fatal cardiac toxicity (severe bradycardia and asystole) in the setting of tricyclic antidepressant overdose.

Mechanism of Action
Physostigmine reversibly inhibits cholinesterases in both the central and peripheral nervous systems. The bioavailability of physostigmine is very low (less than 5%-12%).

Physostigmine is metabolized by the liver and a very small percentage of it is excreted in the urine.