Classifications: cholinesterase inhibitor;
Therapeutic: anticholinergic antidote, cholinesterase inhibitor

Prototype: Neostigmine
Pregnancy Category: C


1 mg/mL injection


Physostigmine competes with acetylcholine (ACE) for its binding site on acetylcholinesterase, thereby potentiating action of ACE on the skeletal muscle, GI tract and within the CNS. Chief effect is increasing concentration of acetylcholine at cholinergic transmission sites that prolongs and exaggerates its action.

Therapeutic Effect

Effective in reversing anticholingeric toxicity.


To reverse anticholinergic toxicity.


Asthma; diabetes mellitus; gangrene, cardiovascular disease; mechanical obstruction of intestinal or urogenital tract; peptic ulcer disease; asthma; any vagotonic state; closed angle glaucoma; secondary glaucoma; inflammatory disease of iris or ciliary body; concomitant use with choline esters (e.g., methacholine, bethanechol) or depolarizing neuromuscular blocking agents (e.g., decamethonium, succinylcholine), pregnancy (category C), lactation.

Cautious Use

Epilepsy; parkinsonism; bradycardia; hyperthyroidism; seizure disorders; hypotension.

Route & Dosage

Reversal of Anticholinergic Effects
Adult: IM/IV 0.5–2 mg (IV not faster than 1 mg/min), repeat as needed
Child: IV 0.02 mg/kg/dose, may repeat q5–10min (max: total dose of 2 mg)


  • Give undiluted.
  • Use only clear, colorless solutions. Red-tinted solution indicates oxidation, and such solutions should be discarded.
  • Note: Verify correct rate of IV injection for infants or children with physician.

PREPARE: Direct: Give undiluted.  

ADMINISTER: Direct for Adult: Give slowly at a rate of no more than 1 mg/min. ??Rapid administration and overdosage can cause a cholinergic crisis. Direct for Child: Give 0.5 mg or fraction thereof over at least 1 min. ??Rapid administration and overdosage can cause a cholinergic crisis. 

INCOMPATIBILITIES Solution/additive: Phenytoin, ranitidine. Y-site: Dobutamine.

Adverse Effects (≥1%)

Body as a Whole: Sweating, cholinergic crisis (acute toxicity), hyperactivity, respiratory distress, convulsions. CNS: Restlessness, hallucinations, twitching, tremors, sweating, weakness, ataxia, convulsions, collapse. GI: Nausea, vomiting, epigastric pain, diarrhea, salivation. Urogenital: Involuntary urination or defecation. Special Senses: Miosis, lacrimation, rhinorrhea. Respiratory: Dyspnea, bronchospasm, respiratory paralysis, pulmonary edema. Cardiovascular: Irregular pulse, palpitations, bradycardia, rise in BP.


Drug: Antagonizes effects of echothiophate, isoflurophate.


Absorption: Readily from mucous membranes, muscle, subcutaneous tissue; 10–12% absorbed from GI tract. Onset: 3–8 min IM/IV. Duration: 0.5–5 h IM/IV. Distribution: Crosses blood–brain barrier. Metabolism: In plasma by cholinesterase. Elimination: Small amounts in urine. Half-Life: 15–40 min.

Nursing Implications

Assessment & Drug Effects

  • Monitor vital signs and state of consciousness closely in patients receiving drug for atropine poisoning. Since physostigmine is usually rapidly eliminated, patient can lapse into delirium and coma within 1 to 2 h; repeat doses may be required.
  • Monitor closely for adverse effects related to CNS and for signs of sensitivity to physostigmine. Have atropine sulfate readily available for clinical emergency.
  • Discontinue parenteral or oral drug if following symptoms arise: Excessive salivation, emesis, frequent urination, or diarrhea.
  • Eliminate excessive sweating or nausea with dose reduction.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

© 2006-2022 Last Updated On: 11/26/2022 (0)
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