PHYSOSTIGMINE SALICYLATE
(fi-zoe-stig'meen)
Antilirium
Classifications: autonomic nervous system agent; cholinergic (parasympathomimetic); cholinesterase inhibitor
Prototype: Neostigmine
Pregnancy Category: C

Availability

1 mg/mL injection

Actions

Reversible anticholinesterase and tertiary amine. Chief effect is increasing concentration of acetylcholine at cholinergic transmission sites which prolongs and exaggerates its action.

Therapeutic Effects

Similar to neostigmine in actions and adverse effects, but produces greater secretion of glands, constriction of pupils, and effect on BP and less action on skeletal muscle. Also has direct blocking action on autonomic ganglia. Parenteral physostigmine can produce transient decrease in manic symptoms as well as precipitate mental depression.

Uses

To reverse CNS and cardiac effects of tricyclic antidepressant overdose, to reverse CNS toxic effects of atropine, scopolamine, and similar anticholinergic drugs, and to antagonize CNS depressant effects of diazepam. Orphan Drug: For hereditary ataxias.

Contraindications

Asthma; diabetes mellitus; gangrene, cardiovascular disease; mechanical obstruction of intestinal or urogenital tract; any vagotonic state; 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). Safety during pregnancy (category C) or lactation is not established.

Cautious Use

Epilepsy; Parkinsonism; bradycardia; hyperthyroidism; peptic ulcer; hypotension.

Route & Dosage

Reversal of Anticholinergic Effects
Adult: IM/IV 0.5–3 mg (IV not faster than 1 mg/min), repeat as needed
Child: IV 0.01–0.03 mg/kg, may repeat q15–20 min (max: total dose of 2 mg)

Administration

Intramuscular/Intravenous

Give undiluted.
Use only clear, colorless solutions. Red-tinted solution indicates oxidation, and such solutions should be discarded.

Intravenous

Note: Verify correct rate of IV injection for infants or children with physician.

PREPARE: Direct: Give undiluted.

ADMINISTER: Direct: Give at a slow rate, no more than 1 mg/min. Rapid administration and overdosage can cause a cholinergic crisis.

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, palpitation, bradycardia, rise in BP.

Interactions

Drug: Antagonizes effects of echothiophate, isoflurophate.

Pharmacokinetics

Absorption: Readily absorbed 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: Metabolized in plasma by cholinesterase. Elimination: Excretion not fully understood; small amounts excreted 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