Antihistaminics
Severe
Textbook
Partial antagonism of overdose symptoms and coma; however, it may worsen the fall in BP and arrhythmias.
Use is risky.
Source: KDT 7e · p110
Drug reference
physostigmine
Anticholinesterase agent · Anticholinesterase
Anticholinesterase agentAnticholinesterase
CDSCO approved
EXCRETION
—
not curated
INTERACTIONS
8 major
SEVERE in our sources
PREGNANCY
—
not curated
Top interactionssee all 12 →
- AntihistaminicsSevereTextbookKDT 7e · p110
- MirtazapineSevereTextbookKDT 7e · p110
- PhenothiazinesSevereTextbookKDT 7e · p110
- BupropionSevereDatabaseDDInter
Mechanism
Inhibits cholinesterase, thus increasing acetylcholine levels to counteract muscarinic antagonist effects.
Indications
Treatment of atropine poisoning (intravenous injection) to rapidly abolish delirium and comaConfirmation of atropine or related agent intoxicationglaucoma (as miotic, to supplement pilocarpine)belladonna poisoningpoisoning by other anticholinergicsoverdose of tricyclic antidepressants (partial antagonism of anticholinergic property)overdose of phenothiazines (partial antagonism of anticholinergic property)overdose of antihistaminics (partial antagonism of anticholinergic property)CNS depression (modest nonspecific arousal effect, rarely warranted)
Dosing
- Adult
- Intravenous injection; repeated doses may be needed due to rapid metabolism
Pharmacokinetics
Half-life
2-3 hours (destroyed by plasma esterases)
Metabolism
Metabolized rapidly
Excretion
Parentarally administered physostigmine is largely destroyed within 2 to 3 h, mainly by hydrolytic cleavage by plasma esterases.
Side effects
Serious
- Risk of overdose in mild atropine intoxication
- hypotension
- arrhythmias
- undesirable central effects
Drug interactions
Mirtazapine
Severe
Textbook
Partial antagonism of overdose symptoms and coma; however, it may worsen the fall in BP and arrhythmias.
Use is risky.
Source: KDT 7e · p110
Phenothiazines
Severe
Textbook
Partial antagonism of overdose symptoms and coma; however, it may worsen the fall in BP and arrhythmias.
Use is risky.
Source: KDT 7e · p110
Bupropion
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Iohexol
Severe
Database
Clinical effect not specified
Source: DDInter
Iopamidol
Severe
Database
Clinical effect not specified
Source: DDInter
Siponimod
Severe
Database
Clinical effect not specified
Source: DDInter
Tramadol
Severe
Database
Clinical effect not specified
Source: DDInter
Acetylcholine
Moderate
Textbook
Potentiation of acetylcholine's action.
Source: KDT 7e · p57
Anticholinergic Drugs
Moderate
Textbook
Physostigmine is potentially useful in reversing the central anticholinergic syndrome produced by overdosage or an unusual reaction to these drugs, thereby mitigating anticholinergic side effects.
While effective in reversing anticholinergic side effects, the use of physostigmine must be weighed against potential risks, as it may precipitate seizures. It does not reverse other toxic effects of tricyclic antidepressants and phenothiazines, such as intraventricular conduction deficits and ventricular arrhythmias.
Source: G&G 14e · p231
Amitriptyline
Moderate
Database
Partial antagonism of overdose symptoms and coma; however, it may worsen the fall in BP and arrhythmias.
Use is risky.
Source: DDInter
Amoxapine
Moderate
Database
Partial antagonism of overdose symptoms and coma; however, it may worsen the fall in BP and arrhythmias.
Use is risky.
Source: DDInter
Related guidelines
Ask House about physostigmine
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Sources: KD Tripathi 7e, Goodman & Gilman 14e·Verified: 2026-05-10 · House clinical team