Agents With Antimuscarinic Activity
Contraindicated
Textbook
Their antimuscarinic action is likely to intensify the toxicity of atropine poisoning.
Agents with antimuscarinic activity should not be used in atropine poisoning.
Source: G&G 14e · p218
Drug reference
Atropine
Antimuscarinic agent (non-selective muscarinic receptor antagonist) · Antidysrhythmic, Mydriatic, Antidote, Antispasmodic, Pre-anesthetic
Also known as Atropine Sulfate, Atropisol, Isopto Atropine
START
Check HR (must be <60 for bradycardia indication). Verify no angle-closure glaucoma risk. For bradycardia: 0.5mg IV (not 0.4mg—too low). Minimum effective pediatric dose 0.1mg (lower may cause paradoxical bradycardia).
TYPICAL MAX
3mg total IV for bradycardia (total vagolytic dose). Higher doses used in organophosphate poisoning until atropinization achieved.
STOP IF
Tachycardia >120 bpm, acute angle-closure glaucoma symptoms, urinary retention, severe confusion, hyperthermia.
WATCH
Paradoxical bradycardia can occur with very low doses (<0.1mg IV) due to central vagal stimulation—use minimum 0.5mg IV in adults. In organophosphate poisoning, massive doses may be needed (grams over 24h). Ophthalmic: cycloplegia lasts 7-14 days—warn patients about blurred near vision and photophobia. Elderly: high risk of delirium.
CDSCO approvedHJan AushadhiNPPA price-controlledATC A03BA01
KDIGO 2024 + manufacturer label
- ONSET
- 1min · Onset ~1 min
- PEAK
- 3min · IV peak 2-4 minutes
- t½
- 3h · t½ ~2-4 hours
- DURATION
- 4h · 2-6 hours (cardiac)
EXCRETION
Renal unchanged and metabolites (~60%)
route + CYP
INTERACTIONS
6 major
incl. contraindicated
PREGNANCY
Crosses placenta; may cause fetal tachycardia. Use only if clearly needed. Safe for short-term use.
FDA category + note
Top interactionssee all 12 →
- Agents With Antimuscarinic ActivityContraindicatedTextbookG&G 14e · p218
- PhenothiazinesContraindicatedTextbookG&G 14e · p218
- Anti Che AgentsSevereTextbookG&G 14e · p228, p230, p232
- Potassium CitrateSevereDatabaseDDInter
Available in India
59 branded formulations and 10 fixed-dose combinations. Look up specific brands in the Drugs workspace.
Jan Aushadhi — generic available at GoI pharmacies
Mechanism
Competitive antagonist of acetylcholine at all muscarinic receptor subtypes (M1-M5), blocking parasympathetic effects on smooth muscle, cardiac muscle, exocrine glands, and the eye. Increases heart rate, reduces secretions, dilates pupils, relaxes smooth muscle.
Indications
Symptomatic bradycardia / AV block (emergency)Preoperative reduction of salivary and respiratory secretionsOrganophosphate / nerve agent poisoning (with pralidoxime)Anticholinesterase poisoning (e.g., physostigmine overdose)Irritable bowel syndrome / biliary colic (smooth muscle spasm)Cycloplegic refraction and mydriasis (ophthalmic)COPD and asthma (nebulized—limited use)Antidote for mushroom poisoning (muscarinic type)
Dosing
- Adult
- Bradycardia: 0.5mg IV q3-5min (max 3mg total). Organophosphate poisoning: 1-2mg IV q5-10min until atropinization (tachycardia, dry skin, dilated pupils). Preoperative: 0.5mg IM/SC 30-60 min pre-op. Ophthalmic: 1-2 drops 1% solution BID-TID before exam.
- Pediatric
- Bradycardia: 0.02mg/kg IV (min 0.1mg, max 0.5mg child; max 1mg adolescent), may repeat. Organophosphate: 0.05mg/kg IV q5-10min.
- Renal adjustment
- No adjustment needed (hepatically metabolized).
- Hepatic adjustment
- Use caution in severe hepatic impairment.
- Geriatric
- Increased sensitivity to anticholinergic effects; use lowest effective dose; monitor for confusion and urinary retention.
- Max dose
- 3mg total IV (bradycardia); higher doses in organophosphate poisoning (until atropinization)
Pharmacokinetics
Onset
IV: heart rate increase within 1-3 minutes; IM: 15-30 minutes; Ophthalmic: mydriasis within 30-40 minutes
Peak effect
IV: peak in 2-4 minutes; IM: peak in 30-60 minutes; Ophthalmic: peak in 30-60 minutes
Duration
IV: 2-6 hours for cardiac effects; Ophthalmic: 7-14 days (cycloplegia)
Half-life
~2-4 hours (adults); ~7-8 hours (children); longer in elderly
Bioavailability
~80% (oral); 100% (IV/IM)
Protein binding
~44%
Metabolism
Hepatic via hydrolysis to tropine and tropic acid; some urinary excretion unchanged
Excretion
~50-70% renal (unchanged + metabolites); 30-50% fecal
Contraindications
- Angle-closure glaucoma
- Obstructive GI disease (pyloric stenosis, achalasia, paralytic ileus)
- Obstructive uropathy (BPH with urinary retention)
- Tachycardia
- Myasthenia gravis (except for diagnostic use)
- Hypersensitivity to belladonna alkaloids
Side effects
Common
Dry mouthTachycardiaBlurred vision / mydriasisConstipationUrinary retentionFlushingFever (in children)Drowsiness / confusion (elderly)
Serious
- Acute angle-closure glaucoma
- Ventricular arrhythmias (at high doses)
- Hyperthermia (especially in children)
- Severe confusion / delirium (elderly)
- Ileus / gastric retention
- Anaphylaxis (rare)
Pregnancy & lactation
Pregnancy
Crosses placenta; may cause fetal tachycardia. Use only if clearly needed. Safe for short-term use.
Lactation
Excreted in breast milk in small amounts; may reduce milk production. Use lowest effective dose; monitor infant for anticholinergic effects.
Drug interactions
Phenothiazines
Contraindicated
Textbook
Their antimuscarinic action is likely to intensify the toxicity of atropine poisoning.
Phenothiazines should not be used in atropine poisoning.
Source: G&G 14e · p218
Anti Che Agents
Severe
Textbook
Atropine effectively antagonizes muscarinic symptoms of anti-ChE agent poisoning, such as increased tracheobronchial and salivary secretion, bronchoconstriction, and bradycardia. It can also control muscarinic cardiovascular and GI side effects of anti-ChE agents.
In organophosphate poisoning, atropine should be given in doses sufficient to cross the blood-brain barrier: an initial injection of 2 to 4 mg intravenously (or intramuscularly), followed by 2 mg every 5 to 10 minutes until muscarinic symptoms disappear, reappear, or signs of atropine toxicity occur. However, anticholinergic drugs like atropine can mask many side effects of an excessive dose of an anti-ChE agent.
Source: G&G 14e · p228, p230, p232
Potassium Citrate
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Topiramate
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Zonisamide
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Alprazolam
Moderate
Textbook
If marked excitement is present in atropine poisoning and more specific treatment is not available, benzodiazepines can provide sedation and control convulsions.
A benzodiazepine is the most suitable agent for sedation and control of convulsions.
Source: G&G 14e · p218
Antihistamines
Moderate
Textbook
Increased anticholinergic side effects.
Source: KDT 7e · p121
Chloral Hydrate
Moderate
Textbook
If marked excitement is present in atropine poisoning and more specific treatment is not available, benzodiazepines can provide sedation and control convulsions.
A benzodiazepine is the most suitable agent for sedation and control of convulsions.
Source: G&G 14e · p218
Clomethiazole
Moderate
Textbook
If marked excitement is present in atropine poisoning and more specific treatment is not available, benzodiazepines can provide sedation and control convulsions.
A benzodiazepine is the most suitable agent for sedation and control of convulsions.
Source: G&G 14e · p218
Clonazepam
Moderate
Textbook
If marked excitement is present in atropine poisoning and more specific treatment is not available, benzodiazepines can provide sedation and control convulsions.
A benzodiazepine is the most suitable agent for sedation and control of convulsions.
Source: G&G 14e · p218
Diazepam
Moderate
Textbook
If marked excitement is present in atropine poisoning and more specific treatment is not available, benzodiazepines can provide sedation and control convulsions.
A benzodiazepine is the most suitable agent for sedation and control of convulsions.
Source: G&G 14e · p218
Related guidelines
Ask House about Atropine
Continue into a citation-backed clinical answer with the drug context already attached.
Sources: KD Tripathi 7e, Goodman & Gilman 14e, Harrison 22e, Katzung·Verified: 2026-05-19 · House clinical team·Cockpit curated: 2026-05-19