Atropine Sulfate

dl-hyoscyamine (racemic mixture of d-hyoscyamine and l-hyoscyamine)

Anticholinergic / AntimuscarinicIVIMSCPOIOIntratracheal (IT)InhalationDogsCatsSmall MammalsFerretsBirdsReptilesHorsesCattleSwineSheepGoats

Also known as: Atroject · Atropine SA · Atropine L.A. · AtroPen · Sal-Tropine · dl-hyoscyamine · atrop. sulph. · atropine sulphate · atropini sulfas

Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference

0.01-0.02 mg/kgIM, IV· once

Body weight— 🐕

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

Dosing by species

🌎 NA — North America🌍 EU — Europe

Dogs

Indication	Dose	Route	Frequency	Duration	Region
As a preanesthetic adjuvant (geriatric patients)	0.01-0.02 mg/kg	IM, IV	once	—	🌎 NA
As a preanesthetic adjuvant	0.074 mg/kg	IV, IM or SC	once	—	🌎 NA
As a preanesthetic adjuvant	0.02-0.04 mg/kg	SC, IM or IV	once	—	🌎 NA
During cardiopulmonary cerebral resuscitation (CPCR) efforts	0.04 mg/kg (IV or IO); 0.08-0.1 mg/kg (IT)	IV, IO, IT	every 3-5 minutes	maximum of 3 doses	🌎 NA
Adjunctive treatment of bradycardias, Incomplete AV block, etc.	0.02-0.04 mg/kg	IV or IM	as needed	—	🌎 NA
Atropine Response Test (Rishniw Preference)	0.04 mg/kg	IV	once	—	🌎 NA
Atropine Response Test (Kittleson Preference)	0.04 mg/kg	SQ	once	—	🌎 NA
Treatment of cholinergic toxicity	0.2-0.5 mg/kg	IV, IM, SC	as needed	—	🌎 NA
Treatment of bronchoconstriction	0.02-0.04 mg/kg	parenteral	as needed	duration of effect 1-1.5 hours	🌎 NA

As a preanesthetic adjuvant (geriatric patients): Do not use anticholinergics indiscriminately in geriatric patients.
During cardiopulmonary cerebral resuscitation (CPCR) efforts: For IT administration: dilute in 5-10 mL of sterile water before administering.
Atropine Response Test (Rishniw Preference): Wait 15 minutes, record ECG. Persistent sinus tachycardia at >140 bpm expected in vagally-mediated bradycardia.
Atropine Response Test (Kittleson Preference): Wait 30 minutes, record ECG. Persistent sinus tachycardia at >140 bpm expected in vagally-mediated bradycardia.
Treatment of cholinergic toxicity: 1/4 of the dose IV and the remainder IM or SC

Cats

Indication	Dose	Route	Frequency	Duration	Region
As a preanesthetic adjuvant (geriatric patients)	0.01-0.02 mg/kg	IM, IV	once	—	🌎 NA
As a preanesthetic adjuvant	0.074 mg/kg	IV, IM or SC	once	—	🌎 NA
As a preanesthetic adjuvant	0.02-0.04 mg/kg	SC, IM or IV	once	—	🌎 NA
During cardiopulmonary cerebral resuscitation (CPCR) efforts	0.04 mg/kg (IV or IO); 0.08-0.1 mg/kg (IT)	IV, IO, IT	every 3-5 minutes	maximum of 3 doses	🌎 NA
Treatment of bradycardias	0.02-0.04 mg/kg	SC, IM or IV	q4-6h	—	🌎 NA
Treatment of cholinergic toxicity	0.2-2 mg/kg	IV, SC, IM	as needed	—	🌎 NA

As a preanesthetic adjuvant (geriatric patients): Do not use anticholinergics indiscriminately in geriatric patients.
During cardiopulmonary cerebral resuscitation (CPCR) efforts: For IT administration: dilute in 5-10 mL of sterile water before administering.
Treatment of cholinergic toxicity: give 1/4th of the dose IV and the remainder SC or IM

Small Mammals

Indication	Dose	Route	Frequency	Duration	Region
To treat organophosphate toxicity (Rabbits/Rodents)	10 mg/kg	SC	q20 minutes	—	🌎 NA

Ferrets

Indication	Dose	Route	Frequency	Duration	Region
As a premed	0.05 mg/kg	SC or IM	once	—	🌎 NA

Birds

Indication	Dose	Route	Frequency	Duration	Region
Organophosphate poisoning	0.2 mg/kg	IM	every 3-4 hours as needed	—	🌎 NA
To assist in diagnosing organophosphate poisoning	0.02 mg/kg	IV	once	—	🌎 NA
As a preanesthetic	0.04-0.1 mg/kg	IM or SC	once	—	🌎 NA

Organophosphate poisoning: 1/4th the initial dose is administered. Use with pralidoxime (not in raptors) at 10-20 mg/kg IM q8-12h as needed.
To assist in diagnosing organophosphate poisoning: If bradycardia does not reverse, may consider organophosphate toxicity.

Reptiles

Indication	Dose	Route	Frequency	Duration	Region
Organophosphate toxicity in most species	0.1-0.2 mg/kg	SC or IM	as needed	—	🌎 NA
Ptyalism in tortoises	0.05 mg/kg (50 micrograms/kg)	SC or IM	once daily	—	🌎 NA

Horses

Indication	Dose	Route	Frequency	Duration	Region
Treatment of bradyarrhythmias due to increased parasympathetic tone	0.01-0.02 mg/kg	IV	as needed	—	🌎 NA
Treatment of bradyarrhythmias due to increased parasympathetic tone	0.045 mg/kg	parenterally	as needed	—	🌎 NA
As a bronchodilator	5 mg	IV	once	—	🌎 NA
As a bronchodilator (rescue medication for severe airway obstruction)	5-7 mg/kg	IV	single rescue dose	—	🌎 NA
Organophosphate poisoning	Approximately 1 mg/kg	IV, SC	may repeat every 1.5-2 hours as required subcutaneously	—	🌎 NA
Organophosphate poisoning	0.22 mg/kg	IV, SC, IM	as needed	—	🌎 NA

As a bronchodilator: for a 400-500 kg animal
As a bronchodilator (rescue medication for severe airway obstruction): for a 450 kg horse. Abbreviated duration (0.5-2 hours). Adverse effects limit use to a single rescue dose.
Organophosphate poisoning: given to effect, IV (use mydriasis and absence of salivation as therapy endpoints)
Organophosphate poisoning: 1/4th of the dose administered IV and the remainder SC or IM

Cattle

Indication	Dose	Route	Frequency	Duration	Region
As a preanesthetic	0.06-0.12 mg/kg	IM	once	—	🌎 NA
Adjunctive treatment of bovine hypersensitivity disease	1 gram per cow once daily followed by 0.5 gram/cow in 2-3 days	not specified	once daily then in 2-3 days	2-3 days	🌎 NA
Treatment of cholinergic toxicity (organophosphates)	0.5 mg/kg (average dose)	IV, SC, IM	may repeat q3-4h	1-2 days	🌎 NA

As a preanesthetic: Not used routinely as a preoperative agent in ruminants due to lack of extended efficacy and potential adverse reactions.
Treatment of cholinergic toxicity (organophosphates): give 1/4th of the dose IV and the remainder SC or IM

Swine

Indication	Dose	Route	Frequency	Duration	Region
Organophosphate toxicity	Use equine dose	IV, SC, IM	as needed	—	🌎 NA
As an adjunctive preanesthetic agent	0.04 mg/kg	IM	once	—	🌎 NA

Sheep

Indication	Dose	Route	Frequency	Duration	Region
Treating organophosphate toxicity	Use the dose for cattle	IV, SC, IM	as needed	—	🌎 NA

Goats

Indication	Dose	Route	Frequency	Duration	Region
Treating organophosphate toxicity	Use the dose for cattle	IV, SC, IM	as needed	—	🌎 NA

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

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Overview

Atropine sulfate is a naturally occurring belladonna alkaloid and the prototype antimuscarinic (anticholinergic) agent used extensively in veterinary medicine.

Key clinical applications include:

Emergency Medicine & CPCR: Treatment of hemodynamically significant sinus bradycardia, sinoatrial arrest, and incomplete AV block.
Anesthesia: Used as a preanesthetic to prevent or reduce respiratory and salivary secretions, and to mitigate vagally-mediated bradycardia.
Toxicology: Serves as a life-saving antidote for overdoses of cholinergic agents, including organophosphates, carbamates, muscarinic mushrooms, and blue-green algae intoxication.
Respiratory: Adjunctive treatment for bronchoconstrictive disease.

Clinical Pearl: While highly effective, atropine's use is declining in routine premedication protocols in favor of targeted use or alternatives like glycopyrrolate, which does not cross the blood-brain barrier as readily and has a longer duration of action.

Mechanism of action

Atropine acts as a competitive, reversible antagonist at muscarinic acetylcholine receptors (mAChRs) (M1-M5 subtypes) located at postganglionic parasympathetic neuroeffector sites.

By blocking acetylcholine (ACh) binding, it inhibits parasympathetic tone:

Cardiovascular: Blocks vagal tone at the SA and AV nodes → increases heart rate (positive chronotropy) and improves AV conduction (positive dromotropy).
Secretions: Inhibits glandular M3 receptors → decreases salivary, bronchial, and gastric secretions.
Smooth Muscle: Relaxes smooth muscle in the GI, urinary, and biliary tracts → decreases motility and spasm.
Ocular: Blocks M3 receptors in the pupillary sphincter and ciliary muscle → causes pupillary dilation (mydriasis) and paralysis of accommodation (cycloplegia).

Mechanistic Note: At very low doses, atropine can cause a paradoxical, transient bradycardia due to the blockade of presynaptic M1 autoreceptors on vagal postganglionic fibers, which normally inhibit ACh release. High doses may also block nicotinic receptors at autonomic ganglia and the neuromuscular junction.

Safety & warnings

Contraindications

Narrow-angle glaucoma
Synechiae (adhesions) between the iris and lens
Hypersensitivity to anticholinergic drugs
Tachycardias secondary to thyrotoxicosis or cardiac insufficiency
Myocardial ischemia
Unstable cardiac status during acute hemorrhage
GI obstructive disease or paralytic ileus
Severe ulcerative colitis
Obstructive uropathy
Myasthenia gravis (unless used to reverse adverse muscarinic effects secondary to therapy)

Adverse effects

Dry mouth (xerostomia)
Dysphagia
Constipation
Vomiting
Thirst
Urinary retention or hesitancy
CNS stimulation, drowsiness, ataxia, seizures, respiratory depression
Blurred vision, pupil dilation (mydriasis), cycloplegia, photophobia
Sinus tachycardia (at higher doses)
Paradoxical bradycardia (initially or at very low doses)
Hypertension or hypotension
Arrhythmias (ectopic complexes)
Decreased gut motility (can induce colic in horses or rumen stasis in cattle)

Precautions

General Precautions:

Use with extreme caution in patients with known or suspected GI infections; decreased motility can prolong retention of causative agents or toxins.
Use with extreme caution in patients with autonomic neuropathy.
Use cautiously in patients with hepatic or renal disease, geriatric or pediatric patients, hyperthyroidism, hypertension, CHF, tachyarrhythmias, prostatic hypertrophy, or esophageal reflux.

Species-Specific Warnings:

Neonates: Reportedly not effective in treating bradycardias in puppies <14 days old or kittens <11 days old. May damage hypoxic myocardia in neonates.
Rabbits: Glycopyrrolate is preferred, as ~40% of rabbits possess endogenous atropinesterase, rendering atropine ineffective.
Horses: Systemic use may decrease gut motility and induce colic. May reduce arrhythmogenic doses of epinephrine.
Cattle: May result in inappetence and rumen stasis persisting for several days.
Food Animals: FARAD recommends a 28-day meat and 6-day milk withdrawal time when used at doses up to 0.2 mg/kg.