Atropine
Atropine is an antimuscarinic drug used to oppose excessive parasympathetic effects. Systemic veterinary applications include treatment of clinically important vagally mediated bradycardia, selected anesthetic uses and control of muscarinic manifestations of organophosphate or carbamate poisoning. It also relaxes airway smooth muscle in some settings.
Its usefulness depends on the mechanism of the clinical problem: raising heart rate does not correct every cause of poor perfusion, and blocking secretions does not remove an absorbed poison. Topical ophthalmic atropine has separate therapeutic objectives and dosing from these systemic applications.
Group
Antimuscarinic; parasympatholytic
Mechanism of Action
Atropine competitively blocks muscarinic acetylcholine receptors at parasympathetic effector sites. In the heart, blockade of vagal M2 signaling increases sinus rate and can improve conduction when excessive vagal tone is the cause of bradycardia or nodal slowing.
At glandular and smooth-muscle sites, it reduces salivary and respiratory secretion, decreases gastrointestinal motility and relaxes muscarinic-mediated bronchial constriction. The same widespread blockade explains why a desired cardiac or respiratory response can be accompanied by unwanted intestinal or urinary effects.
In cholinesterase-inhibitor poisoning, atropine antagonizes the accumulated acetylcholine at muscarinic receptors. It does not reactivate acetylcholinesterase and does not reliably reverse nicotinic neuromuscular weakness or paralysis. Treatment of poisoning therefore requires attention to respiratory support and other toxin-specific measures as well as control of muscarinic signs.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Anesthesia adjunct and vagal effects | 0.02–0.04 mg/kg | IV, IM, SC | Every 6–8 h | |
| Organophosphate or carbamate toxicosis | 0.2–0.5 mg/kg | IV, IM, SC | As needed | |
| Cardiac arrest | 0.04 mg/kg | IV | Once | Use with other cardiopulmonary resuscitation measures. |
| Geriatric anesthesia adjunct | 0.01–0.02 mg/kg | IM, IV | Once | |
| Anesthesia adjunct – higher historical amount | 0.074 mg/kg | IV, IM, SC | Once | Separate historical product regimen; do not merge into the lower-dose range. |
| Cardiopulmonary resuscitation – repeat-limited course | 0.04 mg/kg | IV, IO | May repeat every 3–5 minutes for a maximum of 3 doses. Minute intervals and administration-count caps are not represented by this calculator. | |
| Cholinergic toxicosis – divided-route course | 0.2–0.5 mg/kg | IV | Total treatment amount: one-quarter IV and the remainder IM or SC. Do not give the full total by each route. | |
| Bradyarrhythmia treatment | 0.02–0.04 mg/kg | IV, IM | As needed | |
| Vagal bradycardia response test | 0.04 mg/kg | IV | Once | Record baseline ECG, wait 15 minutes after administration, then record at least 2 minutes. An incomplete response may prompt reassessment and a repeat test; persistent sinus rate above 140/min is expected with many vagal bradycardias. |
| Vagal bradycardia response test | 0.04 mg/kg | SC | Once | Record baseline ECG, wait 30 minutes after administration, then record at least 2 minutes; persistent sinus rate above 140/min is expected in many vagal cases. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Anesthesia adjunct and vagal effects | 0.02–0.04 mg/kg | IV, IM, SC | Every 6–8 h | |
| Organophosphate or carbamate toxicosis | 0.2–0.5 mg/kg | IV, IM, SC | As needed | |
| Geriatric anesthesia adjunct | 0.01–0.02 mg/kg | IM, IV | Once | |
| Anesthesia adjunct – higher historical amount | 0.074 mg/kg | IV, IM, SC | Once | Separate historical product regimen; do not merge into the lower-dose range. |
| Cardiopulmonary resuscitation – repeat-limited course | 0.04 mg/kg | IV, IO | May repeat every 3–5 minutes for a maximum of 3 doses. Minute intervals and administration-count caps are not represented by this calculator. | |
| Cholinergic toxicosis – divided-route course | 0.2–2 mg/kg | IV | Total treatment amount: one-quarter IV and the remainder IM or SC. Do not give the full total by each route. | |
| Bradyarrhythmia treatment | 0.02–0.04 mg/kg | IV, IM, SC | Every 4–6 h |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cholinesterase-inhibitor toxicosis | 0.02–0.04 mg/kg | IM, SC | As needed | |
| Equine asthma bronchoconstriction | 0.022 mg/kg | IV | Once | One dose only because of gastrointestinal motility effects. |
| Vagally mediated bradyarrhythmia | 0.01–0.02 mg/kg | IV | As needed | |
| Bronchodilation – weight-qualified example | 5 mg/animal | IV | Once | 5 mg total is described for a 400–500 kg horse; a weight-qualified example is not a universal fixed dose. |
| Organophosphate toxicosis – to-effect course | 1 mg/kg | IV | As needed | Titrate to muscarinic response; a subsequent SC repeat every 1.5–2 hours is described. Antidotal amount is distinct from bronchodilator dosing. |
| Organophosphate toxicosis – repeated SC phase — Maintenance | 1 mg/kg | SC | Every 1.5–2 h | Repeat only as required after initial IV titration; amount is approximate and response-guided. |
| Organophosphate toxicosis – divided-route product course | 0.22 mg/kg | IV | One-quarter of total amount IV and remainder SC or IM. Not 0.22 mg/kg independently by each route. |
Pigs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cholinesterase-inhibitor toxicosis — Initial | 0.1 mg/kg | IV | Once | Follow with the IM phase. |
| Cholinesterase-inhibitor toxicosis — Maintenance | 0.4 mg/kg | IM | Follows initial IV treatment; repeat interval not supplied. | |
| Anesthesia adjunct | 0.02 mg/kg | IV | Once | |
| Anesthesia adjunct | 0.04 mg/kg | IM | Once | |
| Organophosphate toxicosis – divided-route product course | 0.22 mg/kg | IV | One-quarter of total amount IV and remainder SC or IM. Not 0.22 mg/kg independently by each route. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cholinesterase-inhibitor toxicosis — Initial | 0.1 mg/kg | IV | Once | Follow with the IM phase. |
| Cholinesterase-inhibitor toxicosis — Maintenance | 0.4 mg/kg | IM | As needed | Follows initial IV treatment; repeat as needed in ruminants. |
| Anesthesia adjunct | 0.02 mg/kg | IV | Once | |
| Anesthesia adjunct | 0.04 mg/kg | IM | Once | |
| Anesthesia adjunct – alternative | 0.06–0.12 mg/kg | IM | Once | Not routine because prolonged gastrointestinal effects and limited useful duration can outweigh benefit. |
| Organophosphate toxicosis – divided-route alternative | 0.5 mg/kg | IV | Up to 2 days; Total amount: one-quarter IV and remainder SC or IM, repeat every 3–4 hours for 1–2 days as required; not the full amount per route. |
Sheep
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cholinesterase-inhibitor toxicosis — Initial | 0.1 mg/kg | IV | Once | Follow with the IM phase. |
| Cholinesterase-inhibitor toxicosis — Maintenance | 0.4 mg/kg | IM | As needed | Follows initial IV treatment; repeat as needed in ruminants. |
| Anesthesia adjunct | 0.02 mg/kg | IV | Once | |
| Anesthesia adjunct | 0.04 mg/kg | IM | Once | |
| Organophosphate toxicosis – divided-route alternative | 0.5 mg/kg | IV | Up to 2 days; Total amount: one-quarter IV and remainder SC or IM, repeat every 3–4 hours for 1–2 days as required; not the full amount per route. |
Goats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cholinesterase-inhibitor toxicosis — Initial | 0.1 mg/kg | IV | Once | Follow with the IM phase. |
| Cholinesterase-inhibitor toxicosis — Maintenance | 0.4 mg/kg | IM | As needed | Follows initial IV treatment; repeat as needed in ruminants. |
| Anesthesia adjunct | 0.02 mg/kg | IV | Once | |
| Anesthesia adjunct | 0.04 mg/kg | IM | Once | |
| Organophosphate toxicosis – divided-route alternative | 0.5 mg/kg | IV | Up to 2 days; Total amount: one-quarter IV and remainder SC or IM, repeat every 3–4 hours for 1–2 days as required; not the full amount per route. |
Ferret
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Anesthesia premedication | 0.05 mg/kg | SC, IM | Once |
Rabbit
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Organophosphate toxicosis – high historical regimen | 10 mg/kg | SC | Every 20 minutes in a rabbit-focused historical regimen. No sterile-product or titration endpoint is specified; do not extrapolate to other small mammals. |
Bird
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Organophosphate toxicosis | 0.2 mg/kg | IM | Every 3–4 h | As needed; text also states one-quarter of the initial amount without defining the staging clearly. Pralidoxime 10–20 mg/kg IM every 8–12 hours is an adjunct only for organophosphate poisoning, not carbamates, and is excluded in raptors. |
| Organophosphate diagnostic adjunct | 0.02 mg/kg | IV | Once | Failure to reverse bradycardia may support poisoning when history and other signs agree. |
| Anesthesia premedication | 0.04–0.1 mg/kg | IM, SC | Once |
Reptile
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Organophosphate toxicosis | 0.1–0.2 mg/kg | SC, IM | As needed |
Tortoise
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Ptyalism | 0.05 mg/kg | SC, IM | Every 24 h |
Indications
- Treatment of clinically consequential vagally mediated bradycardia and selected vagal conduction disturbances, including appropriate peri-anesthetic situations.
- Selected anesthetic premedication to reduce secretions or counter anticipated excessive vagal effects when the patient and procedure justify antimuscarinic treatment.
- Control of muscarinic manifestations of organophosphate and carbamate toxicosis, such as bronchial secretions, bronchoconstriction and bradycardia; it does not treat all components of the poisoning.
- Selected resuscitation circumstances where excessive vagal influence is relevant. Historical inclusion in a monograph should not be interpreted as routine atropine for every cardiac-arrest rhythm.
- Single-dose relief of bronchoconstriction in selected horses with equine asthma, with gastrointestinal effects limiting repeated use.
Contraindications
- Glaucoma, intestinal ileus, gastroparesis or tachycardia.
- Higher doses increase myocardial oxygen demand.
- Large animals have pronounced gastrointestinal motility suppression.
- Urinary obstruction, obstructive gastrointestinal disease, myocardial ischemia or unstable cardiovascular status during hemorrhage.
- Use cautiously in myasthenia gravis except to counter muscarinic treatment effects, and in significant gastrointestinal infection.
- May aggravate hypertension and ileus in amitraz poisoning.
- Routine use in very young neonates may be ineffective and can worsen hypoxic myocardial injury.
Interactions
- Antagonizes cholinergic drugs, including the cholinergic component of metoclopramide action.
- Do not mix with alkaline solutions.
- Other anticholinergics, antihistamines, phenothiazines, amantadine and tricyclic antidepressants can increase antimuscarinic toxicity.
- Combining with alpha2 agonists can cause hypertension, tachycardia or arrhythmias; routine reversal of alpha2-related bradycardia is controversial.
- Slow-dissolving digoxin exposure may increase; separate oral antacids by at least 1 hour and give oral atropine 2 hours after ketoconazole.
Adverse effects
- Dry mouth, ileus, constipation, urinary retention and tachycardia.
Toxicity
Toxicity can cause marked tachycardia, arrhythmias, agitation or CNS depression, urinary retention and severe gastrointestinal hypomotility. Treat supportively with cardiorespiratory monitoring; avoid phenothiazines. Physostigmine reversal is reserved for selected severe cases because it can provoke bradycardia, bronchoconstriction or seizures.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Atropine sulfate 0.4 mg/mL injection | Injection | 0.4 mg / mL | IV, IM, SC |
| Atropine sulfate 0.5 mg/mL injection | Injection | 0.5 mg / mL | IV, IM, SC |
| Atropine sulfate 0.54 mg/mL injection | Injection | 0.54 mg / mL | IV, IM, SC |
| Atropine sulfate 15 mg/mL injection | Injection | 15 mg / mL | IV, IM, SC |
| Atropine sulfate 0.05 mg/mL injection | Injection | 0.05 mg / mL | IV, IM, SC |
| Atropine sulfate 0.1 mg/mL injection | Injection | 0.1 mg / mL | IV, IM, SC |
| Atropine sulfate 0.3 mg/mL injection | Injection | 0.3 mg / mL | IV, IM, SC |
| Atropine sulfate 0.8 mg/mL injection | Injection | 0.8 mg / mL | IV, IM, SC |
| Atropine sulfate 1 mg/mL injection | Injection | 1 mg / mL | IV, IM, SC |
Monitoring and Administration
Monitor heart rate and rhythm. Repeat antidotal treatment according to the clinical response rather than a guessed fixed interval.
For equine airway obstruction only a single dose is described. Keep injection tightly sealed at room temperature.
Canine sinus bradycardia: 0.005–0.01 mg/kg is described, but no explicit route is paired with this amount. Do not infer the route from the separate IV cardiac-arrest regimen.
Dog endotracheal resuscitation alternative: 0.08–0.1 mg/kg diluted in 5–10 mL sterile water. Endotracheal delivery is unsupported by the calculator and is not interchangeable with IV dosing.
Cat endotracheal resuscitation alternative: 0.08–0.1 mg/kg diluted in 5–10 mL sterile water. Endotracheal delivery is unsupported by the calculator and is not interchangeable with IV dosing.
Cattle hypersensitivity treatment is described as 1 g per cow followed by 0.5 g after 2–3 days, but no route is established; this is not a complete treatment regimen. In rabbits, endogenous atropinesterase can reduce response and glycopyrrolate is often preferred. Monitor thirst, urination, defecation and gut motility, especially in horses and ruminants.