The Effects of Atropine on Cats and Dogs

1 Overview

The involuntary nervous system divides into the sympathetic (fight-or-flight) and parasympathetic nerves, which generally oppose each other.

When stimulated, the sympathetic system raises heart rate, blood pressure, and cardiac activity; pupils dilate and gut function drops. The parasympathetic system works mainly through the vagus nerve, slowing heart rate, lowering blood pressure, stimulating digestion, and secreting saliva and digestive juices.

Cells contain targets called receptors, stimulated by chemicals released by nerves. In the parasympathetic system the neurotransmitter is acetylcholine, and its receptors are muscarinic receptors.

Atropine blocks muscarinic receptors, inhibiting acetylcholine and reducing parasympathetic activity of this chemical. Thus atropine is an antimuscarinic drug, sometimes also called an ‘anticholinergic’ or ‘parasympatholytic’—terms describing its action.

When the muscarinic part of the parasympathetic system is blocked, the sympathetic system becomes more prominent. Atropine is prescription-only, obtained from or prescribed by a vet.

Atropine formulations

This drug is registered for use in both humans and animals.

Atropine has only a generic name. Both human and veterinary formulations are available.

Uses of atropine in cats and dogs

1. Before surgical anesthesia, to reduce drooling and respiratory secretions.

2. Often used with anesthetics to prevent slowed heart rate.

3. Also used to treat dangerous slow heart rates; an important drug in CPR.

4. An antidote for some pesticide (e.g., cholinesterase-inhibitor) and mushroom poisonings.

5. Also reduces drooling, vomiting, and nausea.

6. Atropine-like compounds treat motion-sickness vomiting.

7. Atropine-like compounds treat acute diarrhea in animals.

8. Also used in the eye to dilate the pupil, reducing eye pain and preventing complications of various eye diseases.

9. Atropine antagonizes compounds that constrict airways and cause cough, so it and similar compounds can be used in animals with breathing difficulty (e.g., asthma-like disease).

Precautions and side effects

1. Generally safe and effective when vet-prescribed, but it can cause side effects in some animals.

2. Do not use in animals known to be allergic to it.

3. Avoid if gastrointestinal obstruction or infection is suspected.

4. Do not use if the large intestine is inflamed.

5. Never inject atropine in animals diagnosed with glaucoma.

6. Atropine may interact with other drugs. Consult your vet about interactions with drugs your pet takes, including certain antihistamines, pethidine, diazepam, metoclopramide, and procainamide.

7. Use cautiously in animals with fast heart rate or impaired kidney, heart, or liver function.

8. With the eye formulation, some animals—especially cats—may drool heavily from the drug’s bitter taste.

9. Other side effects: dry mouth, constipation, central nervous system stimulation, blurred vision, drowsiness, or ataxia (wobbly walking). Also, dry mouth may make some animals drink excessively.

Atropine specifications

1. Available in several injectable concentrations.

2. Also available as 0.4 mg tablets.

3. Also as 1% or 2% ophthalmic preparations.

Atropine dosage

Note: Always consult a vet before dosing.

1. Typical dose is 0.01–0.02 mg per pound (0.022–0.044 mg/kg). Usually given by injection only.

2. As an antidote for some poisonings, the dose may be 1 mg per pound (2 mg/kg).

3. For eye disease, one drop in the affected eye every 2–24 hours.

4. Duration depends on the condition and response. Even if the pet seems recovered, finish the full course unless the vet directs otherwise.