Atropine

Atropine: Uses, Dosage and Side Effects

Overview

Atropine blocks the action of acetylcholine at muscarinic receptors at the terminal ends of the parasympathetic nervous system, reversing parasympathetic effects and producing :

• Mydriasis.
• Tachycardia.
• Bronchodilation.
• General inhibition of GI function.

Uses of Atropine

• Prevent or correct bradycardia and bradyarrhythmias.
• To dilate pupils.
• Management of organophosphate and carbamate toxicities.
• In conjunction with anticholinesterase drugs during antagonism of neuromuscular blockade

Dose of Atropine in Dogs and Cats

Dogs, Cats:

• Ophthalmic:

1 drop in the affected eye q12–24h to cause mydriasis, then once q24–96h to maintain mydriasis.

• Bradyarrhythmias:

0.01–0.03 mg/kg i.v. Low doses may exacerbate bradycardia; repetition of the dose will usually promote an increase in heart rate. 0.03–0.04 mg/kg i.m. can be given to prevent development of bradycardia during administration of potent opioids such as fentanyl.

• Organophosphate poisoning:

Dose 0.2–0.5 mg/kg (¼ dose i.v., ¾ i.m., s.c.) to effect; repeat as necessary; or 0.1–0.2 mg/kg (½ i.v., ½ i.m.) then i.m. q6h.

• Neuromuscular blockade antagonism:

0.04 mg/kg i.v. with edrophonium (0.5–1.0 mg/kg).

Side Effects of Atropine in Dogs and Cats

• Include sinus tachycardia (usually of short duration after i.v. administration), blurred vision from mydriasis, which may worsen recovery from anesthesia, and drying of bronchial secretions.
• Atropine increases intraocular pressure and reduces tear production.
• Ventricular arrhythmias may be treated with lidocaine if severe.
• Other GI side effects such as ileus and vomiting are rare in small animals.

Contraindications of Atropine in Dogs and Cats

Glaucoma, lens luxation, keratoconjunctivitis sicca.

Some Notes:

• Routine administration prior to anaesthesia as part of premedication is no longer recommended; it is better to monitor heart rate and give atropine to manage a low heart rate if necessary.
• Atropine has a slow onset of action (10 min i.m., 2–3 min i.v.); therefore, it is important to wait for an adequate period of time for the desired effect before redosing.
• The ophthalmic solution tastes very bitter and can cause hypersalivation in cats (and in some dogs).
• Atropine is compatible (for at least 15 min) mixed with various medications but not with bromides, iodides, sodium bicarbonate, other alkalis or noradrenaline.
• The following may enhance the activity of atropine: antihistamines, pethidine, benzodiazepines, phenothiazines, thiazide diuretics, and sympathomimetics.
• Combining atropine and alpha-2 agonists is not recommended.
• Atropine may aggravate some signs seen with amitraz toxicity, leading to hypertension and gut stasis.