Systemic side effects of atropine eye drops

Atropine acts as an antimuscarinic agent, blocking postganglionic muscarinic receptors and thereby inhibiting parasympathetic activity. This enables sympathetic stimulation to dominate, resulting in increased cardiac output and other antimuscarinic effects.1

It is mainly used in the management of bradycardia and also to decrease salivation (e.g. before anaesthesia) or to block or reverse the effects of certain drugs (i.e. to counter anticholinesterase poisoning).1 

Ocular applications of atropine include diagnostic use as a mydriatic and cycloplegic agent, as well as a treatment for amblyopia and myopia control in children. 

The ocular side effects of atropine are well known. Especially at higher concentrations (>0.1%), patients may experience photophobia and mydriasis, which can lead to difficulties during near work.4 Lower concentrations are associated with fewer side effects and are well-tolerated by most children. Additionally, sunglasses or photochromatic lenses can be prescribed to help manage photophobia.5

Allergic reactions can occur in both the ocular and periocular regions, and the likelihood of an allergic response increases with concentration.6 Symptoms include lid oedema, itching and madarosis. Should any of these symptoms occur, atropine use should be immediately ceased, along with appropriate management of the allergic response.

Systemic absorption of atropine can occur if the drug passes through the puncta into the nasolacrimal duct and is absorbed via the nasal mucosa. Although rare, this can produce adverse effects, including:

• Difficulty urinating
• Constipation
• Fever
• Flushing and dryness skin
• Skin rash, hives
• Headache, dizziness, drowsiness and/or weakness
• Nervousness, restlessness, confusion, shaking and/or tremor
• Nausea and vomiting
• Loss of taste
• Dryness of the mouth, nose, and throat

It is almost impossible to achieve lethal toxicity from ophthalmic atropine. 

A 0.1% solution contains approximately 0.5 mg per drop, meaning that a physiologically impossible absorption of around 20 drops would be required to reach a potentially fatal dose. Atropine is also rapidly metabolised, with a half-life of two to five hours, further reducing the risk of complications.8

Systemic absorption can be minimized using the double DOT technique (don’t open the eyes and digital occlusion of the tear duct) immediately after drop instillation.9

1. Ensure clean hands and that the bottle top does not touch the eye. 
2. Retract the lower eyelid and place the drop in the lower conjunctival sac while the patient is looking up. 
3. Instruct the patient to close their eye immediately.
4. Press a finger firmly over the punctum while the eye is closed, and hold for about 1-2 minutes.

Atropine is safe and well-tolerated when prescribed at low concentrations for myopia control. 

But as with any medication, prescribing should be supported by thorough history-taking, consideration of risks versus benefits, and close monitoring.

Atropine does not have any absolute contraindications, but caution is advised in patients with:1,10

• Hypersensitivity to atropine or any component of the product
• Angle-closure glaucoma, increased intraocular pressure
• Myasthenia gravis
• Severe inflammatory gastrointestinal disease or obstruction
• Cardiovascular and pulmonary disease (e.g. arrythmias, chronic lung disease, asthma)
• Concurrent use of drugs with anticholinergic properties

1. Atropine is safe when prescribed at low concentrations for myopia control and can be used for extended periods of time. 
2. Instruct families on practising the ‘double DOT’ technique and store the medication safely out of the reach of children, to mitigate the possibility of systemic absorption.
3. As with any medication, patients should be monitored for tolerance, adherence, and side effects, with regular follow-up to ensure ongoing safety and efficacy.