Can oral atropine (antimuscarinic) drops used for treatment of sialorrhea (excessive oral secretions) cause mydriasis (pupillary dilatation)?

From the Guidelines

Atropine oral drops used for treating excessive oral secretions can cause pupillary dilation as a side effect due to their anticholinergic properties. Atropine is an anticholinergic medication that blocks the action of acetylcholine at muscarinic receptors throughout the body. While oral atropine primarily targets the salivary glands to reduce secretions, some of the medication can be systemically absorbed and affect other organs with muscarinic receptors, including the eyes. When atropine reaches the iris dilator muscles, it blocks the parasympathetic nervous system's action, resulting in pupil dilation (mydriasis). This effect may be more pronounced in patients taking higher doses, those with prolonged use, or individuals particularly sensitive to anticholinergic effects.

Key Considerations

• Healthcare providers should monitor for this side effect, especially in elderly patients who may be more susceptible to anticholinergic adverse effects.
• Patients should be informed about this potential side effect and advised to report any vision changes or eye discomfort while using atropine oral drops. However, the provided evidence 1 does not directly address the use of atropine oral drops for excessive oral secretions and their effect on pupillary dilation. The evidence primarily discusses the side effects of amantadine and rimantadine, which are different medications.

Clinical Implications

• Despite the lack of direct evidence, the anticholinergic properties of atropine suggest that it can cause pupillary dilation as a side effect.
• Clinicians should exercise caution when prescribing atropine oral drops, especially in patients with a history of eye problems or those taking other medications with anticholinergic effects.
• Further research is needed to fully understand the effects of atropine oral drops on pupillary dilation and other potential side effects.

From the FDA Drug Label

Atropine exerts a more potent and prolonged effect on heart, intestine and bronchial muscle than scopolamine, but its action on the iris, ciliary body and certain secretory glands is weaker than that of scopolamine.

The major action of atropine is a competitive or surmountable antagonism which can be overcome by increasing the concentration of acetylcholine at receptor sites of the effector organ

The use of atropine oral drops for treatment of excessive oral secretions may cause a change in pupillary dilatation, as atropine has an effect on the iris and ciliary body, although this effect is weaker compared to scopolamine 2.

• Key points:
  • Atropine has an antimuscarinic action
  • Atropine's effect on the iris and ciliary body is weaker than scopolamine
  • Atropine oral drops may cause changes in pupillary dilatation due to its antimuscarinic action on the iris and ciliary body However, the information provided in the drug label does not directly address the specific question of whether atropine oral drops can cause a change in pupillary dilatation when used for the treatment of excessive oral secretions.

From the Research

Atropine Oral Drops and Pupillary Dilatation

• Atropine is an anticholinergic medication that can cause pupillary dilatation as a side effect 3, 4.
• The use of atropine eye drops has been shown to cause significant pupillary dilatation, even at low concentrations 4.
• A study found that a single eye drop of 0.01% atropine caused significant pupillary dilatation 12 hours after instillation, with pupil sizes still larger in the evening compared to baseline parameters 4.
• Another study reported a case of increased systemic hypertension and pupil dilation related to low-dose atropine eyedrops, highlighting the potential for atropine to cause pupillary dilatation 3.

Mechanism of Action

• Atropine works by blocking the action of acetylcholine at muscarinic receptors, leading to relaxation of the iris sphincter muscle and resulting in pupillary dilatation 5.
• The mechanism of atropine-induced pupillary dilatation is thought to be related to the blockade of muscarinic receptors in the iris, leading to a decrease in the amount of acetylcholine available to stimulate the iris sphincter muscle 6.

Clinical Implications

• The use of atropine oral drops for the treatment of excessive oral secretions may cause pupillary dilatation as a side effect, particularly in patients who are sensitive to the anticholinergic effects of atropine 3, 4.
• Patients using atropine oral drops should be monitored for signs of pupillary dilatation, such as blurred vision, photophobia, or eye discomfort 5.
• The potential for atropine to cause pupillary dilatation should be considered when prescribing atropine oral drops, particularly in patients with a history of glaucoma or other eye conditions 7, 5.