While it might seem unlikely, certain types of eye drops can lead to systemic absorption and, consequently, gastrointestinal upset, including diarrhea. This occurs due to the body’s interconnected systems. This article explores the pathways through which eye drops can influence the digestive tract and highlights specific ingredients that may contribute to such effects.
How Eye Drops Affect the Body Systemically
Eye drops are designed for local action on the eye’s surface. However, the eye is connected to the rest of the body, allowing for systemic absorption of medication. The nasolacrimal duct system is the most significant pathway. This system drains tears and excess eye drop solution from the eye’s surface into the nasal cavity and throat.
Once in the nasal cavity and throat, active ingredients can be absorbed into the bloodstream through the rich network of blood vessels. This absorption bypasses the liver’s initial metabolism, potentially leading to higher drug concentrations in the systemic circulation. Factors increasing systemic absorption include applying too many drops, not closing the eye gently after application, or not blocking the tear duct. Topical ocular drugs can achieve systemic absorption rates ranging from 20% to 80%.
Specific Eye Drop Ingredients and Their Potential Gastrointestinal Effects
Certain active ingredients in eye drops have been associated with gastrointestinal side effects, including diarrhea, due to systemic absorption.
Beta-blocker eye drops, such as timolol (for glaucoma), can be absorbed systemically and may cause diarrhea, stomach discomfort, or upset stomach. This is because beta-blockers affect various bodily systems.
Cholinergic eye drops, like pilocarpine (also for glaucoma), stimulate the parasympathetic nervous system. This increases gut motility and secretions, potentially leading to nausea, vomiting, and diarrhea. These effects are more frequent with repeated use.
Alpha-adrenergic agonists, such as brimonidine, can cause gastrointestinal issues like nausea, stomach discomfort, or stomach pain. While diarrhea is less common for brimonidine, other digestive upset is possible.
Anticholinergic eye drops, like atropine, block parasympathetic nerve impulses, often decreasing gut motility and causing constipation. While diarrhea is not a common side effect, some individuals may still experience general gastrointestinal discomfort, including nausea and stomach pain.
Preservatives like benzalkonium chloride (BAK) can also contribute to gastrointestinal symptoms. If systemically absorbed, BAK can cause taste perversion, dry mouth, nausea, and dyspepsia by entering the nasopharynx. While not directly linked to diarrhea, these general digestive disturbances highlight the potential for systemic effects from various eye drop components.
When to Consult a Doctor About Eye Drop Side Effects
Seek medical advice if you experience persistent or severe diarrhea, or any other concerning symptoms, after starting new eye drops. A healthcare professional can assess if the eye drops are the cause and rule out other conditions.
Do not discontinue prescribed eye drops without consulting a doctor, as this could negatively impact your eye health. Your doctor or pharmacist can offer guidance, adjust your treatment, or suggest alternative medications or management strategies to alleviate side effects.