Eye drops are a common form of medication, available both over-the-counter and by prescription, used to address various eye conditions. While primarily intended for local action within the eye, a common concern among users is whether the ingredients in these drops can enter the broader bodily system and potentially affect organs like the kidneys.
Systemic Absorption of Eye Drops
Eye drops, despite being applied to the eye’s surface, can indeed enter the body’s systemic circulation. A significant pathway for this absorption is the nasolacrimal duct, a drainage system that connects the eye to the nasal cavity. When an eye drop is instilled, excess fluid often drains through this duct into the nose and throat.
The mucous membranes lining the nose and throat are highly vascularized, meaning they contain many blood vessels. This rich blood supply allows the active ingredients in eye drops to be rapidly absorbed directly into the bloodstream, bypassing the liver’s first-pass metabolism that typically processes orally ingested medications. While the amount absorbed from a single drop is generally small, it is possible for a considerable portion, sometimes up to 80%, of the applied drug to enter the systemic circulation this way.
Eye Drop Ingredients and Kidney Health
For most common over-the-counter eye drops, such as lubricating drops or those for minor irritation, the risk to kidney health is generally very low. This is due to their minimal systemic absorption and the non-pharmacological nature of their ingredients. However, certain prescription eye drops, particularly those used for conditions like glaucoma, contain active pharmaceutical ingredients that can have systemic effects.
One class of concern is carbonic anhydrase inhibitors (CAIs), such as dorzolamide or brinzolamide, which are used to lower intraocular pressure in glaucoma. While applied topically, these medications can be systemically absorbed and have been linked to potential kidney-related side effects, particularly metabolic acidosis, especially in patients with advanced chronic kidney disease (CKD). A nationwide population-based study found that CAI users with advanced CKD had a higher incidence of long-term dialysis and hospital admissions due to metabolic acidosis compared to non-users.
Beta-blockers, another class of glaucoma medication like timolol, are also systemically absorbed. While primarily known for cardiovascular side effects like slowed heart rate, their elimination is primarily via the kidneys. Though direct kidney damage from topical beta-blockers is not commonly reported, their systemic presence means caution is advised in patients with pre-existing kidney conditions. Additionally, other eye drops, such as those containing phenylephrine, have been reported to cause renal failure in specific vulnerable populations, such as low birth weight infants, due to systemic absorption leading to renal vessel constriction.
Factors Influencing Systemic Risk
Several individual factors can increase the likelihood or severity of systemic effects from eye drops. Pre-existing kidney conditions are a significant consideration, as impaired kidney function can reduce the body’s ability to process and eliminate absorbed medications, potentially leading to drug accumulation and increased systemic exposure.
Age also plays a role, with very young children and elderly individuals being at higher risk for systemic side effects. Children, particularly infants, have different physiological development and their ocular dosing is not typically weight-adjusted, leading to a higher risk of systemic absorption. Older adults may have reduced organ function, including kidneys, making them more sensitive to systemic drug effects. The duration and dosage of eye drop use, as well as concurrent use of other medications, can further influence systemic exposure and the potential for adverse effects.
When to Consult a Healthcare Professional
If you are using eye drops and experience any symptoms that could indicate a systemic reaction or kidney issue, consult a healthcare professional. Such symptoms might include changes in urination patterns, unexplained swelling, unusual fatigue, or nausea.
It is also advisable to discuss all medications, including over-the-counter and prescription eye drops, with your doctor or pharmacist. This is especially important if you have pre-existing health conditions or are taking other medications, as drug interactions or altered drug processing can occur. Your healthcare provider can assess your individual risk factors and help determine the most appropriate and safest eye drop regimen.