Preservatives are commonly found in eye drops of all types. Typically, preservatives in eye drops belong to two distinct groups, oxidants and surfactants. All preservatives can potentially cause allergies or inflammation, but oxidant preservatives in eye drops generally appear to be less inflammatory than surfactants. Common types of preservatives in eye drops include benzalkolium (BAK) and sodium chlorite.
Types of eye drops include over-the-counter drops for allergies, mildly dry or red eyes and prescription eye drops for dry eyes, glaucoma, eye infections and inflammatory conditions of the eyes. Preservatives are substances typically added to eye drops to extend their shelf life and to keep the formulations free of bacteria. Most medical eye drops are preserved. The two most common types of preservatives in eye drops are surfactants and oxidants.
Benzalkolium is a surfactant. It is one of the most commonly used preservatives in prescription eye drops and over-the-counter preparations for red eyes. It generally is the preservative of choice in eye drops for glaucoma, increased eye pressure and ocular allergies. Its concentration varies depending on the type of formulation. Even in low concentrations, benzalkolium has the potential for inflammatory and allergic reactions in the eyes.
Of the oxidant type of preservatives in eye drops, sodium chlorite is the most commonly used. It typically is found in preparations for corneal edema, dry or tired eyes as well as eye drops for contact lens wearers. Oxidant preservatives generally are less allergenic and inflammatory than surfactants are.
Natural eye drops do exist, and sometimes these can be a suitable alternative to preserved formulations. Natural eye drops usually are free of preservatives. They can be lubricating for dry eyes or contain herbal antihistamine preparations for mild allergic conjunctivitis or redness. Homeopathic natural eye drops also belong in this category. Preservative-free eye drops are usually in individual, disposable sachets to prevent bacterial contamination.
Side effects from preservatives in eye drops typically are dose-related. Patients who have experienced adverse reactions to a surfactant-containing eye drop formulation can be switched to a formulation with a lower concentration of surfactant preservatives or to one that contains oxidant preservatives. Scientific studies indicate that preservative-free prescription eye drops for glaucoma have lower inflammation rates and fewer overall side effects than preserved eye drops. Other types of preservatives in eye drops include sodium perborate, purite and benzododecinium bromide.