What is Purite? Understanding this Advanced Ophthalmic Preservative

October 7, 2025 •

5 min read

In ophthalmology, a 2003 study on rabbits showed eye drops containing Purite were significantly better tolerated and caused less corneal damage than those with the older preservative benzalkonium chloride (BAK). Known pharmacologically as stabilized oxychloro complex (SOC), what is Purite and why is it considered an advanced solution for maintaining sterility in multi-dose eye care products while minimizing irritation?.

Quick Summary

Purite, a type of preservative known as stabilized oxychloro complex, is used in multi-dose eye drops and contact lens solutions and converts to natural tear components upon contact with the eye, making it gentler for sensitive eyes. It provides antimicrobial protection by oxidizing microbial cellular components while causing significantly less ocular surface toxicity than older, detergent-based preservatives like BAK.

Key Points

Oxidative Preservative: Purite (stabilized oxychloro complex) is a preservative that works by oxidizing and disrupting microbial cellular components.
Gentle on the Eye: Upon contact with the eye, Purite breaks down into natural tear components—water, oxygen, and salts—reducing the potential for irritation and ocular surface damage.
Found in Ophthalmic Products: This preservative is used in a range of eye care items, including prescription eye drops for glaucoma (like Alphagan P) and some over-the-counter artificial tears and saline solutions.
Less Toxic than BAK: Compared to older preservatives like benzalkonium chloride (BAK), studies show Purite is significantly less toxic and better tolerated by the ocular surface.
Alternative to Preservative-Free: For patients who need the convenience of a multi-dose bottle but are sensitive to traditional preservatives, Purite offers a safer and more comfortable option.
Still a Preservative: While mild, Purite is not a preservative-free solution. Patients with severe ocular surface disease or high sensitivity may still require truly preservative-free drops.

The Role of Preservatives in Ophthalmic Solutions

Multi-dose ophthalmic products, including eye drops and contact lens solutions, require preservatives to prevent microbial contamination once the bottle is opened. Without these agents, bacteria, fungi, and other microorganisms could thrive in the solution, leading to severe eye infections if introduced into the eye. For decades, the most common preservative was benzalkonium chloride (BAK), a potent detergent. However, chronic exposure to BAK has been widely linked to ocular surface toxicity, causing issues like dry eye symptoms, inflammation, and damage to the corneal epithelium. In response to these concerns, the pharmaceutical industry developed alternative preservatives that are more compatible with the sensitive ocular surface, with Purite emerging as a leading solution.

The Science Behind Purite: Stabilized Oxychloro Complex

Purite is the brand name for stabilized oxychloro complex (SOC), an advanced oxidative preservative. Unlike detergent-based preservatives that disrupt cell membranes, Purite works through oxidation, a process that is carefully controlled to be effective against microbes but gentle on human eye tissue.

How it Works

Chemical Composition: In its bottled state, Purite is a complex mixture primarily of chlorite and chlorate, with trace amounts of chlorine dioxide. This chemical cocktail provides excellent long-term antimicrobial stability within the container.
Oxidative Action: Upon instillation into the eye, the solution is exposed to light. This exposure causes the stabilized oxychloro complex to break down, releasing chlorine dioxide free radicals. These free radicals act as potent antimicrobial agents by oxidizing key cellular components, including unsaturated lipids and glutathione within the microbe's cell. This mechanism effectively kills microorganisms like bacteria, viruses, and fungi.
Harmless Degradation: One of the key advantages of Purite is that its breakdown products are harmless. After acting on the microbes, it rapidly degrades into the natural components of tears: sodium and chloride ions, water, and oxygen.
Ocular Compatibility: Mammalian cells, unlike many microbes, are equipped with protective enzymes and antioxidants like catalases and oxidases that neutralize the oxidative effects of Purite. This built-in defense mechanism is why Purite causes significantly less toxicity and irritation to the human eye compared to detergent-based preservatives like BAK.

Purite in Ophthalmic Products

Purite has been incorporated into various eye care products to offer the benefits of a multi-dose bottle without the harshness of older preservatives. It's often found in products intended for chronic use or for patients with sensitive eyes.

Prescription Ophthalmic Medications: A prominent example is the glaucoma medication Alphagan P (brimonidine tartrate). The use of Purite in this formulation has been shown to result in better tolerability and reduced side effects compared to older versions preserved with BAK.
Over-the-Counter Eye Drops: Several brands of artificial tears, such as certain products in the Refresh family, use Purite as a preservative. This allows the product to maintain sterility in a convenient multi-dose bottle for extended periods while minimizing eye irritation for users with dry or sensitive eyes.
Contact Lens Solutions: Some contact lens saline solutions, like Lens Plus Purite Saline, also use this mild preservative. The formula is designed to match the pH of natural tears and is gentle enough for sensitive contact lens wearers.

Purite vs. Other Ophthalmic Preservatives

To understand Purite's place in eye care, it helps to compare it with other common types of preservatives. While all preservatives maintain sterility, they differ in their mechanism, efficacy, and ocular impact.


Preservative	Type	Mechanism of Action	Ocular Surface Toxicity	Breakdown	Common Examples
Purite (SOC)	Oxidative, "Vanishing"	Oxidizes microbial cell components using chlorine dioxide free radicals	Significantly lower than BAK	Degrades into natural tear components (water, oxygen, salts) on the ocular surface	Alphagan P, some Refresh and Lens Plus products
Benzalkonium Chloride (BAK)	Detergent, Cationic	Disrupts microbial cell membranes, causing cell lysis	High, well-documented ocular surface damage with chronic use	Does not break down quickly	Many generic eye drops
Polyquad (Polyquaternium-1)	Quaternary Ammonium, Cationic	Large, hydrophilic molecule disrupts bacterial cell membranes	Lower than BAK, but still some cytotoxicity observed in studies	Does not break down quickly	Systane artificial tears
SofZia	Oxidative, Ionic Buffered	Oxidative damage to bacteria lacking specific enzymes, spares human cells	Lower than BAK	Degrades quickly upon contact with tear cations	Travatan Z
Sodium Perborate (GenAqua)	Oxidative, Vanishing	Forms hydrogen peroxide, which is converted to water and oxygen by tear enzymes	Lower than BAK	Breaks down into water and oxygen	Genteal artificial tears

Benefits and Considerations of Using Purite

Benefits

Reduced Ocular Surface Toxicity: For patients who must use eye drops chronically, such as those with glaucoma, Purite offers a safer alternative to older preservatives, reducing the risk of developing ocular surface disease.
Broad-Spectrum Antimicrobial Efficacy: It maintains strong effectiveness against a wide range of microbes, ensuring the sterility of multi-dose bottles.
Patient Convenience: Multi-dose bottles are generally easier to handle and more cost-effective than single-use, preservative-free vials, making compliance easier for many patients.
Light-Activated Breakdown: The "vanishing" nature of Purite, which breaks down into natural substances upon light exposure and contact with the eye, contributes to its gentler profile.

Considerations

Individual Sensitivity: While gentler than BAK, some highly sensitive individuals might still experience irritation from any preservative, and some studies suggest even "soft" preservatives aren't perfectly innocuous.
Not for all Conditions: For patients with severe ocular surface disease or a known sensitivity, preservative-free formulations, while potentially more costly and less convenient, might still be the best option.
Relative Effectiveness: While clinical studies have shown positive results for Purite-preserved products, particularly when comparing against BAK, debates continue regarding the absolute long-term effects of any preservative. For more detailed information on ophthalmic preservatives, consult an authoritative resource such as EyeWiki.

Conclusion

In the ever-evolving field of ophthalmology, Purite, or stabilized oxychloro complex, represents a significant advancement in preservative technology. Its oxidative, self-destructing mechanism allows for the production of sterile, multi-dose ophthalmic products that are much better tolerated than those containing older, harsher preservatives like BAK. While it is a better-tolerated option for many, particularly those with sensitive eyes, it is essential for eye care professionals and patients to weigh the benefits of convenience and reduced toxicity against the option of completely preservative-free alternatives for the most compromised ocular surfaces. Ultimately, the development of Purite and other modern preservatives offers a wider, more patient-centric array of choices for safe and effective eye care.

Frequently Asked Questions

Purite, a brand name for stabilized oxychloro complex (SOC), is a mild oxidative preservative used in multi-dose ophthalmic products like eye drops and contact lens solutions to prevent microbial contamination. It breaks down into natural tear components upon exposure to light and the eye's surface, making it gentler than older preservatives.

Purite works by releasing chlorine dioxide free radicals upon contact with the eye. These free radicals oxidize and disrupt the cellular functions of microbes, effectively killing them. In contrast, human eye cells are protected by natural antioxidants.

Studies have shown that Purite causes significantly less ocular surface toxicity and irritation compared to older, detergent-based preservatives like benzalkonium chloride (BAK). It is considered a well-tolerated alternative for many patients, especially those with sensitive eyes.

Purite can be found in various ophthalmic products, including prescription medications like Alphagan P for glaucoma and over-the-counter products such as certain Refresh artificial tears and Lens Plus saline solutions.

For many people with sensitive eyes who react to traditional preservatives, products containing Purite can be a more comfortable alternative. However, some individuals with severe ocular surface disease may still find any preservative irritating and might require a completely preservative-free product.

No, Purite is not a preservative-free solution. It is a "vanishing" preservative, meaning it maintains antimicrobial action in the bottle but breaks down into harmless components upon contact with the eye. True preservative-free products are packaged in single-dose vials.

Purite itself is associated with significantly fewer side effects directly related to the preservative compared to BAK. Any side effects experienced would more likely be related to the active medication in the eye drop or due to individual hypersensitivity.

For patients requiring chronic eye drop therapy, such as those with glaucoma, the long-term use of BAK can cause ocular surface damage. The use of Purite offers the convenience of a multi-dose bottle with a much gentler profile, reducing the risk of developing ocular surface disease.