Which category of preservatives is commonly used in aqueous-containing ophthalmic ointments?

• A. Parabens, phenols, benzoic acid, and sorbic acid
• B. Only water-soluble colors
• C. Heavy metal preservatives
• D. No preservatives are allowed

Answer: (A)

The key idea is that preservatives for products that contain water must be effective in the aqueous phase and safe for ocular use. Parabens, phenols, benzoic acid, and sorbic acid fit this need because they act well in water-containing formulations and have established safety and regulatory acceptance for eye products. Parabens are water-soluble antimicrobial esters, offering broad activity with relatively low irritation. Phenols provide antimicrobial action suitable for aqueous media. Benzoic acid and sorbic acid are weak acids that inhibit microbial growth by disrupting metabolism and lowering intracellular pH, and they remain effective in the watery portion of the ointment. These categories are commonly used because they balance antimicrobial efficacy with compatibility in ophthalmic formulations. Heavy-metal preservatives carry safety concerns and are largely avoided today, and preservatives-free options exist but are not typical for aqueous-containing ointments. Colorants do not serve a preservative function.