Which topical anti-herpes agent is known to use the thimerosal preservative?

• A. Trifluridine (Viroptic)
• B. Ganciclovir (Zirgan)
• C. Acyclovir (Zovirax)
• D. Valacyclovir (Valtrex)

Answer: (A)

Thimerosal is a mercury-containing preservative that has been used in some ophthalmic solutions to prevent microbial growth. Trifluridine, used as an eye drop for herpes simplex infections of the eye, has historically been formulated with thimerosal as its preservative in the Viroptic preparation. This association is why it is the best-known topical anti-herpes agent linked to thimerosal. Ganciclovir ophthalmic solution (Zirgan) uses a different preservative system, not thimerosal, and acyclovir topical ointment and valacyclovir (the latter being a systemic prodrug, not a topical ocular agent) are not the preparations typically associated with thimerosal.