Zirgan is a prescription antiviral eye gel used to treat corneal ulcers caused by the herpes simplex virus. Its active ingredient, ganciclovir, comes in a 0.15% ophthalmic gel that you apply directly to the affected eye. The FDA has approved it for adults and children aged 2 and older with a specific type of herpes eye infection called dendritic keratitis.
What Zirgan Treats
Zirgan targets acute herpetic keratitis, which is a corneal infection caused by herpes simplex virus (HSV). This infection creates branching, tree-like ulcers on the surface of the cornea called dendritic ulcers. Left untreated, these ulcers can scar the cornea and impair vision. Herpetic keratitis is one of the leading infectious causes of corneal blindness in developed countries, which is why having an effective topical antiviral matters.
The medication is not a general-purpose eye drop. It works specifically against herpes virus infections of the eye and won’t help with bacterial conjunctivitis, allergic reactions, or other common eye conditions.
How It Works
Zirgan is designed to selectively target herpes-infected cells rather than damaging healthy tissue. Once applied, the active ingredient gets converted inside virus-infected cells into a form that interferes with viral DNA in two ways: it blocks the enzyme the virus needs to copy its genetic material, and it inserts itself directly into the viral DNA strand, stopping replication in its tracks.
This selectivity is a meaningful advantage. An older antiviral eye drop, trifluridine, works through a nonselective mechanism that is toxic to healthy corneal cells along with infected ones. Zirgan’s targeted approach means less collateral damage to the eye’s surface during treatment.
How You Use It
Treatment follows a two-phase dosing schedule. During the active healing phase, you apply 1 drop to the affected eye 5 times per day, roughly every 3 hours while awake. You continue this schedule until the corneal ulcer heals. Once your doctor confirms healing, you step down to 1 drop 3 times per day for an additional 7 days.
The gel formulation stays on the eye’s surface longer than a liquid drop would, which helps maintain contact with the infected tissue. You should avoid wearing contact lenses during treatment.
How Well It Works
Clinical trials measured healing rates at day 7 of treatment. In the largest study, involving 164 patients with dendritic ulcers, 77% of patients using Zirgan had fully healed ulcers by day 7. Across three additional trials totaling 213 patients, the day-7 healing rate was 72%. These results were comparable to acyclovir ointment, the established standard of care in many countries, which achieved healing rates between 69% and 72% in the same trials.
For most patients, this means the active ulcer clears within the first week of treatment, with the additional week of reduced dosing helping to prevent immediate recurrence.
Common Side Effects
The most frequently reported side effects are local to the eye. Blurred vision is common immediately after applying the gel, which makes sense given its consistency. Eye irritation, a stinging or burning sensation upon application, and mild redness are also typical. These effects are generally temporary and resolve on their own.
Because Zirgan uses benzalkonium chloride as a preservative rather than thimerosal (which is found in older antiviral eye drops), it avoids the allergic sensitivity reactions that some patients experienced with trifluridine. That said, benzalkonium chloride can cause low-grade surface irritation with prolonged or very frequent use.
Who Can Use It
Zirgan is approved for adults and children aged 2 years and older. Its safety and effectiveness have not been established in children under 2. If you are pregnant or breastfeeding, the risks and benefits should be weighed carefully, as ganciclovir belongs to a drug class with known concerns about reproductive toxicity in animal studies.
How Zirgan Compares to Older Treatments
Before Zirgan’s approval, the primary topical antiviral available in the United States for herpes eye infections was trifluridine drops. While trifluridine is effective, it has notable drawbacks. Its nonselective mechanism means it kills healthy corneal cells alongside infected ones, which can slow healing and cause surface toxicity, especially with extended use. It also contains thimerosal, a preservative that triggers allergic reactions in a significant number of patients.
Zirgan offered a meaningful improvement on both fronts: a more targeted antiviral action and a better-tolerated preservative system. Its gel formulation also provides longer contact time with the cornea, potentially improving drug delivery compared to liquid drops that wash away quickly. In clinical trials, Zirgan matched or slightly exceeded the healing rates of acyclovir ointment, putting it on equal footing with the global standard while offering the convenience of a gel drop rather than a thick ointment that can blur vision more substantially.