Famciclovir at 90 mg/kg PO q8h is the most evidence-supported systemic antiviral for feline herpesvirus type 1 (FHV-1) ocular and respiratory disease, producing marked clinical improvement in 51% of cats and mild improvement in 34%, for an overall response rate of 85%, with a median time to improvement of 13 days (range 3–183 days).Journal of the… The high dose (approximately 90 mg/kg) produces significantly shorter time to improvement and significantly greater degree of improvement than the low dose (approximately 40 mg/kg).Journal of the… Most cats (75%) require only one course of treatment, and 53% of owners rate improvement as permanent.Journal of the…
In shelter kittens with infectious upper respiratory and ocular disease, combining famciclovir 90 mg/kg PO q8h with doxycycline is supported by the most recent controlled data. Famciclovir should be administered by crushing the tablet and combining it with doxycycline suspension immediately before dosing — pre-mixed compounded oral suspensions show poor accuracy, precision, and consistency of formulation and should not be used.Journal of Feli… Doses should be adjusted weekly as kittens gain body weight.Journal of Feli… At 90 mg/kg in a 1 kg kitten, the daily drug cost was approximately US$0.33 at the time of the study.Journal of Feli…
For topical ocular antiviral therapy, cidofovir 0.5% ophthalmic solution applied twice daily is the strongest option currently supported by clinical data. Topical cidofovir significantly decreased conjunctival FHV-1 viral load from Day 1 to Day 8 compared with placebo, and 77% of corneal ulcers in antiviral-treated cats healed versus 0% in placebo cats over 7 days.Veterinary Opht… Cidofovir also produced significant weight gain in juvenile cats compared with placebo.Veterinary Opht… Topical ganciclovir 0.15% gel applied q8h is well tolerated in cats and achieves 100% reduction in viral plaque number in vitro at 89 µM, and it produced significant weight gain in juvenile cats, but did not significantly reduce viral load or improve ocular scores compared with placebo in the 7-day shelter trial.Journal of Feli…+1 Ganciclovir 0.15% ophthalmic gel is available commercially or can be compounded as a 0.5% solution with the addition of interferon alpha-2B.MSD Vet Manuals
Valacyclovir is contraindicated in cats — it produces toxic effects severe enough to require early study termination for humane reasons.Journal of the… All antiviral drugs in this species are used off-label.MSD Vet Manuals
Lysine supplementation should not be used. It has no antiviral activity against FHV-1, does not antagonize arginine in cats, and some clinical data show increased infection frequency and disease severity in cats receiving it.BMC Veterinary… Because cats cannot synthesize arginine endogenously, lysine-induced arginine depletion risks hyperammonemia, which may be fatal.BMC Veterinary…
Topical penciclovir 1% cream applied three times daily produces only modest reduction in clinical ocular disease severity and does not prevent geographic corneal ulceration — the most severe manifestation of FHV-1 keratitis was observed only in a penciclovir-treated cat in the most recent experimental study.American Journa… Refinements in concentration, physicochemical properties, and application frequency are needed before penciclovir can be recommended as a primary topical option.American Journa…
Raltegravir at 80 mg PO q12h for 14 days reduced FHV-1 shedding duration and ocular and respiratory disease severity in experimentally infected cats compared with vehicle-treated controls, though conjunctival viral titer and corneal leukocyte infiltration did not differ between groups.American Journa… This agent represents an emerging option but has not been evaluated in naturally infected client-owned cats.
| Drug | Dose / Route / Frequency | Key Efficacy Finding | Key Caveat |
|---|---|---|---|
| Famciclovir (oral) | 90 mg/kg PO q8h | 85% overall improvement; median 13 days to response Journal of the… | Compounded pre-mixed suspension unreliable; crush tablet immediately before dosing Journal of Feli… |
| Cidofovir (topical) | 0.5% solution, q12h × 7 days | Significant viral load reduction; 77% corneal ulcer healing Veterinary Opht… | Compounded formulation required |
| Ganciclovir (topical) | 0.15% gel, q8h | Well tolerated; 100% plaque reduction in vitro Journal of Feli…; weight gain in juveniles Veterinary Opht… | No significant viral load or ocular score improvement vs placebo in 7-day trial Veterinary Opht… |
| Raltegravir (oral) | 80 mg PO q12h × 14 days | Reduced shedding duration and disease severity in experimental infection American Journa… | No data in naturally infected cats |
| Penciclovir (topical) | 1% cream, q8h | Modest reduction in disease severity American Journa… | Geographic ulceration occurred only in treated cats; refinement needed American Journa… |
| Valacyclovir | — | — | Contraindicated — toxic to cats Journal of the… |
| Lysine | — | No efficacy in any clinical trial BMC Veterinary… | Risk of fatal hyperammonemia via arginine depletion BMC Veterinary… |
Would you like guidance on how to select between topical cidofovir and topical ganciclovir based on the specific ocular presentation (e.g., corneal ulceration vs. conjunctivitis only)?