Doxycycline & Famciclovir for Feline Upper Respiratory Disease in Kittens

In the Literature

Vernau KM, Kim S, Thomasy SM, et al. Doxycycline with or without famciclovir for infectious ophthalmic and respiratory disease: a prospective, randomized, masked, placebo-controlled trial in 373 kittens. J Feline Med Surg. 2024;26(11):1098612X241278413. doi:10.1177/1098612X241278413

The Research …

Feline infectious upper respiratory disease is common, particularly in multicat environments.^1,2 Bacterial (eg, Chlamydia felis, Bordetella bronchiseptica, Mycoplasma felis) and viral (eg, feline herpesvirus type 1 [FHV-1], calicivirus) pathogens are frequently implicated.³ Ocular clinical signs are nonspecific and similar across etiologies with the exception of FHV-1, which has an affinity for the cornea and causes increased morbidity and mortality in kittens (Figures 1 and 2).⁴ High incidence of coinfections in patients with infectious upper respiratory disease complicates treatment decisions.^4,5

FIGURE 1 FHV-1 blepharoconjunctivitis in a cat; inflammation of the eyelid margin with significant conjunctival hyperemia, chemosis, epiphora, and elevation of the third eyelid are present.

FIGURE 2 Severe ocular changes in a cat with infectious upper respiratory disease secondary to FHV-1; clinical signs include bilateral periocular accumulation of thick ocular discharge, severe blepharoconjunctivitis, and secondary keratitis of the right eye resulting in corneal perforation with prominent iris prolapse.

This study compared clinical outcomes of kittens 1 to 12 weeks of age with infectious upper respiratory disease treated with doxycycline (5 mg/kg PO every 12 hours) and famciclovir (90 mg/kg PO every 12 hours) or doxycycline and placebo for 21 days. Doxycycline was administered as an oral suspension, and famciclovir was prepared using crushed commercially available tablets. All patients were also treated with 0.3% ofloxacin ophthalmic solution, received supportive care, and were weighed daily.

Kittens were grouped according to disease severity (ie, mild, severe), age, and treatment. Respiratory and ophthalmic signs were scored daily by trained caregivers, and ophthalmic examination was performed on days 1 and 21 by a veterinary ophthalmologist or ophthalmology resident. Rate of clinical improvement and clinical scores were evaluated between groups. Ophthalmic resolution and clinical resolution were defined as scores of zero for all ocular signs and all ocular and respiratory signs, respectively, and ophthalmic and clinical recovery was defined as absence of active inflammation.

Regardless of treatment, a high percentage of clinical and ophthalmic recovery was reported for all groups, and patients with severe disease took longer to reach clinical recovery or resolution. A majority (75%) of patients with mild disease treated with famciclovir achieved clinical resolution more quickly (average, 4-5 days faster) than all other groups. Patients given famciclovir were also less likely to develop corneal disease.

… The Takeaways

Key pearls to put into practice:

• No statistical difference in clinical recovery rates was found between the treatment groups; however, patients with mild disease achieved clinical resolution faster when treated with a combination of topical ofloxacin, oral doxycycline, and oral famciclovir. This study did not assess the safety of famciclovir in kittens, but no adverse events were reported.

• Shelter conditions were not mimicked in this study; kittens were housed individually or in small groups in foster homes, which may have impacted outcomes.

• Studies evaluating combination therapy in adult cats are lacking. In experimental settings, famciclovir is effective and well tolerated, with a low incidence of adverse effects. In shelter settings, a single dose worsened clinical signs and viral shedding,⁶ and twice-daily administration for 1 week reduced viral shedding but not clinical signs.⁷

• The etiology of infectious upper respiratory disease cannot be determined by ocular disease or physical examination findings alone; diagnostic testing is key. Coinfections are common, and a multifactor management approach is recommended.^4,5

• Use of compounded oral formulations warrants monitoring of best-use dates and ordering in small quantities to limit variability in drug concentration and/or activity. Compounded famciclovir was ineffective in one report.⁵