Effects of famciclovir in cats with spontaneous acute upper respiratory tract disease

Kopecny L, Maggs DJ, Leutenegger CM, Johnson LR. Effects of famciclovir in cats with spontaneous acute upper respiratory tract disease. J Feline Med Surg. 2019 Jun 27;1098612X19857587

Upper respiratory tract infections are extremely common in domestic cats, especially those in group housed situations such as multi- cat households, shelters, and catteries. The most common component of the upper respiratory disease complex is Feline Herpesvirus 1 (FHV-1). Though rarely life-threatening, FHV-1 causes significant morbidity, including sneezing, rhinitis, conjunctivitis, corneal ulcers, and more rarely a facial dermatitis syndrome. Traditionally, therapy for FHV-1 has been supportive, with antibiotics utilized to manage secondary or concurrent bacterial infections and allowing FHV-1 to resolve with time. Recently, famciclovir (an antiherpesviral commonly used in human medicine) has been utilized to treat FHV-1 infections, however the dose, frequency of administration, and efficacy have been subject to debate.

This study was designed to assess the clinical and microbiological efficacy of famciclovir in the treatment of spontaneous upper respiratory infections in cats. The study was designed as a prospective double blind placebo controlled trial on cats presenting from foster based rescue programs in California for upper respiratory signs.

Cats were enrolled if they had upper respiratory signs for less than 30 days duration. Previous therapy was allowed if it was unsuccessful and less than 7 days duration.  Age, breed, sex, neuter status and vaccination history were recorded, as was retroviral status if it was known (but testing was not done on all cats). All cats received a full physical exam at study entry and exit, and an oculo-oropharyngeal swab which was PCR tested for common respiratory pathogens. Owners also completed a survey with a semiquantitative grading system on severity of signs.

Cats were stratified randomly to receive either doxycycline at 5mg/kg q12h, or doxycycline at the previous dose plus famciclovir at 90mg/kq q12h. The doxycycline group was given placebo famciclovir. Cats were treated for 7 days after the resolution of clinical signs.

32 cats were enrolled in the study, but 5 were excluded due to incomplete data. One cat died 4 days into enrollment for unknown reasons despite resolution of clinical signs. Two cats in the doxycycline group failed to respond and were transitioned to the combination group. The remaining 24 cats were evenly randomized into the two groups.

100% of cats had sneezing as a clinical sign, and 96% ocular/92% nasal discharge. There was no significant difference between groups for age, sex, clinical signs, pathogen testing, or any other presenting data. FHV-1 was detected in 29% of cats, with Bordetella, chlamydia, mycoplasma, and calicivirus also represented.

Median duration of treatment was 14 days for the combination group and 19 for doxycycline alone, a non-significant difference. Owner reported duration of signs and disease severity score did not differ between groups. Median body weight at end of study and change in body weight were not different.

There was no correlation between number of pathogens isolated and clinical disease score or  number of days of treatment. Both groups had the majority of cats clear FHV-1 infections, with one positive cat in each group at study end.

There are several possible limitations to this study. As the authors mention, the prevalence of FHZV-1 in this group was low, which means many of these cats would not be expected to respond. In many situations, the clinically relevant question is not “should doxycycline be given with famciclovir” so much as “could this be treated with famciclovir alone”, as such a non-inferiority study comparing to doxycycline may be beneficial.  The question of whether specific clinical signs (such as conjunctivitis or corneal ulcers) may be responsive to famciclovir than URTI in general could also be consider.

The authors concluded that the addition of famciclovir to doxycycline was not more effective than doxycycline alone. Despite some further questions that may be spurred by this study, this data suggests that there is little utility to adding famciclovir to doxycycline for routine feline URTI.

See Also

Thomasy SM, Shull O, Outerbridge CA, et al. Oral administration of famciclovir for treatment of spontaneous ocular, respiratory, or dermatologic disease attributed to feline herpesvirus type 1: 59 cases (2006–2013). J Am Vet Med Assoc 2016; 249: 526–538.

Thomasy SM, Whittem T, Bales JL, et al. Pharmacokinetics of penciclovir in healthy cats following oral administration of famciclovir or intravenous infusion of penciclovir. Am J Vet Res 2012; 73: 1092–1099.

Veir JK, Ruch-Gallie R, Spindel ME, et al. Prevalence of selected infectious organisms and comparison of two anatomic sampling sites in shelter cats with upper respiratory tract disease. J Feline Med Surg 2008; 10: 551–557