Chromatography–Based Pharmacokinetic Evaluation of Famciclovir in Cats with Feline Infectious Rhinobronchitis

Feline infectious rhinobronchitis (FVR) is a common and serious infectious upper respiratory disease. While the effectiveness of the human drug famciclovir in treating FVR has been confirmed with several pharmacokinetic studies conducted in cats following oral administration of the drug, the number of cats participating in these experiments is relatively small, and the administration of different doses has not been conducted in parallel studies.

In response, researchers conducted parallel experiments to investigate the pharmacokinetic characteristics in more cats after single and multiple oral administration of famciclovir tablets and intravenous injection of penciclovir, with analysis of blood samples to detect the drug in their plasma analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) for detecting the drug in plasma. A paper based on this research was published in Frontiers in Veterinary Science (1).

FVR is a common and serious infectious upper respiratory disease, FVR may be fatal, especially in young kittens. The disease has an estimated seroprevalence in feline populations ranging 50–97%. The mortality rate of untreated FVR kittens can reach over 70%, and the mortality rate of untreated FVR adult cats is about 20–30% (2-6).

Famciclovir, an antiviral prodrug initially developed for human herpesviruses, demonstrates significant therapeutic efficacy in cats with FVR caused by feline herpesvirus type 1 (FHV-1). In practice, veterinarians empirically prescribe famciclovir tablets at 30–90 mg/kg every 12 h for 14 days. Because of this, the researchers believe that the detailed pharmacokinetic data containing the above dosage in cats need to be determined (1).

To determine the pharmacokinetics of famciclovir in healthy cats after single or multiple oral and intravenous administrations, the researchers administered famciclovir to 40 cats in 4 different dose groups through a single oral dose, while 10 cats received famciclovir every 12 h for 14 days, and another 10 cats received a single intravenous dose of penciclovir-in three different phases. At the predetermined time points, blood samples were collected through the radial vein of the cat. The blood samples were analyzed by LC-MS/MS to detect the concentration of penciclovir in cat plasma. The pharmacokinetic parameters of penciclovir were calculated using a noncompartmental model (1).

After a single oral administration in cats, the researchers found that absorption and exposure of famciclovir tablets also increased with the increase in dose. After multiple oral administrations of famciclovir tablets, the concentration of the drug fluctuated violently in steady state with no accumulation in the body. The absolute bioavailability of the tested cats after single oral administration of 15.625 g, 31.25, 62.5, and 93.75 mg/kg famciclovir tablets was 67.12, 33.94, 26.45, and 18.37%, respectively (1).

“The initial safety of the famciclovir tablet in cats after multiple oral administrations, with 62.5 mg/kg administered twice daily for 14 consecutive days, had been demonstrated,” the researchers stated. They also reported that they believe their research provides a scientific basis for the clinical dosage and duration of treatment of FVR with famciclovir tablets (1).

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References

1. Qu, M.; Ke, X.; Zhang, Z. et al. Non-Linear Pharmacokinetics of Penciclovir in Healthy Cats After Single and Multiple Oral Administration of ZFamciclovir. Front. Vet. Sci. 2025, 12, 1695827. DOI: 10.3389/fvets.2025.1695827
2. Bannasch, M. J.; Foley, J. E. Epidemiologic Evaluation of Multiple Respiratory Pathogens in Cats in Animal Shelters. J. Feline Med. Surg. 2005, 7 (2), 109-119. DOI: 10.1016/j.jfms.2004.07.004
3. Holst, B. S.; Hanås, S.; Berndtsson, L. T. et al. Infectious Causes for Feline Upper Respiratory Tract Disease--A Case-Control Study. J. Feline Med. Surg. 2010, 12 (10), 783-789. DOI: 10.1016/j.jfms.2010.06.002
4. Hurley, K. F. Feline Infectious Disease Control in Shelters. Vet. Clin. North Am. Small Anim. Pract. 2005, 35 (1), 21-37. DOI: 10.1016/j.cvsm.2004.08.002
5. Kang, B. T.; Park, H. M. Prevalence of Feline Herpesvirus 1, Feline Calicivirus and Chlamydophila felis in Clinically Normal Cats at a Korean Animal Shelter. J. Vet. Sci. 2008, 9 (2), 207-209. DOI: 10.4142/jvs.2008.9.2.207
6. Pedersen, N. C.; Sato, R.; Foley, J. E. et al. Common Virus Infections in Cats, Before and After Being Placed in Shelters, with Emphasis on Feline Enteric Coronavirus. J. Feline Med. Surg. 2004, 6 (2), 83-88. DOI: 10.1016/j.jfms.2003.08.008