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Putting evidence into practice

Current treatment of feline herpesvirus type-1 is aimed at reducing clinical signs, but a drug used in humans could target the virus directly

13 April 2018, at 2:20p.m.

Evaluation of three studies investigating the clinical response to the administration of the antiviral famciclovir in cats with confirmed or suspected FHV1 has shown the drug to have a significant positive effect associated signs, with few to no adverse effects.

A crucial intervention

The Knowledge summary ‘In cats infected with feline herpesvirus type-1 (FHV-1) does treatment with famciclovir result in a reduction of respiratory and ocular clinical signs?’ in Veterinary Evidence concluded that famciclovir – normally used in the treatment of shingles and other herpes viruses in people – could be an important intervention in cats showing the signs of FHV-1, particularly if they haven’t responded to antibiotics.

Limitations to the primary literature mean more research is needed before famciclovir can be routinely recommended, but widespread improvement seen in all the evidence, combined with a general lack of side-effects even at high doses, make this antiviral a strong consideration on a case-by-case basis.

Widespread improvement seen in all the evidence, combined with a general lack of side-effects even at high doses, make this antiviral a strong consideration

In addition to a reduction in clinical signs, famciclovir appeared to reduce viral replication, as demonstrated by a reduction in the presence of FHV-1 viral load and antibodies.

Viral shedding was also lessened – an important finding when considering the contagious nature of the disease. However, questions remain over the efficacy of the drug in reducing corneal ulcers and improving abnormal tear film. Additional topical treatments would appear to be necessary in patients with these clinical signs.

Dosing and course of treatment

A dosage regimen is yet to be established, but one study demonstrated a possible correlation between an increased dose (90mg/kg versus 40mg/kg, three times per day) and median duration of improvement.

Based on the evidence, treatment lengths vary widely (from two weeks to four months) and should be adapted depending on the patient’s response.

Metabolism of the drug is unknown in cats, so caution is recommended when treating patients with underlying liver or kidney insufficiency

Dose-related side-effects weren’t apparent, but gastrointestinal clinical signs can occur. Metabolism of the drug is unknown in cats, so caution is recommended when treating patients with underlying liver or kidney insufficiency. For human use, famciclovir usually comes as 125mg tablets and is only available by prescription in the UK. Feline herpesvirus type-1, alongside feline calicivirus, is the most common cause of respiratory infections in cats. Clinical signs, which may include conjunctivitis and dermatological issues as well as breathing problems, can be severe, and permanent damage to the eyes and respiratory tract can occur.

The vast majority of infected cats become lifelong carriers of the virus, which not only predisposes them to relapses, but also makes them reservoirs for the spread of the disease. There are currently no antiviral drugs indicated for the treatment of FHV-1, so the likely efficacy of famciclovir, both in terms of reducing the severity of clinical signs and controlling contagion, offers a new possible avenue of intervention to practitioners.

Full Knowledge summary: https://veterinaryevidence.org/index.php/ve/article/view/105