Cidofovir Ophthalmic for Veterinary Use

Therapeutic Class: Anti-viral nucleoside analogue

Species: Cats

May Be Prescribed For: Feline herpesvirus (FHV-1)

Cidofovir is a powerful, broad-spectrum anti-viral, nucleoside analogue. It has activity against cytomegalovirus (CMV) and other members of the herpes-virus family. After uptake into cells, cidofovir selectively inhibits viral-DNA polymerases relative to host-cell polymerases. It has a long intracellular half-life, allowing for less-frequent dosing.

Intravenous cidofovir is licensed in human medicine to treat CMV infection in AIDS patients. The intravenous product has been compounded for use topically in unresponsive mucocutaneous herpes-simplex infections in humans. There is also a clinical case report of ophthalmic use in a woman with conjunctival squamous-cell carcinoma.

Ophthalmic cidofovir is used in veterinary medicine to treat conjunctivitis and keratitis associated with FHV-1. FHV-1 is a common infectious disease in cats caused by a cytopathic DNA virus. Other drugs that have been used to treat the oculars signs associated with FHV-1 are vidarabine, trifluridine, and idoxuridine. Many of these drugs require frequent administration and some of the more effective drugs have the undesirable side-effects of irritation and ocular discomfort.

Cidofovir has a long intracellular half-life and has been found to be effective with twice daily administration and a relatively short duration of treatment. In experimentally infected animals, cidofovir decreased the severity of clinical signs and viral shedding and was well tolerated.

The most complete information on the use of ophthalmic cidofovir to treat FHV-1 is in a study by Fontenelle J.P. et al. AJVR, Vol. 69, No.2, Feb. 2008: 289-293

Side effects vary with the species and the concentration of the ophthalmic solution. In the study performed by Fontenelle, no irritation or adverse effects were seen with a 0.5% solution. Stronger-concentration solutions caused irritation in other species. Other possible side-effects include ocular hypotonia, superficial punctuate keratitis, and obstruction of the nasolacrimal duct.

Bacterial causes such as Mycoplasma felis and Chlamydophilia felis should be ruled out in cases of acute conjunctivitis.

The anti-viral activity of cidofovir may be decreased by topical ophthalmic corticosteroids.

Conjunctivitis and erythematous eyelids were seen in a human study using 1% solution.