Viral keratitis herpes simplex

Acute epithelial herpes simplex keratitis (dendritic keratitis) fungal diseases of ocular structures vaccinia, varicella and most other viral diseases of the cornea and conjunctiva ocular tuberculosis hypersensitivity after uncomplicated removal of a superficial corneal foreign body mycobacterial eye infection acute, purulent, untreated eye infections that may be masked or enhanced by the presence of steroids. 

Vidarabine [vye DARE a been] arabinofuranosyl adenine, ara-A, adenine arabinoside) is one of the most effective of the nucleoside analogs and is also the least toxic. However, it has been supplanted clinically by acyclovir, which is more efficacious and safe. Although vidarabine is active against herpes simplex virus type 1 (HSV-1), HSV-2, and varicella-zoster virus (VZV), its use is limited to treatment of immunocompromised patients with herpes simplex keratitis or encephalitis, or VZV infections. Vidarabine, an adenosine analog, is converted in the cell to its 5 -triphosphate analog (ara-ATP), which is postulated to inhibit viral DNA synthesis. Some resistant herpes virus... 

Ocular antiviral chemotherapy in the horse is adapted from that used in herpes simplex virus (HSV) and varicella zoster keratitis in humans. The agents used are nucleotide analogs capable of inhibiting viral replication by competitive inhibition of the uptake of the nucleotide into the viral genome. These agents are virustatic and require an intact immune system to suppress or eliminate the virus from the eye. They probably do not eradicate any latent infection. The antiviral drugs available currently do not penetrate intact comeal epithelium and are poorly disseminated within the comeal stroma. The availability of these dmgs will vary in different countries and some may only be obtained from hospital pharmacies. 

Idoxuridine (1 drop into infected eye/hr during the day and q. 2 hours at night) is indicated in the treatment of herpes simplex keratitis. By altering normal DNA synthesis, idoxuridine inhibits the reproduction of herpes simplex virus. IDU replaces thymidine in the enzymatic step of viral replication, produces faulty DNA, and hence a structure that loses its ability to infect and destroy ocular tissue. Corticosteroids can accelerate the spread of a viral infection and are usually contraindicated in herpes simplex epithelial infections. Idoxuridine occasionally causes irritation, pain, pruritus, inflammation or edema of the eyes or lids and allergic reactions, photophobia, corneal clouding, stippling, and punctate defects in the corneal epithelium. The punctate defects may be a manifestation of the infection, as healing usually takes place without interruption of therapy. 

Vidarabine is used mainly in human HSV-1 and HSV-2 encephalitis, decreasing the mortality rate from 70 to 30%. Whitley et al. (57) reported that early vidarabine therapy is helpful in controlling complications of localized or disseminated herpes zoster in immunocompromised patients. Vidarabine also is useful in neonatal herpes labialis or genitalis, vaccinia virus, adenovirus, RNA viruses, papovavirus, CMV, and smallpox virus infections. Given the efficacy of vidarabine in certain viral infections, the U.S. FDA approved a 3% ointment for the treatment of herpes simplex keratoconjunctivitis and recurrent epithelial keratitis, and a 2% IV injection for the treatment of herpes simplex encephalitis and herpes zoster infections (Table 43.3). A topical ophthalmic preparation of vidarabine is useful in herpes simplex keratitis but shows little promise in herpes simplex labialis or genitalis. The monophosphate esters of vidarabine are more water-soluble and can be used in smaller volumes and even intramuscularly. These esters are under clinical investigation for the treatment of hepatitis B, systemic and cutaneous herpes simplex, and herpes zoster virus infections in immunocompromised patients. 

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