indication

For use in keratoconjunctivitis and keratitis caused by herpes simplex virus.

pharmacology

In chemical structure idoxuridine closely approximates the configuration of thymidine, one of the four building blocks of DNA (the genetic material of the Herpes virus). As a result, idoxuridine is able to replace thymidine in the enzymatic step of viral replication or "growth". The consequent production of faulty DNA results in a pseudostructure which cannot infect or destroy tissue. In short, by pre-empting a vital building block in the genetic material of the Herpes simplex virus, Herplex-D topical solution destroys the infective and destructive capacity of the viral material. The virus infected cell may only be attacked during the period of active synthesis of DNA. This occurs early in the development of the Herpes simplex lesion, but at different times in different cells. Therefore, ideally, the affected area should remain saturated with the antiviral agent.

mechanism of action

Idoxuridine acts as an antiviral agent by inhibiting viral replication by substituting itself for thymidine in viral DNA. This in turn inhibits thymidylate phosphorylase and viral DNA polymerases from properly functioning. The effect of Idoxuridine results in the inability of the virus to reproduce or to infect/destroy tissue.

toxicity

Hypersensitivity or increased sensitivity of eyes to light. LD₅₀=3080 mg/kg (orally in mice).

biotransformation

Idoxuridine is rapidly inactivated by deaminases or nucleotidases.

absorption

Systemic absorption is unlikely following ocular administration even when nasolacrimal secretions are swallowed, since vidarabine is rapidly deaminated in the gastrointestinal tract.