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VIRA-A (vidarabine) is rapidly deaminated to arabinosylhypoxanthine (Ara-Hx), the principal metabolite. Ara-Hx also possesses in vitro antiviral activity but this activity is less than that of VIRA-A (vidarabine) . Because of the low solubility of VIRA-A (vidarabine) , trace amounts of both VIRA-A (vidarabine) and Ara-Hx can be detected in the aqueous humor only if there is an epithelial defect in the cornea. If the cornea is normal, only trace amounts of Ara-Hx can be recovered from the aqueous humor.
Systemic absorption of VIRA-A (vidarabine) should not be expected to occur following ocular administration and swallowing lacrimal secretions. In laboratory animals, VIRA-A (vidarabine) is rapidly deaminated in the gastrointestinal tract to Ara-Hx.
In controlled and uncontrolled clinical trials, an average of seven and nine days of continuous VIRA-A (vidarabine) Ophthalmic Ointment, 3%, therapy was required to achieve corneal re-epithelialization. In the controlled trials, 70 of 81 subjects (86%) re-epithelialized at the end of three weeks of therapy. In the uncontrolled trials, 101 of 142 subjects (71%) re-epithelialized at the end of three weeks.
Seventy-five percent of the subjects in these uncontrolled trials had either not healed previously or had developed hypersensitivity to topical idoxuridine therapy.
Vidarabine is a purine nucleoside obtained from fermentation cultures of Streptomyces antibioticus. The antiviral mechanism of action has not been established. Vidarabine appears to interfere with the early steps of viral DNA synthesis.
Vidarabine has been shown to possess antiviral activity against the following viruses in vitro:
Herpes simplex types 1 and 2
Except for Rhabdovirus and Oncornavirus, vidarabine does not display in vitro antiviral activity against other RNA or DNA viruses, including Adenovirus.
No universal, standardized, quantitative in vitro procedures have as yet been developed to estimate the susceptibility of viruses to antiviral agents.
Last reviewed on RxList: 4/8/2009
This monograph has been modified to include the generic and brand name in many instances.
Additional Vira-A Information
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