Vira-A

Vidarabine ophthalmic preparations are used to treat virus infections of the eye.

Vidarabine is available only with your doctor's prescription.

This product is available in the following dosage forms:

• Ointment
• Solution

Acute massive overdosage by oral ingestion of the ophthalmic ointment has not occurred. However, the rapid deamination to arabinosylhypoxanthine should preclude any difficulty. The oral LD50 for vidarabine is greater than 5020 mg/kg in mice and rats. No untoward effects should result from ingestion of the entire contents of the tube.

Overdosage by ocular instillation is unlikely because any excess should be quickly expelled from the conjunctival sac.

No information provided. Please refer to the WARNINGS and PRECAUTIONS sections.

Vira-A is part of the drug classes:

• Opthalmic antivirals

• Nucleosides and nucleotides excl. reverse transcriptase inhibitors

After application, eye ointments usually cause your vision to blur for a few minutes.

It is very important that you keep your appointments with your doctor. If your symptoms become worse, check with your doctor sooner.

This medicine may cause your eyes to become more sensitive to light than they are normally. Wearing sunglasses and avoiding too much exposure to bright light may help lessen the discomfort.

Vira-A 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. Because of the low solubility of Vira-A, trace amounts of both Vira-A 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 should not be expected to occur following ocular administration and swallowing lacrimal secretions. In laboratory animals, Vira-A is rapidly deaminated in the gastrointestinal tract to Ara-Hx.

In contrast to topical idoxuridine, Vira-A demonstrated less cellular toxicity in the regenerating corneal epithelium of the rabbit.

In controlled and uncontrolled clinical trials, an average of seven and nine days of continuous Vira-A 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.

Microbiology

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
Vaccinia
Varicella-Zoster

Except for Rhabdovirus and Oncornavirus, vidarabine does not display in vitro antiviral activity against other RNA or DNA viruses, including Adenovirus.

Susceptibility Tests - No universal, standardized, quantitative in vitro procedures have as yet been developed to estimate the susceptibility of viruses to antiviral agents.

Vira-A Ophthalmic Ointment, 3%, is contraindicated in patients who develop hypersensitivity reactions to it.

Acute massive overdosage by oral ingestion of the ophthalmic ointment has not occurred. However, the rapid deamination to arabinosylhypoxanthine should preclude any difficulty. The oral LD50 for vidarabine is greater than 5020 mg/kg in mice and rats. No untoward effects should result from ingestion of the entire contents of the tube.

Overdosage by ocular instillation is unlikely because any excess should be quickly expelled from the conjunctival sac.

Administer approximately one-half inch of Vira-A Ophthalmic Ointment, 3%, into the lower conjunctival sac five times daily at three-hour intervals.

If there are no signs of improvement after 7 days, or complete re-epithelialization has not occurred by 21 days, other forms of therapy should be considered. Some severe cases may require longer treatment.

Too frequent administration should be avoided.

After re-epithelialization has occurred, treatment for an additional 7 days at a reduced dosage (such as twice daily) is recommended in order to prevent recurrence.

The following topical antibiotics: gentamicin, erythromycin, chloramphenicol; or topical steroids: prednisolone or dexamethasone have been administered concurrently with Vira-A Ophthalmic Ointment, 3%.