vidarabine (adenine arabinoside)
Vira-A

Available forms
Available by prescription only
Ophthalmic ointment: 3% in 3.5-g tube (equivalent to 2.8% vidarabine)

Indications and dosages
 Acute keratoconjunctivitis and recurrent epithelial keratitis caused by herpes simplex virus types 1 and 2. Adults and children: Instill 1/2 inch (1.3 cm) of ointment into lower conjunctival sac five times daily at 3-hour intervals.

Pharmacodynamics
Antiviral action: Exact mechanism unknown. Adenine analogue; presumably involves inhibition of DNA polymerase and viral replication by incorporation into viral DNA.

Pharmacokinetics
Absorption: No systemic absorption occurs with ophthalmic use.
Distribution: Only trace amounts of drug detected in aqueous humor if cornea is intact.
Metabolism: Metabolized into active metabolite arabinosyl-hypoxanthine.
Excretion: No information available.

Contraindications and precautions
Contraindicated in patients hypersensitive to drug and in those with sterile trophic ulcers. Use cautiously in patients receiving corticosteroids.

Interactions
None reported.

Adverse reactions
EENT: temporary burning, itching, mild irritation, pain, lacrimation, foreign body sensation, conjunctival injection, punctal occlusion, sensitivity, superficial punctate keratitis, photophobia.
Other: hypersensitivity reactions.

Effects on lab test results
None reported.

Overdose and treatment
No information available.

Special considerations
• Drug is effective only if patient has at least minimal immunocompetence.
• Definitive diagnosis of herpes simplex conjunctivitis should be made before administration of ophthalmic form.
• Monitor therapeutic effect. If there are no signs of improvement after 7 days or if reepithelialization hasn’t occurred in 21 days, consider other forms of therapy. Patients with severe cases may need longer treatment. Continue drug for 5 to 7 days, twice daily, to prevent recurrence.
• Monitor patient for adverse effects.

Patient education
• Warn patient receiving ophthalmic ointment not to exceed recommended frequency or duration of therapy. Instruct him to wash hands before and after applying ointment, and warn him against allowing tip of tube to touch eye or surrounding area.
• Advise patient to wear sunglasses if photosensitivity occurs.
• Instruct patient to store ophthalmic ointment in tightly sealed, light-resistant container.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use