vidarabine

Action and Spectrum

Actions and spectrum: 

There are two ways in which Vidarabine inhibits the replication of herpes virus DNA: 1) by competitively inhibiting viral DNA polymerase and 2) by incorporating into and breaking the growing viral DNA chain. The active form of Vidarabine, ara-ATP, is produced when kinases phosphorylate it one step at a time.

Ara-ATP functions as a substrate and an inhibitor of viral DNA polymerase. Viral DNA polymerase uses ara-ATP as a substrate, which competitively inhibits dATP and causes “faulty” DNA to form. DNA synthesis can also be disrupted by inserting ara-ATP into the DNA strand in place of numerous adenosine bases.

Drug Interaction

Adverse Reaction

Frequency not defined 

Conjunctival injection 

Irritation 

Punctal occlusion 

Punctate keratitis 

Lacrimation 

Stromal edema 

The feeling of a foreign body in the eye 

Increased light sensitivity of eyes 

Black Box Warning

No special black box warning for this drug is available

Contraindication / Caution

Contraindication/Caution: 

Contraindication: 

Hypersensitivity  

Pregnancy / Lactation

Pregnancy consideration:  

USFDA pregnancy category: C 

Lactation:  

Data about the excretion of Vidarabine into breast milk is not known 

Pregnancy category:  

Category A: Studies that were well-controlled and met expectations revealed no risk to the fetus `in either the first or second trimester. 

Category B: There was a lack of studies on pregnant women and no evidence of risk to the fetus in animal experiments.   

Category C: there was evidence of risk of adverse effects in animal reproduction studies, and no adequate evidence in human studies must take care of potential risks in pregnant women.    

Category D: adequate data with sufficient evidence of human fetal risk from various platforms, but despite the potential risk, and used only in emergency cases for potential benefits.   

Category X: Drugs listed in this category outweigh the risks over benefits. Hence, these categories of drugs need to be avoided by pregnant women.    

Category N: There is no data available for the drug under this category

Pharmacology

Pharmacology: 

Vidarabine, isolated from Streptomyces antibioticus, is a synthetic nucleoside antibiotic. 

Pharmacodynamics: 

Vidarabine is an analog of synthetic purine nucleoside that exhibits inhibitory activity against varicella-zoster virus (VZV), HSV-1, and HSV-2 in vivo and in vitro. Because of Vidarabine’s affinity for the enzyme thymidine kinase (TK), which HSV and VZV encode, the drug has a highly selective inhibitory effect. Vidarabine is changed into its nucleotide analog, Vidarabine monophosphate, by this viral enzyme.

Cellular guanylate kinase transforms the monophosphate into diphosphate, and several other cellular enzymes turn it into triphosphate. By becoming integrated into the DNA strand and preventing the creation of phosphodiester bridges between bases, vidarabine triphosphate inhibits the herpes virus’s ability to replicate its DNA in vitro. Ultimately, this causes the viral DNA strands to become unstable. 

Pharmacokinetics: 

Absorption 

Since Vidarabine is administered through an ophthalmic route, systemic absorption cannot be expected 

Distribution 

24 to 38% of Vidarabine is known to be protein-bound 

Metabolism 

Vidarabine is known to be metabolized in the gastrointestinal tract through deamination to Ara-Hx, as observed in an animal study. 

Adminstartion

Administration: 

Wash your hands first. Next, create a pouch by removing the lower eyelid from the eye. Insert a slender ointment strip into the pouch. Unless the doctor instructs you otherwise, a 1.25-cm (approximately ½-inch) strip of ointment is usually sufficient. To allow the medication to contact the infection, gently close your eyes and keep them closed for one or two minutes. 

Keep the applicator tip away from any surface, including the eye, to keep the medication as sterile as possible. After applying vidarabine eye ointment, firmly close the tube and use a clean tissue to wipe the tip.

Patient Information Leaflet

Patient information leaflet 

Generic Name: vidarabine 

Why do we use Vidarabine? 

Vidarabine, an antiviral agent, exhibits activity against various RNA tumor viruses, rhabdoviruses, hepadnaviruses, herpes viruses, and poxviruses. HSV-1 and HSV-2-related recurrent superficial keratitis and acute keratoconjunctivitis are treated with a 3% ophthalmic ointment called Vira-A. Vidarabine also shortens the duration of viral shedding and lessens the formation of lesions in AIDS patients with herpes zoster.