ANTI-VIRAL DRUGS

Yogapriya.vB.Opt(IIIyr)

INTRODUCTION

• Viruses are intracellular parasites• They depend on the host cell for food,growth and

multiplication• There are two types of viruses=DNAviruses and RNAviruses• Retrovirus is a type of RNA virus which causes AIDS

CLASSIFICATION OF ANTIVIRAL DRUGS

ANTI-HERPES VIRUS AGENT • Acyclovir• Gancyclovir• famcyclovir

ANTI-INFLUENZA VIRUS AGENT • Amantadine• Rimantadine

ANTI-RETROVIRAL AGENTS

i)Nucleoside reverse transcriptase inhibitors(NRTI)

• Zidovudin• Didanosine• Zalcitabine

ii)Non-nucleoside reverse transcriptase inhibitors(NNRTI)

• Nevirapine• Efavirenz• Delavirdine

ACYCLOVIR

• Acyclovir is a purine analogue• The drug is more specific in affecting viral particle• As it is activated only by virus induced thymidine kinase and converted to an

acyclomonophosphate form and then to a triphosohate form• Inhibits virus induced DNA polymerase

Advantage• Penetrates intact corneal epithelium and achieves sufficient viricidal

concentration in aqueos• More selective therefore it is less toxic• More active than other agent• Wider spectrum than other agents• Can cross blood brain barrier and probably blood ocular barrier

Preparations• 3% ophthalmic ointment• 200 mg capsules• 5% dermal cream

Dose for ocular lesion • For primary HSV blepharitis and orofacial lesions, 5% dermal

cream 5 times/day is effective• For HSV superficial and deep corneal lesions 3% ointment 5

times/day till the lesionsheal,then reduced to 2 to 3 times/day• Maximum period of therapy is 14 days• For HSV iritis apart from topical ointment,oral acyclovir 400 mg 5

times/day for 10 days withsteroids can be given

ADENINE ARABINOSIDE

• Adenine arabinoside is apurine analogue• Once phosphorylated by viral thymidine kinase,Ara-A becomes

triphosphorylated• In this form it inhibits DNA polymerase and ribonucleotide

reductase,blocking the DNA synthesis• Thus its action is different from IDU and trifluridine• It doesnot incorporate into viral DNA• Unlike IDU.Ara-A can achieve better viricidal concentration in the

aqueous humour• It can be used in stromal viral keratitis and iritis• It can cross blood ocular barrier too

PreparationsAvailable in 3% ointment

Dosage• 5 times/day• If there is no improvement,the drug should be discontinued in 7

days

Adverse reaction • External ocular reactions are just similar to IDU• Allergic reaction

TRIFLURIDINE

• Trifluridine or triflurothymidine is again a pyrimidine analogue• It is halogenated pyrimidine in which three fluorines,instead of

iodine,occur at 5 methyl group of thymidine• So the mechanism and spectrum is almost equal to IDU

Advantages• It is 10 times more soluble than IDU.therefore it penetrate well• More specific with viral DNA,therefore it is less toxic• Effective against IDU resistant organisms

Adverse effect• Mild burning sensation is common after topical instillation• Other reactions like superficial puctate keratitis,hypersensitivity reaction and

hyperemia can occur• Severe bone marrow depression in systemic administration has been reported

Preparation1% solution is available

Dose• 1 drop every 1hr/day time,every 2hr/night time is advisable• After the epithelium is formed the dose is reduced to 4 times/day for 7 days• If the healing is not complete in 14 days,the drug should be discontinued

IDOXYURIDINE

• Idoxyuridine is a halogenated pyrimidine where 5 methyl group of thymidine is replaced by iodine

• It is otherwise called 5 iodo 2 deoxy uridine• Viral DNA synthesis becomes defective due to the incorporation of IDU

into DNA

Ophthalmic uses • It is topically used against herpes simplex and vaccinia keratitis• It is poorlu soluble in water and doesnot penetrate the stroma• Therefore it is not useful in deeper infections

Preparations• 0.1% ophthalmic ointment• 0.5% ointment• Unstable in heat and light and refrigeration is advisable• Old solution should be discarded

Dose• During first week one drop is instilled in the eye every hour during day

and every 2 hours at night• If ointments is used it can be applied 4 times a day• If there is no response in 5 to 7 days,change to another antiviral agent is

necessary to counteract presumed resistance

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