Which are the popular medicines prescribed for viral infections?

Acyclovir: It gets converted to acyclovir monophosphate by viral thymidine kinase and then undergoes a series of reactions by various enzymes to form acyclovir triphosphate. This form is more selective to the viral DNA polymerase than the cellular DNA and gets incorporated into the former resulting in viral DNA chain termination.

Ritonavir : It inhibits HIV protease and prevents the cleavage of the polyproteins by these enzymes. This in turn blocks the formation of mature virions in the initial stage itself. At low doses, this agent inhibits Cytochrome P450 – 3A4 and this in turn enhances the activity of the other protease inhibitors with which it is used in combination.

Lamivudine : It is a nucleoside reverse transcriptase inhibitor and competitively inhibits HIV reverse transcriptase enzyme and acts as a chain terminator of viral DNA synthesis. The drug is phosphorylated to form lamivudine metabolites that compete to get incorporated into the viral DNA to elicit the action. It also inhibits the reverse transcriptase of hepatitis – B virus.

Efavirenz : It binds to and inhibits reverse transcriptase in a non-competitive manner. This in turn inhibits the polymerization of viral DNA from the corresponding RNA and thereby prevents the synthesis of new virions.

Entecavir : It gets activated invivo to form the triphosphate metabolite that competes with the deoxyguanosine triphosphate, a natural substrate, for incorporation into the viral DNA. It inhibits reverse transcriptase, viral RNA dependent HBV BNA polymerase and thereby stops viral replication.

Sofosbuvir : The active phosphorylated form gets incorporated into the Hepatitis C virus RNA by the NS5B ( Non structural protein 5B) polymerase. This in turn inhibits viral RNA synthesis and induces chain termination.

Valacyclovir : It gets metabolized to form acyclovir initially and this in turn gets converted to the active triphosphate form by a series of reactions. The triphosphate form competitively inhibits and inactivates the viral DNA polymerase by getting incorporated into the growing viral DNA chain.