2. • Antibacterial agents are not effective against
viruses, as the targets for them are absent in
viruses
• Even for viruses, chemotherapy is available for
selected viruses
• Chemotherapy is also not effective against viruses
which become latent in cells (e.g. herpesviruses).
These viruses are usually susceptible to antiviral
agents when they are not in latent stage
3. • Inhibition of early events
• Inhibition of viral nucleic acid synthesis
• Inhibition of integrase
• Inhibition of cleavage of precursor
polypeptides (protease inhibitors)
• Inhibition of viral protein synthesis
• Inhibition of release of virus
4. Inhibition of early events
• Amantadine and rimantidine
• Enfuvirtide
• Maraviroc
• Palivizumab
5. Amantadine and rimantadine
• Blocks the M2 matrix
protein in the virus
prevents uncoating of virus
inside the cell
• Absorption and penetration
are not affected
• Effective only against
influenza A
• Not effective against
influenza B and C
• Rimantadine has fewer side
effects than amantidine
6. Enfuvirtide
• Blocks gp41 of HIV
• Prevents fusion of viral envelope with cell
membrane (‘fusion inhibitors’)
7. Maraviroc
• Some strains of HIV
bind to CCR-5 receptor
on the cell surface,
through their gp120
• Maraviroc binds to CCR-
5, and prevents binding
of gp120 to CCR-5
8. Palivizumab
• Binds to the fusion protein of respiratory
syncytial virus (RSV), and thus prevents its
binding to respiratory tract cells
9. Inhibition of viral nucleic acid synthesis
• Inhibitors of Herpesviruses
• Inhibitors of Retroviruses
• Inhibitors of Hepatitis B virus
• Inhibitors of Hepatitis C virus
• Inhibitors of Other Viruses
11. • Nucleoside inhibitors:
1. Analogues of nucleosides
2. Inhibit DNA polymerase of one or more
members of herpesvirus family
12. Acyclovir
• Guanosine analogue
• It is in inactive form activated only
in virus infected cells by virus-
encoded thymidine kinase to
acyclovir monophosphate
therefore, non-toxic to non-infected
cells
• Acyclovir monophosphate is
converted into diphosphate and then
into triphosphate by cellular kinases
• Acyclovir triphosphate is
incorporated into growing
herpesvirus DNA chain, and acting as
premature chain terminater, inhibits
viral DNA polymerase
• Viral DNA polymerase is inhibited to a
greater extent than cellular DNA
polymerase
13. • Active against HSV-1, HSV-2, and VZV only, as
they can be activated by virus-encoded
thymidine kinases of these viruses
• Ineffective against CMV and Epstein-Barr virus
• Ineffective against viruses which are latent in
cells
• Recently, resistance has been noted against
acyclovir
15. Ganciclovir
• Guanosine analogue
• It is in inactive
formactivated into
active form by a CMV-
encoded
phosphokinasetherefor
e, active only against CMV
• Recently, resistance has
emerged due to mutation
in UL97 gene, which
codes for phosphokinase
• Valganciclovir is a
derivative of ganciclovir
17. Vidarabine
• Adenine analogue
• Mechanism of activation and action similar to
acyclovir
• Effective only against HSV-1
• Less effective and more toxic than acyclovir
18. Idoxuridine and trifluridine
• Thymidine analogues
• Mechanism of activation and action similar to
acyclovir
• But it is incorporated in normal cell DNA as
effectively as viral DNA therefore, too toxic
for systemic usetherefore, used only
topically
19. Non-nucleoside inhibitor-Foscarnet
• Pyrophosphate analogue
• Binds DNA polymerase at pyrophosphate
cleavage site and prevents removal of phosphate
from nucleoside triphosphates (dNTP)this
prevents addition of next dNTP in the elongating
strand of DNA
• It inhibits DNA polymerases of all herpesviruses
• It can be used for treatment of acyclovir-resistant
mutants of HSV-1 and VZV
21. Nucleoside reverse transcriptase
inhibitors (NRTIs)
• Nucleoside analogues
• Bind to the reverse
transcriptase of HIV,
and cause chain
termination
• Bind to the reverse
transcriptase of HIV
preferentially to the
DNA polymerase of
human cells
23. Non-nucleoside reverse transcriptase
inhibitors (NNRTIs)
• NOT nucleoside
analogues
• Bind to the active site of
reverse transcriptase and
cause of conformational
change to the enzyme
• Not used as
monotherapy, as resistant
mutants emerge rapidly
• Typically used in
combination with one or
two NRTIs
25. Inhibitors of Hepatitis B virus
• Are usually nucleoside analogues, which bind to
the DNA polymerase (reverse transcriptase) of
Hepatitis B virus
• Examples include:
1. Lamivudine (already discussed earlier)
2. Tenofovir (already discussed earlier)
3. Adefovir (adenosine analogue)
4. Entecavir (guanosine analogue)
5. Telbivudine (thymidine analogue)
26. Inhibitor of other viruses
• Ribavirin
1. Nucleoside analogue
2. Used in treatment of respiratory syncytial
virus (RSV) infections, influenza B infections,
and treatment of Hepatitis C infections
27. Inhibitors of integrase
• Integrase is an enzyme
in HIV which causes
integration of viral DNA
into host cell DNA
• Examples of integrase
inhibitors are:
1. Raltegravir
2. Dolutegravir
3. Elvitegravir
28. Inhibition of cleavage of precursor
polypeptides (protease inhibitors)
• Protease is an enzyme in HIV
which cleaves several non-
functional precursor
polypeptides into functional
proteins
• These inhibitors bind to this
protease enzyme, thereby
preventing the cleavage of
precursor polypeptides
functional proteins are not
formed replication is halted
• However, they cannot cure
infection, as proviral DNA is
not targeted
29. Protease inhibitors
• Not used as monotherapy, as resistant
mutants emerge rapidly
• Typically used in combination with one or two
NRTIs
32. Inhibition of viral protein synthesis-
Interferons
• Interferons are proteins produced by host cells on
induction by viral or non-viral inducers
• It belongs to the class of cytokines
• Interferon itself has no direct action, but acts on
other cells, making them refractory to viral
infection. It can also have immuno-modulatory
and anti-proliferative actions on certain cells.
• Interferon inhibits translation, and possibly
transcription, of viral proteins by the host cell
33. • The activity of interferon is not virus specific,
and may confer protection against unrelated
viruses also
• Interferon production is increased at higher
temperatures, and inhibited by steroids
34. • Alpha interferon (IFN-α): produced by
leucocytes
• Beta interferon (IFN-β): produced by
fibroblasts and epithelial cells
• Gamma interferon (IFN-γ): produced by T-
lymphocytes, and is more concerned with
immunomodulatory and anti-proliferative
functions
35. • They are inactivated by proteases
• They are poorly antigenic, and hence are
difficult to detect by serological methods
• They are non-toxic
• Potency of IFN is expressed as International
Units (IU) per ml
36. Inhibition of release of virus
• Neuraminidase is an enzyme in influenza virus,
which is essential for release of daughter virions
from the infected cells
• Neuraminidase inhibitors block this enzyme
daughter virions are not releasedother cells are
not infected infection is limited
• Examples include zanamivir and oseltamivir
• They are effective against both influenza A and B
viruses
• They are also effective against amantadine-
resistant strains of influenza virus