Anti retro viral drugs

1. ANTI RETRO VIRAL DRUGS
G Vijay Narasimha Kumar
Asst. Professor,
Dept. of. Pharmacology,
Sri Padmavathi School of Pharmacy

2. RETRO VIRUS
A retrovirus is a virus that has RNA as its genetic
material instead of DNA. When a retrovirus infects a
cell, it makes a DNA copy of its genome that is
inserted into the DNA of the host cell by using an
enzyme reverse transcriptase.
Example: Human immunodeficiency virus (HIV).

3. REVERSE
TRANSCRIPTASE

4. STRUCTURE OF HIV
 HIV is an Icosahedral (20 sided), enveloped virus.
Family : Retroviruses.
Subfamily : Lentivirus
 Retroviruses transcribe RNA to DNA.
 Viral strands of RNA is found in core surrounded by
protein outer coat.
 Outer envelope contains a lipid matrix within which
specific viral glycoproteins are imbedded.
 These knob-like structures are responsible for
binding to target cell.

7. Envelope:
It is an outer lipid surface of the virus which
is embedded with glycoproteins. These glycoproteins
includes gp120 and gp41 which are formed from
gp160.
Functions:
 Gp120- helps in recognition of target cells(CD4+
cells) by binding to target cell receptors.
CD4+ cells – Macrophages
Monocytes
T-helper cells
Microglial cells
Langerhan cells
Dendritic cells.

8.  Gp41 – helps in fusion of virus with host cell
membrane.
 After binding to CD4 cells, Gp120 undergoes
confirmational changes and produce CCR5 and
CXCR4 domains .These domains bind with the CCR5
and CXCR4 chemokine recptors found on
macrophages and Th lymphocytes respectively, which
helps in fusion.

10.  Supporting the glycoproteins, matrix is present
which is made up of P17 proteins.
 Core capsid that contains HIV RNA is made up of
P24 and P7 proteins among which P24 is
abundantly distributed.
[Host macrophages produces antibodies against P24 which are useful
in diagnosis by ELISA and Western blot test]

11. RNA:
 HIV consists of two single stranded RNA.These two strands
are identical but not complementary to each other.
 HIV RNA ressembles eukaryotic m-rna with poly-A tail a
guanosine 5 prime capping. But it was unable to enter in
host ribosomes directly unless, it undergoes rever
transcription.
 HIV RNA consists of three main structural genes:
• Group Specific Antigen - Gag gene
• Envelope- Env gene
• Polymerase- Pol gene

12.  Gag gene codes for P24,P7,P17 proteins of capsid
and matrix.
 Env gene codes for envelope proteins gp160 which is
cleaved into gp120 and gp41.
 These proteins involved with fusion and attachment of
HIV to host cells.
 Pol gene codes for p66 and p51 which are subunits of
reverse transcriptase and p31 an endonuclease
[integrase and protease].

15. VIRAL REPLICATION
 The virus goes through multiple steps to reproduce itself
and create many more virus particles.
 The seven stages of the HIV life cycle are:
1) Binding 2) Fusion
3) Reverse transcription
4) Integration
5)Transcription and translation
6) Assembly
7) Budding

16. BINDING/ ATTACHMENT:
• In early phase HIV infection, initial viruses are M-
tropic. Their envelope glycoprotein gp120 is able to
bind to CD4 molecules and chemokine receptors
called CCR5 found on macrophages .
• In late phase HIV infection, most of the viruses are T-
tropic, having gp120 capable of binding to CD4 and
CXCR4 found on Th-lymphocytes.

17. FUSION :
HIV envelope and the CD4 cell membrane fuse with
the help of gp41 which allows HIV to enter the CD4
cells and uncoating occurs to release the viral RNA.

18. REVERSE TRANSCRIPTION:
 A special enzyme called reverse
transcriptase changes the genetic material of the
virus, i.e., from RNA to DNA, so it can be integrated
into the host DNA.
 RT has two domains namely, RNA dependent DNA
polymerase domain and RNAase domain.

19. RNA dependent DNA
polymerase
Forms complementary
DNA to viral RNA
By using host DNA
polymerase the single
stranded DNA is
converted into double
stranded [pro-viral DNA]
RNAase cleaves the
RNA after DNA
formation
Two identical single
stranded DNAs are
formed

20. INTEGRATION: The virus DNA enters
the nucleus of the CD4 cell and uses an
enzyme called integrase to integrate itself into
host DNA, where it may “hide” and stay
inactive for several years.

21. TRANSCRIPTION : Viral DNA ends are sticky in
nature and contains GAG gene ,POL gene, ENV
gene. It also contains long terminal repeats [LTRs] at
its ends . These LTRs contains promoter box which
promotes the transcription.
Viruses use host transcriptional machinery for its
transcription process and it also use some virus
transcriptional factors like TAT and forms m-RNA.

23. TRANSLATION:
The formed m-RNA translates into inactive long chain
polyproteins.
ASSEMBLY: By using the enzyme called as protease
the poly proteins are cleaved into active viral proteins.
 GAG gene P24, P7, P17 proteins.
 POL gene Reverse transcriptase ,
integrase ,protease.
 ENV gene gp160 [gp41 and gp120]
 If all the three genes continously transcribed at a time,
the genomic RNA was formed.
 All the proteins and RNA assembles to form a new
virus .

24. BUDDING:
This is the final stage of the virus life cycle. In
this stage, the virus pushes itself out of the host
cell [buds] by exocytosis and contains all of the
structures necessary to bind to a new CD4 cell
receptors and begin the process again and infect
the other cells.

25. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
(3) RNA degraded;
second DNA strand
synthesized.
(8) Final viral assembly
and budding
take place.
(5) With host cell
activation, viral
DNA is transcribed,
yielding messenger RNAs
and viral genome RNA.
(6) Viral RNAs are
translated, yielding
viral enzymes
(including protease)
and structural
proteins.
Host cell
nucleus
Host cell
genome
Site of action of AZT
and other reverse
Transcriptase
inhibitors
Site of action
of protease
inhibitors
RNA
DNA
DNA
DNA
(7) Viral membrane proteins are
transported to host cell membrane.
(4) DNA circularizes (unintegrated
provirus) or integrase functions
to incorporate DNA into host cell
genome (integrated provirus).
Site of action
of antiretroviral
drugs
under
development

26. (1) Viral genome
and reverse
transcriptase
enter cell.

27. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
RNA
DNA

28. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
Site of action of AZT
and other reverse
Transcriptase
inhibitors
RNA
DNA
(3) RNA degraded;
second DNA strand
synthesized.
DNA
DNA

29. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
(3) RNA degraded;
second DNA strand
synthesized.
Host cell
nucleus
Host cell
genome
Site of action of AZT
and other reverse
Transcriptase
inhibitors
RNA
DNA
DNA
DNA
(4) DNA circularizes (unintegrated
provirus) or integrase functions
to incorporate DNA into host cell
genome (integrated provirus).
Site of action
of antiretroviral drugs
under development

30. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
(3) RNA degraded;
second DNA strand
synthesized.
(5) With host cell
activation, viral
DNA is transcribed,
yielding messenger RNAs
and viral genome RNA.
Host cell
nucleus
Host cell
genome
Site of action of AZT
and other reverse
Transcriptase
inhibitors
RNA
DNA
DNA
DNA
(4) DNA circularizes (unintegrated
provirus) or integrase functions
to incorporate DNA into host cell
genome (integrated provirus).
Site of action
of antiretroviral drugs
under development

31. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
(3) RNA degraded;
second DNA strand
synthesized.
(5) With host cell
activation, viral
DNA is transcribed,
yielding messenger RNAs
and viral genome RNA.
(6) Viral RNAs are
translated, yielding
viral enzymes
(including protease)
and structural
proteins.
Host cell
nucleus
Host cell
genome
Site of action of AZT
and other reverse
Transcriptase
inhibitors
Site of action
of protease
inhibitors
RNA
DNA
DNA
DNA
(4) DNA circularizes (unintegrated
provirus) or integrase functions
to incorporate DNA into host cell
genome (integrated provirus).
Site of action
of antiretroviral drugs
under development

32. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
(3) RNA degraded;
second DNA strand
synthesized.
(5) With host cell
activation, viral
DNA is transcribed,
yielding messenger RNAs
and viral genome RNA.
(6) Viral RNAs are
translated, yielding
viral enzymes
(including protease)
and structural
proteins.
Host cell
nucleus
Host cell
genome
Site of action of AZT
and other reverse
Transcriptase
inhibitors
Site of action
of protease
inhibitors
RNA
DNA
DNA
DNA
(7) Viral membrane proteins are
transported to host cell membrane.
(4) DNA circularizes (unintegrated
provirus) or integrase functions
to incorporate DNA into host cell
genome (integrated provirus).
Site of action
of antiretroviral drugs
under development

33. (1) Viral genome
and reverse
transcriptase
enter cell.
(2) DNA copy synthesized by
reverse transcriptase.
(3) RNA degraded;
second DNA strand
synthesized.
(8) Final viral assembly
and budding
take place.
(5) With host cell
activation, viral
DNA is transcribed,
yielding messenger RNAs
and viral genome RNA.
(6) Viral RNAs are
translated, yielding
viral enzymes
(including protease)
and structural
proteins.
Host cell
nucleus
Host cell
genome
Site of action of AZT
and other reverse
Transcriptase
inhibitors
Site of action
of protease
inhibitors
RNA
DNA
DNA
DNA
(7) Viral membrane proteins are
transported to host cell membrane.
(4) DNA circularizes (unintegrated
provirus) or integrase functions
to incorporate DNA into host cell
genome (integrated provirus).
Site of action
of antiretroviral drugs
under development

34. REGULATORY PROTEINS :
Some regulatory proteins are produced by the viral
DNA by frame shift process.
 TAT protein : Enhances transcription.
 REV protein : Enhances translation by enhancing the
movement of m-rna into ribosomes.
 VIF protein : Inhibits APOBEC3G, there by enhances
the viral infectivity
 VPR protein : Enhances viral replication
 VPU protein : Enhances viral release by inhibiting the
tethrin [an IFN  protein ]
 NEF protein : Inhibits cell mediated immunity.

35. STAGES OF HIV INFECTION
Normal CD4 count-500 to 1200cells/cumm

36. • The persons of all three stages are able to transmit
HIV infection to others.
DIAGNOSIS :
• Antibody test – ELISA ,western blot test.
• Viral antigen test – P24 antigen test.
• Nucleic acid amplification testing.
• Window periods for this tests are 24 , 16 , 12 days
respectively.

37. ANTI RETROVIRAL DRUGS
• NRTIs (Nucleoside /nucleotide Reverse Transcriptase
Inhibitors) Eg- Didanosine ,
Abacavir , Tenofovir , Emtricitabine , Lmivudine ,
Stavudine , Zidovudine.
• NNRTIs ( Non-Nucleoside Reverse Transcriptase Inhibitors)
Eg -first generation -Nevirapine,Efavirenz , Delaviridine.
second generation- Etravirine, Rilpivirine.
• PI (Protease Inhibitors)
Eg- Saquinavir , Ritonavir , Indinavir , Lopinavir ,
Nelfinavir , Amprenavir ,Fosamprenavir , Atazanavir ,
Darunavir .
• Entry Inhibitors/fusion inhibitors
Eg-Enfuviritide , Maraviroc.
• Integrase Inhibitors

38. gp120
p24
Viral RNA
RT & other
virion prteins
HIV Lifecycleand targetsitesof drugs

39. gp120
p24
Viral RNA
RT & other
virion
proteins
CD4
CXCR4 or CCR5
Binding

40. gp120
p24
Viral RNA
RT & other
virion
proteins
CD4
CXCR4
Binding A. Entry Inhibitors:
CCR5 antagonist, Maraviroc
CCR5

41. gp120
p24
Viral RNA
RT & other
virion
prteins
Fusion & uncoating

42. gp120
p24
Viral RNA
RT & other
virion
proteins
Fusion & uncoating
B. Fusion Inhibitors:
Enfuviritide

43. gp120
p24
Viral RNA
RT & other
virion
prteins
Reverse
transcription

44. gp120
p24
Viral RNA
RT & other
virion
proteins
Reverse
transcription
C. ReverseTranscriptase (RT) Inhibitors:
1. Nucleoside RT inhibitors (NRTIs)
2. Non-Nucleoside RT Inhibitors NNRTIs)

45. gp120
p24
Viral RNA
RT & other
virion
prteins
Nuclear
localization
& entry

46. gp120
p24
Viral RNA
RT & other
virion
prteins
Integration

47. gp120
p24
Viral RNA
RT & other
virion
proteins
Integration
D. Integrase Inhibitors:
Raltegravir , Elvitegravir ,
Dolutegravir

48. gp120
p24
Viral RNA
RT & other
virion prteins
Integrated
provirus

49. gp120
p24
Viral RNA
RT & other
virion prteins
Integrated
provirus

50. gp120
p24
Viral RNA
RT & other
virion prteins
Viral Gene
Transcription

51. gp120
p24
Viral RNA
RT & other
virion prteins
Translation

52. gp120
p24
Viral RNA
RT & other
virion prteins
Post-translational
processing
E. Protease Inhibitors:
e.g. Lopinavir, Indinavir

53. gp120
p24
Viral RNA
RT & other
virion prteins
Assembly

54. gp120
p24
Viral RNA
RT & other
virion prteins Budding

55. gp120
p24
Viral RNA
RT & other
virion
proteins
Budding
Inhibition ofVirion Maturation

56. gp120
p24
Viral RNA
RT & other
virion prteins
This process averages about 1.2 days

57. CD4
CXCR4
Binding
Fusion & Entry
Nuclear
localization
& entry
Reverse
transcription
Integration
gp120
p24
Viral RNA
RT & other
virion
proteins

58. gp120
p24
Viral RNA
RT & other
virion prteins
Budding
Assembly
Viral Gene
Transcription
Translation
Post-translational
processing

59. NRTIs
Adenosine analogues : Didanosine
Tenofovir
Guanosine analogues : Abacavir
Cytidine analogues : Lamivudine
Emtricitabine
Thymidine analogues : Zidovudine
Stavudine

60. Mechanism of action:
 These drugs acts as false nucleotides/sides.
 Due to similar structure as that of
nucleotides,these are incorporated into growing
DNA strand instead of nucleotides and
terminate the synthesis of DNA due to lack of
OH group.

61. PHARMACOKINETICS:
o Orally well absorbed.
o All are metabolised in liver by CYP450 enzymes
except ABACAVIR.
o ABACAVIR is metabolised by Alcohol
dehydrogenase .
o All drugs are renally excreted.

62. Adverse effects :
o These drugs do have some affinity to human
mitochondrial DNA polymerase ( except Abacavir)
which leads to the following adverse effects.
• Bonemarrow toxicity [anaemia,leucopaenia].
• Hepatotoxicity [fatty liver, hepatic steatosis,
hepatomegaly , hepatic lactic acidosis].
• Lipodystrophy.
• Peripheral neuritis.

63. DIDANOSINE
MOA:
Dideoxy-ionisine mono phosphate
liver
Dideoxy adenosine mono phosphate
Dideoxy adenosine tri phosphate
False neucleotide competes with ATP for reverse
transcriptase and inhibits polymerisation.
Major ADRs: peripheral neuritis

64. TENOFOVIR
o It is an acyclic phosphonate of adenosine mono
phosphate and converts to triphosphate in liver. It has
long half life.
o It directly inhibits reverse transcriptase (DNA polymerase)
. But, as it is an nucleoside analogue it is categorised as
NRTI.
ADRs:
o Only GI disturbances.
o Enzyme inducer that may increase the metabolism of
Atazanavir.

65. ABACAVIR
o Not used due to potent ADR’s.
ADR’s:
Hypersensitivity, nausea, vomiting, diarrhea.
LAMIVUDINE
2-Deoxy-thiacytidine
converts
tri phosphate
act as
analogues that competes with dCTP
inhibits
reverse transcriptase.

66. ADRs:
o No bone marrow toxicity due to less affinity to
mitochondrial DNA polymerase.
o But in kidney disease creatinine clearance have to be
monitored.
USE: Besides HIV It also inhibits replication of
hepatitis-B virus.Hence used in Hepatitis also.

67. EMTRICITABINE
o It is flouro derivative of lamivudine.
o High bioavailability.
o Extracelluar:10hrs.
o Intracellular:39hrs.
o Due to it’s low t1/2 it is preffered with TENOFOVIR.
o It Causes hyperpigmentation of palms and soles.

68. ZIDOVUDINE (AZT)
o Zidovudine is an Azido deoxy thymidine
monophosphate which is converted into triphosphate.
o More CNS penetration and crosses placental barrier
and breast milk.
o Causes severe ADR’s except peripheral neuritis.
o Due to its potency it was used in prevention of
perinatal transmission as prophylaxis (Zidovudine IV
was given during labour).

69. STAVUDINE
oNot used widely due to its potency to cause
peripheral neuritis and other potent adverse effects.

70. NNRTIs (lipophillic)
o These are non competitive inhibitors of DNA
polymerase of reverse transcriptase . These drugs
binds with the allosteric site of an enzyme.
NEVIRAPINE:
o Metabolised by liver hence it may cause
hepatotoxicity.
o It cross CNS and cause headache,dizziness, vivid
dreams.
o It causes Type-1 and Type-2 Hypersensitivity
reactions, mostly rashes, stevens johnsons syndrome
, toxic epidermal necrolysis. So not used widely.

71. DELAVIRIDINE
o Poor antiviral activityand hence not used.
EFAVERINZ
o Less toxicities, only skin rashes may occur.
o It is teratogenic hence in pregnancy it is not used.
ETRAVIRINE,RILPIVIRINE
o Second generation and less resistant NNRTIs.
o Use only when in patients who are on HAART therapy
and even though viral load increases.
o NRTI’S have less chance of resistance(these are
analogues),where as NNRTI’S have more chances
for cross resistance(many drugs on same site
directly).

72. PROTEASE INHIBITORS
MOA :
Inhibits HIV aspartyl protease
leads to synthesis of
Non functional long polypeptide chains.
PHARMACOKINETICS:
• Orally well absorbed.
• Have protein binding nature.
• Metabolised in liver.
• Renal excretion .

73. ADRs:
• Protease inhibitors are CYP450 inhibitors there by
inhibits metabolism of other drugs.
Eg: WARFARIN which leads toBleeding.
ATORVASTATIN- Rhabdomyolysis.
ANTIARRHYTHMICS- CVS abnormalities.
ANTIEPILETICS-Sedation.
SEDATIVES-Sedation.

74. o They should not be taken with RIFAMPICIN because
it is an enzyme inducer. Hence it decrease levels of
protease inhibitors.
o GI disturbances like nausea, vomiting, diarrhea.
o Parasthesias.
o They cause various metabolic disturbances like
hyperglycaemia, hyper cholesteraemia which leads to
Buffalo hump and accumulation of fats in abdomen in
males and breast enlargement along with buffalo
hump in females.

75. RITONAVIR
o Not used due to ADR’s but given as pharmacokinetic
booster at subtherapeutic levels 100mg.
o In subtherapeutic levels it inhibits CYP450 enzyme.
Hence it increases bioavailability of other
concomitantly taken protease inhibitors such as
ATAZANAVIR and DARUNAVIR except NELFINAVIR.

76. INTEGRASE STRAND TRANSFER
INHIBITORS
The enzyme integrase contains active site which
contains metal ions.
Integrase inhibitors
forms complexes with metal ions
Inhibits cleavage of DNA and there by integration.
ADR’s:
GI disturbances

77. Fusion inhibitors
ENFUVIRITIDE: Gp41 blocker
Inhibits fusion of virus with host cell membrane.
• It is a polypeptide,so given subcutaneously but not orally.
• It is given in patients who are on HAART therapy and
even though viral load increases.
MARAVIROC: CCR5 antagonist
• Not used due to potential adverse effects.

78. HighlyActiveAnti Retroviral Therapy
[HAART]
GOALS :
 To decrease viral replication.
 To restore/preserve immunological function.
 To prolong the life span of patient.
 To improve the quality of life of the patient.
HAART regimen:
 2NRTIs + 1protease inhibitor/ 1 NNRTI / 1 Integrase
inhibitor

79. Criteria forselection of drugs
No NRTIs
having same
structure
analogues
are selected.
Patient factors like
comorbidities,
oppurtunistic
infections,patient
adherence should
be considered.
Drugs having
drug –drug
interactions
should not be
selected.
Two drugs
having same
toxicities
should not be
selected.

80. Mostly used regimens
 Tenofovir + Emtricitabine + Nevirapine.
 Tenofovir + Emtricitabine + Ritonavir.
 Tenofovir + Emtricitabine + Atazanavir + Ritonavir
booster.
 Tenofovir + Emtricitabine + Darunavir.
 Tenofovir + Emtricitabine + Raltegravir.
NOTE:
 Ritonavir booster was given in sub therapeutic dose
which maintains the Atazanavir concentration as
Tenofovir increase the metabolism of Atazanavir.
 Tenofovir , Emtricitabine was mostly prefered due to
less adverse effects and good bioavailability.

81. HIV in pregnancy
 Viral load should be maintained at <1000 virus/ml.
Rx- ZIDOVUDINE
EMTRICITABINE
LAMIVUDINE
TENOFOVIR
 NRTI’S: NEVIRAPINE was used only when CD4+
count is <200 cells because it cause hepatotoxicity.

82.  Zidovudine IV was given during labour to prevent perinatal
transmission.
 After 6 hours of delivery ,the child was given with HAART
irrespective of infection.
 This therapy was continued upto 6 weeks then Bactrim
was given to prevent pneumonia.
 HIV test was done three times for child i.e., at 16-20 days
, at 4 weeks and at 4-6 months.
 Breast feeding was contraindicated.
 Caesarian delivery at 38 weeks (2 weeks before expected
date of delivery) is prefered rather than normal vaginal
delivery.