anti retro viral drugs

ANTI RETRO VIRAL DRUGS

G Vijay Narasimha KumarAsst. Professor,

Dept. of. Pharmacology,Sri Padmavathi School of Pharmacy

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).

REVERSE

TRANSCRIPTASE

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.

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.

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.

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]

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 and

guanosine 5 prime capping. But it was unable to enter into

host ribosomes directly unless, it undergoes reverse

transcription.

HIV RNA consists of three main structural genes:

• Group Specific Antigen - Gag gene

• Envelope- Env gene

• Polymerase- Pol gene

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].

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

BINDING/ ATTACHMENT:

• In early phase HIV infection, initial viruses are M-tropic. Their envelope glycoprotein gp120 is able tobind to CD4 molecules and chemokine receptorscalled CCR5 found on macrophages .

• In late phase HIV infection, most of the viruses are T-tropic, having gp120 capable of binding to CD4 andCXCR4 found on Th-lymphocytes.

FUSION :

HIV envelope and the CD4 cell membrane fuse withthe help of gp41 which allows HIV to enter the CD4cells and uncoating occurs to release the viral RNA.

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.

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

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.

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.

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 .

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.

(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

nucleusHost cell

genome

Site of action of AZT

and other reverse

Transcriptase

inhibitors

Site of action

of protease

inhibitors

RNADNA

DNADNA

(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

(1) Viral genome

and reverse

transcriptase

enter cell.

(1) Viral genome

and reverse

transcriptase

enter cell.



RNADNA

(1) Viral genome

and reverse

transcriptase

enter cell.




and other reverse

Transcriptase

inhibitors

RNADNA

(3) RNA degraded;

second DNA strand

synthesized.

DNADNA

(1) Viral genome

and reverse

transcriptase

enter cell.



(3) RNA degraded;

second DNA strand

synthesized.

Host cell

nucleusHost cell

genome


and other reverse

Transcriptase

inhibitors

RNADNA

DNADNA





Site of action

of antiretroviral drugs

under development

(1) Viral genome

and reverse

transcriptase

enter cell.



(3) RNA degraded;

second DNA strand

synthesized.

(5) With host cell

activation, viral

DNA is transcribed,



Host cell

nucleusHost cell

genome


and other reverse

Transcriptase

inhibitors

RNADNA

DNADNA





Site of action


under development

(1) Viral genome

and reverse

transcriptase

enter cell.



(3) RNA degraded;

second DNA strand

synthesized.

(5) With host cell

activation, viral

DNA is transcribed,



(6) Viral RNAs are


viral enzymes


and structural

proteins.

Host cell

nucleusHost cell

genome


and other reverse

Transcriptase

inhibitors

Site of action

of protease

inhibitors

RNADNA

DNADNA





Site of action


under development

(1) Viral genome

and reverse

transcriptase

enter cell.



(3) RNA degraded;

second DNA strand

synthesized.

(5) With host cell

activation, viral

DNA is transcribed,



(6) Viral RNAs are


viral enzymes


and structural

proteins.

Host cell

nucleusHost cell

genome


and other reverse

Transcriptase

inhibitors

Site of action

of protease

inhibitors

RNADNA

DNADNA







Site of action


under development

(1) Viral genome

and reverse

transcriptase

enter cell.



(3) RNA degraded;

second DNA strand

synthesized.

(8) Final viral assembly

and budding

take place.

(5) With host cell

activation, viral

DNA is transcribed,



(6) Viral RNAs are


viral enzymes


and structural

proteins.

Host cell

nucleusHost cell

genome


and other reverse

Transcriptase

inhibitors

Site of action

of protease

inhibitors

RNADNA

DNADNA







Site of action


under development

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.

STAGES OF HIV INFECTION

Normal CD4 count-500 to 1200cells/cumm

• 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.

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

Eg- Raltegravir , Elvitegravir , Dolutegravir.

gp120

p24

Viral RNA

RT & othervirion prteins

HIV Lifecycle and target sites of drugs

gp120

p24

Viral RNA

RT & othervirion proteins

CD4

CXCR4 or CCR5

Binding

gp120

p24

Viral RNA


CD4

CXCR4

Binding A. Entry Inhibitors:CCR5 antagonist, Maraviroc

CCR5

gp120

p24

Viral RNA


Fusion & uncoating

gp120

p24

Viral RNA


Fusion & uncoatingB. Fusion Inhibitors:

Enfuviritide

gp120

p24

Viral RNA


Reverse transcription

gp120

p24

Viral RNA



C. Reverse Transcriptase (RT) Inhibitors:1. Nucleoside RT inhibitors (NRTIs)2. Non-Nucleoside RT Inhibitors NNRTIs)

gp120

p24

Viral RNA


Nuclear localization & entry

gp120

p24

Viral RNA


Integration

gp120

p24

Viral RNA


Integration

D. Integrase Inhibitors:Raltegravir , Elvitegravir ,

Dolutegravir

gp120

p24

Viral RNA


Integrated provirus

gp120

p24

Viral RNA


Viral Gene Transcription

gp120

p24

Viral RNA


Translation

gp120

p24

Viral RNA


Post-translationalprocessing

E. Protease Inhibitors:e.g. Lopinavir, Indinavir

gp120

p24

Viral RNA


Assembly

gp120

p24

Viral RNA

RT & othervirion prteins Budding

gp120

p24

Viral RNA


Budding

Inhibition of Virion Maturation

gp120

p24

Viral RNA


This process averages about 1.2 days

CD4

CXCR4

Binding

Fusion & Entry

Nuclear localization & entry


Integration

gp120

p24

Viral RNA


gp120

p24

Viral RNA


Budding

Assembly

Viral Gene Transcription

Translation

Post-translationalprocessing

NRTIs

Adenosine analogues : Didanosine

Tenofovir

Guanosine analogues : Abacavir

Cytidine analogues : Lamivudine

Emtricitabine

Thymidine analogues : Zidovudine

Stavudine

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.

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.

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.

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

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.

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


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.

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.

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).

STAVUDINE

oNot used widely due to its potency to cause

peripheral neuritis and other potent adverse effects.

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.

DELAVIRIDINEo Poor antiviral activityand hence not used.

EFAVERINZo Less toxicities, only skin rashes may occur.

o It is teratogenic hence in pregnancy it is not used.

ETRAVIRINE,RILPIVIRINEo 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).

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 .

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.

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.

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.

INTEGRASE STRAND TRANSFERINHIBITORS

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

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.

Highly Active Anti 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

Criteria for selection of drugs

No NRTIs having same

structure analogues

are selected.

Patient factors like comorbidities, oppurtunistic

infections,patientadherence should

be considered.

Drugs having drug –drug interactions

should not be selected.

Two drugs having same

toxicities should not be

selected.

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.

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.

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.

anti retro viral drugs

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