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{{HIV}}
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{{AIDS}}
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==Overview==
==Overview==


The ability of HIV to mutate and reproduce itself in the presence of antiretroviral drugs is called HIV drug resistance. '''HIV Drug Resistance''' occurs when [[microevolution]] causes [[virions]] to become tolerant to [[antiretroviral]] treatments. Drug resistant virus will continue to replicate in the presence of the drug to which it has become resistant.
The ability of HIV to mutate and reproduce itself in the presence of antiretroviral drugs is called HIV drug resistance. '''HIV Drug Resistance''' occurs when [[microevolution]] causes [[virions]] to become tolerant to [[antiretroviral]] treatments. Drug resistant virus will continue to replicate in the presence of the drug to which it has become resistant.


==Etiology==
==Drug Resistance==
As ART continues to expand, the emergence of some drug resistance is inevitable. Many factors leading to treatment failure and eventually drug resistance are as following:
As ART continues to expand, the emergence of some drug resistance is inevitable. Many factors leading to treatment failure and eventually drug resistance are as follows:
*Insufficient knowledge among patients and health workers.
*'''Factors related to Virus or Drug'''
*Suboptimal adherence to treatment regimens.
** '''HIV biology:''' Human Immunodeficiency Virus replicates at a high rate, with more than 10<sup>9</Sup> virions produced daily. The absence of [[DNA polymerase]] give rise to mutations in the progeny. The combinations of high replication rate and repeated introduction of mutations produces randomly generated mutatant stains that give rise to drug resistance. 
*Drug stock-outs.
** '''Variable response to mutation:''' Although multiple mutations are required to develop drug resistance but resistance can develop even with a single mutation. Example: A single mutation can lead to high-level resistance in [[lamivudine]], [[efavirenz]] and [[nevirapine]]. On the contrary, it takes multiple mutation to develop resistance against [[Protease inhibitor]]s.
*Inadequate patient monitoring mechanisms.
** '''Potency of individual drug: ''' Higher potency drugs are more vigorous in suppressing viral load, thus further controlling viral replications.<ref name="pmid12087139">{{cite journal |author=Walmsley S, Bernstein B, King M, Arribas J, Beall G, Ruane P, Johnson M, Johnson D, Lalonde R, Japour A, Brun S, Sun E |title=Lopinavir-ritonavir versus nelfinavir for the initial treatment of HIV infection |journal=N. Engl. J. Med. |volume=346 |issue=26 |pages=2039–46 |year=2002 |month=June |pmid=12087139 |doi=10.1056/NEJMoa012354 |url=http://dx.doi.org/10.1056/NEJMoa012354 |accessdate=2012-05-30}}</ref>
*'''Other contributing factors:'''
** Insufficient knowledge among patients and health workers.
** Suboptimal adherence to treatment regimens.
** Drug stock-outs.
** Inadequate patient monitoring mechanisms.


==Historical Perspective==
==Historical Perspective==
Line 15: Line 22:
**[[Zidovudine]] (AZT), a [[Reverse transcriptase inhibitor#Nucleoside analog reverse transcriptase inhibitors (NARTIs or NRTIs)|nucleoside reverse transcriptase inhibitor]] (NRTI), was first administered in 1987, and until 1995, monotherapy or dual therapy with NRTIs were the only treatments available.
**[[Zidovudine]] (AZT), a [[Reverse transcriptase inhibitor#Nucleoside analog reverse transcriptase inhibitors (NARTIs or NRTIs)|nucleoside reverse transcriptase inhibitor]] (NRTI), was first administered in 1987, and until 1995, monotherapy or dual therapy with NRTIs were the only treatments available.
**The first [[protease inhibitor]] (PI), [[saquinavir]], was approved for treatment in 1995, followed closely in 1996 by a [[Reverse transcriptase inhibitor# Non-nucleoside reverse transcriptase inhibitors (NNRTIs) | nonnucleoside reverse transcriptase inhibitor]] (NNRTI), [[nevirapine]]. These new drugs generated a major change in the treatment strategy against HIV—highly active antiretroviral therapy (HAART).
**The first [[protease inhibitor]] (PI), [[saquinavir]], was approved for treatment in 1995, followed closely in 1996 by a [[Reverse transcriptase inhibitor# Non-nucleoside reverse transcriptase inhibitors (NNRTIs) | nonnucleoside reverse transcriptase inhibitor]] (NNRTI), [[nevirapine]]. These new drugs generated a major change in the treatment strategy against HIV—highly active antiretroviral therapy (HAART).
 
==Types==
==Current scenario==
HIV drug resistance may be transmitted or acquired.
#'''Acquired drug resistance:''' Drug resistance could develop if patients interrupt their treatment or do not take it according to prescription.
#'''Transmitted drug resistance:''' If people are infected by others who had HIV drug resistance, it is called transmitted drug resistance. 
==Current Scenario==
*Nearly all drugs currently used to treat HIV eventually stop working when patient develops resistance to [[AIDS medical therapy#Anti Retroviral Therapy (ART)|ART]]. HIV develops resistance when it evades the effects of these treatments.<ref name="Freeman">Freeman, S., and J. C. Herron. 2007.  Evolutionary Analysis. 4th ed. A case for evolutionary thinking: understanding HIV. Pearson Benjamin Cummings, San Francisco, CA.</ref> A recent study estimated the percentage of the '''American''' HIV positive population with some form of drug resistance to be 76.3%.<ref>Richman, D. D., S. C. Morton, T. Wrin, N. Hellmann, S. Berry, M. F. Shapiro, and S. A. Bozzette. 2004. The prevalence of antiretroviral drug resistance in the United States. AIDS. 18: 1393-1401.</ref>
*Nearly all drugs currently used to treat HIV eventually stop working when patient develops resistance to [[AIDS medical therapy#Anti Retroviral Therapy (ART)|ART]]. HIV develops resistance when it evades the effects of these treatments.<ref name="Freeman">Freeman, S., and J. C. Herron. 2007.  Evolutionary Analysis. 4th ed. A case for evolutionary thinking: understanding HIV. Pearson Benjamin Cummings, San Francisco, CA.</ref> A recent study estimated the percentage of the '''American''' HIV positive population with some form of drug resistance to be 76.3%.<ref>Richman, D. D., S. C. Morton, T. Wrin, N. Hellmann, S. Berry, M. F. Shapiro, and S. A. Bozzette. 2004. The prevalence of antiretroviral drug resistance in the United States. AIDS. 18: 1393-1401.</ref>
* The extent of HIV drug resistance resulting from recent ART scale up in '''resource-limited countries''' has not systematically been quantified due to the lack of reliable data and information.
* The extent of HIV drug resistance resulting from recent ART scale up in '''resource-limited countries''' has not systematically been quantified due to the lack of reliable data and information.


==Mechanism of drug resistance==
==Mechanism of Drug Resistance==
*As a [[retrovirus]], HIV uses the enzyme [[reverse transcriptase]] to synthesize [[DNA]] from its [[RNA]] [[genome]] and lacks a mechanism for correcting errors made while reproducing its genome.<ref name="Freeman" /> As a result, HIV replicates its genome with the highest known mutation rate of any living organism.<ref name="Freeman" /> This creates an ideal situation for [[natural selection]] to act on the HIV population, as [[genetic variation]] is the raw material for natural selection.
*As a [[retrovirus]], HIV uses the enzyme [[reverse transcriptase]] to synthesize [[DNA]] from its [[RNA]] [[genome]] but it lacks a mechanism for correcting errors made while reproducing its genome.<ref name="Freeman" /> As a result, HIV replicates its genome with the highest known mutation rate of any living organism.<ref name="Freeman" /> This creates an ideal situation for [[natural selection]] to act on the HIV population, as [[genetic variation]] is the raw material for natural selection.<ref name="pmid7824947">{{cite journal |author=Coffin JM |title=HIV population dynamics in vivo: implications for genetic variation, pathogenesis, and therapy |journal=Science |volume=267 |issue=5197 |pages=483–9 |year=1995 |month=January |pmid=7824947 |doi= |url=http://www.sciencemag.org/cgi/pmidlookup?view=long&pmid=7824947 |accessdate=2012-05-30}}</ref>
*These mutations accumulate over generations and in populations, resulting in the great genetic variation within populations of HIV, and an increased probability of a virion developing an evolutionary selective advantage over other virions.<ref name="Freeman" /> Natural selection then acts on HIV by selecting for virions with higher fitness, as all others are eventually killed off by drug treatments.<ref name="Kozal">Kozal, M. J. 2009. Drug-resistant human [[immunodeficiency]] virus. Clin Microbial Infec. 15 (Suppl. 1): 69-73.</ref> The virions that are able to escape the harmful effects of the drug then create an entirely new, drug resistant population.
*These mutations accumulate over generations in the HIV infected population, resulting in great genetic variation and an increased probability of a virion developing an evolutionary selective advantage over other virions.<ref name="Freeman" /> Natural selection then acts on HIV by selecting for virions with higher fitness, as all others are eventually killed off by drug treatments.<ref name="Kozal">Kozal, M. J. 2009. Drug-resistant human [[immunodeficiency]] virus. Clin Microbial Infec. 15 (Suppl. 1): 69-73.</ref> The virions that are able to escape the harmful effects of the drug then create an entirely new, drug resistant population.
*The virions reproduce until the patient has a population of viruses as large as they originally did before treatment reduced these numbers. This creates a cycle in which patients first experiences success with treatment, as their viral levels decrease, then experiences a decline in treatment effectiveness as the virus develops resistance and rebuilds its population of virus particles.
*With HAART, at least 3 drugs are administered at the same time, which substantially reduces viral load and, compared to results of earlier regimens, increases the life expectancy of patients. These advantages follow because the mutations necessary to confer resistance to HAART are generated at a slower rate and are lost more rapidly than those conferring resistance to monotherapy or dual therapy. Moreover, viral strains resistant to HAART are not as efficient at completing their own life cycle (e.g., their replication rates are lower), they may generate less illness and lower proportion of deaths among infected persons, and the viral strains are less likely to be transmitted to other persons.
==Consequences of drug resistance==
 
==Consequences of Drug Resistance==
The consequences of drug resistance include
The consequences of drug resistance include
# [[AIDS medical therapy#Virologic failure|Treatment failure]].
# [[AIDS medical therapy#Virologic failure|Treatment failure]].
Line 30: Line 41:
# The spread of resistant strains of HIV.
# The spread of resistant strains of HIV.
# The need to develop new anti-HIV drugs
# The need to develop new anti-HIV drugs
==Strategies against HIV Drug resistance==
==Strategies against HIV Drug resistance==
WHO and its [[HIV ResNet]] group of experts and organizations have developed a ''Global strategy for prevention and assessment of HIV drug resistance.'' The strategy aims to build evidence on the scale of HIV drug resistance and equip and prepare countries with knowledge, skills and systems to respond should drug-resistant HIV epidemics emerge.
WHO and its [[HIV ResNet]] group of experts and organizations have developed a ''Global strategy for prevention and assessment of HIV drug resistance.'' The strategy aims to build evidence on the scale of HIV drug resistance and equip and prepare countries with knowledge, skills and systems to respond should drug-resistant HIV epidemics emerge.
===[[HIV resistance testing|Resistance Testing]]===
Resistance testing is usually performed for the management of patients with established HIV disease but can also be done before starting therapy. It is also recommended during pregnancy to optimize treatment selection and to decrease the risk of perinatal transmission.
There are 2 main methods to detect antiretroviral resistance in HIV:
#[[HIV resistance testing#Genotypic testing|Genotypic testing]].
#[[HIV resistance testing#Phenotypic testing|Phenotypic testing]].
'''To read in detail about HIV Resistance testing, click [[HIV resistance testing|'''here''']].
===HIV Drug Resistance Database===
The HIV Drug Resistance Database, also known as ''Stanford HIV RT and Protease Sequence Database'' is a database at [[Stanford University]] that tracks 93 common mutations of HIV.  It has been recompiled in 2008 listing 93 common mutations, after its initial mutation compilation in 2007 of 80 mutations.  The latest list utilizes data from other laboratories in Europe, Canada and the United States to include more than 15,000 sequences from untreated individuals.<ref>[http://www.physorg.com/news155558471.html Physorg:New Stanford list of HIV mutations vital to tracking AIDS epidemic]</ref>


==Reference==
==Reference==
{{reflist|2}}
{{reflist|2}}


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Latest revision as of 22:11, 29 July 2020

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Alejandro Lemor, M.D. [2]

Overview

The ability of HIV to mutate and reproduce itself in the presence of antiretroviral drugs is called HIV drug resistance. HIV Drug Resistance occurs when microevolution causes virions to become tolerant to antiretroviral treatments. Drug resistant virus will continue to replicate in the presence of the drug to which it has become resistant.

Drug Resistance

As ART continues to expand, the emergence of some drug resistance is inevitable. Many factors leading to treatment failure and eventually drug resistance are as follows:

  • Factors related to Virus or Drug
    • HIV biology: Human Immunodeficiency Virus replicates at a high rate, with more than 109 virions produced daily. The absence of DNA polymerase give rise to mutations in the progeny. The combinations of high replication rate and repeated introduction of mutations produces randomly generated mutatant stains that give rise to drug resistance.
    • Variable response to mutation: Although multiple mutations are required to develop drug resistance but resistance can develop even with a single mutation. Example: A single mutation can lead to high-level resistance in lamivudine, efavirenz and nevirapine. On the contrary, it takes multiple mutation to develop resistance against Protease inhibitors.
    • Potency of individual drug: Higher potency drugs are more vigorous in suppressing viral load, thus further controlling viral replications.[1]
  • Other contributing factors:
    • Insufficient knowledge among patients and health workers.
    • Suboptimal adherence to treatment regimens.
    • Drug stock-outs.
    • Inadequate patient monitoring mechanisms.

Historical Perspective

  • Over the past decade, access to ART for HIV has dramatically increased in low- and middle-income countries. From preliminary data, more than 6 million people were receiving ART in these countries at the end of 2010, as compared to just 400 000 at the end of 2003.

Types

HIV drug resistance may be transmitted or acquired.

  1. Acquired drug resistance: Drug resistance could develop if patients interrupt their treatment or do not take it according to prescription.
  2. Transmitted drug resistance: If people are infected by others who had HIV drug resistance, it is called transmitted drug resistance.

Current Scenario

  • Nearly all drugs currently used to treat HIV eventually stop working when patient develops resistance to ART. HIV develops resistance when it evades the effects of these treatments.[2] A recent study estimated the percentage of the American HIV positive population with some form of drug resistance to be 76.3%.[3]
  • The extent of HIV drug resistance resulting from recent ART scale up in resource-limited countries has not systematically been quantified due to the lack of reliable data and information.

Mechanism of Drug Resistance

  • As a retrovirus, HIV uses the enzyme reverse transcriptase to synthesize DNA from its RNA genome but it lacks a mechanism for correcting errors made while reproducing its genome.[2] As a result, HIV replicates its genome with the highest known mutation rate of any living organism.[2] This creates an ideal situation for natural selection to act on the HIV population, as genetic variation is the raw material for natural selection.[4]
  • These mutations accumulate over generations in the HIV infected population, resulting in great genetic variation and an increased probability of a virion developing an evolutionary selective advantage over other virions.[2] Natural selection then acts on HIV by selecting for virions with higher fitness, as all others are eventually killed off by drug treatments.[5] The virions that are able to escape the harmful effects of the drug then create an entirely new, drug resistant population.
  • With HAART, at least 3 drugs are administered at the same time, which substantially reduces viral load and, compared to results of earlier regimens, increases the life expectancy of patients. These advantages follow because the mutations necessary to confer resistance to HAART are generated at a slower rate and are lost more rapidly than those conferring resistance to monotherapy or dual therapy. Moreover, viral strains resistant to HAART are not as efficient at completing their own life cycle (e.g., their replication rates are lower), they may generate less illness and lower proportion of deaths among infected persons, and the viral strains are less likely to be transmitted to other persons.

Consequences of Drug Resistance

The consequences of drug resistance include

  1. Treatment failure.
  2. Increased direct and indirect health costs associated with the need to start more costly second-line treatment for patients.
  3. The spread of resistant strains of HIV.
  4. The need to develop new anti-HIV drugs

Strategies against HIV Drug resistance

WHO and its HIV ResNet group of experts and organizations have developed a Global strategy for prevention and assessment of HIV drug resistance. The strategy aims to build evidence on the scale of HIV drug resistance and equip and prepare countries with knowledge, skills and systems to respond should drug-resistant HIV epidemics emerge.

Resistance Testing

Resistance testing is usually performed for the management of patients with established HIV disease but can also be done before starting therapy. It is also recommended during pregnancy to optimize treatment selection and to decrease the risk of perinatal transmission.

There are 2 main methods to detect antiretroviral resistance in HIV:

  1. Genotypic testing.
  2. Phenotypic testing.

To read in detail about HIV Resistance testing, click here.

HIV Drug Resistance Database

The HIV Drug Resistance Database, also known as Stanford HIV RT and Protease Sequence Database is a database at Stanford University that tracks 93 common mutations of HIV. It has been recompiled in 2008 listing 93 common mutations, after its initial mutation compilation in 2007 of 80 mutations. The latest list utilizes data from other laboratories in Europe, Canada and the United States to include more than 15,000 sequences from untreated individuals.[6]


Reference

  1. ↑ Walmsley S, Bernstein B, King M, Arribas J, Beall G, Ruane P, Johnson M, Johnson D, Lalonde R, Japour A, Brun S, Sun E (2002). "Lopinavir-ritonavir versus nelfinavir for the initial treatment of HIV infection". N. Engl. J. Med. 346 (26): 2039–46. doi:10.1056/NEJMoa012354. PMID 12087139. Retrieved 2012-05-30. Unknown parameter |month= ignored (help)
  2. ↑ 2.0 2.1 2.2 2.3 Freeman, S., and J. C. Herron. 2007. Evolutionary Analysis. 4th ed. A case for evolutionary thinking: understanding HIV. Pearson Benjamin Cummings, San Francisco, CA.
  3. ↑ Richman, D. D., S. C. Morton, T. Wrin, N. Hellmann, S. Berry, M. F. Shapiro, and S. A. Bozzette. 2004. The prevalence of antiretroviral drug resistance in the United States. AIDS. 18: 1393-1401.
  4. ↑ Coffin JM (1995). "HIV population dynamics in vivo: implications for genetic variation, pathogenesis, and therapy". Science. 267 (5197): 483–9. PMID 7824947. Retrieved 2012-05-30. Unknown parameter |month= ignored (help)
  5. ↑ Kozal, M. J. 2009. Drug-resistant human immunodeficiency virus. Clin Microbial Infec. 15 (Suppl. 1): 69-73.
  6. ↑ Physorg:New Stanford list of HIV mutations vital to tracking AIDS epidemic
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