The management of HIV/AIDS normally includes the use of multiple antiretroviral drugs in an attempt to control HIV infection. There are several classes of antiretroviral agents that act on different stages of the HIV life-cycle. The use of multiple drugs that act on different viral targets is known as highly active antiretroviral therapy (HAART). HAART decreases the patient's total burden of HIV, maintains function of the immune system, and prevents opportunistic infections that often lead to death.
HIV treatment has been proven so successful that in many parts of the world HIV has become a chronic condition in which progression to AIDS has become increasingly rare. Anthony Fauci, head of the US National Institute of Allergy and Infectious Diseases has written "With collective and resolute action now and a steadfast commitment for years to come, an AIDS-free generation is indeed within reach." In the same paper he notes that an estimated 700,000 lives were saved in 2010 alone due to antiretroviral therapy. As another commentary in The Lancet noted, "Rather than dealing with acute and potentially life-threatening complications, clinicians are now confronted with managing a chronic disease that in the absence of a cure will persist for many decades"
The US Department of Health and Human Services and other organizations recommend offering antiretroviral treatment to all patients with HIV. Because of the complexity of selecting and following a regimen, the potential for side-effects, and the importance of taking medications regularly to prevent viral resistance, such organizations emphasize the importance of involving patients in therapy choices and recommend analyzing the risks and the potential benefits.
The first effective therapy against HIV was the nucleoside reverse transcriptase inhibitor (NRTI) zidovudine (AZT). It was approved by the US FDA in 1987. Subsequently several more NRTIs were developed but even in combination were unable to suppress the virus for long periods of time and patients still inevitably died. To distinguish from this early anti-retroviral therapy (ART), the term highly active anti-retroviral therapy (HAART) was introduced. In 1996 by sequential publications in The New England Journal of Medicine by Hammer and colleagues and Gulick and coinvestigators illustrating the substantial benefit of combining 2 NRTIs with a new class of anti-retrovirals, protease inhibitors, namely indinavir. This concept of 3-drug therapy was quickly incorporated into clinical practice and rapidly showed impressive benefit with a 60% to 80% decline in rates of AIDS, death, and hospitalization.
There are five classes of drugs, which are usually used in combination, to treat HIV infection. Use of these drugs in combination can be termed anti-retroviral therapy (ART), combination anti-retroviral therapy (cART) or highly active anti-retroviral therapy (HAART). Anti-retroviral (ARV) drugs are broadly classified by the phase of the retrovirus life-cycle that the drug inhibits. Typical combinations include 2 NRTIs as a "backbone" along with 1 NNRTI, PI or INSTI as a "base."
The life cycle of HIV can be as short as about 1.5 days from viral entry into a cell, through replication, assembly, and release of additional viruses, to infection of other cells. HIV lacks proofreading enzymes to correct errors made when it converts its RNA into DNA via reverse transcription. Its short life-cycle and high error rate cause the virus to mutate very rapidly, resulting in a high genetic variability of HIV. Most of the mutations either are inferior to the parent virus (often lacking the ability to reproduce at all) or convey no advantage, but some of them have a natural selection superiority to their parent and can enable them to slip past defenses such as the human immune system and antiretroviral drugs. The more active copies of the virus, the greater the possibility that one resistant to antiretroviral drugs will be made.
When antiretroviral drugs are used improperly, multi-drug resistant strains can become the dominant genotypes very rapidly. In the era before multiple drug classes were available (pre-1997), the reverse transcriptase inhibitors zidovudine, didanosine, zalcitabine, stavudine, and lamivudine were used serially or in combination leading to the development of multi-drug resistant mutations.
Antiretroviral combination therapy defends against resistance by suppressing HIV replication as much as possible, thus reducing the potential pool of spontaneous resistance mutations.
Combinations of antiretrovirals create multiple obstacles to HIV replication to keep the number of offspring low and reduce the possibility of a superior mutation. If a mutation that conveys resistance to one of the drugs being taken arises, the other drugs continue to suppress reproduction of that mutation. With rare exceptions, no individual antiretroviral drug has been demonstrated to suppress an HIV infection for long; these agents must be taken in combinations in order to have a lasting effect. As a result, the standard of care is to use combinations of antiretroviral drugs. Combinations usually consist of three drugs from at least two different classes. This three drug combination is commonly known as a triple cocktail. Combinations of antiretrovirals are subject to positive and negative synergies, which limits the number of useful combinations.
In recent years, drug companies have worked together to combine these complex regimens into simpler formulas, termed fixed-dose combinations. For instance, there are now several options that combine 3 drugs into one pill taken once daily. This greatly increases the ease with which they can be taken, which in turn increases the consistency with which medication is taken (adherence), and thus their effectiveness over the long-term. Not taking anti-retrovirals regularly is a cause of resistance development in people who have started taking them previously. Patients who take medications regularly can stay on one regimen without developing resistance. This greatly increases life expectancy and leaves more drugs available to the individual should the need arise.
Fixed dose combinations are multiple antiretroviral drugs combined into a single pill.
|Brand Name||Drug Names (INN)||Date of FDA Approval||Company|
|Combivir||lamivudine + zidovudine||September 26, 1997||GlaxoSmithKline|
|Kaletra||lopinavir + ritonavir||September 15, 2000||Abbott Laboratories|
|Trizivir||abacavir + lamivudine + zidovudine||November 15, 2000||GlaxoSmithKline|
|Epzicom (in USA)
Kivexa (in Europe and Russia)
|abacavir + lamivudine||August 2, 2004||GlaxoSmithKline|
|Truvada||tenofovir + emtricitabine||August 2, 2004||Gilead Sciences|
|Atripla||emtricitabine + tenofovir + efavirenz||July 12, 2006||Gilead Sciences and
|Complera (in USA)
Eviplera (in Europe and Russia)
|emtricitabine + rilpivirine + tenofovir||August 10, 2011||Gilead Sciences and
Janssen Therapeutics (formerly Tibotec)
|Stribild||elvitegravir + cobicistat + emtricitabine + tenofovir||August 27, 2012||Gilead Sciences|
|Triumeq||abacavir + dolutegravir + lamivudine||August 22, 2014||ViiV Healthcare|
|Evotaz||atazanavir + cobicistat||January 29, 2015||Bristol-Myers Squibb|
|Prezcobix||darunavir + cobicistat||January 29, 2015||Janssen Therapeutics|
|Dutrebis||lamivudine + raltegravir||February 6, 2015||Merck & Co.|
Antiretroviral drug treatment guidelines have changed over time. Before 1987, no antiretroviral drugs were available and treatment consisted of treating complications from opportunistic infections and malignancies. After antiretroviral medications were introduced, most clinicians agreed that HIV positive patients with low CD4 counts should be treated, but no consensus formed as to whether to treat patients with high CD4 counts.
In April 1995, Merck and the National Institute of Allergy and Infectious Diseases began recruiting patients for a trial examining the effects of a three drug combination of the protease inhibitor indinavir and two nucleoside analogs. illustrating the substantial benefit of combining 2 NRTIs with a new class of anti-retrovirals, protease inhibitors, namely indinavir. Later that year David Ho became an advocate of this "hit hard, hit early" approach with aggressive treatment with multiple antiretrovirals early in the course of the infection. Later reviews in the late 90s and early 2000s noted that this approach of "hit hard, hit early" ran significant risks of increasing side effects and development of multidrug resistance, and this approach was largely abandoned. The only consensus was on treating patients with advanced immunosuppression (CD4 counts less than 350/μL). Treatment with antiretrovirals was expensive at the time, ranging from $10,000 to $15,000 a year.
The timing of when to initiate therapy has continued to be a core controversy within the medical community. Most recently, the NA-ACCORD study observed patients who started antiretroviral therapy either at a CD4 count of less than 500 versus less than 350 and showed that patients who started ART at lower CD4 counts had a 69% increase in the risk of death.
Other arguments for starting therapy earlier are that people who start therapy later have been shown to have less recovery of their immune systems, and higher CD4 counts are associated with less cancer.
A separate argument for starting antiretroviral therapy that has gained more prominence is its effect on HIV transmission. ART reduces the amount of virus in the blood and genital secretions. This has been shown to lead to dramatically reduced transmission of HIV when one partner with a suppressed viral load (<50 copies/ml) has sex with a partner who is HIV negative. In clinical trial HPTN 052, 1763 serodiscordant heterosexual couples in 9 countries were planned to be followed for at least 10 years, with both groups receiving education on preventing HIV transmission and condoms, but only one group getting ART. The study was stopped early for ethical reasons when it became clear that antiviral treatment provided significant protection. Of the 28 couples where cross-infection had occurred, all but one had taken place in the control group consistent with a 96% reduction in risk of transmission while on ART. The term "treatment as prevention" has been used for the concept of treating patients with HIV to help prevent the spread of HIV. In 2011, the journal Science gave the Breakthrough of the Year award to treatment as prevention.
In summary, as the WHO HIV treatment guidelines state, "The ARV regimens now available, even in the poorest countries, are safer, simpler, more efficacious and more affordable than ever before."
There is a consensus among experts that, once initiated, antiretroviral therapy should never be stopped. This is because the selection pressure of incomplete suppression of viral replication in the presence of drug therapy causes the more drug sensitive strains to be selectively inhibited. This allows the drug resistant strains to become dominant. This in turn makes it harder to treat the infected individual as well as anyone else they infect. One trial where ART therapy was periodically stopped had higher rates of opportunistic infections, cancers, heart attacks and death in patients who interrupted their ART.
There are several treatment guidelines for HIV-1 infected adults in the developed world (that is, those countries with access to all or most therapies and laboratory tests). In the United States there are both the International AIDS Society-USA (IAS-USA) (a 501(c)(3) not-for-profit organization in the USA) as well as the US government's Department of Health and Human Services guidelines. In Europe there are the European AIDS Clinical Society guidelines.
For resource limited countries, most national guidelines closely follow the World Health Organization guidelines.
The current guidelines use new criteria to consider starting HAART, as described below. However, there remain a range of views on this subject and the decision of whether to commence treatment ultimately rests with the patient and his or her doctor.
Current US DHHS guidelines (published April 8, 2015) state:
Alternatively, current World Health Organization guidelines (dated June 30, 2013) state:
• As a priority, initiate ART in all individuals with severe/advanced HIV disease (WHO clinical stage 3 or 4) or CD4 count ≤ 350 cells/mm
• Active TB disease
• HBV coinfection with severe chronic liver disease
• Pregnant and breastfeeding women with HIV
• HIV-positive individual in a serodiscordant partnership (to reduce HIV transmission risk)
Baseline resistance is the presence of resistance mutations in patients who have never been treated before for HIV. In countries with a high rate of baseline resistance, resistance testing is recommended before starting treatment; or, if the initiation of treatment is urgent, then a "best guess" treatment regimen should be started, which is then modified on the basis of resistance testing. In the UK, there is 11.8% medium to high-level resistance at baseline to the combination of efavirenz + zidovudine + lamivudine, and 6.4% medium to high level resistance to stavudine + lamivudine + nevirapine. In the US, 10.8% of one cohort of patients who had never been on ART before had at least one resistance mutation in 2005. Various surveys in different parts of the world have shown increasing or stable rates of baseline resistance as the era of effective HIV therapy continues. With baseline resistance testing, a combination of antiretrovirals that are likely to be effective can be customized for each patient.
Most current HAART regimens consist of three drugs: 2 NRTIs ("backbone")+ a PI/NNRTI/INSTI ("base"). Initial regimens use "first-line" drugs with a high efficacy and low side-effect profile.
The US DHHS preferred initial regimens for adults and adolescents in the United States, as of April 2015, are:
In the case of the protease inhibitor based regimens, ritonavir is used at low doses to inhibit cytochrome p450 enzymes and "boost" the levels of other protease inhibitors, rather than for its direct antiviral effect. This boosting effect allows them to be taken less frequently throughout the day. Cobicistat is used with elvitegravir for a similar effect but does not have any direct antiviral effect itself.
The WHO preferred initial regimen for adults and adolescents as of June 30, 2013 is:
In the first 6 months after infection HIV viral loads tend to be elevated and people are more often symptomatic than in later latent phases of HIV disease. There may be special benefits to starting antiretroviral therapy early during this acute phase, including lowering the viral "set-point" or baseline viral load, reduce the mutation rate of the virus, and reduce the size of the viral reservoir (See section below on viral reservoirs). The SPARTAC trial compared 48 weeks of ART vs 12 weeks vs no treatment in acute HIV infection and found that 48 weeks of treatment delayed the time to decline in CD4 count below 350 cells per ml by 65 weeks and kept viral loads significantly lower even after treatment was stopped. Since viral loads are usually very high during acute infection, this period carries an estimated 26 times higher risk of transmission. By treating acutely infected patients, it is presumed that it could have a significant impact on decreasing overall HIV transmission rates since lower viral loads are associated with lower risk of transmission (See section on treatment as prevention). However an overall benefit has not been proven and has to be balanced with the risks of HIV treatment. Therapy during acute infection carries a grade BII recommendation from the US DHHS.
HIV can be especially harmful to infants and children, with one study in Africa showing that 52% of untreated children born with HIV had died by age 2. By five years old, the risk of disease and death from HIV starts to approach that of young adults. The WHO recommends treating all children less than 5 years old, and starting all children older than 5 with stage 3 or 4 disease or CD4 <500 cells/ml. DHHS guidelines are more complicated but recommend starting all children less than 12 months old and children of any age who have symptoms.
As for which antiretrovirals to use, this is complicated by the fact that many children who are born to mothers with HIV are given a single dose of nevirapine (an NNRTI) at the time of birth to prevent transmission. If this fails it can lead to NNRTI resistance. Also, a large study in Africa and India found that a PI based regimen was superior to an NNRTI based regimen in children less than 3 years who had never been exposed to NNRTIs in the past. Thus the WHO recommends PI based regimens for children less than 3.
The WHO recommends for children less than 3 years:
and for children 3 years to less than 10 years and adolescents <35 kilograms:
US DHHS guidelines are similar but include PI based options for children > 3 years old.
The goals of treatment for pregnant women include the same benefits to the mother as in other infected adults as well as prevention of transmission to her child. The risk of transmission from mother to child is proportional to the plasma viral load of the mother. Untreated mothers with a viral load >100,000 copies/ml have a transmission risk of over 50%. The risk when viral loads are < 1000 copies/ml are less than 1%. ART for mothers both before and during delivery and to mothers and infants after delivery are recommended to substantially reduce the risk of transmission. The mode of delivery is also important, with a planned Caesarian section having a lower risk than vaginal delivery or emergency Caesarian section. HIV can also be detected in breast milk of infected mothers and transmitted through breast feeding. The WHO balances the low risk of transmission through breast feeding from women who are on ART with the benefits of breastfeeding against diarrhea, prneumonia and malnutrition. It also strongly recommends that breastfeeding infants receive prophylactic ART. In the US, the DHHS recommends against women with HIV breastfeeding.
With improvements in HIV therapy, several studies now estimate that patients on treatment in high-income countries can expect a normal life expectancy. This means that a higher proportion of people living with HIV are now older and research is ongoing into the unique aspects of HIV infection in the older adult. There is data that older people with HIV have a blunted CD4 response to therapy but are more likely to achieve undetectable viral levels. However not all studies have seen a difference in response to therapy. Current guidelines do not have separate treatment recommendations for older adults, but it is important to take into account that older patients are more likely to be on multiple non-HIV medications and consider drug interactions with any potential HIV medications. There are also increased rates of HIV associated non-AIDS conditions (HANA) such as heart disease, liver disease and dementia that are multifactorial complications from HIV, associated behaviors, coinfections like Hepatitis B, Hepatitis C, and Human papilloma virus as well as HIV treatment.
There are several concerns about antiretroviral regimens that should be addressed before initiating:
Suppressing the viral load to undetectable levels (<50 copies per ml) is the primary goal of ART. This should happen by 24 weeks after starting combination therapy. Viral load monitoring is the most important predictor of response to treatment with ART. Levels higher than 200 copies per ml is considered virologic failure, and should prompt further testing for potential viral resistance. Lack of viral load suppression on ART is termed virologic failure.
CD4 cell counts are another key measure of immune status and ART effectiveness. CD4 counts should rise 50 to 100 cells per ml in the first year of therapy. There can be substantial fluctuation in CD4 counts of up to 25% based on the time of day or concominant infections. In one long term study, the majority of increase in CD4 cell counts was in the first two years after starting ART with little increase afterwards. This study also found that patients who began ART at lower CD4 counts continued to have lower CD4 counts than those who started at higher CD4 counts. When viral suppression on ART is achieved but without a corresponding increase in CD4 counts it can be termed immunologic nonresponse or immunologic failure. While this is predictive of worse outcomes, there is no consensus on how to adjust therapy to immunologic failure and whether switching therapy is beneficial. DHHS guidelines do not recommend switching an otherwise suppressive regimen.
In patients who have persistently detectable viral loads while taking ART, tests can be done to investigate whether there is drug resistance. Most commonly a genotype is sequenced which can be compared with databases of other HIV viral genotypes and resistance profiles to predict response to therapy. If there is extensive resistance a phenotypic test of a patient's virus against a range of drug concentrations can be performed, but is expensive and can take several weeks, so genotypes are generally preferred. Using information from a genotype or phenotype, a regimen of 3 drugs from at least 2 classes is constructed that will have the highest probability of suppressing the virus. If a regimen cannot be constructed from recommended first line agents it is termed salvage therapy, and when 6 or more drugs are needed it is termed mega-HAART.
Drug holidays (or "structured treatment interruptions") are intentional discontinuations of antiretroviral drug treatment. As mentioned above, randomized controlled studies of structured treatment interruptions have shown higher rates of opportunistic infections, cancers, heart attacks and death in patients who took drug holidays. With the exception of post exposure prophylaxis, current treatment guidelines do not call for the interruption of drug therapy once it has been initiated.
Each class and individual antiretroviral carries unique risks of adverse side effects.
The NRTIs can interfere with mitochondrial DNA synthesis and lead to high levels of lactate and lactic acidosis, liver steatosis, peripheral neuropathy, myopathy and lipoatrophy. Current first line NRTIs such as lamivudine/emtrictabine, tenofovir, and abacavir are less likely to cause mitochondrial dysfunction.
NNRTIs are generally safe and well tolerated. The main reason for discontinuation of efavirenz is neuro-psychiatric effects including suicidal ideation. Nevirapine can cause severe hepatotoxicity, especially in women with high CD4 counts.
Protease inhibitors (PIs) are often given with ritonavir, a strong inhibitor of cytochrome P450 enzymes, leading to numerous drug-drug interactions. They are also associated with lipodystrophy, elevated triglycerides and elevated risk of heart attack.
Integrase inhibitors (INSTIs) are among the best tolerated of the antiretrovirals with excellent short and medium term outcomes. Given their relatively new development there is less long term safety data. They are associated with an increase in creatinine kinase levels and rarely myopathy.
When people are exposed to HIV-positive infectious bodily fluids either through skin puncture, contact with mucous membranes or contact with damaged skin they are at risk for acquiring HIV. Pooled estimates give a risk of transmission with puncture exposures of 0.3% and mucous membrane exposures 0.63%. United States guidelines state that "feces, nasal secretions, saliva, sputum, sweat, tears, urine, and vomitus are not considered potentially infectious unless they are visibly bloody." Given the rare nature of these events, rigorous study of the protective abilities of antiretrovirals are limited but do suggest that taking antiretrovirals afterwards can prevent transmission. It is unknown if 3 medications are better than 2. The sooner after exposure that ART is started the better, but after what period they become ineffective is unknown, with the US Public Health Service Guidelines recommending starting prophylaxis up to a week after exposure. They also recommend treating for a duration of 4 weeks based on animal studies. Their recommended regimen is emtricitabine + tenofovir + raltegravir (an INSTI). The rationale for this regimen is that it is "tolerable, potent, and conveniently administered, and it has been associated with minimal drug interactions." People who are exposed to HIV should have follow up HIV testing at 6, 12, and 24 weeks.
Women with HIV have been shown to have decreased fertility which can affect available reproductive options. In cases where the woman is HIV negative and the man is HIV positive, the primary assisted reproductive method used to prevent HIV transmission is sperm washing followed by intrauterine insemination (IUI) or in vitro fertilization (IVF). Preferably this is done after the man has achieved an undetectable plasma viral load. In the past there have been cases of HIV transmission to an HIV-negative partner through processed artificial insemination, but a large modern series in which followed 741 couples where the man had a stable viral load and semen samples were tested for HIV-1, there were no cases of HIV transmission.
For cases where the woman is HIV positive and the man is HIV negative, the usual method is artificial insemination. With appropriate treatment the risk of mother-to-child infection can be reduced to below 1%.
People living with HIV can currently expect to live a normal life span if able to achieve durable viral suppression on combination antiretroviral therapy. However this requires lifelong medication and will still suffer from higher rates of cardiovascular, renal, liver and neurologic disease. This has prompted further research towards a cure for HIV.
So far only one adult (the so-called "Berlin patient") has been potentially cured and gone over six years without treatment with no detectable virus. This was achieved through two bone marrow transplants that replaced his immune system with a donor's that did not have the CCR5 cell surface receptor which is needed for some variants of HIV to enter a cell. Bone marrow transplants carry their own significant risks including potential death and was only attempted because it was necessary to treat a blood cancer he had. Attempts to replicate this have not been successful and given the risks, expense and rarity of CCR5 negative donors, bone marrow transplant is not seen as a mainstream option. It has inspired research into other methods to try to block CCR5 expression through gene therapy. A zinc-finger nuclease has been used in a Phase I trial of 12 humans and led to an increase in CD4 count and decrease in their viral load while off antiretroviral treatment.
The main obstacle to conventional antiretroviral therapy eliminating HIV infection is that HIV is able to integrate itself into the DNA of host cells and rest in a latent state, while antiretrovirals only attack actively replicating HIV. The cells in which HIV lays dormant are called the viral reservoir, and one of the main sources is thought to be central memory and transitional memory CD4+ T cells. Recent reports of the cure of HIV in two infants are presumably due to the fact that treatment was initiated within hours of infection, preventing HIV from establishing a deep reservoir. Currently there is work being done to try and activate reservoir cells into replication so that the virus is forced out of latency and can be attacked by antiretrovirals and the host immune system. Targets include histone deacetylase (HDAC) which represses transcription and if inhibited can lead to increased cell activation. The HDAC inhibitors valproic acid and vorinostat have been used in human trials with only preliminary results so far.
Even with all latent virus deactivated, it is thought that a vigorous immune response will need to be induced to clear all the remaining infected cells. Current strategies include using cytokines to restore CD4+ cell counts as well as therapeutic vaccines to prime immune responses.
全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.
|拡張検索||「highly-active antiretroviral therapy」「highly active antiretroviral therapy」|