(Last updated:08/04/2015; last reviewed:08/04/2015)
Rating of Recommendations: A = Strong; B = Moderate; C = Optional
Antiretroviral (ARV) regimens currently recommended for initial therapy of HIV-infected patients have a high likelihood of achieving and maintaining plasma HIV RNA levels below the lower limits of detection (LLOD) of currently used assays (see What to Start). Patients on antiretroviral therapy (ART) who do not achieve this treatment goal or who experience virologic rebound often develop resistance mutations to one or more components of their regimen. Based on surveillance data for HIV patients in care in selected cities in the United States in 2009, an estimated 89% of the patients were receiving ART, of whom 72% had viral loads <200 copies/mL.1 Many patients with detectable viral loads are non-adherent to treatment. Depending on their treatment histories, some of these patients may have minimal or no drug resistance; others may have extensive resistance. Managing patients with extensive resistance is complex and usually requires consultation with an HIV expert. This section of the guidelines defines virologic failure in patients on ART and discusses strategies to manage these individuals.
Virologic Suppression: A confirmed HIV RNA level below the LLOD of available assay.
Virologic Failure: The inability to achieve or maintain suppression of viral replication to an HIV RNA level <200 copies/mL.
Incomplete Virologic Response: Two consecutive plasma HIV RNA levels ≥200 copies/mL after 24 weeks on an ARV regimen. Baseline HIV RNA may affect the time course of response; some regimens will take longer than others to suppress HIV RNA levels.
Virologic Rebound: Confirmed HIV RNA ≥200 copies/mL after virologic suppression.
Virologic Blip: After virologic suppression, an isolated detectable HIV RNA level that is followed by a return to virologic suppression.
Goal of ART Treatment and Virologic Responses
The goal of ART is to suppress HIV replication to a level below which drug-resistance mutations do not emerge. Although the evidence is not conclusive, it is generally believed that selection of drug resistance mutations does not occur in patients with HIV RNA levels persistently suppressed to below the LLOD of current assays.3
Viremia “blips”—defined by viral suppression followed by an isolated detectable HIV RNA level and subsequent return to undetectable levels—are not usually associated with subsequent virologic failure.3 In contrast, there is controversy regarding the clinical implications of persistent HIV RNA levels between the LLOD and <200 copies/mL in patients on ART. Furthermore, viremia at this threshold is detected with some frequency by commonly used real-time polymerase chain reaction (PCR) assays, which are more sensitive than PCR-based viral load platforms used in the past.4-6 Findings from a large retrospective analysis showed that, as a threshold for virologic failure, HIV RNA levels of 200 copies/mL and <50 copies/mL had the same predictive value for subsequent rebound to >200 copies/mL.7 Two other retrospective studies also support the supposition that virologic rebound is more likely to occur in patients with viral loads >200 copies/mL than in those with low-level viremia between 50 to 199 copies/mL.8,9 However, other studies have suggested that viremia at this low level (<200 copies/mL) can be predictive of progressive viral rebound10,11 and can be associated with the evolution of drug resistance.12
Persistent HIV RNA levels ≥200 copies/mL are often associated with evidence of viral evolution and accumulation of drug-resistance mutation.12 This association is particularly common when HIV RNA levels are >500 copies/mL.13 Therefore, persistent plasma HIV RNA levels ≥200 copies/mL should be considered virologic failure.
Causes of Virologic Failure:
Virologic failure can occur in a patient for many reasons. Data from patient cohorts in the earlier era of combination ART suggested that suboptimal adherence and drug intolerance/toxicity accounted for 28% to 40% of virologic failure and regimen discontinuations.15,16 More recent data suggest that most virologic failure on first-line regimens occurs because of either pre-existing (transmitted) drug resistance or suboptimal adherence.17 Virologic failure is associated with both patient- and regimen-related factors.
- Higher pretreatment or baseline HIV RNA level (depending on the specific regimen used)
- Lower pretreatment or nadir CD4 T-cell count (depending on the specific regimen used)
- Comorbidities (e.g., active substance abuse, psychiatric disease, neurocognitive deficits)
- Presence of drug-resistant virus, either transmitted or acquired
- Prior treatment failure
- Incomplete medication adherence and missed clinic appointments
- Interruption of or intermittent access to ART
ARV Regimen-Related Factors:
- Drug adverse effects and toxicities
- Suboptimal pharmacokinetics (variable absorption, metabolism, or, theoretically, penetration into reservoirs)
- Suboptimal virologic potency
- Prior exposure to suboptimal regimens (e.g., functional monotherapy)
- Food requirements
- High pill burden and/or dosing frequency
- Adverse drug-drug interactions with concomitant medications
- Prescription errors
Management of Patients with Virologic Failure:
Assessment of Virologic Failure
If virologic failure is suspected or confirmed, a thorough work-up that includes consideration of the factors listed in the Causes of Virologic Failure section above is indicated. In many cases, the cause(s) of virologic failure can be identified. In some cases, however, no obvious cause(s) may be found. It is important to distinguish among the causes for virologic failure because the approaches to subsequent therapy differ. The following potential causes of virologic failure should be explored in depth.
Incomplete Adherence. Assess the patient’s adherence to the regimen. Identify and address the underlying cause(s) for incomplete adherence (e.g., drug intolerance, difficulty accessing medications, depression, active substance abuse) and, if possible, simplify the regimen (e.g., decrease pill count or dosing frequency) (see Adherence).
Medication Intolerance. Assess the patient’s tolerance of the current regimen and the severity and duration of side effects, keeping in mind that even minor side effects can affect adherence. Management strategies to address intolerance in the absence of drug resistance may include:
- Using symptomatic treatment (e.g., antiemetics, antidiarrheals)
- Changing one ARV in a regimen to another agent in the same drug class (see Adverse Effects section)
- Changing from one drug class to another class (e.g., from a Non-Nucleoside Reverse Transcriptase Inhibitor [NNRTI] to a protease inhibitor [PI] or an integrase strand transfer inhibitor [INSTI]) if necessary (see Adverse Effects section).
- Review food requirement for each medication, and assess whether the patient adheres to the requirement.
- Review recent history of gastrointestinal symptoms such as vomiting or diarrhea that may result in short-term malabsorption.
- Review concomitant medications and dietary supplements for possible adverse drug-drug interactions (consult Drug Interactions section and tables for common interactions) and make appropriate substitutions for ARV agents and/or concomitant medications, if possible.
- Consider therapeutic drug monitoring (TDM) if pharmacokinetic drug-drug interactions or impaired drug absorption leading to decreased ARV exposure is suspected (see also Exposure-Response Relationship and Therapeutic Drug Monitoring).
Suspected Drug Resistance. Perform resistance testing while the patient is still taking the failing regimen or within 4 weeks after the regimen is discontinued if the patient’s plasma HIV RNA level is >1000 copies/mL (AI), and possibly even if between 500 to 1000 copies/mL (BII) (see Drug-Resistance Testing). In some patients, resistance testing should be considered even after treatment interruptions of more than 4 weeks—recognizing that the lack of evidence of resistance in this setting does not exclude the possibility that resistance mutations may be present at low levels (CIII). Evaluate the extent of drug resistance, taking into account the patient’s past treatment history and prior resistance test results. Drug resistance is cumulative; thus, all prior treatment history and resistance test results should be considered when evaluating resistance. Routine genotypic or phenotypic testing provides information relevant for selecting nucleoside reverse transcriptase inhibitors (NRTIs), NNRTIs, and PIs. Additional drug-resistance tests for patients experiencing failure on INSTIs and/or a fusion inhibitor (AII), and viral tropism tests for patients experiencing failure on a CCR5 antagonist (BIII) are also available. Typically, these tests must be ordered separately from tests for resistance to NRTIs, NNRTIs, and PIs. (See Drug-Resistance Testing)
Managing Virologic Failure
Once virologic failure is confirmed, every effort should be made to assess if poor adherence and drug-drug or drug-food interactions may be contributing to the inadequate virologic response to ART. In general, if virologic failure persists after these issues have been adequately addressed, the regimen should be changed as soon as possible to avoid progressive accumulation of resistance mutations.>18In addition, several studies have shown that virologic responses to new regimens are greater in individuals with lower HIV RNA levels8,19and/or higher CD4 cell counts at the time of regimen changes.8,19 Discontinuing or briefly interrupting therapy in a patient with viremia may lead to a rapid increase in HIV RNA and a decrease in CD4 cell count and increases the risk of clinical progression.20,21Therefore, this strategy is not recommended (AIDiscontinuation or Interruption of Antiretroviral Therapy).
Ideally, a new ARV regimen should contain at least two, and preferably three, fully active drugs whose expected activity is based on the patient’s drug treatment history, resistance testing, or the mechanistic action of a new drug class (AI).8,22-31 Despite drug resistance, some ARV drugs (e.g., NRTIs) may contribute partial ARV activity to a regimen21, but other agents (e.g., enfuvitide [T-20], NNRTIs, raltegravir [RAL]) likely will not.32-34 Using a “new” drug that a patient has not previously taken does not ensure that the drug will be fully active; there is still the potential for drug-class cross-resistance that reduces drug activity. In addition, archived drug-resistance mutations may not be detected by standard drug-resistance tests, particularly if testing is performed when the patient is not taking the drug in question. This illustrates the importance of considering both treatment history and prior and current drug-resistance test results when designing a new regimen. Drug potency and viral susceptibility are more important factors to consider than the number of component drugs.
In general, patients who receive at least three active drugs selected on the basis of past and present drug resistance test results and treatment history, experience better and more sustained virologic responses than those receiving regimens with fewer active drugs. However, in select cases, adding a fully active ritonavir (RTV)-boosted PI (PI/r) to a single active drug may result in a regimen that is as effective as a regimen that includes more active agents.37-40 Active ARV drugs are those with activity against drug-resistant viral strains. These include newer members of existing drug classes that are active against HIV that are resistant to older drugs in the same classes (e.g., ETR, DRV and tipranavir [TPV], and dolutegravir [DTG])8,31 and drugs with unique mechanisms of action (e.g., the fusion inhibitor T-20, the CCR5 antagonist maraviroc [MVC] in patients with no detectable CXCR4-using virus). In the presence of certain drug resistance mutations, the recommended doses of select ARVs, such as DRV/r and DTG need to be given twice daily instead of once daily to achieve higher drug concentrations.37,38 Drug-resistance tests for patients experiencing failure on a FI and/or INSTIs, and viral tropism tests for patients experiencing failure on a CCR5 antagonist are also available, although these assays must be performed independent of routine drug resistance testing (see Drug-Resistance Testing).
Clinical Scenarios of Virologic Failure
- HIV RNA above the LLOD and <200 copies/mL. Confirm that levels remain above the LLOD and assess adherence and drug-drug interactions (including those with over the counter products and supplements) and drug-food interactions. Patients with HIV RNA typically below the LLOD with transient increases in HIV RNA (i.e., blips) do not require a change in treatment (AII).5 Although there is no consensus on how to manage patients with persistent HIV RNA levels above the LLOD and <200 copies/mL, the risk of emerging resistance is believed to be relatively low. Therefore, these patients should be followed on their current regimens with HIV RNA levels monitored at least every 3 months to assess the need for changes in ART in the future (AIII).
HIV RNA ≥200 and <1000 copies/mL. Confirm that levels remain in this range, assess adherence, drug-drug interactions (including those with over the counter products and supplements), and drug-food interactions. In contrast to patients with HIV RNA levels persistently <200 copies/mL, those with persistent HIV RNA levels ≥200 copies/mL often develop drug resistance, particularly when their HIV RNA levels are >500 copies/mL.8,9 Persistent plasma HIV RNA levels in the 200 to 1,000 copies/mL range should be considered as virologic failure and resistance testing should be attempted if the HIV RNA level is >500 copies/mL. When resistance testing can successfully be performed and no resistance is detected, manage the patient as outlined below in the section on HIV RNA >1,000 copies/mL and no drug resistance identified. If drug resistance is detected, manage the patient as outlined below in the section on HIV RNA >1,000 copies/mL and drug resistance identified. When resistance testing cannot be performed because of low-level viremia, the decision whether to empirically change ARVs should be made on a case-by-case basis.
- HIV RNA >1000 copies/mL and NO drug resistance identified. This scenario is almost always associated with non-adherence. Conduct a thorough assessment to determine the level of adherence and identify any drug-drug and drug-food interactions. Consider the timing of the drug-resistance test (e.g., Was the patient off ART for more than 4 weeks and/or nonadherent with the regimen at the time testing was performed?). Consider resuming the same regimen or starting a new regimen. Two to four weeks after treatment is resumed repeat viral load testing and—if viral load remains >500 copies/mL—perform genotypic testing to determine whether a resistant viral strain emerges (CIII).
HIV RNA >1000 copies/mL and drug resistance identified. The goals in this situation are to suppress HIV RNA levels maximally (i.e., to below the LLOD) and to prevent further selection of resistance mutations. With the availability of several newer ARVs, including some with new mechanisms of action, it is now possible to achieve these goals in many patients, including in those with extensive treatment experience and drug resistance. In the case of virologic failure, consider changing the treatment regimen sooner, rather than later, to minimize continued selection of resistance mutations. In a patient with ongoing viremia and evidence of resistance, some drugs in a regimen (e.g., NNRTIs, T-20, or INSTIs) should be discontinued promptly to decrease the risk of selection of additional drug-resistance mutations and to preserve the activity of these drug classes in future regimens. A new regimen should include at least two, and preferably three, fully active agents (AII). If only two active drugs can be identified, whenever possible, an active ritonavir-boosted PI (PI/r) should be prescribed as part of the regimen because of its higher genetic barrier for resistance. In a new regimen, it is the number of active agents and not necessarily the drug class that is most important. This principle was demonstrated in the OPTIONS study; virologic outcomes in those taking at least 2 fully active drugs were equal, whether or not the regimen was supplemented with NRTIs.39
First Regimen Failure
Failing an NNRTI plus NRTI regimen. Patients failing an NNRTI-based regimen often have viral resistance to the NNRTI, with or without lamivudine (3TC) and emtricitabine (FTC) resistance. Although several options are available for these patients, several studies have explored the activity of a pharmacokinetically boosted PI with NRTIs or an INSTI.43-45 Two of the studies found that regimens containing a ritonavir-boosted PI (PI/r) combined with NRTIs were as active as regimens containing the PI/r combined with RAL.43,45 Two studies also demonstrated higher rates of virologic suppression with use of a PI/r plus NRTIs than with a PI/r alone.44,45 On the basis of these studies, even patients with NRTI resistance can often be treated with a pharmacokinetically boosted PI plus NRTIs or RAL (AI). Although LPV/r was used in these studies, it is likely that other pharmacokinetically boosted PIs would behave similarly. Although data are limited, the second-generation NNRTI ETR or the other INSTIs (i.e., elvitegravir [EVG] or DTG) combined with a pharmacokinetically boosted PI may also be options in this setting.>
Failing a pharmacokinetically boosted PI plus NRTI regimen. In this scenario, most patients will have either no resistance or resistance limited to 3TC and FTC.46,47 Failure in this setting is often attributed to poor adherence, drug-drug interactions, or drug-food interactions. A systematic review of multiple randomized trials of PI/r first-line failure showed that maintaining the same regimen, presumably with efforts to enhance adherence, is as effective as changing to new regimens with or without drugs from new classes.48 In this setting, resistance testing should be performed along with an assessment of overall adherence and tolerability of the regimen. If the regimen is well tolerated and there are no concerns regarding drug-drug or drug-food interactions, the regimen can be continued with adherence support and viral monitoring. Alternatively, if poor tolerability or interactions may be contributing to virologic failure, the regimen can be modified to include a different pharmacokinetically boosted PI plus NRTIs—even if not all of the NRTIs are fully active—or to a new non-PI-based regimen that includes more than two fully active agents (AII).
Failing an INSTI plus NRTI regimen. Virologic failure with a regimen consisting of RAL plus two NRTIs or with EVG/cobicistat/tenofovir disoproxil fumarate/FTC may be associated with emergent resistance to 3TC and FTC and possibly the INSTI.49 Viruses with INSTI resistance often have virus still susceptible to DTG.19 In contrast, persons failing DTG plus two NRTI first-line therapy in clinical trials have not yet been shown to develop phenotypic resistance to DTG.49 There are no clinical trial data to guide therapy for first-line INSTI failures, although one can likely extrapolate from the data for NNRTI failures. Thus, patients with first-line INSTI failure should respond to a pharmacokinetically boosted PI plus NRTIs (AII). A pharmacokinetically boosted PI plus an INSTI may also be a viable option in patients with no INSTI resistance (BII). In the setting the virus is found to have resistance to RAL and EVG but remains susceptible to DTG, DTG can be used in combination with a pharmacokinetically boosted PI. If no resistance is identified, the patient should be managed as outlined above in the section on virologic failure without resistance.
Second-Line Regimen Failure and Beyond
Drug resistance with treatment options allowing for full virologic suppression. Depending on treatment history and drug-resistance data, one can predict whether or not to have a fully active pharmacokinetically boosted PI to include in future regimens. For example, those who have no documented PI resistance and previously have never been treated with an unboosted PI are likely to harbor virus that is fully susceptible to ARVs in the PI class. In this setting, viral suppression should be achievable using a pharmacokinetically boosted PI combined with either NRTIs or an INSTI—provided the virus is susceptible to the INSTI. If a fully susceptible pharmacokinetically boosted PI is not an option, the new regimen should include at least two, and preferably three, fully active agents, if possible. Drugs to be included in the regimen should be selected based on the likelihood that they will be active as determined by the patient’s treatment history, past and present drug-resistance testing, and tropism testing if a CCR5 antagonist is being considered.
Multidrug resistance without treatment options allowing for full virologic suppression. Use of currently available ARVs has resulted in a dramatic decline in the number of patients who have few treatment options because of multi-class drug resistance.50,51 Despite this progress, there remain patients who have experienced toxicities and/or developed resistance to all or most currently available drugs. If maximal virologic suppression cannot be achieved, the goals of ART will be to preserve immunologic function, prevent clinical progression, and minimize increasing resistance to drug classes that may eventually include new drugs that may be important for future regimens. Consensus on the optimal management of these patients is lacking. If resistance to NNRTIs, T20, EVG or RAL are identified, there is rarely a reason to continue these drugs, as there is little evidence that keeping them in the regimen helps delay disease progression (BII). Moreover, continuing these drugs, in particular INSTIs, may allow for further increasing resistance and within-class cross resistance that may limit future treatment options.It should be noted that even partial virologic suppression of HIV RNA to >0.5 log10 copies/mL from baseline correlates with clinical benefits.50,52 Cohort studies provide evidence that continuing therapy, even in the presence of viremia and the absence of CD4 count increases, reduces the risk of disease progression.53 Other cohort studies suggest continued immunologic and clinical benefits with even modest reductions in HIV RNA levels.54,55 However, all these potential benefits must be balanced with the ongoing risk of accumulating additional resistance mutations. In general, adding a single fully active ARV to the regimen isnot recommended because of the risk of rapid development of resistance (BII).
Highly drug resistant HIV. In recent years, use of currently available ARV drugs has resulted in a dramatic decline in the number of patients who have few treatment options because of multi-class drug resistance.44 Despite this decline, there remains a subset of patients who have experienced toxicity and/or developed resistance to all or most currently available drugs such that design of a regimen with two or three fully active drugs is not possible. These patients may have started therapy before newer, more potent ARVs were available; thus, they developed resistance but had no options for salvage therapy. Standard genotypic testing for RT and PR mutations may be inadequate to identify fully active drugs to add to a new regimen. Additional testing for INSTI resistance, as well as genotypic and phenotypic testing for PR and RT mutations, may be necessary. A tropism assay can also help to determine whether MVC can be added to the new regimen.
Patients with ongoing viremia who lack sufficient treatment options to construct a fully suppressive regimen may be candidates for research studies or expanded access programs or may qualify for single-patient access of an investigational new drug as specified in Food and Drug Administration regulations. Information about these programs may also be available from the sponsoring pharmaceutical manufacturer.
- Previously treated patient with suspected drug resistance and in need of care but with limited information (i.e., incomplete or no self-reported history, medical records, or resistance data). Every effort should be made to obtain the patient’s medical records and prior drug-resistance testing results; however, this may not always be possible. One strategy is to restart the most recent ARV regimen and assess drug resistance in 2 to 4 weeks to guide selection of the next regimen. Another strategy is to start two or three drugs known to be active on the basis of the patient’s treatment history (e.g., MVC if the patient has no detectable X4 virus and an INSTI if there is no prior history of treatment with drugs in this class).
In heavily treatment-experienced patients, where treatment options are limited by drug resistance, toxicities or other issues, enrolment in a clinical trial of a new antiretroviral agent (if available), or use of an agent not yet Therapeutic Goods Administration (TGA) approved for marketing but available through the Special Access Scheme, can be considered.
October 2017 - Feedback
Treatments not currently licensed in Australia, or for which an application for reimbursement through the Pharmaceutical Benefits Scheme (PBS) is not currently approved, may be available through access mechanisms such as the Special Access Scheme, or compassionate use programs, or through discussions with relevant pharmaceutical manufacturers.
Eligibility criteria for these programs vary for individual agents. Information about current access programs may be obtained by contacting the relevant sponsor company and/or manufacturer.
In heavily treatment-experienced patients, where treatment options are limited by drug resistance, toxicities or other issues, enrolment in a clinical trial of a new antiretroviral agent (if available), or use of an agent not yet Therapeutic Goods Administration (TGA) approved for marketing but available through the Special Access Scheme, can be considered.
October 2017 - Feedback
In an antiretroviral experienced patient, who has experienced virological failure after at least one antiretroviral regimen, and who has no darunavir associated mutations or other major PI mutations on resistance testing, darunavir may be used as 800 mg with ritonavir 100 mg once daily in combination with other antiretroviral drugs. If there has been more than one episode of virological failure with PI based regimens, it would be prudent to use darunavir 600 mg combined with ritonavir 100 mg twice daily.
Patients who are currently virologically suppressed; have not failed more than one PI containing regimen and have no prior evidence of darunavir associated mutations may be switched to once daily darunavir (800mg + 100mg ritonavir) in an attempt to simplify the antiretroviral therapy regimen or improve lipids. Cobicistat boosted darunavir is available as a single pill and is considered bioequivalent to DRV/r although lacks the original clinical trial data of DRV/r in treatment experienced patients.
 Arribas JR, et al. HIV Med. 2012;13:398-405.
October 2017 - Feedback
Maraviroc with an optimised background of other antiretroviral drugs may be effective in patients who experience virological failure after receiving drugs from at least three classes of ART and who are infected with a CCR5-tropic strain of HIV.
HIV RNA Genotypic tropism testing is available at:
- HIV Characterisation Lab, VIDRL, Melbourne, VIC (03) 9342 2623
- NSW State Reference Lab for HIV/AIDS, St Vincent's Hospital, Sydney, NSW (02) 8382 9178
- Institute for Immunology and Infectious Disease, Perth, WA (08) 9360 1363
 Hardy WD et al. JAIDS 2010;55:558-64.
Isolated Central Nervous System (CNS) Virologic Failure and New Onset Neurologic Symptoms
Presentation with new-onset CNS signs and symptoms has been reported as a rare form of virologic failure. These patients present with new, usually subacute, neurological symptoms associated with breakthrough of HIV infection within the CNS compartment despite plasma HIV RNA suppression.56,57 Clinical evaluation frequently shows abnormalities on MRI brain imaging and abnormal cerebrospinal fluid (CSF) findings with characteristic lymphocytic pleocytosis. When available, measurement of CSF HIV RNA shows higher concentrations in the CSF than in plasma, and in most patients, evidence of drug-resistant CSF virus. Drug- resistance testing of HIV in CSF, if available, can be used to guide changes in the treatment regimen according to principles outlined above for plasma HIV RNA resistance (CIII). In these patients it may be useful to consider CNS pharmacokinetics in drug selection (CIII). If CSF HIV resistance testing is not available, the regimen may be changed based on the patient’s treatment history or on predicted drug penetration into the CNS58-60 (CIII). This “neurosymptomatic” CNS viral escape should be distinguished from: (1) other CNS infections that can induce a transient increase in CSF HIV RNA (e.g., herpes zoster61), (2) incidental detection of asymptomatic mild CSF HIV RNA elevation likely equivalent to plasma blips,62 or (3) relatively common chronic, usually mild, neurocognitive impairment in HIV-infected patients without evidence of CNS viral breakthrough.63 None of these latter conditions currently warrant a change in ART.64
In summary, the management of treatment-experienced patients with virologic failure often requires expert advice to achieve the goal of constructing virologically suppressive regimens. It is critical to carefully evaluate the cause of virologic failure including assessment of adherence, drug and food interactions, tolerability, HIV RNA and CD4 cell count changes over time, treatment history, and drug-resistance test results before switching regimens. If HIV RNA suppression with use of currently approved agents is not possible, consider use of investigational agents that are available through clinical trials or expanded/single-patient access programs. If virologic suppression is still not achievable, the choice of regimens should focus on minimizing toxicity and preserving treatment options while maintaining CD4 cell counts to delay clinical progression.
- Blair JM, Fagan JL, Frazier EL, et al. Behavioral and clinical characteristics of persons receiving medical care for HIV infection - Medical Monitoring Project, United States, 2009. Morb Mortal Wkly Rep Surveill Summ. 2014;63 Suppl 5:1-22. Available at http://www.ncbi.nlm.nih.gov/pubmed/24941443.
- Kieffer TL, Finucane MM, Nettles RE, et al. Genotypic analysis of HIV-1 drug resistance at the limit of detection: virus production without evolution in treated adults with undetectable HIV loads. J Infect Dis. 2004;189(8):1452-1465. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=15073683.
- Lima V, Harrigan R, Montaner JS. Increased reporting of detectable plasma HIV-1 RNA levels at the critical threshold of 50 copies per milliliter with the Taqman assay in comparison to the Amplicor assay. J Acquir Immune Defic Syndr. 2009;51(1):3-6. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=19247185.
- Gatanaga H, Tsukada K, Honda H, et al. Detection of HIV type 1 load by the Roche Cobas TaqMan assay in patients with viral loads previously undetectable by the Roche Cobas Amplicor Monitor. Clin Infect Dis. 2009;48(2):260-262. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=19113986.
- Willig JH, Nevin CR, Raper JL, et al. Cost ramifications of increased reporting of detectable plasma HIV-1 RNA levels by the Roche COBAS AmpliPrep/COBAS TaqMan HIV-1 version 1.0 viral load test. J Acquir Immune Defic Syndr. 2010;54(4):442-444. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=20611035.
- Ribaudo H, Lennox J, Currier J, et al. Virologic failure endpoint definition in clinical trials: Is using HIV-1 RNA threshold <200 copies/mL better than <50 copies/mL? An analysis of ACTG studies. Paper presented at: 16th Conference on Retroviruses and Opportunistic Infections; 2009; Montreal, Canada.
- Antiretroviral Therapy Cohort C. Impact of low-level viremia on clinical and virological outcomes in treated HIV-1- infected patients. AIDS. 2015;29(3):373-383. Available at http://www.ncbi.nlm.nih.gov/pubmed/25686685
- Boillat-Blanco N, Darling KE, Schoni-Affolter F, et al. Virological outcome and management of persistent low-level viraemia in HIV-1-infected patients: 11 years of the Swiss HIV Cohort Study. Antivir Ther. 2014. Available at http://www.ncbi.nlm.nih.gov/pubmed/24964403.
- Eron JJ, Cooper DA, Steigbigel RT, et al. Efficacy and safety of raltegravir for treatment of HIV for 5 years in the BENCHMRK studies: final results of two randomised, placebo-controlled trials. Lancet Infect Dis. 2013;13(7):587-596. Available at http://www.ncbi.nlm.nih.gov/pubmed/23664333.
- Laprise C, de Pokomandy A, Baril JG, Dufresne S, Trottier H. Virologic failure following persistent low-level viremia in a cohort of HIV-positive patients: results from 12 years of observation. Clin Infect Dis. 2013;57(10):1489-1496. Available at http://www.ncbi.nlm.nih.gov/pubmed/23946221.
- Taiwo B, Gallien S, Aga S, al e. HIV drug resistance evolution during persistent near-target viral suppression. Antiviral Therapy 2010;15:A38.
- Siliciano JD, Kajdas J, Finzi D, et al. Long-term follow-up studies confirm the stability of the latent reservoir for HIV-1 in resting CD4+ T cells. Nat Med. 2003;9(6):727-728. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=12754504.
- Aleman S, Soderbarg K, Visco-Comandini U, Sitbon G, Sonnerborg A. Drug resistance at low viraemia in HIV-1-infected patients with antiretroviral combination therapy. AIDS. 2002;16(7):1039-1044. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=11953470.
- Karlsson AC, Younger SR, Martin JN, et al. Immunologic and virologic evolution during periods of intermittent and persistent low-level viremia. AIDS. 2004;18(7):981-989. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=15096800.
- Nettles RE, Kieffer TL, Kwon P, et al. Intermittent HIV-1 viremia (Blips) and drug resistance in patients receiving HAART. JAMA. 2005;293(7):817-829. Available at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&;db=PubMed&dopt=Citation&list_uids=15713771.
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