The Potential of Spirulina platensis to Ameliorate the Adverse Effects of Highly Active Antiretroviral Therapy (HAART)

The human immunodeficiency virus (HIV) is one of the most prevalent diseases globally. It is estimated that 37.7 million people are infected with HIV globally, and 8.2 million persons are infected with the virus in South Africa. The highly active antiretroviral therapy (HAART) involves combining various types of antiretroviral drugs that are dependent on the infected person’s viral load. HAART helps regulate the viral load and prevents its associated symptoms from progressing into acquired immune deficiency syndrome (AIDS). Despite its success in prolonging HIV-infected patients’ lifespans, the use of HAART promotes metabolic syndrome (MetS) through an inflammatory pathway, excess production of reactive oxygen species (ROS), and mitochondrial dysfunction. Interestingly, Spirulina platensis (SP), a blue-green microalgae commonly used as a traditional food by Mexican and African people, has been demonstrated to mitigate MetS by regulating oxidative and inflammatory pathways. SP is also a potent antioxidant that has been shown to exhibit immunological, anticancer, anti-inflammatory, anti-aging, antidiabetic, antibacterial, and antiviral properties. This review is aimed at highlighting the biochemical mechanism of SP with a focus on studies linking SP to the inhibition of HIV, inflammation, and oxidative stress. Further, we propose SP as a potential supplement for HIV-infected persons on lifelong HAART.

Twenty-Five Years of Lamivudine: Current and Future Use for the Treatment of HIV-1 Infection

Supplemental Digital Content is Available in the Text.

Innovation in medicine is a dynamic, complex, and continuous process that cannot be isolated to a single moment in time. Anniversaries offer opportunities to commemorate crucial discoveries of modern medicine, such as penicillin (1928), polio vaccination (inactivated, 1955; oral, 1961), the surface antigen of the hepatitis B virus (1967), monoclonal antibodies (1975), and the first HIV antiretroviral drugs (zidovudine, 1987). The advent of antiretroviral drugs has had a profound effect on the progress of the epidemiology of HIV infection, transforming a terminal, irreversible disease that caused a global health crisis into a treatable but chronic disease. This result has been driven by the success of antiretroviral drug combinations that include nucleoside reverse transcriptase inhibitors such as lamivudine. Lamivudine, an L-enantiomeric analog of cytosine, potently affects HIV replication by inhibiting viral reverse transcriptase enzymes at concentrations without toxicity against human polymerases. Although lamivudine was approved more than 2 decades ago, it remains a key component of first-line therapy for HIV because of its virological efficacy and ability to be partnered with other antiretroviral agents in traditional and novel combination therapies. The prominence of lamivudine in HIV therapy is highlighted by its incorporation in recent innovative treatment strategies, such as single-tablet regimens that address challenges associated with regimen complexity and treatment adherence and 2-drug regimens being developed to mitigate cumulative drug exposure and toxicities. This review summarizes how the pharmacologic and virologic properties of lamivudine have solidified its role in contemporary HIV therapy and continue to support its use in emerging therapies.

HIV-1 drug resistance testing is essential for heavily-treated patients switching from first- to second-line regimens in resource-limited settings: evidence from routine clinical practice in Cameroon

Background

With the phase-out of stavudine (d4T), change to first-line regimens with zidovudine (AZT) or tenofovir (TDF) in resource-limited settings (RLS) might increase risks of cross-resistance to nucleos(t) ide reverse transcriptase inhibitors (NRTI). This would restrict the scope of switching to the World Health Organisation (WHO)-recommended standard second-line combinations (SLC) without HIV drug resistance (HIVDR)-testing in routine clinical practice.

Methods

An observational study was conducted among 101 Cameroonian patients (55.4% male, median [IQR] age 34 [10–41] years) failing first-line antiretroviral therapy (ART) in 2016, and stratified into three groups according to NRTIs exposure: exposure to both thymidine analogues AZT “and” D4T (group-A, n = 55); exposure to both TDF and AZT “or” D4T (group-B, n = 22); exposure solely to D4T (group-C, n = 24). Protease-reverse transcriptase HIVDR was interpreted using the HIVdb penalty scores (≥60: high-resistance; 20–59: intermediate-resistance; < 20: susceptible). The acceptable threshold for potential-efficacy was set at 80%.

Results

The median [IQR] CD4, viral RNA, and time on ART, were respectively 129 [29–466] cells/μl, 71,630 [19,041-368,000] copies/ml, and 4 [2–5] years. Overall HIVDR-level was 89.11% (90/101), with 83.2% harbouring M184 V (high-level 3TC/FTC-resistance) and only 1.98% (2/101) major HIVDR-mutations to ritonavir-boosted protease-inhibitors (PI/r). Thymidine-analogue mutations (TAMs)-1 [T215FY (46.53%), M41 L (22.77%), L210 W (8.91%)], with cross-resistance to AZT and TDF, were higher compared to TAMs-2 [D67N (21.78%), K70R (19.80%), K219QE (18.81%)]. As expected, K65R was related with TDF-exposure: 0% (0/55) in group-A, 22.72% (5/22) group-B, 4.17% (1/24) group-C (p = 0.0013). The potential-efficacy of AZT vs. TDF was respectively 43.64% (24/55) vs. 70.91% (39/55) in group-A (p = 0.0038); 63.64% (14/22) vs. 68.28% (15/22) in group-B (p = 1.0000); and 37.50% (9/24) vs. 83.33% (20/24) in group-C (p = 0.0032). CRF02_AG was the prevailing subtype (63.40%), followed by CRF11.cpx (8.91%), A₁ (7.92%), G (5.94%); without any significant effect of the subtype-distribution on HIVDR (92.2% in CRF02_AG vs. 83.8% in non-AG; p = 0.204).

Conclusion

First-line ART-failure exhibits high-level NRTI-resistance, with potential lower-efficacy of AZT compared to TDF. Significantly, using our 80% efficacy-threshold, only patients without NRTI-substitution on first-line could effectively switch to SLC following the WHO-approach. Patients with multiple NRTI-substitutions (exposed to both thymidine-analogues and TDF) on first-line ART would require HIVDR-testing to select active NRTIs for SLC.

Electronic supplementary material

The online version of this article (10.1186/s12879-019-3871-0) contains supplementary material, which is available to authorized users.

Emergence of resistance mutations in simian immunodeficiency virus (SIV)-infected rhesus macaques receiving non-suppressive antiretroviral therapy (ART)

Two SIVmac251-infected rhesus macaques received tenofovir/emtricitabine with raltegravir intensification. Viral rebound occurred during treatment and sequencing of reverse transcriptase and integrase genes identified multiple resistance mutations. Similar to HIV infection, antiretroviral-resistance mutations may occur in SIV-infected nonhuman primates receiving nonsuppressive ART. As ART administration to nonhuman primates is currently dramatically expanding, fueled by both cure research and the study of HIV-related comorbidities, viral resistance should be factored in the study design and data interpretation.

A spatio-temporal assessment of simian/human immunodeficiency virus (SHIV) evolution reveals a highly dynamic process within the host

The process by which drug-resistant HIV-1 arises and spreads spatially within an infected individual is poorly understood. Studies have found variable results relating how HIV-1 in the blood differs from virus sampled in tissues, offering conflicting findings about whether HIV-1 throughout the body is homogeneously distributed. However, most of these studies sample only two compartments and few have data from multiple time points. To directly measure how drug resistance spreads within a host and to assess how spatial structure impacts its emergence, we examined serial sequences from four macaques infected with RT-SHIV_mne027, a simian immunodeficiency virus encoding HIV-1 reverse transcriptase (RT), and treated with RT inhibitors. Both viral DNA and RNA (vDNA and vRNA) were isolated from the blood (including plasma and peripheral blood mononuclear cells), lymph nodes, gut, and vagina at a median of four time points and RT was characterized via single-genome sequencing. The resulting sequences reveal a dynamic system in which vRNA rapidly acquires drug resistance concomitantly across compartments through multiple independent mutations. Fast migration results in the same viral genotypes present across compartments, but not so fast as to equilibrate their frequencies immediately. The blood and lymph nodes were found to be compartmentalized rarely, while both the blood and lymph node were more frequently different from mucosal tissues. This study suggests that even oft-sampled blood does not fully capture the viral dynamics in other parts of the body, especially the gut where vRNA turnover was faster than the plasma and vDNA retained fewer wild-type viruses than other sampled compartments. Our findings of transient compartmentalization across multiple tissues may help explain the varied results of previous compartmentalization studies in HIV-1.

HIV-1 is difficult to treat because the virus can evolve to become drug-resistant within the body, but we have an incomplete understanding of where drug-resistant viruses originate and how they spread within a person. In this study, four macaques were infected with RT-SHIV, a simian immunodeficiency virus with an HIV-1 reverse transcriptase coding region, which can be targeted with standard HIV drugs. We sampled virus from the macaques before, during and after their viral population became resistant to administered drugs and determined the genetic viral sequences in several parts of the body: blood, lymph nodes, gut, and vagina. We found that drug resistance emerged across compartments nearly simultaneously, and drug resistance evolved multiple independent times within each macaque. Although migration of RT-SHIV between compartments is fast, compartments do not have the same distribution of viral genotypes. This is important because although studies typically sample virus from the blood to study how HIV-1 evolution in humans, our study suggests that it is not fully representative of other parts of the body, particularly the gut.

Cytotoxic chemotherapy and the evolution of cellular and viral resistance to antiretroviral therapy in HIV- infected individuals with lymphoma

BACKGROUND

The use of combination antiretroviral therapy (cART) and cytotoxic chemotherapy for HIV-associated lymphoma runs the risks of inducing HIV drug resistance. This study examined two possible mechanisms: altered expression of membrane drug transporter protein (MTP) and acquisition of mutations in pro-viral DNA.

METHODS

Expression levels of MTP and pro-viral DNA resistance mutation analysis were performed on peripheral blood mononuclear cells (PBMC) before, during, and after chemotherapy.

RESULTS

Twenty nine patients completed the three time point estimations. There were no significant variations before, during, and after chemotherapy in the expression of four MTPs: ABCB1, ABCC1, ABCC2, and SLCO3A1 (OATP3A1). Pro-viral DNA sequencing revealed that only one patient developed a new nucleos/tide reverse transcriptase inhibitor-associated mutation (184V) during the course of the study, giving a mutation rate of 0.0027 per person per year.

CONCLUSIONS

In conclusion, concomitant administration of cytotoxic chemotherapy and cART does not induce expression of MTP. Furthermore, no significant changes in viral resistance were observed pre- and post-chemotherapy, suggesting mutagenic cytotoxic chemotherapy seems not to induce mutations in HIV pro-viral DNA.

Antiretroviral drugs for prevention of mother-to-child transmission: pharmacologic considerations for a public health approach

OBJECTIVE

Efavirenz-based antiretroviral therapy is recommended for prevention of mother-to-child transmission of HIV with two programmatic options: lifelong therapy for all women or treatment until cessation of breastfeeding. However, the risk of HIV resistance emerging after discontinuing efavirenz-based antiretroviral therapy is unclear. We review present knowledge surrounding the emergence of resistance after stopping efavirenz-based antiretroviral regimens.

DESIGN

An expert review.

METHODS

A literature review was conducted to identify studies assessing risk for emergence of efavirenz-related resistance following discontinuation of efavirenz-based antiretroviral regimens containing either lamivudine and zidovudine or tenofovir disoproxil fumarate and lamivudine. Discontinuation strategies including the use of 'pharmacologic tails' are discussed in the light of what is known about the pharmacology of the drugs.

RESULTS

We found no head-to-head comparisons between zidovudine, lamivudine and efavirenz and tenofovir disoproxil fumarate, lamivudine and efavirenz. The risk for HIV resistance exists, even with a 5-7 day tail of zidovudine and lamivudine. For tenofovir disoproxil fumarate, lamivudine and efavirenz, we found no clinical data to inform a recommendation for a tail.

CONCLUSION

In order to prevent emergence of resistance, a tail of at least 2 weeks in duration may be required when discontinuing efavirenz in a regimen containing zidovudine and lamivudine. Studies are needed to characterize the risk of resistance among women who discontinue tenofovir disoproxil fumarate, lamivudine and efavirenz.

A significant reduction in the frequency of HIV-1 drug resistance in Québec from 2001 to 2011 is associated with a decrease in the monitored viral load

Background

HIV drug resistance represents a major threat for effective treatment. We assessed the trends in the frequency of drug resistance mutations and the monitored viral load (VL) in treatment-naïve (TN) and treatment-experienced (TE) individuals infected with HIV-1 in Québec, Canada, between 2001 and 2011.

Methods and Findings

Resistance data were obtained from 4,105 and 5,086 genotypic tests performed on TN and TE patients, respectively. Concomitantly, 274,161 VL tests were carried out in the Province. Changes over time in drug resistance frequency and in different categories of VL were assessed using univariate logistic regression. Multiple logistic regression was used to evaluate associations between the rates of certain mutations and antiretroviral prescriptions. From 2001 to 2011, the proportion of undetectable VL test results continually increased, from 42.1% to 75.9%, while a significant decrease in the frequency of resistance mutations associated with protease inhibitors [PI (from 54% to 16%)], nucleoside [NRTI (from 78% to 37%) and non-nucleoside reverse transcriptase inhibitors [NNRTI (from 44% to 31%)] was observed in TE patients. In TN individuals, the overall frequency of transmitted drug resistance was 13.1%. A multiple logistic regression analysis indicated that the introduction of co-formulated emtricitabine/tenofovir or emtricitabine/tenofovir/efavirenz was positively associated with the decrease of the frequency of the M184I/V mutations observed overtime (p = 0.0004).

Conclusions

We observed a significant decrease in the frequency of drug resistance mutations in TE patients, concomitant with a decrease in the proportion of patients with detectable viremia. These findings may be related to both the increased potencies and adherence to therapy associated with newer antiretroviral regimens. Nevertheless, our data demonstrate that broad use of antiretrovirals does not increase the level of circulating drug resistant variants.

Effectiveness of antiretroviral therapy in individuals who for economic reasons were switched from a once-daily single-tablet regimen to a triple-tablet regimen

BACKGROUND

To assess the impact on virological outcomes of a switch from branded single-tablet regimen (STR) including tenofovir, efavirenz, and emtricitabine (STR-TEE) to generic triple-tablet regimen (TTR), including tenofovir, efavirenz, and lamivudine (TTR-TEL), which was implemented on April 1, 2011 to obtain economic savings.

METHODS AND FINDINGS

From the Capital Region of Denmark (covering two-thirds of the Danish HIV patients), we included combination antiretroviral therapy (cART)-naive patients who administered STR-TEE from April 1, 2010 to March 31, 2011 (n = 111) or TTR-TEL from April 1, 2011 to March 31, 2012 (n = 56) and cART-experienced HIV patients who were on STR-TEE from April 1, 2010 (n = 356) or were switched from STR-TEE to TTR-TEL after April 1, 2011 (n = 512). We estimated the fraction with detectable HIV-RNA, development of the 184V/I resistance mutations, and time to switch of cART. Approximately 96.2% of cART-experienced patients on STR-TEE were shifted to TTR-TEL after April 1, 2011. For the naive STR-TEE and TTR-TEL patients, the fractions with detectable HIV-RNA at week 48 were 7.0% and 8.3% and for the cART experienced 4.0% and 4.4%, respectively. The 184V/I resistance mutation was detected in 1 cART-experienced patient on TTR-TEL with virological failure. The risk of switch to a new cART regimen was slightly increased in the cART-experienced population (difference in 1-year risk: 1.5%; 95% confidence interval: -2.4% to 5.4%).

CONCLUSIONS

In settings comparable with the Danish health care system, the estimated economic savings from a switch from STR-TEE to TTR-TEL can be realized with negligible short-term risk of adverse outcomes.

Antiretroviral treatment French guidelines 2013: economics influencing science

Guidelines for the preferred choice of initial combination antiretroviral therapy in those living with HIV are provided by several national and international committees. Following the recent presentation of the 2013 French guidelines on antiretroviral therapy, there has been a debate regarding whether and/or how economics should influence guideline decisions and to what extent this should counterbalance valid scientific evidence. We discuss here the reasons for the unique nature of some of the proposals made by the French guidelines panel. Indeed, some recommendations are debatable. In the new French guidelines, economic considerations significantly influence and, in some instances, take precedence over the scientific evidence, leading to guidelines that are significantly different from those of other national and international committees.

The emergence of drug resistant HIV variants at virological failure of HAART combinations containing efavirenz, tenofovir and lamivudine or emtricitabine within the UK Collaborative HIV Cohort

BACKGROUND

Lamivudine (3TC) and emtricitabine (FTC) are guideline choices for combination highly active antiretroviral therapy (HAART). 3TC has a shorter intracellular half life than FTC and may be more likely to lead to the development of drug resistant HIV variants.

METHODS

In this study we analysed linked data from the observational UK Collaborative HIV Cohort (CHIC) Study and UK HIV Drug Resistance Database (HDRD) to investigate the rate of development of K65R or M184V resistance mutations in patients failing on combinations containing tenofovir (TDF) and efavirenz (EFV) with either 3TC or FTC. Virological failure was defined as 1 viral load >400 copies/ml. Rates were stratified by demographic variables, baseline viral load, current CD4 count, current viral load and year of starting regimen. Significant associations were identified using Poisson regression models and multivariable analyses were performed adjusting for the variables above. Logistic regression was used to determine whether there were any significant associations between type of regimen and detection of resistance mutation.

RESULTS

5455 patients received either (or both) 3TC, TDF and EFV or FTC, TDF and EFV contributing 6465 treatment episodes over 9962 person-years follow up. 47 of these episodes were preceded by resistance tests showing development of K65R or M184V mutation and were hence excluded. The majority of treatment episodes consisted of FTC- (n = 5190) rather than 3TC- (n = 1228) based regimens. 21 cases of K65R were detected over the course of follow up, giving an overall event rate of 0.21 (95% CI: 0.12-0.31)/100 person years follow up (PYFU). The overall event rate for detection of M184V was 0.38 (95% CI: 0.26-0.5)/100 PYFU. 201 patients receiving either regimen for the first time experienced virological failure. Of those receiving 3TC (n = 53), 7 (13.2%), 12 (22.6%) and 15 (28.3%) developed K65R, M184V and either K65R or M184V respectively. Of those receiving FTC (n = 148), 13 (8.8%), 20 (13.5%) and 26 (17.6%) developed K65R, M184V and either K65R or M184V respectively. Although patients on 3TC were more likely to develop resistance, this was not statistically significant in univariable (OR 1.85 (95% CI: 0.89-3.85, p = 0.09)) or multivariable analyses (OR 1.89 (95% CI: 0.89-4.01, p = 0.1)).

CONCLUSIONS

We have not found evidence of an increased risk of development of M184V and K65R in patients exposed to 3TC.

NRTI backbone in HIV treatment: will it remain relevant?

Nucleoside reverse transcriptase inhibitors (NRTIs) remain a critical component of therapy for HIV-infected patients. The drugs are effective, relatively inexpensive and an important component of antiretroviral therapy (ART), particularly in areas where the introduction of effective therapy has been delayed. They are an essential part of initial therapy for HIV and for prevention of mother-to-child transmission; however, toxicities and resistance may limit their use. The role for pre-exposure prophylaxis (PrEP) to reduce sexual transmission of HIV is still undefined, but this use may have a significant impact on NRTI resistance worldwide, most particularly in areas where subtype C predominates. With increasing prevalence of resistant HIV, the approval of new agents that are effective against resistant virus, and those that use novel cellular targets, are essential. Large studies are now in progress examining the safety and efficacy of NRTI-sparing regimens, but results are not currently available. NRTIs may lose relevance in the not distant future unless steps are put in place to reduce the development and spread of NRTI-resistant viruses, and new NRTIs with minimal toxicity are developed that have a novel resistance profile. This article describes the principal NRTIs, their mechanism of action, and resistance and selected toxicities of the class and of the individual drugs.

Emtricitabine/tenofovir in the treatment of HIV infection: current PK/PD evaluation

INTRODUCTION

Emtricitabine/tenofovir disoproxil fumarate fixed-dose combination (FTC/TDF FDC) is the co-formulation of a nucleoside and a nucleotide, respectively. After oral administration, both drugs exhibit plasma and intracellular half-lives suitable for once-daily dosing. Within the host cells, active metabolites FTC-TP and TFV-DP act as chain terminators to the newly synthesized proviral DNA, showing synergy at enzymatic level (viral reverse transcriptase). When given in HAART combinations, FTC/TDF FDC has a remarkable effectiveness in controlling HIV replication and securing a significant CD4(+) cell recovery. If patients treated with FTC/TDF FDC fail, a lower incidence of TDF-associated K65R resistance mutation seems to develop. Furthermore, cytidine analog-associated M184V is less likely to appear with FTC than with lamivudine when both are given with TDF. FTC and TFV are not metabolized by CYP450 enzymes and are eliminated by the renal route. TFV may accumulate in tubular cells and cause a decrease in GFR and a loss of phosphates. As a onsequence, patients treated with FTC/TDF FCD may experience varied degrees of renal impairment and osteopenia/osteoporosis.

AREAS COVERED

This paper has focused on the PK/PD features of FTC and TDF, when given as single agent or when administered as FDC. The interpretation of efficacy/toxicity was guided by PK/PD features. The review of the available literature included also conference presentations and recent guidelines (as of May 2012).

EXPERT OPINION

FTC/TDF FDC is a potent and reliable component of most HAART combinations due to its maintained activity across time, as demonstrated in many trials and studies. Toxicity issues (kidney, bone) are still to be entirely elucidated and the drug-induced component well separated from patient- and HIV-related ones. However, the clinical gain associated with the use of FTC/TDF FDC is fully acknowledged by its leading position in most current treatment guidelines.

Cost analysis of HIV treatment and drug-related adverse events when fixed-dose combinations of antiretrovirals (FDCs) were stopped, versus continuation with FDCs

BACKGROUND

The lower sales price of generic lamivudine has caused healthcare administrators to consider abolishing fixed-dose antiretroviral combinations (FDCs) that contain lamivudine and emtricitabine. The alternative is to administer the individual components of the FDCs separately, thus incorporating the new generic lamivudine medication.

METHODS

The Balearic Islands Health Service ordered the discontinuation of the treatment with FDCs in July 2010, but FDCs were reintroduced in August 2010. At that point, an independent, retrospective cost analysis was performed by Son Llàtzer Hospital. A total of 75 patients who were treated from July to August 2010 underwent replacement of their FDC treatment with the individual components. Additionally, 150 patients who continued using FDCs were randomly selected. For both patient groups, the antiretroviral therapy that was administered and the costs associated with management of adverse events were recorded. The study period used for the cost calculations was the average number of days that patients used separate components of FDCs (120 days). An alternative analysis was performed to consider the costs of the extra follow-up visit (consultation and clinical tests) that was required for patients who changed their antiretroviral therapy.

RESULTS

Considering antiretroviral therapies and adverse events, the administration of the separate components increased the total daily cost by 0.72 € per patient compared to treatment with FDCs. When the cost of an extra follow-up visit was considered, the daily cost increased by 3.61 € per patient.

CONCLUSIONS

Our study suggests that the discontinuation of FDC treatment and the replacement with the administration of separate antiretroviral agents could lead to an increase in healthcare costs due to the higher rate of adverse events that was observed with the discontinuation of FDCs.

Practical Considerations For Developing Nucleoside Reverse Transcriptase Inhibitors

Nucleoside reverse transcriptase inhibitors (NRTI) remain a cornerstone of current antiretroviral regimens in combinations usually with a non-nucleoside reverse transcriptase inhibitor (NNRTI), a protease inhibitor (PI), or an integrase inhibitor (INI). The antiretroviral efficacy and relative safety of current NRTI results from a tight and relatively specific binding of their phosphorylated nucleoside triphosphates (NRTI-TP) with the HIV-1 reverse transcriptase which is essential for replication. The intracellular stability of NRTI-TP produces a sustained antiviral response, which makes convenient dosing feasible. Lessons learned regarding NRTI pharmacology screening, development, and use are discussed. NRTI and prodrugs currently under clinical development are outlined.

Persistence versus reversion of 3TC resistance in HIV-1 determine the rate of emergence of NVP resistance

When HIV-1 is exposed to lamivudine (3TC) at inhibitory concentrations, resistant variants carrying the reverse transcriptase (RT) substitution M184V emerge rapidly. This substitution confers high-level 3TC resistance and increased RT fidelity. We established a novel in vitro system to study the effect of starting nevirapine (NVP) in 3TC-resistant/NNRTI-naïve clinical isolates, and the impact of maintaining versus dropping 3TC pressure in this setting. Because M184V mutant HIV-1 seems hypersusceptible to adefovir (ADV), we also tested the effect of ADV pressure on the same isolates. We draw four conclusions from our experiments simulating combination therapy in vitro. (1) The presence of low-dose (1 μM) 3TC prevented reversal to wild-type from an M184V mutant background. (2) Adding low-dose 3TC in the presence of NVP delayed the selection of NVP-associated mutations. (3) The presence of ADV, in addition to NVP, led to more rapid reversal to wild-type at position 184 than NVP alone. (4) ADV plus NVP selected for greater numbers of mutations than NVP alone. Inference about the "selection of mutation" is based on two statistical models, one at the viral level, more telling, and the other at the level of predominance of mutation within a population. Multidrug pressure experiments lend understanding to mechanisms of HIV resistance as they bear upon new treatment strategies.