High virological failure rate in HIV patients after switching to a regimen with two nucleoside reverse transcriptase inhibitors plus tenofovir

A systematic review of a single-class maintenance strategy with nucleoside/nucleotide reverse transcriptase inhibitors in HIV/AIDS

BACKGROUND

Single-drug class regimens with nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) are generally not recommended as initial therapy because they are inferior compared with therapy with two NRTIs plus efavirenz. However, triple-NRTI combinations can be useful in specific circumstances such as in tuberculosis coinfection, pregnancy or dyslipidaemia. Here, we review the potential of such combinations to maintain viral suppression after induction of suppression by standard combination antiretroviral therapy (cART) and to evaluate the trade-off of NRTI-only regimens for metabolic control.

METHODS

We conducted a systematic search of the literature in two databases from 1 January 1998 up to 1 March 2013: Medline, through the search engine PubMed, and Embase.

RESULTS

A total of 11 randomized controlled trials (RCTs) with 2,105 patients and 3 observational studies with 2,639 patients were included. Studies including patients with mono- or dual-NRTI treatment before start of effective cART showed a tendency to higher failure rate because of resistance based on archived viral mutations. In studies with ART-naive subjects before start of cART, triple-NRTI combination showed virological activity comparable to two NRTIs plus a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor in all RCTs, but not in one cohort study. Switching improved serum lipids significantly.

CONCLUSIONS

Of the studied triple-NRTI combinations only abacavir/lamivudine/zidovudine was sufficiently potent. Triple-NRTI maintenance after successful induction with two-class cART appeared successful in treatment-naive subjects and remains a useful option in specific circumstances, especially when other drugs are not available or drug interactions are an issue.

[AIDS Study Group/Spanish AIDS Plan consensus document on antiretroviral therapy in adults with human immunodeficiency virus infection (updated January 2010)]

OBJECTIVE

This consensus document is an update of antiretroviral therapy recommendations for adult patients with human immunodeficiency virus infection.

METHODS

To formulate these recommendations a panel made up of members of the Grupo de Estudio de Sida (Gesida, AIDS Study Group) and the Plan Nacional sobre el Sida (PNS, Spanish AIDS Plan) reviewed the advances in the current understanding of the pathophysiology of human immunodeficiency virus (HIV) infection, the efficacy and safety of clinical trials, and cohort and pharmacokinetic studies published in biomedical journals or presented at scientific meetings. Three levels of evidence were defined according to the data source: randomized studies (level A), cohort or case-control studies (level B), and expert opinion (level C). The decision to recommend, consider or not to recommend ART was established in each situation.

RESULTS

Currently, the treatment of choice for chronic HIV infection is the combination of three drugs of two different classes, including 2 nucleosides or nucleotide analogs (NRTI) plus 1 non-nucleoside (NNRTI) or 1 boosted protease inhibitor (PI/r), but other combinations are possible. Initiation of ART is recommended in patients with symptomatic HIV infection. In asymptomatic patients, initiation of ART is recommended on the basis of CD4 lymphocyte counts, plasma viral load and patient co-morbidities, as follows: 1) therapy should be started in patients with CD4 counts below 350 cells/microl; 2) When CD4 counts are between 350 and 500 cells/microl, therapy should be started in case of cirrhosis, chronic hepatitis C, high cardiovascular risk, HIV nephropathy, HIV viral load above 100,000 copies/ml, proportion of CD4 cells under 14%, and in people aged over 55; 3) Therapy should be deferred when CD4 are above 500 cells/microl, but could be considered if any of previous considerations concurs. Treatment should be initiated in case of hepatitis B requiring treatment and should be considered for reduce sexual transmission. The objective of ART is to achieve an undetectable viral load. Adherence to therapy plays an essential role in maintaining antiviral response. Therapeutic options are limited after ART failures but undetectable viral loads maybe possible with the new drugs even in highly drug experienced patients. Genotype studies are useful in these situations. Drug toxicity of ART therapy is losing importance as benefits exceed adverse effects. Criteria for antiretroviral treatment in acute infection, pregnancy and post-exposure prophylaxis are mentioned as well as the management of HIV co-infection with hepatitis B or C.

CONCLUSIONS

CD4 cells counts, viral load and patient co-morbidities are the most important reference factors to consider when initiating ART in asymptomatic patients. The large number of available drugs, the increased sensitivity of tests to monitor viral load, and the ability to determine viral resistance is leading to a more individualized therapy approach in order to achieve undetectable viral load under any circumstances.

Viral fitness: relation to drug resistance mutations and mechanisms involved: nucleoside reverse transcriptase inhibitor mutations

PURPOSE OF REVIEW

Nucleoside and nucleotide reverse transcriptase inhibitors constitute the backbone of highly active antiretroviral therapy in the treatment of HIV-1 infection. One of the major obstacles in achieving the long-term efficacy of anti-HIV-1 therapy is the development of resistance. The advent of resistance mutations is usually accompanied by a change in viral replicative fitness. This review focuses on the most common nucleoside reverse transcriptase inhibitor-associated mutations and their effects on HIV-1 replicative fitness.

RECENT FINDINGS

Recent studies have explained the two main mechanisms of resistance to nucleoside reverse transcriptase inhibitors and their role in HIV-1 replicative fitness. The first involves mutations directly interfering with binding or incorporation and seems to impact replicative fitness more adversely than the second mechanism, which involves enhanced excision of the newly incorporated analogue. Further studies have helped explain the antagonistic effects between amino acid substitutions, K65R, L74V, M184V, and thymidine analogue mutations, showing how viral replicative fitness influences the evolution of thymidine analogue resistance pathways.

SUMMARY

Nucleoside reverse transcriptase inhibitor resistance mutations impact HIV-1 replicative fitness to a lesser extent than protease resistance mutations. The monitoring of viral replicative fitness may help in the management of HIV-1 infection in highly antiretroviral-experienced individuals.

In vitro analysis of synergism and antagonism of different nucleoside/nucleotide analogue combinations on the inhibition of human immunodeficiency virus type 1 replication

In this study we have developed an in vitro system to evaluate the combined effect of two NRTIs on HIV replication and to assess their antagonism or synergy. Synergy or antagonism effect was determined in peripheral blood mononuclear cells (PBMCs) to approach a more physiological model than T-cell lines. PBMCs were infected with a full-length HIV-1 clone carrying the luciferase gene as a reporter. The following combinations were investigated: zidovudine+stavudine (ZDV + d4T), lamivudine + abacavir (3TC + ABC), lamivudine + didanosine (3TC + ddI), lamivudine + stavudine (3TC + d4T), tenofovir + stavudine (TDF + d4T), tenofovir + didanosine (TDF + ddI), tenofovir + abacavir (TDF + ABC), tenofovir + lamivudine (TDF + 3TC), tenofovir + zidovudine (TDF + ZDV), stavudine + didanosine (d4T + ddI), zidovudine + lamivudine (ZDV + 3TC), abacavir + didanosine (ABC + ddI), zidovudine + didanosine (ZDV + ddI), and abacavir + stavudine (ABC + d4T). The effect of combining two drugs was evaluated with a quantitative method based on the median-effect principle of Chou and Talalay. A synergistic effect was observed with combinations containing TDF and ZDV or d4T, d4T and ddI and ZDV plus 3TC. In contrast, combinations including TDF + ddI, 3TC + ddI, ABC + ddI, and ZDV + ddI showed an antagonistic effect on the inhibition of viral replication at all levels of inhibition tested. Lower antagonistic effect was also found in drug combinations that included 3TC + ABC, 3TC + TDF, 3TC + d4T, and TDF + ABC. In conclusion, the method developed allows to measure in vitro the effect of different combinations of two NRTIs on HIV replication. The results suggest that combined therapy including TDF with thymidine analogues may be considered for future therapeutic options in contrast to clearly antagonistic combinations such us TDF plus ddI or 3TC plus ddI, that would explain virological failure in clinical studies when these combinations were used.

Development of an optimized dose for coformulation of zidovudine with drugs that select for the K65R mutation using a population pharmacokinetic and enzyme kinetic simulation model

In vitro selection studies and data from large genotype databases from clinical studies have demonstrated that tenofovir disoproxil fumarate and abacavir sulfate select for the K65R mutation in the human immunodeficiency virus type 1 polymerase region. Furthermore, other novel non-thymine nucleoside reverse transcriptase (RT) inhibitors also select for this mutation in vitro. Studies performed in vitro and in humans suggest that viruses containing the K65R mutation remained susceptible to zidovudine (ZDV) and other thymine nucleoside antiretroviral agents. Therefore, ZDV could be coformulated with these agents as a "resistance repellent" agent for the K65R mutation. The approved ZDV oral dose is 300 mg twice a day (b.i.d.) and is commonly associated with bone marrow toxicity thought to be secondary to ZDV-5'-monophosphate (ZDV-MP) accumulation. A simulation study was performed in silico to optimize the ZDV dose for b.i.d. administration with K65R-selecting antiretroviral agents in virtual subjects using the population pharmacokinetic and cellular enzyme kinetic parameters of ZDV. These simulations predicted that a reduction in the ZDV dose from 300 to 200 mg b.i.d. should produce similar amounts of ZDV-5'-triphosphate (ZDV-TP) associated with antiviral efficacy (>97% overlap) and reduced plasma ZDV and cellular amounts of ZDV-MP associated with toxicity. The simulations also predicted reduced peak and trough amounts of cellular ZDV-TP after treatment with 600 mg ZDV once a day (q.d.) rather than 300 or 200 mg ZDV b.i.d., indicating that q.d. dosing with ZDV should be avoided. These in silico predictions suggest that 200 mg ZDV b.i.d. is an efficacious and safe dose that could delay the emergence of the K65R mutation.

Observational study on HIV-infected subjects failing HAART receiving tenofovir plus didanosine as NRTI backbone

We evaluated the efficacy of tenofovir (TDF) - and didanosine (ddI)-containing backbones in HIV-infected experienced subjects. We included in the study 245 subjects who started a TDF/ddI-containing HAART with HIV-RNA > 3 log(10) cp/ml and an available genotypic resistance test at baseline. At baseline, median CD4 counts and HIV-RNA were 278 cell/mmc and 4.32 log(10) cp/ml, respectively. Seventy-four subjects (30.2%) discontinued TDF and/or ddI, 23 of them for drug-related toxicities or intolerance. One-hundred and twenty-six (51.4%) subjects achieved virologic success (HIV-RNA < 50 copies/ml in two consecutive determinations) in a median time of 6.1 months; higher HIV-RNA levels (HR: 0.66, 95% CI: 0.54- 0.79, p < 0.001 for each additional log(10) copies/ml), and the total number of mutations either for PI and NNRTI at baseline (HR: 0.87, 95% CI: 0.81-0.92, p < 0.001 for each additional mutation) were both predictors of virologic success. M184V was marginally associated with virologic success (HR: 1.34, 95% CI: 0.94-1.90, p = 0.10 vs no M184V), whilst the number of TAMs was not associated. One-hundred-thirty-three (54.3%) subjects achieved immunologic success (increase of > or = 100 cells/mm(3) from baseline) in a median time of 7.5 months; immunologic success was associated with HIV-RNA levels at baseline (HR: 0.91, 95% CI: 0.79-0.98, p = 0.04 for each additional log(10) copies/ml), the total number of mutations either for PI or NNRTI (HR: 0.91, 95% CI: 0.85-0.98, p = 0.01 for each additional mutation) and CD4 count at baseline (HR: 1.11, 95% CI: 1.00-1.23, p = 0.05 for each additional 100 cells/mm(3)). Results obtained by the on-treatment analyses were comparable. In our study, HAART containing TDF/ddI seem associated with a virologic and immunologic response, when such regimens are chosen according to a genotypic resistance test.

Didanosine enteric-coated capsule: current role in patients with HIV-1 infection

Didanosine, which is a synthetic nucleoside analogue intracellularly phosphorylated to the active metabolite, inhibits the activity of HIV-1 reverse transcriptase by competing with the natural substrate. Currently, didanosine is mainly provided as an enteric-coated capsule. In vitro, the molecule is active against laboratory strains and clinical isolates of HIV-1 in resting and activated T cells and monocyte/macrophages. Didanosine may select for resistance mutations that may render the drug inactive against the virus; L74V and K65R remain as the main didanosine-related mutations. In vitro, phenotypic susceptibility to didanosine was decreased beyond a defined fold change clinical cut-off (1.7), and it is considered that genotypic resistance exists when five thymidine-associated mutations or four plus M184V are present. In vivo, clinical studies have shown that didanosine retains significant antiviral activity in patients who have up to five nucleoside analogue mutations at baseline. Didanosine is useful in patients with no previous therapy, as well as in experienced patients in whom one or more antiretroviral regimens has failed.Enteric-coated didanosine is taken once daily, its co-administration with food has been recently evaluated and a reduction of the efficacy of the antiretroviral treatment was not observed. Administered with lamivudine (or emtricitabine), it can be considered a good alternative for use in the nucleoside analogue backbone included in combination therapies for antiretroviral-naive patients. Didanosine could be used in initial treatments for patients intolerant of zidovudine, abacavir or tenofovir. It can be included in once-daily combination regimens, which are more convenient and patient friendly.Prospective, observational and open-label studies, as well as clinical trials (with durations between 24 and 96 weeks), have demonstrated the safety and efficacy of didanosine plus lamivudine (or emtricitabine) plus efavirenz (or nevirapine) in previously untreated HIV-1-infected patients. The administration of didanosine to treatment-experienced patients has been evaluated in two different contexts: patients in whom previous therapies have failed (rescue therapy) and those with controlled viraemia who are switched to a didanosine-containing regimen for simplification.Adverse events associated with the administration of didanosine have been well known since the initial clinical trials with the drug. Gastrointestinal intolerance, peripheral neuropathy and hyperamylasaemia/pancreatitis were the most frequently reported. In the highly active antiretroviral therapy (HAART) era, the rate of adverse events has decreased. The tolerability of didanosine has been clearly improved with the development of the enteric-coated capsule. Severe manifestations of mitochondrial toxicity, including lactic acidosis and abnormal fat distribution, are rare complications, and occur most frequently when didanosine is used in combination with stavudine.

Quadruple Nucleoside Therapy with Zidovudine, Lamivudine, Abacavir and Tenofovir in the Treatment of HIV

Highly active antiretroviral therapy (HAART) has significantly reduced morbidity and mortality in HIV-infected patients. However, problems such as short-term or long-term toxicity and the development of drug resistance could necessitate a change in the therapy regimen. Whereas various HAART options with low pill burden and favourable long-term tolerability profiles are available for naive patients, treatment of experienced patients tends to be more complex and remains a challenge. Treatment with class sparing nucleoside-only regimens could be an option in this context, but the combination of zidovudine (AZT), lamivudine (3TC) and abacavir (ABC) has shown to be inferior in terms of virological efficacy compared with the standard regimen. More promising data were obtained when AZT, 3TC and ABC were intensified with tenofovir (TDF), resulting in a quadruple nucleoside therapy. This regimen has demonstrated comparable potency to a standard regimen with AZT, 3TC and efavirenz in treatment-naive patients. Additionally, it has shown to be an efficient treatment option especially in moderately pretreated patients. This is accredited to the potency of the single components and the antagonistic selection pressure of AZT and TDF. The presence of L210W, or at least two of the mutations 41L, 67N, 70R, 215F/Y or 219Q/E, at or before baseline seems to be a predictor of non-response, whereas the presence of M184V does not impede virological response and might even be advantageous. This review summarizes current data on the combined use of AZT, 3TC, ABC and TDF in regard to virological and immunological outcome as well as genotypic predictors of response.

[Recommendations from the GESIDA/Spanish AIDS Plan regarding antiretroviral treatment in adults with human immunodeficiency virus infection (update January 2007)]

OBJECTIVE

This consensus document is an update of antiretroviral therapy (ART) recommendations for adult patients infected with the human immunodeficiency virus (HIV-1).

METHODS

To formulate these recommendations, a panel composed of members of the Grupo de Estudio de Sida (GESIDA; AIDS Study Group) and the Plan Nacional sobre el Sida (PNS; Spanish AIDS Plan) reviewed the advances in the current understanding of the pathophysiology of HIV, the safety and efficacy findings from clinical trials, and the results from cohort and pharmacokinetic studies published in biomedical journals or presented at scientific meetings over the last years. Three levels of evidence were defined according to the source of the data: randomized studies (level A), cohort or case-control studies (level B), and expert opinion (level C). The decision to recommend, consider or not recommend ART was established in each situation.

RESULTS

Currently, the treatment of choice for chronic HIV infection is the combination of three drugs of two different classes, including 2 nucleosides or nucleotide analogs (NRTI) plus 1 non-nucleoside (NNRTI) or 1 boosted protease inhibitor (PI/r). Initiation of ART is recommended in patients with symptomatic HIV infection. In asymptomatic patients, initiation of ART is recommended on the basis of CD4+ lymphocyte counts and plasma viral load, as follows: 1) therapy should be started in patients with CD4+ counts of < 200 cells/microl; 2) therapy should be started in most patients with CD4+ counts of 200-350 cells/microl, although it can be delayed when CD41 count persists at around 350 cells/microL and viral load is low, and 3) initiation of therapy can be delayed in patients with CD4+ counts of > 350 cells/microL. The initial objective of ART is to achieve an undetectable viral load. Adherence to therapy plays an essential role in maintaining the antiviral response. Therapeutic options are limited with the development of cross resistance and ART failure. Genotype studies are useful in these cases. More information regarding the studies analyzed and the panel recommendations for adherence, toxicity, treatment during pregnancy, patients with hepatitis B or C virus co-infection, and post-exposure prophylaxis can be accessed at www.gesida.seimc.org.

CONCLUSIONS

CD4+ lymphocyte count is the most important reference factor for initiating ART in asymptomatic patients. The large number of available drugs, the increased sensitivity of tests to monitor viral load, and the ability to determine viral resistance is leading to a more individualized approach to therapy.

Virologic response of zidovudine, lamivudine, and tenofovir disoproxil fumarate combination in antiretroviral-naive HIV-1-infected patients

BACKGROUND

High rates of virologic failure have been reported in antiretroviral-naive patients receiving triple-nucleoside reverse transcriptase inhibitor (NRTI) combinations containing tenofovir disoproxil fumarate (TDF) with lamivudine (3TC) and didanosine or 3TC and abacavir (ABC). A regimen of once-daily zidovudine (ZDV), 3TC, ABC, and TDF showed an acceptable virologic success rate, however.

METHODS

This was a pilot prospective cohort study. Treatment-naive subjects were offered a fixed-dose combination of ZDV/3TC (300 mg/150 mg) twice daily and 300 mg of TDF once daily.

RESULTS

Fifty-one patients were enrolled between April 2002 and March 2005. At baseline, the median CD4 count was 230 cells/microL (range: 23-425 cells/microL), 20 (39%) of 51 subjects had CD4 counts of < 200 cells/microL, the median HIV-1 viral load was 4.89 log (3.14 to >5.87 log), and 24 (47%) of 51 subjects had a viral load >5 log. The median follow-up was 12 months (range: 1 week to 38 months). On-treatment analysis showed a median HIV RNA load decrease of -1.7 log after 1 to 2 weeks of treatment and -2.41 log after 1 month, and 34 (89%) of 38 subjects had a viral load < 50 copies/mL at month 6, 21 (78%) of 27 at month 12, and 13 (81%) of 16 after 18 months (intent-to-treat results were 34 [72%] of 47 subjects, 21 [56%] of 36 subjects, and 13 [50%] of 25 subjects at months 6, 12, and 18, respectively). The median CD4 count increase at month 18 was 142 cells/microL. Nine (17.6%) of 51 treatment interruptions for adverse effects were seen. Six viral failures occurred, including 2 with K65R mutations (alone or associated with Y115F and M184V).

CONCLUSION

The combination of ZDV/3TC + TDF in treatment-naive HIV-infected subjects induces a rapid and sustained HIV-1 RNA decrease and is associated with a good immunologic response. No severe adverse events occurred. This triple-NRTI combination needs to be evaluated further.

Short-term safety and tolerability of didanosine combined with high- versus low-dose tenofovir disproxil fumarate in ambulatory HIV-1-infected persons

Coadministration of didanosine (ddI) and tenofovir (TDF) results in increased ddI serum concentrations, which may lead to increased risk of ddI-associated toxicities. To evaluate the safety and tolerability of ddI/TDF, we performed a retrospective cohort analysis of patients seen in the HIV Outpatient Study, an ongoing dynamic cohort study of HIV-infected persons in clinical care. Study subjects were those who received at least 14 days of combined ddI/TDF before October 2003. Of 260 subjects who received ddI/TDF-based antiretroviral therapy, 155 (60%) received high-dose ddI (400 mg daily dose) and 105 (40%) received low-dose ddI (100-250 mg daily). Forty-two of the high-dose ddI recipients were later switched to low-dose ddI. The median time of observation for those on high-dose ddI only was 5 months, high-dose ddI switched to low-dose ddI was 16 months, and low-dose ddI only was 5 months (p < 0.05). Discontinuations because of toxicity were more frequent on high-dose ddI regimens (34/155, 22%) than on low-dose ddI regimens (9/105, 9%) (unadjusted odds ratio [OR(unadj)] 3.0, 95% confidence interval [95% CI] 1.30-7.09; p = 0.007). Among subjects without preexisting peripheral neuropathy, 12 (12%) of 101 subjects ever on high-dose ddI regimens had treatment-emergent peripheral neuropathy compared to 2 (4%) of 55 subjects on low-dose ddI regimens (OR(unadj) 3.57; 95% CI, 0.72-24.1; p = 0.14). Among patients without a history of pancreatitis, 6 (4%) of 153 subjects developed pancreatitis after starting high-dose ddI regimens, compared to none of the 103 subjects on low-dose ddI regimens (OR(adj) and 95% CIs undefined; p = 0.08). Severe laboratory abnormalities of creatinine, phosphorous, and bicarbonate were not different between the groups. A summary variable for any event--discontinuation for toxicity, treatment- emergent adverse event or abnormal laboratory values--indicated that 44 (28%) of 155 of those on high-dose ddI versus 13 (12%) of 105 on low-dose ddI developed any event (OR(unadj) 2.81; 95% CI, 1.36-5.86; p = 0.004). In conclusion, high-dose ddI/TDF-based therapy was more frequently associated with drug-related toxicity, adverse events, and treatment discontinuation than low-dose ddI/TDF regimens; low-dose ddI with TDF was generally well tolerated in these HIV-infected persons.

Antiviral Efficacy and Genotypic Resistance Patterns of Combination Therapy with Stavudine/Tenofovir in Highly Active Antiretroviral Therapy Experienced Patients

Objectives

To evaluate antiviral efficacy of stavudine/tenofovir (d4T/TDF) backbone combination in late-line antiretroviral therapy, and to assess clinical and virological determinants of treatment success.

Design

Multicentric retrospective analysis on patients starting d4T/TDF after highly active antiretroviral therapy (HAART) failure.

Methods

The primary endpoint was the change in plasma HIV-1 RNA from the baseline (time of d4T/TDF initiation) to 6 months of therapy; secondary endpoint was the risk of virological failure.

Results

Among 172 patients included, a mean change in HIV-1 RNA of -1.69 (+1.23) and -1.53 (+1.43) log10 cp/ml was observed respectively at weeks 24 and 48 after starting d4T/TDF combination. Any single type-1 thymidine analogue mutation (TAM; M41L, L210W, T215Y) had a negative effort on the change in HIV RNA at 6 months, whereas among type-2 TAMs (D67N, K70R, K219Q), only D67N showed a trend for a negative effect. Presence of M184V mutation was related with a greater reduction in HIV RNA during d4T/TDF exposure. The risk of virological failure at 6 months after d4T/TDF starting was 22%. Type-1 TAMs were associated with a greater risk of failure (adjusted hazard ratio [HR]=1.65; 95% confidence interval [CI] 1.19–2.29). Conversely, M184V showed a protective effect. In 17 genotypic tests available at failure, no K65R mutation was detected, whereas a trend for an increasing prevalence of d4T-associated mutations was found.

Conclusions

Combining TDF with a thymidine analogue as d4T may be effective as component of antiretroviral rescue regimens in HIV-infected patients with previous exposure to nucleoside analogue reverse transcriptase inhibitor. Previous selection of type-1 TAMs induces a detrimental effect over virological response.

The distribution of the anti-HIV drug, tenofovir (PMPA), into the brain, CSF and choroid plexuses

Background

Tenofovir disoproxil fumarate, a prodrug of the nucleotide reverse transcriptase inhibitor, tenofovir (9-[9(R)-2-(phosphonomethoxy)propyl]adenine; PMPA), was recently approved for use in the combination therapy of human immunodeficiency virus (HIV)-1 infection. This study was undertaken to understand PMPA distribution to the virus sanctuary sites located in the brain, CSF and choroid plexuses and to clarify its possible role in reducing the neurological problems associated with HIV infection.

Methods

The methods used included an established bilateral carotid artery perfusion of [³H]PMPA and a vascular marker, D-[¹⁴C]mannitol, in anaesthetised guinea-pigs followed by scintillation counting, HPLC and capillary depletion analyses. Movement of [³H]PMPA into the brain, cisternal CSF and lateral ventricle choroid plexus was also examined in the absence and presence of additional anti-HIV drugs and a transport inhibitor. Control and test groups were compared by ANOVA or Student's t-test, as appropriate.

Results

The distribution of [³H]PMPA in the cerebrum, cerebellum, pituitary gland and cerebral capillary endothelial cells was not significantly different to that measured for D-[¹⁴C]mannitol. However, [³H]PMPA accumulation was significantly higher than that of D-[¹⁴C]mannitol in the choroid plexus and CSF. Further experiments revealed no cross-competition for transport of [³H]PMPA by probenecid, a non-specific inhibitor of organic anion transport, or the nucleoside reverse transcriptase inhibitors into any of the CNS regions studied. The octanol-saline partition coefficient measurement for [³H]PMPA was 0.0134 ± 0.00003, which is higher that the 0.002 ± 0.0004 measured for D-[¹⁴C]mannitol in an earlier study.

Conclusion

There is negligible transport of [³H]PMPA across the blood-brain barrier, but it can cross the blood-CSF barrier. This is a reflection of the differing physiological and functional characteristics of the blood-CNS interfaces. Self- and cross-inhibition studies did not suggest the involvement of a transport system in the CNS distribution of this drug. However, the ability of PMPA to accumulate in the choroid plexus tissue, but not the cerebral capillary endothelial cells, and the hydrophilic nature of PMPA, does point to the possibility of a transporter at the level of the choroid plexus. PMPA that has crossed the choroid plexus and is in the CSF could treat HIV-infected perivascular and meningeal macrophages, but it is unlikely to reach the infected microglia of deep brain sites.

Exploring Mitochondrial Nephrotoxicity as a Potential Mechanism of Kidney Dysfunction among HIV-Infected Patients on Highly Active Antiretroviral Therapy

Background

Tenofovir (TDF) exposure has been associated with renal dysfunction. Mitochondrial nephrotoxicity was investigated as an underlying mechanism. Given the interaction between TDF and didanosine (ddI), their concurrent use was also investigated.

Design

Relative kidney biopsy mitochondrial DNA (mtDNA) to nuclear DNA ratios were measured retrospectively. HIV+ individuals on TDF within 6 months preceeding the biopsy (HIV+/TDF+, n=21) were compared to HIV+ individuals who never received TDF (HIV+/TDF-, n=10) and to HIV uninfected controls (HIV–, n=22). Twelve of the HIV+/TDF+ individuals received concurrent ddI, 10 of those once at unadjusted ddI dosage. Tubular mitochondria morphology was also examined by electron microscopy. Statistical analyses were done on log-transformed mtDNA/nDNA, using non-parametric tests.

Results

Kidney mtDNA levels were different among the three groups ( P=0.046). mtDNA ratios were lower in HIV+/TDF+ subjects (7.5 [2.0–12.1]) than in HIV- ones (14.3 [6.0–16.5], P=0.014), but not lower than HIV+/TDF-controls (6.4 [2.8–11.9], P=0.82). Among HIV+ subjects, there was a difference between TDF-, TDF+/ddI- and TDF+/ddI+ ( P=0.005), with concurrent TDF/ddI use associated with lower mtDNA (2.1 [1.9–5.5], n=12) than TDF+/ddI- (13.8 [7.5–16.4], n=9, P=0.003). No TDF–/ddI+ biopsies were available. In regression analyses, only HIV infection ( P=0.03), and TDF/ddI use ( P=0.003) were associated with lower mtDNA. At the ultrastructural level, abnormal tubular mitochondria was more prevalent in HIV+/TDF+ biopsies than HIV+/TDF- and HIV- ones together ( P<0.001) but not more so in TDF+/ddI+ biopsies than TDF+/ddI- ones ( P=0.67).

Conclusions

Renal dysfunction in this population may be mediated through mitochondrial nephrotoxicity that involves more than one drug and/or pathogenesis. Kidney mtDNA depletion was associated with HIV infection and concurrent TDF/ddI therapy but not TDF use alone, while kidney ultrastructural mitochondrial abnormalities were seen with TDF use. The interaction between TDF and ddI may be relevant in the kidney where both drugs are cleared. The clinical relevance of our findings needs to be evaluated given the current recommendation for reduced doses of ddI when used in conjunction with TDF.

High rate of virological failure in maintenance antiretroviral therapy with didanosine and tenofovir

We evaluated the virological outcome of tenofovir plus didanosine-based regimens in 67 HIV-suppressed patients. After a median follow-up of 26 months (IQR 10.5-40.5), 12 (18%) discontinued the therapy because of virological failure. At virological failure 'de novo' selected mutations were identified in 11 of the 12 failing patients, including the K65R mutation in seven patients. These results argue against the use of tenofovir-didanosine not only in naive patients, but also in previously suppressed patients.

Simplification Therapy with Once-Daily Didanosine, Tenofovir and Efavirenz in HIV-1-Infected Adults with Viral Suppression Receiving a More Complex Antiretroviral Regimen: Final Results of the EFADITE Trial

Background

High pill burden and side effects often impact on the long-term success of highly active anti-retroviral therapy (HAART), which has led clinicians to search for more convenient regimens.

Patients and methods

A prospective, multicentre, open, comparative study in which HIV-1-infected patients on HAART and with plasma HIV-1 RNA <50 copies/ml for longer than 6 months were switched to tenofovir, didanosine and efavirenz (QD arm) or remained on the same treatment regimen (control arm). Patients with grade 4 toxicities or plasma HIV-1 RNA values repeatedly >1000 copies/ml discontinued the study.

Results

A total of 390 patients were included in the trial (309 in the QD arm and 81 in the control arm). The main baseline characteristics were well balanced between groups. In the QD arm, 41% of patients received high (standard) didanosine doses and 59% received reduced doses. At 12 months, plasma HIV-1 RNA <400 copies/ml was attained in 66% of QD patients and 73% of controls in the intent-to-treat (ITT) analysis ( P=NS). However, the number of individuals with HIV-1 RNA <400 copies/ml in the QD arm was 56% versus 71% when comparing the use of high versus low didanosine doses ( P=0.007). Treatment discontinuation occurred in 87 QD cases (28%) and 17 controls (21%). Twenty QD individuals (6.5%) and 2 controls (2.5%) discontinued because of virological failure ( P=NS). The median CD4+ cell count change at 12 months was -26 and +27 cells/μl in QD patients and controls, respectively ( P=0.001). In individuals who attained HIV-1 RNA <400 copies/ml, CD4+ cell changes were -25 and +15 cells/μl in QD patients and controls, respectively ( P=0.001). Moreover, CD4+ cell declines in the QD arm were significantly greater in patients taking high versus low didanosine doses (-59 versus -15 cells/μl; P=0.04). The lipid profile improved significantly in the QD arm, particularly in patients who were on protease inhibitors prior to simplification.

Conclusions

Simplification to didanosine–tenofovir–efavirenz provides a virological suppression rate at 12 months similar to that seen in patients who do not change therapy, as long as low didanosine doses are administered. Decreases in CD4+ cell levels in patients in the QD arm (especially decreases seen with high didanosine doses) and dyslipidaemias along with less convenient pill burden and schedules in controls were the main long-term concerns for each option.