Antiretroviral effect and safety of abacavir alone and in combination with zidovudine in HIV-infected adults. Abacavir Phase 2 Clinical Team

Abacavir adverse reactions related with HLA-B*57: 01 haplotype in a large cohort of patients infected with HIV

OBJECTIVE

Carriage of human leukocyte antigen (HLA)-B*57:01 allele increases the risk of abacavir hypersensitivity reaction. Therefore, since 2008 HIV treatment guidelines recommend HLA-B*57:01 screening before abacavir administration, greatly reducing hypersensitivity reaction rate. However, clinically suspected abacavir-related hypersensitivity reactions are described in allele non-carriers. Major aim of this study was to evaluate the relationship between HLA-B*57:01 pattern and abacavir-related hypersensitivity reaction, focusing on hypersensitivity reaction prevalence in allele non-carriers.

METHODS

We included all outpatients aged >18 years old with HIV infection and known HLA-B*57:01 pattern, followed at our Department from January 2000 until December 2017. Patients were divided according to HLA-B*57:01 pattern and first antiretroviral treatment prescribed (containing or not abacavir) as follows: HLA-B*57:01 allele carriers treated with abacavir and HLA-B*57:01 allele non-carriers treated with abacavir. We considered all adverse events reported during first abacavir administration, differentiating between confirmed hypersensitivity reactions and non-hypersensitivity reactions, according to abacavir hypersensitivity reaction definition included in the abacavir EU Summary of Product Characteristics and the US Prescribing Information.

RESULTS

A total of 3144 patients had a known HLA-B*57:01 pattern. About 5.4% of them showed allele polymorphism; Caucasian ethnicity was the most represented. In this cohort, 1801 patients were treated with a first abacavir-containing regimen (98.2% of them was represented by allele non-carriers). 191 out of 1801 patients discontinued abacavir because of toxicity/intolerance; among them 107 described adverse events fulfilled the criteria of confirmed abacavir hypersensitivity reaction (22/32 allele-positive patients and 85/1769 allele-negative patients). After having experienced a confirmed abacavir hypersensitivity reaction, abacavir was re-administered to eight HLA-B*57:01 negative patients. Seven of them re-experienced a syndrome consistent with hypersensitivity reaction, finally leading to drug discontinuation. Overall, no fatal reactions were described.

CONCLUSION

Not all abacavir-related side effects occur as a result of classic HLA-B*57:01-mediated hypersensitivity reaction, as they can develop irrespective of HLA-B*57:01 status. Clinical vigilance must be an essential part of the management of individuals starting abacavir, at any time during treatment. In a 'real-life' setting, clinical diagnosis of suspected abacavir hypersensitivity reaction in allele non-carriers remains crucial for further clinical decision making.

Abacavir usage patterns and hypersensitivity reactions in the EuroSIDA cohort

OBJECTIVES

Five to eight per cent of HIV-positive individuals initiating abacavir (ABC) experience potentially fatal hypersensitivity reactions (HSRs). We sought to describe the proportion of individuals initiating ABC and to describe the incidence and factors associated with HSR among those prescribed ABC.

METHODS

We calculated the proportion of EuroSIDA individuals receiving ABC-based combination antiretroviral therapy (cART) among those receiving cART after 1 January 2009. Poisson regression was used to identify demographic, and current clinical and laboratory factors associated with ABC utilization and discontinuation.

RESULTS

Between 2009 and 2016, of 10 076 individuals receiving cART, 3472 (34%) had ever received ABC-based cART. Temporal trends of ABC utilization were also heterogeneous, with 28% using ABC in 2009, dropping to 26% in 2010 and increasing to 31% in 2016, and varied across regions and over time. Poisson models showed lower ABC utilization in older individuals, and in those with higher CD4 cell counts, higher cART lines, and prior AIDS. Higher ABC utilization was associated with higher HIV RNA and poor renal function, and was more common in Central-East and Eastern Europe and lowest during 2014. During 779 person-years of follow-up (PYFU) in 2139 individuals starting ABC after 1 January 2009, 113 discontinued ABC within 6 weeks of initiation for any reason [incidence rate (IR) 14.5 (95% confidence interval (CI) 12.1, 17.5) per 100 PYFU], 13 because of reported HSR [IR 0.3 (95% CI 0.1, 1.0) per 100 PYFU] and 35 because of reported HSR/any toxicity [IR 4.5 (95% CI 3.2, 6.3) per 100 PYFU]. There were no factors significantly associated with ABC discontinuation because of reported HSR/any toxicity.

CONCLUSIONS

ABC remains commonly used across Europe and the incidence of discontinuation because of reported HSR was low in our study population.

Collaborative update of a rule-based expert system for HIV-1 genotypic resistance test interpretation

INTRODUCTION

HIV-1 genotypic resistance test (GRT) interpretation systems (IS) require updates as new studies on HIV-1 drug resistance are published and as treatment guidelines evolve.

METHODS

An expert panel was created to provide recommendations for the update of the Stanford HIV Drug Resistance Database (HIVDB) GRT-IS. The panel was polled on the ARVs to be included in a GRT report, and the drug-resistance interpretations associated with 160 drug-resistance mutation (DRM) pattern-ARV combinations. The DRM pattern-ARV combinations included 52 nucleoside RT inhibitor (NRTI) DRM pattern-ARV combinations (13 patterns x 4 NRTIs), 27 nonnucleoside RT inhibitor (NNRTI) DRM pattern-ARV combinations (9 patterns x 3 NNRTIs), 39 protease inhibitor (PI) DRM pattern-ARV combinations (13 patterns x 3 PIs) and 42 integrase strand transfer inhibitor (INSTI) DRM pattern-ARV combinations (14 patterns x 3 INSTIs).

RESULTS

There was universal agreement that a GRT report should include the NRTIs lamivudine, abacavir, zidovudine, emtricitabine, and tenofovir disoproxil fumarate; the NNRTIs efavirenz, etravirine, nevirapine, and rilpivirine; the PIs atazanavir/r, darunavir/r, and lopinavir/r (with "/r" indicating pharmacological boosting with ritonavir or cobicistat); and the INSTIs dolutegravir, elvitegravir, and raltegravir. There was a range of opinion as to whether the NRTIs stavudine and didanosine and the PIs nelfinavir, indinavir/r, saquinavir/r, fosamprenavir/r, and tipranavir/r should be included. The expert panel members provided highly concordant DRM pattern-ARV interpretations with only 6% of NRTI, 6% of NNRTI, 5% of PI, and 3% of INSTI individual expert interpretations differing from the expert panel median by more than one resistance level. The expert panel median differed from the HIVDB 7.0 GRT-IS for 20 (12.5%) of the 160 DRM pattern-ARV combinations including 12 NRTI, two NNRTI, and six INSTI pattern-ARV combinations. Eighteen of these differences were updated in HIVDB 8.1 GRT-IS to reflect the expert panel median. Additionally, HIVDB users are now provided with the option to exclude those ARVs not considered to be universally required.

CONCLUSIONS

The HIVDB GRT-IS was updated through a collaborative process to reflect changes in HIV drug resistance knowledge, treatment guidelines, and expert opinion. Such a process broadens consensus among experts and identifies areas requiring further study.

Abacavir-induced fulminant hepatic failure in a HIV/HCV co-infected patient

Abacavir hypersensitivity is a rare, yet significant adverse reaction that results in a spectrum of physical and laboratory abnormalities, and has been postulated to stem from a variety of aetiological factors. The major histocompatibility complex haplotype human leucocyte antigen (HLA)-B5701 is a significant risk factor in development of hypersensitivity reactions, yet only 55% of HLA-B5701+ individuals develop such reactions, suggesting a multifactorial aetiology. Nevertheless, prospective screening and avoidance of abacavir in these patients has limited adverse events. Within this spectrum of adverse events, abacavir-induced liver toxicity is exceedingly rare and reported events have ranged from mild elevations of aminotransferases to fulminant hepatic failure. We report the case of a 50-year-old Caucasian woman with a history significant for HIV, hepatitis C virus and a HLA-B5701+ status, transferred to our emergency department in a hypotensive state and found to have acute liver failure, acute renal failure and significant rhabdomyolysis following a change of highly active antiretroviral therapy regimen.

Efficacy and safety of abacavir-containing combination antiretroviral therapy as first-line treatment of HIV infected children and adolescents: a systematic review and meta-analysis

BACKGROUND

Abacavir is one of the recommended nucleoside reverse transcriptase inhibitors (NRTIs) for the treatment of HIV infections among children and adolescents. However, there are concerns that the antiviral efficacy of abacavir might be low when compared to other NRTIs especially among children. There are also concerns that abacavir use may lead to serious adverse events such as hypersensitivity reactions and has potential predisposition to developing cardiovascular diseases

METHODS

We searched four electronic databases, four conference proceedings and two clinical trial registries in August 2014, without language restrictions. Experimental and observational studies with control groups that examined the efficacy and safety of abacavir-containing regimens in comparison with other NRTIs as first-line treatment for HIV-infected children and adolescents aged between one month and eighteen years were eligible. Two authors independently screened search results, extracted data and assessed the risk of bias of included studies using a pre-specified, standardised data extraction form and validated risk of bias tools. We also assessed the quality of evidence per outcome with the GRADE tool.

RESULTS

We included two randomised controlled trials (RCTs) and two analytical cohort studies with a total of 10,595 participants. Among the RCTs we detected no difference in virologic suppression after a mean duration of 48 weeks between abacavir- and stavudine-containing regimens (2 trials; n = 326: RR 1.28; 95 % CI 0.67-2.42) with significant heterogeneity (P = 0.02; I(2) = 81 %). We also found no significant differences between the two groups for adverse events and death. After five years of follow-up, virologic suppression improved with abacavir (1 trial; n = 69: RR 1.96; 95 % CI 1.11-3.44). For cohort studies, we detected that the virologic suppression activity of abacavir was less effective than stavudine in both the lopinavir/ritonavir (1 study, n = 2165: RR 0.79, 95 % CI 0.67-0.92) and efavirenz sub-groups (1 study, n = 3204: RR 0.79, 95 % CI 0.67-0.92) respectively. The quality of evidence from RCTs was moderate for virologic suppression but low for death and adverse events, while that of cohort studies was low for all three these outcomes.

CONCLUSIONS

Available evidence showed little or no difference between abacavir-containing regimen and other NRTIs regarding efficacy and safety when given to children and adolescents as a first-line antiretroviral therapy.

A novel vaginal drug delivery system: anti-HIV bioadhesive film containing abacavir

Women are very much susceptible for acquired immunodeficiency syndrome (AIDS) and other sexually transmitted diseases (STDs), mainly due to unprotected heterosexual vaginal intercourse and for some other social and economical disadvantages. Our aim was to formulate and optimize vaginal film of abacavir, a potent nucleoside reverse transcriptase inhibitor, for the treatment of AIDS and HIV. Abacavir films were prepared by solvent evaporation method using sodium alginate (Na-alginate) as the main polymer, Hydroxypropyl Methylcellulose E 15 (HPMC E 15) as the copolymer and glycerol as a humectant. Abacavir sulphate (ABC) was used here as a drug. Films were optimized for various physicochemical parameters such as tensile strength, % elongation at break, swelling capacity, drug content (mg/cm(2)), thickness, folding endurance, bioadhesion, pH, moisture content and SEM. Drug polymer interaction was studied by FTIR Spectra. The drug release study was accomplished in dissolution apparatus. In vivo study was also carried out. This newly formed film was one kind of sustain release type and can be considered as a novel drug carrier system for the treatment of AIDS and other STDs. It was suitable for local as well as systemic effect. The films showed good physicochemical property with good aesthetic appeal.

Early virologic response to abacavir/lamivudine and tenofovir/emtricitabine during ACTG A5202

BACKGROUND

ACTG A5202 randomized treatment-naïve individuals to tenofovir-emtricitabine (TDF/FTC) or abacavir-lamivudine (ABC/3TC) combined with efavirenz (EFV) or atazanavir/ritonavir (ATV/r). Individuals in the high screening viral load (VL) stratum (≥100,000 copies/mL) had increased rates of virologic failure with ABC/3TC.

OBJECTIVE

To compare regimen-specific early virologic response.

METHODS

Using Wilcoxon rank-sum tests, we compared regimen-specific VL changes from entry to week 4 in A5202 subjects (N = 1,813) and from entry to week 1, 2, and 4 in substudy subjects (n = 179). We evaluated associations between week 4 VL change and time to virologic failure with Cox proportional hazards models.

RESULTS

TDF/FTC and ABC/3TC produced similar week 4 VL declines in the entire study population and in the high VL stratum. EFV produced greater VL declines from baseline at week 4 than ATV/r (median -2.1 vs -1.9 log10 copies/mL; P < .001). In the substudy of subjects with week 1, 2, and 4 VL data, there was no difference in VL decline in individuals randomized to TDF/FTC versus ABC/3TC, but EFV resulted in greater VL decline from entry at each of these timepoints than ATV/r. Smaller week 4 VL decline was associated with increased risk of virologic failure.

CONCLUSIONS

Within all treatment arms, a less robust week 4 virologic response was associated with higher risk for subsequent virologic failure. However, between-regimen differences in week 4 VL declines did not parallel the previously reported differences in longer term virologic efficacy in A5202, suggesting that between-regimen differences in responses were not due to intrinsic differences in antiviral activity.

Abacavir (Ziagen(®)) use between 2003 and 2008 in France according to the electronic medical record NADIS(®)

OBJECTIVE

The authors had for objective to describe HIV-infected patients treated with ABC (Ziagen(®), ABC), and the immune, virological, and clinical treatment outcome between 2003 and 2008.

PATIENTS AND METHODS

We performed a retrospective analysis of the Dat'AIDS database on patients who were treated with ABC for the first time between 2003 and 2008.

RESULTS

Eight hundred and thirty-six patients were included. Before initiation of ABC, 26.3% has stopped the previous treatment because of immuno-virological failure, 30.5% because of adverse events, and 29.8% for other reasons. Thirteen percent were antiretroviral naive. One third of patients were ranked as CDC class C, and more than 2/3 had a viral load<5 log copies/mL or a CD4 count≥200mm(3). ABC was mainly included in a combination containing 2 NRTI and 1 PI (63%), or 1 non-NRTI (16%). Thirty-two percent of patients were still treated with ABC after 2years of treatment and the median of ABC treatment was 11months (IQ 84days-2years). The main causes for stopping ABC were therapeutic simplification (47.4% of patients), intolerance (19.0%), and immuno-virological failure (9.8%). Suspected hypersensitivity reactions were the main cause of discontinuation due to intolerance (27.6%); the rate was 3.8% when ABC had been introduced before the routine use of the screening test HLA-B*5701. The incidence of myocardial infarction was 3.8 per 1000 patient-years; 70.6% of patients received a fixed combination including ABC after discontinuation of ABC as a single agent (Ziagen(®)).

CONCLUSION

This retrospective analysis confirmed the effectiveness and the good tolerance of ABC in the therapeutic strategy, between 2003 and 2008.

Standardized comparison of the relative impacts of HIV-1 reverse transcriptase (RT) mutations on nucleoside RT inhibitor susceptibility

Determining the phenotypic impacts of reverse transcriptase (RT) mutations on individual nucleoside RT inhibitors (NRTIs) has remained a statistical challenge because clinical NRTI-resistant HIV-1 isolates usually contain multiple mutations, often in complex patterns, complicating the task of determining the relative contribution of each mutation to HIV drug resistance. Furthermore, the NRTIs have highly variable dynamic susceptibility ranges, making it difficult to determine the relative effect of an RT mutation on susceptibility to different NRTIs. In this study, we analyzed 1,273 genotyped HIV-1 isolates for which phenotypic results were obtained using the PhenoSense assay (Monogram, South San Francisco, CA). We used a parsimonious feature selection algorithm, LASSO, to assess the possible contributions of 177 mutations that occurred in 10 or more isolates in our data set. We then used least-squares regression to quantify the impact of each LASSO-selected mutation on each NRTI. Our study provides a comprehensive view of the most common NRTI resistance mutations. Because our results were standardized, the study provides the first analysis that quantifies the relative phenotypic effects of NRTI resistance mutations on each of the NRTIs. In addition, the study contains new findings on the relative impacts of thymidine analog mutations (TAMs) on susceptibility to abacavir and tenofovir; the impacts of several known but incompletely characterized mutations, including E40F, V75T, Y115F, and K219R; and a tentative role in reduced NRTI susceptibility for K64H, a novel NRTI resistance mutation.

Abacavir pharmacokinetics during chronic therapy in HIV-1-infected adolescents and young adults

The pharmacokinetics of abacavir and its metabolites were investigated in 30 human immunodeficiency virus (HIV)-infected adolescents and young adults 13-25 years of age, equally divided into two groups: <18 years of age and >or=18 years of age. All the subjects received the recommended adult dose of 300 mg twice daily. The area under the plasma concentration-time curve (AUC) and half-life of abacavir did not differ significantly between the age groups or by gender or race, and there were only modest associations of age with apparent abacavir clearance and with volume of distribution. There were no significant correlations of carboxylate or glucuronide metabolite levels with age or gender, although glucuronide AUC was higher in Hispanic subjects than in African-American subjects. Zidovudine and lamivudine concentration profiles were also similar in the two age groups. A novel aspect of the study included an assessment of intracellular carbovir, zidovudine, and lamivudine triphosphate levels, and these were found to be similar in the two age-based groups. Overall, these findings suggest that current recommendations relating to adult dosages are appropriate for adolescents and young adults.

The anti-HIV activity of entecavir: a multicentre evaluation of lamivudine-experienced and lamivudine-naive patients

BACKGROUND

Entecavir, an antiviral with potent anti-hepatitis B virus activity, was recently shown to have anti-HIV activity in three patients and the ability to select for the lamivudine-resistant HIV polymerase mutation M184V in a patient with prior antiretroviral therapy.

OBJECTIVES

To further characterize entecavir's anti-HIV activity and identify risk factors for selection of the M184V.

DESIGN

Retrospective cohort study.

METHODS

We evaluated the virological characteristics of HIV and hepatitis B virus in 17 HIV-hepatitis B virus coinfected patients (10 antiretroviral therapy-naive and seven antiretroviral therapy-experienced) prior to and during entecavir monotherapy. Descriptive statistics were used to assess changes in HIV RNA and hepatitis B virus DNA. Variables associated with development of the M184V were determined by univariate analysis.

RESULTS

Of the 17 patients, 13 (76%) demonstrated a reduction in HIV RNA by at least 0.5 log10 copies/ml. Of the remaining four patients, two had the M184V detected prior to entecavir therapy and the other two had wild-type HIV. The median reduction in HIV RNA for the cohort was 1.2 log10 copies/ml, which was similar in antiretroviral therapy-naive and antiretroviral therapy-experienced patients. The M184V mutation emerged in six patients receiving entecavir, including three antiretroviral therapy-naive patients. No other HIV mutations were consistently detected. Risk factors for the emergence of the M184V mutation were a decline in hepatitis B virus DNA (P = 0.04) and duration of entecavir use (P = 0.05).

CONCLUSION

Entecavir monotherapy in HIV-hepatitis B virus coinfected patients, including antiretroviral therapy-naive patients, has significant anti-HIV activity and can result in the development of the M184V variant. Entecavir should not be used in such co-infected patients without concomitant antiretroviral therapy.

Adverse cutaneous reactions to antimicrobials in patients with human immunodeficiency virus infection

Adverse reactions to medication are significant contributors to morbidity and mortality in patients with human immunodeficiency virus (HIV) infection. Cutaneous events not only constitute a significant portion of these reactions, they may also herald developing systemic reactions such as hemato-, nephro-, and hepatotoxicity. The identification of cutaneous adverse reactions and drug culprits and the proper management of reactions are of paramount importance for these patients. This review focuses specifically on adverse cutaneous reactions to antimicrobials that are commonly used in the management of patients with HIV infection.

Testing antiretroviral drug efficacy in conventional mice infected with chimeric HIV-1

OBJECTIVE

We previously described chimeric HIV-1, EcoHIV, which can infect mouse cells in culture and cause spreading infection in conventional immunocompetant mice. We have now applied this system as a model for preclinical evaluation of anti-retroviral drugs.

DESIGN AND METHODS

We used chimeric virus EcoHIV/NDK constructed on the backbone of subtype D NDK. EcoHIV/NDK expression in mice was characterized 5-10 days after infection by testing viral DNA, RNA, and protein burdens in spleen and macrophages by real-time PCR (QPCR), RT-PCR, and p24 ELISA. For antiviral evaluation, groups of 5-7 mice were pretreated with 2',3'-dideoxycytidine (ddC), abacavir, or vehicle; mice were then infected with EcoHIV/NDK, treatment maintained for additional 48 h, and tested for viral DNA and RNA burdens in spleens and macrophages by QPCR.

RESULTS

EcoHIV/NDK infected mice reproducibly showed viral burdens of up to 1.4 x 10 viral DNA copies and 200 pg p24 per 10 spleen cells and expressed spliced Vif RNA and mature p24 in macrophages 5-10 days after infection. Treatment of mice with 60 or 300 mg ddC/kg/day blocked EcoHIV/NDK infection in a dose-dependent manner with significantly lower viral DNA and RNA burdens at both drug doses (P < 0.001) in the spleens of infected mice. Abacavir tested at 100 mg/kg/day caused 96% inhibition of viral DNA synthesis in spleen and it almost completely abolished viral spliced RNA synthesis in spleens and macrophages.

CONCLUSIONS

The system of chimeric HIV-1 infection of mice permits rapid, statistically powerful, and inexpensive evaluation of antiretroviral drugs in vivo.

Liver toxicity induced by non-nucleoside reverse transcriptase inhibitors

Liver toxicity is one of the most relevant adverse effects of antiretroviral therapy. Within the non-nucleoside reverse transcriptase inhibitors (NNRTIs), efavirenz can be considered a safer drug for the liver than nevirapine. In fact, the frequency of severe increased liver enzymes in patients on efavirenz ranges from 1 to 8%, whereas in patients treated with nevirapine, it ranges from 4 to 18%. Likewise, nevirapine is more commonly associated than efavirenz with early acute hepatitis, which is produced by a hypersensitivity mechanism and has a defined risk profile that often makes it avoidable. Despite the fact that most cases of NNRTI-induced liver toxicity are asymptomatic, the rates of symptomatic events in patients treated with nevirapine are greater than in subjects on efavirenz. In any case, it is unusual for an NNRTI to be suspended due to liver toxicity.

Salvage therapy with abacavir and other reverse transcriptase inhibitors for human immunodeficiency-associated encephalopathy

BACKGROUND

HIV-associated encephalopathy (HIV-AE) is a severe neurologic condition that affects HIV-infected children. The potential benefit of antiretroviral (ARV) agents with good cerebrospinal fluid (CSF) penetration remains to be defined. Abacavir (ABC) achieves good CSF concentrations and studies of high-dose ABC showed benefit in adults with HIV dementia. The present study evaluated the safety and virologic, immunologic and neuropsychological responses of an ARV regimen including high-dose ABC in children with HIV-AE.

METHODS

Children between 3 months and 18 years old and abacavir-naive with HIV-AE and virologic failure were eligible.

RESULTS

: Seventeen children (16 ARV-experienced) were enrolled and 14 children completed 48 weeks of therapy. The overall tolerability was good; 2 children had a possible hypersensitivity reaction. At week 48, 53% and 59% of the children achieved HIV RNA levels below the limit of quantitation in plasma and CSF, respectively. The median (25%-75% range) change of HIV RNA from baseline to week 48 was -2.29 (-0.81 to -2.47) log10 copies/mL in plasma and -0.94 (0 to -1.13) log10 copies/mL in CSF. The mean increases in CD4 (+/-standard error of mean) cell count and CD4% were 427 (+/-169) cells/mm and 8% (+/-2), respectively. Concentrations of soluble tumor necrosis factor receptor II were reduced in plasma and CSF. Children less than 6 years of age demonstrated significant neuropsychological improvement at week 48.

CONCLUSIONS

In the present study with a limited number of children, highly active ARV therapy including high-dose ABC showed a safety profile similar to standard dose ABC and provided clinical, immunologic and virologic response in children with HIV-AE at week 48. Children less than 6 years of age also demonstrated significant neuropsychological improvement.

HIV and liver diseases: recent clinical advances

Because the life expectancy of patients infected with HIV has been prolonged, liver diseases have assumed far greater importance as a cause of morbidity and mortality in these patients. Given the shared risks of transmission, patients who have HIV often are coinfected with hepatotrophic viruses such as hepatitis C and hepatitis B. Further, antiretroviral therapy (ART) used by patients who have HIV is often hepatotoxic, contributing to liver damage. With increasing immunosuppression caused by AIDS, patients who have HIV have to deal with these issues and the increased risk of infection with opportunistic viral, fungal, bacterial, and protozoal pathogens. In addition, steatosis and lipodystrophy now are recognized more commonly in patients who have HIV, particularly in the setting of ART. Thus, understanding of liver diseases in the setting of HIV infection becomes an important focus in caring these individuals. There have been numerous advances in the treatment of liver disease in patients who have HIV, particularly in treating viral hepatitis C and B. This article reviews various liver manifestations in patients who have HIV and the recent advances in diagnostic and therapeutic options.

Weight related differences in the pharmacokinetics of abacavir in HIV-infected patients

AIM

To study the possible influence of patient characteristics on abacavir pharmacokinetics.

METHODS

A population pharmacokinetic model for abacavir was developed using data from 188 adult patients by the use of a nonlinear mixed effects modelling method performed with NONMEM.

RESULTS

Abacavir pharmacokinetics was well described by a two-compartment open model with linear absorption and elimination. Typical population estimates for the absorption rate constant (Ka), the apparent central distribution volume (Vc/F), the apparent peripheral distribution volume (Vp/F), the apparent intercompartmental clearance (Q/F) and the apparent plasma clearance (CL/F) were 1.8 h(-1), 75 l, 23.6 l, 10 l h(-1) and 47.5 l h(-1), respectively. Apparent plasma clearance was positively related to bodyweight. Individual Bayesian estimates of CL/F were used to calculate abacavir AUC. The latter decreased from 10.7 +/- 5.0 to 5.7 +/- 1.6 mgh l(-1) when bodyweight increased from 36 to 102 kg. This drop in abacavir exposure could lead to suboptimal treatment for the heaviest patients, as antiviral efficacy of abacavir is known to be related to its AUC. A 400 mg abacavir dose would be necessary to achieve adequate exposure to abacavir in patients weighing more than 60 kg.

CONCLUSIONS

The apparent plasma clearance of abacavir was positively related to bodyweight. The efficacy of the current recommended abacavir dosage for patients with high bodyweight should be evaluated in further studies.

[Therapeutic strategies for HIV infection: early response to antiretroviral treatment, predictive factor for the longer term response]

Despite the wide armamentarium available against the human immunodeficiency virus, the efficacy of therapeutic molecules is reduced by the selection of resistant viral strains. Several data argue in favour of an early control of viral replication ever since the first treatment: the intensity of the initial viral replication, as well as results of studies on antiretroviral drugs given as first line treatment and on the early inhibitory response of viral replication. Although an early control is essential for long-term antiviral success, the optimal time limit for the virologic response still needs to be established early knowledge of the virologic response could prove useful in the evaluation of new and more successful therapeutic combinations. Nevertheless, the impact of an earlier control of viral replication on long-term treatment efficacy and on the prevention of resistance emergence deserves further investigation.

Triple nucleoside reverse transcriptase inhibitor therapy in children

Much of the success attributed to HIV therapy in the last few years has resulted from improved ways of using existing drugs in combination therapy regimens. The availability of new, more potent drugs such as protease inhibitors and more accurate viral load tests to aid decisions to start or change treatment has also contributed to the success. Published recommendations for pediatric HIV therapy, generated by a panel of experts and specialists, are readily available and regularly updated. Preferred regimens of 'potent' therapy (referred to as highly active antiretroviral therapy, or HAART) currently consist of two nucleoside reverse transcriptase inhibitors (NRTIs) combined with either a non-nucleoside reverse transcriptase inhibitor (NNRTI) or a protease inhibitor. More intense four-drug regimens using an NNRTI or a second protease inhibitor as a fourth drug are being evaluated. Problems with HAART include: unpalatable drug formulations and adverse effects, coupled with lack of data on the pharmacokinetics, efficacy, and safety of various drug combinations. Adherence is a major factor influencing the efficacy and outcome of antiretroviral therapy. Many children cannot adhere to complex multidrug regimens, which cause virologic failure, despite excellent CD4+ cell count responses. This means a rapid progression through the limited number of treatment regimens available. Simpler regimens such as those containing three NRTIs have been proposed as a method of treatment that will allow suppression of the virus, yet circumvent many of the problems previously mentioned. An additional benefit would be the preservation of antiretroviral drugs from other classes for future treatment options if required. The major advantages of triple NRTI regimens are the simplicity of the regimen, good tolerability, few drug-drug interactions, and infrequent adverse effects coupled with a low pill burden. However, abacavir hypersensitivity remains a major problem. Up to 3% of patients may develop an early idiosyncratic hypersensitivity reaction - fever, malaise, and mucositis with or without rash, which can progress to more advanced stages of shock and death. A major concern is the apparently inferior virologic control of triple NRTI therapy as demonstrated in the AIDS Clinical Trials Group A5095 study with zidovudine/lamivudine/abacavir (Trizivir) combination in adults. Such a combination should only be considered in special situations. Examples cited include informed patient choice based on anticipated poor adherence on other treatment regimens, or if concomitant drugs such as tuberculosis medication are prescribed. The low pill burden of triple NRTI regimens (especially if combined in a single pill such as Trizivir), offers hope that regimen simplification may still be possible in the future.

Membrane permeation characteristics of abacavir in human erythrocytes and human T-lymphoblastoid CD4+ CEM cells: comparison with (-)-carbovir

Abacavir, (-)-(1S,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene-1-methanol, is a novel purine carbocyclic nucleoside analogue that has been approved by the FDA for the treatment of HIV (as Ziagen trade mark [abacavir sulfate]). Chemically, abacavir and (-)-carbovir (CBV) differ only at the 6-position of the purine ring; abacavir contains a cyclopropylamino moiety in place of the 6-lactam functionality of CBV. Intracellularly both are ultimately metabolized to CBV triphosphate. We compared the membrane permeation characteristics of these two compounds at 20 degrees C in human erythrocytes and in human T-lymphoblastoid CD4+ CEM cells, using a "papaverine-stop" assay. In erythrocytes, abacavir influx was rapid, nonsaturable (rate constant=200 pmol/s/mM/microl cell water), and unaffected by inhibitors of nucleoside or nucleobase transport. CBV influx was slow, saturable, strongly inhibited by adenine or hypoxanthine, and occurred via both the nucleobase carrier (Vmax=0.67 pmol/s/microl cell water; Km=50 microM) and the nucleoside carrier (Vmax=0.47 pmol/s/microl cell water; Km=440 microM). Similar qualitative results were obtained with CD4+ CEM cells, although CBV influx rates were somewhat higher and abacavir influx rates lower, compared to the corresponding rates in erythrocytes. Equilibrium studies further revealed that both compounds are concentrated intracellularly, but nonmetabolically, in both cell types, apparently due to cytosolic protein binding (absent in erythrocyte ghosts). We conclude that, in both cell types, while CBV influx is slow and carrier-dependent, abacavir influx occurs rapidly by nonfacilitated diffusion. The membrane permeation characteristics of abacavir are consistent with its superior oral bioavailability and its impressive ability to penetrate the central nervous system.

Zidovudine, lamivudine, and abacavir have different effects on resting cells infected with human immunodeficiency virus in vitro

We have previously described an in vitro model for the evaluation of the effects of different immunomodulatory agents and immunotoxins (ITs) on cells latently infected with human immunodeficiency virus (HIV). We demonstrated that latently infected, replication-competent cells can be generated in vitro after eliminating CD25+ cells with an IT. Thus, by selectively killing the productively infected cells with an anti-CD25 IT we can generate a population of latently infected cells. CD25- cells generated in this manner were treated with nucleoside analog reverse transcriptase inhibitors and subsequently activated with phytohemagglutinin in the presence of the drugs. The antiviral activities of zidovudine (ZDV), lamivudine (3TC), and abacavir (ABC) were evaluated by using this model. 3TC and ABC demonstrated significant activity in decreasing HIV production from recently infected resting cells following their activation, whereas the effect of ZDV was more modest. These results suggest that the differences in antiviral activity of nucleoside analogs on resting cells should be considered when designing drug combinations for the treatment of HIV infection. The model presented here offers a convenient alternative for evaluating the mechanism of action of new antiretroviral agents (J. Saavedra, C. Johnson, J. Koester, M. St. Claire, E. Vitteta, O. Ramilo, 37th Intersci. Conf. Antimicrob. Agents Chemother., abstr. I-59, 1997).

Abacavir versus zidovudine combined with lamivudine and efavirenz, for the treatment of antiretroviral-naive HIV-infected adults

BACKGROUND

Zidovudine, lamivudine, and efavirenz comprise a highly effective and well-tolerated triple regimen for antiretroviral-naive patients. Evaluating other unique nucleoside reverse-transcriptase inhibitor (NRTI) combinations for long-term viral suppression is desirable.

METHODS

This multicenter, randomized, double-blind noninferiority clinical trial compared the efficacy and safety of abacavir with that of zidovudine plus lamivudine and efavirenz in 649 antiretroviral-naive HIV-infected patients. The primary objective was a comparison of proportions of patients achieving plasma HIV-1 RNA levels <or=50 copies/mL through week 48 of the study.

RESULTS

At study week 48, 70% of patients in the abacavir group, compared with 69% in the zidovudine group, maintained confirmed plasma HIV-1 RNA levels of <or=50 copies/mL (in the intent-to-treat exposed population). Virologic failure was infrequent (6% in the abacavir group and 4% in the zidovudine group). There was a significant CD4(+) cell response (209 cells/mm(3) in the abacavir group and 155 cells/mm(3) in the zidovudine group). Safety profiles were as expected.

CONCLUSION

Abacavir provided an effective and durable antiretroviral response that was noninferior to zidovudine, when combined with lamivudine and efavirenz.

Epidemiological risk factors for hypersensitivity reactions to abacavir

We investigated risk factors for hypersensitivity reactions (HSR) to abacavir in a case-control study. In a multivariate analysis, white race [odds ratio (OR), 5.16; 95% confidence interval (CI), 1.16-22.97] and a higher CD8 cell count at initiation of abacavir (>850 vs. < or =850 cells: OR, 3.74; 95% CI, 1.19-11.77) were found to be significantly associated with the development of HSR. Age, gender, stage of disease, prior antiretroviral exposure and type of concurrent antiretroviral therapy were not associated with HSR. Differences in predisposition to HSR according to ethnicity and baseline CD8 cell count may be explained by the reported MHC genetic associations with HSR.

Antiretroviral Therapy-associated Serious and Life-threatening Toxicities

In the late 1980s and early 1990s, when HIV/AIDS had become the leading cause of death in 25- to 44-year-old persons in the United States, it was acceptable to prescribe newer antiretroviral therapy such as zidovudine, which has significant bone marrow toxicities but can potentially improve patient survival. Although current antiretroviral therapy is not likely to eradicate HIV-1 infection, the advances in the use of combination antiretroviral therapy (including protease inhibitors and non-nucleoside reverse transcriptase inhibitors) have dramatically improved the overall survival, immune status, and productivity of HIV-infected individuals in developed countries. Instead of prevention and treatment of HIV-associated complications, many of the patients" clinic visits are focused on finding strategies to manage and prevent antiretroviral therapy-associated complications. Because only a few HIV-infected persons fulfilling stringent inclusion criteria were included in premarketing clinical trials and because the US Food and Drug Administration"s (FDA) accelerated approval process for antiretroviral therapy requires only 24-week safety and efficacy data, newly emerging and previously unrecognized adverse effects of antiretroviral therapy continue to surface when these drugs are administered to a larger patient population for a longer duration. Unfortunately, some of these adverse effects can be unpredictable and serious, and, if not recognized early and managed aggressively, can lead to fatality. This article reviews four of the most serious, life-threatening toxicities associated with antiretroviral therapy.

Therapeutic drug monitoring in the treatment of HIV-infection

The use of therapeutic drug monitoring (TDM) in the treatment of HIV-infection is gaining momentum in resource-rich countries. However, data justifying its use is still in short supply. In this manuscript we review the necessary components of TDM before it should be implemented in widespread clinical use. In addition, we provide specific examples of clinical situations where TDM is likely to useful. The overall conclusion of this review is that TDM is a promising therapeutic modality for improving antiretroviral efficacy and reducing toxicity. However, more prospective clinical trials are necessary in order to validate the therapeutic concentrations of antiretroviral drugs suggested by various investigators. In addition, both the clinical utility and cost effectiveness of TDM will need to be demonstrated by well-designed and adequately powered clinical trials in both antiretroviral nai;ve and experienced subjects. At this point in time we consider TDM in the treatment of HIV-infection as experimental with significant promise for the future.

Hyperlactataemia syndromes associated with HIV therapy

Hyperlactataemia is seen in 8-18.3% of HIV-infected patients taking nucleoside-analogue reverse transcriptase inhibitors (NRTIs). Recent epidemiological studies suggest that most episodes are transient and subclinical. However, symptomatic and occasionally life-threatening cases accompanied by metabolic acidosis and hepatic steatosis (ie, lactic acidosis syndrome) have also been described. Though yet to be fully elucidated, the proposed mechanism is NRTI-induced inhibition of mitochondrial DNA polymerase culminating in derangements in oxidative phosphorylation and lactate homeostasis. Signs and symptoms range from mild hyperlactataemia accompanied by nausea, abdominal discomfort, and weight loss to severe, intractable lactic acidosis complicated by coma and multi-organ failure. Significant progress has recently been made with regard to the natural history of NRTI-related hyperlactataemia. However, other important aspects of the disorder, such as its pathogenesis, predisposing conditions, and management, remain poorly understood. This article reviews the current published work on these issues, identifies areas of controversy, and addresses directions for future research.

Determining the antiviral activity of tenofovir disoproxil fumarate in treatment-naive chronically HIV-1-infected individuals

OBJECTIVE

To assess the efficacy of tenofovir disoproxil fumarate (TDF) monotherapy by following the initial rate of decline in plasma viral load, which is a measure of the efficacy of therapy in blocking viral replication.

DESIGN

An open-label, single-site study of TDF monotherapy in 10 antiretroviral drug-naive chronically HIV-1-infected individuals.

METHODS

Antiviral responses were assessed at baseline and during 21 days of monotherapy with TDF by measuring plasma HIV-1 RNA levels. The rate of change in HIV-1 RNA from baseline was determined both by linear regression and by fitting to a published model. Slopes were compared with those previously determined for ritonavir monotherapy.

RESULTS

Over 21 days, mean plasma HIV-1 RNA levels in the TDF-treated patients fell 1.5 log(10) copies/ml (range, 0.7-2.0). The initial rates of decline in plasma HIV-1 RNA in the 10 TDF-treated patients and in 25 protease inhibitor-naive subjects treated with ritonavir monotherapy were nearly identical.

CONCLUSIONS

The reduction in plasma HIV-1 RNA with TDF monotherapy was comparable with the decline observed in previous studies of protease inhibitor monotherapy. TDF is a potent antiretroviral agent and has comparable inherent antiviral activity with that of ritonavir, a potent protease inhibitor. These data support further study of TDF-based regimens in simplified combinations of antiviral agents as initial treatment for chronic HIV-1 infection.

Antiretroviral-associated liver injury

ART-related hepatotoxicity can manifest in a variety of ways. Although benign, asymptomatic LEEs predominate, liver injury occurring in the context of either hypersensitivity or hyperlactatemia, represents a medical emergency and mandates immediate cessation of ART. Underpinning this broad spectrum of presentations are several, as yet poorly understood, mechanisms of liver damage that reflect contributions by constituents of HAART and host factors. Thus far, the most significant predisposing condition to emerge from clinical studies is chronic viral hepatitis. A more precise understanding, however, of the processes and factors that underlie ART-related hepatotoxicity is critical not only to the management of liver injury from current antiretroviral drugs but also to the design of safer drugs in the future.

K65R with and without S68: A New Resistance Profile in Vivo Detected in Most Patients Failing Abacavir, Didanosine and Stavudine

Antiretroviral treatment with three nucleoside reverse transcriptase inhibitors (NRTIs) is widely used, but the combination of abacavir, didanosine and stavudine has never been investigated.

We describe the surprising and consistent genotypic and phenotypic outcome in patients failing this combination. As part of a Danish multicentre study, 60 antiretroviral-naive patients were randomized to treatment with abacavir, didanosine and stavudine. Failure was defined as one HIV-1 RNA >400 copies/ml. Genotyping was performed using TrueGene™ HIV-1 assay (Visible Genetics, London, UK). Phenotypic susceptibilities were determined with the Virco Antivirogram assay.

Eight patients failed treatment with a median viral load of 2.980 copies/ml (range 478-5.950).

At baseline, five patients were wild-type. Three patients harboured nucleoside excision mutations (NEMs), but phenotypic susceptibilities were within normal range.

All five patients with wild-type virus developed K65R and four of these patients also acquired the S68G mutation. Phenotypic susceptibility decreased towards abacavir (median 8.9-fold) and didanosine (median 3.2-fold), while susceptibility towards stavudine was unchanged (median 0.8-fold). Susceptibility towards lamivudine and tenofovir decreased median 14.2- and 4.0-fold, respectively. In two patients with baseline resistance mutations, further accumulation of NEMs and V75T or L74V was observed. One patient developed Q151M.

Failure of a triple NRTI regimen is possible and frequent with only the K65R mutation. Under adequate selection pressure K65R can easily emerge in vivo and may compromise several future treatment options including newer NRTIs. The unexpected high incidence of S68G suggests a functional role of this mutation in viruses harbouring K65R.

The abacavir hypersensitivity reaction: a review

BACKGROUND

Abacavir sulfate is a recent addition to the nucleoside reverse-transcriptase inhibitor class of antiretroviral agents used in the treatment of HIV infection. It is approved for use in combination with other antiretroviral agents. Its tolerability has been studied, but the overall clinical relevance of the findings has yet to be determined.

OBJECTIVES

This review investigates available data on the abacavir hypersensitivity reaction (HSR) and provides a clinical perspective on maximizing this agent's tolerability and effective incorporation into antiretroviral regimens.

METHODS

Relevant data were identified through MEDLINE and AIDSLINE searches of the English-language literature from 1966 through 2002 using the terms abacavir and 1592U89, the investigational new drug designation for abacavir. The reference lists of identified articles were searched for additional documents. Additional information was obtained from the US Food and Drug Administration and the drug's manufacturer.

RESULTS

The abacavir HSR occurs in <5% of all patients started on therapy; the incidence appears to be unaffected by specific demographic characteristics or disease stage. Accurate diagnosis and appropriate patient education are essential, because reintroduction of abacavir in a patient with a history of possible HSR has been shown to result in a profound worsening of symptoms, including acute, severe hypersensitivity syndrome and possible death-even with aggressive treatment. Careful evaluation is necessary to distinguish an HSR from other manifestations of antiretroviral therapy. Despite the risk of HSR, compared with other anti-HIV medications, abacavir has demonstrated an overall favorable adverse-event profile.

CONCLUSIONS

The risk of abacavir HSR must be taken into consideration when selecting initial antiretroviral therapy for patients with HIV infection. Careful, appropriate evaluation is necessary to rule out an HSR and determine whether the medication can be continued.

Abacavir hypersensitivity reaction

A hypersensitivity reaction occurs in association with initiation of abacavir therapy as part of combination antiretroviral therapy in approximately 3.7% of patients. The reaction is possibly the result of a combination of altered drug metabolism and immune dysfunction, which is poorly understood. White patients appear to be at higher risk and patients of African descent at lower risk of abacavir hypersensitivity. Clinical management involves supportive measures and discontinuation of abacavir therapy. Rechallenge with abacavir in a hypersensitive patient should be avoided because it might precipitate a life-threatening reaction.

Comparison of dual nucleoside-analogue reverse-transcriptase inhibitor regimens with and without nelfinavir in children with HIV-1 who have not previously been treated: the PENTA 5 randomised trial

INTRODUCTION

Treatment options for children with HIV-1 are limited. We aimed to compare activity and safety of three dual-nucleoside analogue reverse-transcriptase inhibitor (NRTI) regimens with or without a protease inhibitor in previously untreated children with HIV-1.

METHODS

In our multicentre trial, we randomly assigned 36 children to zidovudine and lamivudine, 45 to zidovudine and abacavir, and 47 to lamivudine and abacavir. Children who were symptom-free (n=55) were also randomly assigned to receive nelfinavir or placebo. Children with more advanced disease received open-label nelfinavir (73). Primary endpoints were change in plasma HIV-1 RNA at 24 and 48 weeks for the NRTI comparison and occurrence of serious adverse events for both randomised comparisons. Analyses were by intention to treat.

FINDINGS

Children had a median CD4 percentage of 22% (IQR 15-29) and a mean HIV-1 RNA concentration of 5.0 log copies/mL (SD 0.8). One child was lost to follow-up and one died of sepsis. At 48 weeks, in the zidovudine/lamivudine, zidovudine/abacavir, and lamivudine/abacavir groups, mean HIV-1 RNA had decreased by 1.71, 2.19, and 2.63 log copies/mL, respectively (estimated in absence of nelfinavir) (p=0.02 after adjustment for baseline factors). One child had a hypersensitivity reaction to abacavir; and three with possible reactions stopped abacavir. There were 24 serious adverse events--six in the symptom-free children (all on nelfinavir), but none were attributed to nelfinavir.

INTERPRETATION

Regimens containing abacavir were more effective than zidovudine/lamivudine. Such regimens could be combined with protease inhibitors and non-nucleoside reverse transcriptase inhibitors for safe and effective treatment of previously untreated children with HIV-1.

Hypersensitivity reactions during therapy with the nucleoside reverse transcriptase inhibitor abacavir

BACKGROUND

Hypersensitivity reactions consist of a variable group of clinical findings and have been described for a wide variety of chemical compounds.

OBJECTIVE

This review characterizes the clinical profile of hypersensitivity to the nucleoside reverse transcriptase inhibitor abacavir sulfate.

METHODS

We performed a retrospective medical review of pooled adverse events data from approximately 200,000 patients who received abacavir in clinical trials, through expanded-access programs, or by prescription from 1996 through 2000. Screened cases of hypersensitivity were classified as either definitive or probable. Definitive cases were identified when initial symptoms resolved on interruption of abacavir therapy and returned on reintroduction of abacavir therapy.

RESULTS

A total of 1803 cases were identified, 1302 in the 30,595 patients participating in clinical trials or the expanded-access program and 501 in patients from the post-marketing experience. On review, 176 (9.8%) of these cases were considered definitive and the remainder probable. Based on the 1302 cases identified in clinical trials or the expanded-access program, the calculated incidence of hypersensitivity was 4.3%. Symptoms reported in > or = 20% of cases of this multiorgan reaction included fever, rash, malaise/fatigue, and gastrointestinal symptoms such as nausea, vomiting, and diarrhea, among others. Respiratory symptoms occurred in 30% of cases and included dyspnea (12%), cough (10%), and pharyngitis (6%). In 90% of cases, hypersensitivity reactions occurred within the first 6 weeks after initiation of abacavir (median time, 11 days); after an initial reaction, rechallenge with abacavir resulted in the reappearance of symptoms within hours of reexposure. Hypotension was present in 25% of these rechallenge reactions. Among patients who received abacavir in clinical trials, the mortality rate was 0.03% (3 per 10,000 patients).

CONCLUSIONS

Hypersensitivity to abacavir is an idiosyncratic reaction and a distinct clinical syndrome characterized predominantly by systemic involvement. It can be expected to appear as a treatment-limiting event in approximately 5% of patients. The appearance of clinical symptoms consistent with this syndrome mandates immediate discontinuation of abacavir. Hypersensitivity to abacavir is an absolute contraindication to subsequent treatment with any formulation that includes this agent.

Impact of immune interventions on proviral HIV-1 DNA decay in patients receiving highly active antiretroviral therapy

OBJECTIVE

To measure the evolution of proviral HIV-1 DNA levels in patients receiving highly active antiretroviral therapy (HAART) compared to those treated with HAART plus interleukin-2 (IL-2) and hydroxyurea.

DESIGN

Prospective randomised trial.

METHODS

Twenty-two HIV-1 infected patients were randomly assigned to a five-drug antiretroviral regimen for 72 weeks, with or without IL-2, followed by a three-drug regimen up to week 120 with additional hydroxyurea in patients having received IL-2. HIV-1 DNA levels in peripheral blood mononuclear cells (PBMC) were measured regularly using the Amplicor Monitor kit from Roche Diagnostics (Meylan, France). Potentially infectious HIV-1 was cultured in enhanced conditions from circulating CD4 T cells at week 120.

RESULTS

During the study period of 120 weeks, HIV-1 DNA levels in PBMC decreased by -1.1 log in patients treated with HAART only compared with -1.8 log in patients with additional IL-2 and hydroxyurea. A two-phase decay rate was observed, with an inflexion point at 12 weeks. The second decay was slow, with mean half-lives of 130.1 +/- 21.3 weeks and 95.1 +/- 26.3 weeks for patients on HAART and those receiving additional IL-2 and hydroxyurea, respectively. At week 120, one out of 11 patients with HAART alone compared to six out of 11 in the group with IL-2 and hydroxyurea had undetectable proviral DNA levels and three of them had unsuccessful recovery of replication-competent HIV-1 from blood CD4 T cells.

CONCLUSION

Therapeutic strategies combining HAART and immune interventions have higher potency to decrease the number of infected cells than HAART alone.

Simultaneous determination of Ziagen and its phosphorylated metabolites by ion-pairing high-performance liquid chromatography-tandem mass spectrometry

An ion-paring HPLC-MS-MS method with positive ion mode electrospray ionization has been developed to simultaneously quantify Ziagen, carbovir monophosphate, carbovir diphosphate and carbovir triphosphate. N',N'-Dimethylhexylamine was used as the ion-pairing agent. The presence of this ion-pairing agent allowed the retention and separation of the four compounds on a reversed-phase HPLC column as well as the detection of the nucleotides with positive ion mode electrospray ionization. The limits of detection were found to be better than 25 nM for all the analytes. Calibration curves of the analytes showed excellent linearity over the range of 25 nM to 5 microM. The relative standard deviations and accuracies for replicate analyses of quality control samples were less than 15%. The method has been successfully applied to the analysis of these compounds in human liver cells treated with Ziagen.

Differential susceptibility of retroviruses to nucleoside analogues

Retroviruses may cause diseases in their vertebrate hosts. They are distinguished by their common means of replication involving reverse transcription, a process inhibited by nucleoside reverse transcriptase inhibitors (NRTIs) and other compounds used in antiretroviral chemotherapy. Previous work on NRTIs has been limited to their effect on human immunodeficiency virus (HIV) (for review see Ho & Hitchcock, 1989; Weller, 1999) and little information exists regarding the efficacy and therapeutic potential of these drugs against other retroviruses. We have tested all six NRTIs licensed for HIV treatment [didanosine (ddI), zalcitabine (ddC), lamivudine (3TC), stavudine (d4T), zidovudine (AZT) and abacavir (ABC)] against seven retroviruses representative of the traditional subfamilies: Spumavirinae, Lentivirinae and the Oncovirinae. As expected, each drug showed a range of activities against the panel of retroviruses, some drugs inhibiting other viruses at concentrations well below those required for HIV. Overall, AZT was the most active inhibitor (IC50 range, 0.032-1.0 microM), being most active against the Spuma (foamy) viruses. Abacavir was inhibitory for HIV-1, MN strain (HIV-1 MN), amphotrophic murine leukemia virus (MLV-A) and simian foamy virus type 6 (SFV-6). The least effective inhibitor, 3TC (IC50 range, 0.32->100 microM), was most potent against simian retrovirus types 1 and 2 (SRV-1, SRV-2) and HIV-1, but did not inhibit foamy viruses and MLV-A. Additionally, there were differences in the concentration of drug required to inhibit closely related viruses. Taken together, these data suggest that NRTIs have a wide spectrum of antiretroviral activity and the activity of compounds, even against closely related retroviruses, cannot be predicted.

Antiretroviral Activity and Safety of Abacavir in Combination with Selected HIV-1 Protease Inhibitors in Therapy-Naive HIV-1-Infected Adults

Objective

To assess antiretroviral efficacy and safety of abacavir in combination with selected HIV-1 protease inhibitors.

Design

A 48-week, open-label study.

Materials and Methods

Eighty-two antiretroviral naive HIV-1-infected adults (CD4 cell count ≥100 cells/mm3, plasma HIV-1 RNA ≥5000 copies/ml) were randomly assigned to receive abacavir (300 mg twice daily) in combination with standard doses of one of five protease inhibitors: indinavir, saquinavir soft-gel, ritonavir, nelfinavir or amprenavir. Adults who met protocol-defined switch criteria at or after week 8 could modify their randomized therapy. Antiretroviral activity was assessed by the proportion of subjects with plasma HIV-1 RNA ≤400 and ≤50 copies/ml, and by changes in plasma HIV-1 RNA levels and CD4 cell counts. Safety was assessed by monitoring clinical adverse events and laboratory abnormalities.

Results

At week 48, the proportion of subjects in the indinavir, saquinavir, ritonavir, nelfinavir and amprenavir groups with plasma HIV-1 RNA ≤400 copies/ml was 53, 50, 50, 41 and 56%, respectively, and the proportion with HIV-1 RNA ≤50 copies/ml was 47, 56, 50, 47, and 44%, respectively (by intent-to-treat analysis). Median reductions from baseline in plasma HIV-1 RNA for each group ranged from 1.7 to 2.4 log10 copies/ml. The median CD4 cell count increase from baseline was 195, 131, 116, 136 and 259 cells/mm3 in the indinavir, saquinavir, ritonavir, nelfinavir, and amprenavir groups, respectively. Overall, the most common adverse events attributed to study drugs were diarrhoea, nausea, malaise/fatigue, headache and perioral paresthesia. The frequency of treatment-limiting adverse events did not differ between groups. Conclusions: Abacavir is safe and effective when used in combination with a protease inhibitor.

Treatment Intensification with Abacavir in HIV-Infected Patients with at Least 12 Weeks Previous Lamivudine/Zidovudine Treatment

Objectives

To demonstrate that lamivudine and zidovudine, given separately (lamivudine/zidovudine) or as a single combination tablet (Combivir™), had equivalent efficacy. To evaluate the safety and antiretroviral activity of intensification with abacavir in patients treated with lamivudine/zidovudine for ≥12 weeks.

Design

A 12-week, equivalence study of lamivudine/ zidovudine versus Combivir. Patients who completed this study could enter a 48-week, intensification study of Combivir plus abacavir.

Methods

In the equivalence study, treatment-naive patients were assessed for HIV-1 RNA, CD4 cell count and genotype. The same assessments plus phenotype were made in the intensification study. Serious adverse events were recorded in the equivalence study and all adverse events in the intensification study.

Results

Lamivudine/zidovudine ( n=40) and Combivir ( n=35) gave equivalent reductions in plasma HIV-1 RNA levels at week 12. An identical proportion of patients (74%) in each treatment group harboured virus with the M184V mutation after 12 weeks. Fifty-two patients entered the intensification study and 44 completed 48 weeks of treatment. At the time of intensification with abacavir, all 35 patients with evaluable isolates harboured HIV-1 containing M184V. Addition of abacavir to Combivir led to further decreases in plasma HIV-1 RNA and increases in CD4 cell counts compared with the start of intensification ( P<0.001 at week 48). After 48 weeks of triple therapy, multi-nucleoside resistance mutations at codons 69 and 151 were not detected in any patients. All treatment regimens were generally well tolerated. Conclusion: Lamivudine/zidovudine and Combivir have equivalent antiretroviral activity over 12 weeks. Adding abacavir to Combivir can be a safe and effective therapeutic option for patients, including those harbouring virus with the M184V mutation.

A randomized, double-blind study of triple nucleoside therapy of abacavir, lamivudine, and zidovudine versus lamivudine and zidovudine in previously treated human immunodeficiency virus type 1-infected children. The CNAA3006 Study Team

OBJECTIVES

Abacavir (ABC) is a potent inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. We compared the efficacy, safety, and tolerability of combination therapy with ABC, lamivudine (3TC), and zidovudine (ZDV) versus 3TC and ZDV in antiretroviral experienced HIV-1-infected children over 48 weeks.

METHODS

Two hundred five HIV-1-infected children who had received previous antiretroviral therapy and had CD4(+) cell counts >/=100 cells/mm(3) were stratified by age and by previous treatment. Participants were randomly assigned to receive ABC (8 mg/kg twice daily [BID]) plus 3TC (4 mg/kg BID) and ZDV (180 mg/m(2) BID; ABC/3TC/ZDV group) or ABC placebo plus 3TC (4 mg/kg BID) and ZDV (180 mg/m(2); 3TC/ZDV group). Participants who met a protocol-defined switch criteria (plasma HIV-1 RNA >0.5 log(10) copies/mL above baseline at week 8 or >10 000 copies/mL after week 16) had the option to switch to open-label ABC plus any antiretroviral combination or continue randomized therapy or withdraw from the study.

RESULTS

The Kaplan-Meier estimates (95% confidence interval) of the proportion of participants who maintained HIV-1 RNA levels </=10 000 copies/mL for 48 weeks or more was significantly better in the ABC/3TC/ZDV group compared with the 3TC/ZDV group: 33% (23%-42%) versus 21% (13%-29%). At week 48, the proportions of participants with HIV-1 RNA </=10 000 copies/mL were 36% versus 26% for the ABC/3TC/ZDV and 3TC/ZDV groups, respectively, by intent-to-treat analysis. For the subgroup of participants with baseline HIV-1 RNA >10 000 copies/mL, a significantly higher proportion of participants in the ABC/3TC/ZDV group had HIV-1 RNA </=10 000 copies/mL compared with the 3TC/ZDV group (29% vs 12%) but no difference was observed in the subgroup of participants with baseline HIV-1 RNA </=10 000 copies/mL (78% vs 72%). The median changes from baseline in CD4(+) cell counts were greater in the ABC/3TC/ZDV group than in the 3TC/ZDV group. Few participants (3%) experienced abacavir-related hypersensitivity reaction.

CONCLUSIONS

ABC, in combination with 3TC and ZDV, provides additional antiretroviral activity over 48 weeks, compared with combination therapy with 3TC and ZDV in antiretroviral experienced HIV-1-infected children. ABC was safe and generally well-tolerated and should be considered an active component of combination antiretroviral therapy in this pediatric population.

Significant Toxicities Associated with Antiretroviral Therapy

Use of at least three potent antiretroviral agents has become the standard of care in the management of HIV infection. The potential toxicities associated with highly active antiretroviral therapy (HAART) however, may limit a patient’s ability to adhere to and tolerate these agents. Although a comprehensive discussion of all toxicities associated with HAART is beyond the scope of this article, selected short-term and long-term significant toxicities will be reviewed. Short-term toxicities that will be discussed include abacavir-induced hypersensitivity reactions, efavirenz-associated central nervous system side effects and rash associated with the non-nucleoside reverse transcriptase inhibitors (NNRTIs) and the protease inhibitor (PI) amprenavir. Several long-term toxicities associated with the nucleoside reverse transcriptase inhibitors (NRTIs) are hypothesized to be due to mitochondrial toxicity. These toxicities include myositis and lactic acidosis with hepatic steatosis, pancreatitis and peripheral neuropathy. Some experts also hypothesize that mitochondrial toxicity is responsible for the lipodystrophy syndrome, which includes hyperglycemia, abnormal fat redistribution and dyslipidemia. Finally, indinavir-associated nephrolithiasis, which may present with either short term or long term use will be discussed. This article will provide the practicing pharmacist with a review of these significant toxicities, the implicated agents, incidence, usual clinical presentation, and recommendations for management.

Antiretroviral therapy of HIV-1 infection: established treatment strategies and new therapeutic options

Recently, studies have shown that non-nucleoside reverse transcriptase inhibitors, such as efavirenz or nevirapine, in combination with two nucleoside analogues have an antiretroviral potency comparable to protease inhibitor containing regimens. Triple combination therapy that includes a non-nucleoside reverse transcriptase inhibitor can therefore be regarded as an effective alternative first-line treatment of HIV-1 infection.

Immunological and virological responses in HIV-1-infected adults at early stage of established infection treated with highly active antiretroviral therapy

OBJECTIVE

To evaluate the immunological and virological responses to highly active antiretroviral therapy (HAART) in blood and lymphoid compartments of HIV-1-infected patients at an early stage of infection.

DESIGN

An open-label, observational, non-randomized, prospective trial of outpatients attending the Centre of Clinical Investigation in Infectious Diseases, Centre Hospitalier Universitaire Vaudois, University of Lausanne, Switzerland.

SUBJECTS

Forty-one antiretroviral-naive HIV-1-infected adults with 400 CD4 T cells/microl or greater and 5000 plasma HIV-1-RNA copies/ml or greater were enrolled, and 32 finished the study. Forty-nine HIV-negative individuals were included as controls. All subjects gave written informed consent.

INTERVENTIONS

All patients received abacavir 300 mg by mouth every 12 h and amprenavir 1200 mg by mouth every 12 h for 72 weeks.

MAIN OUTCOME MEASURES

The extent of immune reconstitution in blood and lymph nodes after 72 weeks of HAART was evaluated, and compared with immunological measures of 49 HIV-negative subjects.

RESULTS

Virus replication was effectively suppressed (-3.5 log10 at week 72). Substantial increments of CD4 T cell count in blood and percentage in lymph nodes were observed over time, and these measures were comparable to HIV-negative subjects by week 24 in blood and by week 48 in lymph nodes. The increase was equally distributed between naive and memory CD4 T cells. Recovery of HIV-specific CD4 responses occurred in 40% of patients.

CONCLUSION

The initiation of HAART at an early stage of established HIV infection induces systemic quantitative normalization of CD4 T cells, a partial recovery of HIV-specific CD4 cell responses, and effective and durable suppression of virus replication.

Abacavir: a review of its clinical potential in patients with HIV infection

Abacavir is a carbocyclic 2'-deoxyguanosine nucleoside analogue. It is metabolised intracellularly to a 2'-deoxyguanosine nucleoside analogue which competitively inhibits HIV reverse transcriptase and terminates proviral DNA chain extension. In double-blind trials in antiretroviral therapy-experienced or -naive patients, reductions in HIV RNA levels were greater and more prolonged in patients receiving abacavir in combination with other antiretroviral drugs than in those receiving placebo in combination with the same agents. Furthermore, abacavir in combination with lamivudine and zidovudine reduced viral load to below detectable levels in a proportion of patients, and to a similar extent to the protease inhibitor indinavir in combination with lamivudine and zidovudine. Greatest viral load reductions were seen in antiretroviral therapy-naive patients. Preliminary results suggest that the viral suppression achieved with a protease inhibitor plus 2 nucleoside reverse transcriptase inhibitors (NRTIs) can be maintained as effectively with abacavir in combination with 2 NRTIs as it can be by continuing the protease inhibitor-containing treatment regimen. Initial virological data from studies of combination regimens including abacavir and protease inhibitors appear promising but larger controlled trials are required to confirm these observations. Nausea is the most frequently reported adverse event in patients receiving abacavir-containing combination therapy. Adverse events tend to be reported most frequently soon after starting treatment; the majority of events are mild or moderate in intensity and transient. Other adverse events reported in >5% of patients include vomiting, malaise and fatigue, headache, diarrhoea, sleep disorders, cough, anorexia and rash. A major cause of abacavir treatment discontinuation is the development of a hypersensitivity reaction which has been reported in 3 to 5% of patients. The reaction usually occurs within 6 weeks of commencing treatment, shows evidence of multiorgan system involvement and typically includes fever and/or rash. Symptoms resolve rapidly after discontinuation of treatment. Continuing treatment or rechallenge can result in more severe symptoms, life-threatening hypotension and even death.

CONCLUSION

Abacavir used in combination with other antiretroviral drugs effectively reduces viral load in both adults and children with HIV infection. Although these responses are greatest in individuals with little or no previous antiretroviral treatment, useful responses are still sometimes achieved in heavily pretreated individuals. Abacavir in combination with lamivudine and zidovudine provides a simple and convenient dosage regimen which is generally well tolerated, able to produce sustained suppression of viral replication and has the advantage of sparing other classes of antiretroviral drugs for subsequent use. This triple combination represents an alternative antiretroviral regimen for patients intolerant to protease inhibitors or those wishing to retain the option of protease inhibitors for later use. Further clinical studies are needed to define the activity of abacavir in combination with protease inhibitors and non-nucleoside reverse transcriptase inhibitors.