Abacavir: absolute bioavailability, bioequivalence of three oral formulations, and effect of food

Chemometrics as a valuable tool for evaluating interactions between antiretroviral drugs and food

AIMS

Clinically significant interactions with food occur for more than half of antiretroviral drugs. Different physiochemical properties deriving from the chemical structures of antiretroviral drugs may contribute to the variable food effect. Chemometric methods allow analysing a large number of interrelated variables concomitantly and visualizing correlations between them. We used a chemometric approach to determine the types of correlations among different features of antiretroviral drugs and food that may influence interactions.

METHODS

Thirty-three antiretroviral drugs were analysed: ten nucleoside reverse transcriptase inhibitors, six non-nucleoside reverse transcriptase inhibitors, five integrase strand transfer inhibitors, ten protease inhibitors, one fusion inhibitor and one HIV maturation inhibitor. Input data for the analysis were collected from already published clinical studies, chemical records and calculations. We constructed a hierarchical partial least squares (PLS) model with three response parameters: postprandial change of time to reach maximum drug concentration (ΔTmax ), albumin binding (%) and logarithm of partition coefficient (logP). Predictor parameters were the first two principal components of principal component analysis (PCA) models for six groups of molecular descriptors.

RESULTS

PCA models explained 64.4% to 83.4% of the variance of the original parameters (average: 76.9%), whereas the PLS model had four significant components and explained 86.2% and 71.4% of the variance in the sets of predictor and response parameters, respectively. We observed 58 significant correlations between ΔTmax , albumin binding (%), logP and constitutional, topological, hydrogen bonding and charge-based molecular descriptors.

CONCLUSIONS

Chemometrics is a useful and valuable tool for analysing interactions between antiretroviral drugs and food.

Effect of Food on the Pediatric Dispersible Tablet Formulations of TRIUMEQ and DOVATO in Healthy Adult Participants

This randomized food effect study in healthy adult participants examined dispersible tablet formulations of fixed-dose combinations of dolutegravir/abacavir/lamivudine (TRIUMEQ) and dolutegravir/lamivudine (DOVATO). While adult tablet formulations of these combinations are currently approved for the treatment of human immunodeficiency virus, alternate formulations for children are urgently needed to facilitate appropriate pediatric dosing for patients who may have difficulty swallowing a conventional tablet. This study compared the effect of a high-fat, high-calorie meal on the pharmacokinetics, safety, and tolerability of dispersible tablet (DT) formulations of the two-drug and three-drug regimens, with administration under fasting conditions. Both the two-drug and three-drug dispersible tablet formulations, administered under fasting conditions and following a high-fat, high-calorie meal, were well tolerated in healthy participants. There were no clinically relevant differences in drug exposure for either regimen when administered with a high-fat meal as compared to under fasting conditions. Safety observations were similar for both treatments, either in the fed or fasted state. Both TRIUMEQ DT and DOVATO DT formulations can be administer with or without food.

Interactions of Antiretroviral Drugs with Food, Beverages, Dietary Supplements, and Alcohol: A Systematic Review and Meta-analyses

Multiple factors may affect combined antiretroviral therapy (cART). We investigated the impact of food, beverages, dietary supplements, and alcohol on the pharmacokinetic and pharmacodynamic parameters of 33 antiretroviral drugs. Systematic review in adherence to PRISMA guidelines was performed, with 109 reports of 120 studies included. For each drug, meta-analyses or qualitative analyses were conducted. We have found clinically significant interactions with food for more than half of antiretroviral agents. The following drugs should be taken with or immediately after the meal: tenofovir disoproxil, etravirine, rilpivirine, dolutegravir, elvitegravir, atazanavir, darunavir, lopinavir, nelfinavir, ritonavir, saquinavir. Didanosine, zalcitabine, zidovudine, efavirenz, amprenavir, fosamprenavir, and indinavir should be taken on an empty stomach for maximum patient benefit. Antiretroviral agents not mentioned above can be administered regardless of food. There is insufficient evidence available to make recommendations about consuming juice or alcohol with antiretroviral drugs. Resolving drug-food interactions may contribute to maximized cART effectiveness and safety.

Pharmacokinetics and Drug-Drug Interactions of Abacavir and Lamuvudine Co-administered With Antituberculosis Drugs in HIV-Positive Children Treated for Multidrug-Resistant Tuberculosis

Given the high prevalence of multidrug-resistant (MDR)-TB in high HIV burden settings, it is important to identify potential drug-drug interactions between MDR-TB treatment and widely used nucleoside reverse transcriptase inhibitors (NRTIs) in HIV-positive children. Population pharmacokinetic models were developed for lamivudine (n = 54) and abacavir (n = 50) in 54 HIV-positive children established on NRTIs; 27 with MDR-TB (combinations of high-dose isoniazid, pyrazinamide, ethambutol, ethionamide, terizidone, fluoroquinolones, and amikacin), and 27 controls without TB. Two-compartment models with first-order elimination and transit compartment absorption described both lamivudine and abacavir pharmacokinetics, respectively. Allometric scaling with body weight adjusted for the effect of body size. Clearance was predicted to reach half its mature value ∼ 2 (lamivudine) and ∼ 3 (abacavir) months after birth, with completion of maturation for both drugs at ∼ 2 years. No significant difference was found in key pharmacokinetic parameters of lamivudine and abacavir when co-administered with routine drugs used for MDR-TB in HIV-positive children.

Abacavir pharmacokinetics in African children living with HIV: A pooled analysis describing the effects of age, malnutrition and common concomitant medications

Aims

Abacavir is part of WHO‐recommended regimens to treat HIV in children under 15 years of age. In a pooled analysis across four studies, we describe abacavir population pharmacokinetics to investigate the influence of age, concomitant medications, malnutrition and formulation.

Methods

A total of 230 HIV‐infected African children were included, with median (range) age of 2.1 (0.1–12.8) years and weight of 9.8 (2.5–30.0) kg. The population pharmacokinetics of abacavir was described using nonlinear mixed‐effects modelling.

Results

Abacavir pharmacokinetics was best described by a two‐compartment model with first‐order elimination, and absorption described by transit compartments. Clearance was predicted around 54% of its mature value at birth and 90% at 10 months. The estimated typical clearance at steady state was 10.7 L/h in a child weighing 9.8 kg co‐treated with lopinavir/ritonavir, and was 12% higher in children receiving efavirenz. During coadministration of rifampicin‐based antituberculosis treatment and super‐boosted lopinavir in a 1:1 ratio with ritonavir, abacavir exposure decreased by 29.4%. Malnourished children living with HIV had higher abacavir exposure initially, but this effect waned with nutritional rehabilitation. An additional 18.4% reduction in clearance after the first abacavir dose was described, suggesting induction of clearance with time on lopinavir/ritonavir‐based therapy. Finally, absorption of the fixed dose combination tablet was 24% slower than the abacavir liquid formulation.

Conclusion

In this pooled analysis we found that children on lopinavir/ritonavir or efavirenz had similar abacavir exposures, while concomitant TB treatment and super‐boosted lopinavir gave significantly reduced abacavir concentrations.

The crosstalk between antiretrovirals pharmacology and HIV drug resistance

INTRODUCTION

The clinical development of antiretroviral drugs has been followed by a rapid and concomitant development of HIV drug resistance. The development and spread of HIV drug resistance is due on the one hand to the within-host intrinsic HIV evolutionary rate and on the other to the wide use of low genetic barrier antiretrovirals.

AREAS COVERED

We searched PubMed and Embase on 31 January 2020, for studies reporting antiretroviral resistance and pharmacology. In this review, we assessed the molecular target and mechanism of drug resistance development of the different antiretroviral classes focusing on the currently approved antiretroviral drugs. Then, we assessed the main pharmacokinetic/pharmacodynamic of the antiretrovirals. Finally, we retraced the history of antiretroviral treatment and its interconnection with antiretroviral worldwide resistance development both in , and middle-income countries in the perspective of 90-90-90 World Health Organization target.

EXPERT OPINION

Drug resistance development is an invariably evolutionary driven phenomenon, which challenge the 90-90-90 target. In high-income countries, the antiretroviral drug resistance seems to be stable since the last decade. On the contrary, multi-intervention strategies comprehensive of broad availability of high genetic barrier regimens should be implemented in resource-limited setting to curb the rise of drug resistance.

Pharmacokinetics of nucleoside/nucleotide reverse transcriptase inhibitors for the treatment and prevention of HIV infection

INTRODUCTION

Despite dramatic increases in new drugs and regimens, a combination of two nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) remains the backbone of many regimens to treat HIV.

AREA COVERED

This article summarizes the pharmacokinetic characteristics of approved NRTIs that are currently in the international treatment and prevention guidelines.

EXPERT OPINION

Compared to other NRTIs, tenofovir alafenamide fumarate (TAF) is more advantageous in terms of potency and safety. It is therefore a preferred choice in combination with emtricitabine (FTC) in most HIV treatment guidelines. The efficacy of the two-drug combination of NRTI/Integrase strand-transfer inhibitor, i.e. lamivudine/dolutegravir has been approved as an option for initial therapy. This regimen however has some limitations in patients with HBV coinfection. The two NRTI combinations tenofovir disproxil fumarate (TDF)/FTC and TAF/FTC have also been approved for pre-exposure prophylaxis (PrEP). Interestingly, a promising long-acting nucleoside reverse transcriptase translocation inhibitor, islatravir, formulated for implant was well tolerated and remained effective for up to a year, suggesting its potential as a single agent for PrEP. In the next decade, it remains to be seen whether NRTI-based regimens will remain the backbone of preferred ART regimens, or if the treatment will eventually move toward NRTI-sparing regimens to avoid long-term NRTI-toxicity.

Abacavir Exposure in Children Cotreated for Tuberculosis with Rifampin and Superboosted Lopinavir-Ritonavir

In children requiring lopinavir coformulated with ritonavir in a 4:1 ratio (lopinavir-ritonavir-4:1) and rifampin, adding ritonavir to achieve a 4:4 ratio with lopinavir (LPV/r-4:4) overcomes the drug-drug interaction. Possible drug-drug interactions within this regimen may affect abacavir concentrations, but this has never been studied. Children weighing <15 kg needing rifampin and LPV/r-4:4 were enrolled in a pharmacokinetic study and underwent intensive pharmacokinetic sampling on 3 visits: (i) during the intensive and (ii) continuation phases of antituberculosis treatment with LPV/r-4:4 and (iii) 1 month after antituberculosis treatment completion on LPV/r-4:1.

In children requiring lopinavir coformulated with ritonavir in a 4:1 ratio (lopinavir-ritonavir-4:1) and rifampin, adding ritonavir to achieve a 4:4 ratio with lopinavir (LPV/r-4:4) overcomes the drug-drug interaction. Possible drug-drug interactions within this regimen may affect abacavir concentrations, but this has never been studied. Children weighing <15 kg needing rifampin and LPV/r-4:4 were enrolled in a pharmacokinetic study and underwent intensive pharmacokinetic sampling on 3 visits: (i) during the intensive and (ii) continuation phases of antituberculosis treatment with LPV/r-4:4 and (iii) 1 month after antituberculosis treatment completion on LPV/r-4:1. Pharmacometric modeling and simulation were used to compare exposures across weight bands with adult target exposures. Eighty-seven children with a median (interquartile range) age and weight of 19 (4 to 64) months and 8.7 (3.9 to 14.9) kg, respectively, were included in the abacavir analysis. Abacavir pharmacokinetics were best described by a two-compartment model with first-order elimination and transit compartment absorption. After allometric scaling adjusted for the effect of body size, maturation could be identified: clearance was predicted to be fully mature at about 2 years of age and to reach half of this mature value at about 2 months of age. Abacavir bioavailability decreased 36% during treatment with rifampin and LPV/r-4:4 but remained within the median adult recommended exposure, except for children in the 3- to 4.9-kg weight band, in which the exposures were higher. The observed predose morning trough concentrations were higher than the evening values. Though abacavir exposure significantly decreased during concomitant administration of rifampin and LPV/r-4:4, it remained within acceptable ranges. (This study is registered in ClinicalTrials.gov under identifier NCT02348177.)

Crushing of dolutegravir fixed-dose combination tablets increases dolutegravir exposure

Background

If HIV patients are unconscious or cannot swallow tablets for other reasons, antiretroviral medication is crushed and dissolved prior to administration. Crushing can alter drug exposure, possibly leading to treatment failure, development of resistance or toxicity. Currently, there is no information about crushing of the branded fixed-dose combination of dolutegravir/abacavir/lamivudine (Triumeq®, referred to as TRI); therefore, crushing of TRI is not recommended.

Objectives

To investigate whether the TRI fixed-dose combination tablet can be crushed and combined with enteral nutrition without influencing pharmacokinetics (PK).

Methods

We carried out an open-label, three-period, randomized, single-dose, crossover trial in 22 healthy adult volunteers. Subjects randomly received whole-tablet TRI with fasting (reference), crushed and suspended TRI with fasting or crushed and suspended TRI with oral intake of enteral nutrition. Bioequivalence criteria (80%-125% acceptance range) of AUC0-∞ and Cmax were used. ClinicalTrials.gov: NCT02569346.

Results

Crushing TRI leads to higher dolutegravir exposure (AUC0-∞: +26% and Cmax: +30%) and, if crushed TRI is combined with enteral nutrition, to a decrease in abacavir Cmax (-17%). Lamivudine concentrations were not affected as geometric mean ratios with 90% CIs fell within the 80%-125% range.

Conclusions

Bioequivalence could not be demonstrated for a crushed and suspended tablet or a crushed and suspended tablet with oral intake of enteral nutrition compared with whole-tablet TRI with fasting. Both scenarios led to higher dolutegravir exposure, but this did not exceed exposure after intake with food or in twice-daily dosing. In our opinion, TRI can be crushed for patients with swallowing difficulties and can be simultaneously administered with enteral nutrition.

HLA-B*57:01 screening and hypersensitivity reaction to abacavir between 1999 and 2016 in the OPERA® observational database: a cohort study

Background

HLA-B*57:01 screening was added to clinical care guidelines in 2008 to reduce the risk of hypersensitivity reaction from abacavir. The uptake of HLA-B*57:01 screening and incidence of hypersensitivity reaction were assessed in a prospective clinical cohort in the United States to evaluate the effectiveness of this intervention.

Methods

We included all patients initiating an abacavir-containing regimen for the first time in the pre-HLA-B*57:01 screening period (January 1, 1999 to June 14, 2008) or the post-HLA-B*57:01 screening period (June 15, 2008 to January 1, 2016). Yearly incidence of both HLA-B*57:01 screening and physician panel-adjudicated hypersensitivity reactions were calculated and compared.

Results

Of the 9619 patients eligible for the study, 33% initiated abacavir in the pre-screening period and 67% in the post-screening period. Incidence of HLA-B*57:01 screening prior to abacavir initiation increased from 43% in 2009 to 84% in 2015. The incidence of definite or probable hypersensitivity reactions decreased from 1.3% in the pre-screening period to 0.8% in 2009 and further to 0.2% in 2015 in the post-screening period.

Conclusions

Frequency of HLA-B*57:01 screening increased steadily since its first inclusion in treatment guidelines in the United States. This increase in screening was accompanied by a decreasing incidence of definite or probable hypersensitivity reactions over the same period. However, a considerable proportion of patients initiating abacavir were not screened, representing a failed opportunity to prevent hypersensitivity reactions. Where HLA-B*57:01 screening is standard of care, patients should be confirmed negative for this allele before starting abacavir treatment.

Abacavir/lamivudine/dolutegravir single tablet regimen in patients with human immunodeficiency virus and end-stage renal disease on hemodialysis

No single-tablet antiretroviral (ARV) regimens (STRs) are approved for patients with human immunodeficiency virus (HIV) and end-stage renal disease (ESRD) on hemodialysis (HD). Based on known pharmacokinetic (PK) properties, abacavir (ABC)/lamivudine (3TC)/dolutegravir (DTG) STR may represent a promising option. This case series presents the safety and efficacy of ABC/3TC/DTG STR in patients with HIV and ESRD on HD. Patients were included if they were HIV-positive, maintained on intermittent HD for ESRD, switched to an ARV regimen containing ABC/3TC/DTG, and had at least one set of virologic data before and after the switch. Average age (±standard deviation) was 59 (±8) years. The majority of patients were cis-gender male and non-Hispanic Black. Only one demonstrated clinically significant resistance at baseline. All were on multiple-tablet regimens prior to the switch. Five patients (83%) achieved undetectable HIV-RNA after the switch while only four patients (46%) were undetectable immediately prior. No decline in immune function was noted. ABC/3TC/DTG STR was well tolerated. Only one patient self-reported an adverse event (nausea), which resolved without drug discontinuation. Based on these data, it appears that ABC/3TC/DTG may be a safe and effective ARV-STR option for patients with HIV and ESRD on HD. A larger trial including a PK analysis is needed to confirm these findings.

Clinical pharmacokinetics and pharmacodynamics of dolutegravir used as a single tablet regimen for the treatment of HIV-1 infection

INTRODUCTION

With the introduction of the coformulated dolutegravir, abacavir and lamivudine , a new single tablet regimen (STR) is made available for the use in treatment-naive and treatment-experienced HIV-infected patients. This drug combination is the fourth STR that will be positioned next to the STRs with efavirenz, rilpivirine or elvitegravir as third agents, respectively.

AREAS COVERED

The objective of this review is to provide an overview of the efficacy and safety of the combined dolutegravir/abacavir/lamivudine coformulation. The review will focus on dolutegravir and includes both published data as well as data presented at recent major international HIV/AIDS conferences.

EXPERT OPINION

The dolutegravir/abacavir/lamivudine regimen is highly effective in achieving sustained suppression of HIV-1 RNA plasma concentrations. The STR has a favorable safety profile and a low potential for drug interactions, which will contribute to a prominent role in therapy. As this STR contains abacavir as backbone component, the use requires patients to be HLA-B*5701 negative, with good hepatic function. Other first-line treatment combinations are preferred for patients with hepatitis B co-infection or with a high cardiovascular risk.

Absence of Food Effect on the Pharmacokinetics of Telbivudine Following Oral Administration in Healthy Subjects

The influence of food on the pharmacokinetics of telbivudine, a candidate antiviral agent against hepatitis B virus (HBV), was investigated in healthy adult subjects following a 600-mg oral dose administered with and without a high-fat/high-calorie meal. Telbivudine was well tolerated under fasting and fed conditions. Oral absorption of telbivudine as measured by maximum plasma concentration (Cmax), time to reach Cmax (Tmax), and area under the plasma concentration-time curve (AUC(0-t) and AUC(0-infinity)) was not altered by food intake immediately before oral dosing. Values of Cmax, Tmax, and AUC were comparable when telbivudine was administered under fed and fasting conditions. Results from this study indicated that the absorption of telbivudine was not affected by a high-fat/high-calorie meal; telbivudine can therefore be administered orally with no regard to the timing of meals.

Combination nucleoside/nucleotide reverse transcriptase inhibitors for treatment of HIV infection

INTRODUCTION

The combination of two nucleoside/nucleotide reverse transcriptase inhibitors (N(t)RTIs) and a third agent from another antiretroviral class is currently recommended for initial antiretroviral therapy. In general, N(t)RTIs remain relevant in subsequent regimens. There are currently six nucleoside reverse transcriptase inhibitors and one nucleotide reverse transcriptase inhibitor drug entities available, and several formulations that include two or more N(t)RTIs in a fixed-dose combination. These entities have heterogeneous pharmacological and clinical properties. Accordingly, toxicity, pill burden, dosing frequency, potential drug-drug interaction, preexisting antiretroviral drug resistance and comorbid conditions should be considered when constructing a regimen. This approach is critical in order to optimize virologic efficacy and clinical outcomes.

AREAS COVERED

This article reviews N(t)RTI combinations used in the treatment of HIV-infected adults. The pharmacological properties of each N(t)RTI, and the clinical trials that have influenced treatment guidelines are discussed.

EXPERT OPINION

It is likely that N(t)RTIs will continue to dominate the global landscape of HIV treatment and prevention, despite emerging interest in N(t)RTI-free combination therapy. Clinical domains where only few alternatives to N(t)RTIs exist include treatment of HIV/HBV coinfection and HIV-2. There is a need for novel N(t)RTIs with enhanced safety and resistance profiles compared with current N(t)RTIs.

Abacavir/lamivudine fixed-dose combination antiretroviral therapy for the treatment of HIV

In the past 15 years, improvements in the treatment of HIV infection have dramatically reduced morbidity and mortality. Nucleoside reverse transcriptase inhibitors are the backbone of combination antiretroviral therapy for the treatment of HIV. One of the recommended and commonly used therapies in this class is the once-daily fixed-dose combination of abacavir/lamivudine. Clinical studies and practice have shown these drugs to be potent, safe, and easy to use in a variety of settings; however, several recent reports have challenged the safety and efficacy claims among certain patient populations, including those at risk for cardiovascular disease and in those with high viral loads prior to treatment initiation. We reviewed abacavir/lamivudine as a treatment for HIV and discussed limitations of its use due to these controversial issues.

Abacavir and metabolite pharmacokinetics in HIV-1-infected children and adolescents

OBJECTIVES

Abacavir (ABC) oral clearance, adjusted for body size, is approximately 2 times higher for children than adults with a corresponding difference in dose regimens. However, there are limited data available in the adolescent population. The pharmacokinetics (PKs) of ABC and primary metabolites were determined in HIV-1-infected children and adolescents to evaluate age and patient characteristics as a basis for adjusting ABC dose regimens and to assess the influence of metabolite formation on PK parameters.

METHODS

Pediatric subjects 9-18 years of age receiving antiretroviral therapy for HIV-1 infection were stratified by Tanner stage and given a single 8 mg/kg dose of ABC oral solution. Blood samples (n = 10) were obtained over 8 hours and measured for ABC, glucuronide, and carboxylate metabolites using high-performance liquid chromatography. PK parameters for children (Tanner stages 1-2; TS1) and adolescents (Tanner stages 3-5; TS2) were compared.

RESULTS

Twenty-five subjects were enrolled. ABC mean (range) maximum concentration (Cmax; microg/mL), area under the curve (microg.hr/mL), half-life (hours), and apparent clearance (CL/F; mL/min per kg) for TS1 and TS2 were 3.5 (1.2-5.6) vs 3.4 (1.8-5.9), 8.0 (2.1-18.6) vs 8.9 (3.1-17.2), 1.3 (0.7-2.5) vs 1.4 (0.9-1.9), and 22.1 (7.0-59.2) vs 18.4 (7.7-42.9) and not significantly different. Age, Tanner stage, and sex were not correlated with ABC clearance by univariate analysis. The ratios of metabolites to ABC area under the curve were correlated with ABC clearance as were the ratios of metabolites to ABC concentrations at the 6-hour time point.

CONCLUSIONS

ABC oral clearance in HIV-1-infected pediatric patients does not change during puberty, is similar to younger children, and is higher than previously published in adults. Therefore, dosing adolescents as adults should be reexamined. Intersubject PK variability is substantial and is not correlated with body size or age but more likely due to differences in metabolite formation that may be genetic in origin.

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.

Prodrugs of nucleoside analogues for improved oral absorption and tissue targeting

Nucleoside analogues are widely used for the treatment of antiviral infections and anticancer chemotherapy. However, many nucleoside analogues suffer from poor oral bioavailability due to their high polarity and low intestinal permeability. In order to improve oral absorption of these polar drugs, prodrugs have been employed to increase lipophilicity by chemical modification of the parent. Alternatively, prodrugs targeting transporters present in the intestine have been exploited to facilitate the transport of the nucleoside analogues. Valacyclovir and valganciclovir are two successful valine ester prodrugs transported by the PepT1 transporter. Recently, research efforts have focused on design of prodrugs for tissue specific delivery to improve efficacy and safety. This review presents advances of prodrug approaches for improved oral absorption of nucleoside analogues and recent developments in tissue targeting.

Mitochondrial Toxicity of Tenofovir, Emtricitabine and Abacavir Alone and in Combination with Additional Nucleoside Reverse Transcriptase Inhibitors

Background

Some nucleoside/nucleotide reverse transcriptase inhibitor (NRTI) combinations cause additive or synergistic interactions in vitro and in vivo.

Methods

We evaluated the mitochondrial toxicity of tenofovir (TFV), emtricitabine (FTC) and abacavir as carbovir (CBV) alone, with each other, and in combination with additional NRTIs. HepG2 human hepatoma cells were incubated with TFV, FTC, CBV, didanosine (ddI), stavudine (d4T), lamivudine (3TC) and zidovudine (AZT) at concentrations equivalent to 1 and 10x clinical steady-state peak plasma levels (Cmax). NRTIs were also used in double and triple combinations. Cell growth, lactate production, intracellular lipids, mtDNA and the mtDNA-encoded respiratory chain subunit II of cytochrome c oxidase (COXII) were monitored for 25 days.

Results

TFV and 3TC had no or minimal toxicity. FTC moderately reduced hepatocyte proliferation independent of effects on mtDNA. ddI and d4T induced a time- and dose-dependent loss of mtDNA and COXII, decreased cell growth and increased levels of lactate and intracellular lipids. CBV and AZT strongly impaired hepatocyte proliferation and increased lactate and lipid production, but did not induce mtDNA depletion. The dual combination of TFV plus 3TC had only minimal toxicity; TFV plus FTC slightly reduced cell proliferation without affecting mitochondrial parameters. All other combinations exhibited more pronounced adverse effects on mitochondrial endpoints. Toxic effects on mitochondrial parameters were observed in all combinations with ddI, d4T, AZT or CBV. TFV and 3TC both attenuated ddI-related cytotoxicity, but worsened the effects of CBV and AZT.

Conclusions

The data demonstrate unpredicted interactions between NRTIs with respect to toxicological endpoints and provide an argument against the liberal use of NRTI cocktails without first obtaining data from clinical trials.

Predicting effect of food on extent of drug absorption based on physicochemical properties

PURPOSE

To develop a statistical model for predicting effect of food on the extent of absorption (area under the curve of time-plasma concentration profile, AUC) of drugs based on physicochemical properties.

MATERIALS AND METHODS

Logistic regression was applied to establish the relationship between the effect of food (positive, negative or no effect) on AUC of 92 entries and physicochemical parameters, including clinical doses used in the food effect study, solubility (pH 7), dose number (dose/solubility at pH 7), calculated Log D (pH 7), polar surface area, total surface area, percent polar surface area, number of hydrogen bond donor, number of hydrogen bond acceptors, and maximum absorbable dose (MAD).

RESULTS

For compounds with MAD >or= clinical dose, the food effect can be predicted from the dose number category and Log D category, while for compounds with MAD < clinical dose, the food effect can be predicted from the dose number category alone. With cross validation, 74 out of 92 entries (80%) were predicted into the correct category. The correct predictions were 97, 79 and 68% for compounds with positive, negative and no food effect, respectively.

CONCLUSIONS

A logistic regression model based on dose, solubility, and permeability of compounds is developed to predict the food effect on AUC. Statistically, solubilization effect of food primarily accounted for the positive food effect on absorption while interference of food with absorption caused negative effect on absorption of compounds that are highly hydrophilic and probably with narrow window of absorption.

Abacavir sulfate/lamivudine/zidovudine fixed combination in the treatment of HIV infection

Treatment of HIV infection has typically been carried out using two nucleoside analogs and a protease inhibitor. Such regimens can be complex and have high pill burdens. Use of alternative regimens, such as triple nucleoside-based regimens, can improve adherence and decrease toxicities associated with protease inhibitor therapy. A formulation of abacavir sulfate/lamivudine/zidovudine allows a dosing schedule of one pill twice daily. The components have performed favorably compared with protease inhibitor-based regimens, such as indinavir. Compared with efavirenz-based regimens, abacavir sulfate/lamivudine/zidovudine has not performed as well. The combination is being studied as a cornerstone for induction maintenance strategies, in which switching a patient to abacavir sulfate/lamivudine/zidovudine has been associated with similar virologic outcomes as continuing with either protease inhibitor- or efavirenz-based regimens. Administration of abacavir sulfate/lamivudine/zidovudine also avoids side effects of antiretroviral therapy, such as hyperlipidemia, but its use is associated with a hypersensitivity reaction in a small number of patients. The combination of abacavir sulfate/lamivudine/zidovudine is an important part of the HIV armamentarium. Its potency and ease of administration make it worth consideration in the treatment of HIV, either by itself or in combination with other agents.

Fixed-dose combination of abacavir, lamivudine and zidovudine for HIV therapy

Triple-nucleoside therapy with abacavir (ABV)/lamivudine (3TC)/zidovudine (ZDV) combination tablets provides simple, nonfood-dependent, twice-daily, well-tolerated therapy with the potential to improve long-term adherence at a lower cost than other triple-drug regimens. Of all the triple nucleoside reverse transcriptase inhibitor combinations currently available, ABV/3TC/ZDV is most extensively studied. Although ABV/3TC/ZDV is possibly less potent than other treatment options when used alone, other attributes described in this review make it an attractive option for selected patients. This combination spares the use of protease inhibitors and their associated side effects, such as metabolic abnormalities, which may contribute to premature cardiovascular disease. Furthermore, by using only one drug class, it may maintain a greater number of future treatment options. Data from ongoing clinical trials may result in expanding the use of ABV/3TC/ZDV as a component of multidrug, highly active antiretroviral therapy regimens.

Impact of pregnancy on abacavir pharmacokinetics

OBJECTIVE

To describe abacavir pharmacokinetics during pregnancy and postpartum; physiological changes during pregnancy are known to affect antiretroviral drug disposition.

DESIGN

The Pediatric AIDS Clinical Trials Group P1026s study is an on-going, prospective, non-blinded pharmacokinetic study of pregnant women receiving one or more antiretroviral drugs for routine clinical care, including a cohort receiving abacavir 300 mg twice daily.

METHODS

Serial plasma samples (predose, 1, 2, 4, and 6 h postdose) obtained antepartum (30-36 weeks of gestation) and again postpartum (6-12 weeks after delivery) were assayed for abacavir concentration by reversed-phase high-performance liquid chromatography.

RESULTS

Antepartum evaluations were available for 25 women [mean age, 28.6 years (SD, 6); mean third-trimester weight 92 kg (SD, 35.4); and race/ethnicity 52% black, 28% Hispanic, 16% white, 4% Asian], with geometric mean abacavir area under the concentration-time curve (AUC) of 5.9 mg.h/l [90% confidence interval (CI), 5.2-6.8] and maximum plasma concentration (Cmax) of 1.9 mg/l (90% CI, 1.6-2.2). Seventeen women completed postpartum sampling, and the ratios of antepartum to postpartum AUC and Cmax were 1.04 (90% CI, 0.91-1.18) and 0.79 (90% CI, 0.65-0.98), respectively.

CONCLUSIONS

Abacavir AUC during pregnancy was similar to that at 6-12 weeks postpartum and to that for non-pregnant historical controls (5.8 mg.h/l). Consequently, pregnancy does not appear to affect overall abacavir exposure significantly or to necessitate dose adjustments.

Classification of orally administered drugs on the World Health Organization Model list of Essential Medicines according to the biopharmaceutics classification system

Since its inception in 1995, the biopharmaceutical classification system (BCS) has become an increasingly important tool for regulation of drug products world-wide. Until now, application of the BCS has been partially hindered by the lack of a freely available and accurate database summarising solubility and permeability characteristics of drug substances. In this report, orally administered drugs on the Model list of Essential Medicines of the World Health Organization (WHO) are assigned BCS classifications on the basis of data available in the public domain. Of the 130 orally administered drugs on the WHO list, 61 could be classified with certainty. Twenty-one (84%) of these belong to class I (highly soluble, highly permeable), 10 (17%) to class II (poorly soluble, highly permeable), 24 (39%) to class III (highly soluble, poorly permeable) and 6 (10%) to class IV (poorly soluble, poorly permeable). A further 28 drugs could be provisionally assigned, while for 41 drugs insufficient or conflicting data precluded assignment to a specific BCS class. A total of 32 class I drugs (either certain or provisional classification) were identified. These drugs can be further considered for biowaiver status (drug product approval based on dissolution tests rather than bioequivalence studies in humans).

Determination of abacavir in human plasma by high-performance liquid chromatography with ultraviolet detection and the analytical error function

A rapid and simple high-performance liquid chromatography method has been developed for the determination of the HIV-1 reverse transcriptase inhibitor abacavir in human plasma. It included a single liquid-liquid extraction procedure with a mixture of ethyl acetate-diethyl ether prior to reversed-phase chromatography on a C18 column and C18 precolumn insert. Ultraviolet detection was set at 285 nm. The mobile phase consisted of water-acetonitrile (83:17, v/v) and the flow rate was kept at 1 mL/min. The total run time for a single analysis was 10 min. The method has been validated over the range 50-2500 ng/mL. The assay was linear over the entire concentration range (r2 = 0.9993). Intra- and inter-day precision and accuracy were less than 8.1 and -5.2%, respectively. The extraction recovery was greater than 94.3%. Abacavir was stable under the relevant storage conditions tested. After the validation, the analytical error function was established as standard deviation (SD; ng/mL) = -1.072 + 0.037C (C = theoretical concentration value). The method developed and its associated analytical error function will be suitable for pharmacokinetic studies and monitoring of HIV-1 patients.

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.

Trizivir

Treatment of HIV infection has typically been carried out using two nucleoside analogues and a protease inhibitor (PI). Such regimens can be complex and have high pill burdens. Use of alternative regimens, such as triple nucleoside based regimens, can improve adherence and decrease toxicities associated with PI therapy. Trizivir is a combination tablet of zidovudine, lamivudine and abacavir. This formulation allows a dosing schedule of one pill twice-daily. The components of have performed favourably compared to PI-based regimens, such as indinavir. However, in one study the individual components of Trizivir did not suppress HIV-1 viral replication as well as the PI-based regimen in a subset of patients with very high HIV-1 plasma RNA. Trizivir also avoids side effects of antiretroviral therapy, such as hyperlipidaemia, but its use is associated with a hypersensitivity reaction in a small number of patients. Trizivir is an important part of the HIV armamentarium. The potency and ease of administration of Trizivir make it worth consideration in HIV therapy, either by itself or in combination with other agents.

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.

Abacavir/lamivudine/zidovudine as a combined formulation tablet: bioequivalence compared with each component administered concurrently and the effect of food on absorption

A single-center, open-label, three-way crossover study was conducted in 24 healthy subjects to assess (1) the bioequivalence of a combined abacavir 300 mg/lamivudine 150 mg/zidovudine 300 mg (A/L/Z) combination tablet relative to the separate brand-name components administered simultaneously and (2) the effect of food on the bioavailability of the drugs from the combination tablet. The subjects were randomly assigned to receive each of the following three treatments, separated by a 2-day washout period: one A/L/Z combination tablet after an overnight fast, one abacavir 300 mg tablet + one lamivudine 150 mg tablet + one zidovudine 300 mg tablet sequentially after an overnight fast, or one A/L/Z combination tablet 5 minutes after completing a standardized high-fat breakfast (67 g fat, 58 g carbohydrate, and 33 g protein). Serial blood samples were collected up to 24 hours postdose for determination of abacavir, lamivudine, and zidovudine serum concentrations. Standard pharmacokinetic parameters were estimated. Treatments were considered bioequivalent if 90% confidence intervals (CI) for geometric least squares (GLS) mean ratios for abacavir, lamivudine, and zidovudine area under the serum concentration-time curve (AUC(infinity)) and maximum observed serum concentration (Cmax) fell entirely within 0.80 to 1.25 for log-transformed parameters. The combined A/L/Z tablet was bioequivalent in the extent (AUC) and rate of absorption (Cmax and time of Cmax [tmax]) to the individual brand-name drug components administered concurrently under fasted conditions. GLS ratios and 90% CI for AUC(infinity) and Cmax were 0.99 (0.96, 1.03) and 1.00 (0.90, 1.11), respectively, for abacavir; 0.95 (0.91, 0.99) and 0.90 (0.84, 0.99), respectively, for lamivudine; and 0.95 (0.89, 1.02) and 0.96 (0.80, 1.15), respectively, for zidovudine. The extent of absorption of abacavir, lamivudine, and zidovudine from the combination tablet was not altered by administration with meals, indicating that this formulation may be administered with or without food. However, food slowed the rate of absorption, delayed the tmax, and reduced the Cmax of abacavir, lamivudine, and zidovudine. These changes, which were consistent with those observed with the individual reference formulations when administered with food, were not considered clinically important. All formulations were well tolerated underfasted and fed conditions.

Liquid chromatographic assay for simultaneous determination of abacavir and mycophenolic acid in human plasma using dual spectrophotometric detection

A combined bio-analytical assay for abacavir, a reversed transcriptase inhibitor, and mycophenolic acid (MPA), based on reversed-phase liquid chromatography and both ultraviolet (UV) absorption and fluorescence detection, is reported. Both analytes are extracted from plasma with acetonitrile. After centrifugation, evaporation of the supernatant and reconstitution in water, the sample is injected into the chromatograph. Abacavir is detected using UV detection at 285 nm and MPA spectrofluorometrically at 345 and 430 nm for excitation and emission, respectively. The method has been validated in the 80-2000 ng/ml range for abacavir and in the 10-10,000 ng/ml range for MPA for 200-microl plasma samples. The lower limits of quantification are 80 and 10 ng/ml for abacavir and MPA, respectively. Precisions and accuracies are < or = 8% in the valid concentration ranges of both analytes.

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.

Multiple-dose pharmacokinetics and pharmacodynamics of abacavir alone and in combination with zidovudine in human immunodeficiency virus-infected adults

Abacavir (1592U89) is a nucleoside reverse transcriptase inhibitor with potent activity against human immunodeficiency virus type 1 (HIV-1) when used alone or in combination with other antiretroviral agents. The present study was conducted to determine the multiple-dose pharmacokinetics and pharmacodynamics of abacavir in HIV-1-infected subjects following oral administration of daily doses that ranged from 600 to 1,800 mg, with and without zidovudine. Seventy-nine subjects received abacavir monotherapy for 4 weeks (200, 400, or 600 mg every 8 hours [TID] and 300 mg every 12 h [BID]) and thereafter received either zidovudine (200 mg TID or 300 mg BID) or matching placebo with abacavir for 8 additional weeks. Pharmacokinetic parameters were calculated for abacavir after administration of the first dose and at week 4 and for abacavir, zidovudine, and its glucuronide metabolite at week 12. The concentrations of abacavir in cerebrospinal fluid were determined in a subset of subjects. Steady-state plasma abacavir concentrations were achieved by week 4 of monotherapy and persisted to week 12. At steady state, abacavir pharmacokinetic parameters (area under the plasma concentration-time curve for a dosing interval [AUC(tau)] and peak concentration [C(max)]) were generally proportional to dose over the range of a 600- to 1,200-mg total daily dose. Coadministration of zidovudine with abacavir produced a small and inconsistent effect on abacavir pharmacokinetic parameters across the different doses. At the clinical abacavir dose (300 mg BID) zidovudine coadministration had no effect on the abacavir AUC(tau), which is most closely associated with efficacy. Zidovudine pharmacokinetics appeared to be unaffected by abacavir. Statistically significant but weak relationships were found for the change in the log(10) HIV-1 RNA load from the baseline to week 4 versus total daily AUC(tau) and C(tau) (P < 0.05). The incidence of nausea was significantly associated with total daily AUC(tau) and C(max). In conclusion, abacavir has predictable pharmacokinetic characteristics following the administration of multiple doses.

Pharmacokinetics of [(14)C]abacavir, a human immunodeficiency virus type 1 (HIV-1) reverse transcriptase inhibitor, administered in a single oral dose to HIV-1-infected adults: a mass balance study

Abacavir (1592U89) ((-)-(1S, 4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene- 1-m ethanol) is a 2'-deoxyguanosine analogue with potent activity against human immunodeficiency virus (HIV) type 1. To determine the metabolic profile, routes of elimination, and total recovery of abacavir and metabolites in humans, we undertook a phase I mass balance study in which six HIV-infected male volunteers ingested a single 600-mg oral dose of abacavir including 100 microCi of [(14)C]abacavir. The metabolic disposition of the drug was determined through analyses of whole-blood, plasma, urine, and stool samples, collected for a period of up to 10 days postdosing, and of cerebrospinal fluid (CSF), collected up to 6 h postdosing. The radioactivity from abacavir and its two major metabolites, a 5'-carboxylate (2269W93) and a 5'-glucuronide (361W94), accounted for the majority (92%) of radioactivity detected in plasma. Virtually all of the administered dose of radioactivity (99%) was recovered, with 83% eliminated in urine and 16% eliminated in feces. Of the 83% radioactivity dose eliminated in the urine, 36% was identified as 361W94, 30% was identified as 2269W93, and 1.2% was identified as abacavir; the remaining 15.8% was attributed to numerous trace metabolites, of which <1% of the administered radioactivity was 1144U88, a minor metabolite. The peak concentration of abacavir in CSF ranged from 0.6 to 1.4 microg/ml, which is 8 to 20 times the mean 50% inhibitory concentration for HIV clinical isolates in vitro (0.07 microg/ml). In conclusion, the main route of elimination for oral abacavir in humans is metabolism, with <2% of a dose recovered in urine as unchanged drug. The main route of metabolite excretion is renal, with 83% of a dose recovered in urine. Two major metabolites, the 5'-carboxylate and the 5'-glucuronide, were identified in urine and, combined, accounted for 66% of the dose. Abacavir showed significant penetration into CSF.