Steady-state pharmacokinetics of abacavir in plasma and intracellular carbovir triphosphate following administration of abacavir at 600 milligrams once daily and 300 milligrams twice daily in human immunodeficiency virus-infected subjects

Abacavir Drug Exposures in African Children Under 14 kg Using Pediatric Solid Fixed Dose Combinations According to World Health Organization Weight Bands

BACKGROUND

The pharmacokinetics of abacavir (ABC) in African children living with HIV (CLHIV) weighing <14 kg and receiving pediatric fixed dose combinations (FDC) according to WHO weight bands dosing are limited. An ABC population pharmacokinetic model was developed to evaluate ABC exposure across different World Health Organization (WHO) weight bands.

METHODS

Children enrolled in the LIVING study in Kenya and Uganda receiving ABC/lamivudine (3TC) dispersible tablets (60/30 mg) according to WHO weight bands. A population approach was used to determine the pharmacokinetic parameters. Monte Carlo simulations were conducted using an in silico population with demographic characteristics associated with African CLHIV. ABC exposures (AUC0-24) of 6.4-50.4 mg h/L were used as targets.

RESULTS

Plasma samples were obtained from 387 children. A 1-compartment model with allometric scaling of clearance (CL/F) and volume of distribution (V/F) according to body weight best characterized the pharmacokinetic data of ABC. The maturation of ABC CL/F was characterized using a sigmoidal Emax model dependent on postnatal age (50% of adult CL/F reached by 0.48 years of age). Exposures to ABC were within the target range for children weighing 6.0-24.9 kg, but children weighing 3-5.9 kg were predicted to be overexposed.

CONCLUSIONS

Lowering the ABC dosage to 30 mg twice daily or 60 mg once daily for children weighing 3-5.9 kg increased the proportion of children within the target and provided comparable exposures. Further clinical study is required to investigate clinical implications and safety of the proposed alternative ABC doses.

Microphysiological model reveals the promise of memory-like natural killer cell immunotherapy for HIV± cancer

Numerous studies are exploring the use of cell adoptive therapies to treat hematological malignancies as well as solid tumors. However, there are numerous factors that dampen the immune response, including viruses like human immunodeficiency virus. In this study, we leverage human-derived microphysiological models to reverse-engineer the HIV-immune system interaction and evaluate the potential of memory-like natural killer cells for HIV+ head and neck cancer, one of the most common tumors in patients living with human immunodeficiency virus. Here, we evaluate multiple aspects of the memory-like natural killer cell response in human-derived bioengineered environments, including immune cell extravasation, tumor penetration, tumor killing, T cell dependence, virus suppression, and compatibility with retroviral medication. Overall, these results suggest that memory-like natural killer cells are capable of operating without T cell assistance and could simultaneously destroy head and neck cancer cells as well as reduce viral latency.

HIV post-treatment controllers have distinct immunological and virological features

HIV post-treatment controllers (PTCs) are rare individuals who maintain low levels of viremia after stopping antiretroviral therapy (ART). Understanding the mechanisms of HIV post-treatment control will inform development of strategies aiming at achieving HIV functional cure. In this study, we evaluated 22 PTCs from 8 AIDS Clinical Trials Group (ACTG) analytical treatment interruption (ATI) studies who maintained viral loads ≤400 copies/mL for ≥24 wk. There were no significant differences in demographics or frequency of protective and susceptible human leukocyte antigen (HLA) alleles between PTCs and post-treatment noncontrollers (NCs, n = 37). Unlike NCs, PTCs demonstrated a stable HIV reservoir measured by cell-associated RNA (CA-RNA) and intact proviral DNA assay (IPDA) during analytical treatment interruption (ATI). Immunologically, PTCs demonstrated significantly lower CD4+ and CD8+ T cell activation, lower CD4+ T cell exhaustion, and more robust Gag-specific CD4+ T cell responses and natural killer (NK) cell responses. Sparse partial least squares discriminant analysis (sPLS-DA) identified a set of features enriched in PTCs, including a higher CD4+ T cell% and CD4+/CD8+ ratio, more functional NK cells, and a lower CD4+ T cell exhaustion level. These results provide insights into the key viral reservoir features and immunological profiles for HIV PTCs and have implications for future studies evaluating interventions to achieve an HIV functional cure.

Persistent HIV transcription and variable antiretroviral drug penetration in lymph nodes during plasma viral suppression

OBJECTIVE

The ability of antiretroviral drugs to penetrate and suppress viral replication in tissue reservoir sites is critical for HIV remission. We evaluated antiretroviral concentrations in lymph nodes and their impact on HIV transcription.

METHODS

Participants of the RV254/SEARCH010 Acute HIV Infection Cohort in Thailand were enrolled. Group 1 (n  = 6) initiated and continued antiretrovirals with two nucleoside reverse transcriptase inhibitors (NRTIs), dolutegravir (DTG) and mar- aviroc (MVC). Group 2 (n = 12) initiated antiretrovirals with two NRTIs as well as efavirenz and were switched to two NRTIs as well as DTG. Antiretroviral concentrations were measured by mass spectroscopy. HIV RNA+ and DNA+ cells were measured by in-situ hybridization.

RESULTS

All participants were MSM. At lymph node biopsy, all had plasma HIV RNA less than 20 copies/ml. Group 2 had longer durations of antiretroviral and DTG use (medians of 135 and 63 weeks, respectively) compared with Group 1 (median 44 weeks for both). TFV-DP, 3TC-TP, DTG and MVC were quantifiable in all lymph node samples from participants receiving those drugs versus carbovir-triphosphate (CBV-TP) in four out of 14. Median ratios of lymph node to peripheral blood concentrations were DTG, 0.014; MVC, 6.9; CBV-TP, 0.38; 3TC-TP, 0.32; and TFV-DP, 3.78. Median inhibitory quotients [ratios of lymph node concentrations to in-vitro inhibitory levels (IC50-or-90)] were DTG, 0.8; MVC, 38.8; CBV-TP, 0.5; 3TC- TP, 4.1; and TFV-DP, 1.8. Ongoing viral transcription was detected in lymph node of all participants. Median lymph node RNA+ cells were 71 350 versus 99 750 cells/g for Groups 1 and 2, respectively (P = 0.111).

CONCLUSION

MVC has enhanced lymph node penetration and thereby may contribute to more complete viral suppression in the lymph node.

Abacavir Increases Purinergic P2X7 Receptor Activation by ATP: Does a Pro-inflammatory Synergism Underlie Its Cardiovascular Toxicity?

The cardiovascular toxicity of Abacavir is related to its purinergic structure. Purinergic P2X7-receptors (P2X7R), characterized by activation by high concentrations of ATP and with high plasticity, seem implicated. We appraise the nature of the interplay between Abacavir and P2X7R in generating vascular inflammation. The effects of Abacavir on leukocyte-endothelium interactions were compared with those of its metabolite carbovir triphosphate (CBV-TP) or ATP in the presence of apyrase (ATP-ase) or A804598 (P2X7R-antagonist). CBV-TP and ATP levels were evaluated by HPLC, while binding of Abacavir, CBV-TP and ATP to P2X7R was assessed by radioligand and docking studies. Hypersensitivity studies explored a potential allosteric action of Abacavir. Clinical concentrations of Abacavir (20 µmol/L) induced leukocyte-endothelial cell interactions by specifically activating P2X7R, but the drug did not show affinity for the P2X7R ATP-binding site (site 1). CBV-TP levels were undetectable in Abacavir-treated cells, while those of ATP were unaltered. The effects of Abacavir were Apyrase-dependent, implying dependence on endogenous ATP. Exogenous ATP induced a profile of proinflammatory actions similar to Abacavir, but was not entirely P2X7R-dependent. Docking calculations suggested ATP-binding to sites 1 and 2, and Abacavir-binding only to allosteric site 2. A combination of concentrations of Abacavir (1 µmol/L) and ATP (0.1 µmol/L) that had no effect when administered separately induced leukocyte-endothelium interactions mediated by P2X7R and involving Connexin43 channels. Therefore, Abacavir acts as a positive allosteric modulator of P2X7R, turning low concentrations of endogenous ATP themselves incapable of stimulating P2X7R into a functional proinflammatory agonist of the receptor.

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.)

The effect of veno-arterial extracorporeal oxygenation and nasogastric tube administration on the pharmacokinetic profile of abacavir, lamivudine and dolutegravir: a case report

BACKGROUND

Pharmacokinetic (PK) changes can affect antiretroviral (ARV) systemic exposure for critically ill patients living with HIV (CI-PLWH). Studies to guide ARV adjustments in this population are limited.

METHODS

A PK analysis was conducted in a 44-year-old CI-PLWH who presented for a heart and lung transplant on veno-arterial extracorporeal membrane oxygenation (VA ECMO). Home ARV therapy (ART) of co-formulated abacavir/lamivudine/dolutegravir (ABC/3TC/DTG) was continued. ARV serum concentrations were obtained during and after VA ECMO. Two blood levels were drawn at 1 h, for maximum serum concentration (C_max) and a serum trough (C_t). ARVs were given as a single tablet crushed via nasogastric tube.

RESULTS

Area under the concentration-time curve (AUC_0-t) was calculated using non-compartmental analysis. C_max and AUC_0-t were higher during VA ECMO compared with post-decannulation. The C_max of ABC was >2.5-fold higher than the mean in the reference. C_max and C_t post VA ECMO were within range of referenced literature for all ARVs. C_max and AUC_0-t of DTG post VA ECMO was approximately four- to fivefold lower than referenced literature. HIV virological suppression was maintained throughout the hospitalization.

CONCLUSIONS

ART adjustments would not be required for this patient. Additional studies are needed to assess effects of VA ECMO and crushed tube administration of ARVs in CI-PLWH.

Direct and indirect quantification of phosphate metabolites of nucleoside analogs in biological samples

Nucleoside reverse transcriptase inhibitors (NRTIs) are prodrugs that require intracellular phosphorylation to active triphosphate nucleotide metabolites (NMs) for their pharmacological activity. However, monitoring these pharmacologically active NMs is challenging due to their instability, high hydrophilicity, and their low concentrations in blood and tissues. Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is the gold standard technique for the quantification of NRTIs and their phosphorylated NMs. In this review, an overview of the publications describing the quantitative analysis of intracellular and total tissue concentration of NMs is presented. The focus of this review is the comparison of the different approaches and challenges associated with sample collection, tissue homogenization, cell lysis, cell counting, analyte extraction, sample storage conditions, and LC-MS analysis. Quantification methods of NMs via LC-MS can be categorized into direct and indirect methods. In the direct LC-MS methods, chromatographic retention of the NMs is accomplished by ion-exchange (IEX), ion-pairing (IP), hydrophilic interaction (HILIC), porous graphitic carbon (PGC) chromatography, or capillary electrophoresis (CE). In indirect methods, parent nucleosides are 1st generated from the dephosphorylation of NMs during sample preparation and are then quantified by reverse phase LC-MS as surrogates for their corresponding NMs. Both approaches have advantages and disadvantages associated with them, which are discussed in this review.

The dawn of precision medicine in HIV: state of the art of pharmacotherapy

INTRODUCTION

Combination antiretroviral therapy (ART) reduces viral load to under the limit of detection, successfully decreasing HIV-related morbidity and mortality. Due to viral mutations, complex drug combinations and different patient response, there is an increasing demand for individualized treatment options for patients.

AREAS COVERED

This review first summarizes the pharmacokinetic and pharmacodynamic profile of clinical first-line drugs, which serves as guidance for antiretroviral precision medicine. Factors which have influential effects on drug efficacy and thus precision medicine are discussed: patients' pharmacogenetic information, virus mutations, comorbidities, and immune recovery. Furthermore, strategies to improve the application of precision medicine are discussed.

EXPERT OPINION

Precision medicine for ART requires comprehensive information on the drug, virus, and clinical data from the patients. The clinically available genetic tests are a good starting point. To better apply precision medicine, deeper knowledge of drug concentrations, HIV reservoirs, and efficacy associated genes, such as polymorphisms of drug transporters and metabolizing enzymes, are required. With advanced computer-based prediction systems which integrate more comprehensive information on pharmacokinetics, pharmacodynamics, pharmacogenomics, and the clinically relevant information of the patients, precision medicine will lead to better treatment choices and improved disease outcomes.

Crushed dolutegravir/abacavir/lamivudine given via nasogastric tube in gastric outlet obstruction caused by cancer resulted in rapid viral load suppression

Alternative modes of antiretroviral administration are sought for people with impaired intestinal passage and/or absorption. We present a case of late HIV diagnosis (CD4+ count 160 cells/µL) with gastric outlet obstruction due to stomach adenocarcinoma. Co-morbidities included oesophageal candidiasis, Helicobacter pylori-positive duodenal ulcers and cytomegalovirus duodenitis. The gastric outlet obstruction required total parenteral nutrition and parenteral medication during four weeks of diagnostic work-up leading to pyloric resection. Crushed dolutegravir, abacavir and lamivudine were administered during this time in the evening via nasogastric tube, which was kept clamped overnight. The tube was unclamped in the morning and stomach content was drained during the daytime. This mode of administration resulted in rapid and sustained viral load suppression (from 300,000 to 115 copies per mL in 28 days, 81 copies/mL after 42 days of treatment and less than 40 copies/mL thereafter). Therapeutic drug monitoring confirmed sufficient antiretroviral plasma levels during this mode of administration. The absorption of crushed dolutegravir, abacavir and lamivudine in the stomach may be considered in people with questionable gastrointestinal passage or impaired gastric emptying to achieve viral load suppression.

Out of focus: tailoring the cascade of care to the needs of women living with HIV

Around half of the global adult HIV-positive population are women, yet historically women have been under-represented in clinical studies of antiretroviral therapy (ART) and there has been minimal exploration of gender-specific factors related to the response to and appropriateness of treatment choices in women living with HIV (WLWH). There are several key issues pertaining to the cascade of HIV care that make it important to differentiate WLWH from men living with HIV. Factors that are gender specific may impact on the status of WLWH, affecting access to diagnosis and treatment, optimal clinical management, ART outcomes, retention in care, and the overall long-term wellbeing of WLWH. In this review, we discuss the results of recently reported women-only clinical trials and highlight the key unmet needs of WLWH as they pertain to the cascade of HIV care across World Health Organization European Region countries. As significant knowledge gaps remain, the review identifies key areas where further research is required, in order to support improved management of WLWH and guide informed clinical decision-making, including addressing psychosocial factors as part of comprehensive care.

Simultaneous quantification of intracellular lamivudine and abacavir triphosphate metabolites by LC-MS/MS

Nucleoside reverse transcriptase inhibitors (NRTIs) require intracellular phosphorylation to active triphosphate (TP) nucleotide metabolites before they can inhibit the HIV reverse transcriptase. However, monitoring these pharmacologically active TP metabolites is challenging due to their instability and their low concentrations at the pg/ml levels in blood and tissues. The combination of lamivudine (3TC) and abacavir (ABC) is one of the first lines for HIV therapy. Therefore, a sensitive, selective, accurate, and precise LC-MS/MS method was developed and validated for the simultaneous quantification of 3TC- and ABC-TP metabolites in mouse blood and tissues. Calibration curves were linear over the range of 10-100,000 pg/ml for 3TC-TP and 4-40,000 pg/ml for carbovir-TP (CBV-TP; phosphorylated metabolite of ABC). This corresponds to 2.1-21,322 fmol/10⁶ cells for 3TC-TP and 0.8-8000 fmol/10⁶ cells for CBV-TP. Accuracy and precision were less than 15% for all quality control sample (QCs), and absolute extraction recovery of were >65% for 3TC-TP and >90% for CBV-TP. The method was optimized to ensure stability of TP samples and standards during sample collection, preparation, analysis, and storage conditions. This method has enhanced sensitivity and requires smaller amounts of blood and tissue samples compared to previous LC-MS/MS methods for 3TC- and CBV-TP quantification. The developed method was successfully applied to characterize the pharmacokinetic profile of TP metabolites in mouse peripheral blood mononuclear cells (PBMCs), spleen, lymph nodes, and liver cells. In addition, another direct, simple, and high-throughput method for the quantification of TP standards was developed and used for the analysis of stability samples.

Intracellular Tenofovir-Diphosphate and Emtricitabine-Triphosphate in Dried Blood Spots following Directly Observed Therapy

Studies of daily emtricitabine-tenofovir disoproxil fumarate (FTC-TDF) for HIV preexposure prophylaxis (PrEP) in men who have sex with men (MSM) modeled intracellular tenofovir-diphosphate (TFV-DP) in dried blood spots (DBS) to assess adherence and corresponding PrEP outcomes. We conducted a prospective, randomized, crossover pharmacokinetic study of TFV-DP in DBS during 33%, 67%, or 100% of daily dosing under directly observed therapy (DOT). Participants were assigned to two 12-week dosing regimens, separated by a 12-week washout. Forty-eight adults (25 women) from Denver and San Francisco were included. TFV-DP exhibited a median half-life of 17 days, reaching steady state in 8 weeks. TFV-DP was dose proportional with mean (SD) steady-state concentrations of 530 (159), 997 (267), and 1,605 (405) fmol/punch for the 33%, 67%, and 100% arms, respectively. Prior work in MSM demonstrated clinically meaningful TFV-DP thresholds of 350, 700, and 1,250 fmol/punch, which were estimated 25th percentiles for 2, 4, and 7 doses/week. In the present study, corresponding TFV-DP was within 3% of the prior estimates, and subgroups by site, race, and sex were within 14% of prior estimates, although males had 17.6% (95% confidence intervals [CIs], 6.5, 27.4%) lower TFV-DP than females. The thresholds of 350, 700, and 1,250 fmol/punch were achieved by 75% of men taking ≥1.2, 3.2, and 6 doses/week and 75% of women taking ≥0.6, 2.0, and 5.3 doses/week, indicating that lower dosing reached these thresholds for both sexes. In conclusion, TFV-DP arising from DOT was similar to previous estimates and is useful for interpreting PrEP adherence and study outcomes. (This study has been registered at ClinicalTrials.gov under identifier NCT02022657.).

Cardiovascular toxicity of abacavir: a clinical controversy in need of a pharmacological explanation

: There is a long-lasting controversy surrounding an association between abacavir (ABC) and an increased risk of cardiovascular disease in HIV-positive patients. Although differing in their specifics, a number of published cohort studies and clinical trials support such an association, usually relating it to recent exposure to the drug, independently of traditional predisposing factors. However, other clinical trials have failed to reveal such a relation and have pointed to methodological differences to explain discrepancies. Significantly, the controversy has been fueled by the lack of a credible mechanism of action to justify the putative detrimental actions of ABC. There is a myriad of contradictory clinical indicators which are not clearly compatible with known profiles of either vascular physiopathology or pharmacological interference. However, basic research has recently hinted at altered homeostatic mechanisms, though this requires clinical validation. In particular, recurrent evidence - both clinical and experimental - relates ABC with vascular inflammation, a leading contributor to the atherosclerotic plaque and thrombosis. ABC's chemical structure is very close to that of endogenous purines (ATP, ADP and AMP), major paracrine signaling molecules capable of triggering prothrombotic and proinflammatory vascular programs. Other proposed mechanisms are a competitive inhibition of guanylyl cyclase in platelets and a subsequent decrease in cyclic guanosine monophosphate (cGMP). The present review aims to shed light on this complex subject by summarizing and critically evaluating all the available clinical data regarding a relationship between ABC and cardiovascular disease, and to put forward potential pharmacological explanations compatible with both the clinical scenario and experimental findings.

Abacavir induces platelet-endothelium interactions by interfering with purinergic signalling: A step from inflammation to thrombosis

The controversy connecting Abacavir (ABC) with cardiovascular disease has been fuelled by the lack of a credible mechanism of action. ABC shares structural similarities with endogenous purines, signalling molecules capable of triggering prothrombotic/proinflammatory programmes. Platelets are leading actors in the process of thrombosis. Our study addresses the effects of ABC on interactions between platelets and other vascular cells, while exploring the adhesion molecules implicated and the potential interference with the purinergic signalling pathway. The effects of ABC on platelet aggregation and platelet-endothelium interactions were evaluated, respectively, with an aggregometer and a flow chamber system that reproduced conditions in vivo. The role of adhesion molecules and purinergic receptors in endothelial and platelet populations was assessed by selective pre-incubation with specific antagonists and antibodies. ABC and carbovir triphosphate (CBT) levels were evaluated by HPLC. The results showed that ABC promoted the adherence of platelets to endothelial cells, a crucial step for the formation of thrombi. This was not a consequence of a direct effect of ABC on platelets, but resulted from activation of the endothelium via purinergic ATP-P2X₇ receptors, which subsequently triggered an interplay between P-selectin and ICAM-1 on endothelial cells with constitutively expressed GPIIb/IIIa and GPIbα on platelets. ABC did not induce platelet activation (P-selectin expression or Ca²⁺ mobilization) or aggregation, even at high concentrations. CBT levels in endothelial cells were lower than those required to induce platelet-endothelium interactions. Thus, ABC interference with endothelial purinergic signalling leads to platelet recruitment. This highlights the endothelium as the main cell target of ABC in this interaction, which is in line with previous experimental evidence that ABC induces manifestations of vascular inflammation.

Nucleotide Reverse Transcriptase Inhibitors: A Thorough Review, Present Status and Future Perspective as HIV Therapeutics

BACKGROUND

Human immunodeficiency virus type-1 (HIV-1) infection leads to acquired immunodeficiency syndrome (AIDS), a severe viral infection that has claimed approximately 658,507 lives in the US between the years 2010-2014. Antiretroviral (ARV) therapy has proven to inhibit HIV-1, but unlike other viral illness, not cure the infection.

OBJECTIVE

Among various Food and Drug Administration (FDA)-approved ARVs, nucleoside/ nucleotide reverse transcriptase inhibitors (NRTIs) are most effective in limiting HIV-1 infection. This review focuses on NRTIs mechanism of action and metabolism.

METHODS

A search of PubMed (1982-2016) was performed to capture relevant articles regarding NRTI pharmacology.

RESULTS

The current classical NRTIs pharmacology for HIV-1 prevention and treatment are presented. Finally, various novel strategies are proposed to improve the efficacy of NRTIs, which will increase therapeutic efficiency of present-day HIV-1 prevention/treatment regimen.

CONCLUSION

Use of NRTIs will continue to be critical for successful treatment and prevention of HIV-1.

Interference with purinergic signalling: an explanation for the cardiovascular effect of abacavir?

OBJECTIVE

The association of abacavir (ABC), a guanosine analogue, with cardiovascular toxicity is a long-lasting matter of controversy engendered by the lack of a mechanism of action. Clinical data point to an acute mechanism of vascular inflammation. Previous studies have shown that ABC induces leukocyte-endothelial cell interactions, an indicator of vascular inflammation. These effects are reproduced by another purine analogue, didanosine, but not by pyrimidine or acyclic nucleotide analogues, hinting at an interference with the purinergic system. The aim of the present study was to assess the role of ATP-receptors in leukocyte accumulation induced by ABC.

DESIGN AND METHODS

Clinical concentrations of ABC were analysed in an animal model in vivo (intravital microscopy using male C57BL/6 wild-type or P2rx7 knockout mice), in human endothelial cells and leukocytes in vitro (flow chamber), or in leukocyte Mac-1 expression (flow cytometry).

RESULTS

ABC reduced leukocyte rolling velocity and increased rolling flux and adhesion both in vivo and in vitro. These effects were absent in P2rx7 knockout mice and following the specific blockade of ATP-P2X7 receptors in wild-type animals. Further pharmacological characterization in flow chamber experiments confirmed the role of ATP-P2X7 receptors and suggested that those located on leukocytes were particularly implicated. Activation of ATP-P2X7 receptors is needed for expression of leukocytic Mac-1. Similar effects were obtained with didanosine.

CONCLUSION

ABC induces leukocyte-endothelial cell interactions through a mechanism involving interference with purine-signalling pathways via ATP-P2X7 receptors located mainly on leukocytes. Our data are compatible with existing clinical data revealing an increased cardiovascular risk in ABC-treated patients.

Dolutegravir and elvitegravir plasma concentrations following cessation of drug intake

OBJECTIVES

To evaluate dolutegravir and elvitegravir/cobicistat pharmacokinetics in HIV-negative volunteers up to 10 days after drug cessation.

METHODS

Healthy volunteers received 50 mg of dolutegravir once-daily for 10 days, then underwent a 9 day wash-out period, and then received elvitegravir/cobicistat as part of Stribild(®) (245 mg of tenofovir, 200 mg of emtricitabine, 150 mg of elvitegravir and 150 mg of cobicistat) for 10 days. Serial pharmacokinetic (PK) sampling occurred prior to the final dose of each course and at regular intervals for up to 216 h (10 days) after drug cessation. Concentrations were determined by LC-MS/MS, and PK parameters were illustrated as geometric mean and 90% CI.

RESULTS

Seventeen volunteers completed the study. For dolutegravir, plasma terminal elimination t1/2 to the last measurable concentration (within 216 h) was longer than its t1/2 within the dosing interval (0-24 h): 14.3 h (12.9-15.7 h) versus 23.1 h (19.7-26.6 h); conversely, the terminal elimination t1/2 for elvitegravir was lower than its t1/2 within the dosing interval (0-24 h): 10.8 h (9.7-13.0 h) versus 5.2 h (4.7-6.1 h). Dolutegravir concentrations were above the protein-adjusted (PA) IC90 (64 ng/mL) in 100% of subjects after 36 and 48 h and in 94% after 60 and 72 h. All subjects had detectable dolutegravir concentrations at 96 h, a mean of 23.5% above the IC90. Elvitegravir concentrations were above the PA IC95 (45 ng/mL) in 100% of subjects at 24 h, 65% at 36 h but 0% after 48 h.

CONCLUSIONS

Our data show marked differences in the elimination rates of dolutegravir and elvitegravir following treatment interruption, which is likely to impact the extent to which drug doses can be delayed or missed. They suggest that clinical differences may emerge in patients who have suboptimal adherence.

Effects of abacavir administration on structural and functional markers of platelet activation

BACKGROUND

Current abacavir exposure has been reported to be associated with cardiovascular disease. Changes in platelet reactivity could plausibly explain the clinically observed pattern of association.

OBJECTIVE

To determine if platelet reactivity changed following abacavir exposure and whether this effect was reversible on cessation of the drug.

METHODS

In an open-label, interventional study abacavir, 600 mg daily, was added to a suppressive antiretroviral regimen in 20 adult HIV-positive men. Platelet function, estimated by the phosphorylated vasodilator-stimulated phosphoprotein (P-VASP) assay and through measurement of the expression and shedding of platelet-specific receptors, was assessed at baseline, following 15 days of abacavir and at completion of a 28-day washout period.

RESULTS

The VASP-index decreased significantly from 79.1% [interquartile range (IQR) 47.8-87.6] to 32.6% (IQR -11.5-51.0) following 15 days of abacavir administration (P = 0.010), and returned to baseline levels following the washout period (day 43 =76.3%; IQR 40.7-92.3). There was no change in resting (prostaglandin E1 alone) P-VASP but a slight increase in P-VASP within stimulated platelets (prostaglandin E1 and adenosine diphosphate). Integrin β3 levels decreased significantly [208.5 ng/ml (IQR 177.0-231.1) to 177.5 ng/ml (IQR 151.7-205) P < 0.001] and there was a nonsignificant trend towards decreased soluble glycoprotein VI levels [baseline; 72.5 ng/ml (95% CI 58.3-81.5) vs. day 15; 45.0 ng/ml (95% CI 33.0-98.2) P = 0.79].

CONCLUSION

Abacavir led to reversible changes in platelet function and structure. The clinical implications of these changes are uncertain; they may represent negative feedback mechanisms in response to an abacavir-associated prothrombotic state.

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.

Plasma pharmacokinetics of once-daily abacavir- and lamivudine-containing regimens and week 96 efficacy in HIV-infected Thai children

BACKGROUND

Abacavir and lamivudine are approved for once-daily use in HIV-infected adults. Limited pharmacokinetic (PK) data for abacavir and lamivudine in children are available.

METHODS

A crossover study to compare PK of once- versus twice-daily abacavir and lamivudine was conducted in virologically suppressed HIV-infected Thai children aged <18years, with bodyweight of at least 14 kg, HIV RNA <50 copies/mL and HLA-B*5701 negative. Abacavir and lamivudine daily doses by bodyweight were 300 and 150 mg for 14-<20 kg, 450 and 300 mg for 20-<25 kg, and 600 and 300 mg for ≥25 kg, respectively. Originator abacavir and lamivudine scored tablets were administered. Intensive PK sampling was performed after 14 days of each dose. PK parameters were determined using non-compartmental analysis.

RESULTS

Thirty children (57% male) were enrolled, 10 per weight band. Median (IQR) age was 8.8 (6.6-11.3) years and bodyweight was 21.9 (19.2-30.6) kg. The geometric means (GM) AUC0-24 of once- and twice-daily abacavir were 14.43 and 10.65 mg.h/L, respectively. The geometric mean ratio (GMR) of AUC0-24 for once- versus twice-daily abacavir dosing was 1.36 [90% confidence interval (CI) 1.11-1.66]. The GM AUC0-24 of once- and twice-daily lamivudine were 17.70 and 18.11 mg.h/L, respectively. The GMR of AUC0-24 for once- versus twice-daily lamivudine dosing was 0.98 (90% CI 0.84-1.14). At 96 weeks, 90% had HIV RNA <50 copies/mL and there were no serious adverse events.

CONCLUSION

Abacavir exposure was greater with once-daily dosing, while lamivudine once- and twice-daily exposures were bioequivalent. Once-daily abacavir and lamivudine using weight-band dosing is a treatment option for children.

Quantification of cell-associated atazanavir, darunavir, lopinavir, ritonavir, and efavirenz concentrations in human mononuclear cell extracts

An ultrasensitive assay utilizing high-pressure liquid chromatography and mass spectrometry detection was developed and validated for the quantification of the antiretrovirals atazanavir (ATV), darunavir (DRV), lopinavir (LPV), ritonavir (RTV), and efavirenz (EFV) in human mononuclear cell (MNC) extracts. The assay utilizes 20 μl of cellular extract that contains as few as 50,000 MNCs. The analytical range of the assay is 0.0200 to 10.0 fmol/μl for ATV, 0.0500 to 25.0 fmol/μl for DRV, LPV, and RTV, and 0.200 to 100 fmol/μl for EFV. The assay has proven to be a clinically useful tool for investigating antiretroviral drug concentrations in virologic sanctuaries where harvested cell numbers are extremely low. The assay provides a tool for investigators to explore the clinical pharmacology of strategies for prevention, treatment, and cure in pathophysiologically relevant sites.

Profile of leukocyte-endothelial cell interactions induced in venules and arterioles by nucleoside reverse-transcriptase inhibitors in vivo

BACKGROUND

There is controversy regarding cardiovascular (CV) toxicity of the nucleoside reverse-transcriptase inhibitors used to treat human immunodeficiency virus infection.

METHODS

We evaluated the effects of nucleoside reverse-transcriptase inhibitors on leukocyte-endothelium interactions, a hallmark of CV diseases, in rat mesenteric vessels using intravital microscopy and in human arterial cells using a flow chamber system.

RESULTS

Abacavir and didanosine increased rolling, adhesion and emigration in rat vessels. These effects were reversed with antibodies against Macrophage-1 antigen (Mac-1) or intercellular adhesion molecule 1 and were reproduced in human cells. Lamivudine, zidovudine, emtricitabine, and tenofovir had no effects.

CONCLUSIONS

Our results support the association of abacavir and didanosine with CV diseases.

[Consensus statement on assistance to women with human immunodeficiency virus infection in the health care sector. National AIDS Plan (PNS) and AIDS Study Group (GeSIDA)]

OBJECTIVE

To develop a consensus document on clinical recommendations for the health care of women with human immunodeficiency virus (HIV) infection.

METHODS

We assembled a panel of experts appointed by the Secretariat of the National AIDS Plan and GeSIDA that included internal medicine physicians with expertise in the field of HIV infection, gynecologists, pediatricians and psychologists, and two panel members acting as coordinators. Scientific information was reviewed in publications and conference reports up to October 2012. In keeping with the criteria of the Infectious Disease Society of America, two levels of evidence were applied to support the proposed recommendations: the strength of the recommendation according to expert opinion (A, B, C), and the level of empirical evidence (i, ii, iii), already used in previous documents from SPNS/GeSIDA.

RESULTS

We provide multiple recommendations for the clinical management of women with HIV infection, considering both the diagnostic and possible therapeutic strategies. The consensus recommends gender mainstreaming in health care, and promoting training for healthcare professionals in order to avoid gender bias. With currently available data it seems that the effectiveness of the treatment is the same in both men and women, there being no limitation as to the use of any antiretroviral for this reason. Women have more treatments suspended for reasons other than virological failure, thus they require better monitoring.

CONCLUSIONS

This document presents recommendations for addressing women with HIV infection. This must be multidisciplinary, taking into account the differences that can be found in the diagnosis, disease development, and treatment between men and women.

In vivo platelet activation and platelet hyperreactivity in abacavir-treated HIV-infected patients

Abacavir (ABC) has been associated with ischaemic cardiovascular events in HIV-infected patients, but the pathogenic mechanisms are unknown. Aim of our study was to assess whether ABC induces in vivo platelet activation and ex vivo platelet hyper-reactivity. In a retrospective, case-control study, in vivo platelet activation markers were measured in 69 HIV-infected patients, before starting therapy and after 6-12 months of either ABC (n=35) or tenofovir (TDF) (n=34), and compared with those from 20 untreated HIV-infected patients. A subgroup of patients was restudied after 28-34 months for ex vivo platelet reactivity. In vivo platelet activation markers were assessed by ELISA or flow cytometry, ex vivo platelet reactivity by light transmission aggregometry (LTA) and PFA-100®. Thein vitro effects of the ABC metabolite, carbovir triphosphate, on aggregation and intra-platelet cGMP were also studied. sPLA2, sPsel and sGPV increased significantly 6-12 months after the beginning of ABC, but not of TDF or of no treatment. Ex vivo platelet function studies showed enhanced LTA, shorter PFA-100® C/ADP closure time and enhanced platelet expression of P-sel and CD40L in the ABC group. The intake of ABC blunted the increase of intraplatelet cGMP induced by nitric oxide (NO) and acutely enhanced collagen-induced aggregation. Preincubation of control platelets with carbovir triphosphate in vitro enhanced platelet aggregation and blunted NO-induced cGMP elevation. In conclusion, treatment with ABC enhances in vivo platelet activation and induces platelet hyperreactivity by blunting the inhibitory effects of NO on platelets. These effects may lead to an increase of ischaemic cardiovascular events.

Stress Degradation Behavior of Abacavir Sulfate and Development of a Suitable Stability-Indicating UHPLC Method for the Determination of Abacavir, its Related Substances, and Degradation Products

A novel, stability-indicating UHPLC method was developed for the quantitative determination of Abacavir sulfate, its related substances, and forced degradation impurities in bulk drugs. The chromatographic separation was achieved on a Waters Acquity BEH C₈, 50 mm × 2.1 mm, 1.7 μm particle size column with a mobile containing a gradient mixture of solution A (0.10 % v/v o-phosphoric acid in water) and solution B (0.10% v/v o-phosphoric acid in methanol). The flow rate was set at 0.40 mL/min and the run time was 6.0 min. The drug substance was subjected to the stress studies of hydrolysis, oxidation, photolysis, and thermal degradation. Abacavir sulfate was found to degrade significantly under acidic hydrolysis and oxidative stress conditions. The formed degradation products were reported and were well-resolved from Abacavir and its related substances. The mass balance was found to be satisfactory in all of the stress conditions, thus proving the stability-indicating capability of the method. The developed UHPLC method was validated to be in agreement with ICH requirements and found to be rapid, accurate, precise, linear, specific, and suitable for the quantitative determination of related substances and degradants in the bulk drug samples of Abacavir sulfate.

Pharmacokinetics of abacavir and its anabolite carbovir triphosphate without and with darunavir/ritonavir or raltegravir in HIV-infected subjects

BACKGROUND

Here, we aimed to investigate the pharmacokinetics of abacavir and carbovir triphosphate (CBV-TP) with darunavir/ritonavir 900/100 mg once daily or raltegravir 400 mg twice daily.

METHODS

HIV-infected subjects on abacavir (600 mg once daily) underwent steady-state pharmacokinetic assessments without and with darunavir/ritonavir or raltegravir. Within-subject changes in plasma and intracellular pharmacokinetic parameters were evaluated by geometric mean ratios (GMRs) and 90% CIs.

RESULTS

A total of 19 patients completed the study. With darunavir/ritonavir (versus abacavir alone), abacavir GMRs (90% CI) were 0.73 (0.66, 0.80), 0.62 (0.50, 0.77) and 0.78 (0.69, 0.87) for area under the curve (AUC), trough concentration (C(trough)) and maximum concentration (C(max)), respectively. With raltegravir, they were 1.03 (0.97, 1.10), 0.83 (0.62, 1.11) and 1.06 (0.95, 1.18), respectively. Intracellular CBV-TP GMRs (90% CI) were 0.88 (0.72, 1.07), 0.68 (0.48, 0.95) and 0.98 (0.79, 1.23) for AUC, C(trough) and C(max), respectively, with darunavir/ritonavir, and 0.96 (0.76, 1.20), 0.57 (0.33, 1.00) and 1.07 (0.85, 1.35), respectively, with raltegravir.

CONCLUSIONS

There was a 27% decrease in abacavir plasma exposure with darunavir/ritonavir and no changes with raltegravir. CBV-TP C(trough) was significantly decreased with darunavir/ritonavir (32%) and showed a high inter-individual variability with raltegravir.

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 increases platelet reactivity via competitive inhibition of soluble guanylyl cyclase

OBJECTIVE

To provide a molecular mechanism that explains the association of the antiretroviral guanosine analogue, abacavir, with an increased risk of myocardial infarction.

DESIGN

Drug effects were studied with biochemical and cellular assays.

METHODS

Human platelets were incubated with nucleoside analogue drugs ex vivo. Platelet activation stimulated by ADP was studied by measuring surface P-selectin with flow cytometry. Inhibition of purified soluble guanylyl cyclase was quantified using an ELISA to measure cGMP production.

RESULTS

Pre-incubation of platelets in abacavir significantly increased activation in response to ADP in a time and dose-dependent manner. The active anabolite of abacavir, carbovir triphosphate, competitively inhibited soluble guanylyl cyclase activity with a K(i) of 55 μmol/l.

CONCLUSION

Abacavir competitively inhibits guanylyl cyclase, leading to platelet hyperreactivity. This may explain the observed increased risk of myocardial infarction in HIV patients taking abacavir.

Abacavir and lamivudine for the treatment of human immunodeficiency virus

INTRODUCTION

The introduction of combination antiretroviral therapy (cART) in 1996 dramatically changed the survival and the quality of life of people living with human immunodeficiency virus (HIV). Viral replication can be controlled by using a combination of more than 30 licensed drugs. Despite the fact that many advances have been made in the last 20 years of experience with antiretrovirals, certain needs remain to be addressed, such as the presence of chronic inflammation, the long-term side effects of newly introduced drugs and eradication. Abacavir (ABC) and lamivudine (3TC) are licensed in a fixed-dose combination to be administered once daily with other antiretroviral agents for the treatment of HIV.

AREAS COVERED

This article provides an extensive review of the evidence on the combination of ABC 600 mg and 3TC 300 mg. Specifically, it discusses the chemistry-- including the phrarmacodynamics, resistance to treatment, pharmacokinetics and metabolism--and formulations available. It also looks at clinical efficacy, including safety and tolerability.

EXPERT OPINION

In the last few years, new data regarding human leukocyte antigen (HLA) B*5701 testing to prevent the hypersensitivity reaction due to ABC have been presented, providing a landmark in the management of adverse events in HIV, and later a previously unexpected correlation of the recent exposure to ABC with an increased risk of cardiovascular disease. This review presents the current situation with regard to the long-term efficacy and safety data on the ABC/3TC combination.

Pharmacokinetics and acceptability of once- versus twice-daily lamivudine and abacavir in HIV type-1-infected Ugandan children in the ARROW Trial

BACKGROUND

No data on once-daily dosing of nucleoside analogues in African children currently exist. We compared the pharmacokinetics (PK) of once- versus twice-daily lamivudine and abacavir treatment using the World Health Organization recommended weight band dosing of scored adult tablets.

METHODS

HIV type-1 (HIV-1)-infected Ugandan children aged 3-12 years receiving antiretroviral therapy that included lamivudine and abacavir twice daily (total 150+300 mg, 225+450 mg and 225/300+600 mg daily for 12-<20, 20-<25 and ≥25 kg, respectively) were enrolled in a crossover study. Plasma PK sampling (at 0, 1, 2, 4, 6, 8 and 12 h after observed morning intake) was performed for the twice-daily regimen at steady-state. Children were then switched to once-daily treatment with PK sampling repeated 4 weeks later (with an additional 24 h sample). Acceptability questionnaires were completed at both time points. Daily area under the curve (AUC(0-24)) and maximum concentrations (C(max)) were compared by geometric mean ratios (GMRs).

RESULTS

A total of 41 HIV-1-infected children (median age of 7 years) and n=23, n=14 and n=4 in 12-<20, 20-<25 and ≥25 kg weight bands, respectively, were enrolled. Mean AUC(0-24) was 13.0 and 12.0 mg•h/l for once- and twice-daily lamivudine (GMR 1.09, 90% confidence intervals [CI] 0.98-1.20) and 15.3 and 15.6 mg•h/l for once- and twice-daily abacavir (GMR 0.98, 90% CI 0.89-1.08), respectively, with no difference in 3-6 versus 7-12 year olds. C(max) was 76% (lamivudine) and 64% (abacavir) higher on once-daily regimens. For both children and caregivers, once-daily dosing of lamivudine plus abacavir was highly acceptable and strongly preferred over twice-daily.

CONCLUSIONS

In children aged 3-12 years, AUC(0-24) of lamivudine and abacavir were bioequivalent on once- and twice-daily regimens. Once-daily dosing of abacavir and lamivudine could provide an alternative dosing strategy for HIV-1-infected children, with high acceptability and strong preference suggesting the potential for improved adherence.

Mass spectrometry in the quantitative analysis of therapeutic intracellular nucleotide analogs

Nucleoside analogs are widely used in anti-cancer, anti-(retro)viral, and immunosuppressive therapy. Nucleosides are prodrugs that require intracellular activation to mono-, di-, and finally triphosphates. Monitoring of these intracellular nucleotides is important to understand their pharmacology. The relatively involatile salts and ion-pairing agents traditionally used for the separation of these ionic analytes limit the applicability of mass spectrometry (MS) for detection. Both indirect and direct methods have been developed to circumvent this apparent incompatibility. Indirect methods consist of de-phosphorylation of the nucleotides into nucleosides before the actual analysis. Various direct approaches have been developed, ranging from the use of relatively volatile or very low levels of regular ion-pairing agents, hydrophilic interaction chromatography (HILIC), weak anion-exchange, or porous graphitic carbon columns to capillary electrophoresis and matrix-assisted light desorption--time of flight (MALDI-TOF) MS. In this review we present an overview of the publications describing the quantitative analysis of therapeutic intracellular nucleotide analogs using MS. The focus is on the different approaches for their direct analysis. We conclude that despite the technical hurdles, several useful MS-compatible chromatographic approaches have been developed, enabling the use of the excellent selectivity and sensitivity of MS for the quantitative analysis of intracellular nucleotides.

Clinical pharmacology profile of raltegravir, an HIV-1 integrase strand transfer inhibitor

Raltegravir is an HIV-1 integrase inhibitor approved to treat HIV infection in adults in combination with other antiretrovirals. Data from healthy volunteers demonstrate that raltegravir is rapidly absorbed with a mean half-life of approximately 7 to 12 hours, with steady state achieved in approximately 2 days. Raltegravir is characterized by both high intra- and interindividual variabilities, although neither gender, race, age, body mass index, food intake, nor renal or hepatic insufficiency has a clinically meaningful effect on raltegravir pharmacokinetics. Raltegravir lacks activity as a perpetrator of drug-drug interactions and demonstrates a low propensity to be subject to drug-drug interactions. Raltegravir is metabolized primarily by UGT1A1 and is not affected by P450 inhibitors or inducers. Inhibitors of UGT1A1 (eg, atazanavir) can increase plasma concentrations of raltegravir, although this increase has not been found to be clinically meaningful. Likewise, inducers of UGT1A1 (eg, rifampin) can reduce plasma concentrations of raltegravir, and the clinical significance of this reduction is being investigated in ongoing clinical studies. Raltegravir demonstrates favorable clinical pharmacology and a drug interaction profile that permits administration to a wide, demographically diverse patient population and coadministration with many other therapeutic agents, including antiretroviral agents and supportive medications, without restrictions or dose adjustment.

Lack of association between stavudine exposure and lipoatrophy, dysglycaemia, hyperlactataemia and hypertriglyceridaemia: a prospective cross sectional study

BACKGROUND

Stavudine continues to be widely used in resource poor settings despite its toxicity. Our objective was to determine association between plasma stavudine concentrations and lipoatrophy, concentrations of glucose, lactate and triglycerides.

METHODS

Participants were enrolled in a cross-sectional study with lipoatrophy assessment, oral glucose tolerance test, fasting triglycerides, finger prick lactate, and stavudine concentrations. Individual predictions of the area under the concentration curve (AUC) were obtained using a population pharmacokinetic approach. Logistic regression models were fitted to assess the association between stavudine geometric mean ratio > 1 and impaired fasting glucose, impaired glucose tolerance, hyperlactataemia, hypertriglyceridaemia, and lipoatrophy.

RESULTS

There were 47 study participants with a median age of 34 years and 83% were women. The median body mass index and waist:hip ratio was 24.5 kg/m2 and 0.85 respectively. The median duration on stavudine treatment was 14.5 months. The prevalence of lipoatrophy, impaired fasting glucose, impaired glucose tolerance, hyperlactataemia, and hypertriglyceridaemia were 34%, 19%, 4%, 32%, and 23% respectively. Estimated median (interquartile range) stavudine AUC was 2191 (1957 to 2712) ng*h/mL. Twenty two participants had stavudine geometric mean ratio >1. Univariate logistic regression analysis showed no association between stavudine geometric mean ratio >1 and impaired fasting glucose (odds ratio (OR) 2.00, 95% CI 0.44 to 9.19), impaired glucose tolerance (OR 1.14, 95% CI 0.07 to 19.42), hyperlactataemia (OR 2.19, 95%CI 0.63 to 7.66), hypertriglyceridaemia (OR 1.75, 95%CI 0.44 to 7.04), and lipoatrophy (OR 0.83, 95% CI 0.25 to 2.79).

CONCLUSIONS

There was a high prevalence of metabolic complications of stavudine, but these were not associated with plasma stavudine concentrations. Until there is universal access to safer antiretroviral drugs, there is a need for further studies examining the pathogenesis of stavudine-associated toxicities.

Abacavir and didanosine induce the interaction between human leukocytes and endothelial cells through Mac-1 upregulation

OBJECTIVE

Abacavir and didanosine are nucleoside reverse transcriptase inhibitors (NRTI) widely used in therapy for HIV-infection but which have been linked to cardiovascular complications. The objective of this study was to analyze the effects of clinically relevant doses of abacavir and didanosine on human leukocyte-endothelium interactions and to compare them with those of other NRTIs.

DESIGN AND METHODS

The interactions between human leukocytes - specifically peripheral blood polymorphonuclear (PMN) or mononuclear (PBMC) cells - and human umbilical vein endothelial cells were evaluated in a flow chamber system that reproduces conditions in vivo. The expression of adhesion molecules was analyzed by flow cytometry.

RESULTS

Abacavir induced a dose-dependent increase in PMN and PBMC rolling and adhesion. This was reproduced by didanosine but not by lamivudine or zidovudine. Both abacavir and didanosine increased Mac-1 expression in neutrophils and monocytes, but produced no effects on either lymphocytes or the expression of endothelial adhesion molecules. The PMN/PBMC rolling and adhesion induced by abacavir or didanosine did not occur when antibodies against Mac-1 or its ligand ICAM-1 were blocked.

CONCLUSION

Abacavir induces significant human leukocyte accumulation through the activation of Mac-1, which in turn interacts with its endothelial ligand ICAM-1. The fact that didanosine exhibits similar effects and that lamivudine and zidovudine do not points to a relationship between the chemical structure of NRTIs and the induction of leukocyte/endothelial cell interactions. This mechanism may be especially relevant to the progression of the vascular damage associated with atherosclerosis and myocardial infarction in abacavir and didanosine-treated patients.

Abacavir and tenofovir disoproxil fumarate co-administration results in a nonadditive antiviral effect in HIV-1-infected patients

OBJECTIVES

To evaluate a potential pharmacodynamic/pharmacokinetic interaction between abacavir (ABC) and tenofovir disoproxil fumarate (TDF).

DESIGN AND METHODS

This randomized trial compared 7 days of ABC or TDF monotherapy, separated by a 35-day washout, with 7 days of ABC + TDF dual-therapy in treatment-naive, HIV-1-infected patients. During each 7-day course, the slope of the phase I viral decay was estimated and steady-state intracellular concentrations of carbovir triphosphate (CBV-TP), deoxyguanosine triphosphate (dGTP), tenofovir diphosphate (TFV-DP) and deoxyadenosine triphosphate (dATP) were determined.

RESULTS

Twenty-one participants were randomized to initial monotherapy with ABC (n = 11) or TDF (n = 10). The addition of TDF did not increase the slope of viral decay compared to ABC alone (-0.15 log10 per day vs. -0.16 log10 per day, respectively). No decrease in CBV-TP or TFV-DP between monotherapy and dual-therapy was observed. However, intracellular dATP concentrations increased between monotherapy and dual-therapy [median dATP (fmol/10 cells) 3293 vs. 4638; P = 0.08], although this difference was significant only among patients randomized to TDF [median dATP (fmol/10 cells) 3238 vs. 4534; P = 0.047]. A lower TFV-DP-to-dATP ratio was associated with reduced viral decay during dual-therapy (rho = -0.529; P = 0.045).

CONCLUSION

In this study, the viral decay during ABC and TDF dual-therapy was similar to that during ABC therapy alone, suggesting a nonadditive antiviral effect. This negative pharmacodynamic interaction was not explained by changes in CBV-TP or TFV-DP concentrations. Rather, modest increases in endogenous dATP pools were associated with reduced antiviral potency of TDF during co-administration with ABC.

Abacavir/lamivudine combination in the treatment of HIV: a review

Abacavir has been at the center of research and clinical interest in the last two years. The frequency of the associated abacavir hypersensitivity syndrome has decreased substantially since the introduction of routine testing for the HLA-B*5701 allele; the activity of the drug in HIV-infected persons with HIV RNA values more than 100,000 copies/mL has been questioned; the possible increased risk of myocardial infarction after recent exposure to abacavir has been debated; and the drug has been moved from the “recommended” category to the “alternative” category in several guidelines. Still, the drug remains a useful agent in combination with other drugs, including lamivudine, for the treatment of HIV infection. This review will focus on the pharmacokinetics, activity, side effects, and resistance profile of both abacavir and lamivudine, including a thorough review of all of the recent studies relevant to both drugs.

Pharmacokinetic study of once-daily versus twice-daily abacavir and lamivudine in HIV type-1-infected children aged 3-<36 months

BACKGROUND

Once-daily dosing of abacavir and lamivudine has been approved for adults, but paediatric data are insufficient. We conducted a pharmacokinetic study of once-daily and twice-daily abacavir and lamivudine in children aged 3-<36 months.

METHODS

Children with stable HIV type-1 (HIV-1) RNA levels after 12 weeks treatment with twice-daily abacavir (8 mg/kg) with or without lamivudine (4 mg/kg) underwent plasma pharmacokinetic sampling. Children then switched to once-daily abacavir (16 mg/kg) with or without lamivudine (8 mg/kg), and sampling was repeated 4 weeks later. The area under the plasma concentration-time curve over 24 h (AUC(0-24)) and the maximum concentration (C(max)) were compared using geometric mean ratios (GMRs); 90% confidence intervals (CIs) within the range of 0.80-1.25 were considered bioequivalent.

RESULTS

A total of 18 children (4, 6 and 8 in the 3-<12, 12-<24 and 24-<36 month age ranges, respectively) provided pharmacokinetic data for abacavir (17 for lamivudine). The GMR of AUC(0-24), once-daily versus twice-daily, was 1.07 (90% CI 0.92-1.23) for abacavir and 0.91 (90% CI 0.79-1.06) for lamivudine. C(max) almost doubled on once-daily versus twice-daily dosing: abacavir and lamivudine GMRs were 2.04 (90% CI 1.73-2.42) and 1.78 (90% CI 1.52-2.09), respectively. At baseline, 12, 24 and 48 weeks, 89%, 94%, 100% and 89% of children had HIV-1 RNA<400 copies/ml, respectively.

CONCLUSIONS

Bioequivalence was demonstrated on AUC(0-24) between twice-daily and once-daily abacavir; very similar AUC(0-24) values were seen for twice-daily and once-daily lamivudine. Given that viral load suppression rates were maintained, these data suggest that once-daily abacavir and lamivudine might be an option for children aged 3-<36 months.

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.