Pharmacodynamic Effects of Zidovudine 600 mg Once/Day versus 300 mg Twice/Day in Therapy-Naïve Patients Infected with Human Immunodeficiency Virus

Recent Advancement in Nanotechnology-Based Drug Delivery System Against Viral Infections

In the last few decades, the exponential rise in the incidence of viral infections sets a global health emergency across the world. The biomimetic architecture, the ability to hijack host immune responses, continuous antigen shifting, and drafting are the major critical factors that are responsible for the unavailability of a concrete therapeutic regimen against viral infections. Further, inappropriate pharmacodynamic physicochemical and biological parameters such as low aqueous solubility, poor permeability, high affinity for plasm proteins, short biological half-lives, and fast elimination from the systemic circulation are the major critical factors that govern the suboptimal drug concentration at the target site that leads to the development of drug resistance. To address this issue, nanotechnology-based drug delivery approach is emerged as an altering method to attain the optimal drug concentration at the target site for a prolonged period by integrating the nanoengineering tools in the synthesis of nanoparticles. Nanodimensional configuration with enhanced permeability and retention effect, increased surface-area-to-volume ratio, provision for surface functionalization, etc., are the privileged aspects that make it an effective drug delivery system for dispensing the antiviral therapeutics. However, size, shape, charge, and surface topology of nanoparticles are the greater influential factors that determine target-specific drug delivery, optimum cellular uptake, degree of opsonization by the host immune cells, drug retention time, transcytosis, the extension of biological half-life, in vivo stability, and cytotoxicity. The review will enlighten the elaborative role of nanotechnology-based drug delivery and the major challenging aspect of clinical safety and efficacy.

Comparative study of antiretroviral drug regimens and drug-drug interactions between younger and older HIV-infected patients at a tertiary care teaching hospital in South Korea

Background

With the advent of combination antiretroviral therapy (ART), people living with HIV have lived to older age. So they have experienced age-related illnesses and have taken non-antiretroviral (ARV) medications to manage these illnesses. The aims of this study were to investigate the use patterns of ARV agents in HIV-positive patients by age and to evaluate potential or contraindicated drug-drug interactions (DDIs) between ARV and non-ARV.

Methods

This study was retrospectively conducted with HIV-infected patients receiving ART medications between October 2011 and September 2017 at Chonbuk National University Hospital in South Korea. Data were collected by reviewing patients' electronic medical charts.

Results

Among 207 patients diagnosed with HIV infection, 183 (86.9% males; 104 aged <50 years and 79 aged ≥50 years) were selected based on inclusion criteria. In 2017, the most frequently prescribed ART regimen was nucleoside reverse transcriptase inhibitors (NRTIs)/integrase strand transfer inhibitors (INSTIs; total, 66.3%; <50 years, 36.3%; ≥50 years, 30.0%) followed by NRTIs/protease inhibitors (PIs; total, 23.8%; <50 years, 15.0%; ≥50 years, 8.8%). In 2017, the most frequently prescribed NRTI combination was abacavir/lamivudine (total, 34.4%; <50 years, 20.6%; ≥50 years, 13.8%) followed by tenofovir alafenamide/emtricitabine (FTC; total, 31.3%; <50 years, 16.3%; ≥50 years, 15.0%) and tenofovir disoproxil fumarate/FTC (total, 28.1%; <50 years, 16.9%; ≥50 years, 11.3%). In 2017, elvitegravir (EVG)/cobicistat (COBI; total, 57.1%; <50 years, 30.4%; ≥50 years, 26.8%) was most frequently prescribed followed by dolutegravir (total, 32.1%; <50 years, 19.6%; ≥50 years, 12.5%). Potential or contraindicated DDIs between boosted PIs with ritonavir or EVG/COBI and coprescribed drugs occurred most frequently.

Conclusion

Currently, NRTIs/INSTIs is the most frequently prescribed ARV combination. Abacavir/lamivudine, tenofovir alafenamide/FTC, and tenofovir disoproxil fumarate/FTC are the most used NRTIs, and EVG/COBI followed by dolutegravir is the most prescribed INSTIs. Potential or contraindicated DDIs occur mainly between boosted PIs or EVG/COBI and non-ARV medications.

Impact of disease, drug and patient adherence on the effectiveness of antiviral therapy in pediatric HIV

INTRODUCTION

Maintaining effective antiretroviral treatment for life is a major problem in both resource-limited and resource-rich countries. Despite the progress observed in paediatric antiretroviral therapy, approximately 12% of children still experience treatment failure due to drug resistance, inadequate dosing and poor adherence. We explore the current status of antiretroviral therapy in children with focus on the interaction between disease, drug pharmacokinetics and patient behavior, all of which are strongly interconnected and determine treatment outcome. Areas covered: An overview is provided of the viral characteristics and available drug combinations aimed at the prevention of resistance. In this context, the role of patient adherence is scrutinized. A detailed assessment of factors affecting adherence is presented together with the main strategies to enhance treatment response in children. Expert opinion: Using modeling and simulation, a framework for characterizing the forgiveness of non-adherence for specific antiretroviral drugs in children is proposed in which information on pharmacokinetics, pharmacokinetic-pharmacodynamic relationships and viral dynamics is integrated. This approach represents an opportunity for the simplification of dosing regimens taking into account the interaction between these factors. Based on clinical trial simulation scenarios, we envisage the possibility of assessing the impact of variable adherence to antiretroviral drug combinations in HIV-infected children.

Once-Daily Abacavir/Lamivudine/Zidovudine plus Tenofovir for the Treatment of HIV-1 Infection in Antiretroviral-NaïveSubjects: A 48-Week Pilot Study

PURPOSE

To assess the safety and efficacy of a 4-drug, 3-tablet, once-daily (qd) regimen consisting of abacavir/lamivudine/zidovudine (ABC/3TC/ZDV; 2 tablets) and tenofovir (TDF) in antiretroviral-naïve patients with plasma HIV-1 RNA 30,000 copies/mL at 48 weeks.

METHOD

All participants received ABC/3TC/ZDV (300/150/300 mg) and TDF (300 mg) qd in this pilot, open-label, multicenter study. Intent-to-treat (ITT) analyses were conducted to evaluate virologic and immunologic efficacy.

RESULTS

Of the 123 participants enrolled, 52 (42%) prematurely discontinued study for adverse events (14), were lost to follow-up (13), had virologic nonresponse (12), and withdrew for other reasons (13). At week 48, by ITT missing=failure analysis, 41% (51/123) and 51% (63/123) of participants had plasma HIV-1 RNA <50 copies/mL and <400 copies/mL, respectively; by ITT-observed analysis, 75% (51/68) and 93% (63/68) had plasma HIV-1 RNA <50 copies/mL and <400 copies/mL, respectively; 11% (14/123) met virologic nonresponse criteria. Median week 48 change in CD4+ cell count from baseline was +127 cells/mm3. Median week 48 changes from baseline for fasting lipids were as follows: cholesterol (-9 mg/dL), HDL (+1 mg/dL), LDL (-9 mg/dL), and triglycerides (-4 mg/dL).

CONCLUSION

A high rate of premature discontinuations contributed to the overall suboptimal virologic response to ABC/3TC/ZDV+TDF qd; however, the regimen was not associated with high rates of virologic failure previously observed with TDF+ABC/3TC.

Initial viral decay to assess the relative antiretroviral potency of protease inhibitor-sparing, nonnucleoside reverse transcriptase inhibitor-sparing, and nucleoside reverse transcriptase inhibitor-sparing regimens for first-line therapy of HIV infection

OBJECTIVES

To evaluate the effects of sex and initial antiretroviral regimen on decay of HIV-RNA and virologic outcome.

METHODS

We conducted a viral dynamics substudy of A5142, a trial comparing lopinavir (LPV)/ritonavir with efavirenz (LPV/EFV) versus LPV and two nucleoside reverse transcriptase inhibitor (NRTI) (LPV) versus EFV and two NRTI (EFV) in antiretroviral (ARV)-naive individuals. HIV-RNA was measured at days 2, 10, and 14 in the substudy and at weeks 1, 4, and 8 in A5142 participants. Two-phase viral decay was estimated in the substudy with biexponential mixed-effects modeling and compared using Wilcoxon tests. Week 1 HIV-RNA change was assessed as a predictor of virologic failure (HIV-RNA above 50 or 200  copies/ml) at weeks 24-96 using logistic regression.

RESULTS

Sixty-eight individuals were enrolled in the substudy (median HIV-RNA 4.9 log(10)  copies/ml). Median rates of phase 1 viral decay by treatment were 0.61(EFV/LPV), 0.53(LPV), and 0.63(EFV) per day. Phase 1 decay was significantly faster for EFV than LPV (P = 0.023); other comparisons were not significant (P > 0.11). Viral decay did not differ by sex (P = 0.10). Week 1 HIV-RNA change, calculated in 571 participants of A5142, was greater for the EFV (median -1.47 log(10)  copies/ml) than either the LPV/EFV or LPV groups (-1.21 and -1.16 log(10 ) copies/ml, respectively; P < 0.001). Week 1 HIV-RNA change was associated with virologic failure above 50  copies/ ml at weeks 24 and 48 (P < 0.018), but not above 200  copies/ml at these time points or for any value at week 96.

CONCLUSION

Phase 1 decay was faster for EFV than LPV or LPV/EFV. Week 1 HIV-RNA change predicted virologic outcome up to week 48, but not at week 96.

Recent developments in the clinical pharmacology of anti-HIV nucleoside analogs

PURPOSE OF REVIEW

This review summarizes recent developments regarding the unique clinical pharmacologic profile of nucleoside analog reverse transcriptase inhibitors for management of HIV.

RECENT FINDINGS

First, intracellular data in patients suggest that nucleoside reverse transcriptase inhibitor-triphosphates are compartmentalized in different cell types. Additionally, intracellular drug-drug interactions were identified, which were undetectable in plasma. Second, extracellular data illustrate multiple bidirectional plasma drug-drug interactions between renally eliminated tenofovir and liver-metabolized drugs. Definitive mechanistic details for these interactions are lacking but they appear to involve renal and/or enteric drug transporters. Furthermore, the plasma versus female genital tract disposition of these agents was recently elucidated, which is important for currently investigated indications for pre-exposure and post-exposure prophylaxis. Finally, tenofovir/emtricitabine and abacavir (using a promising human leukocyte antigen-B*5701 genetic test for hypersensitivity)/lamivudine have emerged as common first-line nucleoside analog reverse transcriptase inhibitors because of co-formulations, once-daily dosing, and favorable tolerability and adverse effect profiles. Nevertheless, elucidating the long-term safety profile for all nucleoside analog reverse transcriptase inhibitors remains a priority.

SUMMARY

Knowledge of nucleoside analog reverse transcriptase inhibitor disposition intracellularly and extracellularly has expanded. This provides a basis for rational use of these agents clinically and adds new perspectives for future research.

Pharmacokinetic-pharmacodynamic relationship of NRTIs and its connection to viral escape: an example based on zidovudine

In HIV disease, the mechanisms of drug resistance are only poorly understood. Incomplete suppression of HIV by antiretroviral agents is suspected to be a main reason. The objective of this in silico study is to elucidate the pharmacokinetic origins of incomplete viral suppression, exemplified for zidovudine (AZT) as a representative of the key class of nucleoside reverse transcriptase inhibitors (NRTIs). AZT, like other NRTIs, exerts its main action through its intra-cellular triphoshate (AZT-TP) by competition with natural thymidine triphosphate. We developed a physiologically based pharmacokinetic (PBPK) model describing the intra-cellular pharmacokinetics of AZT anabolites and subsequently established the pharmacokinetic-pharmacodynamic relationship. The PBPK model has been validated against clinical data of different dosing schemes. We reduced the PBPK model to derive a simple three-compartment model for AZT and AZT-TP that can readily be used in population analysis of clinical trials. A novel machanistic, and for NRTIs generic effect model has been developed that incorporates the primary effect of AZT-TP and potential secondary effect of zidovudine monophosphate. The proposed models were used to analyze the efficacy and potential toxicity of different dosing schemes for AZT. Based on the mechanism of action of NRTIs, we found that drug heterogeneities due to temporal fluctuations can create a major window of unsuppressed viral replication. For AZT, this window was most pronounced for a 600 mg/once daily dosing scheme, in which insufficient viral suppression was observed for almost half the dosing period.

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

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

Intracellular pharmacokinetics of once versus twice daily zidovudine and lamivudine in adolescents

Zidovudine (ZDV) and lamivudine (3TC) metabolism to triphosphates (TP) is necessary for antiviral activity. The aims of this study were to compare ZDV-TP and 3TC-TP concentrations in adolescents receiving twice daily (BID) and once daily (QD) regimens and to determine the metabolite concentrations of ZDV and 3TC during chronic therapy on a QD regimen. Human immunodeficiency virus-infected patients (12 to 24 years) taking ZDV (600 mg/day) and 3TC (300 mg/day) as part of a highly active antiretroviral therapy regimen received QD and BID regimens of ZDV and 3TC for 7 to 14 days in a crossover design. Serial blood samples were obtained over 24 h on the QD regimen. Intracellular mono-, di-, and triphosphates for ZDV and 3TC were measured. The median ratio of BID/QD for ZDV-TP predose concentrations was 1.28 (95% confidence interval [CI] = 1.00 to 2.45) and for 3TC-TP was 1.12 (95% CI = 0.81 to 1.96). The typical population estimated half-lives (+/- the standard error of the mean) were 9.1 +/- 0.859 h for ZDV-TP and 17.7 +/- 2.8 h for 3TC-TP. Most patients had detectable levels of the TP of ZDV (24 of 27) and 3TC (24 of 25) 24 h after dosing, and half-lives on a QD regimen were similar to previously reported values when the drugs were given BID. Lower, but not significantly different, concentrations of ZDV-TP were demonstrated in the QD regimen compared to the BID regimen (P = 0.056). Although findings were similar between the BID and QD groups, the lower concentrations of ZDV and the number of patients below the level of detection after 24 h suggests that ZDV should continue to be administered BID.

Pharmacology of current and promising nucleosides for the treatment of human immunodeficiency viruses

Nucleoside antiretroviral agents are chiral small molecules that have distinct advantages compared to other classes including long intracellular half-lives, low protein binding, sustained antiviral response when a dose is missed, and ease of chemical manufacture. They mimic natural nucleosides and target a unique but complex viral polymerase that is essential for viral replication. They remain the cornerstone of highly active antiretroviral therapy (HAART) and are usually combined with non-nucleoside reverse [corrected] transcriptase and protease inhibitors to provide powerful antiviral responses to prevent or delay the emergence of drug-resistant human immunodeficiency virus (HIV). The pharmacological and virological properties of a selected group of nucleoside analogs are described. Some of the newer nucleoside analogs have a high genetic barrier to resistance development. The lessons learned are that each nucleoside analog should be treated as a unique molecule since any structural modification, including a change in the enantiomeric form, can affect metabolism, pharmacokinetics, efficacy, toxicity and resistance profile.

Pharmacokinetic properties of nucleoside/nucleotide reverse transcriptase inhibitors

Options for antiretroviral therapy in patients infected with HIV continue to expand as new drugs are integrated into treatment regimens. Nonetheless, nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs/NtRTIs) remain the backbone of highly active antiretroviral therapy (HAART). With the approval of emtricitabine in 2003, there are now 8 Food and Drug Administration (FDA)-approved NRTIs/NtRTIs. Several of these agents are effective as once-daily therapy, including didanosine, lamivudine, extended-release stavudine (FDA approved, but not currently available), tenofovir DF, and emtricitabine. Recent results from pharmacokinetic and clinical trials indicate that another NRTI, abacavir, may also be effective as a once-daily therapy, and FDA approval of once-daily dosing is anticipated. NRTIs are inactive as administered, requiring anabolic phosphorylation within target cells to achieve their antiretroviral effects. All NRTIs are converted to nucleoside triphosphates, which serve as the active metabolites (the NtRTI, tenofovir DF, only requires conversion to the diphosphate form). Frequency of drug administration is closely related to the pharmacokinetic properties of a drug. The key parameter is the half-life; however, the plasma elimination half-life of the NRTIs/NtRTIs as administered is of little use in developing a dosing schedule. Rather, the intracellular half-life of the nucleoside triphosphate is the relevant parameter. This article reviews the pharmacokinetic properties, particularly those of the various phosphorylation steps, of the NRTIs/NtRTIs.

The pharmacology of antiretroviral nucleoside and nucleotide reverse transcriptase inhibitors: implications for once-daily dosing

The trend toward once-daily dosing in HIV antiretroviral therapy is based on the association between adherence, treatment outcome, and patient preferences. Patients prefer simpler treatments, fewer pills, less frequent dosing, and no food restrictions. When a regimen meets a patient's preferences, the patient is more likely to be adherent, and with good adherence, the regimen is more likely to be effective. Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) have been a prime focus for developing once-daily therapies primarily because they form the backbone of most current regimens. Within the NRTI class, however, drugs differ in their pharmacokinetic properties, such as plasma and intracellular half-lives, and thus in their suitability for once-daily dosing. For example, newer NRTIs, such as tenofovir and emtricitabine, combine longer plasma half-lives with longer intracellular half-lives, prolonging exposure and the period of pharmacologic activity. Of equal importance, the clinical impact of systemic and intracellular interactions between concomitant drugs defines which once-daily drugs may be combined in once-daily regimens. To construct simplified and effective therapies for individual patients, clinicians require an understanding of the plasma and intracellular pharmacokinetic properties of NRTIs and how these properties determine a drug's appropriateness for once-daily dosing and placement within a once-daily regimen.

Once-daily versus twice-daily lamivudine, in combination with zidovudine and efavirenz, for the treatment of antiretroviral-naive adults with HIV infection: a randomized equivalence trial

A randomized, double-blind, double-dummy controlled, multicenter trial was conducted that involved 554 antiretroviral-naive human immunodeficiency virus-infected adults (plasma HIV type 1 [HIV-1] RNA level, >or=400 copies/mL; CD4(+) cell count, >100 cells/mm(3)) and compared a 300-mg once-daily (q.d.) regimen of lamivudine (3TC) versus a 150-mg twice-daily (b.i.d.) regimen of 3TC, combined with zidovudine (300 mg b.i.d.) and efavirenz (600 mg q.d.), during a 48-week period. Treatments were considered equivalent if the 95% confidence interval (CI) for the difference in proportions of patients achieving an HIV-1 RNA level of <400 copies/mL was within the bound of -12% to 12%. At week 48 of the study, an intent-to-treat analysis in which patients with missing data were considered to have experienced treatment failure showed that the 3TC q.d. and 3TC b.i.d. regimens were equivalent (HIV-1 RNA level <400 copies/mL, 178 [64%] of 278 vs. 174 [63%] of 276; treatment difference, 1% [95% CI, -7.1% to 8.9%]; HIV-1 RNA level <50 copies/mL, 165 [59%] of 278 vs. 168 [61%] of 276; treatment difference, 1.7% [95% CI, -9.7% to 6.6%]). Median increase above baseline in CD4(+) cell count was similar (q.d. group, +144 cells/mm(3); b.i.d. group, +146 cells/mm(3)), and the incidences of adverse events, disease progression, and HIV-associated conditions were comparable.