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Developing long-acting products and formulations for infectious diseases is a nontrivial undertaking that is frequently classified as high risk and low reward by the pharmaceutical industry. The Long-Acting/Extended Release Antiretroviral Research Resource Program (LEAP) was founded in 2015 with the support of the National Institutes of Health to encourage, promote, and accelerate the development of such products. Assessment methodology for any new proposal brought to this group is part of a framework—the LEAP Process—that includes a landscape analysis of what is currently available in the public domain. This is followed by in silico modeling and simulation offered as a service to the relevant scientific community. A variety of preclinical and clinical outcome metrics are applied to each new agent as part of a continuous feedback loop to improve product characteristics. This allows us to catalog knowledge gaps and barriers that can be addressed by engaged stakeholders. Results are communicated in scientific articles, reviews, and position papers. This undertaking serves to de-risk discovery, development, and implementation by bridging the gaps between academic, regulatory, and industrial investigators, and by engaging those in the community who will be the eventual users of these medicines. The LEAP Process has supported formulations now approved for human immunodeficiency virus, as well as products in clinical and preclinical development for tuberculosis and hepatitis viruses B and C. [ABSTRACT FROM AUTHOR]

Background: Cabotegravir and rilpivirine are 2 long-acting (LA) antiretrovirals that can be administered intramuscularly; their interaction with rifampicin, a first-line antituberculosis agent, has not been investigated. The aim of this study was to simulate and predict drug-drug interactions (DDIs) between these LA antiretroviral agents and rifampicin using physiologically based pharmacokinetic (PBPK) modeling.Methods: The designed PBPK models were qualified (according to European Medicines Agency guidelines) against observed data for oral formulations of cabotegravir, rilpivirine, and rifampicin. Induction potential of rifampicin was also qualified by comparing the DDI between oral cabotegravir and oral rilpivirine with rifampicin. Qualified PBPK models were utilized for pharmacokinetic prediction of DDIs.Results: PBPK models predicted a reduction in both area under the curve (AUC0-28 days) and trough concentration (Ctrough, 28th day) of LA cabotegravir of 41%-46% for the first maintenance dose coadministered with 600 mg once-daily oral rifampicin. Rilpivirine concentrations were predicted to decrease by 82% for both AUC0-28 days and Ctrough, 28th day following the first maintenance dose when coadministered with rifampicin.Conclusions: The developed PBPK models predicted the theoretical effect of rifampicin on cabotegravir and rilpivirine LA intramuscular formulations. According to these simulations, it is likely that coadministration of rifampicin with these LA formulations will result in subtherapeutic concentrations of both drugs. [ABSTRACT FROM AUTHOR]

Background Dolutegravir combined with darunavir/cobicistat is a promising NRTI-sparing and/or salvage strategy for the treatment of HIV-1 infection. Methods This Phase I, open-label, 57 day, crossover, pharmacokinetic (PK) study, enrolled healthy volunteers aged 18–65 years, who were randomized to one of two groups. Group 1 received dolutegravir (50 mg) once daily for 14 days followed by a 7 day washout, then a 14 day dolutegravir/darunavir/cobicistat (DTG/DRV/COBI) once-daily co-administration period followed by a 7 day washout and finally a 14 day period of darunavir/cobicistat (800/150 mg) once daily. Group 2 followed the same sequence starting with darunavir/cobicistat and concluding with dolutegravir. Each group underwent intensive PK sampling over 24 h on day 14 of each drug period and DTG/DRV/COBI concentrations were measured using validated LC-MS/MS methods. Results Twenty participants completed all PK phases. Thirteen were female and median age and BMI were 33.5 years and 27 kg/m2. Dolutegravir geometric mean ratios (GMR, DTG/DRV/COBI versus dolutegravir alone) and 90% CI for C max, AUC0–24 and C 24 were 1.01 (0.92–1.11), 0.95 (0.87–1.04) and 0.9 (0.8–1.0), respectively. Darunavir GMR (DRV/COBI/DTG versus darunavir/cobicistat alone) and 90% CI for C max, AUC0–24 and C 24 were 0.90 (0.83–0.98), 0.93 (0.86–1.00) and 0.93 (0.78–1.11), respectively. No grade 3 or 4 adverse events or laboratory abnormalities were observed. Conclusions Concentrations of dolutegravir and darunavir, when boosted with cobicistat, decreased by <10% during co-administration, suggesting this combination can be prescribed safely in the treatment of HIV-1, with no adjustment to current guideline-recommended dosages. [ABSTRACT FROM AUTHOR]

Background and Objectives: Long-acting injectable antiretrovirals represent a pharmacological alternative to oral formulations and an innovative clinical option to address adherence and reduce drug costs. Clinical studies in children and adolescents are characterised by ethical and logistic barriers complicating the identification of dose optimisation. Physiologically-based pharmacokinetic modelling represents a valuable tool to inform dose finding prior to clinical trials. The objective of this study was to simulate potential dosing strategies for existing long-acting injectable depot formulations of cabotegravir and rilpivirine in children and adolescents (aged 3-18 years) using physiologically-based pharmacokinetic modelling.Methods: Whole-body physiologically-based pharmacokinetic models were developed to represent the anatomical, physiological and molecular processes and age-related changes in children and adolescents through allometric equations. Models were validated for long-acting injectable intramuscular cabotegravir and rilpivirine in adults. Subsequently, the anatomy and physiology of children and adolescents were validated against available literature. The optimal doses of monthly administration of cabotegravir and rilpivirine were identified in children and adolescents, to achieve trough concentrations over the target concentrations derived in a recent efficacy trial of the same formulations.Results: Pharmacokinetic data generated through the physiologically-based pharmacokinetic simulations were similar to observed clinical data in adults. Optimal doses of long-acting injectable antiretrovirals cabotegravir and rilpivirine were predicted using the release rate observed for existing clinical formulations, for different weight groups of children and adolescents. The intramuscular loading dose and maintenance dose of cabotegravir ranged from 200 to 600 mg and from 100 to 250 mg, respectively, and for rilpivirine it ranged from 250 to 550 mg and from 150 to 500 mg, respectively, across various weight groups of children ranging from 15 to 70 kg.Conclusions: The reported findings represent a rational platform for the identification of suitable dosing strategies and can inform prospective clinical investigation of long-acting injectable formulations in children and adolescents. [ABSTRACT FROM AUTHOR]

Objectives: Lack of data on the pharmacokinetics of efavirenz in pregnant women at the 400 mg reduced dose currently prevents universal roll-out. Population pharmacokinetic modelling was used to explore pharmacokinetic endpoints at 200, 400 and 600 mg daily doses in pregnant women stratified by CYP2B6 metabolic status.Methods: The analysis was based on 252 plasma efavirenz concentrations from 77 pregnant women (77 sparse, 175 intensive) who received antiretroviral regimens containing 600 mg of efavirenz. The model was developed using NONMEM®. The effect of genetics was investigated and concentration-time courses at steady-state were simulated for individuals (n = 1000 each) classified as CYP2B6 slow, intermediate and fast metabolizers at 200, 400 and 600 mg daily doses.Results: At a 400 mg reduced dose, predicted mean (90% CI) mid-dose efavirenz concentration (C12) was 2.24 μg/mL (0.89-4.18) in pregnant women classified as slow metabolizers, compared with 0.87 μg/mL (0.34-1.64) in intermediate metabolizers and 0.78 μg/mL (0.30-1.47) in fast metabolizers. C12 was below the 0.47 μg/mL threshold determined within the ENCORE 1 trial in 10% at 400 mg, 4.6% at 600 mg and 3.4% with genotype-guided dosing. The 4.0 μg/mL toxicity threshold was exceeded in 4.6% at 400 mg, 13.5% at 600 mg and 5.2% with genotype-guided dosing.Conclusions: These data provide context for the ongoing debate about reduction in efavirenz dose to 400 mg during pregnancy and should be interpreted alongside the lower toxicity expected with the lower dose. Additional research is required to investigate genotype-guided dose reduction in pregnant women. [ABSTRACT FROM AUTHOR]

The antiretroviral drug efavirenz displays many desirable pharmacokinetic properties such as a long half-life enabling once daily dosing but suffers from central nervous system safety issues. Various nanotechnologies have been explored to mitigate some of the limitations with efavirenz. While there has been progress in increasing the bioavailability, there has been no attempt to assess the impact of increased exposure to efavirenz on central nervous system safety. The uptake of aqueous and solid drug nanoparticle (SDN) formulations of efavirenz was assessed in the human cerebral microvessel endothelial cells/D3 brain endothelial cell line. The mechanisms of uptake were probed using a panel of transport and endocytosis inhibitors. The cellular accumulation of an efavirenz aqueous solution was significantly reduced by amantadine, but this was not observed with SDNs. The uptake of efavirenz SDNs was reduced by dynasore, but concentrations of the efavirenz aqueous solution were not affected. These data indicate that efavirenz is a substrate for transporters in brain endothelial cells (amantadine is an inhibitor of organic cation transporters 1 and 2), and formation of SDNs may bypass this interaction in favour of a mechanism involving dynamin-mediated endocytosis. [ABSTRACT FROM AUTHOR]

Background: Co-administration of antineoplastics with ART is challenging due to potential drug-drug interactions (DDIs). However, trials specifically assessing such DDIs are lacking. Our objective was to simulate DDIs between the antineoplastics erlotinib and gefitinib with key antiretroviral drugs and to predict dose adjustments using a physiologically based pharmacokinetic (PBPK) model.Methods: In vitro data describing chemical properties and pharmacokinetic processes of each drug and their effect on cytochrome P450 isoforms were obtained from the literature. Plasma drug-concentration profiles were simulated in a virtual population of 50 individuals receiving erlotinib or gefitinib alone or with darunavir/ritonavir, efavirenz or etravirine. Simulated pharmacokinetic parameters and the magnitude of DDIs with probe drugs (midazolam, maraviroc) were compared with literature values. Erlotinib and gefitinib pharmacokinetics with and without antiretrovirals were compared and dose-adjustment strategies were evaluated.Results: Simulated parameters of each drug and the magnitude of DDIs with probe drugs were in agreement with reference values. Darunavir/ritonavir increased erlotinib and gefitinib exposure, while efavirenz and etravirine decreased erlotinib and gefitinib concentrations. Based on our predictions, dose-adjustment strategies may consist of once-daily dosing erlotinib at 25 mg and gefitinib at 125 mg with darunavir/ritonavir; or erlotinib at 200 mg and gefitinib at 375 mg with etravirine. The interaction with efavirenz was not overcome even after doubling erlotinib or gefitinib doses.Conclusions: PBPK models predicted the in vivo pharmacokinetics of erlotinib, gefitinib and the antiretrovirals darunavir/ritonavir, efavirenz and etravirine, and the DDIs between them. The simulated dose-adjustments may represent valuable strategies to optimize antineoplastic therapy in HIV-infected patients. [ABSTRACT FROM AUTHOR]

Objectives: Antiretroviral pharmacokinetics is defined by numerous factors affecting absorption, distribution, metabolism and elimination. Biological processes underpinning drug distribution are only partially characterized and multiple genetic factors generate cumulative or antagonistic interactions, which complicates the implementation of pharmacogenetic markers. The aim of this study was to assess the degree to which heredity influences pharmacokinetics through the quantification of the relative genetic contribution (rGC) for key antiretrovirals.Methods: A total of 407 patients receiving lopinavir/ritonavir, atazanavir/ritonavir, atazanavir, efavirenz, nevirapine, etravirine, maraviroc, tenofovir or raltegravir were included. Intra-patient variability (SDw) and inter-patient (SDb) variability were measured in patients with plasma concentrations available from more than two visits. The rGC was calculated using the following equation: 1 - (1 / F) where F = SDb(2) / SDw(2).Results: Mean (95% CI) rGC was calculated to be 0.81 (0.72-0.88) for efavirenz, 0.74 (0.61-0.84) for nevirapine, 0.67 (0.49-0.78) for etravirine, 0.65 (0.41-0.79) for tenofovir, 0.59 (0.38-0.74) for atazanavir, 0.47 (0.27-0.60) for atazanavir/ritonavir, 0.36 (0.01-0.48) for maraviroc, 0.15 (0.01-0.44) for lopinavir/ritonavir and 0 (0-0.33) for raltegravir.Conclusions: The rank order for genetic contribution to variability in plasma concentrations for the study drugs was efavirenz > nevirapine > etravirine > tenofovir > atazanavir > atazanavir/ritonavir > maraviroc > lopinavir/ritonavir > raltegravir, indicating that class-specific differences exist. The rGC strategy represents a useful tool to rationalize future investigations as drugs with higher rGC scores may represent better candidates for pharmacogenetic-pharmacokinetic studies. [ABSTRACT FROM AUTHOR]

Background. The antiretroviral drug efavirenz is widely used during breastfeeding. Evaluating its safety requires an understanding of its breast milk pharmacokinetics, level of breastfed infants' exposure, and potential influence of polymorphisms in drug disposition genes. Methods. For this observational study, we investigated plasma and breast milk pharmacokinetics of efavirenz and breastfed infants' exposure in human immunodeficiency virus positive nursing mothers and their breastfed infants. We also evaluated potential variability due to genetic polymorphisms in CYP2B6, NR1I3, CYP2A6, ABCB1, ABCB5, and ABCG2. Results. CYP2B6 516G>T was independently associated with efavirenz concentrations in maternal plasma, breast milk, and infant plasma (n = 134). When stratified based on CYP2B6 516G>T (n = 29 ; 11 GG, 10 GT and 8 TT), efavirenz pharmacokinetic parameters in plasma and breast milk differed significantly between patient groups. The median time-averaged milk-to-plasma concentration ratio was 1.10 (range: 0.57-1.71). The estimated maximum infant efavirenz dose from breast milk was 809 µg/kg/day (215-2760) and pediatric dose weight-adjusted exposure index was 4.05% (1.08-13.8). Infant plasma concentrations did not change significantly during the dosing interval, 157 ng/mL (28.6-1360) in pooled analysis and 315 ng/mL (108-1360) in CYP2B6 516TT group. Infant plasma concentrations were highest up to 8 days of age at 1590 ng/mL (190-4631) and decreased by about 90% in the age stratum day 9 to 3 months. No efavirenz related toxicity was reported. Conclusions. Most breastfed infants are exposed to <10% of the weight-adjusted therapeutic pediatric dose, the safety threshold for exposure to maternal drugs from breast milk. [ABSTRACT FROM AUTHOR]

Background and Objectives: Antiretrovirals are currently used for the treatment and prevention of HIV infection. However, poor adherence and low tolerability of some existing oral formulations can hinder their efficacy. Long-acting (LA) injectable nanoformulations could help address these complications by simplifying antiretroviral administration. The aim of this study is to inform the optimisation of intramuscular LA formulations for eight antiretrovirals through physiologically based pharmacokinetic (PBPK) modelling. Methods: A whole-body PBPK model was constructed using mathematical descriptions of molecular, physiological and anatomical processes defining pharmacokinetics. These models were validated against available clinical data and subsequently used to predict the pharmacokinetics of injectable LA formulations Results: The predictions suggest that monthly intramuscular injections are possible for dolutegravir, efavirenz, emtricitabine, raltegravir, rilpivirine and tenofovir provided that technological challenges to control their release rate can be addressed. Conclusions: These data may help inform the target product profiles for LA antiretroviral reformulation strategies. [ABSTRACT FROM AUTHOR]

The SLC22A1 influx transporter is expressed on the basolateral membrane of hepatocytes and is involved in the excretion of numerous cations. Inhibition of SLC22A1 by several antiretrovirals, such as the protease inhibitor darunavir, has not previously been determined. In order to better understand and predict drug-SLC22A1 interactions, a range of antiretrovirals were screened for SLC22A1-associated inhibition and transport. Stable SLC22A1-expressing KCL22 cells were produced previously by nucleofection. Control KCL22 cells were transfected with the empty vector pcDNA3.1. Accumulation of tetraethylammonium (5.5µM, 30 min) was determined in SLC22A1-expressing and mock-transfected cells with and without 50µM of SLC22A1 inhibitor prazosin, or 50µM of each antiretroviral drug. SLC22A1 IC50 values for efavirenz, darunavir, and prazosin were determined. Cellular accumulation of efavirenz and darunavir was also assessed in SLC22A1-expressing KCL22 cells and reversibility of this accumulation was assessed using prazosin. Tetraethylammonium accumulation was higher in SLC22A1-expressing cells compared to mock-transfected cells (10.6 ± 0.8µM vs. 0.3 ± 0.004µM, p = 0.009) and was significantly reduced in SLC22A1-expressing cells when co-incubated with all antiretrovirals tested except atazanavir, lamivudine, tenofovir, zidovudine, and raltegravir. Particularly noticeable was the predominance of SLC22A1 inhibitors in the protease inhibitor and non-nucleoside reverse transcriptase inhibitor classes. Absolute SLC22A1 IC50 values for efavirenz, darunavir, and prazosin were 21.8, 46.2, and 2.8µM, respectively. Efavirenz accumulation was higher in SLC22A1-expressing cells compared to mock-transfected cells (17% higher, p = 0.009) which was reversed using prazosin, whereas no difference was observed for darunavir (p = 0.86). These data inform the mechanistic basis for disposition, drug-drug interactions and pharmacogenetic candidate gene selection for antiretroviral drugs. [ABSTRACT FROM AUTHOR]

Background. The optimal penetration of antiretroviral agents into the central nervous system may be a balance between providing adequate drug exposure to inhibit human immunodeficiency virus (HIV) replication while avoiding concentrations associated with neuronal toxicities. Methods. Cerebrospinal fluid (CSF) exposure of efavirenz and the metabolites 7-hydroxy (7OH) and 8-hydroxy (8OH) efavirenz were assessed after at least 12 weeks of therapy in HIV-infected subjects randomized to commence antiretroviral regimens containing efavirenz at either 400 mg or 600 mg once daily. Results. Of 28 subjects (14 and 14 on efavirenz 400 mg and 600 mg, respectively), CSF HIV RNA was undetectable in all. Geometric mean CSF efavirenz, 7OH-, and 8OH-efavirenz concentrations (with 90% confidence intervals [CIs]) for the 400-mg and 600-mg dosing groups were 16.5 (13-21) and 19.5 (15-25) ng/mL; 0.6 (.4-.9) and 0.6 (.4-1) ng/mL; and 5.1 (4.0-6.4) and 3.1 (2.1-4.4) ng/mL, respectively. Efavirenz concentration in CSF was >0.51 ng/mL (proposed CSF 50% maximal inhibitory concentration for wild-type virus) in all subjects, and 8OH-efavirenz concentration in CSF was >3.3 ng/mL (a proposed toxicity threshold) in 11 of 14 and 7 of 14 subjects randomized to the 400 mg and 600 mg doses of efavirenz, respectively. Whereas CSF efavirenz concentration was significantly associated with plasma concentration (P < .001) and cytochrome P450 2B6 genotype (CSF efavirenz GG to GT/TT geometric mean ratio, 0.56 [90% CI, .42-.74]), CSF 8OH-efavirenz concentration was not (P = .242 for association and CSF 8OH-efavirenz GG to GT/TT geometric mean ratio, 1.52 [90% CI, .97- 2.36]). Conclusions. With both doses of efavirenz studied, CSF concentrations were considered adequate to inhibit HIV replication, although concentrations of 8OH-efavirenz were greater than those reportedly associated with neuronal toxicity. CSF exposure of 8OH-efavirenz was not dependent on plasma exposure and, as we postulate, may be subject to saturable pharmacokinetic effects. [ABSTRACT FROM AUTHOR]

Background and Objectives: In clinical practice, antiretroviral regimens are often interrupted or modified for intolerance and toxicity. The objective of this study was to develop an in vitro to in vivo extrapolation (IVIVE) approach to describe the interaction when efavirenz is switched to either maraviroc or nevirapine and to test different switching scenarios to identify the best strategy. Methods: In vitro data describing the chemical and absorption, tissue distribution, metabolism and excretion (ADME) characteristics of efavirenz, maraviroc and nevirapine were obtained from the literature, and used to simulate plasma exposures of these drugs using the Simcyp Population-Based Simulator. The predicted maraviroc and nevirapine exposures were compared with data from clinical studies evaluating their exposures following a switch from efavirenz. Results: Model predictions for maraviroc and nevirapine exposure were in agreement with observed data. The simulations suggest that the waning efavirenz induction effect following discontinuation necessitated increasing maraviroc to 600 mg twice daily for 1 week after efavirenz cessation. Alternatively, adequate exposure of maraviroc was shown with a dose of 450 mg for 2 weeks. Efavirenz waning induction did not affect nevirapine exposure. Conclusion: IVIVE modelling successfully predicted patient drug exposure. This modelling technique is able to inform the design of clinical studies, and allows assessment of pragmatic dosing strategies under complex therapeutic scenarios. [ABSTRACT FROM AUTHOR]

Objectives Efavirenz is widely used in first-line antiretroviral therapy in sub-Saharan Africa. However, exposure to efavirenz shows marked interindividual variability that is genetically mediated with potential for important pharmacodynamic consequences. The aims of this study were to assess the frequencies of CYP2B6, CYP2A6, UGT2B7 and CAR single nucleotide polymorphisms (SNPs) and their impact on plasma efavirenz concentration and clinical/immunological responses in Ghanaian patients. Methods Genomic DNA from 800 HIV-infected patients was genotyped for selected SNPs by real-time PCR-based allelic discrimination. Mid-dose plasma efavirenz concentrations were measured for 521 patients using HPLC with UV detection. Clinical outcomes in 299 patients on efavirenz were retrospectively assessed. Univariate and multivariate linear regression were performed using best subset selection. Time-to-event outcomes were analysed using a Cox proportional hazards regression model. Results The variant allele frequencies for CYP2B6 516G>T (rs3745274), CYP2B6 983T>C (rs28399499), CYP2A6 −48T>G (CYP2B6*9B; rs28399433), UGT2B7 802C>T (UGT2B7*2; rs7439366), UGT2B7 735A>G (UGT2B7*1c; rs28365062) and CAR 540C>T (rs2307424) were 48%, 4%, 3%, 23%, 15% and 7%, respectively. CYP2B6 516G>T, CYP2B6 983T>C and CYP2A6 −48T>G were associated with significantly elevated efavirenz concentrations. A trend towards association between plasma efavirenz concentration and CAR 540C>T was observed. CYP2B6 516G homozygosity was associated with immunological failure [adjusted hazards ratio compared with T homozygosity, 1.70 (1.04–2.76); P = 0.03]. Conclusions CYP2B6 and CYP2A6 SNPs were associated with higher plasma efavirenz concentrations due to reduction in major and minor phase I routes of elimination, respectively. Further prospective studies are needed to validate the pharmacodynamic correlates of these polymorphisms in this population. [ABSTRACT FROM PUBLISHER]

Background: Non-nucleoside reverse transcriptase inhibitor (NNRTI)-resistant mutants have been shown to emerge after interruption of suppressive NNRTI-based antiretroviral therapy (ART) using routine testing. The aim of this study was to quantify the risk of resistance by sensitive testing and correlate the detection of resistance with NNRTI concentrations after treatment interruption and virologic responses after treatment resumption. Methods: Resistance-associated mutations (RAMs) and NNRTI concentrations were studied in plasma from 132 patients who interrupted suppressive ART within SMART. RAMs were detected by Sanger sequencing, allele-specific PCR, and ultra-deep sequencing. NNRTI concentrations were measured by sensitive high-performance liquid chromatography. Results: Four weeks after NNRTI interruption, 19/31 (61.3%) and 34/39 (87.2%) patients showed measurable nevirapine (>0.25 ng/ml) or efavirenz (>5 ng/ml) concentrations, respectively. Median eight weeks after interruption, 22/131 (16.8%) patients showed ≥1 NNRTI-RAM, including eight patients with NNRTI-RAMs detected only by sensitive testing. The adjusted odds ratio (OR) of NNRTI-RAM detection was 7.62 (95% confidence interval [CI] 1.52, 38.30; p = 0.01) with nevirapine or efavirenz concentrations above vs. below the median measured in the study population. Staggered interruption, whereby nucleos(t)ide reverse transcriptase inhibitors (NRTIs) were continued for median nine days after NNRTI interruption, did not prevent NNRTI-RAMs, but increased detection of NRTI-RAMs (OR 4.25; 95% CI 1.02, 17.77; p = 0.03). After restarting NNRTI-based ART (n = 90), virologic suppression rates <400 copies/ml were 8/13 (61.5%) with NNRTI-RAMs, 7/11 (63.6%) with NRTI-RAMs only, and 51/59 (86.4%) without RAMs. The ORs of re-suppression were 0.18 (95% CI 0.03, 0.89) and 0.17 (95% CI 0.03, 1.15) for patients with NNRTI-RAMs or NRTI-RAMs only respectively vs. those without RAMs (p = 0.04). Conclusions: Detection of resistant mutants in the rebound viremia after interruption of efavirenz- or nevirapine-based ART affects outcomes once these drugs are restarted. Further studies are needed to determine RAM persistence in untreated patients and impact on newer NNRTIs. [ABSTRACT FROM AUTHOR]

Objectives We designed two different studies to evaluate two different combination antiretroviral therapy (cART) stopping strategies namely a ‘staggered stop’ approach (STOP 1 study) and a ‘protected stop’ approach (STOP 2 study) to find the best ‘universal stop’ strategy. Patients and methods Patients who stopped cART for any reason were recruited. In STOP 1, 10 patients on efavirenz continued dual nucleos(t)ide reverse transcriptase inhibitors (NRTIs) for 1 week after discontinuing efavirenz. Efavirenz concentrations were measured weekly for up to 3 weeks. In STOP 2, 20 patients stopped their cART and replaced it with two tablets of lopinavir/ritonavir (Kaletra) (100/50 mg) twice daily for 4 weeks. Lopinavir, efavirenz, nevirapine and tenofovir concentrations were measured weekly for up to 4 weeks. Virological and resistance testing were performed. Results In STOP 1 five patients still had efavirenz present (median t1/2 = 148.4 h) 3 weeks after stopping. In STOP 2, 15/20 patients had a viral load (VL) of <40 copies/mL and 3/20 patients had a reduction in VL by 4 weeks. Six patients opted not to stop lopinavir/ritonavir and still had <40 copies/mL at week 8. Week 1–4 median trough lopinavir concentrations were well above the EC95. Six patients still had detectable concentrations of original cART persisting for >1 week after stopping. No patients developed new resistance mutations. Conclusions Plasma efavirenz concentrations can persist up to 3 weeks after patients stop efavirenz-containing regimens. This suggests a strategy of stopping efavirenz only 1 week before NRTIs may not be long enough for some individuals. The use of lopinavir/ritonavir monotherapy for a 4 week period may be an alternative pharmacologically and virologically effective universal stopping strategy which warrants further investigation. [ABSTRACT FROM PUBLISHER]

Background. Plasma human immunodeficiency virus type 1 (HIV-1) RNA suppression <50 copies/mL is regarded as the optimal outcome of highly active antiretroviral therapy (HAART). Current viral load (VL) assays show increased sensitivity, but the significance of RNA detection <50 copies/mL is unclear. Methods. This study investigated the virologic outcomes of 1247 patients with VL <50 copies/mL at an arbitrary time point during HAART (= T0), according to whether the actual, unreported T0VL was 40-49 copies/mL, RNA detected <40 copies/mL (RNA1), or RNA not detected (RNA2), as measured by the Abbott Real Time assay. Predictors of rebound >50 and >400 copies/mL over 12 months following T0 were analyzed with Cox proportional hazards models incorporating the T0VL and demographic and clinical data. Results. Rebound rates >50 copies/mL were 34.2% for T0VL 40-49 copies/mL, 11.3% for RNA+, and 4.0% for RNA-; rebound rates >400 copies/mL were 13.0%, 3.8%, and 1.2%, respectively. The adjusted hazard ratios for rebound >50 copies/mL were 4.67 (95% confidence interval, 2.91-7.47; P < .0001) and 1.97 (1.25-3.11; P < .0001) with TOVL 40-49 copies/mL and RNA+, respectively, relative to RNA-, and 6.91 (2.90-16.47; P, .0001) and 2.88 (1.24-6.69; P < .0001), respectively, for rebound >400 copies/mL. The association was independent of adherence levels. Conclusions. In treated patients monitored by RealTime, a VL of 40-49 copies/mL and, to a lesser extent, RNA detection <40 copies/mL predict rebound >50 and >400 copies/mL independently of other recognized determinants. The goal of HAART may need to be revised to a lower cutoff than 50 copies/mL. [ABSTRACT FROM AUTHOR]

Background Nevirapine is metabolized by CYP2B6 and polymorphisms within the CYP2B6 gene partly explain inter-patient variability in pharmacokinetics. The aim of this study was to model the complex relationship between nevirapine exposure, weight and genetics (based on combined analysis of CYP2B6 516G > T and 983T > C single nucleotide polymorphisms). Methods Non-linear mixed-effects modelling was used to estimate pharmacokinetic parameters from 275 patients. Simulations of the nevirapine concentration profile were performed with dosing regimens of 200 mg twice daily and 400 mg once daily for individuals with body weights of 50, 70 and 90 kg in combination with CYP2B6 genetic variation. Results A one-compartment model with first-order absorption best described the data. Population clearance was 3.5 L/h with inter-patient variability of 24.6%. 516T homozygosity and 983C heterozygosity were associated with 37% and 40% lower clearance, respectively. Body weight was the only significant demographic factor influencing clearance, which increased by 5% for every 10 kg increase. For individuals with higher body weight, once-daily nevirapine was associated with a greater risk of sub-therapeutic drug exposure than a twice-daily regimen. This risk was offset in individuals who were 516T homozygous or 983C heterozygous in which drug exposure was optimal for > 95% of patients with body weight of ≤70 kg. Conclusions The data suggest that a 400 mg once-daily dose could be implemented in accordance with CYP2B6 polymorphism and body weight. However, the use of nevirapine once daily (immediate release; off-label) in the absence of therapeutic drug monitoring is not recommended due to the risk of inadequate exposure to nevirapine in a high proportion of patients. There are different considerations for the extended-release formulation (nevirapine XR) that demonstrate minimal peak-to-trough fluctuations in plasma nevirapine levels. [ABSTRACT FROM PUBLISHER]

Objectives: Efavirenz is extensively metabolized by CYP2B6, and associations between CYP2B6 polymorphisms and plasma efavirenz exposure have been reported. The objective of this study was to investigate CYP2B6 haplotype structure and functional consequences in a Latin American population. Patients and methods: Two hundred and nineteen patients were recruited at Fundacio'n Arriara'n, Chile, between September and December 2008. Plasma efavirenz concentrations were determined using liquid chromatography with mass spectrometry. Genotyping for 30 single nucleotide polymorphisms (SNPs) with a minor allele frequency of >0.05 in the HapMap CEU population at intervals of ~1 kb across the CYP2B6 locus was conducted using Sequenom iPLEX MALDI-TOF. Results: Thirteen SNPs passed quality control and, of these, statistically significant associations (P<0.001) with plasma efavirenz concentrations were observed for 11. Pairwise tagging SNP analysis (R²>.0.8) identified 3 SNPs (rs10403955, rs2279345 and rs8192719) representative of the 11 associated SNPs. A composite genetic model of these three alleles was constructed, and an association between carriers of four to six of these alleles and the risk of efavirenz plasma concentrations >4 µg/mL was identified with an odds ratio of 48.1 (95% confidence interval: 13.5-207.7). This represents a positive predictive value of 80.9% and a negative predictive value of 91.8%, with sensitivity of 57.9% and specificity of 97.2%. Conclusions: A composite genetic model of CYP2B6 SNPs in a Chilean HIV-positive cohort may have value in predicting concentrations of efavirenz associated with a higher likelihood of CNS toxicity. Further investigation of the functional basis of these associations is now required. [ABSTRACT FROM AUTHOR]

Background: Interaction of antiretrovirals with drug transporters such as P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), breast cancer resistance protein (BCRP) and solute carrier organic anion transporter (SLCO) may influence the emergence of viral mutants by altering intracellular drug concentrations. Here we characterize the effect of transporter expression in a variety of cell types such as control CEM, CEMVBL (P-gp-overexpressing), CEME1000 (MRP1-overexpressing), MT4, control MDCKII, MDCKIIMDR1 (P-gp-overexpressing) and peripheral blood mononuclear cells (PBMCs) on the uptake of [14C]efavirenz and [3H]nevirapine. We also investigated the lipophilicity of [14C]efavirenz and [3H]nevirapine. [ABSTRACT FROM PUBLISHER]

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Antiretroviral protease inhibitors such as lopinavir and saquinavir have been shown to be substrates of ABCB1. Co-administration with the potent ABCB1 and CYP3A4 inhibitor, ritonavir, has shown improved pharmacokinetics and subsequent therapeutic effects of protease inhibitors. Darunavir is a recently licensed protease inhibitor with potent antiretroviral effects but has yet to be characterized as a potential substrate for drug transporters. WHAT THIS STUDY ADDS • Darunavir was shown to be a substrate of ABCB1 using different in vitro models. Inhibition of ABCB1 alone does not increase cellular accumulation of darunavir in PBMCs. However, inhibition of ABCB1 and ABCCs significantly increased cellular accumulation of darunavir whereas inhibition of influx transporters significantly reduced the cellular accumulation of darunavir in PBMCs. AIMS ABCB1, some ABCCs and SLCOs have been reported to affect the intracellular accumulation of various protease inhibitors in vitro and ex vivo. Darunavir is the most recently licensed protease inhibitor and we sought to investigate the ability of transport inhibitors to influence its intracellular accumulation in lymphocytes from healthy volunteers. METHODS The intracellular accumulation of radiolabelled darunavir was assessed using CEM cells and ABCB1-overexpressing CEMVBL cells. Apical and basolateral transport of radiolabelled darunavir through MDCKII monolayers was also studied. Finally the ability of known inhibitors to influence intracellular accumulation of darunavir in peripheral blood mononuclear cells (PBMC) was investigated. RESULTS CEMVBL cells (1.4 ± 0.6, P < 0.001, 95% CI for the difference = 0.46, 0.80, n= 7) had significantly lower accumulation of darunavir compared with CEM cells (5.6 ± 0.7, n= 7) and this was reversed by addition of tariquidar (30 nm, 4.6 ± 0.8, P < 0.001, 95% CI =−0.64, −0.41, n= 4). In MDCKII-ABCBI cells, transport from the basal to the apical compartment was observed and this was also reversible with the addition of tariquidar. In PBMCs, dipyridamole (6.9 ± 1.3, P < 0.01, 95% CI for the difference =−1.16, −0.30, ( n= 8) significantly increased whilst montelukast (5.7 ± 1.0, P < 0.01, 95% CI for the difference = 0.16, 0.79, n= 8) significantly decreased the intracellular accumulation of darunavir when compared with control (6.2 ± 1.1, n= 8). CONCLUSIONS Darunavir is a substrate for efflux and influx transporters in PBMC and intracellular concentrations can be manipulated using known inhibitors. [ABSTRACT FROM AUTHOR]

Background. Tenofovir is one of the most widely used antiretroviral drugs. Tenofovir undergoes renal clearance by a combination of glomerular filtration and active tubular secretion. Although rare, the mechanism by which tenofovir causes renal damage is not well characterized. We have explored the association between kidney tubular dysfunction (KTD) and polymorphisms in genes encoding drug transporters. Methods. All consecutive, human immunodeficiency virus (HIV)-infected patients receiving tenofovir-containing antiretroviral regimens who were seen at a single institution during the first trimester of 2008 were enrolled in the study. KTD was defined by the presence of at least 2 of the following abnormalities: nondiabetic glucosuria, urine phosphate wasting, hyperaminoaciduria, β2-microglobulinuria, and increased fractional excretion of uric acid. Twelve single-nucleotide polymorphisms in the ABCC2, ABCC4, SCL22A6, SLC22A11, and ABCB1 genes were analyzed using TaqMan 5′-nuclease assays. Results. A total of 115 HIV-infected patients were examined, of whom 19 (16.5%) had KTD. The percentage of patients with KTD was higher among those with genotype CC at position -24 of ABCC2 than among those with genotypes CT and TT (24% [16 of 68 patients] vs. 6% [3 of 47 patients]; Pp.020). In a multivariate analysis, older age (odds ratio [OR], 1.1; 95% confidence interval [CI], 1.0-1.2; Pp.024), lower body weight (OR, 0.9; 95% CI, 0.8-0.9; Pp.048), and genotype CC at ABCC2 position -24 (OR, 5; 95% CI, 1.2-21; Pp.027) were independently associated with KTD. Conclusions. Approximately 17% of HIV-infected patients treated with tenofovir had KTD. Homozygosity for the C allele at position -24 of the ABCC2 gene was strongly associated with KTD in this population. This polymorphism may help to identify patients at greater risk for developing tenofovir-associated tubulopathy, and close monitoring of renal function is warranted for these patients. [ABSTRACT FROM AUTHOR]

Aims Carbamazepine (CBZ) is an inducer of cytochrome P450 enzymes, which have been implicated in many drug interactions. However, for immunosuppressant and anti-HIV drugs, whose main site of action is the lymphocyte, induction of P-glycoprotein (Pgp) may also be important. In this study, we have investigated whether CBZ acts as an inducer of Pgp in lymphocytes. Methods Pgp expression was assessed by flow cytometry and real-time reverse transcriptase-polymerase chain reaction using lymphocytes from four healthy subjects after incubation with therapeutic concentrations of CBZ, using rifampicin as a positive control. Binding to DR-4 elements in the MDR1 promoter was assessed by electrophoretic mobility shift assay (EMSA) and a luciferase-reporter construct. Results CBZ increased MDR1 mRNA expression at 6 h by 3.7-fold [95% confidence interval (CI) 0, 7.6) when compared with controls. CBZ increased lymphocyte Pgp expression at 72 h by 7.6-fold (95% CI 2.1, 13.2) over control values. EMSA revealed a 2.1-fold (95% CI 1.5, 2.7) increased binding to the DR-4 element of CBZ when compared with control values. Activation of the DR-4 element was confirmed using reporter constructs. Rifampicin also had similar effects in all experiments. Conclusions Carbamazepine induces Pgp in a manner comparable to rifampicin, by increasing binding to the DR4 element. This has implications for interactions involving drugs whose site of action is the lymphocyte. [ABSTRACT FROM AUTHOR]

Highly active anti-retroviral therapy (HAART) has drastically altered the course of HIV-1 infection, resulting in a major decrease in morbidity and mortality. However, adverse drug reactions and long-term toxicities associated with HAART are now a concern. A major toxicity that has been highlighted by the increased use of HAART is related to mitochondrial side-effects. At the same time, analysis of the biochemical pathways involved in programmed cell death has revealed that mitochondria are main sensors in this process. In this article, the regulation of mitochondrial damage following the use of nucleoside analogue reverse transcriptase inhibitors (NRTIs) and protease inhibitors is discussed, with a particular focus on the putative molecular mechanisms involved. [Copyright &y& Elsevier]

Existing HIV therapy using oral antiretrovirals (ARVs) can result in pill fatigue and sub-optimal adherence. Microneedle array patches (MAPs) offer non-invasive, blood-free and painless drug delivery, and may improve patient adherence. The objective of this study was to develop a novel physiologically-based pharmacokinetic (PBPK) model to simulate the systemic pharmacokinetics of cabotegravir and rilpivirine MAPs using the intradermal route. The developed PBPK models were qualified against observed pharmacokinetic data after intramuscular (IM) and intradermal administration of long-acting nanoformulated rilpivirine to rats, and for IM administration of both drugs to healthy adults. Qualified models were then utilised to estimate suitable MAP characteristics (e.g. nanoformulation dose and release rates) and inform dosing strategies to maintain plasma concentrations above target trough concentrations for the designated dosing interval. PBPK models simulated q4-weekly loading and maintenance doses of 360 mg and 180 mg for long-acting formulated cabotegravir between the release rates of 1 × 10−3–3 × 10−3h−1 and 1 × 10−3–1.5 × 10−3h−1 respectively, for a 70 kg adult. Estimated patch size was 60 cm2 for a 360 mg dose of cabotegravir. For q4-weekly dosing, rilpivirine required a 1080 mg loading dose and a 540 mg maintenance dose with release rates of 1.5 × 10−3–2.5 × 10−3h−1 and 5 × 10−4–1 × 10−3h−1, respectively. Weekly dosing was also evaluated to assess the potential application from a smaller patch size. The ability to self-administer via a patch that is only left in place for a short duration makes longer durations less important than for some other long-acting approaches. Weekly cabotegravir required 60 mg between release rates 7 × 10−3–9 × 10−3h−1 and rilpivirine required 270 mg and 180 mg respectively between release rates of 7 × 10−3–9 × 10−3h−1. This model estimated optimal dose and release rates for cabotegravir and rilpivirine MAPs. Our approach provides a computational platform to support rational development of intradermal administration strategies to tackle problems associated with chronic oral ARV administration. [ABSTRACT FROM AUTHOR]

We evaluated the pharmacokinetics of double-dose levonorgestrel (LNG) implants to overcome the drug–drug interaction with efavirenz-based antiretroviral therapy (ART). We conducted a nonrandomized, open-label, parallel-group, longitudinal pharmacokinetic study among Ugandan women ages 18–45 years. Participants with HIV on ART containing efavirenz 600 mg received 300 mg of LNG implants (Jadelle®, Bayer, New Zealand): 300LNG+ART group. We compared our outcomes with women without HIV using standard dose, 150 mg of LNG implants: 150LNG group. The implant was placed on day zero in both groups, and we quantified plasma LNG concentrations over 48 weeks post implant insertion. LNG pharmacokinetic parameters were estimated using noncompartmental techniques. Our primary outcome was the geometric mean ratio with 90% confidence intervals of LNG area under the concentration–time curve over 24 weeks (AUC 0–24w) between groups. Demographic data were described as median (interquartile range). A secondary outcome compared between-group percent of LNG concentrations ≥300 pg/mL, a minimum threshold selected a priori based on observed pregnancies in Ugandan women on standard-dose LNG implants plus efavirenz. We enrolled 27 women in the 300LNG+ART group (34 [28.0 to 40.5] years and 61.0 [49.8–66.0] kg) and 19 women in the 150LNG group (33 [30.0 to 34.5] years and 64.9 [59.0 to 74.5] kg). LNG AUC 0–24w was 34% lower for 300LNG+ART versus 150LNG (geometric mean 9998 vs. 15,231 pg*week/mL, respectively [geometric mean ratio 0.66 (90% confidence intervals, 0.54 to 0.80)]). The percentage of participants with LNG concentrations ≥300 pg/mL was not statistically different between groups at week 24 (300LNG+ART: 74.1%; 150LNG: 89.5%; p = 0.27). Double-dose LNG implant did not completely overcome the drug–drug interaction with efavirenz. In women using ART containing efavirenz, placing two implant systems (300 mg) did not normalize LNG pharmacokinetics compared with the standard-dose implant (150 mg), and some women had evidence of ovulatory activity. Alternative ART without drug–drug interactions, such as dolutegravir, is recommended with contraceptive implants. [ABSTRACT FROM AUTHOR]

An abstract of the article "The Importance of HIV RNA Detection Below 50 Copies per mL in HIV-Positive Patients on Antiretroviral Therapy: An Observational Study" by Tomas Doyle et al. is presented.