Therapeutic drug monitoring in children with HIV/AIDS

Virological failure of antiretroviral therapy and associated social and clinical factors in children and adolescents living with HIV

   According to the World Health Organization, sustained virological suppression of 90 % should be achieved among children and adolescents living with HIV / AIDS, which makes it important to assess the prevalence of virological failure of antiretroviral therapy.   The aim of this study was to determine the prevalence of virological failure and the clinical factors associated with it, as well as therapeutic drug monitoring in groups divided by the viral load level among children and adolescents with HIV.   Materials and Methods: A retrospective analysis of the medical records of 184 children and adolescents receiving antiretroviral therapy and registered at the Irkutsk Regional Center for the Prevention and Control of AIDS and Infectious Diseases, Irkutsk, was carried out. The study included 172 children aged 1-18 years with perinatal HIV infection. Patients were divided into groups depending on the level of viral load: group 1 – 21 patients with viral load > 1000 copies/ml of plasma, group 2 – 42 patients with viral load 50– 1000 copies/ml of plasma, group 3 – 109 patients with undetectable viral load (< 50 copies/ml). All patients underwent standard tests in accordance with clinical guidelines for the treatment of HIV infection in children, as well as therapeutic drug monitoring.   Results. Against the background of ongoing antiretroviral therapy, a significant number of patients 21 / 172 (12,2 %) experienced virological failure. The proportion of children and adolescents with incomplete suppression of HIV replication is 42 / 172 (24,4 %). Statistically significant differences were obtained by changing the ART regimen (p = 0,031). In the first group, the proportion of patients who changed the therapy regimen is 7 / 21 (33,3 %), which is two times less than in the group with a zero viral load of 70 / 109 (64,2 %). There are differences in the proportion of children and adolescents with zero concentrations of ritonavir and lopinavir (p = 0,020 and p = 0,012) in the three compared groups. The distribution of patients with zero concentrations was as follows: for ritonavir in the first group 3 / 17 (17,6 %), in the second – 8/37 (21,6 %), in the third group – 4/80 (5 %); for lopinavir – 4/17 (23,5 %), 6/36 (16,7 %), 3/80 (3,8 %), respectively.   Conclusion. This study demonstrates that the prevalence of virological failure among children and adolescents receiving ART remains high. To achieve sustained virological suppression in children and adolescents taking a protease inhibitor regimen, adherence to therapy must be increased. As one of the methods for assessing adherence, therapeutic drug monitoring can be used.

Impact of Single Nucleotide Polymorphisms on Plasma Concentrations of Efavirenz and Lopinavir/Ritonavir in Chinese Children Infected with the Human Immunodeficiency Virus

Single nucleotide polymorphisms (SNPs) in the genes that encode the cytochrome P450 (CYP) drug metabolizing enzymes and drug transporters have been reported to influence antiretroviral drug pharmacokinetics. Although primarily metabolized by CYP2B6 and -3A, efavirenz (EFV) and lopinavir/ritonavir (LPV/r) are substrates of P-glycoprotein and the solute carrier organic (SLCO) anion transporter, respectively. We investigated the association between SNPs and efavirenz (EFV) or lopinavir/ritonavir (LPV/r) concentrations in Chinese children infected with the human immunodeficiency virus (HIV). Genotyping was performed on CYP2B6 516G→T, -1459C→T, and -983T→C, ABCB1 3435C→T, and SLCO1B1 521T→C in 229 HIV-infected Chinese pediatric patients (age range 4.0 to 17.5 yrs). Plasma concentrations of EFV and LPV/r were measured using validated high-performance liquid chromatography coupled with the mass spectrum method among 39 and 69 children who received EFV- and LPV/r-containing regimens, respectively. The frequencies of CYP2B6 516G→T in the study participants were 71%, 25%, and 4% for the G/G, G/T, and T/T genotypes, respectively. Among the children under therapeutic drug monitoring, 21% and 39% experienced EFV and LPV concentrations, respectively, above the upper threshold of the therapeutic window. CYP2B6 516G→T was significantly associated with EFV concentrations (p<0.001). Older children (older than 10 yrs) were more likely to have significantly higher EFV concentrations than the younger ones (p=0.0314). CYP2B6 genotyping and EFV concentration monitoring may help optimize antiretroviral therapy in pediatric patients who initiate an EFV-based regimen.

Effect of Lopinavir and Nevirapine Concentrations on Viral Outcomes in Protease Inhibitor-experienced HIV-infected Children

BACKGROUND

Adequate exposure to antiretroviral drugs is necessary to achieve and sustain viral suppression. However, the target antiretroviral concentrations associated with long-term viral suppression have not been adequately defined in children. We assessed the relationship between plasma lopinavir or nevirapine concentrations and the risk of subsequent viremia in children initially suppressed on antiretroviral therapy.

METHODS

After an induction phase of antiretroviral treatment, 195 children with viral suppression (viral load ≤400 copies/mL) were randomized to continue a lopinavir/ritonavir-based regimen or to switch to a nevirapine-based regimen (together with lamivudine and stavudine). Viral load and lopinavir or nevirapine concentrations were measured at clinic visits 4, 8, 12, 16, 20, 24, 36, 52, 64 and 76 weeks post randomization. Cox multiple failure event models were used to estimate the effects of drug concentrations on the hazard of viremia (viral load >50 copies/mL) RESULTS:: At randomization, the median (interquartile range) age, CD4 T-Lymphocyte percentage, weight-for-age and weight-for-height z scores were 19 (16-24) months, 29% (23-37), -0.6 (-1.3 to 0.2) and -3.2 (-4.1 to -2.1), respectively. The proportion of children with viral load 51-400 copies/mL at randomization was 43%. The hazard of subsequent viremia during follow-up was increased for lopinavir concentrations <1 versus ≥1 mg/L [adjusted hazard ratio 0.62 (95% confidence interval, 0.40-0.94)] and for children with viral loads 51-400 copies/mL at randomization. Nevirapine concentrations were not significantly associated with subsequent viremia.

CONCLUSIONS

Plasma lopinavir concentrations predicted viral outcomes in children receiving lopinavir-based antiretroviral therapy. Our findings support a minimum target concentration of ≥1 mg/L of lopinavir to ensure sustained viral suppression.

The physical and psychological effects of HIV infection and its treatment on perinatally HIV-infected children

INTRODUCTION

As highly active antiretroviral therapy (HAART) transforms human immunodeficiency virus (HIV) into a manageable chronic disease, new challenges are emerging in treating children born with HIV, including a number of risks to their physical and psychological health due to HIV infection and its lifelong treatment.

METHODS

We conducted a literature review to evaluate the evidence on the physical and psychological effects of perinatal HIV (PHIV+) infection and its treatment in the era of HAART, including major chronic comorbidities.

RESULTS AND DISCUSSION

Perinatally infected children face concerning levels of treatment failure and drug resistance, which may hamper their long-term treatment and result in more significant comorbidities. Physical complications from PHIV+ infection and treatment potentially affect all major organ systems. Although treatment with antiretroviral (ARV) therapy has reduced incidence of severe neurocognitive diseases like HIV encephalopathy, perinatally infected children may experience less severe neurocognitive complications related to HIV disease and ARV neurotoxicity. Major metabolic complications include dyslipidaemia and insulin resistance, complications that are associated with both HIV infection and several ARV agents and may significantly affect cardiovascular disease risk with age. Bone abnormalities, particularly amongst children treated with tenofovir, are a concern for perinatally infected children who may be at higher risk for bone fractures and osteoporosis. In many studies, rates of anaemia are significantly higher for HIV-infected children. Renal failure is a significant complication and cause of death amongst perinatally infected children, while new data on sexual and reproductive health suggest that sexually transmitted infections and birth complications may be additional concerns for perinatally infected children in adolescence. Finally, perinatally infected children may face psychological challenges, including higher rates of mental health and behavioural disorders. Existing studies have significant methodological limitations, including small sample sizes, inappropriate control groups and heterogeneous definitions, to name a few.

CONCLUSIONS

Success in treating perinatally HIV-infected children and better understanding of the physical and psychological implications of lifelong HIV infection require that we address a new set of challenges for children. A better understanding of these challenges will guide care providers, researchers and policymakers towards more effective HIV care management for perinatally infected children and their transition to adulthood.

Tetronic® 904-containing polymeric micelles overcome the overexpression of ABCG2 in the blood-brain barrier of rats and boost the penetration of the antiretroviral efavirenz into the CNS

AIM

To assess the involvement of ABCG2 in the pharmacokinetics of efavirenz in the blood-brain barrier (BBB) and investigate a nanotechnology strategy to overcome its overexpression under a model of chronic oral administration. Materials & methods A model of chronic efavirenz (EFV) administration was established in male Sprague-Dawley rats treated with a daily oral dose over 5 days. Then, different treatments were conducted and drug concentrations in plasma and brain measured.

RESULTS

Chronic treatment with oral EFV led to the overexpression of ABCG2 in the BBB that was reverted after a brief washout period. Moreover, gefitinib and the polymeric amphiphile Tetronic(®) 904 significantly inhibited the activity of the pump and potentiated the accumulation of EFV in CNS. The same effect was observed when the drug was administered within mixed micelles containing TetronicT904 as the main component.

CONCLUSION

Tetronic 904-containing polymeric micelles overcame the overexpression of ABCG2 in the BBB caused by chronic administration of EFV then boosting its penetration into the CNS.

Measuring adherence to antiretroviral therapy in children and adolescents in western Kenya

Introduction

High levels of adherence to antiretroviral therapy (ART) are central to HIV management. The objective of this study was to compare multiple measures of adherence and investigate factors associated with adherence among HIV-infected children in western Kenya.

Methods

We evaluated ART adherence prospectively for six months among HIV-infected children aged ≤14 years attending a large outpatient HIV clinic in Kenya. Adherence was reported using caregiver report, plasma drug concentrations and Medication Event Monitoring Systems (MEMS^®). Kappa statistics were used to compare adherence estimates with MEMS^®. Logistic regression analyses were performed to assess the association between child, caregiver and household characteristics with dichotomized adherence (MEMS^® adherence ≥90% vs. <90%) and MEMS^® treatment interruptions of ≥48 hours. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated.

Results

Among 191 children, mean age at baseline was 8.2 years and 55% were female. Median adherence by MEMS^® was 96.3% and improved over the course of follow-up (p<0.01), although 49.5% of children had at least one MEMS^® treatment interruption of ≥48 hours. Adherence estimates were highest by caregiver report, and there was poor agreement between MEMS^® and other adherence measures (Kappa statistics 0.04–0.37). In multivariable logistic regression, only caregiver-reported missed doses in the past 30 days (OR 1.25, 95% CI 1.14–1.39), late doses in the past seven days (OR 1.14, 95% CI 1.05–1.22) and caregiver-reported problems with getting the child to take ART (OR 1.10, 95% CI 1.01–1.20) were significantly associated with dichotomized MEMS^® adherence. The caregivers reporting that ART made the child sick (OR 1.12, 95% CI 1.01–1.25) and reporting difficulties in the community that made giving ART more difficult (e.g. stigma) (OR 1.14, 95% CI 1.02–1.27) were significantly associated with MEMS^® treatment interruptions in multivariable logistic regression.

Conclusions

Non-adherence in the form of missed and late doses, treatment interruptions of more than 48 hours and sub-therapeutic drug levels were common in this cohort. Adherence varied significantly by adherence measure, suggesting that additional validation of adherence measures is needed. Few factors were consistently associated with non-adherence or treatment interruptions.

Pharmacokinetics of lopinavir determined with an ELISA test in youths with perinatally acquired HIV

OBJECTIVE

To investigate the plasma levels of lopinavir by enzyme-linked immunosorbent assay (ELISA) in a cohort of patients who were vertically infected with human immunodeficiency virus 1 (HIV).

METHODS

Plasma levels of lopinavir (Cmin) were determined by ELISA test in patients treated with lopinavir/ritonavir-based combined antiretroviral therapy who had achieved virological response after 4 wk of therapy. Reference lopinavir concentrations were Cmin 1-8 μg/mL. Correlation between lopinavir plasma concentration and continuous variables was evaluated by mean of Pearson correlation coefficient. Differences in lopinavir (LPV) concentration for binary categorical variables were assessed by Mann-Whitney test, while for variables with more than two categories Kruskal-Wallis test was used.

RESULTS

Thirty-four patients were enrolled; median age was 133 mo (15-265). The median lopinavir dose tested was 383.5 mg/kg (IQR: 266.6-400 mg/kg), with a median plasma concentration of 8.8 μg/mL (IQR: 5-14 μg/mL). Lopinavir Cmin was <1 μg/mL in only one sample (2.9 %), while 14 samples had Cmin between 1 and 8 μg/mL (41.2 %) and 19 (55.9 %) > 8 μg/mL. No significant correlations were found between plasma concentrations of lopinavir and the continuous variables considered in the study. A negative but, not completely significant, correlation was found between plasma drug concentration and body mass index (r = -0.29; p = 0.09).

CONCLUSIONS

The use of a simple and relatively cost-effective methodology might render therapeutic drug monitoring (TDM) appeal in the daily clinical practice.

Are lopinavir and efavirenz serum concentrations in HIV-infected children in the therapeutic range in clinical practice?

BACKGROUND

In antiretroviral treatment the role of therapeutic drug monitoring via measurement of serum levels remains unclear, especially in children.

AIM

To quantify exposure to LPV and EFV in children receiving therapy in a routine clinical setting in order to identify risk factors associated with inadequate drug exposure.

METHOD

A prospective study was conducted in a routine clinical setting in Tygerberg Children's Hospital, South Africa. A total of 53 random serum levels were analyzed. Serum concentrations were determined by an established high-performance liquid chromatography method.

RESULTS

Of 53 HIV-infected children treated with lopinavir (n = 29, median age 1·83 y) or efavirenz (n = 24, median age 9·3 years), 12 showed serum levels outside the therapeutic range (efavirenz) or below Cmin (lopinavir). Low bodyweight, rifampicin co-treatment, and significant comorbidity were potential risk factors for inadequate drug exposure.

CONCLUSION

These findings, together with previous studies, indicate that therapeutic drug monitoring can improve the management of antiretroviral therapy in children at risk.

Extended mathematical model for "in vivo" quantification of the interaction betweeen atazanavir and bilirubin

The objective of the present work was to conduct an "in vivo" analysis of the atazanavir-bilirubin interaction. We developed a new mathematical approach to PK/PDPK models for competitive interaction based on the Michaelis-Menten equation, which was applied to patients with polymorphisms in the gene for UDP-glucuronosyltransferase 1A1 (UGT1A1). Atazanavir is known to induce concentration-dependent increases in bilirubin plasma levels. Thus, we employed our mathematical model to analyse rises in steady state atazanavir and bilirubin concentrations, ultimately plotting a nomogram for detection of suboptimal atazanavir exposure. Application of our model revealed that an absolute value or a steady state increase in bilirubin falling below 3.8Φ µmol/L (where Φ is a correction factor, =1 for UGT1A1 wild type and ≠1 for UGT1A1 variants) could be used to predict suboptimal atazanavir exposure and treatment failure. Thus, we have successfully established a new mathematical approach for pharmacodynamic-pharmacokinetic modelling of the interaction between atazanavir and bilirubin, as it relates to genetic variants of UGT1A1. Taken together, our findings indicate that bilirubin plasma levels represent a valuable marker of atazanavir exposure.

Long-term response to combination antiretroviral therapy in HIV-infected children in the Netherlands registered from 1996 to 2012

OBJECTIVES

To describe demographic and treatment characteristics of the Dutch vertically HIV-infected paediatric population from 1996 to 2012, and to investigate the long-term virological and immunological response to combination antiretroviral therapy (cART), with emphasis on the influence of age at cART initiation and initial CD4 cell counts.

DESIGN

Descriptive cohort study.

METHODS

From 1996 to 2012, all paediatric HIV clinics in the Netherlands provided data on their HIV-infected population. Descriptive statistics, parametric and non-parametric comparative tests, and random-effects linear regression models were performed to investigate the different aspects of this cohort.

RESULTS

A total of 229 vertically HIV-infected children were included. The majority of all mothers (64%) and almost half of the children (43%) originated from sub-Saharan Africa. Ritonavir-boosted lopinavir and efavirenz have replaced indinavir, nelfinavir and nevirapine as preferred first-line cART regimens. Long-term CD4 T-cell reconstitution (with CD4 cell counts corrected for age) was independent of age and CD4 cell count at cART initiation. The decline in HIV viral load after cART introduction occurred faster over the studied time period. The percentage of children with an undetectable viral load rose substantially from 1996 to 2012. Mortality was 0.3 per 100 person-years.

CONCLUSION

A sustained immunological response in the Dutch paediatric HIV-infected population was independent of age as well as CD4 cell count at cART initiation, despite a higher initial HIV viral load in the youngest children. The percentage of children with an undetectable HIV viral load rose substantially over the years and there was a low mortality rate in comparison with reports from other industrialized countries.

Atazanavir-bilirubin interaction: a pharmacokinetic-pharmacodynamic model

Purpose

The aim of this work was to analyze the atazanavir–bilirubin relationship, using a new mathematical approach to pharmacokinetic–pharmacodynamic models, for competitive drug interactions based on Michaelis–Menten equations.

Patients and methods

Because atazanavir induces an increase of plasma bilirubin levels, in a concentration-dependent manner, we developed a mathematical model, based on increments of atazanavir and bilirubin concentrations at steady state, in HIV infected (HIV⁺) patients, and plotted the corresponding nomogram for detecting suboptimal atazanavir exposure.

Results

By applying the obtained model, the results indicate that an absolute value or an increment of bilirubin at steady state below 3.8 μmol/L, are predictive of suboptimal atazanavir exposure and therapeutic failure.

Conclusion

We have successfully implemented a new mathematical approach to pharmacokinetic–pharmacodynamic model for atazanavir–bilirubin interaction. As a result, we found that bilirubin plasma levels constitute a good marker of exposure to atazanavir and of viral suppression.

Children with HIV are not small adults: what is different in pharmacology?

PURPOSE OF REVIEW

The pharmacokinetics of antiretroviral drugs are highly variable among HIV-infected children. This review describes pharmacokinetic processes in children and recent pharmacokinetic data in children with HIV. The general lack of pharmacokinetic data and the potential role of therapeutic drug monitoring are discussed.

RECENT FINDINGS

It was found unexpectedly that exposure to lopinavir is decreased in the first 6 months of life. Recent findings of subtherapeutic efavirenz concentrations in children suggest that pediatric dose recommendations should be re-evaluated. In addition, recommended dosing of lamivudine leads to lower exposure in children younger than 6 years of age. Preliminary results of pediatric fixed-dose combination tablets for HIV-infected children with a higher nevirapine to stavudine and lamivudine ratio than adult fixed-dose combinations suggest adequate drug exposure. As an alternative to plasma sampling, concentrations of nevirapine can be determined in saliva.

SUMMARY

There is a shortage of pharmacokinetic data in the highly variable population of HIV-infected children. Selected pharmacology studies should be undertaken to improve pediatric dose guidance of existing antiretroviral drugs. Therapeutic drug monitoring is a useful tool to optimize treatment in HIV-infected children. More data are needed, however, to establish child-specific reference values.

Population pharmacokinetics and maximum a posteriori probability Bayesian estimator of abacavir: application of individualized therapy in HIV-infected infants and toddlers

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Abacavir is used to treat HIV infection in both adults and children. The recommended paediatric dose is 8 mg kg(-1) twice daily up to a maximum of 300 mg twice daily. Weight was identified as the central covariate influencing pharmacokinetics of abacavir in children.

WHAT THIS STUDY ADDS

A population pharmacokinetic model was developed to describe both once and twice daily pharmacokinetic profiles of abacavir in infants and toddlers. Standard dosage regimen is associated with large interindividual variability in abacavir concentrations. A maximum a posteriori probability Bayesian estimator of AUC(0-) (t) based on three time points (0, 1 or 2, and 3 h) is proposed to support area under the concentration-time curve (AUC) targeted individualized therapy in infants and toddlers.

AIMS

To develop a population pharmacokinetic model for abacavir in HIV-infected infants and toddlers, which will be used to describe both once and twice daily pharmacokinetic profiles, identify covariates that explain variability and propose optimal time points to optimize the area under the concentration-time curve (AUC) targeted dosage and individualize therapy.

METHODS

The pharmacokinetics of abacavir was described with plasma concentrations from 23 patients using nonlinear mixed-effects modelling (NONMEM) software. A two-compartment model with first-order absorption and elimination was developed. The final model was validated using bootstrap, visual predictive check and normalized prediction distribution errors. The Bayesian estimator was validated using the cross-validation and simulation-estimation method.

RESULTS

The typical population pharmacokinetic parameters and relative standard errors (RSE) were apparent systemic clearance (CL) 13.4 () h−1 (RSE 6.3%), apparent central volume of distribution 4.94 () (RSE 28.7%), apparent peripheral volume of distribution 8.12 () (RSE14.2%), apparent intercompartment clearance 1.25 () h−1 (RSE 16.9%) and absorption rate constant 0.758 h−1 (RSE 5.8%). The covariate analysis identified weight as the individual factor influencing the apparent oral clearance: CL = 13.4 × (weight/12)1.14. The maximum a posteriori probability Bayesian estimator, based on three concentrations measured at 0, 1 or 2, and 3 h after drug intake allowed predicting individual AUC0–t.

CONCLUSIONS

The population pharmacokinetic model developed for abacavir in HIV-infected infants and toddlers accurately described both once and twice daily pharmacokinetic profiles. The maximum a posteriori probability Bayesian estimator of AUC(0-) (t) was developed from the final model and can be used routinely to optimize individual dosing.

Influence of CYP2B6 516G>T polymorphism and interoccasion variability (IOV) on the population pharmacokinetics of efavirenz in HIV-infected South African children

OBJECTIVE

To investigate the influence of CYP2B6 516G>T polymorphism, as a covariate, and of interoccasion variability (IOV) on the oral clearance (CL/F) of efavirenz (EFV) in treatment-naïve black South African children over a period of 24 months post-antiretroviral therapy (ART) initiation.

METHODS

HIV-infected black children (n = 60, aged 3-16 years), with no prior exposure to ART, eligible to commence ART and attending an outpatient clinic were enrolled into this study. Blood samples were taken at mid-dose interval at 1, 3, 6, 12, 18 and 24 months post-ART initiation. EFV plasma samples were determined with an adapted and validated LC/MS/MS method. Genotyping of the CYP2B6 G516T single nucleotide polymorphism (SNP) was performed using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). NONMEM was used for the population pharmacokinetic modelling.

RESULTS

EFV concentrations below 1 μg/mL accounted for 18% (116/649), EFV concentrations >4 μg/mL accounted for 29.5% (192/649) and concentrations within the therapeutic range (1-4 μg/mL) represented 52.5% (341/649) of all the samples determined. The covariates age, weight and CYP2B6 G516Tgenotype were included in the final model with population estimates for CL/F determined as 2.46, 4.60 and 7.33 L/h for the T/T, G/T and G/G genotype groups respectively.

CONCLUSIONS

The inclusion of both age and weight to predict accurate EFV CL values for the respective genotype groups within this paediatric population was required, whereas the addition of gender and body surface area did not improve the predictions. The importance of introducing IOV in a PK model for a longitudinal study with sparsely collected data was again highlighted by this investigation.

Can therapeutic drug monitoring improve pharmacotherapy of HIV infection in adolescents?

Currently, therapeutic drug monitoring (TDM) of antiretroviral therapy (ART) is not performed in the United States as part of routine clinical care of an HIV-infected adolescent patient. TDM is recommended to rule out subtherapeutic drug concentrations and to differentiate among malabsorption, drug interactions, poor adherence, or increased drug metabolism or clearance as possible causes of decreased drug exposure. The use of TDM is also considered to assist in finding the optimal dose of a drug in patients whose virus has shown reduced susceptibility to that drug. The dosing of antiretroviral (ARV) drugs in adolescent patients with HIV infection depends on the chronologic age, weight, height, and the stage of sexual maturation. As a result of the limited data on the pharmacokinetics of ART during puberty, the transition of a dosing regimen from higher pediatric (weight and surface-based) to adult (fixed) range is not well defined. Developmental pharmacokinetic differences contribute to high variability in pediatric and adolescent patients and an increased frequency of suboptimal ARV exposure as compared to in adults. Individualized, concentration-targeted optimal dosing of ARV medications can be beneficial to patients for whom only limited dosing guidelines are available. This article describes three cases of the application of TDM in treatment-experienced adolescent patients whose ART was optimized using ARV TDM. TDM of ARV drugs is useful in managing the pharmacotherapy of HIV in adolescent patients and is well received by the adolescent patients with HIV and their families. Among others, the benefits of TDM provide evidence for adherence interventions and create grounds for enhanced education of the adolescent patient and involved adult caregivers about ART. Finally, TDM in adolescents provides valuable information about the clinical pharmacology of ART during puberty.

Ultra-fast analysis of plasma and intracellular levels of HIV protease inhibitors in children: a clinical application of MALDI mass spectrometry

HIV protease inhibitors must penetrate into cells to exert their action. Differences in the intracellular pharmacokinetics of these drugs may explain why some patients fail on therapy or suffer from drug toxicity. Yet, there is no information available on the intracellular levels of HIV protease inhibitors in HIV infected children, which is in part due to the large amount of sample that is normally required to measure the intracellular concentrations of these drugs. Therefore, we developed an ultra-fast and sensitive assay to measure the intracellular concentrations of HIV protease inhibitors in small amounts of peripheral blood mononuclear cells (PBMCs), and determined the intracellular concentrations of lopinavir and ritonavir in HIV infected children. An assay based on matrix-assisted laser desorption/ionization (MALDI) - triple quadrupole mass spectrometry was developed to determine the concentrations of HIV protease inhibitors in 10 µL plasma and 1×10⁶ PBMCs. Precisions and accuracies were within the values set by the FDA for bioanalytical method validation. Lopinavir and ritonavir did not accumulate in PBMCs of HIV infected children. In addition, the intracellular concentrations of lopinavir and ritonavir correlated poorly to the plasma concentrations of these drugs. MALDI-triple quadrupole mass spectrometry is a new tool for ultra-fast and sensitive determination of drug concentrations which can be used, for example, to assess the intracellular pharmacokinetics of HIV protease inhibitors in HIV infected children.

Italian consensus statement on paediatric HIV infection

The objective of this document is to identify and reinforce current recommendations concerning the management of HIV infection in infants and children in the context of good resource availability. All recommendations were graded according to the strength and quality of the evidence and were voted on by the 57 participants attending the first Italian Consensus on Paediatric HIV, held in Siracusa in 2008. Paediatricians and HIV/AIDS care specialists were requested to agree on different statements summarizing key issues in the management of paediatric HIV. The comprehensive approach on preventing mother-to-child transmission (PMTCT) has clearly reduced the number of children acquiring the infection in Italy. Although further reduction of MTCT should be attempted, efforts to personalize intervention to specific cases are now required in order to optimise the treatment and care of HIV-infected children. The prompt initiation of treatment and careful selection of first-line regimen, taking into consideration potency and tolerance, remain central. In addition, opportunistic infection prevention, adherence to treatment, and long-term psychosocial consequences are becoming increasingly relevant in the era of effective antiretroviral combination therapies (ART). The increasing proportion of infected children achieving adulthood highlights the need for multidisciplinary strategies to facilitate transition to adult care and maintain strategies specific to perinatally acquired HIV infection.

Efavirenz plasma concentrations at 1, 3, and 6 months post-antiretroviral therapy initiation in HIV type 1-infected South African children

The aim of this study was to quantify the plasma efavirenz concentrations over 6 months in black HIV-1-infected South African children (3-14 years), from resource-limited households, attending an outpatient clinic. The children were antiretroviral treatment (ART) naive and received efavirenz in combination with two nucleoside reverse transcriptase inhibitors according to South African national guidelines. Two blood samples were taken between 12 and 20 h after the last efavirenz dose at 1 (n = 58), 3 (n = 54), and 6 (n = 54) months post-ART initiation. A total of 328 efavirenz mid-dose plasma samples from 58 patients was determined with a validated liquid chromatography tandem mass spectrometry method. Viral suppression (<25 copies/ml) was achieved in 95% of the children after 6 months on ART. The median (range) plasma concentration at time points 1 and 2 were 2.06 (0.10-11.14) and 1.80 (0.14-10.70) microg/ml with respective mean (+/-SD) blood sampling times of 15.24 (2.03) and 16.91 (2.03) h post-evening dose. Efavirenz plasma samples within the therapeutic range of 1-4 microg/ml accounted for 58%; 17% were <1 microg/ml and 25% were >4 microg/ml over the 6 months. Efavirenz levels persistently >4 microg/ml were recorded for 13 (23%) children and 3 (5%) children had persistent efavirenz levels <1 microg/ml. Possible reasons for efavirenz plasma levels outside the accepted therapeutic range include genetic variation in drug metabolism, incorrect dosing, drug-drug interactions, and nonadherence. However, these need to be further explored and the importance of sequential plasma levels has been highlighted in this study.

Comparison of levels of antiretroviral drugs with efficacy in children with HIV infection

OBJECTIVE

To determine the prevalence of low and high antiretroviral (ARV) plasma levels and to analyze correlation between ARV concentrations and the appearance of therapeutic failure and toxicity.

METHODS

The authors present here a study evaluating antiretroviral plasma concentrations in HIV infected children on nonnucleoside reverse transcriptase inhibitors and protease inhibitors based therapy. The authors carried out a multicentre, cross-sectional study, including HIV-infected children from five large Hospitals in Madrid, Spain. Clinical, haematological, biochemical and immuno-virological parameters were assessed. Antiretroviral plasma trough levels were performed using a validated high performance liquid chromatography method.

RESULTS

Between April 2006 and April 2008, 129 children were enrolled in the present study, with median treatment duration of 39.2 months. 25.5% of the non-nucleoside reverse transcriptase inhibitors levels were low and 17.6%, high. 27.9% percent of the protease inhibitors levels were low and 12.5%, high. A correlation was found among adequate or high levels of antiretrovirals and normal CD4 percentage and low viral load. Lopinavir/ritonavir plasma levels were correlated with an increase in lipodystrophy. Patients with Tanner stage 1 presented the lowest ARV plasma levels. Full adherence was reported for all the participants by a questionnaire.

CONCLUSION

Many HIV-infected children show ARV plasma levels out of the therapeutic range which demands a child-adjusted approach. However, larger studies are urgently needed in pediatric populations to define optimal reference values.

Practical therapeutic drug management in HIV-infected patients: use of population pharmacokinetic models supplemented by individualized Bayesian dose optimization

Individualized, model-based, target-oriented optimal concentration-controlled dosing of HIV medications can be beneficial to patients for whom there are limited dosing guidelines, such as children, adolescents, or patients with altered physiologic function. Barriers to this approach include lack of training, expertise, and access to appropriate software to assist the clinician. The authors present 4 illustrative clinical cases of HIV-infected patients whose therapy was optimized using population pharmacokinetic models (here generated from published studies) and supplemented by individualized Bayesian adaptive control of dosage regimens as implemented in the MM-USCPACK software. These 4 cases illustrate how clinicians can maximize therapeutic success in (1) patients with reduced drug clearance, (2) young adolescents transitioning to adult physiology, (3) patients with dose-dependent toxicity, and (4) adolescents with limited therapeutic options.

Hepatitis infection in the treatment of opioid dependence and abuse

Many new and existing cases of viral hepatitis infections are related to injection drug use. Transmission of these infections can result directly from the use of injection equipment that is contaminated with blood containing the hepatitis B or C virus or through sexual contact with an infected individual. In the latter case, drug use can indirectly contribute to hepatitis transmission through the dis-inhibited at-risk behavior, that is, unprotected sex with an infected partner. Individuals who inject drugs are at-risk for infection from different hepatitis viruses, hepatitis A, B, or C. Those with chronic hepatitis B virus infection also face additional risk should they become co-infected with hepatitis D virus. Protection from the transmission of hepatitis viruses A and B is best achieved by vaccination. For those with a history of or who currently inject drugs, the medical management of viral hepatitis infection comprising screening, testing, counseling and providing care and treatment is evolving. Components of the medical management of hepatitis infection, for persons considering, initiating, or receiving pharmacologic therapy for opioid addiction include: testing for hepatitis B and C infections; education and counseling regarding at-risk behavior and hepatitis transmission, acute and chronic hepatitis infection, liver disease and its care and treatment; vaccination against hepatitis A and B infection; and integrative primary care as part of the comprehensive treatment approach for recovery from opioid abuse and dependence. In addition, participation in a peer support group as part of integrated medical care enhances treatment outcomes. Liver disease is highly prevalent in patient populations seeking recovery from opioid addiction or who are currently receiving pharmacotherapy for opioid addiction. Pharmacotherapy for opioid addiction is not a contraindication to evaluation, care, or treatment of liver disease due to hepatitis virus infection. Successful pharmacotherapy for opioid addiction stabilizes patients and improves patient compliance to care and treatment regimens as well as promotes good patient outcomes. Implementation and integration of effective hepatitis prevention programs, care programs, and treatment regimens in concert with the pharmacological therapy of opioid addiction can reduce the public health burdens of hepatitis and injection drug use.

Plasma Concentrations of the HIV-Protease Inhibitor Lopinavir are Suboptimal in Children Aged 2 Years and Below

Background

Lopinavir/ritonavir (LPV/r) has been licensed for the treatment of HIV-infected children >6 months in the US and >2 years in the EU. Limited LPV paediatric pharmacokinetic data are available. We studied LPV pharmacokinetics to determine whether the recommended dose (230/57.5 mg/m2 twice daily) results in optimal LPV exposure in all age groups. Virological efficacy was a secondary objective.

Methods

HIV-1-infected children who started treatment with LPV/r and two nucleoside reverse transcriptase inhibitors underwent a 12-h pharmacokinetic curve. LPV plasma concentrations were determined with a validated HPLC method with UV detection. If Cmin was <1.0 mg/l LPV/r dose was increased by 33%. Plasma trough levels were drawn subsequently. HIV-1 RNA was followed-up until week 48.

Results

A total of 23 children were included (seven girls; 16 boys), with a median (range) age of 5.6 (0.4–13.2) years. Mean (±SD) AUC0–12h, Cmax and Cmin of LPV were 75.3 (±33.7) mg/l.h, 9.33 (±3.27) mg/l and 3.68 (±2.48) mg/l, respectively, which is similar to previously published data. Interindividual variability was large. Cmin was inadequate in 7/23 children. Significantly more children <2 years had inadequate Cmin compared with children >2 years. Dose increase to ±300/75 mg/m2 LPV/r led to Cmin >1.0 mg/l. The studied regimen provided excellent viral suppression for naive and pretreated patients.

Conclusions

Mean LPV pharmacokinetic parameters in these HIV-infected children are similar to published data, but exposure is significantly reduced in children <2 years. Prospective pharmacokinetic studies using 300/75 mg/m2 LPV/r in this age population are urgently warranted.

Increasing antiretroviral drug access for children with HIV infection

Although there have been great gains in the prevention of pediatric HIV infection and provision of antiretroviral therapy for children with HIV infection in resource-rich countries, many barriers remain to scaling up HIV prevention and treatment for children in resource-limited areas of the world. Appropriate testing technologies need to be made more widely available to identify HIV infection in infants. Training of practitioners in the skills required to care for children with HIV infection is required to increase the number of children receiving antiretroviral therapy. Lack of availability of appropriate antiretroviral drug formulations that are easily usable and inexpensive is a major impediment to optimal care for children with HIV. The time and energy spent trying to develop liquid antiretroviral formulations might be better used in the manufacture of smaller pill sizes or crushable tablets, which are easier to dispense, transport, store, and administer to children.

Monitoring of lopinavir and ritonavir in peripheral blood mononuclear cells, plasma, and ultrafiltrate using a selective and highly sensitive LC/MS/MS assay

For the determination of the HIV protease inhibitors lopinavir and ritonavir in human plasma, plasma ultrafiltrate, and peripheral blood mononuclear cells (PBMCs) a highly sensitive and selective method has been developed, validated, and applied to samples of a healthy volunteer. BD Vacutainer CPT and Amicon Centriplus centrifugal filter devices were used for separation of PBMCs and for ultrafiltrate generation, respectively. After liquid/liquid-extraction extracts were chromatographed isocratically within 6 min on a Jupiter Proteo column. The drugs were quantified using 2H5-saquinavir as internal standard and electrospray tandem mass spectrometry in the selected reaction monitoring mode. Limits of quantification for both analytes were 4.0 ng/mL in plasma, 0.2 ng/mL in ultrafiltrate, and 0.1 ng/cell pellet (approximately 3 x 10(6) cells) in PBMCs. The calibration ranges were linear over more than three logs with an over-all accuracy varying between 98.7% and 111.5% and an over-all precision ranging from 6.2% to 14.0% (SD batch-to-batch). After a regular oral dose of Kaletra (400 mg lopinavir, 100 mg ritonavir) analyte concentrations were detectable over a full dosing interval in plasma, ultrafiltrate, and PBMCs. The method is well suited for monitoring of free and total plasma, and intracellular lopinavir/ritonavir concentrations in samples from clinical trials.

Pharmacokinetics of a Once-Daily Regimen of Lopinavir/Ritonavir in HIV-1-Infected Children

Introduction

Lopinavir is an HIV protease inhibitor that is co-formulated with ritonavir. The approved paediatric dose is 230/57.5 mg/m2 twice daily. Once-daily dosing may offer an advantage to adherence. We studied the pharmacokinetics of lopinavir/ritonavir in a once-daily regimen in HIV-1-infected children.

Methods

HIV-1-infected children on stable antiretroviral therapy with a viral load <50 copies/ml for at least 6 months received lopinavir/ritonavir 460/115 mg/m2 once daily with zidovudine and lamivudine. Blood samples were collected at 0, 2, 4, 6, 8, 12, 18 and 24 h after observed intake during steady state. Target level for lopinavir Cmin was 1.0 mg/l, based on in vitro IC50 data.

Results

Nineteen HIV-1-infected children with a median (range) age of 4.5 (1.4–12.9) years were enrolled. The median (interquartile range) dose of lopinavir was 456 (444–477) mg/m2. The mean (standard deviation) AUC0–24, Cmax and Cmin of lopinavir were 149.8 ±58.8 h*mg/l, 10.77 ±2.90 mg/l and 2.88 ±3.74 mg/l respectively. These values are comparable to data observed in adults using lopinavir/ritonavir 800/200 mg once daily. In 10/19 (53%) children Cmin was considered to be too low (<1.0 mg/l). Younger children more often experienced subtherapeutic trough levels.

Conclusion

Our findings indicate that 460/115 mg/m2 lopinavir/ritonavir once daily leads to mean pharmacokinetic parameters comparable to data of 800/200 mg lopinavir/ritonavir once daily in adults, although the variability observed in the trough levels is much higher in children. Further research, especially in young children, is necessary to determine whether a higher dosage of lopinavir/ritonavir once daily must be given to reach the target level for Cmin.

Therapeutic Drug Monitoring and Human Immunodeficiency Virus (HIV) Antiretroviral Therapy

Treatment with antiretroviral drugs such as the HIV protease inhibitors and non-nucleoside reverse transcriptase inhibitors have contributed to the improvement of life of many HIV-infected patients in recent years, but antiretroviral therapy is not without problems. In some patients, treatment is not effective and suppression of viral replication is not achieved. Other patients experience toxicity and have to stop treatment or change to a less effective treatment. Several studies have demonstrated a relationship between plasma concentrations of the protease inhibitors and non-nucleoside reverse transcriptase inhibitors and viral suppression and toxicity. Therapeutic drug monitoring uses drug concentrations to individualize and optimise therapy by dosage adjustments and many clinicians have advocated for the use of therapeutic drug monitoring in HIV antiretroviral therapy. Evidence from a number of randomized clinical trials supports the use of therapeutic drug monitoring, but the studies have limitations and might not apply to all the antiretroviral drugs. However, the consensus is that certain patients are very likely to benefit from therapeutic drug monitoring. Additionally, the combination of therapeutic drug monitoring and genotypic or phenotypic resistance testing might further improve antiretroviral therapy.

Pharmacokinetics of antiretroviral therapy in HIV-1-infected children

The initiation of antiretroviral therapy has resulted in an impressive reduction in the rate of disease progression in AIDS and HIV-1-related deaths in children; however, there are still several major challenges to be faced in order to improve therapy. A major topic that needs to be dealt with is the establishment of the optimal dosage of antiretroviral therapy for children. This review presents the currently available peer-reviewed data on the pharmacokinetics of nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs) and fusion inhibitors (FIs) in children. In addition, the data are discussed in relation to the currently available European and US guidelines and the US FDA-approved drug labels. High intra- and interpatient variability in pharmacokinetics are often observed for all antiretroviral drugs. The number of children included in the pharmacokinetic studies is often small and children are often divided into divergent groups using different dosage levels and/or drug formulations. For a substantial number of antiretroviral drugs, dosage recommendations, especially for young children, are still absent in the European and US guidelines. The recommended drug dosages in the guidelines are often different from that in the officially approved drug product label. In addition, the recommended drug dosages may deviate between the European and US guidelines. Thus, while practioners aim to meet the recommendations in the official guidelines, patients may receive highly divergent dosages of medication. The high intra- and interpatient variability in pharmacokinetics of antiretroviral drugs in children hampers the application of fixed dosages of antiretroviral drugs. For PIs and NNRTIs, plasma drug levels correlate with viral suppression and drug toxicity. NRTIs are prodrugs that are intracellularly converted to their active triphosphate form and, therefore, plasma NRTI levels correlate poorly with viral suppression. Therapeutic drug monitoring of PIs and NNRTIs should be considered to optimise HIV therapy in children.

Children with HIV: improved mortality and morbidity with combination antiretroviral therapy

PURPOSE OF REVIEW

Advances in the management of children with vertical HIV-1 infection in the developing and developed worlds are discussed in reference to literature published in 2003/4. Studies in mother-to-child transmission are beyond the scope of this review.

RECENT FINDINGS

Improvements in mortality and morbidity from HIV-1 infection following combination antiretroviral therapy are extremely encouraging. There is an increase in the understanding of the immune response to HIV-1 in infants and children and a possible future role for immunomodulatory therapies. Preliminary data are available on the timing of initiation of antiretroviral therapy, the optimization of drug combinations and the clinical interpretation of genotypic resistance testing and therapeutic drug monitoring. Evidence is emerging that early antiretroviral therapy can protect the central nervous system in infants. In resource-limited settings, mortality and morbidity remain extremely high but low-cost health interventions such as prophylactic co-trimoxazole can reduce mortality prior to the expansion of antiretroviral therapy programmes.

SUMMARY

Further randomized controlled trials assessing antiretroviral therapy combinations with a sustained virological/immunological response with minimal toxicities are required. The roles of therapeutic drug monitoring and resistance testing require further elucidation. The expansion of antiretroviral therapy programmes is essential for children with HIV living in resource-limited settings.

Therapeutic drug monitoring: Pharmacologic considerations for antiretroviral drugs

Therapeutic drug monitoring (TDM) is the process by which a patient's dosing regimen is guided by repeated measures of plasma drug concentrations. An enormous challenge with regard to TDM of antiretroviral drugs (ARV) is that the concentration goals can be moving targets. Well-designed prospective studies demonstrating that prospectively altering ARV doses based on TDM leads to virologic success and increased tolerability are needed. Nevertheless, there are specific clinical instances where this experimental intervention should be considered to potentially reduce toxicity and improve therapeutic outcomes.

Recomendaciones CEVIHP/SEIP/AEP/PNS respecto al tratamiento antirretroviral en niños y adolescentes infectados por el VIH

OBJECTIVE

To update antiretroviral recommendations in antiretroviral therapy (ART) in HIV-infected children and adolescents.

METHODS

Theses guidelines have been formulated by a panel of members of the Plan Nacional sobre el SIDA (PNS) and the Asociacion Espanola de Pediatria (AEP) by reviewing the current available evidence of efficacy, safety, and pharmacokinetics in pediatric studies. Three levels of evidence have been defined according to the source of data: Level A: randomized and controlled studies; Level B: Cohort and case-control studies; Level C: Descriptive studies and experts' opinion.

RESULTS

When to start ART should be made on an individual basis, discussed with the family, considering the risk of progression according to age, CD4 and viral load, the ART-related complications and adherence. The ART goal is to reach a maximum and durable viral suppression. This is not always possible, even with clinical and immunologic improvement. The difficulties of permanent adherence and side-effects are resulting in a more conservative trend to initiate ART, and to less toxic and simpler strategies. Currently, combinations of at least three drugs are of first choice both in acute and chronic infection. They must include 2 NA 1 1 NN or 2 NA 1 1 PI. ART is recommended in all symptomatic patients and, with few exceptions, in all infants in the first year of life. Older asymptomatic children should start ART according to CD4 count, especially CD4 percentage, that vary with age. Despite potent salvage therapies, it is common not to reach viral undetectability. Therapeutical options when ART fails are scarce due to cross-resistance. The cause of failure must be identified. Occasionally, there exists clinical and/or immunological progression, and a change of therapy with at least two new drugs still active for the patient, is warranted with the aim of increasing the CD4 count to a lower level of risk. Toxicity and adherence must be regularly monitored. Some aspects about post exposure prophylaxis and coinfection with HCV or HBV are discussed.

CONCLUSIONS

A higher level of evidence with regard to ART effectiveness and toxicity in pediatrics is currently available, leading to a more conservative and individualized approach. Clinical symptoms and CD4 count are the main determinants to start and change ART.