Position paper on therapeutic drug monitoring of antiretroviral agents

Status and Quality of Guidelines for Therapeutic Drug Monitoring Based on AGREE II Instrument

BACKGROUND

With the progress of therapeutic drug monitoring (TDM) technology and the development of evidence-based medicine, many guidelines were developed and implemented in recent decades.

OBJECTIVE

The aim was to evaluate the current status of TDM guidelines and provide suggestions for their development and updates based on Appraisal of Guidelines for Research and Evaluation (AGREE) II.

METHODS

The TDM guidelines were systematically searched for among databases including PubMed, Embase, China National Knowledge Infrastructure, Wanfang Data, and the Chinese biomedical literature service system and the official websites of TDM-related associations. The search period was from inception to 6 April 2023. Four researchers independently screened the literature and extracted data. Any disagreement was discussed and reconciled by another researcher. The quality of guidelines was assessed using the AGREE II instrument.

RESULTS

A total of 92 guidelines were included, including 57 technical guidelines, three management guidelines, and 32 comprehensive guidelines. The number of TDM guidelines has gradually increased since 1979. The United States published the most guidelines (20 guidelines), followed by China (15 guidelines) and the United Kingdom (ten guidelines), and 23 guidelines were developed by international organizations. Most guidelines are aimed at adult patients only, while 28 guidelines include special populations. With respect to formulation methods, there are 23 evidence-based guidelines. As for quality evaluation results based on AGREE II, comprehensive guidelines scored higher (58.16%) than technical guidelines (51.36%) and administrative guidelines (50.00%).

CONCLUSION

The number of TDM guidelines, especially technical and comprehensive ones, has significantly increased in recent years. Most guidelines are confronted with the problems of unclear methodology and low quality of evidence according to AGREE II. More evidence-based research on TDM and high-quality guideline development is recommended to promote individualized therapy.

Brief Report: Hormonal Contraception Use and Cabotegravir Pharmacokinetics in HIV-Uninfected Women Enrolled in HPTN 077

OBJECTIVES

To evaluate whether hormonal contraceptive use among cisgender women is associated with differences in pharmacokinetic (PK) parameters of a long-acting injectable formulation of the integrase strand transfer inhibitor, cabotegravir (CAB-LA).

SETTING

This is a secondary analysis of 85 cisgender women enrolled in HPTN 077, a phase 2a multicenter study that enrolled HIV-uninfected, low-risk individuals in Malawi, Brazil, South Africa, and the United States.

METHODS

Participants received 4-week daily oral cabotegravir lead-in, followed by CAB-LA 800 mg injection every 12 weeks (cohort 1) or 600 mg every 8 weeks (after 4-week initial interval between injections, cohort 2), over 41 weeks. Participants were followed 52-76 weeks subsequent to final injection. Generalized estimating equations and linear regression were used to evaluate differences in CAB-LA PK parameters (peak concentration, trough concentration, area under the curve, apparent terminal half-life, and time to lower limit of quantification) and self-reported hormonal contraceptive stratified by type (oral, injectable, implants, and other), controlling for body mass index and cohort.

RESULTS

Compared to women reporting no hormonal contraception (n = 6), oral contraceptive use (n = 18) was associated with lower CAB-LA peak concentration but was not associated with differences in other PK parameters. No other hormonal contraceptive type (injectable, implants, and other) was associated with significant differences in CAB-LA PK parameters.

CONCLUSION

Although oral contraceptive use was associated with differences in CAB-LA peak concentration, no differences were observed in other PK parameters, suggesting that this association is not likely to be clinically significant. However, these data highlight the need for further research exploring potential drug-drug interactions between CAB-LA and hormonal contraceptives.

Benefits and Limits of Antiretroviral Drug Monitoring in Routine Practice

BACKGROUND

HIV infection is a chronic disease for which therapeutic adherence and tolerance require particular attention.

OBJECTIVE

This study aimed to assess whether and when therapeutic drug monitoring (TDM) could be associated with a benefit in routine practice.

METHODS

All HIV-infected patients who underwent at least one TDM at the University Hospital of Dijon (France) between 1st January 2009 and 31st December 2012 were retrospectively included. Compliance with the recommendations, the results (antiretroviral concentrations), any subsequent therapeutic modifications, and the virological results at 4-8 months were analysed each time TDM was performed. TDM was defined as "practically relevant" when low or high antiretroviral concentrations led to a change in therapy.

RESULTS

Of the 571 patients who followed-up, 43.4% underwent TDM. TDM complying with recommendations (120 patients) was associated with a higher proportion of antiretroviral concentrations outside the therapeutic range (p=0.03). Antiretroviral treatment was modified after TDM in 22.6% of patients. Protease inhibitors, non-nucleoside reverse transcriptase inhibitors and raltegravir were more significantly modified when the measured concentration was outside the therapeutic range (p=0.008, p=0.05 and p=0.02, respectively). Overall, 11.7% of TDM was considered "practically relevant", though there was no significant correlation between subsequent changes in antiretroviral treatment and undetectable final HIV viral load.

CONCLUSION

TDM may be a useful tool in the management of HIV infection in specific situations, but the overall benefit seems moderate in routine practice. TDM cannot be systematic and/or a decision tool per se, but should be included in a comprehensive approach in certain clinical situations.

Pharmacokinetics, Placental and Breast Milk Transfer of Antiretroviral Drugs in Pregnant and Lactating Women Living with HIV

BACKGROUND

Remarkable progress has been achieved in the identification of HIV infection in pregnant women and in the prevention of vertical HIV transmission through maternal antiretroviral treatment (ART) and neonatal antiretroviral drug (ARV) prophylaxis in the last two decades. Millions of women globally are receiving combination ART throughout pregnancy and breastfeeding, periods associated with significant biological and physiological changes affecting the pharmacokinetics (PK) and pharmacodynamics (PD) of ARVs. The objective of this review was to summarize currently available knowledge on the PK of ARVs during pregnancy and transport of maternal ARVs through the placenta and into the breast milk. We also summarized main safety considerations for in utero and breast milk ARVs exposures in infants.

METHODS

We conducted a review of the pharmacological profiles of ARVs in pregnancy and during breastfeeding obtained from published clinical studies. Selected maternal PK studies used a relatively rich sampling approach at each ante- and postnatal sampling time point. For placental and breast milk transport of ARVs, we selected the studies that provided ratios of maternal to the cord (M:C) plasma and breast milk to maternal plasma (M:P) concentrations, respectively.

RESULTS

We provide an overview of the physiological changes during pregnancy and their effect on the PK parameters of ARVs by drug class in pregnancy, which were gathered from 45 published studies. The PK changes during pregnancy affect the dosing of several protease inhibitors during pregnancy and limit the use of several ARVs, including three single tablet regimens with integrase inhibitors or protease inhibitors co-formulated with cobicistat due to suboptimal exposures. We further analysed the currently available data on the mechanism of the transport of ARVs from maternal plasma across the placenta and into the breast milk and summarized the effect of pregnancy on placental and of breastfeeding on mammal gland drug transporters, as well as physicochemical properties, C:M and M:P ratios of individual ARVs by drug class. Finally, we discussed the major safety issues of fetal and infant exposure to maternal ARVs.

CONCLUSIONS

Available pharmacological data provide evidence that physiological changes during pregnancy affect maternal, and consequently, fetal ARV exposure. Limited available data suggest that the expression of drug transporters may vary throughout pregnancy and breastfeeding thereby possibly impacting the amount of ARV crossing the placenta and secreted into the breast milk. The drug transporter's role in the fetal/child exposure to maternal ARVs needs to be better understood. Our analysis underscores the need for more pharmacological studies with innovative study design, sparse PK sampling, improved study data reporting and PK modelling in pregnant and breastfeeding women living with HIV to optimize their treatment choices and maternal and child health outcomes.

Quality of therapeutic drug monitoring guidelines is suboptimal: an evaluation using the Appraisal of Guidelines for Research and Evaluation II instrument

OBJECTIVES

Although therapeutic drug monitoring (TDM) guidelines are available, systematic evaluations of their methodological quality are scarce. This study aimed to assess the quality of current TDM guidelines using the Appraisal of Guidelines for Research and Evaluation (AGREE) II instrument.

STUDY DESIGN AND SETTING

We performed a systematic search to identify the relevant TDM guidelines in PubMed, EMBASE, CNKI, Wan Fang Database, CBM, VIP, four main guideline databases (NICE, NGC, GIN, and WHO guideline databases), and official websites of the governments and societies associated with TDM from the inception date to May 2018. Four independent appraisers rated the quality of each TDM guideline using the AGREE II instrument, and the mean score of each AGREE II item was calculated. The overall agreement among the appraisers was evaluated using the intraclass correlation coefficient (ICC).

RESULTS

Twenty-eight TDM guidelines satisfied the eligibility criteria from among 12,235 references. The overall agreement among the appraisers was substantial (0.700-0.880). The mean scores for the six AGREE II domains were scope and purpose, 67.7% (95% CI, 64.0-71.4%); stakeholder involvement, 39.8% (95% CI, 33.3-46.3%); rigor of development, 36.0% (95% CI, 28.1-43.9%); clarity and presentation, 61.6% (95% CI, 55.7-67.4%); applicability, 30.6% (95% CI, 26.4-34.8%); and editorial independence, 49.2% (95% CI, 40.0-58.6%). The reviewers recommended only four guidelines, and most of the TDM guidelines were rated as "recommended with modifications."

CONCLUSION

Overall, the quality of TDM guidelines is suboptimal according to the evaluation using the AGREE II instrument. The domains of applicability, rigor of development, stakeholder involvement, and editorial independence of the guidelines need to be reported. In addition, guideline developers closely adhering to the AGREE II instrument and the Grading of Recommendations Assessment Development and Evaluation system are required to draft high-quality and reliable TDM guidelines.

Sleeve Gastrectomy in Morbidly Obese HIV Patients: Focus on Anti-retroviral Treatment Absorption After Surgery

CONTEXT

Anti-retroviral therapy (ART) dramatically reduced AIDS development, thus enabling patients to live as long as the general population. New challenges have emerged particularly cardiometabolic diseases and weight gain, with some HIV patients seeking bariatric surgery (BS). However, BS outcomes during HIV remain poorly described, with scarce data on ART pharmacokinetic post-BS.

OBJECTIVE

Describing sleeve gastrectomy (SG) results in HIV patients in terms of ART pharmacokinetic, HIV control, weight loss, and metabolic outcomes.

DESIGN, SETTING, AND PATIENTS

Prospective study of HIV patients undergoing SG in a referral academic center, with at least 6 months follow-up.

MAIN OUTCOME MEASURE

Clinical and biological parameters, HIV medical history, and ART pharmacokinetics were gathered before and post-SG.

RESULTS

Seventeen patients (mean BMI = 44.2 ± 5.7 kg m^-2) and major obesity-related diseases (47% type-2 diabetes, 64% obstructive sleep apnea, 70% hypertension) underwent SG during a mean 2 years of follow-up. They displayed an average of 20% reduction of initial BMI and improved body composition, similarly to obese non-HIV patients. SG improved metabolic status. All patients had undetectable viral load before BS. Upon HIV follow-up, 12 patients had undetectable viral load with correct ART kinetic parameters (3 and 6 months); 4 displayed detectable viral load along with significant decrease in raltegravir and atazanavir treatment exposure, leading to ART change with subsequent undetectable viral load; and 1 had persistent detectable viral load despite ART change.

CONCLUSIONS

SG seems effective and safe in obese HIV patients. However, ART treatment should be monitored post-SG to control HIV infection. We suggest that some ART should be adapted before SG conjoints with infectious disease specialists.

Antiretroviral considerations in HIV-infected patients undergoing bariatric surgery

WHAT IS KNOWN AND OBJECTIVE

With the advent of antiretroviral therapy and the resultant decrease in mortality among adults living with human immunodeficiency virus (HIV), there is now an increased incidence of obesity and obesity-related comorbidities in these patients. Bariatric surgery is becoming an increasingly common treatment option for patients who are classified as clinically obese. There are limited data regarding the use of antiretroviral therapy in patients who have undergone bariatric surgery. The purpose of this review was to evaluate the available literature regarding antiretroviral therapy and pharmaceutical properties in this special population.

METHODS

Literature review was performed through PubMed, utilizing search terms of bariatric surgery, sleeve gastrectomy, Roux-en-Y, HIV infection, obesity and antiretroviral. Direct medical information requests to antiretroviral pharmaceutical manufacturers were also completed.

RESULTS

Several case series and case reports have been published which demonstrate minimal risk of complications and maintenance of virologic suppression in the vast majority of patients. Bariatric surgery appears to be an effective mechanism for assistance in controlling obesity in patients infected with HIV; however, numerous factors may impact the safe and effective use of antiretroviral therapy.

WHAT IS NEW AND CONCLUSION

Due to the physiologic changes and postoperative management following bariatric surgery, evaluation of the patients' medication regimens must be considered and several factors should be taken into account when choosing the appropriate antiretroviral regimen for these patients. Furthermore, communication between the patients' surgeon, HIV provider and a clinical pharmacist should occur prior to surgery to ensure the patient is optimized to achieve the best outcome including maintaining virologic suppression.

Comparison of Population Pharmacokinetics Based on Steady-State Assumption Versus Electronically Monitored Adherence to Lopinavir, Atazanavir, Efavirenz, and Etravirine: A Retrospective Study

BACKGROUND

Population pharmacokinetic (PopPK) analyses often rely on steady state and full adherence to prescribed dosage regimen assumptions from data gathered during therapeutic drug monitoring (TDM). Nonadherence is common in chronic diseases such as HIV. This study evaluates the impact of adherence measurement by electronic monitoring on PopPK parameter estimation and individual concentration profile predictions, and also the influence of adherence issues on the clinical interpretation of a concentration measurement.

METHODS

Published PopPK models for lopinavir, atazanavir, efavirenz, and etravirine were applied to estimate PK parameters and individual concentrations in 140 HIV patients taking part in a medication adherence program using 2 dosing data sets. The first set included the last dose reported by the patient with steady-state and full adherence assumptions; the second set used detailed electronic dosing history. PopPK parameter estimates and individual predictions were compared between the 2 dosing entries.

RESULTS

Clearance estimates and likewise predicted concentrations did not markedly differ between the 2 dosing histories. However, certain patterns of nonadherence such as sparse missed doses or consecutive missed doses lead to suboptimal drug exposure. The interpretation based on self-reported information would have concluded on a wrongly appropriate individual exposure.

CONCLUSIONS

PopPK analysis assuming steady state with full adherence produced similar results to those based on detailed electronic dosing history reconciled with patients' allegations. Self-reported last dose intake appeared reliable for concentration predictions and therapeutic drug monitoring interpretation for most patients followed at the medication adherence program. Yet, clinicians should be aware that concentration predictions based on self-reported last dose intake might be overestimated in case of undetected patterns of nonadherence, increasing the risk of forthcoming therapeutic failure.

Plasma Efavirenz Exposure, Sex, and Age Predict Virological Response in HIV-Infected African Children

BACKGROUND

Owing to insufficient evidence in children, target plasma concentrations of efavirenz are based on studies in adults. Our analysis aimed to evaluate the pediatric therapeutic thresholds and characterize the determinants of virological suppression in African children.

METHODS

We analyzed data from 128 African children (aged 1.7-13.5 years) treated with efavirenz, lamivudine, and one among abacavir, stavudine, or zidovudine, and followed up to 36 months. Individual pharmacokinetic (PK) measures [plasma concentration 12 hours after dose (C12h), plasma concentration 24 hours after dose (C24h), and area under the curve (AUC0-24)] were estimated using population PK modeling. Cox multiple failure regression and multivariable fractional polynomials were used to investigate the risks of unsuppressed viral load associated with efavirenz exposure and other factors among 106 initially treatment-naive children, and likelihood profiling was used to identify the most predictive PK thresholds.

RESULTS

The risk of viral load >100 copies per milliliter decreased by 42% for every 2-fold increase in efavirenz mid-dose concentration [95% confidence interval (CI): 23% to 57%; P < 0.001]. The most predictive PK thresholds for increased risk of unsuppressed viral load were C12h 1.12 mg/L [hazard ratio (HR): 6.14; 95% CI: 2.64 to 14.27], C24h 0.65 mg/L (HR: 6.57; 95% CI: 2.86 to 15.10), and AUC0-24 28 mg·h/L (HR: 5.77; 95% CI: 2.28 to 14.58). Children older than 8 years had a more than 10-fold increased risk of virological nonsuppression (P = 0.005); among children younger than 8 years, boys had a 5.31 times higher risk than girls (P = 0.007). Central nervous system adverse events were infrequently reported.

CONCLUSIONS

Our analysis suggests that the minimum target C24h and AUC0-24 could be lowered in children. Our findings should be confirmed in a prospective pediatric trial.

A pharmacist’s role in the individualization of treatment of HIV patients

The pharmacological treatment of HIV is complex and varies considerably among patients, as does the response of patients to therapy, requiring treatment plans that are closely tailored to individual needs. Pharmacists can take an active role in individualizing care by employing their knowledge of pharmacokinetics and pharmacogenetics and by interacting directly with patients in counseling sessions. These strategies promote the following: maintenance of plasma concentrations of antiretroviral agents within therapeutic ranges, prediction of pharmacological response of patients with certain genetic characteristics, and clinical control of HIV through the correct use of antiretroviral treatments. Together, these strategies can be used to tailor antiretroviral therapy to individual patients, thus improving treatment efficacy and safety.

On the Slow Diffusion of Point-of-Care Systems in Therapeutic Drug Monitoring

Recent advancements in point-of-care (PoC) technologies show great transformative promises for personalized preventative and predictive medicine. However, fields like therapeutic drug monitoring (TDM), that first allowed for personalized treatment of patients' disease, still lag behind in the widespread application of PoC devices for monitoring of patients. Surprisingly, very few applications in commonly monitored drugs, such as anti-epileptics, are paving the way for a PoC approach to patient therapy monitoring compared to other fields like intensive care cardiac markers monitoring, glycemic controls in diabetes, or bench-top hematological parameters analysis at the local drug store. Such delay in the development of portable fast clinically effective drug monitoring devices is in our opinion due more to an inertial drag on the pervasiveness of these new devices into the clinical field than a lack of technical capability. At the same time, some very promising technologies failed in the clinical practice for inadequate understanding of the outcome parameters necessary for a relevant technological breakthrough that has superior clinical performance. We hope, by over-viewing both TDM practice and its yet unmet needs and latest advancement in micro- and nanotechnology applications to PoC clinical devices, to help bridging the two communities, the one exploiting analytical technologies and the one mastering the most advanced techniques, into translating existing and forthcoming technologies in effective devices.

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.

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.

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.

Plasma concentrations of efavirenz and nevirapine among HIV-infected patients with immunological failure attending a tertiary hospital in North-western Tanzania

BACKGROUND

Sub-therapeutic and supra-therapeutic plasma concentrations of antriretrovirals are the significant causes of treatment failure and toxicity respectively among HIV-infected patients. We conducted this study to determine the pattern of efavirenz and nevirapine plasma drug concentrations among adult HIV-infected patients with immunological failure attending at a tertiary hospital in North-western Tanzania.

MATERIALS AND METHODS

A cross-sectional study was conducted among adult HIV-infected patients with immunological failure who have been on either efavirenz or nevirapine based antiretroviral regimen for more than 6 months. Patients were serially enrolled through routine Care and Treatment Clinic (CTC) activities. Plasma drug concentrations for efavirenz and nevirapine were determined by high performance liquid chromatography (HPLC) and Gas Chromatography (GC) respectively. Demographic, clinical and laboratory data such as viral load and CD4 counts were collected. Data analysis was done using STATA 12.

RESULTS

Of the 152 patients with immunological failure enrolled, the sub-therapeutic, therapeutic and supra-therapeutic plasma antiretroviral drug concentrations were found in 43/152 (28.3%), 76/152 (50.0%) and 33/152 (21.7%) respectively. Half of the patients were outside therapeutic window with either sub-therapeutic or supra-therapeutic plasma ARV drug concentrations. There was a significant difference in distribution of ARV adherence (p-value<0.001), NRTI backbone (p-value = 0.039), HIV stage (p-value = 0.026) and viral load (p-value = 0.007) within sub-therapeutic, therapeutic and supra-therapeutic ARV plasma drug concentrations.

CONCLUSION

There is a wide inter-individual variability of plasma ARV concentrations among HIV patients with immunological failure, with a large proportion of patients being outside therapeutic window. This variability is significant based on ARV adherence, NRTI backbone, viral load and HIV stage. Routine therapeutic drug monitoring (TDM) could assist identifying these patients early and making timely correction to avoid virological failure, poor immunological outcome and prevent associated drug toxicities. Nonetheless, ARV adherence should be strictly emphasized on HIV patients with immunological failure.

Pharmacokinetics of Nelfinavir in Subjects With Hepatic Impairment

HIV-seronegative subjects with hepatic impairment (6 mild, 6 moderate) and 12 matched healthy controls received nelfinavir 1250 mg every 12 hours with food for 2 weeks. Mild impairment did not significantly change nelfinavir or major metabolite (M8) steady-state exposures compared with controls. In subjects with moderate impairment, steady-state area under the plasma concentration time-curve over the dosing interval and maximum observed plasma concentrations were 62% and 22% higher for nelfinavir than for controls, and for M8 were 46% and 35% of control values. With increasing degree of impairment, no trend toward increase in unbound nelfinavir was observed, but there was an increase in unbound M8 levels. Nelfinavir was safe and well tolerated. One subject with moderate impairment was discontinued because of transient leucopenia. Observed changes are unlikely to affect nelfinavir efficacy or markedly influence safety. Dose reduction of nelfinavir does not appear necessary for subjects with mild/moderate impairment. Further long-term evaluations of nelfinavir pharmacokinetics and safety in HIV-seropositive subjects with hepatic impairment may be useful.

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.

Pharmacokinetics and safety of a new paediatric fixed-dose combination of zidovudine/lamivudine/nevirapine in HIV-infected children

BACKGROUND

Alternatives to the available stavudine-containing paediatric fixed-dose combination (FDC) tablets are rapidly needed due to concerns regarding the cumulative toxicity of long-term stavudine exposure. We report the bioavailability and short-term safety of a novel paediatric FDC tablet of zidovudine (ZDV)/lamivudine (3TC)/nevirapine (NVP; 30/15/28 mg) in HIV-infected children.

METHODS

In this Phase I/II open-label pharmacokinetic study, 42 children weighing 6-30 kg treated with NVP-based HAART for ≥4 weeks were randomized to receive the FDC tablets (GPO-VIR Z30) or the liquid formulations. Dosing was weight-based. Intensive 12-h blood sampling was performed after 2 weeks; subjects then crossed-over to the alternate formulation at equal doses and sampling repeated 2 weeks later. Pharmacokinetic parameters were determined by non-compartmental analysis. Buccal-swab samples were collected for cytochrome P450 (CYP)2B6 polymorphism analysis.

RESULTS

With the FDC tablet, the geometric mean (90% CI) area under the curve (AUC) for ZDV, 3TC and NVP was 1.58 (1.49-1.68), 7.78 (7.38-8.19) and 68.88 (62.13-76.36) μg•h/ml, respectively. Rules for NVP therapeutic inadequacy were defined a priori, and despite lower NVP exposure with the tablet (P<0.001), the levels remained therapeutically adequate. ZDV AUC was similar between formulations. 3TC exposure was significantly higher with the tablet but comparable to historical data in adults and children taking branded tablets. While receiving the tablet, NVP AUC in children with CYP2B 516 GG (45%), GT (45%) and TT (10%) genotypes were 67.0, 74.5 and 106.4 μg•h/ml, respectively (P=0.04).

CONCLUSIONS

Disparities in drug exposure between formulations were observed; however, the FDC tablet delivered therapeutically adequate exposures of each drug and could well play an important role in simplifying antiretroviral treatment for children.

Antiretroviral drug interactions: overview of interactions involving new and investigational agents and the role of therapeutic drug monitoring for management

Antiretrovirals are prone to drug-drug and drug-food interactions that can result in subtherapeutic or supratherapeutic concentrations. Interactions between antiretrovirals and medications for other diseases are common due to shared metabolism through cytochrome P450 (CYP450) and uridine diphosphate glucuronosyltransferase (UGT) enzymes and transport by membrane proteins (e.g., p-glycoprotein, organic anion-transporting polypeptide). The clinical significance of antiretroviral drug interactions is reviewed, with a focus on new and investigational agents. An overview of the mechanistic basis for drug interactions and the effect of individual antiretrovirals on CYP450 and UGT isoforms are provided. Interactions between antiretrovirals and medications for other co-morbidities are summarized. The role of therapeutic drug monitoring in the detection and management of antiretroviral drug interactions is also briefly discussed.

Therapeutic drug monitoring of protease inhibitors and efavirenz in HIV-infected individuals with active substance-related disorders

BACKGROUND

Achieving targeted antiretroviral (ARV) plasma concentrations during long-term treatment in human immunodeficiency virus (HIV)-infected patients with substance-related disorders (SRDs) may be challenging due to a number of factors, including medication adherence, coinfection with hepatitis B or C virus, medication intolerance, and drug interactions. One approach to investigate these factors is to conduct therapeutic drug monitoring to measure ARV exposure during treatment. The objective of this study was to utilize therapeutic drug monitoring to compare efavirenz (EFV) and protease inhibitor pharmacokinetics in patients with and without SRDs.

METHODS

This was a multicenter, cross-sectional open-label study in patients with HIV-1 infection receiving antiretroviral therapy (ART), with active (n=129) or without (n=146) SRD according to National Institute on Drug Abuse criteria. Two hundred seventy-five subjects who were receiving either protease inhibitor-based or EFV-based ART regimens for >6 months were enrolled at 4 HIV treatment centers with an equal distribution of SRD and non-SRD at each site. The patients were instructed during enrollment visits with regard to the importance of adherence before and after study visits. Demographics and routine clinical laboratory tests were recorded.

RESULTS

Among the 275 patients, 47% had SRD with at least 1 substance. There were no significant differences between SRD and non-SRD groups for race, gender, age, or CD4 count at entry. A significantly higher proportion of patients with SRD had an entry HIV RNA plasma concentration>75 copies per milliliter compared with patients without SRD (40% vs 28%, P=0.044). Logistic regression modeling revealed an association between HIV RNA plasma concentration and African American race (P=0.017). A significantly higher proportion of SRDs also had an EFV or protease inhibitor trough concentration below the desired range (23% vs 9%, P=0.048). Significantly lower trough concentrations were noted in patients with SRDs receiving atazanavir (0.290 vs 0.976 μg/mL) or lopinavir (3.75 vs 5.30 μg/mL).

CONCLUSIONS

The pharmacokinetic data indicate differences between HIV-infected patients with and without SRDs that may influence viral load suppression during long-term ART. These findings require additional investigation in a randomized design with more intensive pharmacokinetic assessment to identify individual factors that are contributing to suboptimal ARV exposure in patients with SRDs.

HIV protease inhibitors alter innate immune response signaling to double-stranded RNA in oral epithelial cells: implications for immune reconstitution inflammatory syndrome?

In this investigation, several HIV protease inhibitors altered the virally associated, double-stranded RNA (dsRNA)-stimulated, innate immune response. Lopinavir, the most potent inducer of interleukin (IL)-8 expression, also inhibited dsRNA-induced monocyte chemotactic protein 1 expression. Further analyses demonstrated that nuclear factor-κB is required for lopinavir's induction of IL-8. These findings demonstrate that protease inhibitors, such as lopinavir, differentially dysregulate innate immune signaling in a manner that could affect immune (reconstitution) inflammatory responses in oral epithelium.

A chewable pediatric fixed-dose combination tablet of stavudine, lamivudine, and nevirapine: pharmacokinetics and safety compared with the individual liquid formulations in human immunodeficiency virus-infected children in Thailand

BACKGROUND

Pediatric fixed-dose combinations (FDCs) are needed to facilitate antiretroviral therapy in children. We evaluated the relative bioavailability, safety, and therapeutic adequacy of a novel chewable pediatric FDC tablet of stavudine (7 mg), lamivudine (30 mg), and nevirapine (50 mg), referred to as GPO-VIR S7, and compared it with the individual original brand-name liquid formulations in human immunodeficiency virus-infected Thai children.

METHODS

The International Maternal Pediatric Adolescent AIDS Clinical Trials group (IMPAACT) P1056 study was a phase I/II, 2-arm, randomized, open-label, multidose pharmacokinetic cross-over study. Children ≥6 to ≤30 kg receiving nevirapine-based HAART for at least 4 weeks were randomized to receive GPO-VIR S7 chewable tablets or the equivalent liquid formulations. Children were stratified by weight and dosing was weight-based. Intensive 12-hour blood sampling was performed on day 28, and subjects then crossed-over to the alternate formulation at equal doses with identical 12-hour sampling on day 56. Pharmacokinetic indices were determined by noncompartmental analysis.

RESULTS

Thirty-four children completed the study. While taking Government Pharmaceutical Organization (GPO)-VIR S7 the geometric mean (90% CI) area under the curve was 1.54 μg·hr/mL (1.42-1.67) for stavudine, 6.39 (5.82-7.00) for lamivudine, and 74.06 (65.62-83.60) for nevirapine. Nevirapine drug exposure for GPO-VIR S7 was therapeutically adequate. Geometric mean area under the curve ratios (90% CI) of GPO-VIR S7/liquid formulation for stavudine, lamivudine, and nevirapine were 0.97 (0.92-1.02), 1.41 (1.30-1.53), and 1.08 (1.04-1.13), respectively. No serious drug-related toxicity was reported.

CONCLUSIONS

The chewable FDC was safe and provided therapeutically adequate plasma drug exposures in human immunodeficiency virus-infected children. Substituting the FDC for liquid formulations can simplify antiretroviral therapy.

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.

Pharmacogenomics of CYP3A: considerations for HIV treatment

The understanding of the cytochrome P450 3A SNP in antiretroviral therapy is important, because it is highly inducible, extremely polymorphic and metabolizes many of the drugs that are key components of highly active antiretroviral therapy regimens. This enzyme is prolific and promiscuous towards drug and xenobiotic substrate selection and it is also unpredictable among individuals, having a 5- to 20-fold variability in its ability to contribute to drug clearance. The importance of human CYP3A pharmacogenetics is also gaining attention in other established areas of pharmacotherapy as it may contribute to the goal of predicting efficacy and/or toxicity, specifically with the discovery of null allele CYP3A4*20. This review summarizes the current understanding, implications of genetic variation in the CYP3A enzymes, the central role of CYP3A in linking human genetics, the pharmacokinetics and resulting pharmacodynamic responses to certain antiretroviral drugs, and their eventual place in applied clinical pharmacotherapy.

HIV protease inhibitors block oral epithelial cell DNA synthesis

OBJECTIVES

Anti-retroviral therapy regimens that include HIV protease inhibitors (PIs) are associated with diverse adverse effects including increased prevalence of oral warts, oral sensorial deficits and gastrointestinal toxicities suggesting that PIs may perturb epithelial cell biology. To test the hypothesis that PIs could affect specific biological processes of oral epithelium, the effects of these agents were evaluated in several oral epithelial cell-lines.

DESIGN

Primary and immortalized oral keratinocytes and squamous carcinoma cells of oropharyngeal origin were cultured in the presence of pharmacologically relevant concentrations of PIs. Their affects on cell viability, cytotoxicity and DNA synthesis were assessed by enzymatic assays and incorporation of 5-bromo-2'-deoxyuridine (BrdU) into DNA.

RESULTS

Viability of primary and immortalized oral keratinocytes as well as squamous carcinoma cells of oropharyngeal origin was significantly reduced by select PIs at concentrations found in plasma. Of the seven PIs evaluated, nelfinavir was the most potent with a mean 50% inhibitory concentration [IC(50)] of 4.1 microM. Lopinavir and saquinavir also reduced epithelial cell viability (IC(50) of 10-20 microM). Atazanavir and ritonovir caused minor reductions in viability, while amprenavir and indinavir were not significant inhibitors. The reduced cell viability, as shown by BrdU incorporation assays, was due to inhibition of DNA synthesis rather than cell death due to cytotoxicity.

CONCLUSION

Select PIs retard oral epithelial cell proliferation in a drug and dose-dependent manner by blocking DNA synthesis. This could account for some of their adverse effects on oral health.

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.

Effects of minocycline and valproic acid coadministration on atazanavir plasma concentrations in human immunodeficiency virus-infected adults receiving atazanavir-ritonavir

Minocycline and valproic acid are potential adjuvant therapies for the treatment of human immunodeficiency virus (HIV)-associated cognitive impairment. The purpose of this study was to determine whether minocycline alone or in combination with valproic acid affected atazanavir plasma concentrations. Twelve adult HIV-infected subjects whose regimen included atazanavir (300 mg)-ritonavir (100 mg) daily for at least 4 weeks were enrolled. Each subject received atazanavir-ritonavir on day 1, atazanavir-ritonavir plus 100 mg minocycline twice daily on days 2 to 15, and atazanavir-ritonavir plus 100 mg minocycline twice daily and 250 mg valproic acid twice daily on days 16 to 30 with meals. The subjects had 11 plasma samples drawn over a dosing interval on days 1, 15, and 30. The coadministration of minocycline and valproic acid with atazanavir-ritonavir was well tolerated in all 12 subjects (six male; mean [+/- standard deviation] age was 43.1 [8.2] years). The geometric mean ratios (GMRs; 95% confidence interval [CI]) for the atazanavir area under the concentration-time curve from 0 to 24 h at steady state (AUC(0-24)), the plasma concentration 24 h after the dose (C(min)), and the maximum concentration during the dosing interval (C(max)) with and without minocycline were 0.67 (0.50 to 0.90), 0.50 (0.28 to 0.89), and 0.75 (0.58 to 0.95), respectively. Similar decreases in atazanavir exposure were seen after the addition of valproic acid. The GMRs (95% CI) for atazanavir AUC(0-24), C(min), and C(max) with and without minocycline plus valproic acid were 0.68 (0.43 to 1.06), 0.50 (0.24 to 1.06), and 0.66 (0.41 to 1.06), respectively. Coadministration of neither minocycline nor minocycline plus valproic acid appeared to influence the plasma concentrations of ritonavir (P > 0.2). Minocycline coadministration resulted in decreased atazanavir exposure, and there was no evidence that the addition of valproic acid mediated this effect.

A Randomized Controlled Trial of Therapeutic Drug Monitoring in Treatment-Naive and -Experienced HIV-1-Infected Patients

OBJECTIVE

To improve the utility of therapeutic drug monitoring (TDM) by defining the proportion of patients with and predictors of above or below target protease inhibitor (PI) or nonnucleoside reverse transcriptase inhibitor (NNRTI) concentrations.

METHODS

This 48-week, multicenter, open-label clinical trial randomized patients to TDM versus standard of care (SOC). Serial pharmacokinetics, including a week-2 3-sample sparse collection, and expert committee TDM recommendations were given to TDM-arm patients' providers.

RESULTS

Seventy-four (39%) of 190 patients had week-2 concentrations outside of targets and 122 (64%) of 190 had nontarget exposure at least once over 48 weeks. Providers accepted 75% of TDM recommendations. Among patients with below-target concentrations, more TDM-arm than SOC-arm patients achieved targets (65% vs. 45%; P = 0.09). Increased body weight and efavirenz or lopinavir/ritonavir use were significant predictors of nontarget concentrations. Patients at target and patients who achieved targets after TDM-directed dose modifications trended toward greater viral load reductions at week 48 than patients with below-target exposures (HIV RNA reductions: 2.4, 2.3, and 1.9 log10 copies/mL, respectively; P = 0.09).

CONCLUSIONS

Most patients had nontarget PI and/or NNRTI concentrations over 48 weeks. TDM recommendations were well accepted and improved exposure. Patients below TDM targets trended toward worse virologic response.

Assessing the Impact of Substance use and Hepatitis Coinfection on Atazanavir and Lopinavir Trough Concentrations in HIV-Infected Patients During Therapeutic Drug Monitoring

Atazanavir (ATV) and lopinavir (LPV) are widely used HIV-1 protease inhibitors. Like with other protease inhibitors, careful monitoring of potential drug-drug and drug-disease interactions in clinical practice is necessary. The aim of this study was to assess the impact of substance use and hepatitis virus coinfection on plasma ATV and LPV trough concentrations in HIV-positive substance users and nonusers. Individuals established on ATV (300 mg and 100 mg ritonavir daily) or LPV (400 mg and 100 mg ritonavir twice daily)-containing regimens completed two clinical visits (trough and directly observed therapy) during which dosing characteristics, concomitant medication, and substance use were recorded. Trough plasma concentrations (22-26 hours for ATV and 10-14 hours for LPV) were measured using LCMSMS. The influence of substance use was evaluated by Kruskal-Wallis test. Substance use was associated with a marked decrease in trough LPV concentrations during the trough visit (median, 5.536 and 3.791 microg/mL for nonsubstance users and substance users, respectively, P = 0.029). Significantly lower LPV trough levels were also noted among patients with active hepatitis C virus coinfection evaluated as an independent variable (median, 2.253 and 5.927 microg/mL for active and inactive/no hepatitis C virus infection, respectively, P = 0.032). Substance use and hepatitis virus coinfection had limited effects on ATV trough levels. In this cohort, despite the wide interindividual variability of ATV and LPV trough concentrations, significant associations between substance use and active hepatitis C virus infection and low LPV trough concentrations were observed. Further work is needed to assess the optimal dosing regimen when using LPV in HIV-infected substance users.

Safety, Tolerability, and Pharmacokinetics of Raltegravir After Single and Multiple Doses in Healthy Subjects

Raltegravir is a novel human immunodeficiency virus-1 integrase inhibitor with potent in vitro activity (95% inhibitory concentration (IC95)=33 nM in 50% human serum). Three double-blind, randomized, placebo-controlled, pharmacokinetic, safety, and tolerability studies were conducted: (1) single-dose escalation study (10-1,600 mg), (2) multiple-dose escalation study (100-800 mg q12 h x 10 days), and (3) single-dose female study (400 mg). Raltegravir was rapidly absorbed with a terminal half-life (t1/2) approximately 7-12 h. Approximately 7-14% of raltegravir was excreted unchanged in urine. Area under the curve (AUC)(0-infinity) was similar between male and female subjects. After multiple-dose administration, steady state was achieved within 2 days; there was little to modest accumulation of raltegravir. Trough levels were >33 nM for dose levels of 100 mg and greater. Raltegravir is generally well tolerated at doses of up to 1,600 mg/day given for up to 10 days and exhibits a pharmacokinetic profile supportive of twice-daily dosing with multiple doses of 100 mg and greater achieving trough levels >33 nM.

Nevirapine concentration in nonstimulated saliva: an alternative to plasma sampling in children with human immunodeficiency virus infection

BACKGROUND

The monitoring of nevirapine (NVP) concentrations in pediatric patients has gained interest since the introduction of NVP as part of the preferred first-line antiretroviral regimen for human immunodeficiency virus (HIV)-infected children in resource-limited settings. Adequate trough concentrations of NVP predict successful therapy, whereas subtherapeutic levels are correlated with virologic failure and development of resistance. The aim of this study was to determine the extent of agreement between total and free plasma NVP concentrations and nonstimulated saliva NVP concentrations and to evaluate the feasibility of saliva sampling as an alternative tool for therapeutic drug monitoring of NVP in children.

DESIGN AND METHODS

The study was designed as an observational cohort analysis. NVP concentrations were obtained in paired plasma and saliva samples of pediatric patients receiving antiretroviral therapy, including NVP. NVP plasma and saliva concentrations were determined by a tandem-mass spectrometric method. The intraclass correlation coefficient and Bland-Altman analysis were used to evaluate agreement and to assess pattern in any discrepancies between measurements.

RESULTS

For the random paired plasma and saliva NVP sampling, 19 African-American children (8 boys, 11 girls) with a median age of 8.0 years were enrolled. Two male subjects were recruited for the 12 hour NVP plasma and saliva pharmacokinetics study. The intraclass correlations between saliva and serum measurements of NVP concentrations indicated >90% agreement between these two modes of measurement. The saliva concentrations reflected the free concentrations very closely but were on average 34% higher. The Bland-Altman plots indicated that the discrepancy between saliva and plasma measures is consistent across the range of average NVP concentrations.

CONCLUSIONS

Our study results strongly indicate agreement between saliva and plasma NVP concentrations in pediatric patients with HIV infection, on the basis of Bland-Altman analysis. Nonstimulated NVP saliva concentrations can be used as an alternative noninvasive, reliable, cost-effective method for direct measurement of adherence and application of therapeutic drug monitoring in NVP therapy.

Pilot study of a novel short-cycle antiretroviral treatment interruption strategy: 48-week results of the five-days-on, two-days-off (FOTO) study

PURPOSE

The challenges associated with daily lifelong antiretroviral therapy (ART) have stimulated interest in alternative treatment schedules, including planned, cyclical interruptions of therapy in patients with virologic suppression and sufficient CD4+ T-cell counts.

METHOD

We conducted a 48-week, open-label, single-arm, prospective pilot study of a novel short-cycle treatment interruption strategy. Upon enrollment, 30 HIV+ individuals with a history of durable viral suppression on daily ART changed their weekly treatment schedule to 5 consecutive days on treatment (typically Monday through Friday) followed by 2 days off treatment (five-on, two-off, or FOTO treatment schedule).

RESULTS

At 24 and 48 weeks, as-treated analysis revealed that virologic suppression was maintained in 26/29 subjects (89.6%), including 100% of subjects taking efavirenz-based regimens. Participants adhered well to the FOTO treatment schedule and expressed a strong preference for the FOTO treatment schedule compared to daily ART.

CONCLUSION

If validated, the FOTO treatment strategy with efavirenz-based regimens could avoid the viremia witnessed in longer cycle structured treatment interruptions yet still ameliorate a number of problems associated with the current paradigm of daily ART for HIV infection, including the high cost of therapy and the pill fatigue that, in many patients, leads to erratic adherence and ultimately treatment failure.

Current role of LC-MS in therapeutic drug monitoring

The role of liquid chromatography coupled with mass spectrometry (LC-MS) techniques in routine therapeutic drug monitoring activity is becoming increasingly important. This paper reviews LC-MS methods published in the last few years for certain classes of drugs subject to therapeutic drug monitoring: immunosuppressants, antifungal drugs, antiretroviral drugs, antidepressants and antipsychotics. For each class of compounds, we focussed on the most interesting methods and evaluated the current role of LC-MS in therapeutic drug monitoring.

A Computer-Based System to aid in the Interpretation of Plasma Concentrations of Antiretrovirals for Therapeutic Drug Monitoring

Objectives

To develop a computer-based system for modelling and interpreting plasma antiretroviral concentrations for therapeutic drug monitoring (TDM).

Methods

Data were extracted from a prospective TDM study of 199 HIV-infected patients (CCTG 578). Lopinavir (LPV) and efavirenz (EFV) pharmacokinetic (PK) parameters were modelled using a Bayesian method and interpreted by an expert committee of HIV specialists and pharmacologists who made TDM recommendations. These PK models and recommendations formed the knowledge base to develop an artificial intelligence (AI) system that could estimate drug exposure, interpret PK data and generate TDM recommendations. The modelled PK exposures and expert committee TDM recommendations were considered optimum and used to validate results obtained by the AI system.

Results

A group of patients, 67 on LPV, 46 on EFV and three on both drugs, were included in this analysis. Correlations were high for LPV and EFV estimated trough and 4 h post-dose concentrations between the AI estimates and modelled values (r>0.79 for all comparisons; P<0.0001). Although trough concentrations were similar, significant differences were seen for mean predicted 4 h concentrations for EFV (4.16 μg/ml versus 3.89 μg/ml; P=0.02) and LPV (7.99 μg/ml versus 8.79 μg/ml; P<0.001). The AI and expert committee TDM recommendations agreed in 53 out of 69 LPV cases [kappa (κ)=0.53; P<0.001] and 47 out of 49 EFV cases (κ=0.91; P<0.001).

Conclusions

The AI system successfully estimated LPV and EFV trough concentrations and achieved good agreement with expert committee TDM recommendations for EFV- and LPV-treated patients.

Once-daily nevirapine dosing: a pharmacokinetics, efficacy and safety review

In the context of attempts to simplify treatment regimens and enhance adherence, there is great interest in once-daily dosing regimens for the treatment of HIV-1 infection. Nevirapine has a long half-life and achieves high steady-state plasma concentrations relative to the concentration required to inhibit 50% viral replication in vitro (IC(50)) in patients. For this reason, it has been considered as a once-daily antiretroviral. Pharmacokinetic and efficacy data support the use of this dosing approach, but excess rash and lingering concerns over liver toxicity preclude use of once-daily dosed nevirapine at this time. Tolerance to high nevirapine concentrations may develop when dose escalation is used during initiation of therapy. It is theoretically possible that the benefits of once-daily dosing may be achieved without excess toxicity by switching to once-daily nevirapine following several months of twice-daily administration. This dosing strategy is currently under evaluation.

Practical and conceptual challenges in measuring antiretroviral adherence

Accurate measurement of antiretroviral adherence is essential for targeting and rigorously evaluating interventions to improve adherence and prevent viral resistance. Across diseases, medication adherence is an individual, complex, and dynamic human behavior that presents unique measurement challenges. Measurement of medication adherence is further complicated by the diversity of available measures, which have different utility in clinical and research settings. Limited understanding of how to optimize existing adherence measures has hindered progress in adherence research in HIV and other diseases. Although self-report is the most widely used adherence measure and the most promising for use in clinical care and resource-limited settings, adherence researchers have yet to develop evidence-based standards for self-reported adherence. In addition, the use of objective measures, such as electronic drug monitoring or pill counts, is limited by poor understanding of the source and magnitude of error biasing these measures. To address these limitations, research is needed to evaluate methods of combining information from different measures. The goals of this review are to describe the state of the science of adherence measurement, to discuss the advantages and disadvantages of common adherence measurement methods, and to recommend directions for improving antiretroviral adherence measurement in research and clinical care.

Quality assurance program for pharmacokinetic assay of antiretrovirals: ACTG proficiency testing for pediatric and adult pharmacology support laboratories, 2003 to 2004: a requirement for therapeutic drug monitoring

Proficiency testing (PT) is a mandated requirement for clinical laboratories doing therapeutic drug monitoring and is an invaluable tool to help laboratories identify and correct problems in analytical procedures. The AIDS Clinical Trial Group Pharmacology Quality Assurance Committee implemented a new antiretroviral PT program for all currently available antiretroviral drugs in 2001. The PT program was designed for the AIDS Clinical Trial Group Pharmacology Specialty Laboratories actively involved in assaying these drugs in clinical trial samples so as to comply with the Clinical Laboratory Improvement Amendments. Results from the first 3 rounds of PT have been analyzed and reported and provided support for formalizing the guidelines of the PT testing program. The PT program has expanded with the addition of nucleoside reverse transcription inhibitors (NRTIs) and atazanavir. This report includes results from rounds 4 to 7 over 2 additional years of standard operations. Additionally we include results from NRTIs for all rounds and atazanavir for a single round. There were 9 participating laboratories. Eight used high-performance liquid chromatography as the primary method of detection and 2/8 also reported LC-MS-MS results. One laboratory used LC-MS-MS as their primary detection method. All laboratories measured protease inhibitors, most measured at least 1 non-nucleoside reverse transcription inhibitor and 5 had NRTI capabilities. Results were normally distributed and the acceptance range of +/-20% best corresponded to a 95% confidence interval. Overall score for 9 participating laboratories was 96% correct out of 1826 challenges over 4 rounds. Laboratories scored 95, 98 and 97% correct for protease inhibitors, non-nucleoside reverse transcription inhibitorss and NRTIs, respectively. Three laboratories reporting LC-MS-MS results had 92% correct (347/378) challenges for all drugs. The percentage of correct results is about the same as previously reported. There is a continued need for a PT program to help participating laboratories maintain essential quality assurance and quality control.

An Update on Therapeutic Drug Monitoring for Antiretroviral Drugs

There is an increasing uptake of TDM of antiretroviral drugs, particularly in Europe. There is consensus that current antiretroviral drugs meet most of the criteria of drugs that can be considered as candidates for a TDM strategy. This review examines the pharmacokinetic-pharmacodynamic relationship for protease inibitors and non nucleoside reverse transcriptase inhibitor, give an overview of the published randomised clinical trials and then summarises the scenarios for use of TDM. Finally the development of the inhibitory quotient (IQ) concept is discussed.

Pharmacokinetic parameters of nevirapine and efavirenz in relation to antiretroviral efficacy

Optimal adherence is essential for successful antiretroviral therapy. We analyzed the relation between minimum plasma drug concentration (Cmin) and total drug exposure over 24 hr (AUC24) with virologic failure for therapy-adherent patients in the nevirapine (NVP) and efavirenz (EFV) groups of the double nonnucleoside study (2NN), which compared the efficacy of NVP and/or EFV together with stavudine and lamivudine. The objective was to find cutoff values of the Cmin and AUC24 below which the risk of virologic failure increased. The relation between Cmin and AUC24 with virologic failure (never a plasma viral load [pVL] < 50 copies/ml or a rebound to two consecutive pVL > 50 copies/ml) was analyzed with proportional hazard analyses. Data were censored at end of study or change of allocated treatment. The risk of virologic failure with NVP (n = 511) started to increase at a Cmin < 3.1 mg/L (hazard ratio [HR], 1.33; 95% confidence interval [CI], 0.89-1.97), but there was no cutoff value below which a statistically significant increased risk occurred. Neither was such a cutoff point identified for the AUC24. The risk of virologic failure with EFV (n = 312) was significantly increased at a Cmin < 1.1 mg/L (HR, 1.95; 95% CI, 1.08-3.54) and an AUC24 < 40 mg x hr x L1 (HR, 1.95; 95% CI, 1.07-3.54). Both cutoff values represent the median values for adherent patients. These associations were driven by patients from Thailand. Adjusting for geographical region made the association between Cmin and AUC24 with virologic failure statistically nonsignificant. The sensitivity of the Cmin values was too low (29% for NVP, 64% for EFV) to be an adequate predictor for virologic failure. We conclude that identifying the Cmin value for the sole purpose of predicting virologic failure in patients who report to be adherent to NVP or EFV is questionable because of the absence of a concentration-response relation (NVP) or the low sensitivity for such a cutoff value (NVP and EFV).

Simultaneous determination of 16 anti-HIV drugs in human plasma by high-performance liquid chromatography

Therapeutic drug monitoring (TDM) is pivotal to improve the management of HIV infection. Here, a HPLC-UV method has been developed to quantify simultaneously seven HIV protease inhibitors (amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir, and saquinavir; PIs), seven nucleoside reverse transcriptase inhibitors (abacavir, didanosine, emtricitabine, lamivudine, stavudine, zalcitabine, and zidovudine; NRTIs), and two non-nucleoside reverse transcriptase inhibitors (efavirenz and nevirapine; NNRTIs) in human plasma. The volume of the plasma sample was 600 microL. This method involved automated solid-phase extraction with Oasis HLB Cartridge 1 cc (divinylbenzene and N-vinylpyrrolidone) and evaporation in a water bath under nitrogen stream. The extracted samples were reconstituted with 100 microL methanol. Twenty microliters of these samples were injected into a HPLC-UV system, the analytes were eluted on an analytical C(18) Symmetry column (250 mm x 4.6mm I.D.) with a particle size of 5 microm. The mobile phase (0.01 M KH(2)PO(4) and acetonitrile) was delivered at 1.0 mL/min with linear gradient elution. The total run time for a single analysis was 35 min, the anti-HIV drugs were detected by UV at 240 and 260 nm. The calibration curves were linear up to 10 microg/mL. The absolute recovery ranged between 88 and 120%. The in vitro stability of anti-HIV drugs (0.005-10 microg/mL) in plasma has been studied at 24.0 degrees C. On these bases, a two to four analyte method has been tailored to the individual needs of the HIV-infected patient. The HPLC-UV method here reported has been validated and is currently applied to monitor PIs, NRTIs, and NNRTIs in plasma of HIV-infected patients. It allows to monitor the largest number of anti-HIV drugs simultaneously, appearing useful in a routine laboratory, and represents an essential step to elucidate the utility of a formal therapeutic drug monitoring for the optimal follow-up of HIV-infected patients.