The genotypic inhibitory quotient and the (cumulative) number of mutations predict the response to lopinavir therapy

Optimizing Pediatric Dosing Recommendations and Treatment Management of Antiretroviral Drugs Using Therapeutic Drug Monitoring Data in Children Living With HIV

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Introduction:

This review summarizes the current dosing recommendations for antiretroviral (ARV) drugs in the international pediatric guidelines of the World Health Organization (WHO), US Department of Health and Human Services (DHHS), and Pediatric European Network for Treatment of AIDS (PENTA), and evaluates the research that informed these approaches. We further explore the role of data generated through therapeutic drug monitoring in optimizing the dosing of ARVs in children.

Methods:

A PubMed search was conducted for the literature on ARV dosing published in English. In addition, the registration documentation of European Medicines Agency and the US Food and Drug Administration for currently used ARVs and studies referenced by the WHO, DHHS, and EMA guidelines were screened. Resulting publications were screened for papers containing data on the area under the concentration–time curve, trough concentration, and peak concentration. Studies with enrolled participants with a median or mean age of ≥18 years were excluded. No restriction on publishing date was applied.

Discussion and conclusion:

Pediatric ARV dosing is frequently based on data obtained from small studies and is often simplified to facilitate dosing in the context of a public health approach. Pharmacokinetic parameters of pediatric ARVs are subject to high interpatient variation and this leads to a potential risk of underdosing or overdosing when drugs are used in real life. To ensure optimal use of ARVs and validate dosing recommendations for children, it is essential to monitor ARV dosing more thoroughly with larger sample sizes and to include diverse subpopulations. Therapeutic drug monitoring data generated in children, where available and affordable, have the potential to enhance our understanding of the appropriateness of simplified pediatric dosing strategies recommended using a public health approach and to uncover suboptimal dosing or other unanticipated issues postmarketing, further facilitating the ultimate goal of optimizing pediatric ARV treatment.

Physiologically based pharmacokinetic models for the optimization of antiretroviral therapy: recent progress and future perspective

Anti-HIV therapy is characterized by the chronic administration of antiretrovirals (ARVs), and consequently, several problems can arise during the management of HIV-positive patients. ARV disposition can be simulated by combining system data describing a population of patients and in vitro drug data through physiologically based pharmacokinetic (PBPK) models, which mathematically describe absorption, distribution, metabolism and elimination. PBPK modeling can find application in the investigation of clinically relevant scenarios, while providing the opportunity for a better understanding of the mechanisms regulating drug distribution. In this review, we have analyzed the most recent applications of PBPK models for ARVs and highlighted some of the most interesting areas of use, such as drug–drug interaction, pharmacogenetics, factors regulating absorption and tissue penetration, as well as therapy optimization in special populations. The application of the PBPK modeling approach might not be limited to the investigation of hypothetical clinical issues, but could be used to inform future prospective clinical trials.

A randomized clinical trial evaluating therapeutic drug monitoring (TDM) for protease inhibitor-based regimens in antiretroviral-experienced HIV-infected individuals: week 48 results of the A5146 study

BACKGROUND

We devised an open-label, randomized trial to evaluate whether therapeutic drug monitoring (TDM) of protease inhibitors (PIs) and dose escalation based upon a normalized inhibitory quotient (NIQ), which integrates PI trough concentration and drug resistance, could improve virologic outcome in PI-experienced patients with treatment failure. Secondary analyses through 48 weeks are presented.

METHODS

Eligible HIV-infected subjects with a screening viral load of ≥ 1000 copies/mL initiated a new PI-based regimen at entry and had NIQ performed at week 2. Subjects with an NIQ ≤1 were randomized at week 4 to a standard-of-care (SOC) arm or TDM arm featuring PI dose escalation.

RESULTS

One hundred and eighty-three subjects were randomized. There was no significant treatment difference in change from randomization to week 48 in HIV-1 RNA [ P = .13, median (25th, 75th percentile log10 copies/mL change): -0.03 (-0.74, 0.62) with TDM and 0.11 (-2.3, 0.82) with SOC]. In subgroup analysis, patients with ≥ 0.69 active PIs benefited from TDM compared to those with <0.69 active PIs ( P = .05).

CONCLUSIONS

While the TDM strategy of PI dose escalation did not improve virologic response at week 48 overall, in subgroup analysis, TDM favorably impacted virologic outcome in subjects taking PI-based regimens with moderate antiviral activity.

[Evidence-based therapeutic drug monitoring of lopinavir]

The HIV protease inhibitor lopinavir presents a wide inter-individual variability related to liver and intestinal metabolism involving CYP3A. Published studies were analyzed to establish whether there is evidence that therapeutic drug monitoring of lopinavir could improve patient care. In naïve or pretreated HIV-infected patients, no relationship could be evidenced between virological efficacy and trough lopinavir concentration, most likely because concentrations are above inhibitory concentrations. Although data are limited, patients with elevated triglycerides and cholesterol had trough lopinavir concentrations >8 000 ng/mL. These data suggest that the level of evidence of interest of lopinavir therapeutic drug monitoring is may be recommended in some situations such as children, pregnant women, pretreated patients if the number of mutations is <5, when coadministration with drug with metabolizing enzyme inducing properties is warranted and toxicity.

[AIDS Study Group/Spanish AIDS Plan consensus document on antiretroviral therapy in adults with human immunodeficiency virus infection (updated January 2010)]

OBJECTIVE

This consensus document is an update of antiretroviral therapy recommendations for adult patients with human immunodeficiency virus infection.

METHODS

To formulate these recommendations a panel made up of members of the Grupo de Estudio de Sida (Gesida, AIDS Study Group) and the Plan Nacional sobre el Sida (PNS, Spanish AIDS Plan) reviewed the advances in the current understanding of the pathophysiology of human immunodeficiency virus (HIV) infection, the efficacy and safety of clinical trials, and cohort and pharmacokinetic studies published in biomedical journals or presented at scientific meetings. Three levels of evidence were defined according to the data source: randomized studies (level A), cohort or case-control studies (level B), and expert opinion (level C). The decision to recommend, consider or not to recommend ART was established in each situation.

RESULTS

Currently, the treatment of choice for chronic HIV infection is the combination of three drugs of two different classes, including 2 nucleosides or nucleotide analogs (NRTI) plus 1 non-nucleoside (NNRTI) or 1 boosted protease inhibitor (PI/r), but other combinations are possible. Initiation of ART is recommended in patients with symptomatic HIV infection. In asymptomatic patients, initiation of ART is recommended on the basis of CD4 lymphocyte counts, plasma viral load and patient co-morbidities, as follows: 1) therapy should be started in patients with CD4 counts below 350 cells/microl; 2) When CD4 counts are between 350 and 500 cells/microl, therapy should be started in case of cirrhosis, chronic hepatitis C, high cardiovascular risk, HIV nephropathy, HIV viral load above 100,000 copies/ml, proportion of CD4 cells under 14%, and in people aged over 55; 3) Therapy should be deferred when CD4 are above 500 cells/microl, but could be considered if any of previous considerations concurs. Treatment should be initiated in case of hepatitis B requiring treatment and should be considered for reduce sexual transmission. The objective of ART is to achieve an undetectable viral load. Adherence to therapy plays an essential role in maintaining antiviral response. Therapeutic options are limited after ART failures but undetectable viral loads maybe possible with the new drugs even in highly drug experienced patients. Genotype studies are useful in these situations. Drug toxicity of ART therapy is losing importance as benefits exceed adverse effects. Criteria for antiretroviral treatment in acute infection, pregnancy and post-exposure prophylaxis are mentioned as well as the management of HIV co-infection with hepatitis B or C.

CONCLUSIONS

CD4 cells counts, viral load and patient co-morbidities are the most important reference factors to consider when initiating ART in asymptomatic patients. The large number of available drugs, the increased sensitivity of tests to monitor viral load, and the ability to determine viral resistance is leading to a more individualized therapy approach in order to achieve undetectable viral load under any circumstances.

Inhibitory quotient in HIV pharmacology

PURPOSE OF REVIEW

This review discusses the use of the inhibitory quotient in light of therapeutic drug monitoring of antiretroviral drugs. The inhibitory quotient is a parameter that combines viral resistance data with drug exposure data, and has its main role in therapeutic drug monitoring of protease inhibitors in experienced patients. Data from recent clinical studies investigating inhibitory quotient cutoffs to be used in therapeutic drug monitoring will be reviewed. In addition points for discussion regarding the use and study of inhibitory quotients will be presented.

RECENT FINDINGS

A number of studies generated data on the use of the inhibitory quotient in general and the genotypic inhibitory quotient in particular. Most of these studies define a cutoff inhibitory quotient value, above which the virological response rate is higher. These cutoff values can be used in therapeutic drug monitoring and give guidance to the clinician on dose adjustments. Genotypic inhibitory quotient cutoff values are available for amprenavir, atazanavir, darunavir, lopinavir, saquinavir and tipranavir.

SUMMARY

The inhibitory quotient is becoming a valuable tool in therapeutic drug monitoring. At this moment most data are available for the genotypic inhibitory quotient. Nevertheless, a consensus needs to be reached on a number of items, including the methods to study inhibitory quotient as well as the mathematical and virological background.

Population analysis of the pregnancy-related modifications in lopinavir pharmacokinetics and their possible consequences for dose adjustment

OBJECTIVES

To investigate the possible necessity of an increase in lopinavir dose during pregnancy in order to achieve the concentrations previously defined as predictive of virological efficacy.

PATIENTS AND METHODS

Lopinavir pharmacokinetics were investigated by a population approach performed on 145 HIV-infected women, including 74 pregnant women. The final model was used to determine the probability of achievement of the target trough concentrations by Monte Carlo simulations.

RESULTS

The typical population estimates (inter-individual variability %) of apparent clearance (CL/F) and volume of distribution were 4.38 L/h (24%) and 58.4 L (59%), respectively. Pregnancy associated with a gestational age >15 weeks and delivery were found to increase lopinavir CL/F by 39% and 58%, respectively. With the standard 400 mg twice-a-day regimen, the probability of reaching the 1 mg/L target trough concentration for protease inhibitor (PI)-naive patients was 99% and 96% for non-pregnant and pregnant women, respectively. An important decrease in the probability of achieving the 5.7 mg/L target trough concentration for salvage therapy was observed for non-pregnant women (55%), this decrease being even greater for pregnant women (21%). Raising the lopinavir dose to 600 mg twice daily increased these probabilities to 87% and 53% for non-pregnant and pregnant women, respectively.

CONCLUSIONS

Modification of the lopinavir dose is unlikely to be required for PI-naive pregnant women; however, in pregnant women who have previously received a PI, therapeutic drug monitoring and/or empirical increasing of the dose should be considered.

Predictive value of pharmacokinetics-adjusted phenotypic susceptibility on response to ritonavir-enhanced protease inhibitors (PIs) in human immunodeficiency virus-infected subjects failing prior PI therapy

The activities of protease inhibitors in vivo may depend on plasma concentrations and viral susceptibility. This nonrandomized, open-label study evaluated the relationship of the inhibitory quotient (IQ [the ratio of drug exposure to viral phenotypic susceptibility]) to the human immunodeficiency virus type 1 (HIV-1) viral load (VL) change for ritonavir-enhanced protease inhibitors (PIs). Subjects on PI-based regimens replaced their PIs with ritonavir-enhanced indinavir (IDV/r) 800/200 mg, fosamprenavir (FPV/r) 700/100 mg, or lopinavir (LPV/r) 400/200 mg twice daily. Pharmacokinetics were assessed at day 14; follow-up lasted 24 weeks. Associations between IQ and VL changes were examined. Fifty-three subjects enrolled, 12 on IDV/r, 33 on FPV/r, and 8 on LPV/r. Median changes (n-fold) (FC) of 50% inhibitory concentrations (IC(50)s) to the study PI were high. Median 2-week VL changes were -0.7, -0.1, and -1.0 log(10) for IDV/r, FPV/r, and LPV/r. With FPV/r, correlations between the IQ and the 2-week change in VL were significant (Spearman's r range, -0.39 to -0.50; P < or = 0.029). The strongest correlation with response to FPV/r was the IC(50) FC (r = 0.57; P = 0.001), which improved when only adherent subjects were included (r = 0.68; P = 0.001). In multivariable analyses of the FPV/r arm that included FC, one measure of the drug concentration, corresponding IQ, baseline VL, and CD4, the FC to FPV was the only significant predictor of VL decline (P < 0.001). In exploratory analyses of all arms, the area under the concentration-time curve IQ was correlated with the week 2 VL change (r = -0.72; P < 0.001). In conclusion, in PI-experienced subjects with highly resistant HIV-1, short-term VL responses to RTV-enhanced FPV/r correlated best with baseline susceptibility. The IQ improved correlation in analyses of all arms where a greater range of virologic responses was observed.

A randomized trial of therapeutic drug monitoring of protease inhibitors in antiretroviral-experienced, HIV-1-infected patients

OBJECTIVE

Whether therapeutic drug monitoring of protease inhibitors improves outcomes in HIV-infected patients is controversial. We evaluated this strategy in a randomized, open-label clinical trial, using a normalized inhibitory quotient (NIQ), which incorporates drug exposure and viral drug resistance. NIQs < or = 1 may predict poor outcome and identify patients who could benefit from dose escalation.

DESIGN/METHODS

Eligible patients had a viral load > or =1000 copies/ml on a failing regimen, and began a new protease inhibitor containing regimen at entry. All FDA-approved protease inhibitors available during the study recruitment (June 2002-May 2006) were allowed. One hundred and eighty-three participants with NIQ < or = 1, on the basis of their week 2 protease inhibitor trough concentration and pre-entry drug resistance test, were randomized at week 4 to standard of care (SOC) or protease inhibitor dose escalation (TDM). The primary endpoint was change in log10 plasma HIV-1 RNA concentration from randomization to 20 weeks later.

RESULTS

Ninety-one patients were randomized to SOC and 92 to TDM. NIQs increased more in the TDM arm compared to SOC (+69 versus +25%, P = 0.01). Despite this, TDM and SOC arms showed no difference in outcome (+0.09 versus +0.02 log10, P = 0.17). In retrospective subgroup analyses, patients with less HIV resistance to their protease inhibitors benefited from TDM (P = 0.002), as did black and Hispanic patients (P = 0.035 and 0.05, respectively). Differences between black and white patients persisted when accounting for protease inhibitor susceptibility.

CONCLUSIONS

There was no overall benefit of TDM. In post hoc subgroup analyses, TDM appeared beneficial in black and Hispanic patients, and in patients whose virus retained some susceptibility to the protease inhibitors in their regimen.

Predictive values of the human immunodeficiency virus phenotype and genotype and of amprenavir and lopinavir inhibitory quotients in heavily pretreated patients on a ritonavir-boosted dual-protease-inhibitor regimen

The inhibitory quotient (IQ) of human immunodeficiency virus (HIV) protease inhibitors (PIs), which is the ratio of drug concentration to viral susceptibility, is considered to be predictive of the virological response. We used several approaches to calculate the IQs of amprenavir and lopinavir in a subset of heavily pretreated patients participating in the French National Agency for AIDS Research (ANRS) 104 trial and then compared their potentials for predicting changes in the plasma HIV RNA level. Thirty-seven patients were randomly assigned to receive either amprenavir (600 mg twice a day [BID]) or lopinavir (400 mg BID) plus ritonavir (100 or 200 mg BID) for 2 weeks before combining the two PIs. The 90% inhibitory concentration (IC(90)) was measured using a recombinant assay without or with additional human serum (IC(90+serum)). Total and unbound PI concentrations in plasma were measured. Univariate linear regression was used to estimate the relation between the change in viral load and the IC(90) or IQ values. The amprenavir phenotypic IQ values were very similar when measured with the standard and protein binding-adjusted IC(90)s. No relationship was found between the viral load decline and the lopinavir IQ. During combination therapy, the amprenavir and lopinavir genotypic IQ values were predictive of the viral response at week 6 (P = 0.03). The number of protease mutations (< 5 or > or = 5) was related to the virological response throughout the study. These findings suggest that the combined genotypic IQ and the number of protease mutations are the best predictors of virological response. High amprenavir and lopinavir concentrations in these patients might explain why plasma concentrations and the phenotypic IQ have poor predictive value.

Predictive Factors for Response to a Boosted Dual HIV-Protease Inhibitor Therapy with Saquinavir and Lopinavir in Extensively Pre-Treated Patients

Objective

To evaluate predictive factors for therapy outcome of a boosted double-protease inhibitor (PI) regimen in 58 extensively pre-treated patients with HIV.

Methods

Patients received lopinavir/ritonavir 400/100 mg and saquinavir 1,000 mg twice daily without reverse transcriptase inhibitors (RTI). The primary outcome parameter was HIV RNA <400 copies/ml at week 48, secondary parameters were HIV-1 RNA and CD4+ T-cell count changes from baseline to week 48. Pharmacokinetics, genotypic resistance and clinical and individual parameters were correlated with the clinical outcome in regression analyses. Covariates for the analyses were minimum plasma concentration (Cmin), maximum plasma concentration, area under the concentration versus time curve, half-life and clearance of lopinavir and saquinavir, the genotypic inhibitory quotients (GIQ) of archived (GIQarch) and baseline PI resistance mutations, previously taken antiretrovirals, archived and baseline viral resistance mutations, baseline HIV-1 RNA and CD4+ T-cell count.

Results

The analyses detected correlations between the primary outcome parameter and several factors: baseline CD4+ T-cell count ( P=0.001); absence of mutations at V82T/A/F/I/S plus I54M/V/L ( P=0.002) or K20M/R ( P=0.010); and lopinavir CminGIQarch ( P=0.046). This regression model had a predictability of 97.0% for response to therapy. Covariates for the decrease of HIV-1 RNA from baseline to week 48 were baseline HIV-1 RNA ( P<0.001), lopinavir CminGIQarch ( P=0.013), presence/absence of mutations at V82T/A/F/I/S or I84A/V plus L10I/R/V/F, I54M/V/L or L63P ( P=0.018), and previously taken antiretrovirals ( P=0.034).

Conclusions

Baseline HIV-1 RNA <5.0 log10 and CD4+ T-cell count >200 cells/μl, lopinavir CminGIQarch >2,000 ng/ml and the absence of viral resistance mutations at V82T/A/F/I/S and I54M/V/L are highly predictive for therapeutic success of a regimen of saquinavir/lopinavir/ ritonavir without RTI in a heterogenic cohort of patients with an extensive pre-treatment history and highly variable pharmacokinetics.

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.

Lopinavir plus ritonavir: a novel protease inhibitor combination for HIV infections

Lopinavir is a protease inhibitor (PI) for the treatment of HIV infection that was specifically designed to overcome the shortcomings of earlier agents in this class. It is the only PI coformulated with ritonavir, whose pharmacological boosting effect results in a highly potent, well-tolerated, clinically effective antiretroviral agent with a high genetic barrier to resistance. Lopinavir/ritonavir is a recommended first-line option for antiretroviral-naive patients initiating PI-based therapy, and has an equally important role in the management of treatment-experienced individuals. Its favorable pharmacological and clinical characteristics have recently prompted investigators to explore its potential novel applications in HIV monotherapy and double-boosted regimens.

The use of drug resistance algorithms and genotypic inhibitory quotient in prediction of lopinavir–ritonavir treatment response in human immunodeficiency virus type 1 protease inhibitor-experienced patients

BACKGROUND

Different approaches using genotypic, pharmacokinetic parameters or combination of both have been recently developed to monitor antiretroviral treatment in HIV-1-infected individuals. Their uses in clinical practice may improve the benefit of protease inhibitor-based salvage therapy while reducing treatment toxicity and emergence of viral resistance.

OBJECTIVES

To assess the prediction of genotypic inhibitory quotient (GIQ) using different genotypic drug resistance interpretation's algorithms and lopinavir plasma concentration in PI-experienced patients treated by lopinavir/ritonavir (LPV/r). Genotypic susceptibility score (GSS) was also evaluated.

STUDY DESIGN

Forty-seven HIV-1 PI-experienced, but LPV naïve patients were included in a retrospective cohort study. Plasma HIV-1 viral load (VL), CD4 cell count and LPV plasma concentrations were assessed at weeks (W) 12 and 24. Interpretation of baseline resistance genotype was achieved according to four different algorithms and GSS calculated using two expert systems. GIQ was defined as the ratio of LPV concentration to the number of LPV resistance mutations at day 0 (D0) and patients classified by units of GIQ. The end point of the study was the virological response expressed in HIV VL median decrease from D0 to W24.

RESULTS

The overall median VL decrease from D0 to W24 was -2.42 log(10)copies/mL and 60% of patients had VL below 400 copies/mL. The LPV mutation score was predictive of response for all algorithms whereas plasma concentrations of LPV were not. Mean VL decrease was greater for higher GIQ classes and difference reached statistical significance at W24. When considering virological response at W24, GSS calculated with ANRS and Stanford system were good predictor scores as areas under the receiver operating characteristics (ROC) curves were 0.76 for both.

CONCLUSION

GIQ was found to be a useful drug-monitoring tool which could be helpful in targeting LPV concentrations in order to achieve long-term undetectable viral load, particularly in genotypic resistant patients.