Clinical pharmacodynamics of HIV-1 protease inhibitors: use of inhibitory quotients to optimise pharmacotherapy

In Silico Pharmacokinetics Evaluation of Forgiveness for Doravirine and Rilpivirine

BACKGROUND

This study aimed to evaluate the concentrations of rilpivirine (RLP) and doravirine (DOR) after 3 days-off using simulations from population pharmacokinetics models.

METHODS

The authors conducted a series of 500 sets of 10,000 Monte Carlo simulations to examine the steady-state conditions for 2 common dosage levels: 25 mg/d for RLP and 100 mg/d for DOR. These simulations were conducted under 2 scenarios: 1 without drug cessation and another after a 3-day break. The validity of the implementation was established through a comparison of median trough concentrations (C24h) with previously reported data. Subsequently, the proportion of simulated patients with C24h and C72h after 3 days-off (C72h/3do) that exceeded the inhibitory concentration 50 (IC50), 5.2 mcg/L for DOR and 20.5 mcg/L for RLP respectively, was calculated. The inhibitory quotient (IQ) was also computed, which was 6 times IC50 for DOR and 4.5 times IC50 for RLP. Finally, nomograms were constructed to estimate the probability of having C72h/3do > IC50 or > IQ for different ranges of C24h.

RESULTS

Simulated C24h median ± SD for RLP were 61.8 ± 0.4 mcg/L and for DOR 397 ± 0 mcg/L. For RLP, 99.3 ± 0.1% exceeded IC50 at C24h, 16.4 ± 0.4% at C72h/3do, and none surpassed the IQ threshold. In contrast, DOR had 100% ± 0% above IC50 at C24h, 93.6 ± 0.2% at C72h/3do, and 58.6 ± 0.5% exceeded the IQ.

CONCLUSIONS

These findings suggest that treatment with DOR may offer a more forgiving therapeutic profile than RLP, given the larger proportion of patients achieving effective drug exposure with DOR. However, it is important to acknowledge a significant limitation of this study, namely, the assumption that drug concentration is a perfect surrogate for drug effectiveness.

Impact of Therapeutic Drug Monitoring of Antiretroviral Drugs in Routine Clinical Management of People Living With HIV: A Narrative Review

BACKGROUND

The treatment of HIV infection has evolved significantly since the advent of highly active antiretroviral therapy. As a result, a response rate of 90%-95% now represents a realistically achievable target. Given this background, it is difficult to imagine the additional benefits that therapeutic drug monitoring (TDM) could provide in the management of HIV infection.

METHODS

This article is not intended to provide a systematic literature review on TDM of antiretroviral agents; rather, the authors aim to discuss the potential added value of TDM in the optimal management of people living with HIV (PLWH) in selected real-life clinical scenarios based on data collected over 10 years by their TDM service.

RESULTS

Some clinical situations, in which the selection of the optimal antiretroviral therapy is challenging, have been identified. These include poorly compliant patients, suboptimal antiretroviral therapies (in terms of both efficacy and toxicity), polypharmacy with a high risk of drug-drug interactions, and different patient populations, such as pregnant women.

CONCLUSIONS

The transformation of HIV infection from a near-universally fatal illness to a lifelong chronic disease has resulted in an HIV population that is growing and aging, placing new and increasing demands on public programs and health services. Increasingly, the management of comorbidities, polypharmacy, and drug-drug interaction, and their impact on antiretroviral therapy will have to be undertaken. These clinical settings represent some of the new frontiers for the use of TDM with the goal of achieving optimal prescription and outcome for PLWH.

Defining the optimal dose of rifapentine for pulmonary tuberculosis: Exposure-response relations from two phase II clinical trials

Rifapentine is a highly active antituberculosis antibiotic with treatment-shortening potential; however, exposure-response relations and the dose needed for maximal bactericidal activity have not been established. We used pharmacokinetic/pharmacodynamic data from 657 adults with pulmonary tuberculosis participating in treatment trials to compare rifapentine (n = 405) with rifampin (n = 252) as part of intensive-phase therapy. Population pharmacokinetic/pharmacodynamic analyses were performed with nonlinear mixed-effects modeling. Time to stable culture conversion of sputum to negative was determined in cultures obtained over 4 months of therapy. Rifapentine exposures were lower in participants who were coinfected with human immunodeficiency virus, black, male, or fasting when taking drug. Rifapentine exposure, large lung cavity size, and geographic region were independently associated with time to culture conversion in liquid media. Maximal treatment efficacy is likely achieved with rifapentine at 1,200 mg daily. Patients with large lung cavities appear less responsive to treatment, even at high rifapentine doses.

Therapeutic drug monitoring of antiretroviral drugs in HIV-infected patients

INTRODUCTION

Therapeutic drug monitoring (TDM) may be beneficial when applied to antiretroviral (ARV). Even though TDM can be a valuable strategy in HIV management, its role remains controversial. Areas covered: This review provides a comprehensive update on important issues relating to TDM of ARV drugs in HIV-infected patients. Articles from PubMed with keywords relevant to each topic section were reviewed. Search strategies limited to articles published in English. Expert commentary: There is evidence supporting the use of TDM in HIV treatment. However, some limitations need to be considered. The evidence supporting the use of routine TDM for all patients is limited, as it is not clear that this strategy offers any advantages over TDM for selected indications. Selected groups of patients including patients with physiological changes, patients with drug-drug interactions or toxicity, and the elderly could potentially benefit from TDM, as optimized dosing is challenging in these populations.

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.

Comparative Effectiveness of Darunavir 1,200 mg Daily and Approved Dosing Strategies for Protease Inhibitor-Experienced Patients

Background. HIV protease inhibitors exhibit concentration-dependent viral inhibition. Higher once daily doses of darunavir boosted with ritonavir (DRV/r) may achieve viral suppression in place of twice daily dosing. International antiretroviral adherence guidelines recommend once daily regimens whenever possible. We present data on virologic suppression achieved with DRV 1,200 mg and ritonavir 100 mg once daily compared to approved DRV regimens. Methods. This retrospective observational study included all patients treated with DRV after documented use of another protease inhibitor at an urban immunodeficiency clinic. Data collection from inception of DRV use in August 2006 through March 2012 included patient demographics, viral loads, CD4+ cell counts, and resistance test results. The primary outcome of virologic suppression was defined as <50 copies/mL at 24 weeks. Differences in baseline characteristics and virologic outcomes across dosing groups were analyzed via one-way analysis of variance. Results. One hundred and thirty-five patients were included in the ITT analysis. Most patients had no known DRV RAMs at baseline. Virologic suppression rate was not different among treatment groups: 53.6% of patients on 1,200 mg daily, 52.3% on 600 mg twice daily, and 42.9% on 800 mg daily (P = 0.568). Conclusions. Darunavir 1,200 mg daily should be investigated for use in protease inhibitor-experienced patients.

Plasma protein binding: from discovery to development

The importance of plasma protein binding (PPB) in modulating the effective drug concentration at pharmacological target sites has been the topic of significant discussion and debate amongst drug development groups over the past few decades. Free drug theory, which states that in absence of energy-dependent processes, after steady state equilibrium has been attained, free drug concentration in plasma is equal to free drug concentration at the pharmacologic target receptor(s) in tissues, has been used to explain pharmacokinetics/pharmacodynamics relationships in a large number of cases. Any sudden increase in free concentration of a drug could potentially cause toxicity and may need dose adjustment. Free drug concentration is also helpful to estimate the effective concentration of drugs that potentially can precipitate metabolism (or transporter)-related drug-drug interactions. Disease models are extensively validated in animals to progress a compound into development. Unbound drug concentration, and therefore PPB information across species is very informative in establishing safety margins and guiding selection of First in Human (FIH) dose and human efficacious dose. The scope of this review is to give an overview of reported role of PPB in several therapeutic areas, highlight cases where PPB changes are clinically relevant, and provide drug metabolism and pharmacokinetics recommendations in discovery and development settings.

CSF penetration by antiretroviral drugs

Severe HIV-associated neurocognitive disorders (HAND), such as HIV-associated dementia, and opportunistic CNS infections are now rare complications of HIV infection due to comprehensive highly active antiretroviral therapy (HAART). By contrast, mild to moderate neurocognitive disorders remain prevalent, despite good viral control in peripheral compartments. HIV infection seems to provoke chronic CNS injury that may evade systemic HAART. Penetration of antiretroviral drugs across the blood-brain barrier might be crucial for the treatment of HAND. This review identifies and evaluates the available clinical evidence on CSF penetration properties of antiretroviral drugs, addressing methodological issues and discussing the clinical relevance of drug concentration assessment. Although a substantial number of studies examined CSF concentrations of antiretroviral drugs, there is a need for adequate, well designed trials to provide more valid drug distribution profiles. Neuropsychological benefits and neurotoxicity of potentially CNS-active drugs require further investigation before penetration characteristics will regularly influence therapeutic strategies and outcome.

Unboosted atazanavir for treatment of HIV infection: rationale and recommendations for use

Atazanavir (Reyataz®) is a protease inhibitor (PI) for the treatment of HIV infection. Several trials have demonstrated the good efficacy and toxicity profile of atazanavir boosted by ritonavir (atazanavir/r). However, several toxicity events and pharmacokinetic issues due to drug-to-drug interactions (partly related to ritonavir) may complicate atazanavir/r therapy. This is why regimens with unboosted atazanavir have been experimented with and are used in clinical practice. The aim of this article is to identify the clinical settings in which unboosted atazanavir may be a safe and effective option for the long-term control of HIV replication. Despite the fact that a favourable lipid profile and good gastrointestinal tolerability have been reported in comparative trials, unboosted atazanavir should not be considered an optimal choice for treatment-naive patients. In fact, boosting with ritonavir produces higher atazanavir plasma levels, which are beneficial in terms of efficacy, especially in untreated patients with high plasma HIV RNA. Clinical data indicate that, in patients with sustained undetectable HIV RNA and without previous virological failure or HIV drug resistance-associated mutations, a switch to unboosted atazanavir-based regimens is a feasible option to control and prevent toxicity events, especially in patients who cannot tolerate ritonavir and in those with severe hyperbilirubinaemia on atazanavir/r. Moreover, while unboosted atazanavir must not be used in pregnant women, it is a recommended option in special populations, such as patients with moderate liver insufficiency. Lastly, unboosted atazanavir in combination with raltegravir may allow the construction of a well tolerated and effective regimen without nucleoside reverse transcriptase inhibitors in patients for whom these drugs are contraindicated. In conclusion, there is a good rationale, significant clinical interest and accumulating clinical experience with unboosted atazanavir-based regimens, although this formulation should be used only in specific situations and as a maintenance strategy. Moreover, therapeutic drug monitoring could be useful in specific circumstances (such as in patients with liver impairment or in case of potential drug-drug interactions).

Novel method to assess antiretroviral target trough concentrations using in vitro susceptibility data

Durable suppression of HIV-1 replication requires the establishment of antiretroviral drug concentrations that exceed the susceptibility of the virus strain(s) infecting the patient. Minimum plasma drug concentrations (C(trough)) are correlated with response, but determination of target C(trough) values is hindered by a paucity of in vivo concentration-response data. In the absence of these data, in vitro susceptibility measurements, adjusted for serum protein binding, can provide estimations of suppressive in vivo drug concentrations. We derived serum protein binding correction factors (PBCF) for protease inhibitors, nonnucleoside reverse transcriptase inhibitors, and an integrase inhibitor by measuring the effect of a range of human serum concentrations on in vitro drug susceptibility measured with the PhenoSense HIV assay. PBCFs corresponding to 100% HS were extrapolated using linear regression and ranged from 1.4 for nevirapine to 77 for nelfinavir. Using the mean 95% inhibitory concentration (IC(95)) for ≥1,200 drug-susceptible viruses, we calculated protein-bound IC(95) (PBIC(95)) values. PBIC(95) values were concordant with the minimum effective C(trough) values that were established in well-designed pharmacodynamic studies (e.g., indinavir, saquinavir, and amprenavir). In other cases, the PBIC(95) values were notably lower (e.g., darunavir, efavirenz, and nevirapine) or higher (nelfinavir and etravirine) than existing target recommendations. The establishment of PBIC(95) values as described here provides a convenient and standardized approach for estimation of the minimum drug exposure that is required to maintain viral suppression and prevent the emergence of drug-resistant variants, particularly when in vivo concentration-response relationships are lacking.

The role of therapeutic drug monitoring in the management of patients with human immunodeficiency virus infection

Therapeutic drug monitoring (TDM) is a well-established method to optimize dosing regimens in individual patients for drugs that are characterized by a narrow therapeutic range and large interindividual pharmacokinetic variability. For some antiretroviral drugs, mainly nonnucleoside reverse transcriptase inhibitors and protease inhibitors, TDM has been proposed as a means to improve the response in human immunodeficiency virus-infected patients. In contrast, nucleoside reverse transcriptase inhibitors do not show a predictable plasma concentration-response (toxicity, efficacy) relationship, and intracellular analyses are expensive. Therefore, TDM is generally not recommended for this class of drugs. TDM has been successfully applied in the clinical practice for certain antiretroviral drugs, but there are ongoing research efforts on the use and refinement of TDM for human immunodeficiency virus treatment, and convincing data from randomized trials are still needed. The best pharmacokinetic measures of drug exposure such as trough and peak concentrations or concentration ratios have not been unambiguously established.

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.

In vitro characterization of GS-8374, a novel phosphonate-containing inhibitor of HIV-1 protease with a favorable resistance profile

GS-8374 is a novel bis-tetrahydrofuran HIV-1 protease (PR) inhibitor (PI) with a unique diethylphosphonate moiety. It was selected from a series of analogs containing various di(alkyl)phosphonate substitutions connected via a linker to the para position of a P-1 phenyl ring. GS-8374 inhibits HIV-1 PR with high potency (K(i) = 8.1 pM) and with no known effect on host proteases. Kinetic and thermodynamic analysis of GS-8374 binding to PR demonstrated an extremely slow off rate for the inhibitor and favorable contributions of both the enthalpic and entropic components to the total free binding energy. GS-8374 showed potent antiretroviral activity in T-cell lines, primary CD4(+) T cells (50% effective concentration [EC(50)] = 3.4 to 11.5 nM), and macrophages (EC(50) = 25.5 nM) and exhibited low cytotoxicity in multiple human cell types. The antiviral potency of GS-8374 was only moderately affected by human serum protein binding, and its combination with multiple approved antiretrovirals showed synergistic effects. When it was tested in a PhenoSense assay against a panel of 24 patient-derived viruses with high-level PI resistance, GS-8374 showed lower mean EC(50)s and lower fold resistance than any of the clinically approved PIs. Similar to other PIs, in vitro hepatic microsomal metabolism of GS-8374 was efficiently blocked by ritonavir, suggesting a potential for effective pharmacokinetic boosting in vivo. In summary, results from this broad in vitro pharmacological profiling indicate that GS-8374 is a promising candidate to be further assessed as a new antiretroviral agent with potential for clinical efficacy in both treatment-naïve and -experienced patients.

Instantaneous inhibitory potential is similar to inhibitory quotient at predicting HIV-1 response to antiretroviral therapy

BACKGROUND

The instantaneous inhibitory potential (IIP), a measure of antiviral activity that incorporates the slope of the dose-response curve, has been proposed as a better predictor of clinical efficacy than the inhibitory quotient (IQ). However, there are no quantitative analyses supporting this hypothesis.

METHODS

The correlation between differences in log10(IQ) (Deltalog10(IQ)) or differences in IIP (DeltaIIP) and the differences in percentage of subjects with plasma human immunodeficiency virus type 1 (HIV-1) RNA levels <50 copies/mL at week 48 was determined for antiretroviral drugs compared in 17 randomized clinical trials. The Deltalog10(IQmin), Deltalog10(IQmax), DeltaIIPmin, DeltaIIPmax, Deltalog10(IQ12), Deltalog10(IQ24), DeltaIIP12, and DeltaIIP24 for comparative drugs were correlated with differences in percentage of subjects with HIV-1 RNA levels <50 copies/mL in each trial. log10(IQ24), log10(IQ12), IIP24, and IIP12 were calculated using published median effect model slope values and t1/2 values; r2 values from linear regression and Spearman correlation coefficients were calculated for each analysis; and correlation coefficients were compared between log10(IQ) and IIP.

RESULTS

r2 values were greatest for the Deltalog10(IQ12) and Deltalog10(IQ24) comparisons using intention-to-treat outcomes from the 17 trials. Differences in r2 values between Deltalog10(IQ24) and DeltaIIP24 and between Deltalog10(IQ12) and DeltaIIP12 were 0.05 and 0.18, respectively. Differences in Spearman rank correlation coefficients between log10(IQ) and IIP at each drug concentration were not significantly different, with the exception of Deltalog10(IQmax) and DeltaIIPmax; the Deltalog10(IQmax) correlation was significantly stronger than the DeltaIIPmax correlation.

CONCLUSIONS

IIP was not substantially better than log10(IQ) in describing the modest relationship between antiviral activity, pharmacokinetics, and virologic outcomes for antiretroviral drugs.

A novel method for determining the inhibitory potential of anti-HIV drugs

In the absence of cure, most HIV-1-infected individuals will require lifelong treatment. It is therefore essential to optimize highly active antiretroviral therapy. Recent research has shown that the slope parameter or Hill coefficient, which describes the steepness of a dose-response curve, is a critical missing dimension in the evaluation of the activity of antiviral drugs. Based on this finding, instantaneous inhibitory potential (IIP) has been derived as a new measure of antiviral drug activity. IIP incorporates the slope parameter and thus is a more accurate pharmacodynamic measure of antiviral activity than current measures such as IC(50) and inhibitory quotient. Determining how to use IIP to predict the in vivo efficacy of anti-HIV-1 drugs is nevertheless important. This article discusses recent advances in in vitro measures of antiviral activity and the therapeutic implications of the dose-response curve slope and IIP.

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.

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.

Use of different inhibitory quotients to predict early virological response to tipranavir in antiretroviral-experienced human immunodeficiency virus-infected patients

Information about the relationship between pharmacological parameters and an early virological response to tipranavir (TPV) is scarce. Human immunodeficiency virus (HIV)-infected patients who had received TPV as part of a salvage regimen were analyzed retrospectively. A virological response was defined as a decline in the HIV RNA level of > or = 1 log unit or to <50 copies/ml between weeks 4 and 12 of therapy. The virtual inhibitory quotient (vIQ) was calculated as the ratio of the TPV plasma trough concentration (C(trough))/virtual change in the 50% inhibitory concentration. Three genotypic inhibitory quotients (gIQs) were calculated by using different TPV resistance mutation scores (from the International AIDS Society-USA [IAS-USA], Randomized Evaluation of Strategic Intervention in Multidrug-Resistant Patients with Tipranavir [RESIST], and Agence Nationale de Recherches sur le Sida et les Hépatites Virales [ANRS] trials). The sensitivities, specificities, positive predictive values (PPVs), negative predictive values (NPVs), and likelihood ratios for a positive result (LHR+) and a negative result (LHR-) [LHR+ = sensitivity/(1-specificity); LHR- = (1-sensitivity)/specificity] were calculated. A total of 57 HIV-infected patients were analyzed. A virological response was achieved by 77% of the patients. TPV resistance mutations, TPV C(trough), vIQs, and gIQs were all significantly associated with a virological response. The vIQ had the best PPV and NPV (97% and 78%, respectively). The values of the LHR+ were 7.8 for vIQ, 3.4 for the RESIST gIQ, 3.3 for the IAS-USA gIQ, 3.1 for the ANRS gIQ, 2.2 for TPV C(trough), and 1.3 for the IAS-USA and RESIST scores. The values of LHR- were 0 for the RESIST score, 0.07 for vIQ, 0.09 for the IAS-USA score, 0.27 for the RESIST gIQ, 0.32 for the IAS-USA gIQ, 0.37 for the ANRS gIQ, and 0.48 for TPV C(trough). HIV-infected patients who initiate a salvage regimen based on TPV may benefit from baseline drug resistance testing and TPV plasma concentration determination, as vIQ is the best predictor of a virological response.

Aging and infectious diseases: workshop on HIV infection and aging: what is known and future research directions

Highly active antiretroviral treatment has resulted in dramatically increased life expectancy among patients with HIV infection who are now aging while receiving treatment and are at risk of developing chronic diseases associated with advanced age. Similarities between aging and the courses of human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome suggest that HIV infection compresses the aging process, perhaps accelerating comorbidities and frailty. In a workshop organized by the Association of Specialty Professors, the Infectious Diseases Society of America, the HIV Medical Association, the National Institute on Aging, and the National Institute on Allergy and Infectious Diseases, researchers in infectious diseases, geriatrics, immunology, and gerontology met to review what is known about HIV infection and aging, to identify research gaps, and to suggest high priority topics for future research. Answers to the questions posed are likely to help prioritize and balance strategies to slow the progression of HIV infection, to address comorbidities and drug toxicity, and to enhance understanding about both HIV infection and aging.

Pharmacokinetics of high-dose lopinavir-ritonavir with and without saquinavir or nonnucleoside reverse transcriptase inhibitors in human immunodeficiency virus-infected pediatric and adolescent patients previously treated with protease inhibitors

Human immunodeficiency virus (HIV)-infected children and adolescents who are failing antiretrovirals may have a better virologic response when drug exposures are increased, using higher protease inhibitor doses or ritonavir boosting. We studied the pharmacokinetics and safety of high-dose lopinavir-ritonavir (LPV/r) in treatment-experienced patients, using an LPV/r dose of 400/100 mg/m(2) orally every 12 h (p.o. q12h) (without nonnucleoside reverse transcriptase inhibitor [NNRTI]), or 480/120 mg/m(2) p.o. q12h (with NNRTI). We calculated the LPV inhibitory quotient (IQ), and when the IQ was <15, saquinavir (SQV) 750 mg/m(2) p.o. q12h was added to the regimen. We studied 26 HIV-infected patients. The median age was 15 years (range, 7 to 17), with 11.5 prior antiretroviral medications, 197 CD4 cells/ml, viral load of 75,577 copies/ml, and a 133-fold change in LPV resistance. By treatment week 2, 14 patients had a viral-load decrease of >0.75 log(10), with a median maximal decrease in viral load of -1.57 log(10) copies/ml at week 8. At week 2, 19 subjects showed a median LPV area under the concentration-time curve (AUC) of 157.2 (range, 62.8 to 305.5) microg x h/ml and median LPV trough concentration (C(trough)) of 10.8 (range, 4.1 to 25.3) microg/ml. In 16 subjects with SQV added, the SQV median AUC was 33.7 (range, 4.4 to 76.5) microg x h/ml and the median SQV C(trough) was 2.1 (range, 0.2 to 4.1) microg/ml. At week 24, 18 of 26 (69%) subjects remained in the study. Between weeks 24 and 48, one subject withdrew for nonadherence and nine withdrew for persistently high virus load. In antiretroviral-experienced children and adolescents with HIV, high doses of LPV/r with or without SQV offer safe options for salvage therapy, but the modest virologic response and the challenge of adherence to a regimen with a high pill burden may limit the usefulness of this approach.

Viral reservoirs, residual viremia, and the potential of highly active antiretroviral therapy to eradicate HIV infection

Although highly active antiretroviral therapy (HAART) can reduce HIV-1 viremia to levels that are below the limit of detection of clinical assays, the virus persists in reservoirs, and trace levels of free virions can be found in the plasma. Whether this residual viremia represents ongoing cycles of replication continuing despite HAART or simply the release of virus from stable reservoirs has been controversial. Here we summarize the evidence that HAART can stop ongoing cycles of replication. The evidence comes from a detailed analysis of the residual viremia, which shows it to be archival and nonevolving in character. In addition, new pharmacodynamic measures incorporating a previously ignored slope parameter have provided the first real indication of how well HAART actually suppresses viral replication in vivo. Together, these results argue that the ultimate theoretical potential of HAART to control viral replication has already been reached. Progress toward eradication of the infection will require novel approaches to target the stable reservoirs that persist even when viral replication is completely halted.

Dose-response curve slope sets class-specific limits on inhibitory potential of anti-HIV drugs

Highly active antiretroviral therapy (HAART) can control HIV-1 replication, but suboptimal treatment allows for the evolution of resistance and rebound viremia. A comparative measure of antiviral activity under clinically relevant conditions would guide drug development and the selection of regimens that maximally suppress replication. Here we show that current measures of antiviral activity, including IC(50) and inhibitory quotient, neglect a key dimension, the dose-response curve slope. Using infectivity assays with wide dynamic range, we show that this slope has noteworthy effects on antiviral activity. Slope values are class specific for antiviral drugs and define intrinsic limitations on antiviral activity for some classes. Nucleoside reverse transcriptase inhibitors and integrase inhibitors have slopes of approximately 1, characteristic of noncooperative reactions, whereas non-nucleoside reverse transcriptase inhibitors, protease inhibitors and fusion inhibitors unexpectedly show slopes >1. Instantaneous inhibitory potential (IIP), the log reduction in single-round infectivity at clinical drug concentrations, is strongly influenced by slope and varies by >8 logs for anti-HIV drugs. IIP provides a more accurate measure of antiviral activity and in general correlates with clinical outcomes. Only agents with slopes >1 achieve high-level inhibition of single-round infectivity, a finding with profound implications for drug and vaccine development.

Advances in pharmacogenomics of antiretrovirals: an update

Recent developments in the pharmacogenomics of antiretroviral drugs provide new prospects for predicting the efficacy of treatment and potential adverse effects. HIV/AIDS is a serious but treatable infectious disease, yet current treatment is limited by high rates of adverse drug reactions and development of resistance due to suboptimal drug concentrations in a significant proportion of patients. Antiretroviral therapy is especially suitable for pharmacogenomic investigation as both drug exposure and treatment response can be quantified and certain adverse effects can be assessed with validated measures. Additionally, there is increasing knowledge of the pharmacokinetics and dynamics of antiretroviral drugs, and some candidate genes implicated in the metabolism, transport and adverse effects have been identified. However, recent studies of the association of particular genes and their genetic variants with HIV management and adverse drug reactions have not provided unifying conclusions. This article reviews the most recently published work and summarizes the state of research in this area. Future directions for research and the application of this technology to the clinical practice of individualizing treatment for HIV management are discussed.

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.

Multidrug resistance 1 polymorphisms and trough concentrations of atazanavir and lopinavir in patients with HIV

INTRODUCTION

HIV-infected patients receiving protease inhibitors may benefit from therapeutic drug monitoring-assisted dose adjustment to achieve target plasma concentrations. However, efflux pumps such as permeability-glycoprotein, which is encoded by the multidrug resistance (MDR)1 gene, may decrease intracellular drug concentrations, thus reducing the amount of drug at the site of action. Plasma concentrations of protease inhibitors and CD4 cell count response have been associated with the T allele at the MDR1 C3435T locus. We examined MDR1 single nucleotide polymorphisms in a cohort of patients in whom therapeutic drug monitoring is ongoing through a research protocol.

METHODS

In a multicenter study, genotypic analyses at two MDR1 loci, C3435T and G2677T, were performed by a real-time polymerase chain reaction method using DNA from 103 patients categorized as substance users or nonusers on atazanavir or lopinavir as the primary antiretrovirals. Allelic frequencies were determined as a function of racial/ethnic background, substance use status and trough concentrations of atazanavir and lopinavir.

RESULTS

The C/T and G/T alleles at the MDR1 C3435T and G2677T loci were equally frequent in the Caucasian population, but the wild-type alleles were more prevalent in the African-American population (59% homozygous [CC] and 32% heterozygous [CT] for C3435T; 80% homozygous [GG] and 16% heterozygous [GT] for G2677T). The frequencies in the Hispanic population were 46% CC and 38% CT for C3435T, and 58% GG and 38% GT for G2677T. No significant differences were seen in allele frequencies for MDR1 polymorphisms in substance user versus nonuser groups. Trough plasma concentrations of atazanavir or lopinavir were not correlated with the variant T allele.

CONCLUSIONS

These data confirm the higher prevalence of wild-type alleles of the MDR1 gene in African-Americans and the linkage disequilibrium between C3435T and G2677T loci. The T allele at the MDR1 C3435T and G2677T loci was not associated with higher atazanavir or lopinavir trough concentrations.

Quantification of darunavir (TMC114) in human plasma by high-performance liquid chromatography with ultra-violet detection

A precise and accurate high-performance liquid chromatography (HPLC) method with UV detection has been developed and validated for darunavir, a peptidic protease inhibitor. An internal standard, methylclonazepam, was added to 100 microL of plasma before a solid-phase extraction on C18 Bond Elut column. The eluted solutions were evaporated to dryness and reconstituted with 100 microL of mobile phase before being injected in the chromatographic system. The separation was performed on a C8 column using an acetonitrile and ultrapure water mixture (40:60, v/v) as mobile phase. All compounds were detected at a wavelength of 266 nm. The method was linear and validated over a concentration range of 0.25-20mg/L. The within-day precision, ranged from 3.0 to 7.9%, while the within-day accuracy ranged from -11.4 to 0.5%. The between day precision and accuracy were respectively less than 13.7 and -11.4%. The mean recovery was 75.7% for darunavir and 66.7% for methylclonazepam. This method provides a useful tool for therapeutic drug monitoring in HIV patients.

Integration of atazanavir into an existing liquid chromatography UV method for protease inhibitors: validation and application

Atazanavir (ATV) is a widely used human immunodeficiency virus (HIV)-1 protease inhibitor (PI) that, like other approved PIs, has been considered as a candidate for therapeutic drug monitoring (TDM). To provide ATV assay results that can be applied to patient management through TDM, the assay would need to perform in a manner consistent with Clinical Laboratory Improvement Amendments (CLIA) standards. To quantitate ATV concentrations in human plasma, the authors added ATV to a previously published reversed-phase high-performance liquid chromatography (HPLC) method from their laboratory. Detection was effected with use of a photodiode-array detector (PDA) collecting spectra at 248 nm. This method allows for detection of ATV to a lower limit of quantitation of 0.05 microg/mL, with an intra-assay coefficient of variation (CV%) of 8.9% or less over 5 days of testing and an interassay CV% ranging from 1.4 to 6.4%. The assay has met passing requirements for interlaboratory proficiency testing for 2 years nationally and internationally, with accuracy within +/-15% over all test samples. During 2 years, more than 100 batches of analyses have been performed and have proved the method is rugged, specific, and accurate. This assay method is currently used in the authors' clinical research program in TDM.

Approach to salvage antiretroviral therapy in heavily antiretroviral-experienced HIV-positive adults

Despite dramatic declines in HIV-associated morbidity and mortality as a result of highly active antiretroviral therapy, management of heavily treatment-experienced patients remains complex and challenging. Treatment response rates with subsequent antiretroviral regimens are lower than with initial antiretroviral therapy. Additionally, increased mortality has been associated with multidrug-resistant HIV. We review data relevant to management of such patients and offer a systematic approach to constructing a salvage antiretroviral regimen.