Toxicity, efficacy, plasma drug concentrations and protease mutations in patients with advanced HIV infection treated with ritonavir plus saquinavir. Swiss HIV Cohort Study

Advances in Molecular Genetics Enabling Studies of Highly Pathogenic RNA Viruses

Experimental work with viruses that are highly pathogenic for humans and animals requires specialized Biosafety Level 3 or 4 facilities. Such pathogens include some spectacular but also rather seldomly studied examples such as Ebola virus (requiring BSL-4), more wide-spread and commonly studied viruses such as HIV, and the most recent example, SARS-CoV-2, which causes COVID-19. A common characteristic of these virus examples is that their genomes consist of single-stranded RNA, which requires the conversion of their genomes into a DNA copy for easy manipulation; this can be performed to study the viral life cycle in detail, develop novel therapies and vaccines, and monitor the disease course over time for chronic virus infections. We summarize the recent advances in such new genetic applications for RNA viruses in Switzerland over the last 25 years, from the early days of the HIV/AIDS epidemic to the most recent developments in research on the SARS-CoV-2 coronavirus. We highlight game-changing collaborative efforts between clinical and molecular disciplines in HIV research on the path to optimal clinical disease management. Moreover, we summarize how the modern technical evolution enabled the molecular studies of emerging RNA viruses, confirming that Switzerland is at the forefront of SARS-CoV-2 research and potentially other newly emerging viruses.

Permanent control of HIV-1 pathogenesis in exceptional elite controllers: a model of spontaneous cure

Elite controllers (EC) represent a small subset of HIV-1-infected people that spontaneously control viral replication. However, natural virological suppression and absence of immune dysfunction are not always long-term sustained. We define exceptional EC (EEC) as HIV-1 subjects who maintain the EC characteristics without disease progression for more than 25 years. We analyzed three EEC, diagnosed between 1988 and 1992, who never showed signs of clinical disease progression in absence of any antiretroviral treatment. A comprehensive clinical, virological, and immunological study was performed. The individuals simultaneously exhibited ≥3 described host protective alleles, low levels of total HIV-1 DNA (<20 copies/106 CD4+ T-cells) without evidence of replication-competent viruses (<0.025 IUPM), consistent with high levels of defective genomes, strong cellular HIV-1-specific immune response, and a high poly-functionality index (>0.50). Inflammation levels of EEC were similar to HIV-1 negative donors. Remarkably, they showed an exceptional lack of viral evolution and 8-fold lower genetic diversity (<0.01 s/n) in env gene than other EC. We postulate that these EEC represent cases of spontaneous functional HIV-1 cure. A non-functional and non-genetically evolving viral reservoir along with an HIV-1-specific immune response seems to be key for the spontaneous functional cure.

Clinical use of cobicistat as a pharmacoenhancer of human immunodeficiency virus therapy

The pharmacoenhancement of plasma concentrations of protease inhibitors by coadministration of so-called boosters has been an integral part of antiretroviral therapy for human immunodeficiency virus (HIV) for 1.5 decades. Nearly all HIV protease inhibitors are combined with low-dose ritonavir or cobicistat, which are able to effectively inhibit the cytochrome-mediated metabolism of HIV protease inhibitors in the liver and thus enhance the plasma concentration and prolong the dosing interval of the antiretrovirally active combination partners. Therapies created in this way are clinically effective regimens, being convenient for patients and showing a high genetic barrier to viral resistance. In addition to ritonavir, which has been in use since 1996, cobicistat, a new pharmacoenhancer, has been approved and is widely used now. The outstanding property of cobicistat is its cytochrome P450 3A-selective inhibition of hepatic metabolism of antiretroviral drugs, in contrast with ritonavir, which not only inhibits but also induces a number of cytochrome P450 enzymes, UDP-glucuronosyltransferase, P-glycoprotein, and other cellular transporters. This article reviews the current literature, and compares the pharmacokinetics, pharmacodynamics, and safety of both pharmacoenhancers and discusses the clinical utility of cobicistat in up-to-date and future HIV therapy.

Pharmacokinetic and Pharmacodynamic Analysis of Amprenavir-Containing Combination Therapy in HIV-1-Infected Children

Several factors influence the antiviral response to antiretroviral therapy. In this pharmacokinetic and pharmacodynamic analysis, the relationship of drug exposure, demographics, and cotherapy measures to antiviral response in a cohort of largely treatment-experienced children treated with amprenavir and nucleoside reverse transcriptase inhibitors was examined. Multiple pharmacodynamic and demographic factors were examined, but only the minimum plasma concentration (C(min))/protein-binding-adjusted 50% inhibitory drug concentration (IC(50)) ratio and whether individuals received 2 versus fewer than 2 nucleosides to which their viral isolates were susceptible were associated with the magnitude of the time-weighted average change in HIV-1 RNA log(10) copies/mL from baseline (AAUCMB). In multivariate logistic regression analysis, only the C(min)/IC(50) ratio was independently associated with having a >or=1 log(10) AAUCMB decline. The probability in the study population of having a >or=1log(10) AAUCMB was 50% and 85% at C(min)/IC(50) ratios of approximately 1 and 4, respectively. Of the multiple factors examined, only the C(min)/IC(50) ratio was a significant predictor of antiviral response in the first 8 weeks on amprenavir-containing combination antiretroviral therapy.

The genotypic inhibitory quotient: a predictive factor of atazanavir response in HIV-1-infected treatment-experienced patients

OBJECTIVE

To evaluate the predictive value of the genotypic inhibitory quotient (GIQ) on the atazanavir response in treatment-experienced HIV-1-infected patients.

PATIENTS AND METHODS

Thirty-six patients receiving an atazanavir-containing regimen were enrolled in the study. Atazanavir plasma concentrations were measured at month (M) 1, and genotype was performed at baseline. Virologic response was defined as a viral load <400 copies/mL or a decrease > or =1 log10.

RESULTS

The median numbers (range) of previous regimens, baseline protease inhibitors, and atazanavir resistance mutations were 8 (0 to 20), 3 (0 to 15), and 1 (0 to 10), respectively. The atazanavir-GIQ was associated with virologic response at M6, with a median value (range) of 365 (50 to 1172) in responder patients compared with 126 (23 to 1126) in nonresponders (P = 0.05). The cutoff value estimated for the atazanavir-GIQ was 183 (receiver operating characteristic curve test: 60% specificity, 74% sensitivity). Virologic response was achieved in 74% of patients with an atazanavir-GIQ >183 compared with only 26% of patients with an atazanavir-GIQ <183 (P = 0.02). Neither the number of mutations nor the atazanavir trough concentration was predictive of the virologic response.

CONCLUSION

In pretreated patients, the atazanavir-GIQ might be useful to predict early virologic response and allow the determination of the target atazanavir trough concentration required to achieve virologic response and overcome drug resistance emergence in a given patient.

Development of a population simulation model for HIV monotherapy virological outcomes using lamivudine

Current highly active antiretroviral therapy (HAART) requires the use of combinations of three drugs to minimize the early emergence of drug-resistant HIV strains. Therefore, long-term monotherapy data with new agents are unavailable. However, the development of computer models for Monte-Carlo-type simulations of antiviral monotherapy, which incorporate HIV infection dynamic distributions from previously studied populations, together with pharmacokinetics and pharmacodynamic parameters of the new agent, could serve as an important tool. The nucleoside lamivudine (3TC) was used as a representative drug to standardize an improved pharmacodynamic and infection dynamic monotherapy model. 3TC plasma concentration versus time profiles was used to drive the cellular accumulation of 3TC-triphosphate (TP) in primary human lymphocytes in the model, over a 16 week period. The fraction of HIV reverse transcription inhibited was calculated using the median inhibitory concentration and intracellular 3TC-TP levels. Virus loads and activated CD4+ T-cell counts were generated for 2,200 theoretical individuals and compared with the outcomes of an actual 3TC monotherapy trial at the same dose. Pharmacokinetic variance alone did not account for the interindividual HIV-load variability. However, selection of appropriate distributions of the various pharmacokinetic and infection dynamics parameters produced a similar range of virus load reductions to actual observations. Therefore, once parameter and variance distributions are standardized, this modelling approach could be helpful in planning clinical trials and predicting the antiviral contribution of each agent in a HAART modality.

Estimating the rate of accumulating drug resistance mutations in the HIV genome

OBJECTIVE

HIV mutation accumulation has great implications for pharmacoeconomics and clinical care, yet scarcity of data has hindered its representation in decision analytic models. Our objective is to determine the accuracy with which mutation accumulation and other unmeasured parameters could be estimated during model calibration.

METHODS

We used a second-order Monte Carlo simulation of HIV natural history that had been calibrated by varying two unmeasured parameters (mutation accrual rate and probability of adherence) to minimize differences between estimated and observed clinical outcomes (time to treatment failure and survival). We compared these estimated values first with only those results that had been already published at the time of model calibration, and second including results that were published after model calibration.

RESULTS

The value for mutation accrual rate assigned during calibration was 0.014 mutations per month for antiretroviral-naïve patients, at the lower bound of the results for nine heterogeneous studies published at the time of calibration (pooled 95% confidence interval [CI] 0.014-0.039 mutations per month). In contrast, this estimate accurately anticipated results from 11 larger and more homogeneous studies published after calibration (pooled 95% CI for antiretroviral-naïve patients, 0.012-0.015 mutations per month). The value for probability of adherence assigned during calibration (75%) was also within the range of published results (pooled 95% CI 62-76%).

CONCLUSION

Estimates for unobserved parameters derived during model calibration were not only within the range of clinical observations, but anticipated with accuracy clinical results that were not yet available. It may be feasible to use models to estimate unobserved parameters.

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.

Pharmacology of current and promising nucleosides for the treatment of human immunodeficiency viruses

Nucleoside antiretroviral agents are chiral small molecules that have distinct advantages compared to other classes including long intracellular half-lives, low protein binding, sustained antiviral response when a dose is missed, and ease of chemical manufacture. They mimic natural nucleosides and target a unique but complex viral polymerase that is essential for viral replication. They remain the cornerstone of highly active antiretroviral therapy (HAART) and are usually combined with non-nucleoside reverse [corrected] transcriptase and protease inhibitors to provide powerful antiviral responses to prevent or delay the emergence of drug-resistant human immunodeficiency virus (HIV). The pharmacological and virological properties of a selected group of nucleoside analogs are described. Some of the newer nucleoside analogs have a high genetic barrier to resistance development. The lessons learned are that each nucleoside analog should be treated as a unique molecule since any structural modification, including a change in the enantiomeric form, can affect metabolism, pharmacokinetics, efficacy, toxicity and resistance profile.

Updated clinical pharmacologic considerations for HIV-1 protease inhibitors

Many data associate low protease inhibitor plasma concentrations with suboptimal virologic responses, whereas fewer data associate high plasma concentrations with toxicity. Knowledge of relationships between concentrations and virologic response is important because significant variability in concentrations exists among patients. For antiretroviral-naïve patients, target trough concentrations have been suggested on the basis of retrospective associations with virologic responses. Two prospective studies demonstrated improved virologic responses when indinavir and nelfinavir doses were managed based on these troughs. Investigations among antiretroviral-experienced patients have identified a relationship between the trough concentration and the in-vitro susceptibility of the patient's virus with virologic outcome. However, differences in virologic response may further depend on other pharmacologic factors, such as protein binding, intracellular kinetics, function of drug transporters, and the activity of other drugs in the regimen. In the future, dosing strategies that accommodate the variability in pharmacokinetics and pharmacodynamics may improve virologic outcomes.

The normalized inhibitory quotient of boosted protease inhibitors is predictive of viral load response in treatment-experienced HIV-1-infected individuals

OBJECTIVE

The normalized inhibitory quotient (NIQ) has been proposed as a measure for refining the precision of HIV resistance testing when selecting antiretroviral therapy (ART). We undertook an assessment of NIQ and 48-week virological outcome in patients commencing ritonavir-boosted protease inhibitor (PI) regimens.

DESIGN

A cohort of 87 HIV-infected individuals who all had extensive prior exposure to ART were assigned a new boosted PI regimen following resistance testing. PI therapy consisted of lopinavir, indinavir, saquinavir and amprenavir at 50, 32, 11 and 6%, respectively. Fold change (FC) for each PI was determined from the resistance test at baseline. Trough drug concentration (Cmin) was determined at week 4.

METHODS

NIQ was derived individually by taking the logarithm of the ratio of Cmin/FC divided by the fixed ratio of population mean trough drug concentration/clinical cut off. Associations between viral load (VL) response over 48 weeks with baseline VL, FC, Cmin, NIQ and selected PI were assessed.

RESULTS

Mean change from baseline VL reduced by 0.83 log at week 48. In multivariate analyses, baseline VL and NIQ were the parameters most associated with change from baseline VL at week 48 (P = 0.012 and 0.003, respectively). FC, Cmin and selected PI were not significantly associated with VL changes.

CONCLUSION

In this cohort of highly treatment-experienced individuals treated with boosted PI regimens, baseline VL and NIQ were significantly predictive of virological response over 48 weeks whereas FC and Cmin were not. These results support the use of a NIQ at week 4, as a tool for predicting response to therapy in this setting.

Management of HIV Infection in Persons Co-infected With Hepatitis

Co-infection with hepatitis C virus (HCV) and/or hepatitis B virus (HBV) is becoming a rampant disparity in HIV-infected patients. The advent of antiretroviral therapy has led to agents that are effective for suppression of both HIV and HBV; however, this can not be extrapolated to patients who are coinfected with HCV. Treatment of HCV disease is often strenuous and can lead to untoward adverse effects. Co-infection with HIV often leads to higher rates of cirrhosis and liver failure in patients with HBV or HCV, compromising antiretroviral treatment in this patient population due to the hepatotoxicity of these agents. The purpose of this review is to familiarize health care providers to the management of HIV infection in patients who are also co-infected with HBV or HCV.

Development and automation of a 384-well cell fusion assay to identify inhibitors of CCR5/CD4-mediated HIV virus entry

This article describes the automation of an in vitro cell-based fusion assay for the identification of novel inhibitors of receptor mediated HIV-1 entry. The assay utilises two stable cell lines: one expressing CD4, CCR5 and an LTR-promoter/beta-galactosidase reporter construct, and the other expressing gp160 and tat. Accumulation of beta-galactosidase can only occur following fusion of these two cell lines via the gp160 and receptor mediators, as this event facilitates the transfer of the tat transcription factor between the two cell types. Although similar cell fusion systems have been described previously, they have not met the requirements for HTS due to complexity, throughput and reagent cost. The assay described in this article provides significant advantage, as (a) no transfection/infection events are required prior to the assay, reducing the potential for variability, (b) cells are mixed in solution, enhancing fusion efficiency compared to adherent cells, (c) miniaturization to low volume enables screening in 384-well plates; and (d) online cell dispensing facilitates automated screening. This assay has been employed to screen approximately 650,000 compounds in a singleton format. The data demonstrate that the assay is robust, with a Z' consistently above 0.6, which compares favourably with less complex biochemical assays.

Effect of antacids and ranitidine on the single-dose pharmacokinetics of fosamprenavir

Single doses of MAALOX TC and ranitidine were administered separately with 1,400 mg of fosamprenavir (FPV). MAALOX TC decreased the area under the concentration-time curve from 0 to 24 h (AUC(0-24)) for plasma amprenavir (APV) by 18% and the maximum concentration of drug in serum (C(max)) by 35%; the plasma APV concentration at 12 h (C(12)) increased by 14%. Ranitidine at 300 mg decreased the AUC(0-24) for plasma APV by 30% and C(max) by 51%; C(12) was unchanged. FPV may be coadministered with antacids without concern and without separation in dosing; however, caution is recommended when FPV is coadministered with histamine(2)- receptor antagonists or proton pump inhibitors.

Practical guidelines to interpret plasma concentrations of antiretroviral drugs

Several relationships have been reported between antiretroviral drug concentrations and the efficacy of treatment, and toxicity. Therefore, therapeutic drug monitoring (TDM) may be a valuable tool in improving the treatment of HIV-1-infected patients in daily practice. In this regard, several measures of exposure have been studied, e.g. trough and maximum concentrations, concentration ratios and the inhibitory quotient. However, it has not been unambiguously established which pharmacokinetic parameter should be monitored to maintain optimal viral suppression. Each pharmacokinetic parameter has its pros and cons. Many factors can affect the pharmacokinetics of antiretroviral agents, resulting in variability in plasma concentrations between and within patients. Therefore, plasma concentrations should be considered on several occasions. In addition, the interpretation of the drug concentration of a patient should be performed on an individual basis, taking into account the clinical condition of the patient. Important factors herewith are viral load, immunology, occurrence of adverse events, resistance pattern and comedication. In spite of the described constraints, the aim of this review is to provide a practical guide for TDM of antiretroviral agents. This article outlines pharmacokinetic target values for the HIV protease inhibitors amprenavir, atazanavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir, and the non-nucleoside reverse transcriptase inhibitors efavirenz and nevirapine. Detailed advice is provided on how to interpret the results of TDM of these drugs.

The NIQ of Lopinavir is Predictive of a 48-Week Virological Response in Highly Treatment-Experienced HIV-1-Infected Subjects Treated with a Lopinavir/Ritonavir-Containing Regimen

Objective

To investigate the normalized inhibitory quotient (NIQ) of lopinavir (LPV) as a predictor of 48-week virological responses to a lopinavir/ritonavir (LPV/RTV)-containing regimen in highly treatment-experienced patients.

Design

We calculated the NIQ for 59 patients who completed 48 weeks’ treatment and assessed the factors predicting a week-48 virological response.

Methods

The NIQ was calculated by dividing each subject's IQ (LPV Ctrough/fold change in LPV susceptibility, as assessed by VirtualPhenotype™) by a reference IQ (mean population LPV Ctrough/fold change in LPV IC50, as assessed by VirtualPhenotype™). HIV-1 RNA was assessed by NASBA (quantification limit: 80 copies/ml). The general linear model and multiple logistic regression, respectively, were used to estimate the independent predictors of a change in viral load and HIV-1 RNA <80 copies/ml.

Results

The median (interquartile range) baseline levels of CD4+ cells and HIV-1 RNA were 251 (141–385) cells/μl and 4.85 (4.49–5.23) log10 copies/ml, respectively. The median NIQ was 2.2 (0.5–14). At week 48, the median decrease in HIV-1 RNA was 1.4 (0.59–2.79) log10 copies/ml ( P<0.0001), with 24 subjects (41%) reaching <80 copies/ml. Baseline HIV-1 RNA ( P=0.001), CD4+ cells ( P=0.002) and NIQ ( P=0.0006) independently predicted the week-48 change in viral load, whereas baseline CD4+ cells ( P=0.011) and NIQ ( P=0.009) independently predicted a week-48 HIV-1 RNA level of <80 copies/ml.

Conclusion

The LPV NIQ independently predicts virological responses to an LPV/RTV-containing regimen in highly treatment-experienced HIV-1-infected patients.

Pharmacodynamics and clinical use of anti-HIV drugs

Antiretroviral drug exposure has been linked to both antiviral efficacy and the development of toxicity and further research in this area is ongoing and necessary. Use of these data may have important implications for TDM of HAART regimens in clinical practice. TDM, in conjunction with an assessment of the patient's viral resistance in the form of an IQ, needs to be examined and validated in large clinical trials.

Changes in Body Fat Composition after 1 Year of Salvage Therapy with Lopinavir/Ritonavir-Containing Regimens and Its Relationship with Lopinavir Plasma Concentrations

Objective

To determine whether an association existed between lopinavir (LPV) plasma concentrations and changes in body fat composition.

Design

A prospective, non-randomized study.

Setting

HIV clinic of a University Hospital. Subjects, participants: HIV-infected subjects who had virological failure on protease inhibitor-containing regimens. Twenty-two consecutive patients were enrolled, 19 completed 24 weeks of treatment and 16 completed the full 48-week study period. Intervention: Patients were treated with LPV/ritonavir (LPV/r) in combination with other antiretroviral agents. LPV trough plasma concentrations were measured at baseline and weeks 4, 8, 12, 24, 36 and 48. Body fat composition was quantified by computerized tomographic scanning at baseline, and weeks 24 and 48.

Results

LPV trough concentrations correlated with absolute and proportional changes in limb fat from baseline to week 48. Significant differences were found in mean LPV trough concentrations between patients losing less than 5% of limb fat, those experiencing a limb fat loss between 5 and 20%, and those losing more than 20% at week 24 [mean (SD), 4.67 (1.67); 8.57 (1.77); 9.49 (2.67) μg/ml, respectively; P=0.013] and week 48 [mean (SD), 4.5 (2.24); 7.04 (1.77); 9.7 (2.8) μg/ml, respectively; P=0.027]. Most patients losing more than 5% of limb fat during LPV/r therapy had mean LPV trough concentrations ≥8 μg/ml.

Conclusions

In patients receiving salvage therapy with LPV/r there was an association between LPV plasma trough concentrations and limb fat loss. The risk of peripheral limb fat loss may be greater among patients achieving higher LPV trough concentrations.

Lopinavir plasma concentrations and changes in lipid levels during salvage therapy with lopinavir/ritonavir-containing regimens

OBJECTIVE

To determine whether an association existed between lopinavir (LPV) plasma concentrations and changes in lipid levels.

DESIGN

A prospective, nonrandomized study.

SUBJECTS

HIV-infected subjects with virologic failure on protease inhibitor-containing regimens. Twenty-two consecutive patients were enrolled, 19 completed 24 weeks of treatment, and 16 completed the full 48-week study period. INTERVENTION Patients were treated with LPV/ritonavir (LPV/r) in combination with other antiretroviral agents. Subjects were evaluated at baseline and weeks 4, 8, 12, 24, 36, and 48. LPV trough plasma concentrations and lipid levels were measured.

RESULTS

LPV trough concentrations were higher in patients experiencing grade 3 or higher lipid elevations (mean [SD]: 9.71 microg/mL (5.62) vs. 6.09 microg/mL (3.83); P = 0.002) and in those developing grade 2 or higher hypercholesterolemia (mean [SD]: 8.48 microg/mL [4.64] vs. 5.71 microg/mL [3.94]; P = 0.003). All patients developing grade 2 or higher cholesterol elevation had an LPV trough concentration at week 4 greater than 8 microg/mL. Significant positive correlations were found between LPV trough concentrations and changes in triglyceride and cholesterol levels.

CONCLUSIONS

In patients receiving salvage therapy with LPV/r, there is an association between LPV plasma concentrations and lipid changes. Patients achieving higher LPV trough concentrations may be at greater risk of experiencing dyslipidemia. Further investigations are warranted to support a direct cause and effect relationship.

Therapeutic drug monitoring: an aid to optimising response to antiretroviral drugs?

Therapeutic drug monitoring (TDM) has been proposed as a means to optimise response to highly active antiretroviral therapy (HAART) in HIV infection. Protease inhibitors (PIs) and the non-nucleoside reverse transcriptase inhibitors (NNRTIs) efavirenz and nevirapine satisfy many criteria for TDM. Nucleoside reverse transcriptase inhibitors (NRTIs) are not suitable candidates for TDM, since no clear plasma concentration-effect relationships have been established for these drugs. Several important limitations to the application of TDM for antiretroviral drugs should be recognised, including uncertainty about the best pharmacokinetic predictor of response and insufficient validation of target concentrations for individual PIs and NNRTIs. Data from two clinical trials support the use of TDM in treatment-naive HIV-infected patients who start with an indinavir- or nelfinavir-based regimen. TDM either prevented virological failures (presumably by preventing the development of resistance) or treatment discontinuations due to concentration-related toxicity. Application of routine TDM in other patient groups (treatment-experienced patients) or for drugs other than indinavir or nelfinavir (NNRTIs, other PIs, combination of PIs) is speculative at this moment. However, TDM can be used in selected patient groups (children, pregnant women, patients with renal or hepatic dysfunction) to confirm adequate drug concentrations, and for management of drug-drug interactions.TDM in treatment-experienced patients may be optimally used in conjunction with resistance testing. The integration of pharmacological and virological measures in the inhibitory quotient (IQ) needs to be standardised and elaborated further. TDM should be accompanied by careful assessment of adherence and can itself help identify non-adherence, although a drug concentration only reflects the last few drug doses taken by a patient. Additional clinical trials are needed before routine TDM can be adopted as standard of care in the treatment of HIV infection.

Selection of high-level resistance to human immunodeficiency virus type 1 protease inhibitors

Protease inhibitors represent some of the most potent agents available for therapeutic strategies designed to inhibit human immunodeficiency virus type 1 (HIV-1) replication. Under certain circumstances the virus develops resistance to the inhibitor, thereby negating the benefits of this therapy. We have carried out selections for high-level resistance to each of three protease inhibitors (indinavir, ritonavir, and saquinavir) in cell culture. Mutations accumulated over most of the course of the increasing selective pressure. There was significant overlap in the identity of the mutations selected with the different inhibitors, and this gave rise to high levels of cross-resistance. Virus particles from the resistant variants all showed defects in processing at the NC/p1 protease cleavage site in Gag. Selections with pairs of inhibitors yielded similar patterns of resistance mutations. A virus that could replicate at near-toxic levels of the three protease inhibitors combined was selected. The pro sequence of this virus was similar to that of the viruses that had been selected for high-level resistance to each of the drugs singly. Finally, a molecular clone carrying the eight most common resistance mutations seen in these selections was characterized. The sequence of this virus was relatively stable during selection for revertants in spite of displaying poor processing at the NC/p1 site and having significantly reduced fitness. These results reveal patterns of drug resistance that extend to near the limits of attainable selective pressure with these inhibitors and confirm the patterns of cross-resistance for these three inhibitors and the attenuation of virion protein processing and fitness that accompanies high-level resistance.

Rapid quantification of HIV protease inhibitors in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

HIV protease inhibitors are important antiretroviral drugs which have substantially reduced the morbidity and mortality associated with HIV-1 infection. Recent data have shown relationships between plasma concentrations of the protease inhibitors and clinical response, which makes therapeutic drug monitoring valuable. We have developed and validated an assay, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS), for the routine quantification of the six licensed protease inhibitors (amprenavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir) and the pharmacologically active nelfinavir metabolite M8 in plasma. The sample pretreatment consisted of protein precipitation with a mixture of methanol and acetronitrile using only 100 microl of plasma. Chromatographic separation was performed on an Inertsil ODS3 column (50 x 2.0 mm i.d., particle size 5 microm), with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.5 ml min(-1). The analytical run time was 5.5 min. The use of a 96-well plate autosampler allowed batch sizes up to 150 patient samples. The triple-quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over the concentration ranges 0.01-10 microg ml(-1) for indinavir and saquinavir, 0.1-10 microg ml(-1) for amprenavir, 0.05-10 microg ml(-1) for nelfinavir and ritonavir, 0.1-20 microg ml(-1) for lopinavir and 0.01-5 microg ml(-1) for M8. Saquinavir-d(5) and indinavir-d(6) were used as internal standards. The coefficients of variation were always <10% for both intra-day and inter-day precisions for each compound. Mean accuracies were also between the designated limits (+/-15%). The validated concentration ranges proved to be adequate in daily practice. This robust and fast LC/MS/MS assay is now successfully applied for routine therapeutic drug monitoring and pharmacokinetic studies in our hospital.

Measurement of adherence to antiretroviral medications

Measurement of adherence may be important in determining why patients fail antiretroviral therapy. Although patient self-report is by far the most frequently used means of assessing adherence, it overestimates adherence. However, patients who state they are nonadherent almost always are. The pill identification test is a recently described tool that may be useful in clinical practice. The best methods of adherence measurement are pill counts and electronic monitoring. Pill counts suffer from inability to record the time of consumption of therapy. Electronic monitoring enables timing of pill consumption and is the closest to a gold standard for measuring adherence. However, this is only the case if patients are carefully instructed in how to use the device, e.g., not to remove extra doses from their pill bottle. A composite adherence score has been developed that uses electronic monitoring, pill counts, and patient self-report. The authors believe that careful measurement of adherence is essential in the assessment of a patient failing to respond to antiretroviral therapy.

Virtual inhibitory quotient predicts response to ritonavir boosting of indinavir-based therapy in human immunodeficiency virus-infected patients with ongoing viremia

Depending on the degree of underlying resistance present, optimization of the pharmacokinetics of protease inhibitors may result in improved virologic suppression. Thirty-seven human immunodeficiency virus (HIV)-infected subjects who had chronic detectable viremia and who were receiving 800 mg of indinavir three times a day (TID) were switched to 400 mg of indinavir BID with 400 mg of ritonavir two times a day (BID) for 48 weeks. Full pharmacokinetic evaluations were obtained for 12 subjects before the switch and 3 weeks after the switch. Combination therapy increased the indinavir predose concentrations in plasma by 6.47-fold, increased the minimum concentration in serum by 3.41-fold, and reduced the maximum concentration in serum by 57% without significantly changing the area under the plasma concentration-time curve at 24 h. At week 3, 58% (21 of 36) of the subjects for whom postbaseline measurements were available achieved a viral load in plasma of <50 copies/ml or a reduction from the baseline load of > or =0.5 log(10) copies/ml. Of these subjects, 82% (14 of 17) whose viruses had three or fewer protease inhibitor mutations and 88% (14 of 16) whose viruses had an indinavir virtual phenotypic susceptibility test of more than sixfold less than that for the baseline isolate were considered virologic responders. The indinavir virtual inhibitory quotient, which is a function of baseline indinavir phenotypic resistance (estimated by virtual phenotype) and the indinavir predose concentration in plasma achieved with indinavir-ritonavir combination therapy, was the best predictor of a viral load reduction. Sixteen subjects discontinued the study by week 48 due to adverse events, predominantly related to hyperlipidemia. Pharmacokinetic intensification of indinavir-based therapy with ritonavir reduced the viral loads in subjects but added toxicity. The virtual inhibitory quotient, which incorporates both baseline viral resistance and the level of drug exposure in plasma, was superior to either baseline resistance or drug exposure alone in predicting the virologic response.

Position paper on therapeutic drug monitoring of antiretroviral agents

Monitoring drug concentrations in humans to optimize efficacy and reduce toxicity is not a new concept in clinical pharmacology. It has been successfully applied to many different classes of drugs. As a result of considerable concentration and response data, the concept of therapeutic drug monitoring (TDM) has been expanded to certain antiretroviral compounds. In particular, protease inhibitors and nonnucleoside reverse transcriptase inhibitors may be viable candidates for TDM, and limited clinical trial data suggest monitoring plasma concentrations of these agents may indeed clinically benefit patients with HIV infection. A primary distinction between TDM of antiretroviral drugs compared with other drugs is that multiple agents are concomitantly used to treat HIV infection. As with all illnesses that require self-administered drug therapy, poor adherence is a major impediment to success. However, in the treatment of HIV infection, inadequate drug concentrations will result in the appearance or evolution of drug resistance mutations that can endanger present and future drug treatment options. Procedures for sample collection, cross-validation of analytical procedures, and interpretation of assay results should be standardized. More clinical data are needed to confirm this approach and methods of implementing TDM should be further explored. This position paper offers guidelines to aid clinicians who choose to incorporate TDM into the routine care of their patients.

Both baseline HIV-1 drug resistance and antiretroviral drug levels are associated with short-term virologic responses to salvage therapy

BACKGROUND

To determine the impact of HIV-1 drug resistance at baseline and antiretroviral drug levels (DL) during follow-up on virologic response to the next antiretroviral regimen.

METHODS

Baseline genotypic and phenotypic susceptibility was obtained for plasma virus from patients failing a protease inhibitor-containing regimen. Untimed plasma antiretroviral DL were performed and the distribution of DL after 12 weeks of follow-up was classified as above (DLHigh) or below (DLLow) the median. Inhibitory quotients [IQ = (DL at week 12)/(fold change in IC50 to wild-type)] were determined for each drug in the regimen. Primary outcome was change in log10 plasma HIV-1 RNA viral load (DeltaVL) from baseline to 12 weeks.

RESULTS

There were 137 patients who had baseline resistance data available for the antiretroviral drugs used in the salvage regimen, and DL at week 12. Each drug with DLHigh was associated with DeltaVL = -0.40 (P = 0.0002) while each drug with DLLow had DeltaVL = -0.16 (P = 0.11). In multivariate models DeltaVL associated with each active drug (defined by genotype) with DLHigh was -0.48 log10 (P < 0.0001), and with each active drug with DLLow was -0.22 (P = 0.03). The DeltaVL was -0.18 if no drugs in the regimen had an IQ > median, compared to -0.58 for one drug, -1.06 for two drugs, -0.86 for three drugs, and -1.44 for four or five drugs with IQ > median (P < 0.0001 for trend).

CONCLUSIONS

In salvage therapy, both the number of active drugs and the DL for each drug in the new regimen determine the antiviral response.

The relationship between ritonavir plasma trough concentration and virological and immunological response in HIV-infected children

BACKGROUND

We studied a number of factors, including ritonavir plasma levels, and their capability of predicting response to therapy with ritonavir (RTV).

METHODS

Eleven HIV-positive children, nucleoside reverse transcriptase inhibitor (NRTI)-experienced, protease inhibitor (PI) naive, receiving RTV in combination with two NRTIs were enrolled in the study. Demographic parameters were: median age (range) 10 (2-13) years, weight 26 (10-38) kg, body surface area (BSA) 0.93 (0.47-1.21) m(2). Baseline values of CD4, percent CD4 and viral load were 137 (2-1390) cells/microL, 9.5 (0.4-32.4)%, and 5.15 (4.30-6.18) log10 copies/mL, respectively. The dose of RTV was 318 (266-409) mg/m(2) twice daily. Peak (3.5 h after administration) and trough (predose) plasma concentrations of RTV were determined on one occasion at steady-state after a morning dose. Virological response to treatment was quantified as the difference between the baseline value of viral load and the value observed at 6 months of therapy (Delta(6)).

RESULTS

The relationship between Delta(6) and demographic parameters (age, weight, BSA, and baseline CD4, percent CD4, and viral load) and plasma concentrations of RTV was studied by linear regression. Median (range) Delta(6) was 0.88 (0.77-2.62) log10 copies/mL. Peak and trough of RTV were 14.9 (3.2-31.4) and 5.0 (0.1-15.6) mg/L, respectively. Trough concentration of RTV was the best predictor of Delta(6), although the relationship between these two variables was not statistically significant (r = 0.56, P = 0.075).

CONCLUSION

Our observation of a trend for a greater decrease in viral load in patients with higher trough concentration of RTV warrants further pharmacodynamic studies of PI in paediatric patients.

Therapeutic drug monitoring in HIV infection: current status and future directions

BACKGROUND

Highly active antiretroviral therapy (HAART) can suppress viral replication and prolong patient life substantially. However, HAART can fail for a number of reasons, including incomplete adherence, pharmacokinetic factors and the emergence of resistance. Because the number of possible antiretroviral combinations is limited, the use of existing treatment options must be optimized. Whether the application of therapeutic drug monitoring (TDM) in routine clinical practice may help with this purpose remains a subject of debate. However, TDM has been introduced in some centres despite the lack of guidelines for optimal use of this test.

OBJECTIVE

In October 2000, a panel of experts met in Perugia, Italy, to discuss the key issues surrounding the introduction of TDM into routine clinical practice. The purpose of the meeting was to achieve a consensus among panel members on the following issues: (i) validity of data suggesting the utility of TDM in HAART; (ii) patient categories and clinical settings in which TDM may be of most benefit; (iii) target levels of antiretroviral agents; (iv) influence of covariables on target levels of drugs; (v) blood sampling and dosage adjustment strategies; and (vi) future research steps needed to elucidate issues regarding the applicability of TDM in clinical practice.

OUTCOME

This report, which has been updated to include data published or presented at conferences up to the end of August 2001, summarizes the data presented and issues discussed at the meeting. This article will guide the reader through the data and discussions that have allowed the panel to formulate a series of position statements regarding the current status and future applications of TDM in antiretroviral therapy. These statements have been formulated to provide suggestions for the design of future TDM clinical trials, as well as to provide useful points of reflection for centres in which TDM is already in use.

Pharmacokinetic modeling and simulations of interaction of amprenavir and ritonavir

Data from three pharmacokinetic drug interaction studies of amprenavir and ritonavir were used to develop a pharmacokinetic interaction model using NONMEM (nonlinear mixed-effect model). A two-compartment linear model with first-order absorption best fit the amprenavir data, while a one-compartment model was used to describe the ritonavir data. The inhibition of elimination of amprenavir by ritonavir was modeled with a maximum effect (Emax) inhibition model and the observed ritonavir concentration. Monte Carlo simulation was then used to predict amprenavir concentrations for various combinations of amprenavir and ritonavir in twice-daily and once-daily dosing regimens. Simulated minimum amprenavir concentrations in plasma (Cmin) in twice-daily and once-daily dosing regimens were compared with protein binding-adjusted 50% inhibitory concentrations (IC50s) for clinical human immunodeficiency virus isolates with different susceptibilities to protease inhibitors (central tendency ratios). The model based on the first two studies predicted the results of the third study. Data from all three studies were then combined to refine the final model. The observed and simulated noncompartmental pharmacokinetic parameters agreed well. From this model, several candidate drug regimens were simulated. These simulations suggest that, in patients who have clinically failed a traditional amprenavir regimen, a regimen of 600 mg of amprenavir with 100 mg of ritonavir twice daily would result in Cmin-to-IC50 ratios similar to that of 1,200 mg of amprenavir twice daily alone for wild-type viruses. In addition, once-daily regimens that result in C(min)s above the protein binding-corrected IC50s for wild-type virus are clearly feasible.

Plasma drug levels, genotypic resistance, and virological response to a nelfinavir plus saquinavir-containing regimen

OBJECTIVE

To determine the importance of resistance and drug levels in the response to a dual-protease inhibitor (PI) combination.

METHODS

Prospective study of 62 HIV-positive patients who switched to a salvage regimen including nelfinavir plus saquinavir. Virological response was defined as a decrease in viraemia > 0.5 log10 after 24 weeks. Optimal PI levels were defined as those above the protein binding-corrected 95% inhibitory concentration (IC95), as estimated in the presence of 50% human serum.

RESULTS

Baseline median HIV load was 4.78 log10 copies/ml. The median number of mutations in the protease gene was nine (range, 2-25), predominantly at residues 82 (52%), and 90 (40%). After 24 weeks, 45% of patients had responded and 19% were < 50 copies/ml. A higher number of mutations in the protease gene (12 versus 8;P = 0.001), and the L90M mutation (36% versus 67%; P = 0.001) were associated with treatment failure. Trough levels of nelfinavir and saquinavir were two- and fivefold, respectively, greater than those reached when used as the only PI (2480 and 260 ng/ml, respectively), and they were above the estimated protein-corrected IC95 in 96% and 32% of cases. Thus, the Cmin : IC95 ratio ranged from 0.1 to 10 for nelfinavir and from 0.12 to 3.24 for saquinavir. Suboptimal PI levels were associated with a poorer response, but there was no correlation between optimal drug levels and a better response.

CONCLUSION

Genotypic resistance predicts the virological response to a nelfinavir-saquinavir salvage regimen. Our data suggest that higher than optimal drug levels could be necessary to control the replication of many PI-resistant viruses.

Clinical pharmacology and pharmacokinetics of amprenavir

OBJECTIVE

To review the pharmacokinetics, pharmacodynamics, drug interactions, and dosage and administration information of amprenavir.

DATA SOURCE

An extensive review of the literature (MEDLINE search from 1994 to April 2001) relating to the clinical pharmacology of the HIV protease inhibitors was conducted. Meeting abstracts or full presentations and data submitted to the Food and Drug Administration were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

The data on pharmacokinetics, pharmacodynamics, drug interactions, and drug resistance were obtained from in vitro studies and open-label and controlled clinical trials.

DATA SYNTHESIS

Like all HIV protease inhibitors, amprenavir interrupts the maturation phase of the HIV replicative cycle by forming an inhibitor-enzyme complex, which prevents HIV protease from binding with its normal substrates (biologically inactive viral polyproteins). Amprenavir has an enzyme inhibition constant (Ki = 0.6 nM) that falls within the Ki range of the other protease inhibitors. Amprenavir's in vitro 50% inhibitory concentration (IC50) against wild-type clinical HIV isolates is 14.6 +/- 12.5 ng/mL (mean +/- SD). Pharmacodynamic modeling indicates that, as is the case with other protease inhibitors, the concentration-response curve for amprenavir plateaus at amprenavir trough values above the IC50 for these isolates. This exposure-activity relationship, plus such favorable pharmacokinetic parameters as a long terminal elimination half-life (7-10 h), makes amprenavir an attractive drug of choice when considering potent antiretrovirals. The higher trough exposure obtained with amprenavir coadministered with ritonavir may allow effective treatment of patients with decreased susceptibility viral isolates and once-daily dosing. Amprenavir has been approved for adults and children; the recommended capsule doses are 1200 mg twice daily for adults and 20 mg/kg twice daily or 15 mg/kg 3 times daily for children < 13 years of age or adolescents < 50 kg. The recommended dose for amprenavir oral solution is 1.5 mL/kg twice daily or 1.1 mL/kg 3 times daily.

CONCLUSIONS

The clinical pharmacology, exposure-activity relationship, and drug resistance profile of amprenavir support the use of this potent HIV protease inhibitor in combination antiretroviral regimens, especially for persons who have experienced virologic failure while on protease inhibitor-containing regimens.

Pharmacokinetic study of human immunodeficiency virus protease inhibitors used in combination with amprenavir

In an open-label, randomized, multicenter, multiple-dose pharmacokinetic study, we determined the steady-state pharmacokinetics of amprenavir with and without coadministration of indinavir, nelfinavir, or saquinavir soft gel formulation in 31 human immunodeficiency virus type 1-infected subjects. The results indicated that amprenavir plasma concentrations were decreased by saquinavir soft gel capsule (by 32% for area under the concentration-time curve at steady state [AUC(ss)] and 37% for peak plasma concentration at steady state [C(max,ss)]) and increased by indinavir (33% for AUC(ss)). Nelfinavir significantly increased amprenavir minimum drug concentration at steady state (by 189%) but did not affect amprenavir AUC(ss) or C(max,ss). Nelfinavir and saquinavir steady-state pharmacokinetics were unchanged by coadministration with amprenavir compared with the historical monotherapy data. Concentrations of indinavir, coadministered with amprenavir, in plasma decreased in both single-dose and steady-state evaluations. The changes in amprenavir steady-state pharmacokinetic parameters, relative to those for amprenavir alone, were not consistent among protease inhibitors, nor were the changes consistent with potential interactions in CYP3A4 metabolism or P-glycoprotein transport. No dose adjustment of either protease inhibitor in any of the combinations studied is needed.

Justification for a new cohort study of people aging with and without HIV infection

This supplement contains a series of papers supporting the justification, design, and implementation of a longitudinal cohort study of an aging HIV-positive and HIV-negative veteran population called the Veterans Aging Cohort Study (VACS). Although the papers cover a wide range of topics and several papers address methodologic issues not unique to a study of aging veterans, all are motivated by a unifying set of assumptions. Specifically: (a) HIV/AIDS is a chronic disease in an aging population; (b) conditions among HIV-positive and -negative patients in care have overlapping etiologies; (c) individuals with pre-existing organ injury are at increased risk for iatrogenic injury; (d) cohort studies are uniquely suited to the study of chronic disease complicated by aging, comorbid conditions, drug toxicities, and substance use/abuse; (e) VACS is well positioned to study HIV as a chronic disease in an aging population.

Value of patient self-report and plasma human immunodeficiency virus protease inhibitor level as markers of adherence to antiretroviral therapy: relationship to virologic response

Three methods of adherence to antiretroviral therapy were evaluated for 149 patients infected with human immunodeficiency virus (HIV): plasma level of protease inhibitors (PIs), patient self-report, and routine biological parameters associated with the use of some antiretroviral drugs. Adherence to therapy was estimated from a score calculated from answers to a self-administered questionnaire and on the basis of measurement of relevant plasma and blood levels. Of the 149 patients, 112 had a virologic response, and 122 had adequate trough PI levels. Plasma PI levels and virologic outcome were significantly correlated (P<.0001). The adherence score was significantly correlated with virologic response (P<.001). Macrocytosis was significantly associated with virologic response in the patients treated with zidovudine or stavudine (P=.006). PI level was the higher significant predictor of virologic response (P=.0003). Self-reported adherence (P=.01) and macrocytosis (P=.05) were also independently associated with antiretroviral efficacy.

Clinical Pharmacologic Considerations for HIV-1 Protease Inhibitors

Many data associate low protease inhibitor plasma concentrations with suboptimal virologic responses, whereas relatively few data associate high plasma concentrations with increased likelihood of toxicity. Knowledge of relationships between concentrations and virologic response is important because significant variability in plasma concentrations exists among HIV-infected persons. Unfortunately, a prospectively confirmed therapeutic range that reduces the risk of virologic failure has not been established for the protease inhibitors. Recent investigations have identified a relationship between the measured minimum plasma concentration, the in vitro susceptibility of the subject's virus, and virologic outcome. However, differences in virologic response may further depend on other pharmacologic factors such as protein binding, intracellular kinetics, expression of drug transporters, and drug synergies or antagonisms. In the future, dosing strategies that accommodate the variability in both pharmacokinetics and pharmacodynamics may improve virologic outcomes. In summary, clinical pharmacologic considerations for protease inhibitors can be used to promote their optimal use.

Pharmacokinetics and resistance mutations affect virologic response to ritonavir/saquinavir-containing regimens

The authors assessed the impact of protease and reverse transcription (RT) mutations and individual pharmacokinetic parameters on virologic response to a four-drug regimen including ritonavir/saquinavir. Treatment was given at the start of the study (M0) to 22 HIV-1 protease inhibitor-naive or pretreated patients. Protease and RT genes were sequenced at M0, at the time of virologic failure, or at the end of the follow-up. Plasma ritonavir and saquinavir peak C(max), C(min), and area under the curve (AUC) were determined based on samples taken 0, 1, 2, 3, 4, 6, 8, and 12 hours after administration. HIV-1 RNA decreased to less than 50 copies/mL in 11 patients (group 1). At M0, five of them had no RT mutation and 10 had three or fewer secondary protease mutations with no new mutation during follow-up. Ritonavir and saquinavir pharmacokinetics showed wide interindividual variability. Treatment failed in 11 patients (group 2): 9 had three to eight protease mutations and a mean of 5.8 RT mutations at M0, with emergence of new mutations during follow-up. Pharmacokinetics was similar to those of group 1. The other two patients with virologic failure showed no baseline primary mutation but were the only patients with insufficient saquinavir and ritonavir AUC. The authors showed the complementarity between drug-resistance genotype and individual pharmacokinetics and the potential utility of AUC and Cmax to manage treatment.

Pharmacokinetics of nelfinavir in human immunodeficiency virus-infected infants

BACKGROUND

Nelfinavir dosed at approximately 20 to 30 mg/kg three times a day (TID) in older children provides exposure similar to 750 mg TID in adults. However, the pharmacokinetics (PK) of nelfinavir in infants who are < 2 years of age is not well-described. The objective of this study was to determine the pharmacokinetics of nelfinavir in infants < 2 years of age.

METHODS

Nelfinavir concentrations were evaluated in 22 HIV-infected infants between 15 days and 2 years of age receiving nelfinavir as part of Pediatric ACTG Study 356. Nelfinavir therapy was initiated at approximately 25 mg/kg TID (n = 18) or approximately 55 mg/kg twice a day (n = 4) and given in combination with nevirapine, stavudine and lamivudine. PK samples were obtained predose and 1.5 and 4 h postdose at approximately 6-month intervals. Eight infants (all < or = 3 months of age) also had intensive PK samples collected at Week 1.

RESULTS

The median apparent clearance in the infants with intensive pharmacokinetic sampling was 2.7 liters/h/kg (range, 1.8 to > or = 10) and was similar between twice a day and TID dosing cohorts. Overall nelfinavir concentrations at all collection times were lower in these infants than previously reported in older pediatric patients.

CONCLUSIONS

Nelfinavir concentrations in infants are highly variable and lower than those seen in adult or older pediatric populations receiving labeled dosing. Therefore it is necessary to further evaluate nelfinavir safety, effectiveness and pharmacokinetics at higher doses than used among other pediatric populations.

Role of therapeutic drug monitoring for protease inhibitors

OBJECTIVE

To review the role of therapeutic drug monitoring (TDM) for protease inhibitors in the treatment of HIV infection.

DATA SOURCES

Primary articles were identified using MEDLINE (1966-October 2000), EMBASE (1987-October 2000), AIDSLINE (1980-October 2000), Current Contents, PubMed, and Medscape. Further articles were identified from bibliographic review of primary articles and review papers. Abstracts presented at the World AIDS Conference, Interscience Conference on Antimicrobial Agents and Chemotherapy, and Conference on Retroviruses and Opportunistic Infections were also identified from 1997 to 2000.

STUDY SELECTION AND DATA EXTRACTION

All English-language, prospective clinical trials, as well as selected retrospective studies and case series, pertaining to therapeutic drug monitoring of protease inhibitors were included.

DATA SYNTHESIS

A number of clinical studies have found a good relationship between concentration and pharmacologic response and/or toxicity as well as wide interpatient variability in the pharmacokinetics of protease inhibitors. There also is some preliminary evidence of the usefulness of plasma drug concentrations to guide dosage adjustments of protease inhibitors in patients with liver dysfunction. Furthermore, there is preliminary evidence of a relationship between drug concentrations and resistance.

CONCLUSIONS

A number of clinical studies support the usefulness of TDM of protease inhibitors. However, before TDM can be of the most value, further evaluation requires simplified and standardized assays to be performed routinely by clinical laboratories; determination of the appropriate target concentration and therapeutic range, as well as the best predictor of pharmacologic response; and refined interpretation of plasma drug concentrations. Randomized, controlled clinical trials of patient outcomes are needed to assess the clinical utility of TDM for protease inhibitors.

Pharmacokinetics and safety of amprenavir and ritonavir following multiple-dose, co-administration to healthy volunteers

OBJECTIVE

To evaluate the safety and pharmacokinetic interaction between amprenavir (APV) and ritonavir (RTV).

METHODS

Three open-label, randomized, two-sequence, multiple-dose studies having the same design (7 days of APV or RTV alone followed by 7 days of both drugs together) used 450 or 900 mg APV with 100 or 300 mg RTV every 12 h with pharmacokinetic assessments on days 7 and 14. Safety was monitored as clinical adverse events (AEs) and laboratory abnormalities.

RESULTS

Relative to APV alone, RTV co-administration resulted in a 3.3- to 4-fold and 10.84 to 14.25-fold increase in the geometric least-square (GLS) mean area under the plasma concentration--time curve (AUC(tau,ss)) and minimum concentration (C(min,ss)), respectively. APV 900 mg with RTV 100 mg resulted in a 2.09-fold and 6.85-fold increase in the GLS mean AUC(tau,ss) and C(min,ss), respectively. On day 14, the geometric mean (95% confidence interval) for 450 mg APV AUC(tau,ss) (micro x h/mL) was 23.49 (19.32--28.57) with 300 mg RTV and 35.42 (30.46--44.42) with 100 microg RTV, and for the 900 mg APV with 100 mg RTV 47.11 (39.47--61.24). The 450 mg APV C(min,ss) (microg/ml) were 1.32 (1.05--1.67) and 2.01 (1.70--2.61), and 2.47 (2.08--3.32) for 900 mg APV. The most common AEs were mild and included diarrhea, nausea/vomiting, oral parasthesias, and rash. The triglyceride and cholesterol increased significantly from RTV exposure.

CONCLUSION

Adding RTV to APV resulted in clinically and statistically significant increases in APV AUC and C(min) with variable effects on maximum concentration. The two RTV doses had similar effects on APV but AEs were more frequent with 300 mg RTV.

Liquid chromatographic–tandem mass spectrometric determination of amprenavir (agenerase) in serum/plasma of human immunodeficiency virus type-1 infected patients receiving combination antiretroviral therapy

A selective assay method for quantitation of amprenavir (agenerase) in human immunodeficiency virus type-1 infected patient serum or plasma using liquid chromatography-tandem mass spectrometry (LC-MS-MS) is described. Amprenavir and an internal standard (reserpine) are extracted by liquid-liquid extraction and chromatographically separated by a reversed-phase C18-analytical column. The triple quadrupole LC-MS-MS system is operated in the positive-ion mode and multiple reaction monitoring is used for drug quantitation. The method has been validated over the range of 0.05-10.0 microg/ml. The RSDs for the intra-day and inter-day determinations ranged from 5.3 to 6.1% and from 4.7 to 6.2%, respectively. The average assay accuracy at two different concentrations ranged from 96.0 to 103.0% and the extraction recovery of amprenavir was 90.8%. The lower limit of quantitation was 0.05 microg/ml. Using a short microbore column, the analysis was completed in less than 5 min.

Monitoring resistance to human immunodeficiency virus type 1 protease inhibitors by pyrosequencing

The emergence of drug-resistant viral variants is the inevitable consequence of incomplete suppression of human immunodeficiency virus type 1 (HIV-1) replication during treatment with antiretroviral drugs. Sequencing to determine the resistance profiles of these variants has become increasingly important in the clinical management of HIV-1 patients, both in the initial design of a therapeutic plan and in selecting a salvage regimen. Here we have developed a pyrosequencing assay for the rapid characterization of resistance to HIV-1 protease inhibitors (PIs). Twelve pyrosequencing primers were designed and were evaluated on the MN strain and on viral DNA from peripheral blood mononuclear cells from eight untreated HIV-1-infected individuals. The method had a limit of detection of 20 to 25% for minor sequence variants. Pattern recognition (i.e., comparing actual sequence data with expected wild-type and mutant sequence patterns) simplified the identification of minor sequence variants. This real-time pyrosequencing method was applied in a longitudinal study monitoring the development of PI resistance in plasma samples obtained from four patients over a 2 1/2-year period. Pyrosequencing identified eight primary PI resistance mutations as well as several secondary mutations. This sequencing approach allows parallel analysis of 96 reactions in 1 h, facilitating the monitoring of drug resistance in eight patients simultaneously and, in combination with viral load analysis, should be a useful tool in the future to monitor HIV-1 during therapy.

Pharmacokinetic Interaction between amprenavir and rifabutin or rifampin in healthy males

The objective of this study was to determine if there is a pharmacokinetic interaction when amprenavir is given with rifabutin or rifampin and to determine the effects of these drugs on the erythromycin breath test (ERMBT). Twenty-four healthy male subjects were randomized to one of two cohorts. All subjects received amprenavir (1,200 mg twice a day) for 4 days, followed by a 7-day washout period, followed by either rifabutin (300 mg once a day [QD]) (cohort 1) or rifampin (600 mg QD) (cohort 2) for 14 days. Cohort 1 then received amprenavir plus rifabutin for 10 days, and cohort 2 received amprenavir plus rifampin for 4 days. Serial plasma and urine samples for measurement of amprenavir, rifabutin, and rifampin and their 25-O-desacetyl metabolites, were measured by high-performance liquid chromatography. Rifabutin did not significantly affect amprenavir's pharmacokinetics. Amprenavir significantly increased the area under the curve at steady state (AUC(ss)) of rifabutin by 2.93-fold and the AUC(ss) of 25-O-desacetylrifabutin by 13.3-fold. Rifampin significantly decreased the AUC(ss) of amprenavir by 82%, but amprenavir had no effect on rifampin pharmacokinetics. Amprenavir decreased the results of the ERMBT by 83%. The results of the ERMBT after 2 weeks of rifabutin and rifampin therapy were increased 187 and 156%, respectively. Amprenavir plus rifampin was well tolerated. Amprenavir plus rifabutin was poorly tolerated, and 5 of 11 subjects discontinued therapy. Rifampin markedly increases the metabolic clearance of amprenavir, and coadministration is contraindicated. Amprenavir significantly decreases clearance of rifabutin and 25-O-desacetylrifabutin, and the combination is poorly tolerated. Amprenavir inhibits the ERMBT, and rifampin and rifabutin are equipotent inducers of the ERMBT.

Combined therapy with saquinavir, ritonavir and stavudine in moderately to severely immunosuppressed HIV-infected protease inhibitor-naive patients

OBJECTIVE

To assess the short-term and long-term effect of a combination of saquinavir, ritonavir and stavudine in moderately to severely immunosuppressed protease inhibitor-naive patients.

DESIGN

Prospective open-label multicentre study.

PATIENTS AND METHODS

A total of 64 protease inhibitor-naive and stavudine-naive HIV-infected patients with a CD4 count of < 250 cells/microL and > 10 000 HIV-1 RNA copies/mL received saquinavir hard-gelatin capsules, ritonavir and stavudine. Full (drop in viraemia of > 2 log10 and/or < 500 copies/mL) and partial responders (drop to between 500 and 5000 viraemia copies/mL) at week 9 (end of phase I) entered the second phase (additional 12-month period).

RESULTS

Fifty-six patients completed phase I, 45 (70%) full responders and nine (14%) partial responders by intent-to-treat analysis. Thirty-nine patients completed phase II, 33 (52%) full responders and two (3%) partial responders. Six patients had < 50 HIV-1 RNA copies/mL at week 9, and 20 (31%) patients at month 12 of phase II. Mean CD4 cell counts increased significantly in the 56 patients from 89 to 184 cells/microL after 9 weeks and from 100 to 292 cells/microL in the 39 patients treated for another 12 months. Higher baseline viraemia and lower baseline CD4 cell counts were not associated with an unfavourable virological response at week 9 and month 12 of phase II. HIV DNA in peripheral blood monocytes decreased substantially (- 1.5 log10) but was detectable in all except one patient at the end of phase II.

CONCLUSION

In protease- and stavudine-naive HIV-infected patients with moderate to severe immunosuppression, saquinavir in combination with ritonavir and stavudine caused a substantial long-term decrease in plasma viral load in approximately half the participants and a substantial increase in CD4 cell counts.