Dual protease inhibitor therapy in HIV-infected patients: pharmacologic rationale and clinical benefits

Lopinavir/Ritonavir: A Review of Analytical Methodologies for the Drug Substances, Pharmaceutical Formulations and Biological Matrices

Lopinavir/ritonavir is a potent coformulation of protease inhibitors used against HIV infection. Lopinavir is the main responsible for viral load suppression, whereas ritonavir is a pharmacokinetic enhancer. Both of them have recently gained relevance as candidate drugs against severe coronavirus disease (COVID-19). However, significant beneficial effects were not observed in randomized clinical trials. This review summarizes the main physical-chemical, pharmacodynamic, and pharmacokinetic properties of ritonavir and lopinavir, along with the analytical methodologies applied for biological matrices, pharmaceutical formulations, and stability studies. The work also aimed to provide a comprehensive impurity profile for the combined formulation. Several analytical methods in four different pharmacopeias and 37 articles in literature were evaluated and summarized. Chromatographic methods for these drugs frequently use C8 or C18 stationary phases with acetonitrile and phosphate buffer (with ultraviolet detection) or acetate buffer (with tandem mass spectrometry detection) as the mobile phase. Official compendia methods show disadvantages as extended total run time and complex mobile phases. HPLC tandem-mass spectrometry provided high sensitivity in methodologies applied for human plasma and serum samples, supporting the therapeutic drug monitoring in HIV patients. Ritonavir and lopinavir major degradation products arise in alkaline and acidic environments, respectively. Other non-chromatographic methods were also summarized. Establishing the impurity profile for the combined formulation is challenging due to a large number of impurities reported. Easier and faster analytical methods for impurity assessment are still needed.

Possible Retinal Impairment Secondary to Ritonavir Use in SARS-CoV-2 Patients: A Narrative Systematic Review

Some reports described a possible ritonavir-related retinal toxicity. The objective of this research was to review and analyze previous studies conducted on ritonavir administration and retinal impairment in a narrative synthesis. PubMed was used to perform a systematic review of ritonavir effects and retinal damage. All studies up to December 2019 were considered. Seven single cases and one case series, reporting a total of 10 patients affected by retinal changes secondary to long-term ritonavir treatment, were included in the review. Variable degrees of outer retina and retinal pigment epithelium changes were detected in most of the patients, with two patients showing macular telangiectasia, four patients presenting intraretinal crystal deposits, two patients disclosing a bull's eye maculopathy, and two patients revealing midperipheral bone spicule-like pigment changes. In the present study, we hypothesized that the use of ritonavir in life-saving treatments of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) pneumonia might expose these patients to the risk of developing a retinotoxicity. We aimed to alert ophthalmologists on the importance of recognizing ritonavir-induced retinal impairment in SARS-CoV-2 patients. These findings are the target for personalized medicine.

Pharmacokinetic drug evaluation of ritonavir (versus cobicistat) as adjunctive therapy in the treatment of HIV

Introduction: Ritonavir and cobicistat are pharmacoenhancers used to improve the disposition of other HIV antiretrovirals. These drugs are, however, characterized by important pharmacokinetic differences.Areas covered: Here, the authors firstly update the available information on the pharmacokinetics of ritonavir and cobicistat. Subsequently, the review focuses on the description of drug-drug interactions (DDIs) involving cobicistat and comedications that might beneficiate from a shift-back to ritonavir. A MEDLINE Pubmed search for articles published from January 1995 to April 2019 was completed matching the term ritonavir or cobicistat with pharmacokinetics, DDIs, and pharmacology. Moreover, additional studies were identified from the reference list of retrieved articles.Expert opinion: Despite more than 20 years after its introduction on the market, ritonavir still represents a valid option for the treatment of selected HIV-infected patients. The large-scale switch to cobicistat may result in some unexpected DDIs not previously reported for ritonavir. Besides the issue of DDIs, additional advantage of ritonavir over cobicistat is its use in pregnancy, and its availability as single component of pharmaceutical formulations allowing the fine-tuning of antiretroviral regimens in patients with heavy polypharmacy when other unboosted-based therapeutic options cannot be used.

Critical Review: What Dose of Rifabutin Is Recommended With Antiretroviral Therapy?

Since the advent of combination antiretroviral therapy to successfully treat HIV infection, drug-drug interactions (DDIs) have become a significant problem as many antiretrovirals (ARVs) are metabolized in the liver. Antituberculous therapy traditionally includes rifamycins, particularly rifampicin. Rifabutin (RBT) has shown similar efficacy as rifampicin but induces CYP3A4 to a lesser degree and is less likely to have DDIs with ARVs. We identified 14 DDI pharmacokinetic studies on HIV monoinfected and HIV-tuberculosis coinfected individuals, and the remaining studies were healthy volunteer studies. Although RBT may be coadministered with most nonnucleoside reverse transcriptase inhibitors, identifying the optimal dose with ritonavir-boosted or cobicistat-boosted protease inhibitors is challenging because of concern about adverse effects with increased RBT exposure. Limited healthy volunteer studies on other ARV drug classes and RBT suggest that dose modification may be unnecessary. The paucity of data assessing clinical tuberculosis endpoints concurrently with RBT and ARV pharmacokinetics limits evidence-based recommendations on the optimal dose of RBT within available ARV drug classes.

Identification of degradation products of saquinavir mesylate by ultra-high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry and its application to quality control

RATIONALE

Saquinavir mesylate (SQM) is an antiviral drug used for the treatment of HIV infections. The identification and characterization of all degradation products are essential for achieving the quality in pharmaceutical product development and also for patient safety.

METHODS

The drug was subjected to hydrolytic (HCl, NaOH and water), oxidative (H₂ O₂ ), photolytic (UV and fluorescence light) and thermal (dry heat) forced degradation conditions as per ICH guidelines. The best chromatographic separation of the drug and all degradation products (DPs) was achieved on a CSH-Phenyl Hexyl column (100 × 2.1 mm, 1.7 μm) with ammonium acetate (10 mM, pH 5.0) and methanol as mobile phase in gradient mode at a flow rate of 0.28 mL/min.

RESULTS

Nine DPs were obtained under various forced degradation conditions. All the DPs were characterized by using ultra-high-performance liquid chromatography/electrospray ionization quadrupole time-of-flight tandem mass spectrometry (UHPLC/ESI-QTOF MS/MS) and the degradation pathway of the drug was justified by mechanistic explanations. The main DPs were formed by amide hydrolysis, conversion into diastereomers, an N-oxide and dehydration as well as oxidation of the alcohol from the drug. The method was validated and can be used in a quality control (QC) laboratory to assure the quality of SQM in bulk and finished formulations.

CONCLUSIONS

A simple UHPLC/photodiode array (PDA) method was developed and successfully transferred to UHPLC/ESI-Q-TOF MS/MS for the identification and characterization of DPs. Very interestingly, diastereomeric DPs were obtained and successfully resolved by the chromatographic method. Copyright © 2017 John Wiley & Sons, Ltd.

Drug-Drug Interactions and HIV Therapy: What Should Pharmacists Know?

Drug-interaction issues continue to present a major dilemma for the clinician caring for complex patients such as those infected with HIV. The inherent possibility of a drug interaction is magnified by the multitude of drugs being administered in highly-active antiretroviral therapy (HAART). In addition, other classes of medications are used to alleviate side effects, reduce toxicities associated with HAART, or treat concomitant diseases. The modification of one drug by another substance or drug-drug interaction is the main focus of this article. Drug-drug interactions may result in toxicity, treatment failure, or loss of effectiveness and can significantly affect a patient’s clinical outcome. An understanding of the fundamental mechanisms of HIV drug-drug interactions may allow for the early detection or avoidance of troublesome regimens and prudent management if they develop. Although HIV drug interactions are usually thought of as detrimental, resulting in a loss of therapeutic effect or toxicity, some drug interactions such as ritonavir boosted protease inhibitor–based antiretroviral treatments are beneficial and are commonly used in clinical practice. Therefore, pharmacists need to understand drug interaction mechanisms, remember key drug interactions, and vigilantly monitor patients for potential complications.

Neuroprotection mediated by inhibition of calpain during acute viral encephalitis

Neurologic complications associated with viral encephalitis, including seizures and cognitive impairment, are a global health issue, especially in children. We previously showed that hippocampal injury during acute picornavirus infection in mice is associated with calpain activation and is the result of neuronal death triggered by brain-infiltrating inflammatory monocytes. We therefore hypothesized that treatment with a calpain inhibitor would protect neurons from immune-mediated bystander injury. C57BL/6J mice infected with the Daniel's strain of Theiler's murine encephalomyelitis virus were treated with the FDA-approved drug ritonavir using a dosing regimen that resulted in plasma concentrations within the therapeutic range for calpain inhibition. Ritonavir treatment significantly reduced calpain activity in the hippocampus, protected hippocampal neurons from death, preserved cognitive performance, and suppressed seizure escalation, even when therapy was initiated 36 hours after disease onset. Calpain inhibition by ritonavir may be a powerful tool for preserving neurons and cognitive function and preventing neural circuit dysregulation in humans with neuroinflammatory disorders.

Drug synergy of tenofovir and nanoparticle-based antiretrovirals for HIV prophylaxis

BACKGROUND

The use of drug combinations has revolutionized the treatment of HIV but there is no equivalent combination product that exists for prevention, particularly for topical HIV prevention. Strategies to combine chemically incompatible agents may facilitate the discovery of unique drug-drug activities, particularly unexplored combination drug synergy. We fabricated two types of nanoparticles, each loaded with a single antiretroviral (ARV) that acts on a specific step of the viral replication cycle. Here we show unique combination drug activities mediated by our polymeric delivery systems when combined with free tenofovir (TFV).

METHODOLOGY/PRINCIPAL FINDINGS

Biodegradable poly(lactide-co-glycolide) nanoparticles loaded with efavirenz (NP-EFV) or saquinavir (NP-SQV) were individually prepared by emulsion or nanoprecipitation techniques. Nanoparticles had reproducible size (d ∼200 nm) and zeta potential (-25 mV). The drug loading of the nanoparticles was approximately 7% (w/w). NP-EFV and NP-SQV were nontoxic to TZM-bl cells and ectocervical explants. Both NP-EFV and NP-SQV exhibited potent protection against HIV-1 BaL infection in vitro. The HIV inhibitory effect of nanoparticle formulated ARVs showed up to a 50-fold reduction in the 50% inhibitory concentration (IC50) compared to free drug. To quantify the activity arising from delivery of drug combinations, we calculated combination indices (CI) according to the median-effect principle. NP-EFV combined with free TFV demonstrated strong synergistic effects (CI50 = 0.07) at a 1∶50 ratio of IC50 values and additive effects (CI50 = 1.05) at a 1∶1 ratio of IC50 values. TFV combined with NP-SQV at a 1∶1 ratio of IC50 values also showed strong synergy (CI50 = 0.07).

CONCLUSIONS

ARVs with different physicochemical properties can be encapsulated individually into nanoparticles to potently inhibit HIV. Our findings demonstrate for the first time that combining TFV with either NP-EFV or NP-SQV results in pronounced combination drug effects, and emphasize the potential of nanoparticles for the realization of unique drug-drug activities.

Metabolism of amyloid β peptide and pathogenesis of Alzheimer's disease

The conversion of what has been interpreted as "normal brain aging" to Alzheimer's disease (AD) via transition states, i.e., preclinical AD and mild cognitive impairment, appears to be a continuous process caused primarily by aging-dependent accumulation of amyloid β peptide (Aβ) in the brain. This notion however gives us a hope that, by manipulating the Aβ levels in the brain, we may be able not only to prevent and cure the disease but also to partially control some very significant aspects of brain aging. Aβ is constantly produced from its precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Aβ seems to lead to pathological deposition upon aging. We have focused our attention on elucidation of the unresolved mechanism of Aβ catabolism in the brain. In this review, I describe a new approach to prevent AD development by reducing Aβ burdens in aging brains through up-regulation of the catabolic mechanism involving neprilysin that can degrade both monomeric and oligomeric forms of Aβ. The strategy of combining presymptomatic diagnosis with preventive medicine seems to be the most pragmatic in both medical and socioeconomical terms.(Communicated by Kunihiko SUZUKI, M.J.A.).

Therapeutic monitoring and variability of atazanavir in HIV-infected patients, with and without HCV coinfection, receiving boosted or unboosted regimens

BACKGROUND

Adequate plasma trough concentrations (Ctrough) of protease inhibitors are required to maintain antiviral activity throughout the dosing interval. Therapeutic drug monitoring is used in clinical practice to optimize dosage and avoid toxic or subtherapeutic drug exposure. The pharmacokinetic variability of Atazanavir (ATV) can be relatively large, as a result of several factors. One of the affecting factors may be hepatic impairment due to hepatitis C virus (HCV) coinfection.

METHODS

We collected trough plasma samples from human immunodeficiency virus (HIV)-1-infected outpatients, with and without HCV coinfection and/or cirrhosis, receiving stable highly active antiretroviral therapy containing ATV. In the total population, we mainly compared the 2 regimens: 300ATV + 100RTV OD [ritonavir (RTV), once daily (OD)] versus 400ATV OD. We used a threshold value of 0.15 μg/mL, based on the proposed therapeutic range (0.15-0.85 μg/mL). Plasma concentrations of ATV were determined by a validated assay using high-performance liquid chromatography with ultraviolet detection. A total of 214 HIV-infected outpatients were included. For each regimen, we compared 3 groups of subjects: HIV+/HCV-, HIV+/HCV+, and HIV+/HCV+ with cirrhosis.

RESULTS

In the whole study population, we observed a large variability and found suboptimal Ctrough levels (<0.15 μg/mL) in 23 subjects (2 belonging to the 300/100 OD group and 21 to the 400 OD group). For the standard dosage regimen of 300ATV + 100RTV OD, we did not find a statistical difference between HIV-infected patients without HCV coinfection versus HIV-infected patients with HCV coinfection: median 0.85 (interquartile range 0.53-1.34) and 0.95 (0.70-1.36) μg/mL, respectively. In HIV+/HCV+-infected patients with cirrhosis, we found a median Ctrough of 0.70 (0.43-1.0) μg/mL, with no statistical difference when compared with HIV+/HCV- infected patients. For the 400ATV OD (n=90) dosage regimen, the total median ATV Ctrough was 0.40 (0.23-1.0) μg/mL. In this group, we found a statistically significant difference between HIV+/HCV- and HIV+/HCV+-infected patients: median Ctrough was 0.23 (0.11-0.42) and 0.52 (0.20-1.0) μg/mL, respectively. In HIV+/HCV+ subjects with cirrhosis, the Ctrough median value was 0.42 (0.13-0.75) μg/mL, and there was a significant difference when compared with HIV patients without coinfection.

CONCLUSIONS

Therapeutic drug monitoring of ATV in patients receiving unboosted regimen may be useful to identify those HIV-infected subjects, with or without HCV coinfection, who may benefit from adding low RTV doses, or the subset of patients in whom removal of RTV could be attempted without the risk of suboptimal plasma ATV exposure.

Inhaled fluticasone causes iatrogenic cushing's syndrome in patients treated with Ritonavir

INTRODUCTION

Ritonavir, a protease inhibitor (PI), is commonly used in the treatment of HIV-1 infection. It is a potent inhibitor of the hepatic cytochrome P450 superfamily. Therefore, its usage with other PI medications leads to significant increases in the levels of the latter PI, which allows a reduction in pill burden. Intranasal and inhaled corticosteroids are widely used for the treatment of allergic rhinitis and asthma. Inhaled steroids do not usually lead to systemic adverse events, since their plasma concentrations are quite low due to extensive first-pass metabolism and clearance by CYP3A4. However, the coadministration of Ritonavir with inhaled (or intranasal) corticosteroids may result in an increase in the plasma corticosteroid levels due to the potent CYP3A4 inhibition by Ritonavir. This may cause Cushing's syndrome (laboratory and clinical) with adrenal suppression.

METHODS

Plasma cortisol and urinary-free cortisol levels were determined using immunoassays. In the Synacthen test, plasma cortisol levels were measured at time 0 as well as at times 60, 120, and 150 minutes following an intramuscular injection of 0.25 mg Synacthen.

RESULTS

We present here three HIV-1 female patients aged 12, 55 and 65 years who developed iatrogenic Cushing's syndrome with adrenal suppression following the coadministration of Ritonavir and inhaled Fluticasone, both at the standard recommended doses.

CONCLUSIONS

The coadministration of Ritonavir and Fluticasone at the recommended doses caused, in our three patients, iatrogenic Cushing's syndrome with adrenal suppression. We suggest that this adverse event is underdiagnosed and high clinical suspicion is needed for early diagnosis and prenention of Addisonian crises. Thus, Fluticasone treatment should be avoided in patients who are treated with Ritonavir. Alternative therapeutic options for asthma control such as oral Montelukast or bronchodilators alone should be considered.

96-Week Efficacy and Safety of Atazanavir, With and Without Ritonavir, in a HAART Regimen in Treatment-Naive Patients

This study assesses virologic response, safety, tolerability, and changes in health-related quality of life (HRQoL) in antiretroviral (ARV)-naive patients treated with 2 atazanavir (ATV)-based regimens over 96 weeks. Treatment-naive adult patients (n = 200) were randomized to receive either ATV 300 mg with ritonavir (RTV) 100 mg (ATV300/r, n = 95) or ATV 400 mg (ATV400; n = 105). At week 96, 75% of ATV300/r-treated and 70% of ATV400-treated patients achieved viral loads <400 copies/mL (difference estimate [95% confidence interval, CI] = 5.1 [-7.1 to 17.2]). Five and 20 patients, respectively, experienced virologic failure. Adverse event-related discontinuations occurred among 8% receiving ATV300/r and 3% receiving ATV400. Plasma lipid elevations were generally low. Both regimens were well tolerated and associated with sustained improvements in HRQoL. These findings demonstrate long-term efficacy, tolerability, and safety of both ATV300/r and ATV400 in ARV-naive patients through 96 weeks with improvements in HRQoL.

Atazanavir pharmacokinetics in genetically determined CYP3A5 expressors versus non-expressors

OBJECTIVES

The objective of this study was to compare atazanavir pharmacokinetics in genetically determined CYP3A5 expressors versus non-expressors.

METHODS

HIV-negative adult volunteers were pre-screened for CYP3A5 *3, *6 and *7 polymorphisms and enrollment was balanced for CYP3A5 expressor status, gender and race (African-American versus non-African-American). Participants received atazanavir 400 mg daily for 7 days followed by atazanavir/ritonavir 300 mg/100 mg daily for 7 days with pharmacokinetic studies on days 7 and 14. Other measures collected were bilirubin, UGT1A1 *28, and ABCB1 1236C > T, 2677G > T/A and 3435C > T genotypes. Data analyses utilized least squares regression.

RESULTS

Fifteen CYP3A5 expressors and 16 non-expressors participated. The day 7 atazanavir oral clearance (CL/F) was 1.39-fold faster (0.25 versus 0.18 L/h/kg; P = 0.045) and the C(min) was half (87 versus 171 ng/mL; P = 0.044) in CYP3A5 expressors versus non-expressors. Non-African-American CYP3A5 expressor males had 2.1-fold faster CL/F (P = 0.003) and <20% the C(min) (P = 0.0001) compared with non-African-American non-expressor males. No overall CYP3A5 expressor effects were observed during the ritonavir phase. One or two copies of wild-type ABCB1 haplotype (1236C/2677G/3435C) was predictive of slower atazanavir and ritonavir CL/F compared with zero copies (P < 0.06). Indirect bilirubin increased 1.6- to 2.8-fold more in subjects with UGT1A1 *28/*28 versus *1/*28 or *1/*1.

CONCLUSIONS

CYP3A5 expressors had faster atazanavir CL/F and lower C(min) than non-expressors. The effect was most pronounced in non-African-American men. Ritonavir lessened CYP3A5 expressor effects. The wild-type ABCB1 CGC haplotype was associated with slower CL/F and the UGT1A1 *28 genotype was associated with increased bilirubin. Thus, CYP3A5, ABCB1 and UGT1A1 polymorphisms are associated with atazanavir pharmacokinetics and pharmacodynamics in vivo.

Therapeutic drug monitoring of antiretrovirals for people with HIV

BACKGROUND

Despite the efficacy of combination antiretroviral therapy (ART) and the improvement in prognosis of those living with HIV/AIDS, a large proportion of individuals on ART does not achieve or maintain adequate virological suppression. Several tools have been proposed to enhance ART outcomes, including therapeutic drug monitoring (TDM) of antiretrovirals (ARVs). The aim of ARV TDM is to identify elevated (potentially toxic) or low (potentially sub-therapeutic) ARV concentrations. ARV TDM may thus optimise efficacy and minimise toxicity of ART.

OBJECTIVES

To evaluate whether ARV TDM reduces mortality and morbidity of adult patients on ART. The primary outcome measures that have been assessed include death (all cause); occurrence of HIV-related events (death or AIDS-defining illness) and the proportion of patients achieving and maintaining an undetectable viral load, as defined by the authors.

SEARCH STRATEGY

We conducted a comprehensive search including both published and unpublished studies in all languages in MEDLINE, EMBASE and The Cochrane Library, between January 1980 and January 2008. Databases listing conference abstracts and reference lists of articles were searched. Additional data were sought from relevant authors; however, no additional data were provided.

SELECTION CRITERIA

Only randomized controlled trials conducted subsequent to the introduction of combination ART were included in this systematic review. Participants could be on either a protease inhibitor (PI)-based regimen or non-nucleoside reverse transcriptase (NNRTI)-based regimen and be either ARV-naive or -experienced.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed and extracted data for analysis. Meta-analysis was conducted where appropriate. Where study outcomes could not be combined, a narrative review was performed. Outcome measures for dichotomous data were reported as a relative risk with 95% confidence intervals. Stratified analyses were conducted by ARV regimen and treatment groups. Heterogeneity between studies was anticipated; therefore, random effects models were chosen to generate pooled effects. Differences in the findings were assessed by the chi square test for heterogeneity (p <0.1) that was quantified by the Higgins I(2) statistic.

MAIN RESULTS

Identified were 1408 records, and eight trials with a total of 1181 participants were included in the review. Trials were conducted in higher income earning countries between 2002 and 2007. Sample sizes ranged between 40 and 230. The methodological quality of the studies was judged to be generally good, although allocation concealment was reported in only three of the eight studies. A meta-analysis including three studies did not show any significant effect on virological suppression below 500 HIV-RNA copies/mL at one year (RR 1.28; [0.86, 1.92] chi(2) = 11.55 (P = 0.003), I(2) = 83%). Two trials including participants predominantly treated with unboosted PI-based regimens reported a 49% increased likelihood of achieving a HIV-RNA viral load below 500 copies/mL at 52 weeks (RR 1.49 [1.20, 1.83] chi(2) = 0.69 (P = 0.4), I(2) = 0%). Safety outcomes were reported in four studies and were similar between TDM and standard of care. Uptake of expert advice based on TDM results was good in two trials (>70%), but low (<35%) in the remaining three studies that reported uptake of the recommendations.

AUTHORS' CONCLUSIONS

Our review does not support routine use of ARV TDM in ARV-naive or -experienced patients on either boosted PI or NNRTI ART regimens. TDM in treatment-naive participants on a PI-based ART regimen, particularly if unboosted by ritonavir, may improve virological outcomes. Trials were underpowered with small sample sizes, short durations of follow-up and generally poor uptake of TDM recommendations. As these trials were conducted in higher income earning countries, results may not be generalisable to resource-limited countries where the burden of HIV is heaviest.

Ritonavir and dexamethasone induce expression of CYP3A and P-glycoprotein in rats

1. The consequences of extended exposure to the human immunodeficiency viral protease inhibitor ritonavir (RIT) on the expression and function of CYP3A isoforms in the liver and in enteric mucosal cells, and on the expression of the efflux transport protein P-glycoprotein (P-gp) in enteric mucosa and in brain microvessel endothelial cells, were evaluated in rat. Dexamethasone (DEX), a known inducer of CYP3A and P-gp in rodents, served as a positive control. 2. Male CD-1 rats received RIT (20 mg kg(-1)), DEX (80 mg kg(-1)) or vehicle by oral/duodenal gavage once daily for 3 days. 3. Compared with vehicle control, CYP3A activity in liver microsomes (intrinsic clearance for triazolam hydroxylation in vitro) was increased by a factor of 2-4 by RIT, and by 10-14-fold by DEX. Similar increases were observed in expression of immunoactive CYP3A protein. Overall, maximum reaction velocity and immunoactive protein were highly intercorrelated (r2 = 0.89). Both RIT and DEX also increased function and expression of enteric CYP3A, although to a more modest extent (about 1.7-fold for RIT, about 3.3-fold for DEX). 4. Enteric P-gp expression was equally induced (by 2.8-fold) by both RIT and DEX. P-gp expressed in brain microvessel endothelial cells was increased by a factor of 1.3 by both compounds. 5. Thus, increased expression of CYP3A isoforms and of P-gp occurs with 3 days of exposure to RIT in rats. Qualitatively similar changes occur in human cell culture models and in clinical studies, and might contribute to drug interactions involving RIT (and other antiretroviral agents) in humans.

Effects of CYP3A4 inhibitors on the pharmacokinetics of maraviroc in healthy volunteers

AIMS

To evaluate the influence of cytochrome P450 (CYP) 3A4 inhibitors on the clinical pharmacokinetics of maraviroc, a novel CCR5 antagonist.

METHODS

Four open-label, randomized, placebo-controlled studies were conducted in healthy subjects to assess the effect of separate and distinct combinations of CYP3A4 inhibitors on the steady-state pharmacokinetics of maraviroc. Study 1 was a two-way crossover study investigating the influence of saquinavir (SQV; 1200 mg t.i.d.) and ketoconazole (400 mg q.d.) on the pharmacokinetics of maraviroc (100 mg b.i.d.). All subjects received maraviroc for 7 days in both study periods. Cohort 1 subjects also received SQV or placebo and cohort 2 subjects also received ketoconazole or placebo. Study 2 was a parallel-group study including four treatment groups investigating the effects of ritonavir-boosted lopinavir (LPV/r; 400 mg/100 mg b.i.d.), ritonavir-boosted saquinavir (SQV/r; 1000 mg/100 mg b.i.d.), and low-dose ritonavir (RTV; 100 mg b.i.d.) on the steady-state pharmacokinetics of maraviroc (100 mg b.i.d.), and exploring whether maraviroc dose adjustment can compensate for interaction effects. Treatment lasted 28 days and comprised three distinct phases: (i) maraviroc alone on days 1-7; (ii) maraviroc + interactant on days 8-21; and (iii) maraviroc (adjusted dose) + interactant on days 22-28. Study 3 was a two-way crossover study investigating the effects of atazanavir (ATZ; 400 mg q.d.) and ritonavir-boosted atazanavir (ATZ/r; 300 mg/100 mg b.i.d.) on the pharmacokinetics of maraviroc (300 mg b.i.d.). All subjects received maraviroc on days 1-14 of both study periods. Subjects also received ATZ on days 1-7 and ATZ/r on days 8-14 of one treatment period, and placebo on days 1-14 of the other treatment period. Study 4 was a two-way crossover study investigating the effects of ritonavir-boosted tipranavir (TPV/r; 500 mg/200 mg b.i.d.) on the pharmacokinetics of maraviroc (150 mg b.i.d.). Subjects received maraviroc plus TPV/r or placebo on days 1-8.

RESULTS

All of the drugs/drug combinations tested (except for TPV/r) increased maraviroc exposure, albeit to different degrees of magnitude. SQV/r caused the largest increase in maraviroc exposure (8.3-fold increase in AUC(tau)), whereas RTV caused the smallest increase in maraviroc exposure (2.6-fold increase in AUC(tau)). Downward adjustment of the maraviroc dose in study 2 during co-administration of HIV protease inhibitors was able to compensate for the interactions. TPV/r had no clinically relevant effect on maraviroc exposure at steady state. There were no treatment-related serious adverse events or discontinuations due to adverse events in any of the studies, and most adverse events were mild or moderate in severity and resolved without intervention.

CONCLUSIONS

Potent CYP3A4 inhibitors, including ketoconazole and protease inhibitors (except TPV/r), increase maraviroc exposure. Downward adjustment of the maraviroc dose during co-administration with protease inhibitors can compensate for the interaction. TPV/r does not affect the steady-state pharmacokinetics of maraviroc, and hence no dose adjustment would be warranted.

Effect of low-dose ritonavir on the pharmacokinetics of the CXCR4 antagonist AMD070 in healthy volunteers

AMD070, a CXCR4 antagonist, has demonstrated antiretroviral activity in human immunodeficiency virus-infected patients. Since AMD070 is a substrate of cytochrome P450 3A4 and P-glycoprotein, both of which may be affected by ritonavir, we tested for a ritonavir effect on AMD070 pharmacokinetics. Subjects were given a single 200-mg dose of AMD070 on days 1, 3, and 17. Ritonavir (100 mg every 12 h) was dosed from day 3 to day 18. Blood samples to test for AMD070 concentrations were collected over 48 h after each administration of AMD070. Twenty-three male subjects were recruited. Among them, 21 completed the study, and 2 were discontinued for reasons other than safety. All adverse events were grade 2 or lower. AMD070 alone had the following pharmacokinetic features, given as medians (ranges): 3 h (0.5 to 4 h) for the time to peak blood concentration, 256 ng/ml (41 to 845 ng/ml) for the peak concentration (C(max)), 934 h x ng/ml (313 to 2,127 h x ng/ml) for the area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)), 214 liters/h (94 to 639 liters/h) for apparent body clearance, and 4,201 liters (1,996 to 9,991 liters) for the apparent volume of distribution based on the terminal phase. The initial doses of ritonavir increased the C(max) of AMD070 [geometric mean (90% confidence interval)] by 39% (3 to 89%) and the AUC(0-infinity) by 60% (29 to 100%). After 14 days of ritonavir dosing, the pharmacokinetic changes in AMD070 persisted. The plasma pharmacokinetics of ritonavir were consistent with previous reports. It is concluded that AMD070 concentrations were increased with concomitant ritonavir dosing for 14 days in healthy volunteers.

An examination of the effect of intestinal first pass extraction on intestinal lymphatic transport of saquinavir in the rat

PURPOSE

To assess the impact of intestinally based efflux/elimination processes on the extent of intestinal lymphatic transport of saquinavir. To compare the relative effects of co-administration of P-gp/CYP modulators on intestinal lymphatic transport versus systemic bioavailability of saquinavir.

METHODS

A cremophor mixed micelle formulation of saquinavir alone, or co-administered with P-gp/CYP modulators, verapamil, ketoconazole or cyclosporine, was dosed intraduodenally in the mesenteric lymph duct cannulated anaesthetized rat model.

RESULTS

Co-administration of P-gp/CYP modulators resulted in significant increases in the extent of intestinal lymphatic transport of saquinavir. A comparison of the relative enhancement of lymphatic transport and plasma bioavailability compared to control (i.e. saquinavir alone) reveals a greater effect of verapamil and ketoconazole on the amount of drug transported by the lymphatic route, an observation consistent with a preferential targeting of saquinavir via the intestinal lymphatics. In contrast co-administration of cyclosporine increased both the extent of lymphatic transport (5.5-fold), and systemic bioavailability (4.1-fold).

CONCLUSIONS

Intestinal P-gp/CYP efflux/elimination restricts saquinavir transport via the intestinal lymphatics in the rat. Targeted increases in intestinal lymphatic levels of saquinavir may be achieved by selective inhibition of intestinal P-gp and/or CYP.

Induction of P-glycoprotein expression and activity by ritonavir in bovine brain microvessel endothelial cells

Extended treatment with human immunodeficiency virus (HIV) protease inhibitors (HPIs) is standard in HIV/AIDS therapy. While these drugs have helped decrease the overall incidence of AIDS defining illnesses, the relative prevalence of HIV/AIDS dementia has increased. HPIs may cause induction of blood-brain barrier (BBB) drug transporters (P-glycoprotein; P-gp) and thereby limit entry of HPIs into brain tissue, increasing the probability that the brain could become an HIV sanctuary site. Using bovine brain microvessel endothelial cells (BMEC) as an in-vitro model of the BBB, the potential for the HIV protease inhibitor ritonavir to cause induction of P-gp activity and expression was examined. BMEC were isolated from fresh cow brain by enzymatic digest and density centrifugation. Primary culture BMEC were co-incubated with ritonavir or vehicle control for 120 h. Quantitative drug accumulation of rhodamine 123 (Rh123) and fluorescence microscopy were used as measures of P-gp activity. P-gp expression was assessed using quantitative Western blotting. Ritonavir decreased Rh123 cell accumulation and increased P-gp immunoreactive protein in a concentration-dependent manner. Fluorescent microscopy mirrored Rh123 quantitative studies. In BMEC pretreated with 30 microM ritonavir, Rh123 accumulation was decreased 40% and immunoreactive P-gp protein increased 2-fold. Collectively, a strong correlation between decreased Rh123 BMEC accumulation and increased P-gp immunoreactive protein was observed (Spearman r2 = 0.77, P < 0.0001). Thus extended exposure of BMEC to ritonavir caused a concentration-dependent increase in P-gp activity and expression. Similar findings may occur at the clinical level with prolonged HIV protease inhibitor use, giving insight into the central nervous system as an HIV sanctuary site and eventual development of HIV dementia.

Review: immunologic response to protease inhibitor-based highly active antiretroviral therapy: a review

A substantial body of evidence indicates that CD4 cell count is an important independent prognostic indicator for progression of HIV disease. Consequently, in addition to plasma HIV RNA levels, CD4 cell count change is considered to be a key surrogate marker for disease progression in clinical practice and in clinical studies. Given the relationship between changes in CD4 count and disease progression, it is notable that protease inhibitor (PI)-based highly active antiretroviral therapy (HAART) can rapidly increase CD4 cell count early in treatment in both therapy-naïve and -experienced patients, and can sustain clinically relevant levels beyond 24 weeks. A number of trials with a follow-up of more than 3 years allow us to conclude that the gains in CD4 counts are maintained in a durable manner. This review evaluated randomized studies of PI-based and PI-boosted HAART (published between January 1996 and February 2006) to determine the effect of PI-based therapy on CD4 cell count. Only studies that assessed CD4 response in the overall patient population were included. Four mechanisms have been proposed to account for the rapid increase in CD4 cell count that occurs with HAART: CD4 cell redistribution from lymphatic tissues, increased CD4 cell production, reduction of apoptotic CD4 cells and the recovery of hematopoietic activity in bone marrow. Further research is required to clarify the relative importance of these mechanisms and ways in which they might be enhanced.

Pharmacogenetic Considerations in the Management of HIV Infection

Potent combination antiretroviral drug therapy has now been available to HIV-infected patients for more than a decade, resulting in a significant decline in disease-related morbidity and mortality. Nonetheless, a number of HIV-infected individuals fail to experience the full benefit of their antiretroviral medications; some lack a robust virologic response, while others experience treatment-limiting toxicities. A number of factors may contribute to variable drug response in patients with HIV infection. Virologic, immunologic, pharmacologic, and pharmacokinetic differences between HIV-infected patients have all been noted to contribute to interpatient variability in drug response. Recent data suggest that pharmacogenetic differences among HIV-infected individuals may also be an important variable that contributes to antiretroviral drug response. Pharmacogenetic studies of antiretroviral drug therapy have explored the influence of single nucleotide polymorphisms in genes responsible for key proteins involved in antiretroviral drug metabolism (cytochrome P50 enzymes) and drug transport (P-glycoprotein). In addition, the human leukocyte antigen genotype (HLA-B*57) has been found to predict abacavir-associated hypersensitivity reactions. Antiretroviral pharmacogenetics offers the possibility of optimizing virologic response and minimizing drug toxicity by individualizing anti-HIV pharmacotherapy. The authors review those genetic polymorphisms that have been shown, or are strongly suspected, to influence antiretroviral drug metabolism, transport, and toxicity.

Ritonavir-Boosted Protease Inhibitors: Impact of Ritonavir on Toxicities in Treatment-Experienced Patients

The purpose of this review is to discuss the basis for ritonavir boosting of protease inhibitors as well as the complications and benefits associated with ritonavir boosting when designing an antiretroviral regimen for treatment-experienced patients. Such patients have fewer viable options because of cross-resistance arising from previous regimen failures. Ritonavir administered at a low dose to boost another protease inhibitor may be a useful strategy for achieving virological efficacy while minimizing the toxicities associated with full-dose ritonavir. There may be an increased risk of adverse events associated with increased plasma concentration of the concurrent protease inhibitor. Still, the incidence of these adverse events is generally low, and clinical trials have suggested that they rarely result in discontinuation or alteration of the regimen. In highly treatment-experienced patients in particular, the potential benefits associated with ritonavir boosting usually outweigh the risks.

Intracellular delivery of saquinavir in biodegradable polymeric nanoparticles for HIV/AIDS

PURPOSE

This study aims at developing poly(ethylene oxide)-modified poly(epsilon-caprolactone) (PEO-PCL) nanoparticulate system as an intracellular delivery vehicle for saquinavir, an anti-HIV protease inhibitor.

MATERIALS AND METHODS

Saquinavir-loaded PEO-PCL nanoparticles were prepared by a solvent displacement process. The formed nanoparticles were characterized for size, surface charge, and surface presence of PEO chains. Cellular uptake and distribution of the nanoparticle was examined in THP-1 human monocyte/macrophage (Mo/Mac) cell line. Intracellular saquinavir concentrations were measured as a function of dose and duration of incubation.

RESULTS

The PEO-PCL nanoparticles had a smooth surface and spherical shape and showed a relatively uniform size distribution with a mean particle diameter of approximately 200 nm. The surface presence of PEO chains was confirmed by an increase in the -C-O-(ether) signature of the C1s spectra in electron spectroscopy for chemical analysis. Rapid cellular uptake of rhodamine-123 encapsulated PEO-PCL nanoparticles was observed in THP-1 cells. Intracellular saquinavir concentrations when administered in the nanoparticle formulation were significantly higher than from aqueous solution.

CONCLUSIONS

This study shows that PEO-PCL nanoparticles provide a versatile platform for encapsulation of saquinavir and subsequent intracellular delivery in Mo/Mac cells.

Effect of Quercetin on the Plasma and Intracellular Concentrations of Saquinavir in Healthy Adults

STUDY OBJECTIVES

To determine if quercetin, a bioflavonoid that inhibits p-glycoprotein, alters plasma saquinavir concentrations, and to explore the potential influence on intracellular concentrations.

DESIGN

Prospective pharmacokinetic analysis.

SETTING

University-affiliated general clinical research center.

SUBJECTS

Ten healthy adults (four women, six men) with a mean +/- SD age of 30.7 +/- 9.4 years.

INTERVENTION

All subjects received saquinavir 1200 mg 3 times/day with food on days 1-11 and quercetin 500 mg 3 times/day with food on days 4-11.

MEASUREMENTS AND MAIN RESULTS

On days 4 and 11, nine blood samples and four peripheral blood mononuclear cell samples were drawn during a steady-state dosing interval. Pharmacokinetic parameters were calculated by using standard noncompartmental techniques. Plasma saquinavir concentrations were similar regardless of quercetin administration. Geometric mean ratios for the area under the concentration-time curve during an 8-hour dosing interval (AUC0-8), maximum concentration in the dosing interval, and minimum concentration in the dosing interval were 0.99 (95% confidence interval [CI] 0.65-1.50), 0.99 (95% CI 0.64-1.54), and 1.06 (95% CI 0.68-1.67), respectively. Intracellular saquinavir concentrations displayed substantial intra- and intersubject variability, which limited the ability to determine the influence of quercetin coadministration (geometric mean ratio for AUC0-8 = 0.51 [95% CI 0.14-1.95], six patients).

CONCLUSION

Quercetin coadministration did not influence plasma saquinavir concentrations. Because of substantial inter- and intrasubject variability, more study is necessary to determine if saquinavir intracellular concentrations are altered by coadministration of quercetin.

Pharmacogenetic characteristics of indinavir, zidovudine, and lamivudine therapy in HIV-infected adults: a pilot study

OBJECTIVE

The aim of the study was to investigate relationships among indinavir, lamivudine-triphosphate, and zidovudine-triphosphate pharmacokinetics and pharmacodynamics with polymorphisms in CYP3A5, MDR1, MRP2, MRP4, BCRP, and UGT1A1 genes.

STUDY DESIGN

Retrospective pilot investigation among 33 subjects who participated in a randomized pharmacological study of indinavir, lamivudine, and zidovudine. Subjects were defined as genetic variant carriers or not. Relationships were investigated with multivariable regression. Indinavir clearance was adjusted for African American race; triphosphates for sex; and HIV-response for study arm, drug exposure, and baseline HIV-RNA.

RESULTS

Genetically determined CYP3A5 expressors had 44% faster indinavir oral clearance versus nonexpressors (P = 0.002). MRP2-24C/T variant carriers had 24% faster indinavir oral clearance (P = 0.05). Lamivudine-triphosphate concentrations were elevated 20% in MRP4 T4131G variant carriers (P = 0.004). A trend for elevated zidovudine-triphosphates was observed in MRP4 G3724A variant carriers (P = 0.06). The log10 changes in HIV-RNA from baseline to week 52 were -3.7 for MDR1 2677 TT, -3.2 for GT, and -2.2 for GG (P < 0.05). Bilirubin increases were 2-fold higher in UGT1A1 [TA]7/[TA]7 genotypes. No relationships were identified with BCRP.

DISCUSSION

Novel relationships were identified among genetic variants in drug transporters and indinavir, lamivudine-triphosphate, and zidovudine-triphosphate concentrations. CYP3A5 expression was associated with faster indinavir oral clearance. These pilot data provide a scientific basis for more rational utilization of antiretroviral drugs.

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.

Metabolism of amyloid beta peptide and pathogenesis of Alzheimer's disease. Towards presymptomatic diagnosis, prevention and therapy

The conversion of what has been interpreted as "normal brain aging" to Alzheimer's disease (AD) via a transition state, i.e. mild cognitive impairment, appears to be a continuous process caused primarily by aging-dependent accumulation of amyloid beta peptide (Abeta) in the brain. This notion give us a hope that, by manipulating the Abeta levels in the brain, we may be able not only to prevent and cure the disease but also to partially control some very significant aspects of brain aging. Abeta is constantly produced from its precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Abeta seems to lead to pathological deposition upon aging. We have focused our attention on elucidation of the unresolved mechanism of Abeta catabolism in the brain. In this review, we describe a new approach to prevent AD development by reducing Abeta burdens in aging brains through up-regulation the catabolic mechanism involving neprilysin that can degrade both monomeric and oligomeric forms of Abeta. The strategy of combining presymptomatic diagnosis with preventive medicine seems to be the most pragmatic in both medical and socio-economical terms. We also introduce a novel non-invasive amyloid imaging approach using a high-power magnetic resonance imaging (MRI) for the presymptomatic diagnosis of AD.

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.

In vitro inhibition of UDP glucuronosyltransferases by atazanavir and other HIV protease inhibitors and the relationship of this property to in vivo bilirubin glucuronidation

Several human immunodeficiency virus (HIV) protease inhibitors, including atazanavir, indinavir, lopinavir, nelfinavir, ritonavir, and saquinavir, were tested for their potential to inhibit uridine 5'-diphospho-glucuronosyltransferase (UGT) activity. Experiments were performed with human cDNA-expressed enzymes (UGT1A1, 1A3, 1A4, 1A6, 1A9, and 2B7) as well as human liver microsomes. All of the protease inhibitors tested were inhibitors of UGT1A1, UGT1A3, and UGT1A4 with IC(50) values that ranged from 2 to 87 microM. The IC50 values found for all compounds for UGT1A6, 1A9, and 2B7 were >100 microM. The inhibition (IC50) of UGT1A1 was similar when tested against the human cDNA-expressed enzyme or human liver microsomes for atazanavir, indinavir, and saquinavir (2.4, 87, and 7.3 microM versus 2.5, 68, and 5.0 microM, respectively). By analysis of the double-reciprocal plots of bilirubin glucuronidation activities at different bilirubin concentrations in the presence of fixed concentrations of inhibitors, the UGT1A1 inhibition by atazanavir and indinavir was demonstrated to follow a linear mixed-type inhibition mechanism (Ki = 1.9 and 47.9 microM, respectively). These results suggest that a direct inhibition of UGT1A1-mediated bilirubin glucuronidation may provide a mechanism for the reversible hyperbilirubinemia associated with administration of atazanavir as well as indinavir. In vitro-in vivo scaling with [I]/Ki predicts that atazanavir and indinavir are more likely to induce hyperbilirubinemia than other HIV protease inhibitors studied when a free Cmax drug concentration was used. Our current study provides a unique example of in vitro-in vivo correlation for an endogenous UGT-mediated metabolic pathway.

Atazanavir trough plasma concentration monitoring in a cohort of HIV-1-positive individuals receiving highly active antiretroviral therapy

OBJECTIVES

Atazanavir is a recently approved HIV protease inhibitor (PI). As with other PIs, careful attention to potential pharmacokinetic drug interactions in clinical practice is necessary. The aim of this study was to assess the clinical associations with plasma atazanavir concentrations in HIV-positive individuals.

METHODS

Individuals established on an atazanavir-containing regimen, completed an interviewer-administered questionnaire recording atazanavir dosing characteristics, concomitant medication use and adherence. After completion, plasma atazanavir concentrations were measured.

RESULTS

Of 100 individuals, mean trough plasma atazanavir concentrations (mug/L) were 282 (95% CI 95-468, n = 19) and 774 (95% CI 646-902, n = 81) in those on non- and ritonavir-boosted atazanavir regimens, respectively. Eighty-five individuals had HIV RNA <50 copies/mL. Seven individuals had atazanavir plasma concentrations below the assay limit of detection (<50 microg/L), all of whom had undetectable plasma HIV RNA. In a multivariate analysis, nevirapine use was associated with significantly lower trough atazanavir concentrations (P = 0.011) and lopinavir/ritonavir use with higher trough atazanavir concentrations (P = 0.032). Dosing characteristics (including food taken), concomitant medications (including drugs used for dyspepsia) and HIV RNA were not significantly associated with trough atazanavir concentrations.

CONCLUSIONS

In this cohort, despite the wide inter-individual variability of atazanavir trough concentrations, no significant association with dosing characteristics, concomitant medication (with the exception of nevirapine and lopinavir/ritonavir) or virological response was observed. Further work is needed to assess the optimal dosing regimen when using atazanavir with nevirapine.

Drug interactions in the management of HIV infection

The availability of antiretroviral therapy has significantly reduced the morbidity and mortality of HIV infection. In addition, improved treatment of opportunistic infections and comorbidities common to patients with HIV is further prolonging the lives of patients. Improvement in the treatment of HIV has led to a significant increase in the number of medications which caregivers are able to utilise to manage HIV/AIDS. Antiretroviral medications, as well as many of the drugs used in the management of opportunistic infections and primary care (e.g., macrolide antibiotics, azole antifungals, cholesterol-lowering medications), are particularly prone to drug interactions. The interpretation of clinically significant interactions is complicated by the rate at which new information on drug metabolism and transport is becoming available. Management of drug interactions in HIV is further confounded by conflicting study results and differences between documented and theoretical inter-actions. The mechanisms and significance of interactions involving antiretrovirals, drugs used for opportunistic infections, and other medications commonly used in HIV patients will be reviewed.

Pharmacokinetics of indinavir and ritonavir administered at 667 and 100 milligrams, respectively, every 12 hours compared with indinavir administered at 800 milligrams every 8 hours in human immunodeficiency virus-infected patients

Human immunodeficiency virus (HIV) patients on nucleoside or nucleotide reverse transcriptase inhibitors with HIV RNA at <1,000 copies/ml were randomized in an open-label study to administration of combined indinavir/ritonavir (IDV/RTV) at 667/100 mg every 12 h (q12h) or IDV alone at 800 mg q8h to determine the regimens' pharmacokinetics. On day 14, plasma IDV and RTV levels were determined over 24 h. Noncompartmental pharmacokinetics (minimum concentration of drug in serum [C(min)], area under the concentration-time curve from 0 to 24 h [AUC(0-24)], and maximum concentration of drug in serum [C(max)]) were expressed as geometric mean values with 90% confidence intervals (CI). The primary hypothesis was that the lower bound of the protocol-specified 90% CI for the geometric mean C(min) ratio of the combination compared to IDV alone regimen would be >/=2. Twenty-seven patients were enrolled, and 24 (15 male; average age, 42 years) completed the study. The C(min), AUC(0-24), and C(max) for IDV/RTV compared to IDV alone were 1,511 versus 250 nM, 119,557 versus 77,034 nM . h, and 10,428 versus 10,407 nM, respectively. Corresponding relationships for IDV/RTV compared to IDV alone were a 6.0-fold increase in C(min) (90% CI, 4.0, 9.3), an increase in AUC(0-24) (1.5-fold, 90% CI, 1.2, 2.0), and no increase in C(max). Adverse events were similar and generally mild, with no cases of nephrolithiasis. The geometric mean ratio of IDV C(min) for IDV/RTV compared to IDV was at least 2 by a lower bound of the 90% CI, satisfying the primary hypothesis. The C(max) was not increased, suggesting an IDV/RTV 667/100-mg toxicity profile may be similar to that of unboosted IDV.

High-performance liquid chromatography assay for the quantification of HIV protease inhibitors and non-nucleoside reverse transcriptase inhibitors in human plasma

An accurate, sensitive, and specific reverse-phase high-performance liquid chromatography (HPLC) assay for the simultaneous quantitative determination of HIV-protease inhibitors (PIs) (indinavir, IDV; amprenavir, APV; saquinavir, SQV; nelfinavir, NFV; ritonavir, RTV; and lopinavir, LPV) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) (nevirapine, NVP; delavirdine, DLV; and efavirenz, EFV) in human blood plasma is described. The method provides excellent resolution and peak shape for nine analytes through a linear gradient (36-86%) of 25% phosphate buffer (pH 4.5), 60% acetonitrile, 15% methanol, and 0.75 ml TFA, with a gradient mobile phase flow rate (0.9-1.1 ml) over 30 min run time. The optimized solid phase extraction (SPE) extraction method using (1.0 ml, 100mg BOND ELUT-C18 Varian) column provides a clean base line and high extraction efficiency using a 550 microl plasma sample. The method was validated over the range of 10-10,000 ng/ml for NVP, IDV, and SQV; 10-5000 ng/ml for EFV; 25-10000 ng/ml for APV; and 25-5000 ng/ml for DLV, NFV, RTV, and LPV. This method is accurate (average accuracies of three different concentrations ranged from 91 to 112%), and precise (within- and between-day precision measures ranged from 0.2 to 5.7% and 0.1 to 5.4%, respectively). This method is suitable for use in clinical pharmacokinetic studies as well as in therapeutic drug monitoring (TDM).

Lopinavir/ritonavir vs. indinavir/ritonavir in antiretroviral naive HIV-infected patients: immunovirological outcome and side effects

We compared immunovirological outcomes and toxicities of HAART regimens including LPV/r and IDV/r in antiretroviral naïve HIV-1 patients. We retrospectively selected 55 patients starting LPV/r and 52 starting IDV/r as first-line HAART. Immunovirological and metabolic parameters were recorded at baseline and every 3 months as were side effects, AIDS-defining events and deaths. Demographic characteristics and NRTIs included in the regimens were comparable. Both groups reached undetectable HIV-RNA plasma viremia from third month and maintained during follow-up. However, patients receiving IDV/r had a lower probability to obtain virological success (RH: 0.46). Patients receiving IDV/r patients showed a greater increase of total cholesterol (P = 0.01). Three patients on LPV/r and 21 on IDV/r discontinued the drug for toxicity, leading to a 8.40 higher risk of discontinuation in the latter group. In our clinical setting IDV/r showed to be less effective and more toxic than LPV/RTV as first-line HAART.

Once-Daily Dosing of Saquinavir Soft-Gel Capsules and Ritonavir Combination in HIV-1-Infected Patients (Imea015 Study)

This was a prospective pilot study evaluating a saquinavir (SQV) soft-gel capsules (SGC)/ritonavir (RTV)-containing once-daily regimen over a follow-up of 3 months. The primary end-point was to determine the number of patients both remaining on treatment at month 3 and with trough SQV plasma concentration 24 h after the last intake (C24h) exceeding the inhibition of 95% of viral replication in vitro (IC95). The secondary end-points were to investigate the immuno-virological efficacy and safety of SQV-SGC/RTV once daily, and to explore SQV concentrations in peripheral blood mononuclear cells (PBMCs). Twenty-three antiretroviral-naive and 17 protease inhibitors (PIs) experienced HIV-1-infected patients with plasma HIV-1 RNA level below 200 copies/ml were enrolled. They were assigned to SQV-SGC/RTV (1600/100 mg once daily) combined with nucleoside and/or non-nucleoside reverse transcriptase inhibitors. In a subgroup of 13 patients, both plasma and intracellular SQV concentrations were determined. By intent to treat analysis the percentage of success at month 3 was 87.5% (confidence interval: 73.2–95.8%) with 78.3% in naive and 100% in PI-experienced patients. SQV C24h and intracellular concentrations [median (range, n)] were 241 ng/ml (40–1209, 35) and 323 ng/ml (168–475, 12), respectively. Intracellular concentrations showed an accumulation of SQV in PBMCs persisting during 24 h. Neither immunological nor virological failure was observed. Clinical and biological tolerance was acceptable in all patients but three with adverse effects leading to discontinuation. These data confirmed the short-term efficacy of SQV-SGC/RTV once-daily regimen based on SQV therapeutic drug monitoring.

This work was presented in part at the 2nd International Conference on Clinical Pharmacology of HIV Infection, Noordwijk, the Netherlands, 2-4 April 2001 (Abstract 3.16); and at the 1st International Conference on HIV Pathogenesis & Treatment, Buenos Aires, Argentina, 8–11 July 2001 (Abstract 344).