Pharmacodynamics of human immunodeficiency virus type 1 protease inhibitors

Comparison of Tolerability and Impact on Metabolic Profiles of Antiretroviral Regimens Containing Darunavir/Ritonavir or Darunavir/Cobicistat in Romanian HIV Infected Patients

The management of the side effects caused by the antiretroviral therapy is one of the main problems facing clinicians. The patient’s tolerability and safety influence the success of the therapy. This retrospective study assesses the tolerability and impact on metabolic profiles of antiretroviral regimens containing darunavir/ritonavir (DRV/r) versus those containing darunavir/cobicistat (DRV/c), in routine clinical practice. The database of Prof. Dr Matei Bals of the National Institute of Infectious Diseases (INBI MB) was studied for the period 2017–2020, allowing the inclusion in the study of 462 HIV-infected patients who received the current regimen at least three months before evaluation. The following parameters were collected and analyzed: significant medical history, associated diseases, serum levels for profile evaluation: carbohydrate, lipidic, serum level of liver and pancreatic enzymes, serum markers of cardiac function, coagulation, and renal function. DRV/c (800 mg/150 mg, once daily) administrated in combination with other antiretroviral (ARV) in HIV-1 infected subjects proved to be better tolerated and with a lower impact on metabolic profile than DRV/r (600 mg/100 mg, twice daily). Patients in DRV/r group are significantly more at risk of developing, over time, side effects and metabolic impairments than those in DRV/c group, in all body functions studied, with statistically significant differences (p < 0.05) between the two groups. Laboratory data were correlated with patient’s demographic and clinical characteristics and statistically significant outcomes have been found, proving that a personalized regimen is needed to minimize the ART side effects and to maximize the success of therapy. The results of the study showed that DRV/c, associated with other antiretroviral drugs in the regimens of Romanian HIV infected subjects, have a more favorable metabolic profile than those containing DRV/r.

Repurposing Saquinavir for Host-Directed Therapy to Control Mycobacterium Tuberculosis Infection

Despite the available antibiotics, tuberculosis (TB) has made its return since the 90’s of the last century as a global threat mostly due to co-infection with HIV, to the emergence of drug resistant strains and the lack of an effective vaccine. Host-directed strategies could be exploited to improve treatment efficacy, contain drug-resistant strains, improve immune responses and reduce disease severity. Macrophages in the lungs are often found infected with Mycobacterium tuberculosis (Mtb) and/or with HIV. The long-term survival of lung macrophages infected with Mtb or with HIV, together with their ability to produce viral particles, especially during TB, makes these niches major contributors to the pathogenicity of the infection. Among the available drugs to control HIV infection, protease inhibitors (PIs), acting at post-integrational stages of virus replication cycle, are the only drugs able to interfere with virus production and release from macrophages during chronic infection. For Mtb we recently found that the pathogen induces a general down-regulation of lysosomal proteases, helping bacteria to establish an intracellular niche in macrophages. Here we found that the PI saquinavir, contrary to ritonavir, is able to induce an increase of endolysosomal proteases activity especially of cathepsin S in Mtb infected macrophages and during co-infection with HIV. Our results indicate that saquinavir treatment of infected macrophages led not only to a significant intracellular killing of Mtb but also: (i) to an improved expression of the HLA class II antigen presentation machinery at the cell surface; (ii) to increased T-lymphocyte priming and proliferation; and (iii) to increased secretion of IFN-γ. All together the results indicate saquinavir as a potential host directed therapy for tuberculosis.

Management of Antiretroviral Therapy with Boosted Protease Inhibitors-Darunavir/Ritonavir or Darunavir/Cobicistat

A major challenge in the management of antiretroviral therapy (ART) is to improve the patient's adherence, reducing the burden caused by the high number of drugs that compose the treatment regimens for human immunodeficiency virus positive (HIV+) patients. Selection of the most appropriate treatment regimen is responsible for therapeutic success and aims to reduce viremia, increase the immune system response capacity, and reduce the incidence rate and intensity of adverse reactions. In general, protease inhibitor (PI) is one of the pillars of regimens, and darunavir (DRV), in particular, is frequently recommended, along with low doses of enzyme inhibitors as cobicistat (COBI) or ritonavir (RTV), by the international guidelines. The potential of clinically significant drug interactions in patients taking COBI or RTV is high due to the potent inhibitory effect on cytochrome CYP 450, which attracts significant changes in the pharmacokinetics of PIs. Regardless of the patient or type of virus, the combined regimens of DRV/COBI or DRV/RTV are available to clinicians, proving their effectiveness, with a major impact on HIV mortality/morbidity. This study presents current information on the pharmacokinetics, pharmacology, drug interactions, and adverse reactions of DRV; it not only compares the bioavailability, pharmacokinetic parameters, immunological and virological responses, but also the efficacy, advantages, and therapeutic disadvantages of DRV/COBI or DRV/RTV combinations.

Benefits and Limits of Antiretroviral Drug Monitoring in Routine Practice

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Relationship between untimed plasma lopinavir concentrations and virological outcome on second-line antiretroviral therapy

BACKGROUND

Resource constraints in low and middle-income countries necessitate practical approaches to optimizing antiretroviral therapy outcomes. We hypothesised that an untimed plasma lopinavir concentration (UPLC) at week 12 would predict loss of virological response in those taking lopinavir as part of a second-line antiretroviral regimen.

METHODS

We measured plasma lopinavir concentration at week 12 on stored samples from the SECOND-LINE study. We characterized UPLC as: detectable and optimal (≥1000 μg/l); detectable but suboptimal (≥25 to < 1000 μg/l); and undetectable (<25 μg/l). We used Cox regression to explore the relationship between UPLC and loss of virological response over 48 weeks and backwards stepwise logistic regression to explore the relationship between UPLC and other predictors of virological failure at week 48.

RESULTS

At week 48, we observed virological failure in 15/32 (47%) and 53/485 (11%) of patients with undetectable and detectable UPLC, respectively, P < 0.001. Both suboptimal [adjusted hazard ratio (HR) 2.94; 95% confidence interval (CI) 1.54-5.62; P = 0.001], and undetectable (adjusted HR 3.55; 95% CI 1.89-6.64; P < 0.001) UPLC were associated with higher rates of loss of virological response over 48 weeks. In multivariate analysis, an independent association with virological failure at week 48 and undetectable UPLC was observed after adjustment (odds ratio 5.48; 95% CI 2.23-13.42; P < 0.01).

CONCLUSION

In low and middle-income countries implementing a public health approach to antiretroviral therapy treatment, an untimed plasma drug concentration may provide a practical method for early identification of patients with inadequate medication adherence and facilitate timely corrective interventions to prevent virological failure.

Concomitant medication polypharmacy, interactions and imperfect adherence are common in Australian adults on suppressive antiretroviral therapy

OBJECTIVES

We quantified concomitant medication polypharmacy, pharmacokinetic and pharmacodynamic interactions, adverse effects and adherence in Australian adults on effective antiretroviral therapy.

DESIGN

Cross-sectional.

METHODS

Patients recruited into a nationwide cohort and assessed for prevalence and type of concomitant medication (including polypharmacy, defined as ≥5 concomitant medications), pharmacokinetic or pharmacodynamic interactions, potential concomitant medication adverse effects and concomitant medication adherence. Factors associated with concomitant medication polypharmacy and with imperfect adherence were identified using multivariable logistic regression.

RESULTS

Of 522 participants, 392 (75%) took a concomitant medication (mostly cardiovascular, nonprescription or antidepressant). Overall, 280 participants (54%) had polypharmacy of concomitant medications and/or a drug interaction or contraindication. Polypharmacy was present in 122 (23%) and independently associated with clinical trial participation, renal impairment, major comorbidity, hospital/general practice-based HIV care (versus sexual health clinic) and benzodiazepine use. Seventeen participants (3%) took at least one concomitant medication contraindicated with their antiretroviral therapy, and 237 (45%) had at least one pharmacokinetic/pharmacodynamic interaction. Concomitant medication use was significantly associated with sleep disturbance and myalgia, and polypharmacy of concomitant medications with diarrhoea, fatigue, myalgia and peripheral neuropathy. Sixty participants (12%) reported imperfect concomitant medication adherence, independently associated with requiring financial support, foregoing necessities for financial reasons, good/very good self-reported general health and at least 1 bed day for illness in the previous 12 months.

CONCLUSION

In a resource-rich setting with universal healthcare access, the majority of this sample took a concomitant medication. Over half had at least one of concomitant medication polypharmacy, pharmacokinetic or pharmacodynamic interaction. Concomitant medication use was associated with several adverse clinical outcomes.

The HIV protease inhibitor, nelfinavir, as a novel therapeutic approach for the treatment of refractory pediatric leukemia

PURPOSE

Refractory pediatric leukemia remains one of the leading causes of death in children. Intensification of current chemotherapy regimens to improve the outcome in these children is often limited by the effects of drug resistance and cumulative toxicity. Hence, the search for newer agents and novel therapeutic approaches are urgently needed to formulate the next-generation early-phase clinical trials for these patients.

MATERIALS AND METHODS

A comprehensive library of antimicrobials, including eight HIV protease inhibitors (nelfinavir [NFV], saquinavir, indinavir, ritonavir, amprenavir, atazanavir, lopinavir, and darunavir), was tested against a panel of pediatric leukemia cells by in vitro growth inhibition studies. Detailed target modulation studies were carried out by Western blot analyses. In addition, drug synergy experiments with conventional and novel antitumor agents were completed to identify effective treatment regimens for future clinical trials.

RESULTS

Several of the HIV protease inhibitors showed cytotoxicity at physiologically relevant concentrations (half-maximal inhibitory concentration values ranging from 1-24 µM). In particular, NFV was found to exhibit the most potent antileukemic properties across all cell lines tested. Mechanistic studies show that NFV leads to the induction of autophagy and apoptosis possibly through the induction of endoplasmic reticulum stress. Furthermore, interference with cell signaling pathways, including Akt and mTOR, was also noted. Finally, drug combination studies have identified agents with potential for synergy with NFV in its antileukemic activity. These include JQ1 (BET inhibitor), AT101 (Bcl-2 family inhibitor), and sunitinib (TK inhibitor).

CONCLUSION

Here, we show data demonstrating the potential of a previously unexplored group of drugs to address an unmet therapeutic need in pediatric oncology. The data presented provide preclinical supportive evidence and rationale for future studies of these agents for refractory leukemia in children.

A model incorporating combined RTIs and PIs therapy during early HIV-1 infection

We develop a within host mathematical model of HIV-1 infection describing the effects of combined RTIs and PIs treatments on early HIV-1 infection when treatment is captured using periodic functions of pharmacokinetics type. We use an alternative of the basic reproduction number to analyze endemicity level of HIV-1 infection. Various treatment scenarios incorporating perfect and imperfect drug adherence in drug administration are explored. Our results show that pharmacokinetics treatment is a more realistic way of administering the treatment. Apart from confirming that PIs drugs are more effective than RTIs drugs and that combined RTIs and PIs therapy is more effective than monotherapy of RTIs or PIs, our results show that imperfect drug adherence leads to the increase of viral in the absence of mutation even though the drug is good.

Therapeutic drug monitoring of antiretroviral drugs in HIV-infected patients

INTRODUCTION

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

HIV Protease Inhibitor-Induced Cathepsin Modulation Alters Antigen Processing and Cross-Presentation

Immune recognition by T cells relies on the presentation of pathogen-derived peptides by infected cells, but the persistence of chronic infections calls for new approaches to modulate immune recognition. Ag cross-presentation, the process by which pathogen Ags are internalized, degraded, and presented by MHC class I, is crucial to prime CD8 T cell responses. The original degradation of Ags is performed by pH-dependent endolysosomal cathepsins. In this article, we show that HIV protease inhibitors (PIs) prescribed to HIV-infected persons variably modulate cathepsin activities in human APCs, dendritic cells and macrophages, and CD4 T cells, three cell subsets infected by HIV. Two HIV PIs acted in two complementary ways on cathepsin hydrolytic activities: directly on cathepsins and indirectly on their regulators by inhibiting Akt kinase activities, reducing NADPH oxidase 2 activation, and lowering phagolysosomal reactive oxygen species production and pH, which led to enhanced cathepsin activities. HIV PIs modified endolysosomal degradation and epitope production of proteins from HIV and other pathogens in a sequence-dependent manner. They altered cross-presentation of Ags by dendritic cells to epitope-specific T cells and T cell-mediated killing. HIV PI-induced modulation of Ag processing partly changed the MHC self-peptidome displayed by primary human cells. This first identification, to our knowledge, of prescription drugs modifying the regulation of cathepsin activities and the MHC-peptidome may provide an alternate therapeutic approach to modulate immune recognition in immune disease beyond HIV.

Sequence-specific alterations of epitope production by HIV protease inhibitors

Ag processing by intracellular proteases and peptidases and epitope presentation are critical for recognition of pathogen-infected cells by CD8+ T lymphocytes. First-generation HIV protease inhibitors (PIs) alter proteasome activity, but the effect of first- or second-generation PIs on other cellular peptidases, the underlying mechanism, and impact on Ag processing and epitope presentation to CTL are still unknown. In this article, we demonstrate that several HIV PIs altered not only proteasome but also aminopeptidase activities in PBMCs. Using an in vitro degradation assay involving PBMC cytosolic extracts, we showed that PIs altered the degradation patterns of oligopeptides and peptide production in a sequence-specific manner, enhancing the cleavage of certain residues and reducing others. PIs affected the sensitivity of peptides to intracellular degradation, and altered the kinetics and amount of HIV epitopes produced intracellularly. Accordingly, the endogenous degradation of incoming virions in the presence of PIs led to variations in CTL-mediated killing of HIV-infected cells. By altering host protease activities and the degradation patterns of proteins in a sequence-specific manner, HIV PIs may diversify peptides available for MHC class I presentation to CTL, alter the patterns of CTL responses, and provide a complementary approach to current therapies for the CTL-mediated clearance of abnormal cells in infection, cancer, or other immune disease.

Pharmacokinetic optimization of antiretroviral therapy in pregnancy

Antiretroviral therapy suppresses replication of HIV allowing restoration and/or preservation of the immune system. Providing combination antiretroviral therapy during pregnancy can treat maternal HIV infection and/or reduce perinatal HIV transmission. However, providing treatment to pregnant women is challenging due to physiological changes that can alter antiretroviral pharmacokinetics. Suboptimal drug exposure can result in HIV RNA rebound, the selection of resistant virus or an increased risk of HIV-1 transmission to the infant. Increased drug exposure can produce unwarranted maternal adverse effects and/or fetal toxicity. Subsequently, dose adjustments may be necessary during pregnancy to achieve comparable antiretroviral exposure to non-pregnant adults. For several antiretrovirals, systemic exposure is decreased during the last trimester of pregnancy. By 6-12 weeks postpartum, concentrations return to those prior to pregnancy. Also, the extent of antiretroviral placental transfer to the fetus and degree of antiretroviral excretion into breast milk varies within, and between, antiretroviral drug classes. It is necessary to consider the pharmacological characteristics of each antiretroviral when optimizing combination therapy during pregnancy to treat maternal HIV infection and prevent perinatal HIV transmission.

Pharmacokinetic study of saquinavir 500 mg plus ritonavir (1000/100 mg twice a day) in HIV-positive pregnant women

Antiretroviral therapy during pregnancy is critical to preventing human immunodeficiency virus vertical transmission. Physiological changes during pregnancy can alter drug kinetics. The aim of this study was to assess the pharmacokinetics (PK) of saquinavir (SQV) boosted with ritonavir during pregnancy and postpartum. Fourteen human immunodeficiency virus-positive pregnant women started SQV 500 mg new tablet formulation plus ritonavir at a dose of 1000/100 mg twice a day + 2 nucleoside retrotranscriptase inhibitors during pregnancy. At weeks 24 and 34 of pregnancy and 6 weeks postpartum, a 12-hour PK study was conducted. PK parameters were calculated using Win Nolin software version 4.1. At week 24, the geometric mean values for SQV area under the plasma concentration-time curve from 0-12 hours (AUC₀₋₁₂), the maximum observed plasma concentration (C(max)), trough plasma concentration (C(min)), and the elimination half-life (t(1/2)) were 24.80 mg·h⁻¹·mL⁻¹, 4.66 mg/mL, 0.93 mg/mL, and 4.31 hours, respectively. At week 34, AUC₀₋₁₂, C(max), C(min), and t(1/2) were 12.71 mg·h⁻¹·mL⁻¹, 3.23 mg/mL, 0.26 mg/mL, and 4.06 hours, respectively. Finally, at 6 weeks postpartum, mean values for SQV AUC₀₋₁₂, C(max), C(min), and t(1/2) were 28.94 mg·h⁻¹·mL⁻¹, 3.92 mg/mL, 0.86 mg/mL, and 3.60 hours, respectively. Although PK parameters in week 24 and postpartum were very similar, those for week 34 showed an important reduction: -71.20%, -30.61%, -48.73%, and -5.81% in C(min), C(max), AUC₀₋₁₂, and t(1/2), respectively, compared with week 24, but no statistically significant differences were shown between patients. No vertical transmissions were reported. Therapeutic drug monitoring of SQV during pregnancy should be considered, mainly during the third trimester, to ensure adequate drug exposure throughout the entire pregnancy.

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

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

[Evidence-based therapeutic drug monitoring for indinavir]

The HIV protease inhibitor indinavir presents a wide inter-individual variability related to an intense hepatic metabolism. Published studies were analyzed to establish whether there is evidence that therapeutic drug monitoring of indinavir could improve patient care. It was reported that indinavir virological efficacy in HIV-infected patients with wild-type virus was significantly associated with trough concentrations > 100-150 ng/mL. Concerning the exposure-toxicity relationship, the risk of occurrence of nephrotoxicity was more frequently associated with trough concentrations > 500-1 000 ng/mL. Studies with concentration-controlled indinavir therapy suggest that therapeutic drug monitoring allows to achieve safe and effective concentrations, therefore, the level of evidence of the interest of indinavir therapeutic drug monitoring is highly recommended when indinavir is not associated with ritonavir and recommended when ritonavir is combined with ritonavir.

Pentacycloundecane-based inhibitors of wild-type C-South African HIV-protease

In this study, we present the first account of pentacycloundecane (PCU) peptide based HIV-protease inhibitors. The inhibitor exhibiting the highest activity made use of a natural HIV-protease substrate peptide sequence, that is, attached to the cage (PCU-EAIS). This compound showed nanomolar IC(50) activity against the resistance-prone wild type C-South African HIV-protease (C-SA) catalytic site via a norstatine type functional group of the PCU hydroxy lactam. NMR was employed to determine a logical correlation between the inhibitory concentration (IC(50)) results and the 3D structure of the corresponding inhibitors in solution. NMR investigations indicated that the activity is related to the chirality of the PCU moiety and its ability to induce conformations of the coupled peptide side chain. The results from docking experiments coincided with the experimental observed activities. These findings open up useful applications for this family of cage peptide inhibitors, considering the vast number of alternative disease related proteases that exist.

Pharmacologic and nonpharmacologic options for the management of HIV infection during pregnancy

Over the past decade, significant advances have been made in the treatment of HIV-1 infection using both pharmacologic and nonpharmacologic strategies to prevent mother-to-child transmission (MTCT). Optimal prevention of the MTCT of HIV requires antiretroviral drugs (ARV) during pregnancy, during labor, and to the infant. ARVs reduce viral replication, lowering maternal plasma viral load and thus the likelihood of MTCT. Postexposure prophylaxis of ARV agents in newborns protect against infection following potential exposure to maternal HIV during birth. In general, the choice of an ARV for treatment of HIV-infected women during pregnancy is complicated by the need to consider the effectiveness of the therapy for the maternal disease as well as the teratogenic or teratotoxic potential of these drugs. Clinicians managing HIV in pregnancy need to discuss the potential risks and benefits of available therapy options so that mothers can make informed decisions in choosing the best treatment regimen for themselves and for their children.

Pharmacokinetics and therapeutic drug monitoring of antiretrovirals in pregnant women

Highly active antiretroviral therapy is recommended for HIV-infected pregnant women to prevent mother-to-child transmission. The specific physiological background induced by pregnancy leads to significant changes in maternal pharmacokinetics, suggesting potential variability in plasma concentrations of antiretrovirals during gestation. Therapeutic drug monitoring (TDM) of protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs) is recommended in certain situations, including pregnancy, but its systematic use in HIV-infected pregnant women remains controversial. This review provides an update of the pharmacokinetic data available for PIs and NNRTIs in pregnant women and highlights the clinical interest of systematic TDM of certain antiretroviral drugs during pregnancy, including nevirapine, nelfinavir, saquinavir, indinavir and lopinavir.

Maintenance of indinavir by dose adjustment in HIV-1-infected patients with indinavir-related toxicity

OBJECTIVE

Treatment with indinavir/ritonavir (IDV/RTV) is very effective but hampered by frequent development of IDV-associated adverse events (mainly nephrotoxicity and skin changes). We tested whether dose reduction of IDV guided by therapeutic drug monitoring resulted in improved tolerability without compromising antiviral efficacy.

PATIENTS

HIV-infected patients with any IDV/RTV regimen who suffer from IDV-related adverse events were included. Viral load had to be adequately controlled for at least 2 months prior to inclusion. Dose reduction from 800 mg to 600 or 400 mg IDV b.i.d. followed a specified protocol. IDV-related toxicity and IDV plasma concentrations were monitored for 24 weeks. IDV concentrations were quantified with a validated high performance liquid chromatography method.

RESULTS

Twenty patients were included. Reasons for inclusion were: skin abnormalities 11, nephrotoxicity five, metabolic disturbances three, and hypertension one. IDV dose could be lowered to 400 mg b.i.d. in 13, to 600 mg b.i.d. in two patients. Five patients discontinued the treatment. Overall tolerability improved with respect to incidence and severity of adverse events. Median trough concentrations decreased from 1.02 mg/l (range 0.08-7.1) at baseline to 0.48 mg/l (0.11-1.4) after 24 weeks (p = 0.03) and remained above the critical threshold of 0.1 mg/l at any time after dose reduction. There was no change of CD4 cell counts or viral suppression. There were no significant changes in other laboratory parameters (creatinine, bilirubin, triglycerides, cholesterol, blood count, and urinalysis).

CONCLUSION

Dose reduction of IDV improved tolerability of IDV-containing highly active antiretroviral treatment (HAART). Sufficient IDV trough concentrations were maintained in all patients as was virologic control.

Steady-state pharmacokinetic and safety profiles of voriconazole and ritonavir in healthy male subjects

Since there is a likelihood of coadministration of voriconazole and ritonavir, two studies were conducted to evaluate the potential of drug interaction. Study A was a randomized, placebo-controlled, two-period, parallel-group trial (n = 34). Study B had the same design without the placebo group (n = 17). In period 1, subjects received 200 mg voriconazole or placebo twice daily (BID) for 3 days (400 mg BID on day 1). In period 2, following a 7-day washout, subjects received ritonavir alone at 400 mg BID (study A) or 100 mg BID (study B) for 10 days (days 11 to 20), and then ritonavir was coadministered with 200 mg BID voriconazole or placebo for the next 10 days (days 21 to 30). Serial plasma samples were collected on days 3, 20, and 30, and safety data were collected throughout the study. High-dose (400 mg BID) ritonavir substantially reduced the steady-state mean voriconazole exposure (area under the concentration-time curve from 0 to 12 h [AUC(0-12)], -82%; maximum concentration [C(max)], -66%). However, the effect of low-dose (100 mg BID) ritonavir was less pronounced (AUC(0-12), -39%; C(max), -24%). The decrease in voriconazole exposure was probably due to the induction of CYP2C19 and CYP2C9 by ritonavir. It is interesting that one subject in each study exhibited the opposite effect of ritonavir on voriconazole exposure (a 2.5- to 3-fold increase), probably due to lack of CYP2C19. Voriconazole had no apparent effect on the exposure of high-dose ritonavir but slightly decreased the exposure of low-dose ritonavir (AUC(0-12), -14%; C(max), -24%). The safety profile of combination therapy was not notably different from that of voriconazole or ritonavir alone. Due to the significant effect of ritonavir on voriconazole exposure, coadministration of voriconazole with 400 mg BID ritonavir is contraindicated; coadministration with 100 mg BID ritonavir should be avoided, unless an assessment of the benefit/risk to the patient justifies the use.

HIV-infected patients receiving lopinavir/ritonavir-based antiretroviral therapy achieve high rates of virologic suppression despite adherence rates less than 95%

BACKGROUND

The observation that extremely high levels of medication adherence are required to achieve complete virologic suppression is based largely on studies of treatment-experienced patients receiving HIV protease inhibitor (PI)-based therapy without ritonavir boosting. This study aims to define the level of adherence needed to achieve virologic suppression in patients receiving boosted PI-based highly active antiretroviral therapy (HAART) with lopinavir/ritonavir.

METHODS

HIV-infected adults receiving a regimen containing lopinavir/ritonavir were recruited into a prospective, observational study of the relation between adherence to lopinavir/ritonavir and virologic outcomes. Adherence was measured using the Medication Event Monitoring System (MEMS; Aardex, Union City, CA). HIV-1 viral load (VL) was measured at week 24.

RESULTS

The final study population contained 64 subjects. Eighty percent had AIDS, 97% received lopinavir/ritonavir before enrollment, and most had more than 7 years of HAART experience. Mean adherence overall was 73%. Eighty percent and 59% achieved a VL <400 copies/mL and a VL <75 copies/mL, respectively. Mean adherence was 75% in those achieving a VL <75 copies/mL. High rates of virologic suppression were observed in all adherence quartiles, including the lowest quartile (range of adherence: 23.5%-53.3%).

CONCLUSIONS

Moderate levels of adherence can lead to virologic suppression in most patients taking lopinavir/ritonavir-based HAART.

Efficacy of Low-Dose Boosted Saquinavir Once Daily Plus Nucleoside Reverse Transcriptase Inhibitors in Pregnant HIV-1-Infected Women With a Therapeutic Drug Monitoring Strategy

The efficacy of low-dose, ritonavir-boosted saquinavir (SQV/rtv) once daily plus 2 nucleoside retrotranscriptase inhibitors (NRTIs) in pregnant human immunodeficiency virus (HIV)-1-infected women was prospectively evaluated, ensuring a SQV minimum concentration (Cmin) >/=100 ng/mL with a therapeutic drug monitoring strategy. The primary clinical endpoint was the percentage of women with an HIV-RNA viral load (VL) of <50 copies/mL at the time of delivery. Forty-nine pregnancy episodes were included, with a median CD4 count and VL of 441/muL and 3710 copies/mL, respectively. Two patients were lost to follow-up and 1 patient discontinued treatment because of abdominal discomfort. SQV levels were in excess of the target Cmin in 43 of 46 episodes (93.4%) in which the end of pregnancy was reached on 1200/100 mg daily. The dosage was increased to 1600/100 mg in the remaining 3 episodes to achieve the target levels. By an intention-to-treat analysis, VL was undetectable at delivery in 43 episodes (87.7%; 95% confidence interval, 78.5-96.9) after a median of 18 weeks of treatment (range, 3-39). In the 3 episodes remaining, VLs of 110,400 copies/mL and no available data were observed after only 3 weeks of treatment. Mild adverse events attributable to SQV/rtv occurred in 6 of 49 pregnancies (12.2%). No cases of HIV vertical transmission were observed. The pharmacokinetics, efficacy, and tolerability of this regimen suggest that once-daily low-dose boosted SQV may be considered an appropriate option in PI-naive or limited-PI-experienced HIV-infected pregnant women. Nevertheless, therapeutic drug monitoring is advisable to maintain appropriate levels throughout pregnancy.

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

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

Successful treatment with atazanavir and lopinavir/ritonavir combination therapy in protease inhibitor-susceptible and protease inhibitor-resistant HIV-infected patients

The combination of atazanavir (ATV) plus lopinavir/ritonavir (LPV/r) has been used in practice. However, clinical data supporting its use are limited. The objective of this study was to evaluate the efficacy and tolerability of regimens with ATV + LPV/r in protease inhibitor (PI)-susceptible and PI-resistant patients. A retrospective review of 2703 charts was performed to identify all patients who received ATV + LPV/r. From June 2003 to January 2005, 33 patients received ATV + LPV/r with nucleoside reverse transcriptase inhibitors (NRTIs) for 3 months or more. Virologic success (HIV-RNA < 400 copies per milliliter) was achieved in 30 patients (91%) in a median of 10 weeks (range, 2-68). Nineteen of the 23 patients (83%) who had ultrasensitive viral load (VL) assays were nondetectable. Among patients with 6 or more protease resistance (PR) mutations (PI-resistant), 11 of 14 (79%) achieved virologic success. Eleven of those received phenotypic testing (10 Virtual Phenotype, VircoLab, Baltimore, MD). Despite predicted phenotypic resistance to ATV (6 patients) and LPV/r (7 patients), virologic success was achieved in 4 of 6 (67%) and 4 of 7 (57%), respectively. The 3 PI-resistant patients who were virologic failures had extensive prior LPV/r use, 8-11 PR mutations, and predicted phenotypic resistance to LPV/r, but 2 of 3 had CD4 increases with ATV + LPV/r. Overall, 28 patients (85%) continue to tolerate ATV + LPV/r for a median of 32 weeks follow-up (range, 12-76). Combination ATV + LPV/r with NRTIs appears safe, tolerable, and efficacious in PI-resistant patients (>/=6 PR mutations) and predicted phenotypic resistance to ATV and LPV/r. Further studies of ATV + LPV/r in HIV-treatment are warranted.

Microwave-accelerated synthesis of P1'-extended HIV-1 protease inhibitors encompassing a tertiary alcohol in the transition-state mimicking scaffold

Two series of P1'-extended HIV-1 protease inhibitors comprising a tertiary alcohol in the transition-state mimic exhibiting Ki values ranging from 2.1 to 93 nM have been synthesized. Microwave-accelerated palladium-catalyzed cross-couplings were utilized to rapidly optimize the P1' side chain. High cellular antiviral potencies were encountered when the P1' benzyl group was elongated with a 3- or 4-pyridyl substituent (EC50 = 0.18-0.22 microM). X-ray crystallographic data were obtained for three inhibitors cocrystallized with the enzyme.

Simple and sensitive high-performance liquid chromatography method for the quantitation of indinavir in rat plasma and central nervous system

A simple and sensitive RP-HPLC method using UV detection (215 nm) was developed for the determination of indinavir concentrations in rat plasma, cerebrospinal fluid (CSF), and brain tissue homogenates. Biological samples were processed using a combination of acid pretreatment and liquid-liquid extraction with verapamil used as the internal standard. This method produced a linear response throughout the indinavir concentration range of 0.05-30 microM in plasma and 0.05-2.5 microM in CSF and brain with a LOD of 12.5 nM for plasma and CSF, and 6.25 nM for brain homogenate. Due to its high sensitivity, this assay is particularly useful for the quantitative determination of indinavir concentrations in brain and CSF.

Adherence-resistance relationships for protease and non-nucleoside reverse transcriptase inhibitors explained by virological fitness

OBJECTIVE

To compare the prevalence of resistance by adherence level in patients treated with non-nucleoside reverse transcriptase inhibitors (NNRTI) or protease inhibitors (PI). Also to examine the mechanism of differential class-specific adherence-resistance relationships, focusing on the patient-derived capacity of wild-type and drug-resistant recombinant variants to replicate in vitro in the presence of variable drug levels.

METHODS

Participants received unannounced pill count measures to assess adherence, viral load monitoring, and genotypic resistance testing. The replicative capacity of drug-susceptible and drug-resistant recombinants was determined using a single-cycle recombinant phenotypic susceptibility assay. Drug exposure was estimated using population-averaged pharmacological measurements adjusted by participant-specific levels of adherence.

RESULTS

In the NNRTI-treated group, 69% had resistance at 0-48% adherence compared to 13% at 95-100% (P = 0.01). PI resistance was less common than NNRTI resistance at 0-48% adherence (69% versus 23%; P = 0.01). In multivariate analysis, the odds for PI resistance increased (P = 0.03) while the odds for NNRTI resistance decreased (P = 0.04) with improving adherence. Individuals with drug-resistant variants were more likely to have levels of drug exposure where the resistant variant was more fit than the drug-susceptible variant in vitro, while those with drug-susceptible virus were more likely to have levels of drug exposure where the drug-susceptible virus was more fit than the drug-resistant variant (P = 0.005).

CONCLUSIONS

NNRTI resistance was more common than PI resistance at low levels of adherence. Class-specific adherence-resistance relationships are associated with the relative replicative capacity of drug-resistant versus wild-type variants to replicate in the presence of clinically relevant drug levels.

Pharmacokinetics of antiretroviral therapy in HIV-1-infected children

The initiation of antiretroviral therapy has resulted in an impressive reduction in the rate of disease progression in AIDS and HIV-1-related deaths in children; however, there are still several major challenges to be faced in order to improve therapy. A major topic that needs to be dealt with is the establishment of the optimal dosage of antiretroviral therapy for children. This review presents the currently available peer-reviewed data on the pharmacokinetics of nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs) and fusion inhibitors (FIs) in children. In addition, the data are discussed in relation to the currently available European and US guidelines and the US FDA-approved drug labels. High intra- and interpatient variability in pharmacokinetics are often observed for all antiretroviral drugs. The number of children included in the pharmacokinetic studies is often small and children are often divided into divergent groups using different dosage levels and/or drug formulations. For a substantial number of antiretroviral drugs, dosage recommendations, especially for young children, are still absent in the European and US guidelines. The recommended drug dosages in the guidelines are often different from that in the officially approved drug product label. In addition, the recommended drug dosages may deviate between the European and US guidelines. Thus, while practioners aim to meet the recommendations in the official guidelines, patients may receive highly divergent dosages of medication. The high intra- and interpatient variability in pharmacokinetics of antiretroviral drugs in children hampers the application of fixed dosages of antiretroviral drugs. For PIs and NNRTIs, plasma drug levels correlate with viral suppression and drug toxicity. NRTIs are prodrugs that are intracellularly converted to their active triphosphate form and, therefore, plasma NRTI levels correlate poorly with viral suppression. Therapeutic drug monitoring of PIs and NNRTIs should be considered to optimise HIV therapy in children.

Tenofovir disoproxil fumarate and an optimized background regimen of antiretroviral agents as salvage therapy for pediatric HIV infection

OBJECTIVES

Highly active antiretroviral therapy has altered the course of HIV infection among children, but new antiretroviral agents are needed for treatment-experienced children with drug-resistant virus. Tenofovir disoproxil fumarate (DF) is a promising agent for use in pediatric salvage therapy, because of its tolerability, efficacy, and resistance profile. We designed this study to provide preliminary pediatric safety and dosing information on tenofovir DF, while also providing potentially efficacious salvage therapy for heavily treatment-experienced, HIV-infected children.

METHODS

Tenofovir DF, alone and in combination with optimized background antiretroviral regimens, was studied among 18 HIV-infected children (age range: 8.3-16.2 years) who had progressive disease with > or = 2 prior antiretroviral regimens, in a single-center, open-label trial. Tenofovir DF monotherapy for 6 days was followed by the addition of individualized antiretroviral regimens. Subjects were monitored with HIV RNA reverse transcription-polymerase chain reaction, flow cytometry, and routine laboratory studies; monitoring for bone toxicity included measurement of lumbar spine bone mineral density (BMD) with dual-energy x-ray absorptiometry. Subjects were monitored through 48 weeks.

RESULTS

Two subjects developed grade 3 elevated hepatic transaminase levels during monotherapy and were removed from the study. The remaining 16 subjects had a median of 4 antiretroviral agents (range: 3-5 agents) added to tenofovir DF. HIV plasma RNA levels decreased from a median pretreatment level of 5.4 log10 copies per mL (range: 4.1-5.9 log10 copies per mL) to 4.21 log10 copies per mL at week 48 (n = 15), with 6 subjects having < 400 copies per mL, including 4 with < 50 copies per mL. The overall median increases in CD4+ T cell counts were 58 cells per mm3 (range: -64 to 589 cells per mm3) at week 24 and 0 cells per mm3 (range: -274 to 768 cells per mm3) at week 48. The CD4+ cell responses among the virologic responders were high and sustained. The major toxicity attributed to tenofovir DF was a >6% decrease in BMD for 5 of 15 subjects evaluated at week 48, necessitating the discontinuation of tenofovir DF therapy for 2; all 5 subjects experienced >2 log10 copies per mL decreases in HIV plasma RNA levels.

CONCLUSIONS

Tenofovir DF-containing, individualized, highly active antiretroviral therapy regimens were well tolerated and effective among heavily treatment-experienced, HIV-infected children. Loss of BMD may limit tenofovir DF use among prepubertal patients.

Comparison of two indinavir/ritonavir regimens in the treatment of HIV-infected individuals

BACKGROUND

Pharmacokinetic enhancement of protease inhibitors (PIs) with low-dose ritonavir (RTV) for salvage therapy is increasingly common. The purpose of this study was to compare the pharmacokinetics, safety, and tolerability of indinavir (IDV)/RTV at 800/200 mg (arm A) and 400/400 mg (arm B) administered twice daily in HIV-infected subjects failing their first PI-based regimen.

METHODS

A phase I/II, randomized, open-label, 24-week study was conducted. Formal 12-hour pharmacokinetic evaluations were performed, and study visits occurred at baseline; at weeks 1, 2, and 4; and every 4 week thereafter for 24 weeks. Clinical symptoms and laboratory assessments were collected. Subjects were allowed to switch arms because of toxicity.

RESULTS

Forty-four subjects were enrolled (22 per arm). IDV predose concentration, maximum plasma concentration and area under the curve were significantly higher in arm A. Fifty-five percent and 45% of subjects in arms A and B responded (<200 copies/mL at week 24; P = 0.76), respectively. CD4 cell responses were similar. All subjects had IDV-sensitive virus at baseline and at virologic failure. Tolerability was comparable, but all grade 3 or higher triglyceride increases occurred in arm B and more subjects in arm B switched because of toxicity (5 vs. 1 triglyceride increases).

CONCLUSIONS

This is the largest formal pharmacokinetic evaluation of 2 dosage combinations of IDV/RTV in HIV-infected individuals. Pharmacokinetic parameters were consistent with previous results in patients but lower than in seronegative controls. Both regimens exhibited similar tolerability and response rates. High toxicity with a low response suggests that the optimum IDV/RTV combination would include an RTV dose <400 mg and an IDV dose <800 mg in this population.

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.

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.

Effects of the human immunodeficiency virus-protease inhibitor, ritonavir, on basal and catecholamine-stimulated lipolysis

Several of the aspartic acid protease inhibitors used to treat HIV infection increase basal lipolysis in adipocytes, but the cellular mechanisms leading to this augmentation are not well understood. We therefore studied the effects of chronic exposure to the HIV protease inhibitor, ritonavir, on the lipolytic cascade in 3T3-L1 adipocytes. Treatment of 3T3-L1 adipocytes with ritonavir for 14 d (during and after differentiation) enhanced basal, isoproterenol (Iso)-stimulated, and cAMP analog-stimulated lipolysis. Enhancement of lipolysis was observed after Iso at concentrations between 0.1 and 10 mum. Despite a significant decrease in cyclic nucleotide phosphodiesterase (PDE)3B activity and protein levels, there were no changes in Iso-stimulated intracellular cAMP, protein kinase A (PKA) expression, or PKA activity. Ritonavir-augmented lipolysis was also observed under conditions that reversed the effect on PDE3B activity via preincubation with 1 mum (-)-N(6)-(2-phenylisopropyl)adenosine. In ritonavir-treated cells, protein expression of the lipid droplet-protective protein, perilipin, was significantly decreased, whereas there was no change in hormone-sensitive lipase. Activation of ERK1/2 by Iso did not play a role in the augmentation. We conclude that ritonavir decreases PDE3B and perilipin protein expression and affects both basal and catecholamine-stimulated lipolysis in 3T3-L1 adipocytes primarily through actions at sites downstream of PKA.

Determination of indinavir and nelfinavir trough plasma concentration efficacy thresholds according to virological response in HIV-infected patients

BACKGROUND

There is evidence to suggest a pharmacokinetic-pharmacodynamic relationship in HIV-infected patients receiving protease inhibitor (PI)-containing highly active antiretroviral therapy (HAART); however, the effective trough PI plasma concentrations achieved have not been precisely determined.

METHODS

The relationship between HIV viral load and concomitant PI trough plasma concentration (C(trough)) was evaluated in 101 patients receiving at least 4 months of thrice daily indinavir (IDV)-containing (n=68) or nelfinavir (NFV)-containing (n=33) HAART. The more discriminating C(trough) efficacy thresholds were determined statistically for each PI by using the raw C(trough) and the time-corrected C(trough), using the precise delay since the last PI intake and the half-life of each PI.

RESULTS

For IDV (P=0.002) and NFV (P=0.019) median C(trough) levels were higher in patients with undetectable viral load [0.23 mg/L (n=30) and 2.3 mg/L (n=16) respectively] than in patients with detectable viral load [0.11 mg/L (n=38) and 0.6 mg/L (n=17) respectively]. C(trough) levels of IDV (r=-0.45; P<0.0001) and NFV (r=-0.43; P=0.011) were correlated with the concomitant viral load. The more discriminating C(trough) efficacy thresholds were estimated statistically as 0.12 mg/L for IDV and 0.5 mg/L for NFV. When C(trough) values were time-corrected, the C(trough) efficacy thresholds, 8 h after the last intake, were 0.15 mg/L for IDV and 0.65 mg/L for NFV.

CONCLUSIONS

These results support the importance of achieving minimal effective C(trough) to improve the virological efficacy of PI-containing HAART, and specify the target concentrations for IDV and NFV.

Pharmacokinetic enhancement of protease inhibitor therapy

Combination antiretroviral therapy with two or more protease inhibitors has become the standard of care in the treatment of HIV infection. Dual protein inhibitor (PI) regimens, such as lopinavir/ritonavir, are commonly used as initial PI therapy. As viral resistance increases and the development of mechanistically novel protease inhibitors decreases, clinicians turn to ritonavir-enhanced dual PI therapy to treat salvage patients. Potency of these combination regimens is increased while pill burden, food restrictions and often, side effects are decreased. These clinical advantages result from the enhancement of their pharmacological properties, including alterations in the absorption and metabolism process. Alterations in the absorption and metabolism of protease inhibitors when co-administered with a cytochrome P450 (CYP) enzyme inhibitor, such as low dose ritonavir, are reflected by impressive changes in pharmacokinetic parameters. For example, the addition of ritonavir 100 or 200 mg to saquinavir 1200-1800 mg has been shown to increase saquinavir area under the concentration-time curve (AUC) by approximately 300-800% compared with saquinavir alone. The ability of ritonavir to increase plasma trough concentrations (C(min)) of concomitantly administered PIs is perhaps the greatest clinical benefit of dual or ritonavir-enhanced dual PI therapy since inadequate concentrations of antiretrovirals may support long term antiretroviral resistance. For example, lopinavir 400mg alone in healthy volunteers produced plasma concentrations that briefly exceeded the concentration required to inhibit 50% of viral replication (IC(50)). Yet, when low doses of ritonavir were added, C(min) values were 50- to 100-fold greater than the concentration required to produce 50% of the maximum effect for wild-type HIV (EC(50)). The following manuscript will discuss the rationale for combining protease inhibitors and will review pertinent pharmacokinetic and clinical data on these combination regimens.

Pharmacokinetic characteristics of ritonavir, zidovudine, lamivudine, and stavudine in children with human immunodeficiency virus infection

STUDY OBJECTIVE

To evaluate and describe the parameters and characteristics of different drug regimens in children infected with human immunodeficiency virus (HIV).

DESIGN

Randomized, open-label, multicenter study.

SETTING

Pediatric HIV research clinics in the United States and Puerto Rico.

PATIENTS

Twenty-one HIV-infected children, aged 3-14 years, who were clinically stable and treated with the same antiretroviral therapy for 16 weeks or longer.

INTERVENTION

In step 1, children were randomized to receive one of three treatment regimens: zidovudine plus lamivudine, ritonavir plus zidovudine and lamivudine, or ritonavir plus stavudine. Patients originally assigned to the zidovudine plus lamivudine group in step 1 were eligible to progress to step 2 if their HIV RNA values at week 12, 24, or 36 were 10,000 copies/ml or greater but 100,000 copies/ml or less. In step 2 they received a regimen of ritonavir plus stavudine and nevirapine.

MEASUREMENTS AND MAIN RESULTS

Seven children were randomized to each of the three treatment regimens. Concentrations of the agents were quantitated at steady state after observed doses, and the pharmacokinetic parameters were determined. Nevirapine concentrations were not determined. One child was excluded from analysis because pharmacokinetic parameters could not be estimated. Ritonavir oral clearance was slower in the pooled cohort of children who received stavudine compared with zidovudine and lamivudine. Stavudine oral clearance was marginally faster when combined with ritonavir and nevirapine compared with only ritonavir.

CONCLUSION

Therapy for HIV is complex, and pharmacodynamic data indicate that relationships exist between systemic concentrations of antiretroviral drugs and virologic response. Careful drug interaction studies have not been conducted for all treatment regimens, and it will not be surprising if unexpected interactions are found. Pharmacokinetic studies to address these considerations should be viewed as a fundamental component of antiretroviral drug development, as they represent a tool to improve pharmacotherapy for HIV-infected children.

Pharmacokinetics of indinavir combined with low-dose ritonavir in human immunodeficiency virus type 1-infected children

So far, no pediatric doses for indinavir combined with ritonavir have been defined. This study evaluated the pharmacokinetics of 400 mg of indinavir/m(2) combined with 125 mg of ritonavir/m(2) every 12 h (q12h) in 14 human immunodeficiency virus type 1-infected children. The area under the concentration-time curve from 0 to 24 h and the minimum concentration of drug in serum for indinavir were similar to those for 800 mg of indinavir-100 mg of ritonavir q12h in adults, while the maximum concentration of drug in serum was slightly decreased, with geometric mean ratios (90% confidence intervals in parentheses) of 1.1 (0.87 to 1.3), 0.96 (0.60 to 1.5), and 0.80 (0.68 to 0.94), respectively.

Pharmacokinetics of saquinavir plus low-dose ritonavir in human immunodeficiency virus-infected pregnant women

The physiologic changes that occur during pregnancy make it difficult to predict antiretroviral pharmacokinetics (PKs), but few data exist on the PKs of protease inhibitors in human immunodeficiency virus (HIV)-infected pregnant women. The objective of the present study was to determine the PKs of ritonavir (RTV)-enhanced saquinavir (SQV) in HIV-infected pregnant women by an area under the curve (AUC)-targeted approach. A phase I, formal PK evaluation was conducted with HIV-infected pregnant woman during gestation, during labor and delivery, and at 6 weeks postpartum. The SQV-RTV regimen was 800/100 mg twice a day (b.i.d.), and nucleoside analogs were administered concomitantly. The SQV exposure targeted was an AUC at 24 h of 10,000 ng. h/ml. Participants were evaluated for 12-h steady-state PKs at each time period. Thirteen subjects completed the PK evaluations during gestation, 7 completed the PK evaluations at labor and delivery, and 12 completed the PK evaluations postpartum. The mean baseline weight was 67.4 kg, and the median length of gestation was 23.3 weeks. All subjects achieved SQV exposures in excess of the target AUC. The SQV AUCs at 12 h (AUC(12)s) during gestation (29,373 +/- 17,524 ng. h/ml [mean +/- standard deviation]), during labor and delivery (26,189 +/- 22,138 ng. h/ml), and during the postpartum period (35,376 +/- 26,379 ng. h/ml) were not significantly different. The mean values of the PK parameters for RTV were lower during gestation than during the postpartum period: for AUC(12), 7,811 and 13,127 ng. h/ml, respectively; for trough concentrations, 376 and 632 ng/ml, respectively; and for maximum concentrations, 1,256 and 2,252 ng/ml, respectively (P </= 0.05 for all comparisons). This is the first formal PK evaluation of a dual protease inhibitor regimen with HIV-infected pregnant women. The level of SQV exposure was sufficient at each time of evaluation. These data demonstrate large variability in SQV and RTV concentrations and suggest that RTV concentrations are altered by pregnancy. These PK results suggest that SQV-RTV at 800/100 mg b.i.d. appears to be a reasonable treatment option for this population.

Comparison of Two Reduced-Dose Regimens of Indinavir (600 Mg Vs 400 Mg Twice Daily) and Ritonavir (100 Mg Twice Daily) in Healthy Volunteers (Coredir)

Objective

To assess the pharmacokinetics and tolerability of reduced dosages of twice daily indinavir (IDV) boosted by low-dose ritonavir (RTV) in healthy volunteers.

Methods

Pharmacokinetics and tolerability of IDV/RTV twice daily (600/100 mg and 400/100 mg) were assessed in a randomized crossover design in 16 healthy volunteers. Each dosage was taken twice daily for 2 weeks before 12 h pharmacokinetics were obtained.

Results

Sixteen subjects were included, with a mean age ±SD of 30 ±4 years; seven female, nine male. Fifteen subjects completed the study. After dose reduction of IDV AUC, Cmax and Cmin decreased significantly. In the 400 mg group three out of 15 subjects had IDV levels below 0.10 mg/l vs none in the 600 mg group. All subjects reported mild to moderate side effects throughout the study period, which were more severe in the 600 mg group (mostly renal, dry skin/lips, paresthesias/oral discomfort). In the 600 mg group four subjects reported dysuria and one subject discontinued because of flank pain, whereas two subjects reported dysuria and no subject discontinued in the 400 mg group, respectively. Eight subjects developed crystalluria without a significant difference between both groups. No significant change in serum creatinine was observed.

Conclusions

IDV/RTV 400/100 mg twice daily resulted in significant lower IDV exposure, with three out of 15 subjects revealing Cmin values below the recommended threshold for wild-type virus of 0.10 mg/l. Tolerability, however, was lower in the 600 mg IDV group. Therapeutic drug monitoring in the individual patient appears to be necessary to guarantee appropriate drug levels and simultaneously minimize toxicity. Presented in part at the 6th International Congress on Drug Therapy in HIV Infection. Glasgow, Scotland, UK, November 2002. Abstract P182.