Tipranavir (TPV) genotypic inhibitory quotient predicts virological response at 48 weeks to TPV-based salvage regimens

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.

Relationship between antiretroviral plasma concentration and emergence of HIV-1 resistance mutations at treatment failure

PURPOSE

The relationship between antiretroviral pharmacokinetic exposure and acquisition of human immunodeficency virus-1 (HIV-1) drug resistance mutations (DRM) is not fully understood. The aim of this study was to investigate whether antiretroviral plasma concentration could predict the emergence of DRM at treatment failure.

METHODS

The study cohort comprised retrospectively selected patients with failing antiretroviral regimens for whom a protease inhibitor (PI) or non-nucleoside reverse transcriptase inhibitor (NNRTI) trough concentration measurement (TDM) had been obtained before failure, a genotypic resistance test (GRT1) had been performed before the TDM, and a genotypic resistance test (GRT2) had been performed at therapeutic failure. Drug levels were classified as undetectable/detectable or subtherapeutic/therapeutic according to limits of quantification of a high-performance liquid chromatography-ultraviolet assay or pre-defined efficacy thresholds, respectively. The number of DRM acquired at treatment failure was evaluated by comparing the results of the GRT2 and GRT1.

RESULTS

A total of ten and 57 failure episodes occurred among our patients on NNRTI-based and PI-based regimens, respectively, and included in the evaluation. PI concentration was subtherapeutic in 28.1% of patients, among which the levels were undetectable in 21.1%. Twenty-five (43.9%) patients acquired at least one new PI-DRM according to the GRT2. Patients with undetectable PI levels showed a lower emergence of PI-DRM (minor + major) than those with detectable levels (8.3 vs. 53.3%, p = 0.007). Multivariate analysis confirmed that undetectable PI levels were independent negative predictors of DRM selection. NNRTI measurements were subtherapeutic in 2/10 (20%) patients. NNRTI-DRM were acquired by all patients regardless of NNRTI levels.

CONCLUSIONS

A PI measurement showing undetectable drug levels prior to treatment failure predicted the lack of emergence of PI-DRM at failure. These results suggest that PI levels can help clinicians interpret the reasons for treatment failure and guide the type of interventions needed.

Efficacy and safety of ritonavir dose reduction based on the tipranavir inhibitory quotient in HIV-infected patients on salvage antiretroviral therapy with tipranavir/ritonavir

Ritonavir-related adverse events have been reported in patients taking tipranavir/ritonavir at the licensed dosage of 500/200 mg twice daily (bid). The aim of this open-label, prospective, single-arm pilot study was to evaluate the efficacy and safety of a ritonavir dose reduction to 100 mg bid guided by the tipranavir virtual inhibitory quotient (vIQ) in HIV-infected patients receiving tipranavir/ritonavir 500/200 mg bid whose viral load was <50 copies/ml and whose tipranavir vIQ was >60. Viral load, blood chemistry, and tipranavir and ritonavir trough concentrations (C(trough)) in plasma were determined at baseline and up to 48 weeks. If the tipranavir vIQ fell to <40, the ritonavir dose was increased to 200 mg bid. The primary endpoint was the percentage of treatment failure after 48 weeks. Eleven patients were enrolled. At baseline, the median (IQR) CD4+ T-cell count and vIQ were 380 (231-520) cells/mm(3) and 233.4 (73.8-584.8), respectively. Ten patients (90.9%) maintained a viral load <50 copies/ml at week 48. Geometric mean (95% confidence interval) tipranavir C(trough) decreased from 24.7 (12.9-47.5) mg/l at baseline to 13.6 (7.1-26.2) mg/l at week 48 (p = 0.194), but the ritonavir dose had to be raised in only one patient. Median triglycerides and ALT concentrations decreased from 177.2 (132.9-292.4) mg/dl and 59 (23-128) IU/l at baseline to 158.0 (131.0-186.0) mg/dl and 28 (20-71) IU/l at week 48 (p = 0.047, p = 0.041), respectively. As a conclusion, ritonavir-dose reduction to 100 mg bid as a treatment-simplification strategy guided by the tipranavir vIQ in patients receiving salvage therapy with tipranavir/ritonavir 500/200 mg bid seems to be safe enough to be tested in adequately powered clinical trials.

Role of tipranavir in treatment of patients with multidrug-resistant HIV

The worldwide emergence of multidrug-resistant human immunodeficiency virus (HIV)-1 strains has the driven the development of new antiretroviral (ARV) agents. Over the past 5 years, HIV-entry and integrase inhibitor ARVs, as well as improved non-nucleoside reverse transcriptase inhibitors (NRTIs) and protease inhibitors (PIs), have become available for treatment. It is important to assess how these new ARVs might be most judiciously used, paying close attention to viral susceptibility patterns, pharmacodynamic parameters, and the likelihood that patients will adhere to their therapy. Herein we review published material in Medline, EMBASE, and ISI for each antiretroviral agent/classes currently approved and summarize the available data on their efficacy, safety, and pharmacologic parameters. We focus on the role of tipranavir, a recently approved nonpeptidic PI, for treating HIV-infected children, adolescents, and adults with a history of multidrug-resistant HIV.

Clinical application of the inhibitory quotient: is there a role in HIV protease inhibitor therapy?

PURPOSE OF REVIEW

The inhibitory quotient of boosted protease inhibitors is a measurement incorporating both plasma drug exposure and resistance testing. Inhibitory quotients have been assessed in over 50 clinical studies to date, many of these studies describe highly significant associations between the inhibitory quotient and virological outcomes. This review will focus on studies that assess the inhibitory quotient in a prospective fashion and with the use of newly available boosted protease inhibitors.

RECENT FINDINGS

Atazanavir, darunavir and tipranavir are the three most recently licensed protease inhibitors. Studies have described associations between the inhibitory quotient and outcomes for all of these agents with cutoff inhibitory quotient values now proposed for all of these protease inhibitors.A prospective study has assessed the use of inhibitory quotient across many different protease inhibitor regimens and although no overall benefit was described, improved clinical outcomes were observed in specific patient groups.

SUMMARY

Although ongoing challenges need to be overcome, recent studies have described associations between this useful parameter and modern day antiretroviral regimens.

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

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

Tipranavir: a new protease inhibitor for the pediatric population

Highly active antiretroviral therapy can provide sustained viral suppression and a beneficial immunological response in both antiretroviral-naive and -experienced pediatric patients infected with HIV. While there have been many antiretroviral studies in adults infected with HIV, considerably less information is available in similar HIV-infected pediatric or adolescent patients. Tipranavir, a new-generation protease inhibitor approved for use in adults with resistant HIV strains, has recently been studied in HIV-infected children and adolescents. In this article, we summarize available pharmacokinetic, safety, tolerability and efficacy data obtained from children and adolescents treated with a pediatric tipranavir formulation.

Tipranavir: a review of its use in the management of HIV infection

Tipranavir (Aptivus) is a selective nonpeptidic HIV-1 protease inhibitor (PI) that is used in the treatment of treatment-experienced adults with HIV-1 infection. Tipranavir is administered orally twice daily and must be given in combination with low-dose ritonavir, which is used to boost its bioavailability. The durable efficacy of tipranavir, in combination with low-dose ritonavir (tipranavir/ritonavir 500 mg/200 mg twice daily), has been demonstrated in well designed trials in treatment-experienced adults infected with multidrug-resistant strains of HIV-1. In treatment-experienced adults with HIV-1 infection receiving an optimized background regimen, viral suppression was greater and immunological responses were better with regimens containing tipranavir/ritonavir than with comparator ritonavir-boosted PI-containing regimens. The efficacy benefit appeared to be more marked in patients receiving two fully active drugs in the regimen, with the combination of tipranavir/ritonavir and enfuvirtide (for the first time) appearing to be the most successful. Although tipranavir is generally well tolerated, clinical hepatitis and hepatic decompensation, and intracranial haemorrhage have been associated with the drug. Tipranavir also has a complex drug-interaction profile. Thus, tipranavir, administered with ritonavir, is an effective treatment option for use in the combination therapy of adults with HIV-1 infection who have been previously treated with other antiretroviral drugs.

Darunavir inhibitory quotient predicts the 48-week virological response to darunavir-based salvage therapy in human immunodeficiency virus-infected protease inhibitor-experienced patients

The aim of this study was to evaluate the relationship between the virological response to darunavir-based salvage antiretroviral therapy and the darunavir genotypic and virtual inhibitory quotients (gIQ and vIQ, respectively). Thirty-seven HIV-infected patients failing protease inhibitor-based antiretroviral regimens who started salvage therapy containing darunavir-ritonavir were prospectively studied. The primary outcome of the study was a viral load (VL) of <50 copies/ml at week 48. The trough concentrations of darunavir in plasma, the number of darunavir resistance mutations, the change in the 50% inhibitory concentration (IC(50)) of darunavir in the virtual phenotype, and the darunavir gIQ and vIQ were correlated with the virological outcome in regression analyses adjusted by the number of active drugs in the background regimen. The VL was <50 copies/ml in 56.8% of patients at week 48. Changes in the VL were not significantly associated with the darunavir concentration (P = 0.304), the number of darunavir resistance mutations (P = 0.695), or the change in the IC(50) (P = 0.750). However, patients with darunavir vIQs of >or=1.5 had a 12-fold greater chance of achieving a >or=1 log(10) reduction in the VL (odds ratio [OR], 12.7; 95% confidence interval [95% CI], 1.9 to 81.6; P = 0.007), and a 5-fold greater chance of achieving a VL of <50 copies/ml (OR, 5.4; 95% CI, 1.2 to 24.5; P = 0.028), at week 48 than patients with darunavir vIQs of <1.5. The positive and negative predictive values of this darunavir vIQ cutoff for achieving a VL of <50 copies/ml at week 48 were 70% and 69%, respectively. The darunavir vIQ predicts virological response to darunavir-based salvage therapy better than the darunavir trough concentration or resistance mutations alone. We suggest targeting a darunavir vIQ of 1.5 for achieving long-term viral suppression.