Negligible Effect of Tenofovir on Atazanavir Trough Concentrations and Genotypic Inhibitory Quotients in the Presence and Absence of Ritonavir

Population pharmacokinetics and dose optimisation of ritonavir-boosted atazanavir in Thai HIV-infected patients

There is evidence that Thai patients receiving standard doses of ritonavir (RTV)-boosted atazanavir (ATV/r) have high exposure to atazanavir (ATV) leading to a higher risk of toxicity. A lower dose of ATV/r may provide adequate exposure in this population. However, pharmacokinetic data on ATV/r in Thai patients required for dose adjustment are limited. This study aimed to develop a population pharmacokinetic model of ATV/r and to determine the influence of patient characteristics on ATV pharmacokinetics. Monte Carlo simulations were performed to estimate the proportion of patients achieving target ATV trough concentration (C_trough) with the standard ATV/r dose of 300/100 mg and a low dose of 200/100 mg once daily (OD). A total of 127 Thai HIV-infected patients were included in this study. One random blood sample was collected to determine ATV and RTV concentrations at each clinic visit from 100 patients. Intensive data from 27 patients enrolled in previous studies were also included. Data were analysed using the non-linear mixed-effects modelling approach. A one-compartment model with first-order absorption and elimination and absorption lag time best described the data. The population mean clearance of ATV/r was 4.93 L/h in female patients and was 28.7% higher in male patients. Simulation results showed a higher proportion of patients achieving ATV C_trough within the target range with ATV/r 200/100 mg compared with 300/100 mg. The 200/100 mg OD dose of ATV/r provides adequate ATV exposure in Thai HIV-infected patients. Therefore, a lower dose of ATV/r should be considered for Thai and Asian populations.

Efficacy and safety of "unboosting" atazanavir in a randomized controlled trial among HIV-infected patients receiving tenofovir DF

OBJECTIVES

To assess safety and efficacy of a switch to unboosted atazanavir (ATV) among HIV-infected adults receiving ATV/ritonavir (r) and tenofovir disoproxil fumarate (TDF).

METHODS

HIV-infected adults with viral load (VL) <40 copies/mL at screening and <150 copies/mL consistently for ≥3 months while receiving a regimen including ATV/r and TDF were randomized to continue ATV/r 300/100 mg daily (control) or change to ATV 400 mg daily (switch), while maintaining their TDF backbone. The primary outcome was proportion of subjects without treatment failure (regimen switch or VL > 200 copies/mL twice consecutively) at 48 weeks.

RESULTS

Fifty participants (46 male, median age 47 years) were randomized, 25 to each arm. At week 48, treatment success occurred in 76% in the control arm and 92% in the switch arm (ITT, p = 0.25). ATV trough levels at week 9 were higher in controls (median 438 ng/mL) than in the switch arm (median 124 ng/mL) (p = 0.003), as was total bilirubin at week 48 (median 38 μmol/L and 28 μmol/L, respectively; p = 0.02). Estimated glomerular filtration rate (eGFR) decreased in the control arm (p = 0.007), but did not change in the switch arm. At week 48, eGFR was higher in the switch arm (median 96 mL/min) than in the control arm (median 85 mL/min) (p = 0.035), but the arms were similar with respect to fasting glucose, C-reactive protein, and lipid parameters.

CONCLUSIONS

Switching from ATV/r to unboosted ATV appears to be safe and effective in selected virologically suppressed patients receiving TDF-containing regimens, and may have favorable effects on bilirubin and renal function.

Is the unbound concentration of atazanavir of interest in therapeutic drug monitoring?

To date, therapeutic drug monitoring (TDM) is carried out with antiretrovirals and is usually based on total concentrations (C_t ). However, for some patients, TDM does not reflect efficacy or the avoidance of toxicity as is the case for atazanavir (ATV), a HIV protease inhibitor. As the unbound concentration (C_u ) is the pharmacological active form, the aim of the study was to evaluate the value of C_u and the unbound fraction (f_u , f_u = C_u /C_t ) for the TDM of ATV. The variability of C_u and the corresponding f_u of ATV was explored in 43 patients treated with ATV for an average of 13.5 months. C_u was determined by coupling ultrafiltration and liquid chromatography. As ATV is highly bound to alpha-1 acid glycoprotein (AAG), the correlation between f_u and AAG was also evaluated. The viral load was monitored to evaluate the patients' virologic response, while total plasma bilirubin and unconjugated plasma bilirubin were used as biomarkers of ATV toxicity. Median trough C_u and C_t were 37.9 μg/L (Interquartile range (IQR) 20.6-94.9 μg/L) and 628.6 μg/L (IQR 362.7-1078.1 μg/L), respectively. f_u , C_u and C_t showed high variability, but the f_u variability was not correlated with the AAG level. The unbound concentration and fraction were unrelated to the virologic response (P = 0.21 and P = 0.65 for C_u and f_u , respectively) nor to the unconjugated bilirubin (Pearson correlation coefficient (ρ), ρ = 0.22; P = 0.17 for C_u ). Neither total nor unbound concentrations of ATV fully explained hyperbilirubinaemia or virologic failure. From this study, we conclude that unbound ATV did not appear to be more relevant than C_t .

Successful pharmacogenetics-based optimization of unboosted atazanavir plasma exposure in HIV-positive patients: a randomized, controlled, pilot study (the REYAGEN study)

BACKGROUND

Atazanavir without ritonavir, despite efficacy and tolerability, shows low plasma concentrations that warrant optimization.

METHODS

In a randomized, controlled, pilot trial, stable HIV-positive patients on atazanavir/ritonavir (with tenofovir/emtricitabine) were switched to atazanavir. In the standard-dose arm, atazanavir was administered as 400 mg once daily, while according to patients' genetics (PXR, ABCB1 and SLCO1B1), in the pharmacogenetic arm: patients with unfavourable genotypes received 200 mg of atazanavir twice daily. EudraCT number: 2009-014216-35.

RESULTS

Eighty patients were enrolled with balanced baseline characteristics. The average atazanavir exposure was 253 ng/mL (150-542) in the pharmacogenetic arm versus 111 ng/mL (64-190) in the standard-dose arm (P < 0.001); 28 patients in the pharmacogenetic arm (75.7%) had atazanavir exposure >150 ng/mL versus 14 patients (38.9%) in the standard-dose arm (P = 0.001). Immunovirological and laboratory parameters had a favourable outcome throughout the study with non-significant differences between study arms.

CONCLUSIONS

Atazanavir plasma exposure is higher when the schedule is chosen according to the patient's genetic profile.

Atazanavir exposure is effective during pregnancy regardless of tenofovir use

BACKGROUND

We studied the effect of pregnancy on atazanavir pharmacokinetics in the presence and absence of tenofovir.

METHODS

This was a non-randomized, open-label, multicentre Phase IV study in HIV-infected pregnant women recruited from European HIV treatment centres. HIV-infected pregnant women treated with boosted atazanavir (300/100 mg or 400/100 mg atazanavir/ritonavir) as part of their combination antiretroviral therapy (cART) were included in the study. 24 h pharmacokinetic curves were recorded in the third trimester and postpartum. Collection of a cord blood and maternal sample at delivery was optional.

RESULTS

31 patients were included in the analysis, 21/31 patients used tenofovir as part of cART. Median (range) gestational age at delivery was 39 weeks (36-42). Approaching delivery 81% (25 patients) had an HIV viral load <50 copies/ml, all <1,000 copies/ml. Least squares means ratios (90% CI) of atazanavir pharmacokinetic parameters third trimester/postpartum were: 0.66 (0.57, 0.75) for AUC0-24h, 0.70 (0.61, 0.80) for Cmax and 0.59 (0.48, 0.72) for C24h. No statistical difference in pharmacokinetic parameters was found between patients using tenofovir versus no tenofovir. None of the patients showed atazanavir concentrations <0.15 mg/l (target for treatment-naive patients). One baby had a congenital abnormality, which was not likely to be related to atazanavir/ritonavir use. None of the children were HIV-infected.

CONCLUSIONS

Despite 34% lower atazanavir exposure during pregnancy, atazanavir/ritonavir 300/100 mg once daily generates effective concentrations for protease inhibitor (PI)-naive patients, even if co-administered with tenofovir. For treatment-experienced patients (with relevant PI resistance mutations) therapeutic drug monitoring of atazanavir should be considered to adapt the atazanavir/ritonavir dose on an individual basis.
 ClinicalTrials.gov number NCT00825929.

A meta-analysis of the efficacy and safety of unboosted atazanavir compared with ritonavir-boosted protease inhibitor maintenance therapy in HIV-infected adults with established virological suppression after induction

OBJECTIVES

Treatment simplification involving induction with a ritonavir (RTV)-boosted protease inhibitor (PI) replaced by a nonboosted PI (i.e. atazanavir) has been shown to be a viable option for long-term antiretroviral therapy. To evaluate the clinical evidence for this approach, we conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) evaluating efficacy and safety in patients with established virological suppression.

METHODS

Several databases were searched without limits on time or language. Searches of conferences were also conducted. RCTs were included if they compared a PI/RTV regimen to unboosted atazanavir, after induction with PI/RTV. The meta-analysis was conducted using a random effects model for the proportion achieving virological suppression (i.e. HIV RNA < 50 and <400 HIV-1 RNA copies/mL), CD4 cell counts, lipid levels and liver function tests. Dichotomous outcomes were reported as risk ratios (RRs) and continuous outcomes as mean differences (MDs).

RESULTS

Five studies (n = 1249) met the inclusion criteria. The meta-analysis demonstrated no statistically significant difference in efficacy (i.e. HIV RNA < 50 copies/mL) between PI/RTV and unboosted atazanavir [RR = 1.04; 95% confidence interval (CI) 0.99 to 1.10], with no heterogeneity. Findings were similar in a subanalysis of studies where atazanavir/RTV was the only PI/RTV used during induction. Additional efficacy results support these findings. A significant reduction in total cholesterol (P < 0.00001), triglycerides (P = 0.0002), low-density lipoprotein (LDL) cholesterol (P = 0.009) and hyperbilirubinaemia (P = 0.02) was observed with unboosted atazanavir vs. PI/RTV.

CONCLUSIONS

The meta-analysis demonstrated that switching patients with virological suppression from an RTV-boosted PI to unboosted atazanavir leads to improvements in safety (i.e. blood parameter abnormalities) without sacrificing virological efficacy.