Variability in non-nucleoside reverse transcriptase and protease inhibitor concentrations among HIV-infected adults in routine clinical practice

Individualized Protease Inhibitor Monotherapy: The Role of Pharmacokinetics and Pharmacogenetics in an Aged and Heavily Treated HIV-Infected Patient

Antiretroviral therapy has changed the history of HIV infection from a lethal disease to a chronic infection, with the emergence of long-term adverse effects. Herein we present a case of a heavily treated HIV-infected man in whom antiretroviral toxicity had been observed. The lopinavir/ritonavir plasma concentrations at standard doses were significantly above the recommended levels. Pharmacogenetic analysis revealed a polymorphism in the DRD3 gene associated with a decrease in the rate of drug metabolism. Additionally, the patient's low body mass index could have contributed to a greater degree of patient exposure to the drug. After the withdrawal of tenofovir disoproxil and the establishment of individualized protease inhibitor monotherapy at reduced doses, a decrease in the intensity of adverse events was observed, while the clinical outcomes were maintained. The pharmacokinetic-pharmacogenetic analysis was shown to be a tool of huge interest for the management and durability of antiretroviral therapy.

Chromatographic methods in HIV medicine: Application to therapeutic drug monitoring

HIV antiretroviral therapy spans several different drug classes, meant to combat various aspects of viral infection and replication. Many authors have argued the benefits of therapeutic drug monitoring (TDM) for the HIV patient including compliance assurance and assessment of appropriate drug concentrations; however, the array of drug chemistries and combinations makes TDM an arduous task. HPLC-UV and LC-MS/MS are both frequent instruments for the quantification of HIV drugs in biological matrices with investigators striving to balance sensitivity and affordability. Plasma, the dominant matrix for these analyses, is prepared using protein precipitation, liquid-liquid extraction or solid-phase extraction depending on the specific complement of analytes. Despite the range of polarities found in drug classes relevant to HIV therapeutics, most chromatographic separations utilize a hydrophobic column (C₁₈ ). Additionally, as the clinically relevant samples for these assays are infected with HIV, along with possible co-infections, another important aspect of sample preparation concerns viral inactivation. Although not routine in clinical practice, many published analytical methods from the previous two decades have demonstrated the ability to conduct TDM in HIV patients receiving various medicinal combinations. This review summarizes the analytical methods relevant to TDM of HIV drugs, while highlighting respective challenges.

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.

CYP3A4 polymorphism and lopinavir toxicity in an HIV-infected pregnant woman

Cytochrome P450 (CYP) 3A4 has been considered to be the most important enzyme system for metabolism of lopinavir/ritonavir (LPV/r), a widely used HIV protease inhibitor (PI) recommended during pregnancy. Herein we present a clinical case of a pregnant HIV-infected woman who was taking standard doses of LPV/r, 400/100 mg twice daily. The trough plasma concentrations for LPV were fourfold above that recommended for PI-pretreated patients and toxicity associated with LPV/r and PI regimens was observed. These high concentrations continued after delivery in spite of a dosage reduction. The pharmacogenetic analysis revealed a genetic polymorphism in the CYP3A4 gene that encodes a non-functional protein. The pharmacokinetic study could indicate the occurrence of a phenomenon of non-linear pharmacokinetics which would justify why dosage reduction after pregnancy did not proportionally affect the patient's degree of exposure to the drug. In addition, an increment in CYP3A activity during pregnancy could explain lower LPV/r exposure during this period compared to postpartum, despite the impaired activity of CYP3A4 caused by the polymorphism.

Population pharmacokinetic/pharmacogenetic model of lopinavir/ritonavir in HIV-infected patients

AIM

This study aims to develop a population pharmacokinetic/pharmacogenetic model for lopinavir/ritonavir (LPV/r) in European HIV-infected patients.

MATERIALS & METHODS

A total of 693 LPV/r plasma concentrations were assessed and 15 single-nucleotide polymorphisms were genotyped. The population pharmacokinetic/pharmacogenetic model was created using a nonlinear mixed-effect approach (NONMEM^® v.7.2.0., ICON Development Solutions, Dublin, Ireland).

RESULTS

Covariates significantly related to LPV/r apparent clearance (CL/F) were ritonavir trough concentration (RTC), BMI, high-density lipoprotein cholesterol (HDL-C) and certain single-nucleotide polymorphisms in genes encoding for metabolizing enzymes, which are representable as follows: CL/F = (0.216BMI + 0.0125HDL-C) × 0.713^RTC × 1.26^{rs28371764[C/T]} × 0.528^{rs6945984[C/C]} × 0.302 ^{CYP3A4[1461insA/del]} Conclusion: The LPV/r standard dose appears to be appropriate for the rs28371764[C/T] genotype. However, lower doses should be recommended for the rs6945984[C/C] and CYP3A4[1461insA/del] genotypes and even for those patients without any of these variants, as the standard dose seems to be higher than that which is required in order to achieve therapeutic levels.

Toxicogenetics of lopinavir/ritonavir in HIV-infected European patients

AIMS

We present a genetic association study in 106 European HIV-infected individuals aimed at identifying and confirming polymorphisms that have a significant influence on toxicity derived from treatment with lopinavir/ritonavir (LPV/r).

PATIENTS & METHODS

Genotyping was performed by matrix-assisted laser desorption/ionization-time of flight and KASPar^® (KBiosciences, Hoddesdon, UK); LPV/r plasma concentrations were quantified using HPLC with an UV detection system and the pharmacokinetic parameters were estimated using Bayesian algorithms. Genetic association analysis was performed with PASW Statistics 18 (SPSS Inc., IL, USA) and R for Windows (Microsoft, WA, USA).

RESULTS

Suggestive relationships have been established between lipid plasma levels and total bilirubin and SNPs in CETP, MCP1, ABCC2, LEP and SLCO1B3 genes and between diarrhea and SNPs in IL6 gene.

CONCLUSION

Replication analysis should confirm the novel results obtained in this study prior to its application in the clinical practice to achieve a safer LPV/r-based combined antiretroviral therapy.

Related factors to atazanavir plasma levels in a cohort of HIV positive individuals with undetectable viral load

Objective

To evaluate the factors associated with plasma concentrations of atazanavir (ATV) in a cohort of well-controlled HIV infected subjects (undetectable viremia).

Design

Cross-sectional study where 69 subjects were consecutively enrolled between April and November, 2011.

Methods

Patients had to be on atazanavir for at least six months, undetectable viral load for a period equal to or longer than 12 months, T CD4+ lymphocyte count higher than 200 cells/mm³, and aged between 18 years and 70 years old. Exclusion criteria were pregnancy, any neurologic disease, active opportunistic disease, hepatitis or cancer. Atazanavir plasma levels were measured by ultra-performance liquid chromatography.

Results and discussion

Overall, 54 patients (mean age of 47 years and 50% women) were included in the analysis. Those without ritonavir (unboosted atazanavir) had statistically lower plasma concentrations than those with ritonavir boosted atazanavir (p = 0.001) and total and indirect bilirubin were statistically associated with plasma concentration of atazanavir (r = 0.32 and r = 0.33 respectively; p < 0.05 in both cases). No statistical association was found among gender, ethnicity, age, weight, body mass index (BMI), lipid profile, and the plasma concentration of atazanavir.

Conclusion

In summary, as expected, concomitant ritonavir use was the only factor associated with atazanavir plasma levels. Prospective studies with a larger sample size might help to observe an association of atazanavir concentrations to other characteristics such as body weight, since the p-value showed to be close to significance (p = 0.068).

Simultaneous population pharmacokinetic model for lopinavir and ritonavir in HIV-infected adults

BACKGROUND

Lopinavir is a protease inhibitor indicated for the treatment of HIV infection. It is coformulated with low doses of ritonavir in order to enhance its pharmacokinetic profile. After oral administration, plasma concentrations of lopinavir can vary widely between different HIV-infected patients.

OBJECTIVE

To develop and validate a population pharmacokinetic model for lopinavir and ritonavir administered simultaneously in a population of HIV-infected adults. The model sought was to incorporate patient characteristics influencing variability in the drug concentration and the interaction between the two compounds.

METHODS

HIV-infected adults on stable therapy with oral lopinavir/ritonavir in routine clinical practice for at least 4 weeks were included. A concentration-time profile was obtained for each patient, and blood samples were collected immediately before and 1, 2, 4, 6, 8, 10 and 12 hours after a morning lopinavir/ritonavir dose. Lopinavir and ritonavir concentrations in plasma were determined by high-performance liquid chromatography. First, a population pharmacokinetic model was developed for lopinavir and for ritonavir separately. The pharmacokinetic parameters, interindividual variability and residual error were estimated, and the influence of different patient characteristics on the pharmacokinetics of lopinavir and ritonavir was explored. Then, a simultaneous model estimating the pharmacokinetics of both drugs together and incorporating the influence of ritonavir exposure on oral clearance (CL/F) of lopinavir was developed. Population analysis was performed using nonlinear mixed-effects modelling (NONMEM version V software). The bias and precision of the final model were assessed through Monte Carlo simulations and data-splitting techniques.

RESULTS

A total of 53 and 25 Caucasian patients were included in two datasets for model building and model validation, respectively. Lopinavir and ritonavir pharmacokinetics were described by one-compartment models with first-order absorption and elimination. The presence of advanced liver fibrosis decreased CL/F of ritonavir by nearly half. The volume of distribution after oral administration (Vd/F) and CL/F of lopinavir were reduced as alpha1-acid glycoprotein (AAG) concentrations increased. CL/F of lopinavir was inhibited by ritonavir concentrations following a maximum-effect model (maximum inhibition [Imax] = 1, concentration producing 50% of the I(max) [IC50] = 0.36 mg/L). The final model appropriately predicted plasma concentrations in the model-validation dataset with no systematic bias and adequate precision.

CONCLUSION

A population model to simultaneously describe the pharmacokinetics of lopinavir and ritonavir was developed and validated in HIV-infected patients. Bayesian estimates of the individual parameters of ritonavir and lopinavir could be useful to predict lopinavir exposure based on the presence of advanced liver fibrosis and the AAG concentration in an individual manner, with the aim of maximizing the chances of treatment success.

Atazanavir: its role in HIV treatment

Azatanavir is a protease inhibitor (PI) approved for the treatment of HIV-1 infection. Atazanavir is a substrate and inhibitor of cytochrome P450 isozyme 3A and an inhibitor and inducer of P-glycoprotein. It has similar virologic efficacy as efavirenz and ritonavir-boosted lopinavir in antiretroviral-naive individuals. Its impact on lipids is less than other PIs and it is suitable for those in whom hyperlipidemia is undesirable. Ritonavir boosting of atazanavir enhances the bioavailability of atazanavir but may result in some elevation of lipids and is recommended for treatment-experienced patients and those receiving efavirenz or tenofovir. Ritonavir-boosted atazanavir has similar antiviral activity as ritonavir-boosted lopinavir in both antiretroviral therapy-naive and -experienced patients. Atazanavir causes unconjugated bilirubinemia in over 40% of patients but results in less than 2% discontinuations. Atazanavir is licensed for once-daily use and atazanavir/ritonavir competes with lopinavir/ritonavir as the most commonly prescribed PI.

Sustained antiretroviral treatment adherence in survivors of the pre-HAART era: attitudes and beliefs

The objective of this study was to assess adherence of HIV-1-infected patients who started treatment in the pre-HAART era and to determine variables associated with better adherence, including relevant attitudes and beliefs. This is a cross-sectional study enrolling patients who had received antiretroviral therapy for >or=10 years. Adherence was evaluated through self-reporting and plasma drug concentrations. Treatment variables, attitudes and beliefs were collected during structured interviews. The results show that for 87 patients the median (interquartile range) time on therapy was 13 (10-19) years; 80 were on therapy at the time of analysis. Adherence was >or=95% in 54 patients (67.5%), 90-94% in 22 (27.5%) and <90% in 4 (5%). Drug concentrations were below the lower limit of detection in five patients. Younger age (p=0.014), female gender (p=0.005), current substance abuse (p=0.004) and hepatitis C virus co-infection (p<0.001) were related to lower adherence. Adherence did not differ in relation to different drug families or once- or twice-daily regimens. Patients with adherence <95% were more likely to have interrupted treatment without doctor's recommendation (p=0.009). Adherent patients exhibited a higher perception of risk of developing the illness and of benefits of therapy, higher self-efficacy and intention to adhere and were more influenced by events that motivate medication intake. To conclude, adherence was >90% in most patients on antiretroviral therapy for >or=10 years. Adherence was more related to beliefs about health and illness than to the characteristics of medication or level of knowledge about treatment. Care adherence interventions should include assessment of health beliefs.

Once- or twice-daily dosing of nevirapine in HIV-infected adults: a population pharmacokinetics approach

OBJECTIVES

The aim of this study was to develop and validate a population pharmacokinetic model for nevirapine in a population of HIV-infected adults and to evaluate the influence of nevirapine dosing regimen and patient characteristics on nevirapine trough concentration.

METHODS

HIV-infected adults receiving oral nevirapine for at least 4 weeks were included. A concentration-time profile was obtained for each patient, and nevirapine concentrations in plasma were determined by HPLC. Pharmacokinetic parameters, inter-individual variability and residual error were estimated using non-linear mixed effects modelling. The influence of patient characteristics on the pharmacokinetics of nevirapine was explored, and the predictive performance of the final model was evaluated in an external data set of observations.

RESULTS

Totals of 40 and 18 Caucasian patients were included in two data sets for model building and model validation, respectively. A mono-compartmental model with first-order absorption and elimination best described the pharmacokinetics of nevirapine. Body weight influenced oral clearance (CL/F) and volume of distribution (V/F). The estimated population pharmacokinetic parameters (inter-individual variability) for an individual weighing 70 kg were CL/F 2.95 L/h (24%), V/F 95.2 L (30%) and k(a) 1.8 h(-1) (96%). The final model predicted nevirapine concentrations in the external model-validation data set with no systematic bias and adequate precision. Bayesian estimates of nevirapine trough concentrations were lower when nevirapine was administered once instead of twice daily, and nearly half of the patients weighing 90 kg had drug concentrations <3.0 mg/L when nevirapine was dosed once daily.

CONCLUSIONS

A population model to describe the pharmacokinetics of nevirapine was developed and validated in HIV-infected patients. Body weight influenced CL/F and V/F. Based on Bayesian estimates of individual nevirapine concentrations, twice- instead of once-daily administration of nevirapine would be more optimal in patients weighing >70 kg.