Pharmacokinetic evidence for the induction of lopinavir metabolism by efavirenz

Induction of CYP2C19 and CYP3A activity following repeated administration of efavirenz in healthy volunteers

Drug-drug interactions involving efavirenz are of major concern in clinical practice. We evaluated the effects of multiple doses of efavirenz on omeprazole 5-hydroxylation (CYP2C19) and sulfoxidation (CYP3A). Healthy volunteers (n = 57) were administered a single 20 mg oral dose of racemic omeprazole either with a single 600 mg oral dose of efavirenz or after 17 days of administration of 600 mg/day of efavirenz. The concentrations of racemic omeprazole, 5-hydroxyomeoprazole (and their enantiomers), and omeprazole sulfone in plasma were measured using a chiral liquid chromatography-tandem mass spectrometry method. Relative to single-dose treatment, multiple doses of efavirenz significantly decreased (P < 0.0001) the area under the plasma concentration-time curve from 0 to infinity (AUC(0-∞)) of racemic-, R- and S-omeprazole (2.01- to 2.15-fold) and the corresponding AUC(0-∞) metabolic ratio (MR) for 5-hydroxyomeprazole (1.36- to 1.44-fold) as well as the MR for omeprazole sulfone (∼2.0) (P < 0.0001). The significant reduction in the AUC of 5-hydroxyomeprazole after repeated efavirenz dosing suggests induction of sequential metabolism and mixed inductive/inhibitory effects of efavirenz on CYP2C19. In conclusion, efavirenz enhances omeprazole metabolism in a nonstereoselective manner through induction of CYP3A and CYP2C19 activity.

Population pharmacokinetics of lopinavir/ritonavir (Kaletra) in HIV-infected patients

BACKGROUND

A relationship between plasma concentrations and viral suppression in patients receiving lopinavir (LPV)/ritonavir (RTV) has been observed. Therefore, it is important to increase our knowledge about factors that determine interpatient variability in LPV pharmacokinetics (PK).

METHODS

The study, designed to develop and validate population PK models for LPV and RTV, involved 263 ambulatory patients treated with 400/100 mg of LPV/RTV twice daily. A database of 1110 concentrations of LPV and RTV (647 from a single time-point and 463 from 73 full PK profiles) was available. Concentrations were determined at steady state using high-performance liquid chromatography with ultraviolet detection. PK analysis was performed with NONMEM software. Age, gender, height, total body weight, body mass index, RTV trough concentration (RTC), hepatitis C virus coinfection, total bilirubin, hospital of origin, formulation and concomitant administration of efavirenz (EFV), saquinavir (SQV), atazanavir (ATV), and tenofovir were analyzed as possible covariates influencing LPV/RTV kinetic behavior.

RESULTS

Population models were developed with 954 drug plasma concentrations from 201 patients, and the validation was conducted in the remaining 62 patients (156 concentrations). A 1-compartment model with first-order absorption (including lag-time) and elimination best described the PK. Proportional error models for interindividual and residual variability were used. The final models for the drugs oral clearance (CL/F) were as follows: CL/F(LPV)(L/h)=0.216·BMI·0.81(RTC)·1.25(EFV)·0.84(ATV); CL/F(RTV)(L/h) = 8.00·1.34(SQV)·1.77(EFV)·1.35(ATV). The predictive performance of the final population PK models was tested using standardized mean prediction errors, showing values of 0.03 ± 0.74 and 0.05 ± 0.91 for LPV and RTV, and normalized prediction distribution error, confirming the suitability of both models.

CONCLUSIONS

These validated models could be implemented in clinical PK software and applied to dose individualization using a Bayesian approach for both drugs.

Assessment of lopinavir pharmacokinetics with respect to developmental changes in infants and the impact on weight band-based dosing

Improved antiretroviral therapies are needed for the treatment of HIV-infected infants, given the rapid progression of the disease and drug resistance resulting from perinatal exposure to antiretrovirals. We examined longitudinal pharmacokinetics (PK) data from a clinical trial of lopinavir/ritonavir (LPV/r) in HIV-infected infants in whom therapy was initiated at less than 6 months of age. A population PK analysis was performed using NONMEM to characterize changes in lopinavir (LPV) PK relating to maturational changes in infants, and to assess dosing requirements in this population. We also investigated the relationship between LPV PK and viral dynamic response. Age and ritonavir concentrations were the only covariates found to be significant. Population PK of LPV was characterized by high apparent clearance (CL/F) in young infants, which decreased with increasing age. Although younger infants had lower LPV concentrations, the viral dynamics did not correlate with initial LPV exposure. Monte Carlo simulations demonstrated that WHO weight band-based dosing recommendations predicted therapeutic LPV concentrations and provided drug exposure levels comparable to those resulting from US Food and Drug Administration (FDA)-suggested dosing regimens.

[Evidence-based therapeutic drug monitoring of lopinavir]

The HIV protease inhibitor lopinavir presents a wide inter-individual variability related to liver and intestinal metabolism involving CYP3A. Published studies were analyzed to establish whether there is evidence that therapeutic drug monitoring of lopinavir could improve patient care. In naïve or pretreated HIV-infected patients, no relationship could be evidenced between virological efficacy and trough lopinavir concentration, most likely because concentrations are above inhibitory concentrations. Although data are limited, patients with elevated triglycerides and cholesterol had trough lopinavir concentrations >8 000 ng/mL. These data suggest that the level of evidence of interest of lopinavir therapeutic drug monitoring is may be recommended in some situations such as children, pregnant women, pretreated patients if the number of mutations is <5, when coadministration with drug with metabolizing enzyme inducing properties is warranted and toxicity.

Factors influencing lopinavir and atazanavir plasma concentration

BACKGROUND

The protease inhibitors lopinavir and atazanavir are both recommended for treatment of HIV-infected patients. Considerable inter-individual variability in plasma concentration has been observed for both drugs. The aim of this study was to evaluate which demographic factors and concomitant drugs are associated with lopinavir and atazanavir plasma concentration.

METHODS

Data from the Liverpool TDM (therapeutic drug monitoring) Registry were linked with the UK Collaborative HIV Cohort (CHIC) study. For each patient, the first measurement of lopinavir (twice daily) or atazanavir [once daily, ritonavir boosted (/r) or unboosted] plasma concentration was included. Linear regression was used to evaluate the association of dose, gender, age, weight, ethnicity and concomitant antiretroviral drugs or rifabutin with log-transformed drug concentration, adjusted for time since last intake.

RESULTS

Data from 439 patients on lopinavir (69% 400 mg/r, 31% 533 mg/r; 3% concomitant rifabutin) and 313 on atazanavir (60% 300 mg/r, 32% 400 mg/r, 8% 400 mg) were included. Multivariable models revealed the following predictors for lopinavir concentration: weight (11% decrease per additional 10 kg; P = 0.001); dose (25% increase for 533 mg/r; P = 0.024); and rifabutin (116% increase; P < 0.001). For atazanavir the predictors were dose (compared with 300 mg/r: 40% increase for 400 mg/r, 67% decrease for 400 mg; overall P < 0.001) and efavirenz (32% decrease; P = 0.016) but not tenofovir (P = 0.54).

CONCLUSIONS

This analysis confirms that efavirenz decreases atazanavir concentrations, and there was a negative association of weight and lopinavir concentrations. The strong impact of rifabutin on lopinavir concentration should be studied further.

Lack of effect of efavirenz on the pharmacokinetics of tipranavir-ritonavir in healthy volunteers

Previously it has been shown that tipranavir-ritonavir (TPV/r) does not affect efavirenz (EFV) plasma concentrations. This study investigates the effect of steady-state EFV on steady-state TPV/r pharmacokinetics. This was a single-center, open-label, multiple-dose study of healthy adult female and male volunteers. TPV/r 500/200 mg twice a day (BID) was given with food for 24 days. After dosing with TPV/r for 10 days, EFV 600 mg once a day was added to the regimen. Intensive pharmacokinetic (PK) sampling was done on days 10 and 24. Validated bioanalytical high-pressure liquid chromatography-tandem mass spectrometry methods were used to determine plasma tipranavir (TPV), ritonavir (RTV), and EFV concentrations. Thirty-four subjects were entered into the study, and 16 subjects completed it. The geometric mean ratios (90% confidence intervals) for TPV and RTV area under the curves, C(max)s, and C(min)s comparing TPV/r alone and in combination with EFV were 0.97 (0.87 to 1.09), 0.92 (0.81 to 1.03), and 1.19 (0.93 to 1.54) for TPV and 1.03 (0.78 to 1.38), 0.92 (0.65 to 1.30), and 1.04 (0.72 to 1.48) for RTV. Frequently observed adverse events were diarrhea, headache, dizziness, abnormal dreams, and rash. EFV had no effect on the steady-state PK of TPV or RTV, with the exception of a 19% increase in the TPV C(min), which is not clinically relevant. TPV/r can be safely coadministered with EFV and without the need for a dose adjustment.

Population analysis of the pregnancy-related modifications in lopinavir pharmacokinetics and their possible consequences for dose adjustment

OBJECTIVES

To investigate the possible necessity of an increase in lopinavir dose during pregnancy in order to achieve the concentrations previously defined as predictive of virological efficacy.

PATIENTS AND METHODS

Lopinavir pharmacokinetics were investigated by a population approach performed on 145 HIV-infected women, including 74 pregnant women. The final model was used to determine the probability of achievement of the target trough concentrations by Monte Carlo simulations.

RESULTS

The typical population estimates (inter-individual variability %) of apparent clearance (CL/F) and volume of distribution were 4.38 L/h (24%) and 58.4 L (59%), respectively. Pregnancy associated with a gestational age >15 weeks and delivery were found to increase lopinavir CL/F by 39% and 58%, respectively. With the standard 400 mg twice-a-day regimen, the probability of reaching the 1 mg/L target trough concentration for protease inhibitor (PI)-naive patients was 99% and 96% for non-pregnant and pregnant women, respectively. An important decrease in the probability of achieving the 5.7 mg/L target trough concentration for salvage therapy was observed for non-pregnant women (55%), this decrease being even greater for pregnant women (21%). Raising the lopinavir dose to 600 mg twice daily increased these probabilities to 87% and 53% for non-pregnant and pregnant women, respectively.

CONCLUSIONS

Modification of the lopinavir dose is unlikely to be required for PI-naive pregnant women; however, in pregnant women who have previously received a PI, therapeutic drug monitoring and/or empirical increasing of the dose should be considered.

Steady-state pharmacokinetics of lopinavir/ritonavir in combination with efavirenz in human immunodeficiency virus-infected pediatric patients

The pharmacokinetics of lopinavir/ritonavir (LPV/RTV) 300 mg/m twice daily and efavirenz (EFV) 350 mg/m once daily were evaluated in HIV-infected children. The minimum concentrations for LPV contained values above the target range, and the estimated minimum concentrations for EFV contained values below the range. Our data support the current LPV/RTV dose, but EFV 350 mg/m may not be sufficient.

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.

Effect of efavirenz on the pharmacokinetics of ketoconazole in HIV-infected patients

OBJECTIVE

To investigate the effect of efavirenz on the ketoconazole pharmacokinetics in HIV-infected patients.

METHODS

Twelve HIV-infected patients were assigned into a one-sequence, two-period pharmacokinetic interaction study. In phase one, the patients received 400 mg of ketoconazole as a single oral dose on day 1; in phase two, they received 600 mg of efavirenz once daily in combination with 150 mg of lamivudine and 30 or 40 mg of stavudine twice daily on days 2 to 16. On day 16, 400 mg of ketoconazole was added to the regimen as a single oral dose. Ketoconazole pharmacokinetics were studied on days 1 and 16.

RESULTS

Pretreatment with efavirenz significantly increased the clearance of ketoconazole by 201%. C(max) and AUC(0-24) were significantly decreased by 44 and 72%, respectively. The T ((1/2)) was significantly shorter by 58%.

CONCLUSION

Efavirenz has a strong inducing effect on the metabolism of ketoconazole.

Influence of tenofovir, nevirapine and efavirenz on ritonavir-boosted atazanavir pharmacokinetics in HIV-infected patients

OBJECTIVE

The influence of nevirapine, efavirenz and tenofovir co-administration on ritonavir-boosted atazanavir pharmacokinetics was investigated in HIV (human immunodeficiency virus)-infected patients.

METHODS

A population pharmacokinetic analysis was performed in the context of therapeutic drug monitoring (87 patients, 121 samples).

RESULTS

A significant increase of atazanavir clearance (Cl/F) was found when either tenofovir (group B), efavirenz (group C), or nevirapine (group D) were co administered with atazanavir/ritonavir in comparison with patients treated with atazanavir/ritonavir and nucleoside reverse transcriptase inhibitors (group A): 6.24+/-0.36 l h(-1) (group A) versus 7.42+/-0.25 l h(-1) (group B) versus 9.60+/-0.27 l h(-1) (group C) versus 17.53+/-0.57 l h(-1) (group D) (P<0.001). However, the decrease of the mean trough plasma concentration of atazanavir was significant only in group D: 1.02+/-0.86 mg/l (group A) versus 0.21+/-013 mg/l (group D) (P<0.001).

CONCLUSION

The increase in atazanavir clearance when it is used in combination with nevirapine, efavirenz and/or tenofovir suggests that therapeutic drug monitoring of atazanavir should be performed in such circumstances.