Differences in the pharmacokinetics of protease inhibitors between healthy volunteers and HIV-infected persons:

Plasma concentrations of antiretroviral drugs in a successful 4-days-a-week maintenance treatment strategy in HIV-1 patients (ANRS 170-Quatuor trial)

OBJECTIVES

Charaterization of the plasma concentrations of antiretrovirals in a 4-days-a-week maintenance treatment strategy in the ANRS-170-QUATUOR study.

METHODS

Patients were randomized in two groups receiving triple therapy taken 4-days-ON and 3-days-OFF (4/7) or continuous therapy (7/7). Plasma antiretroviral concentrations were monitored during the 'ON-treatment period' (Day 3 or 4 of the 4-day treatment block) and the 'OFF-treatment period' (Day 3 of the 3-day drug cessation) for the 4/7 group, or before the daily drug intake for the 7/7 group, until week-48 (W48). After W48, all patients switched to the 4/7 strategy and were followed until W96.

RESULTS

W0 measured concentrations were comparable in both groups, except for raltegravir, concentrations of which were higher in the 4/7 group, and were all above the values usually recommended to be effective in therapeutic drug monitoring. Comparison of ON-period median concentrations between the two groups showed a statistical difference for rilpivirine [88 ng/mL (interquartile range (IQR) = 64-112) for 4/7 arm versus 130 ng/mL (82-160) for 7/7 arm, P < 0.001] and tenofovir [tenofovir disoproxil fumarate: 93 ng/mL (73-135) for 4/7 arm versus 117 ng/mL (83-160) for 7/7 arm, P < 0.001; tenofovir alafenamide: 11 ng/mL (7-15) for 4/7 arm versus 14 ng/mL (11-18) for 7/7 arm, P = 0.001]. Median OFF concentrations were significantly lower (P < 0.001) at the 48 week analysis for all medications except for raltegravir (P = 0.493) and atazanavir (P = 0.105), for which the numbers of patients were very small.

CONCLUSIONS

The 4/7-day treatment option led to antiretroviral blood levels close to continuous treatment after the four consecutive days of medication, and to low levels at the end of the non-treatment period.

Inflammation Induces Changes in the Functional Expression of P-gp, BCRP, and MRP2: An Overview of Different Models and Consequences for Drug Disposition

The ATP-binding cassette (ABC) transporters play a key role in drug pharmacokinetics. These membrane transporters expressed within physiological barriers can be a source of pharmacokinetic variability. Changes in ABC transporter expression and functionality may consequently affect the disposition of substrate drugs, resulting in different drug exposure. Inflammation, present in several acute and chronic diseases, has been identified as a source of modulation in drug transporter expression leading to variability in drug response. Its regulation may be particularly dangerous for drugs with a narrow therapeutic index. In this context, numerous in vitro and in vivo models have shown up- or downregulation in the expression and functionality of ABC transporters under inflammatory conditions. Nevertheless, the existence of contradictory data and the lack of standardization for the models used have led to a less conclusive interpretation of these data.

Effect of Pregnancy and Concomitant Antiretrovirals on the Pharmacokinetics of Tenofovir in Women With HIV Receiving Tenofovir Disoproxil Fumarate-Based Antiretroviral Therapy Versus Women With HBV Receiving Tenofovir Disoproxil Fumarate Monotherapy

Tenofovir disoproxil fumarate (TDF) is recommended as part of antiretroviral therapy (ART) for pregnant women with HIV and as monotherapy for pregnant women with hepatitis B virus (HBV) monoinfection at high risk of transmitting infection to their infants. Tenofovir (TFV) plasma exposures are reduced during pregnancy; however, concomitant antiretrovirals and the viral infection itself can also influence TFV pharmacokinetics. Our aim was to compare TFV pharmacokinetics in pregnant women receiving TDF‐based ART, with or without a ritonavir‐boosted protease inhibitor (r/PI), to pregnant women with HBV receiving TDF monotherapy. Non‐r/PI regimens were primarily integrase strand transfer inhibitors or nonnucleoside reverse transcriptase inhibitor–based regimens. Data were combined from a pharmacokinetic study of pregnant women with HIV on ART (PANNA), and a study assessing TFV pharmacokinetics in pregnant women with HBV (iTAP). A total of 196 pregnant women, 59 with HIV (32 receiving r/PIs) and 137 with HBV monoinfection were included. Intraindividual TFV area under the plasma concentration–time curve from time 0 to 24 hours was 25%, 26%, and 21% lower during the third trimester compared to 1 month postpartum in women with HIV using TDF and an r/PI or TDF and non‐r/PI and women with HBV receiving TDF monotherapy, respectively. TFV area under the plasma concentration–time curve from time 0 to 24 hours was similar in pregnant women receiving non‐r/PI to pregnant women with HBV receiving TDF monotherapy (1.84 vs 1.86 µg • h/mL); however, pregnant women receiving TDF with an r/PI had higher exposures (2.41 µg • h/mL; P < .01). Pregnancy reduces TFV exposure and the relative size was not impacted by concomitant antiretroviral drugs or viral infection, but a drug‐drug interaction between TDF and r/PI remains during pregnancy, leading to higher exposures than those on TDF and non‐r/PI or TDF monotherapy.

Effect of ageing on antiretroviral drug pharmacokinetics using clinical data combined with modelling and simulation

AIMS

The impact of ageing on antiretroviral pharmacokinetics remains uncertain, leading to missing dosing recommendations for elderly people living with human immunodeficiency virus (HIV: PLWH). The objective of this study was to investigate whether ageing leads to clinically relevant pharmacokinetic changes of antiretrovirals that would support a dose adjustment based on the age of the treated PLWH.

METHODS

Plasma concentrations for 10 first-line antiretrovirals were obtained in PLWH ≥55 years, participating in the Swiss HIV Cohort Study, and used to proof the predictive performance of our physiologically based pharmacokinetic (PBPK) model. The verified PBPK model predicted the continuous effect of ageing on HIV drug pharmacokinetics across adulthood (20-99 years). The impact of ethnicity on age-related pharmacokinetic changes between whites and other races was statistically analysed.

RESULTS

Clinically observed concentration-time profiles of all investigated antiretrovirals were generally within the 95% confidence interval of the PBPK simulations, demonstrating the predictive power of the modelling approach used. The predicted decline in drug clearance drove age-related pharmacokinetic changes of antiretrovirals, resulting in a maximal 70% [95% confidence interval: 40%, 120%] increase in antiretrovirals exposure across adulthood. Peak concentration, time to peak concentration and apparent volume of distribution were predicted to be unaltered by ageing. There was no statistically significant difference of age-related pharmacokinetic changes between studied ethnicities.

CONCLUSION

Dose adjustment for antiretrovirals based on the age of male and female PLWH is a priori not necessary in the absence of severe comorbidities considering the large safety margin of the current first-line HIV treatments.

Pharmacokinetics of Coencapsulated Antiretrovirals with Ingestible Sensors

We investigated the use of a system with an ingestible sensor (Proteus Digital Health Feedback system) coencapsulated with antiretrovirals (ARVs) to measure real-time adherence. To assess the safety and impact, if any, coencapsulation might have on ARV concentrations, we evaluated the pharmacokinetics of ARVs coencapsulated with an ingestible sensor for eight commonly used fixed-dose combination ARVs: emtricitabine (FTC)/tenofovir disoproxil fumarate (TDF); FTC/tenofovir alafenamide (TAF); efavirenz (EFV)/FTC/TDF; abacavir (ABC)/lamivudine (3TC); dolutegravir (DTG)/ABC/3TC; rilpivirine (RPV)/TAF/FTC; elvitegravir (EVG)/cobicistat (COBI)/FTC/TAF; and bictegravir (BIC)/FTC/TAF. The steady-state apparent peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) were determined from plasma concentrations measured at predose, 1, 2, 4, and 6 h postdose, and compared with literature values. A total of 49 unique patients on stable regimens for at least 12 weeks with undetectable viral loads were recruited. Cmax and AUC values were not statistically significantly different from literature values for all of the formulations except the Cmax of FTC/TDF, Cmax of BIC, and the Cmax of RPV. In a subsequent evaluation of FTC/TDF and BIC/FTC/TAF using a crossover design, the geometric mean ratio (GMR) between the coencapsulated and the unencapsulated formulations for FTC/TDF were the following: FTC, 84.6% (90% confidence interval [CI] 66.6-107.4) for AUC and 77.5% (60.1-99.9) for Cmax. For tenofovir (TFV), the GMR was 96.2% (90% CI 89.2-103.8) for AUC and 87.3% (64.2-118.7) for Cmax. The GMR for BIC (from the BIC/FTC/TAF formulation) was 98.0% (90% CI 84.5-113.5) for AUC and 89.9% (84.5-95.7) for Cmax. The observed deviation in FTC/TDF (Truvada) may be due to participant characteristics, fasted/fed conditions, and/or random variation and may warrant further investigations with a larger sample size. These findings provide assurance for use of coencapsulated ARVs for future HIV treatment-adherence research.

Effects of Sofosbuvir-Based Hepatitis C Treatment Regimens on Calcineurin Inhibitor Dosing in Liver and Kidney Transplant Recipients

OBJECTIVES

Available data have suggested that directacting antivirals for hepatitis C virus may decrease calcineurin inhibitor concentrations. In this study, our aim was to determine the effects of hepatitis C directacting antivirals on calcineurin inhibitor doses and trough levels.

MATERIALS AND METHODS

This retrospective, singlecenter study included 52 abdominal transplant recipients treated with sofosbuvir-based regimens between 2014 and 2017. The primary outcome was percent change in calcineurin inhibitor troughs and total daily doses between the week before treatment with direct-acting antivirals, days 21 to 35 oftreatment, and days 21 to 35 aftertreatment. Secondary outcomes included sustained virologic response and biopsyproven acute rejection rates.

RESULTS

The median percent difference in calcineurin inhibitor troughs from pretreatment to during treatment was -20.5% (interquartile range, -36.2% to 13.1%) and from pretreatment to posttreatment was -13.5% (interquartile range, -33.7% to 10.7%). Corresponding percent changes in calcineurin inhibitor doses were 0% (interquartile range, 0%-0%) and 0% (interquartile range, -10.5% to 33.3%), respectively. Patients on tacrolimus experienced statistically significant changes in troughs but not doses. During treatment, 65% of patients required no dose change, 23% underwent a dose increase, and 12% had a dose decrease. The sustained virologic response rate was 98%, and the biopsy-proven acute rejection rate was 0%.

CONCLUSIONS

Hepatitis C direct-acting antiviraltherapy may decrease calcineurin inhibitor levels, but this was not associated with clinically different dosing requirements or rejection rates.

Impact of anti-HCV direct antiviral agents on graft function and immunosuppressive drug levels in kidney transplant recipients: a call to attention in the mid-term follow-up in a single-center cohort study

The medium-term impact on graft function and immunosuppressive drug pharmacokinetics of direct antiviral agents (DAAs) among hepatitis C virus (HCV)-infected kidney transplant (KT) recipients remain unclear. We compared pre- and post-treatment 12-month trajectories of estimated glomerular filtration rate (ΔeGFR) and 24-h proteinuria (Δ24-h proteinuria) in 49 recipients treated with DAAs (mostly sofosbuvir plus ledipasvir). Among evaluable patients, 66.7% and 100.0% had undetectable viral load by week 4 and end of therapy (EoT). The sustained virologic response rate at 12 weeks was 95.8%. Overall, 80.6% of patients receiving tacrolimus required dose escalation while on DAA-based therapy (median increase of 66.7%) to maintain target levels. Tacrolimus levels resulted to be higher at 12 months compared to EoT (7.8 ± 2.1 vs. 6.7 ± 2.0 ng/ml; P-value = 0.002). No changes in graft function during the course of therapy were observed. However, eGFR significantly decreased (P-value <0.001) throughout the first 12 months after EoT. Median ΔeGFR and Δ24-h over pre- and post-treatment periods were 3.9% and -6.1% (P-value = 0.002) and -5.3% and 26.2% (P-value = 0.057). Caution should be exercised when adjusting immunosuppression in HCV-infected KT recipients upon initiation of DAAs, followed by mid-term monitoring of immunosuppressive drug levels and graft function.

Intraindividual and Interindividual Variability of Olanzapine Trough Concentrations in Patients Treated With the Long-Acting Injectable Formulation

BACKGROUND

A long-acting injectable (LAI) formulation of olanzapine has been developed as an alternative to oral regimens. A therapeutic range of 20 to 80 ng/mL for oral olanzapine trough concentrations has been proposed. Here, we sought to investigate the intraindividual and interindividual variability of olanzapine concentrations with time in patients on maintenance therapy with the LAI formulation carried out in the routine clinical practice.

METHODS

To address this issue, we carried out a retrospective analysis of therapeutic drug monitoring of olanzapine concentrations in 21 schizophrenic patients on maintenance LAI olanzapine. Drug concentrations were correlated with LAI olanzapine doses, duration of treatment, and main clinical characteristics.

RESULTS

Fifty percent of the patients had olanzapine trough concentrations lower than 20 ng/mL. Only drug doses significantly correlated with olanzapine exposure. Mean interindividual and intraindividual coefficients of variations of olanzapine concentrations were 56% (range, 21%-97%) and 34% (range, 15%-69%), respectively.

CONCLUSIONS

We have documented that, in a real-life setting, a large proportion of patients treated with olanzapine LAI had drug trough concentrations of less than 20 ng/mL; wide intraindividual and interindividual variability of olanzapine concentrations has been also observed. Our results could provide the rationale for the design of larger prospective, concentration-controlled clinical trials specifically designed with the goal to identify ad hoc therapeutic ranges of drug concentrations for olanzapine LAI.

Once-daily atazanavir/cobicistat and darunavir/cobicistat exposure over 72 h post-dose in plasma, urine and saliva: contribution to drug pharmacokinetic knowledge

Background

We investigated the pharmacokinetics (PK) of atazanavir/cobicistat and darunavir/cobicistat once daily over 72 h following drug intake cessation in plasma, saliva and urine.

Methods

Healthy volunteers received a fixed-dose combination of 300/150 mg of atazanavir/cobicistat once daily for 10 days, followed by a 10 day washout period and then a fixed-dose combination of 800/150 mg of darunavir/cobicistat once daily for 10 days. Full PK profiles were assessed for each phase for 72 h following day 10 and parameters determined to the last measurable concentration in plasma, saliva and urine by non-compartmental methods.

Results

Sixteen subjects completed the study. Geometric mean (GM) terminal elimination half-life values to 72 h of atazanavir and darunavir were 6.77 and 6.35 h, respectively. All subjects had atazanavir concentrations above the suggested minimum effective concentration of 150 ng/mL 24 h post-dose and 14/16 subjects had concentrations higher than this target at 30 h post-dose (GM of 759 and 407 ng/mL, respectively). Thirteen out of 16 subjects had darunavir concentrations higher than the target of 550 ng/mL at 24 h post-dose and 5/16 subjects had concentrations higher than the target at 30 h post-dose (GM of 1033 and 382 ng/mL, respectively). Cobicistat half-life to 72 h was 4.21 h with atazanavir and 3.62 h with darunavir. GM values 24 h after the observed dose ( C 24 ) for atazanavir and darunavir were 141 and 43 ng/mL, respectively, in saliva and 24857 and 11878 ng/mL, respectively, in urine. Concentration decay in saliva/urine mirrored plasma concentrations for both drugs.

Conclusions

Different concentration decay patterns were seen for atazanavir and darunavir, which may be partially explained by cobicistat half-life (longer with atazanavir than darunavir). For the first time, we also measured drug PK forgiveness in saliva and urine, which represent easier markers of adherence.

Severe Hyperbilirubinemia in an HIV-HCV-Coinfected Patient Starting the 3D Regimen That Resolved After TDM-Guided Atazanavir Dose Reduction

The combination of ombitasvir, dasabuvir, and paritaprevir/ritonavir (considered as the 3D regimen) has proven to be associated with high sustained virologic response and optimal tolerability in hepatitis C virus-infected patients. Here, we describe an HIV-HCV-coinfected patient who experienced a grade 4 hyperbilirubinemia and a 2.5-fold increase in the atazanavir plasma trough concentrations few days after the start of 3D-based antiviral therapy who benefited from an atazanavir dose reduction guided by therapeutic drug monitoring.

Brief Report: High Need to Switch cART or Comedication With the Initiation of DAAs in Elderly HIV/HCV-Coinfected Patients

BACKGROUND

To describe the use of nonantiretroviral comedication and combination antiretroviral therapy (cART) in patients coinfected with HIV/hepatitis C virus (HCV) and to predict the potential for drug-drug interactions (DDIs) with direct-acting antivirals (DAAs) against HCV.

METHODS

This is a retrospective, cross-sectional study, using the Dutch, nationwide ATHENA observational HIV cohort database. All patients with a known HIV/HCV coinfection on January 1, 2015, were included. Comedication and cART registered in the database were listed. The potential for DDIs between DAAs and comedication/cART were predicted using http://hep-druginteractions.org. DDIs were categorized as: (1) no clinically relevant DDI; (2) possible DDI; (3) contraindication; or (4) no information available.

RESULTS

We included 777 patients of whom 488 (63%) used nonantiretroviral comedication. At risk for a category 2/3 DDI with nonantiretroviral comedications were 299 patients (38%). Most DDIs were predicted with paritaprevir/ritonavir, ombitasvir ± dasabuvir (47% of the drugs) and least with grazoprevir/elbasvir (11% of the drugs). Concerning cART, daclatasvir/sofosbuvir is the most favorable combination as no cART is contraindicated with this combination. In genotype 1/4 patients, grazoprevir/elbasvir is least favorable as 75% of the patients must alter their cART.

CONCLUSIONS

This study showed that comedication use in the aging HIV/HCV population is frequent and diverse. There is a high potential for DDIs between DAAs and comedication/cART.

Inflammation and pharmacokinetics: potential implications for HIV-infection

INTRODUCTION

The physiological changes accompanying inflammation may alter the pharmacokinetics (PK) of certain medications. Individuals infected with HIV have chronically elevated inflammatory markers despite viral suppression following effective antiretroviral therapy (ART), as well as age-related inflammation. Understanding the potential clinical implications of inflammation on the PK of medications is important for understanding dose-response relationships and necessitates future research. Areas covered: An extensive literature search was carried out using PubMed and associated bibliographies to summarize the current state of knowledge regarding altered PK in response to inflammation and its application to the field of HIV. Expert opinion: Preclinical and clinical studies show that inflammation leads to a downregulation of certain drug metabolizing enzymes and both up and down regulation of transporters depending on the transporter and cell type. Decreased gastric acidity, fluid shifts, and plasma protein alterations also occur with inflammation, leading to potential absorption, distribution, and clearance changes. More research is needed including controlled PK studies to address the clinical relevance of these observations, especially in the aging HIV-infected population. Results from future studies will enable us to better predict drug concentrations in individuals with inflammation, in line with efforts to provide personalized pharmacotherapy in our healthcare system.

Decreased tacrolimus plasma concentrations during HCV therapy: a drug-drug interaction or is there an alternative explanation?

Chronic hepatitis C virus (HCV) infection can cause severe liver cirrhosis, for which liver transplantation is the only therapy. To prevent organ rejection, transplanted patients are treated with immunosuppressive agents. We describe two transplanted patients treated with tacrolimus who were simultaneously treated with direct-acting antivirals (DAAs) for their chronic HCV infection. No pharmacokinetic drug-drug interactions (DDIs) were expected between tacrolimus and the selected DAAs. However, in both patients, tacrolimus plasma concentrations decreased during HCV treatment. We hypothesise that decreased plasma concentrations were not caused by a DDI but were an indirect result of the clearance of the HCV infection. During chronic HCV infection, pro-inflammatory cytokines may inhibit cytochrome P450 (CYP) enzymes, which are primarily responsible for tacrolimus metabolism. If this is true, then with clearance of the virus the activity of these enzymes will normalise and tacrolimus metabolism will increase. These changes were clinically relevant because the tacrolimus dosage needed to be adjusted. Therefore, physicians should be aware that CYP substrates with narrow therapeutic ranges might require dose adaption during HCV therapy with DAAs.

Dolutegravir plasma concentrations according to companion antiretroviral drug: unwanted drug interaction or desirable boosting effect?

BACKGROUND

Studies in healthy volunteers have shown that the recently approved HIV integrase inhibitor dolutegravir has limited drug-to-drug interaction profile. Here we carried out a pharmacokinetic survey in HIV-infected patients given dolutegravir as part of their antiretroviral therapy.

METHODS

Dolutegravir plasma trough concentrations were measured in 78 HIV-infected patients given the drug in combination with a protease inhibitor, a non-nucleoside reverse transcriptase inhibitor or abacavir/lamivudine. Drug concentrations were assessed by high performance liquid chromatography method with UV-detection.

RESULTS

All patients were given dolutegravir at 50 mg once daily, with median trough drug concentrations of 1,096 (664-2,356) ng/ml (interindividual coefficient of variation: 85.3%). Patients given dolutegravir with atazanavir had significantly higher drug concentrations compared with those given darunavir, rilpivirine or abacavir/lamivudine (2,399 [1,929-4,070] versus 738 [552-1,048], 603 [432-1,373] or 1,045 [856-1,115] ng/ml; P<0.001 for all comparisons). By multivariate analyses, only companion antiretroviral drug resulted in significant association with dolutegravir plasma trough concentrations (P=0.012).

CONCLUSIONS

Atazanavir coadministration significantly inhibited dolutegravir metabolism, ultimately resulting in a two- to fourfold increase in drug disposition compared with other antiretroviral drugs. This boosting effect of atazanavir could be used to optimize dolutegravir dosing in particular clinical settings.

Drug-Drug Interactions with the NS3/4A Protease Inhibitor Simeprevir

Simeprevir is an NS3/4A protease inhibitor approved for the treatment of hepatitis C infection, as a component of combination therapy. Simeprevir is metabolized by the cytochrome P450 (CYP) system, primarily CYP3A, and is a substrate for several drug transporters, including the organic anion transporting polypeptides (OATPs). It is susceptible to metabolic drug–drug interactions with drugs that are moderate or strong CYP3A inhibitors (e.g. ritonavir and erythromycin) or CYP3A inducers (e.g. rifampin and efavirenz); coadministration of these drugs may increase or decrease plasma concentrations of simeprevir, respectively, and should be avoided. Clinical studies have shown that simeprevir is a mild inhibitor of CYP1A2 and intestinal CYP3A but does not inhibit hepatic CYP3A. The effects of simeprevir on these enzymes are of clinical relevance only for narrow-therapeutic-index drugs that are metabolized solely by these enzymes (e.g. oral midazolam). Simeprevir does not have a clinically relevant effect on the pharmacokinetics of rilpivirine, tacrolimus, oral contraceptives and several other drugs metabolized by CYP enzymes. Simeprevir is a substrate and inhibitor of the transporters P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and OATP1B1/3. Cyclosporine is an inhibitor of OATP1B1/3, BCRP and P-gp, and a mild inhibitor of CYP3A; cyclosporine causes a significant increase in simeprevir plasma concentrations, and coadministration is not recommended. Clinical studies have demonstrated increases in coadministered drug concentrations for drugs that are substrates of the OATP1B1/3, BRCP (e.g. rosuvastatin) and P-gp (e.g. digoxin) transporters; these drugs should be administered with dose titration and or/close monitoring.

Lower Ribavirin Plasma Concentrations in HCV/HIV-Coinfected Patients Than in HCV-Monoinfected Patients Despite Similar Dosage

BACKGROUND

Hepatitis C virus (HCV)/HIV-coinfected patients respond worse to dual therapy with ribavirin (RBV)/peginterferon compared with HCV-monoinfected patients. Several trials found that lower RBV plasma concentrations are associated with impaired virological response rates. The aim of this study was to determine RBV plasma concentrations in a cohort of HCV-monoinfected and HCV/HIV-coinfected patients. Our hypothesis is that HCV/HIV-coinfected patients have lower RBV plasma concentrations, which may in part explain their inferior response to dual therapy.

METHODS

A retrospective cohort study was performed in chronic HCV-monoinfected and HCV/HIV-coinfected patients who received peginterferon and weight-based RBV. Plasma RBV concentrations were determined at weeks 4 and 12 by a validated high-performance liquid chromatography assay. RBV concentrations were compared between monoinfected and coinfected patients. We calculated the proportion of patients with a subtherapeutic RBV plasma concentration defined as <2.0 mg/L.

RESULTS

A total of 61 HCV-infected patients were included, of whom 21 (34%) were coinfected with HIV. Although there was no difference in the weight-based dose of RBV between monoinfected and coinfected patients, RBV exposure was significantly lower in HCV/HIV-coinfected patients than in HCV-monoinfected patients: the mean ± SD RBV plasma concentrations were 1.82 ± 0.63 mg/L versus 2.25 ± 0.80 mg/L (P = 0.04) at week 4 and 2.14 ± 0.65 mg/L versus 2.62 ± 0.81 mg/L (P = 0.05) at week 12, respectively. The percentage of patients with subtherapeutic plasma concentrations of RBV in coinfected patients versus monoinfected patients was 62% versus 46% (P = 0.240) at week 4 and 50% versus 16% (P = 0.01) at week 12 of treatment, respectively.

CONCLUSIONS

HIV/HCV-coinfected patients yield significantly lower plasma concentrations of RBV than HCV-monoinfected patients. This puts them at an increased risk of not achieving sustained virological response.

Pharmacokinetics of fixed-dose combination of tenofovir disoproxil fumarate, lamivudine, and efavirenz: results of a randomized, crossover, bioequivalence study

The objective of this study was to assess the bioequivalence between a fixed-dose combination of tenofovir disoproxil fumarate/lamivudine/efavirenz 300/300/600 mg and the individual innovator products. A randomized, balanced, open-label, two-sequence, two-treatment, two-period, single dose, crossover study in 48 healthy adults was conducted. Dosing was separated by a washout period of 32 days. Twenty-seven blood samples were collected in each period from pre-dose to 72 h post-dose. The data of 45 subjects were analyzed for pharmacokinetics and safety. Ninety percent CIs of geometric mean ratio on Cmax, AUC0–t, and AUC0-inf for tenofovir and lamivudine and on Cmax and AUC0-72 for efavirenz were within the acceptance criteria (80–125%). For tenofovir disoproxil fumarate, the Tmax, Kel, and t1/2 values for the test and reference products were 1.02 versus 0.91 h, 0.04 versus 0.04/h, 18.67 versus 18.46 h, respectively. For lamivudine, the Tmax, Kel, and t1/2 values were: 1.38 versus 1.30 h, 0.21 versus 0.19/h, 3.44 versus 3.91 h, respectively. For efavirenz, the Tmax values for the test and reference products were 3.71 and 3.65 h, respectively. Both the treatments were well tolerated. Our findings suggest that the tested formulation is bioequivalent to the innovators’ formulations, and both treatments were well tolerated.

Dolutegravir and elvitegravir plasma concentrations following cessation of drug intake

OBJECTIVES

To evaluate dolutegravir and elvitegravir/cobicistat pharmacokinetics in HIV-negative volunteers up to 10 days after drug cessation.

METHODS

Healthy volunteers received 50 mg of dolutegravir once-daily for 10 days, then underwent a 9 day wash-out period, and then received elvitegravir/cobicistat as part of Stribild(®) (245 mg of tenofovir, 200 mg of emtricitabine, 150 mg of elvitegravir and 150 mg of cobicistat) for 10 days. Serial pharmacokinetic (PK) sampling occurred prior to the final dose of each course and at regular intervals for up to 216 h (10 days) after drug cessation. Concentrations were determined by LC-MS/MS, and PK parameters were illustrated as geometric mean and 90% CI.

RESULTS

Seventeen volunteers completed the study. For dolutegravir, plasma terminal elimination t1/2 to the last measurable concentration (within 216 h) was longer than its t1/2 within the dosing interval (0-24 h): 14.3 h (12.9-15.7 h) versus 23.1 h (19.7-26.6 h); conversely, the terminal elimination t1/2 for elvitegravir was lower than its t1/2 within the dosing interval (0-24 h): 10.8 h (9.7-13.0 h) versus 5.2 h (4.7-6.1 h). Dolutegravir concentrations were above the protein-adjusted (PA) IC90 (64 ng/mL) in 100% of subjects after 36 and 48 h and in 94% after 60 and 72 h. All subjects had detectable dolutegravir concentrations at 96 h, a mean of 23.5% above the IC90. Elvitegravir concentrations were above the PA IC95 (45 ng/mL) in 100% of subjects at 24 h, 65% at 36 h but 0% after 48 h.

CONCLUSIONS

Our data show marked differences in the elimination rates of dolutegravir and elvitegravir following treatment interruption, which is likely to impact the extent to which drug doses can be delayed or missed. They suggest that clinical differences may emerge in patients who have suboptimal adherence.

Pharmacokinetic interactions between artesunate-mefloquine and ritonavir-boosted lopinavir in healthy Thai adults

Background

Concomitant use of anti-malarial and antiretroviral drugs is increasingly frequent in malaria and HIV endemic regions. The aim of the study was to investigate the pharmacokinetic interaction between the anti-malarial drugs, artesunate-mefloquine and the antiretroviral drug, lopinavir boosted with ritonavir (LPV/r).

Methods

The study was an open-label, three-way, sequential, cross-over, pharmacokinetic study in healthy Thai adults. Subjects received the following treatments: Period 1: standard 3-day artesunate-mefloquine combination; Period 2 (2 months wash-out): oral LPV/r 400 mg/100 mg twice a day for 14 days; and, Period 3: artesunate-mefloquine and LPV/r twice a day for 3 days. Sixteen subjects (eight females) were enrolled and pharmacokinetic parameters were determined by non-compartmental analysis.

Results

In the presence of LPV/r, artesunate C_max and systemic exposure were significantly increased by 45–80 %, while the metabolic ratio of dihydroartemisinin to artesunate was significantly reduced by 72 %. In addition, mefloquine C_max and systemic exposure were significantly reduced by 19–37 %. In the presence of artesunate-mefloquine, lopinavir C_max was significantly reduced by 22 % but without significant change in systemic drug exposure. The 90 % CI of the geometric mean ratio (GMR) of AUC_0−∞ and C_max were outside the acceptable bioequivalent range for each drug. Drug treatments were generally well tolerated with no serious adverse events. Vertigo, nausea and vomiting were the most common adverse events reported.

Conclusion

The reduction in systemic exposure of all investigated drugs raises concerns of an increased risk of treatment failure rate in co-infected patients and should be further investigated.

Viral hepatitis C therapy: pharmacokinetic and pharmacodynamic considerations

Chronic hepatitis C is a global health problem. To prevent or reduce complications, the hepatitis C virus (HCV) infection needs to be eradicated. There have been several developments in treating these patients since the discovery of the virus. As of 1 January 2014, the drugs that are approved for treatment of chronic HCV infection are peginterferon-α, ribavirin, boceprevir, telaprevir, simeprevir and sofosbuvir. In this review we provide an overview of the clinical pharmacokinetic characteristics of these agents by describing their absorption, distribution, metabolism and excretion. In the pharmacodynamic part we summarize what is known about the relationships between the pharmacokinetics of each drug and efficacy or toxicity. We briefly discuss the pharmacokinetics and pharmacodynamics of chronic hepatitis C treatment in special patient populations, such as patients with liver cirrhosis, renal insufficiency or HCV/HIV coinfection, and children. With this knowledge, physicians, pharmacists, nurse practitioners, etc. should be educated to safely and effectively treat HCV-infected patients.

Clinical pharmacokinetic drug interactions associated with artemisinin derivatives and HIV-antivirals

Management of HIV and malaria co-infection is challenging due to potential drug-drug interactions between antimalarial and HIV-antiviral drugs. Little is known of the clinical significance of these drug interactions, and this review provides a comprehensive summary and critical evaluation of the literature. Specifically, drug interactions between WHO-recommended artemisinin combination therapies (ACT) and HIV-antivirals are discussed. An extensive literature search produced eight articles detailing n = 44 individual pharmacokinetic interactions. Only data pertaining to artemether-lumefantrine and two other artesunate combinations are available, but most of the interactions are characterized on at least two occasions by two different groups. Overall, protease inhibitors (PIs) tended to increase the exposure of lumefantrine and decrease the exposures of artemether and dihydroartemisinin, a pharmacologically active metabolite of artemether. Non-nucleoside reverse transcriptase inhibitors (NNRTIs) tended to decrease the exposures of artemether, dihydroartemisinin, and lumefantrine when co-administered with artemether-lumefantrine. Fewer studies characterized the effects of PIs or NNRTIs on artesunate combinations, but nevirapine increased artesunate exposure and ritonavir decreased dihydroartemisinin exposure. On the other hand, artemether-lumefantrine or artesunate combinations had little effect on the pharmacokinetics of HIV-antivirals, with the exception of decreased nevirapine exposure from artemether-lumefantrine or increased ritonavir exposure from pyronaridine/artesunate co-administration. In general, pharmacokinetic interactions can be explained by the metabolic properties of the co-administered drugs. Despite several limitations to the studies, these data do provide valuable insights into the potential pharmacokinetic perturbations, and the consistently marked elevation or reduction in ACT exposure in some cases cannot be overlooked.

Tenofovir, emtricitabine intracellular and plasma, and efavirenz plasma concentration decay following drug intake cessation: implications for HIV treatment and prevention

BACKGROUND

In vivo data on tenofovir (TFV), emtricitabine (FTC), and efavirenz (EFV) concentration decay after intake cessation are limited; determinations of "true" elimination half-lives (t½) have often been based on suboptimal sampling windows. Understanding these parameters is important in managing missed doses and planning HIV pre-exposure prophylaxis (PrEP). This study investigated the pharmacokinetics (PK) of plasma TFV/FTC, their intracellular (IC) anabolites, TFV-diphosphate (DP) and FTC-triphosphate (TP), and plasma EFV over 10 days after intake cessation in HIV-negative volunteers.

METHODS

Volunteers received an Atripla (TFV/FTV/EFV) tablet daily for 14 days. PK sampling occurred before final dose and up to 228 hours after stopping. Peripheral blood mononuclear cells for [IC](drug) and [plasma](drug) were isolated, with analysis by tandem mass spectrometry.

RESULTS

Sixteen participants completed the study. Geometric mean plasma (t½)(228h) of TFV and FTC were 31 and 37 hours. These were longer than the previous reports (TFV 12-18 hours, FTC 10 hours).Geometric mean (t½)(228h) of IC TFV-DP and FTC-TP were 164 and 39 hours, whereas for EFV in plasma was 92 hours. [EFV](plasma) in 5/16 participants were below the suggested MEC of 1000 ng/mL within 48 hours postdose; however, 50% of the participants maintained concentrations above this level after 84 hours.

CONCLUSIONS

These data fully characterize the PK of TFV and TFV-DP, FTC and FTC-TP, and EFV after stopping the drug combination. Although decay in concentrations can be related to a target for EFV, this is more difficult for the IC phosphates. Consensus on 'target' triphosphate/diphosphate concentrations will further our understanding of missed/delayed doses in treatment and prevention strategies.

Influence of chronic hepatitis C infection on cytochrome P450 3A4 activity using midazolam as an in vivo probe substrate

PURPOSE

Inflammation-related changes in pharmacokinetics have been described for a number of disease-states including cancer, infection, and autoimmune disorders. This study examined the impact of chronic hepatitis C infection (CHC) on the pharmacokinetics of the cytochrome P450 3A probe midazolam in patients without significant liver disease who were either treatment naïve or prior interferon null-responders.

METHODS

Data were pooled from three studies which compared the pharmacokinetics of oral midazolam in healthy volunteers (n = 107) and in treatment-naive patients (n = 35) and interferon-null responders (n = 24) with CHC but without significant liver disease. Oral midazolam was administered as a single 2 mg oral dose, followed by frequent pharmacokinetic sampling and determination of the pharmacokinetics of midazolam and its α-hydroxy metabolite. CYP3A activity was determined by the metabolic ratio (MR) of the AUC metabolite/AUC parent and compared across groups as the mean effect ratio (test/reference).

RESULTS

The midazolam MR was lower in treatment-naïve patients with CHC than in health volunteers with a mean effect ratio of 0.63 [90 % confidence interval (CI) 0.56-0.72]. The effect was more pronounced in null-responders, who demonstrated a mean MR effect ratio of 0.46 (90 % CI 0.39-0.53) compared to volunteers. The mean area under the concentration-time curve (AUCinf) for midazolam in healthy volunteers, naïve patients, and null-responders was 32.3 [coefficient of variation (CV%) 41], 36.5 (CV% 33.5), and 55.3 (CV% 36.9) ng.h/mL, respectively.

CONCLUSIONS

The results of this study demonstrate a reduction in CYP3A4 activity between healthy volunteers and patients with CHC, with interferon null-responders demonstrating the most substantial difference. These results may have implications for the pharmacotherapy of patients infected with CHC.

The HIV-1 protease inhibitor nelfinavir activates PP2 and inhibits MAPK signaling in macrophages: a pathway to reduce inflammation

The HIV-1 PI NFV has off-target effects upon host enzymes, including inhibition of the 20S proteasome, resulting in activation of PP1. HIV-1-associated monocyte/macrophage activation, in part a result of systemically elevated levels of microbial products including LPS, is associated with risk of mortality, independent of viremia or CD4 T cell loss. This study tested the hypothesis that activation of protein phosphatases by NFV would reduce activation of monocytes/macrophages through dephosphorylation of signal transduction proteins. NFV uniquely blocked LPS-induced production by human monocyte-derived macrophages of the inflammatory cytokines TNF and IL-6, as well as sCD14. Although NFV failed to modulate NF-κB, NFV treatment reduced phosphorylation of AKT and MAPKs. Inhibition of PP2 with okadaic acid blocked the anti-inflammatory effect of NFV, whereas the PP1 inhibitor calyculin A failed to counter the anti-inflammatory effects of NFV. For in vivo studies, plasma sCD14 and LPS were monitored in a cohort of 31 pediatric HIV-1 patients for over 2 years of therapy. Therapy, including NFV, reduced sCD14 levels significantly compared with IDV or RTV, independent of ΔLPS levels, VL, CD4 T cell frequency, or age. The hypothesis was supported as NFV induced activation of PP2 in macrophages, resulting in disruption of inflammatory cell signaling pathways. In vivo evidence supports that NFV may offer beneficial effects independent of antiviral activity by reducing severity of chronic innate immune activation in HIV-1 infection.

Nevirapine-Based Antiretroviral Therapy Impacts Artesunate and Dihydroartemisinin Disposition in HIV-Infected Nigerian Adults

Background. Nevirapine- (NVP-) based antiretroviral therapy (ART) and artesunate-amodiaquine are frequently coprescribed in areas of HIV and malaria endemicity. We explored the impact of this practice on artesunate and dihydroartemisinin pharmacokinetics. Methods. We conducted a parallel-group pharmacokinetic comparison between HIV-infected patients receiving NVP-based ART (n = 10) and ART-naive controls (n = 11). Artesunate-amodiaquine 200/600 mg was given daily for three days. Measurement of drug concentrations occurred between 0 and 96 hours after the final dose. Pharmacokinetic parameters were determined using noncompartmental analysis. Results. Comparing the NVP group to controls, clearance of artesunate was reduced 50% (1950 versus 2995 L/h; P = 0.03), resulting in a 45% increase in the AUC_0-96 (105 versus 69 ug^∗hr/L; P = 0.02). The half-life of dihydroartemisinin was shorter in the NVP group (1.6 versuss 3.2 h; P = 0.004), but other dihydroartemisinin pharmacokinetic parameters were unchanged. A lower conversion of artesunate to dihydroartemisinin was observed in the NVP group (dihydroartemisinin: artesunate AUC_0-96 = 5.6 versuss 8.5 in NVP and control groups, respectively, P = 0.008). Conclusion. Although NVP-containing ART impacted some pharmacokinetic parameters of artesunate and dihydroartemisinin, overall exposure was similar or better in the NVP group.

Improved oral bioavailability of lopinavir in melt-extruded tablet formulation reduces impact of third trimester on lopinavir plasma concentrations

Lopinavir exposure was reduced during the third trimester in pregnant women receiving standard dosing of the soft-gel capsule (SGC; 400/100 mg twice daily [b.i.d.]). Pharmacokinetic data on the lopinavir tablet in pregnancy are limited. On the basis of the tablet's improved bioavailability, standard dosing (400/100 mg b.i.d.) may provide adequate lopinavir exposure in pregnancy without a need for dose adjustment. Here we compared the total and unbound lopinavir pharmacokinetics throughout pregnancy in the second and third trimesters in HIV-infected women receiving standard dosing of the lopinavir SGC or tablet. Postpartum sampling was also performed in patients continuing therapy postdelivery. Blood samples were collected at 0 to 12 h postdosing, and lopinavir concentrations were determined by high-pressure liquid chromatography-tandem mass spectrometry. Nineteen patients were included: 8 received the SGC (cohort 1) and 11 received the tablet (cohort 2). Total lopinavir exposures in the third trimester were lower than those in the second trimester (35 and 28% for cohorts 1 and 2, respectively) and postpartum (35% for cohort 2). In the third trimester, the area under the concentration-time curve (AUC) from 0 to 12 h (AUC(0-12)) and maximum concentration were ∼15% and 25% higher, respectively, for the lopinavir tablet than the SGC. One SGC patient had lopinavir concentrations of <1,000 ng/ml; all patients on the tablet had concentrations of >1,000 ng/ml. In cohort 2, the percentage of the AUC that was unbound was higher (nonsignificantly) in the second (1.28%) and third (1.18%) trimesters than postpartum (1.01%). Seventeen of 19 patients had an undetectable viral load at delivery. There were no HIV transmissions. Although lopinavir (tablet) exposures were reduced during the third trimester, the higher total and unbound concentrations achieved in women receiving the tablet than in women receiving the SGC suggest that the tablet's improved oral bioavailability may partly compensate for the reduction in lopinavir exposure during the later stages of pregnancy.

Pharmacokinetic drug interactions of antimicrobial drugs: a systematic review on oxazolidinones, rifamycines, macrolides, fluoroquinolones, and Beta-lactams

Like any other drug, antimicrobial drugs are prone to pharmacokinetic drug interactions. These drug interactions are a major concern in clinical practice as they may have an effect on efficacy and toxicity. This article provides an overview of all published pharmacokinetic studies on drug interactions of the commonly prescribed antimicrobial drugs oxazolidinones, rifamycines, macrolides, fluoroquinolones, and beta-lactams, focusing on systematic research. We describe drug-food and drug-drug interaction studies in humans, affecting antimicrobial drugs as well as concomitantly administered drugs. Since knowledge about mechanisms is of paramount importance for adequate management of drug interactions, the most plausible underlying mechanism of the drug interaction is provided when available. This overview can be used in daily practice to support the management of pharmacokinetic drug interactions of antimicrobial drugs.

Effects of the H2-receptor antagonist famotidine on the pharmacokinetics of atazanavir-ritonavir with or without tenofovir in HIV-infected patients

Significant pharmacokinetic interactions can result between acid-suppressing agents and some protease inhibitors (PIs) in the management of HIV infection. In healthy subjects, famotidine, an H(2)-receptor antagonist, reduces exposures of atazanavir by 4-28% at doses of 20-40 mg twice daily. This study evaluated the effect of famotidine 20-40 mg twice daily on the pharmacokinetics of atazanavir/ritonavir 300/100 mg once daily with and without tenofovir disoproxil fumarate (TDF) 300 mg in HIV-infected patients (n=40; 87.5% male; mean age 42, range 26-63 years; 55% white). Coadministration of famotidine 40 mg and atazanavir/ritonavir to HIV-infected patients reduced exposures of atazanavir by approximately 20%. This is comparable to reductions seen in HIV-uninfected subjects. Coadministration of famotidine 20 mg had less impact on atazanavir exposures, with no reduction of atazanavir geometric mean plasma concentration at 24 h postdose (C(min)). In the presence of TDF, administration of famotidine 20-40 mg twice daily 2 h after and 10 h before atazanavir/ritonavir reduced exposures of atazanavir by 19-25%. However, all individual atazanavir C(min) values remained at least five-fold above the population mean protein-binding adjusted 90% maximum effect (EC(90)) against wild-type HIV (14 ng/mL). No viral load rebound was observed at end of study. The results confirmed that coadministration of an H(2)-receptor antagonist with atazanavir/ritonavir in HIV-infected patients resulted in similar magnitude of reductions in atazanavir exposures as in healthy subjects. This supports the current dose recommendations for coadministration of an H(2)-receptor antagonist with atazanavir/ritonavir.

Pharmacokinetics of once-daily darunavir-ritonavir and atazanavir-ritonavir over 72 hours following drug cessation

The object of this study was to investigate the pharmacokinetics of darunavir-ritonavir and atazanavir-ritonavir once-daily dosing over 72 h (h) following drug intake cessation. Volunteers received darunavir-ritonavir at 800 and 100 mg, respectively, once daily for 10 days, followed by a 7-day washout period, and atazanavir-ritonavir at 300 and 100 mg, respectively, once daily for 10 days. Full pharmacokinetic profiles were assessed for each phase for the 72 h following day 10. Pharmacokinetic parameters were determined over 24 h and to the last measurable concentration by noncompartmental methods. Seventeen subjects completed the study. The geometric mean (GM) terminal elimination half-life to 72 h of darunavir was 6.48 h, which was lower than the 0- to 24-h half-life (10.70 h). The terminal elimination half-life of atazanavir was 6.74 h, which was lower than the 0- to 24-h half-life (13.72 h). All subjects but one had darunavir concentrations higher than the target of 550 ng/ml for protease-resistant HIV isolates (equivalent to 10 times the protein-binding-corrected 50% inhibitory concentration [IC(50)] for wild-type virus) at 24 h postdose, and 14 out of 17 had concentrations higher than the target at 30 h postdose (GM of 1,088 and 851 ng/ml). All subjects had atazanavir concentrations above the suggested minimum effective concentration of 150 ng/ml (equivalent to 10 times the protein-binding-corrected IC(50) for wild-type virus) at 24 and 30 h postdose (GM of 693 and 392 ng/ml). Two of 17 and 5 of 17 subjects were above target at 48 h postdose while on darunavir-ritonavir and atazanavir-ritonavir. Ritonavir half-life to 72 h was 6.84 h with darunavir and 6.07 with atazanavir. This study investigated the pharmacokinetic forgiveness of two boosted protease inhibitors. Although the rates of decline of darunavir and atazanavir slightly increased as ritonavir concentrations declined, most individuals had concentrations 6 h after the end of the ideal dosing interval of 24 h which were above the cutoff used to define therapeutic concentrations.

Pharmacokinetics of plasma lopinavir/ritonavir following the administration of 400/100 mg, 200/150 mg and 200/50 mg twice daily in HIV-negative volunteers

OBJECTIVES

Data suggest that some licensed antiretroviral doses could be reduced. We assessed the safety, tolerability and pharmacokinetics of lopinavir/ritonavir at doses of 400/100, 200/150 and 200/50 mg twice daily in HIV-negative volunteers (http://clinicaltrials.gov/ct2/show/NCT00985543).

METHODS

Male and female volunteers were administered lopinavir/ritonavir at doses of 400/100 mg (two lopinavir/ritonavir Meltrex 200/50 mg tablets, Regimen 1), 200/150 mg (one Meltrex tablet, one 100 mg ritonavir capsule, Regimen 2) and 200/50 mg (one Meltrex tablet, Regimen 3). Each dose was given twice daily for 7 days sequentially, separated by a 7 day wash-out period. Lopinavir/ritonavir steady-state pharmacokinetics was assessed over 12 h at the end of each phase (days 7, 21 and 35). Pharmacokinetic parameters were compared using the 400/100 mg twice daily dose as reference, by determining geometric mean ratios (GMRs) and 90% confidence intervals.

RESULTS

Twenty-two subjects (eight females) completed the study. Lopinavir AUC(0-12) (ng h/mL), C(max) (ng/mL) and the minimum concentration (C(trough)) (ng/mL) for the 400/100, 200/150 and 200/50 mg twice daily doses, respectively, were as follows: 99,599, 73,603 and 45,146; 11,965, 8939 and 6404; and 5776, 4293 and 1749. Lopinavir pharmacokinetic parameters were significantly lower for Regimens 2 and 3: GMR (90% CI) AUC(0-12), 0.74 (0.65-0.84) and 0.45 (0.40-0.51); C(max), 0.75 (0.66-0.85) and 0.54 (0.40-0.60); and C(trough), 0.74 (0.62-0.89) and 0.30 (0.25-0.36), respectively. All subjects taking the 400/100 and 200/150 mg twice daily doses, and 19 (86%) subjects taking 200/50 mg twice daily had lopinavir concentrations above the suggested minimum effective concentration of 1000 ng/mL.

CONCLUSIONS

These pharmacokinetic data show that therapeutic plasma concentrations of lopinavir can be achieved with 200/150 mg of lopinavir/ritonavir twice daily (one Meltrex tablet and one 100 mg ritonavir capsule twice daily).

The role of cytokines in the regulation of drug disposition: extended functional pleiotropism?

INTRODUCTION

Drug disposition, metabolism and drug-drug interactions are important considerations for most drugs. Cytokines are integral to the successful resolution of many diseases. Data are emerging on a role for cytokines in regulation of the expression and activity of drug transporters and drug metabolising enzymes. Investigation of the interaction between pharmacological and immunological responses is key to understanding the complex relationships involved in patient response to therapy.

AREAS COVERED

Evidence detailing the ability of cytokines to regulate drug disposition and metabolism is reviewed in the context of different cell and tissue types. The literature search undertaken provides an overview of the current understanding of the interrelationship between pharmacological and immunological factors which may influence successful drug therapy.

EXPERT OPINION

Dysregulation of cytokines and cytokine networks is a hallmark of a number of diseases such as HIV and cancer. The mechanisms by which the immune system can influence drug disposition are relatively understudied but recent work has highlighted the necessity for examining its impact on pharmacokinetics and pharmacodynamics. A more comprehensive approach in clinical studies will allow better determination of the impact of cytokines on drug disposition. In addition, determining the mechanisms that underpin the differential effects of cytokines across different cell types will clarify the responses reported in these studies.

Drug interactions should be evaluated in patients

Drug development involves learning and confirming in healthy volunteers and ultimately in patients. This approach should apply to drug-drug interactions because requirements to extrapolate pharmacokinetic and pharmacodynamic findings from healthy volunteers to patients are not uniformly met, and the designs of interaction studies often have little relevance to actual clinical use. Guidance to health-care professionals on a safe and effective dose for individual patients should include information from drug-drug interaction studies in the intended patients.

Recognition and management of significant drug interactions in HIV patients: challenges in using available data to guide therapy

Combination antiretroviral therapy (cART) has improved survival rates in HIV-infected patients; however, patients now experience comorbidities that require pharmacological intervention, thereby increasing the risk of drug-drug interactions (DDIs). HIV protease inhibitors (PIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), and the CCR5 antagonist maraviroc are primarily metabolized via the cytochrome P450 (CYP) system and are prone to pharmacokinetic interactions.(1,2) This article addresses some key challenges that prescribers face when using available drug interaction-data resources in making day-to-day clinical decisions.

The impact of cytokines on the expression of drug transporters, cytochrome P450 enzymes and chemokine receptors in human PBMC

BACKGROUND AND PURPOSE

The function of transporters in peripheral blood mononuclear cells (PBMC) has been characterized, but less is known about cytochrome P450 (CYP) enzyme function in these cells. Given that cytokines are dysregulated in many diseases, the purpose of this work was to assess the impact of cytokines on the expression of CYPs, transporters and chemokine receptors in PBMC.

EXPERIMENTAL APPROACH

Human PBMC were incubated with cytokines for 48 h. ATP-binding cassette (ABC)B1, ABCC1, ABCC2, CYP2B6, CYP3A4, CXCR4 and CCR5 expression were measured by quantitative polymerase chain reaction and flow cytometry at 0, 4, 8, 24 and 48 h. Enzyme activity was assessed using fluorescent probes.

KEY RESULTS

We show here functional activity of CYP3A4 and CYP2B6 in PBMC. Furthermore, cytokines had a significant impact on the mRNA and protein expression of all proteins. For example, interleukin-2 (IL-2) had a marked impact on ABCB1 mRNA (% control 4745 +/- 11961) and protein (% control 200 +/- 57). Increases in drug efflux transporter expression, in response to cytokines, resulted in reduced cellular accumulation of digoxin [decrease of 17% and 26% for IL-2 and interferon-gamma (IFNgamma) respectively] and saquinavir (decrease of 28% and 30% for IL-2 and IFNgamma respectively). The degree to which drug transporter and chemokine receptor expression changed in response to cytokines was positively correlated (e.g. ABCB1 and CXCR4, r(2) = 0.545).

CONCLUSIONS AND IMPLICATIONS

These data have important implications for diseases in which cytokines are dysregulated and for which pharmacological intervention targets immune cells.

Pharmacokinetics of Atazanavir/Ritonavir Once Daily and Lopinavir/Ritonavir Twice and once Daily over 72 h following drug Cessation

Background

We investigated the pharmacokinetics of atazanavir/ritonavir once daily and lopinavir/ritonavir twice and once daily over 72 h following drug intake cessation.

Methods

This was an open-label, three-session, pharmacokinetic trial. Healthy volunteers received atazanavir/ritonavir 300/100 mg once daily and lopinavir/ ritonavir 400/100 mg twice daily and 800/200 mg once daily separately for 10 days. Pharmacokinetic profiles were assessed for each phase on day 10 over 72 h. Pharmacokinetic parameters were determined over 12 or 24 h and to the last measurable concentration by non-compartmental methods.

Results

Sixteen participants completed the study. Geometric mean terminal elimination half-life to 72 h of atazanavir was 8.35 h and not different from the 0–24 h half-life (9.91 h). Terminal elimination half-life of lopinavir was 2.33 h (twice daily) and 2.44 h (once daily). These values were lower compared with the half-life over the respective dosing intervals (7.15 and 4.88 h for 0–12 and 0–24 h, respectively). No participant on atazanavir had concentrations below the minimum effective concentration (MEC) of 150 ng/ml at 24 h. In total, 44% of the participants on lopinavir once daily had concentrations below the MEC of 1,000 ng/ml at 24 h. At 16 h and 20 h, 13% and 63% of participants were below target for twice daily lopinavir, respectively. At 36 h, all participants on lopinavir and 31% on atazanavir were below target. Ritonavir area under the plasma concentration–time curve was 30% lower and 26% higher when dosed at 100 mg or 200 mg with lopinavir versus atazanavir.

Conclusions

This study investigated the pharmacokinetic forgiveness of two boosted protease inhibitors. Whereas the decline in lopinavir concentrations occured rapidly as the boosting effect of ritonavir diminished, the rate of decline of atazanavir remained constant to 72 h.