Drug-drug interaction profile of the all-oral anti-hepatitis C virus regimen of paritaprevir/ritonavir, ombitasvir, and dasabuvir

Mechanistic Determinants of Daprodustat Drug-Drug Interactions and Pharmacokinetics in Hepatic Dysfunction and Chronic Kidney Disease: Significance of OATP1B-CYP2C8 Interplay

Daprodustat is the first oral hypoxia-inducible factor prolyl hydroxylase inhibitor approved recently for the treatment of anemia caused by chronic kidney disease (CKD) in adults receiving dialysis. We evaluated the role of organic anion transporting polypeptide (OATP)1B-mediated hepatic uptake transport in the pharmacokinetics (PKs) of daprodustat using in vitro and in vivo studies, and physiologically-based PK (PBPK) modeling of its drug-drug interactions (DDIs) with inhibitor drugs. In vitro, daprodustat showed specific transport by OATP1B1/1B3 in the transfected cell systems and primary human and monkey hepatocytes. A single-dose oral rifampin (OATP1B inhibitor) reduced daprodustat intravenous clearance by a notable 9.9 ± 1.2-fold (P < 0.05) in cynomolgus monkeys. Correspondingly, volume of distribution at steady-state was also reduced by 5.0 ± 1.1-fold, whereas the half-life change was minimal (1.5-fold), corroborating daprodustat hepatic uptake inhibition by rifampin. A PBPK model accounting for OATP1B-CYP2C8 interplay was developed, which well described daprodustat PK and DDIs with gemfibrozil (CYP2C8 and OATP1B inhibitor) and trimethoprim (weak CYP2C8 inhibitor) within 25% error of the observed data in healthy subjects. About 18-fold increase in daprodustat area under the curve (AUC) following gemfibrozil treatment was found to be associated with strong CYP2C8 inhibition and moderate OATP1B inhibition. Moreover, PK modulation in hepatic dysfunction and subjects with CKD, in comparison to healthy control, was well-captured by the model. CYP2C8 and/or OATP1B inhibitor drugs (e.g., gemfibrozil, clopidogrel, rifampin, and cyclosporine) were predicted to perpetrate moderate-to-strong DDIs in healthy subjects, as well as, in target CKD population. Daprodustat can be used as a sensitive CYP2C8 index substrate in the absence of OATP1B modulation.

A genetic algorithm-based approach for the prediction of metabolic drug-drug interactions involving CYP2C8 or CYP2B6

BACKGROUND AND OBJECTIVES

A genetic algorithm (GA) approach was developed to predict drug-drug interactions (DDIs) caused by cytochrome P450 2C8 (CYP2C8) inhibition or cytochrome P450 2B6 (CYP2B6) inhibition or induction. Nighty-eight DDIs, obtained from published in vivo studies in healthy volunteers, have been considered using the area under the plasma drug concentration-time curve (AUC) ratios (i.e., ratios of AUC of the drug substrate administered in combination with a DDI perpetrator to AUC of the drug substrate administered alone) to describe the extent of DDI.

METHODS

The following parameters were estimated in this approach: the contribution ratios (CRCYP2B6 and CRCYP2C8, i.e., the fraction of the dose metabolized via CYP2B6 or CYP2C8, respectively) and the inhibitory or inducing potency of the perpetrator drug (IRCYP2B6, IRCYP2C8 and ICCYP2B6, for inhibition of CYP2B6 and CYP2C8, and induction of CYP2B6, respectively). The workflow consisted of three main phases. First, the initial estimates of the parameters were estimated through GA. Then, the model was validated using an external validation. Finally, the parameter values were refined via a Bayesian orthogonal regression using all data.

RESULTS

The AUC ratios of 5 substrates, 11 inhibitors and 19 inducers of CYP2B6, and the AUC ratios of 19 substrates and 23 inhibitors of CYP2C8 were successfully predicted by the developed methodology within 50-200% of observed values.

CONCLUSIONS

The approach proposed in this work may represent a useful tool for evaluating the suitable doses of a CYP2C8 or CYP2B6 substrates co-administered with perpetrators.

Screening of 16 major drug glucuronides for time-dependent inhibition of nine drug-metabolizing CYP enzymes - detailed studies on CYP3A inhibitors

Time-dependent inhibition of cytochrome P450 (CYP) enzymes has been observed for a few glucuronide metabolites of clinically used drugs. Here, we investigated the inhibitory potential of 16 glucuronide metabolites towards nine major CYP enzymes in vitro. Automated substrate cocktail methods were used to screen time-dependent inhibition of CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2J2 and 3A in human liver microsomes. Seven glucuronides (carvedilol β-D-glucuronide, diclofenac acyl-β-D-glucuronide, 4-hydroxyduloxetine β-D-glucuronide, ezetimibe phenoxy-β-D-glucuronide, raloxifene 4'-glucuronide, repaglinide acyl-β-D-glucuronide and valproic acid β-D-glucuronide) caused NADPH- and time-dependent inhibition of at least one of the CYPs investigated, including CYP2A6, CYP2C19 and CYP3A. In more detailed experiments, we focused on the glucuronides of carvedilol and diclofenac, which inhibited CYP3A. Carvedilol β-D-glucuronide showed weak time-dependent inhibition of CYP3A, but the parent drug carvedilol was found to be a more potent inhibitor of CYP3A, with the half-maximal inhibitor concentration (IC50) decreasing from 7.0 to 1.1 µM after a 30-min preincubation with NADPH. The maximal inactivation constant (kinact) and the inhibitor concentration causing half of kinact (KI) for CYP3A inactivation by carvedilol were 0.051 1/min and 1.8 µM, respectively. Diclofenac acyl-β-D-glucuronide caused time-dependent inactivation of CYP3A at high concentrations, with a 4-fold IC50 shift (from 400 to 98 µM after a 30-min preincubation with NADPH) and KI and kinact values of >2,000 µM and >0.16 1/min. In static predictions, carvedilol caused significant (>1.25-fold) increase in the exposure of the CYP3A substrates midazolam and simvastatin. In conclusion, we identified several glucuronide metabolites with CYP inhibitory properties. Based on detailed experiments, the inactivation of CYP3A by carvedilol may cause clinically significant drug-drug interactions.

Drug-drug interactions that alter the exposure of glucuronidated drugs: Scope, UDP-glucuronosyltransferase (UGT) enzyme selectivity, mechanisms (inhibition and induction), and clinical significance

Drug-drug interactions (DDIs) arising from the perturbation of drug metabolising enzyme activities represent both a clinical problem and a potential economic loss for the pharmaceutical industry. DDIs involving glucuronidated drugs have historically attracted little attention and there is a perception that interactions are of minor clinical relevance. This review critically examines the scope and aetiology of DDIs that result in altered exposure of glucuronidated drugs. Interaction mechanisms, namely inhibition and induction of UDP-glucuronosyltransferase (UGT) enzymes and the potential interplay with drug transporters, are reviewed in detail, as is the clinical significance of known DDIs. Altered victim drug exposure arising from modulation of UGT enzyme activities is relatively common and, notably, the incidence and importance of UGT induction as a DDI mechanism is greater than generally believed. Numerous DDIs are clinically relevant, resulting in either loss of efficacy or an increased risk of adverse effects, necessitating dose individualisation. Several generalisations relating to the likelihood of DDIs can be drawn from the known substrate and inhibitor selectivities of UGT enzymes, highlighting the importance of comprehensive reaction phenotyping studies at an early stage of drug development. Further, rigorous assessment of the DDI liability of new chemical entities that undergo glucuronidation to a significant extent has been recommended recently by regulatory guidance. Although evidence-based approaches exist for the in vitro characterisation of UGT enzyme inhibition and induction, the availability of drugs considered appropriate for use as 'probe' substrates in clinical DDI studies is limited and this should be research priority.

ABT-333 (Dasabuvir) Increases Action Potential Duration and Provokes Early Afterdepolarizations in Canine Left Ventricular Cells via Inhibition of IKr

ABT-333 (dasabuvir) is an antiviral agent used in hepatitis C treatment. The molecule, similarly to some inhibitors of hERG channels, responsible for the delayed rectifier potassium current (IKr), contains the methanesulfonamide group. Reduced IKr current leads to long QT syndrome and early afterdepolarizations (EADs), therefore potentially causing life-threatening arrhythmias and sudden cardiac death. Our goal was to investigate the acute effects of ABT-333 in enzymatically isolated canine left ventricular myocardial cells. Action potentials (APs) and ion currents were recorded with a sharp microelectrode technique and whole-cell patch clamp, respectively. Application of 1 μM ABT-333 prolonged the AP in a reversible manner. The maximal rates of phases 0 and 1 were irreversibly decreased. Higher ABT-333 concentrations caused larger AP prolongation, elevation of the early plateau potential, and reduction of maximal rates of phases 0, 1, and 3. EADs occurred in some cells in 3–30 μM ABT-333 concentrations. The 10 μM ABT-333-sensitive current, recorded with AP voltage clamp, contained a late outward component corresponding to IKr and an early outward one corresponding to transient outward potassium current (Ito). ABT-333 reduced hERG-channel-mediated ion current in a concentration-dependent, partially reversible manner with a half-inhibitory concentration of 3.2 μM. As the therapeutic plasma concentration of ABT-333 is 1 nM, the arrhythmic risk of ABT-333 is very low, even in the case of drug overdose.

Effects of a ritonavir-containing regimen on the pharmacokinetics of sirolimus or everolimus in healthy adult subjects

The immunosuppressive agents sirolimus and everolimus are sensitive CYP3A4 substrates with narrow therapeutic index. Ritonavir is a strong CYP3A inhibitor. A phase 1 study was conducted to evaluate the pharmacokinetics, safety, and tolerability of the co-administration of sirolimus or everolimus with the ritonavir-containing 3D regimen of the direct-acting antiviral agents ombitasvir, ritonavir-boosted paritaprevir, and dasabuvir in healthy subjects. This study had two independent arms, each with a two-period, single-sequence, crossover study design. A single dose of sirolimus 2 mg (N = 12) or everolimus 0.75 mg (N = 12) was administered in Period 1. In Period 2, multiple doses of the 3D regimen (ombitasvir/paritaprevir/ritonavir 25/150/100 mg once daily and dasabuvir 250 mg twice daily) were administered for 34 or 28 days, with a single dose of sirolimus 0.5 mg or everolimus 0.75 mg co-administered on Day 15. Following co-administration with the 3D regimen, the sirolimus dose-normalized maximum observed blood concentration (Cmax ) and area under the blood concentration-time curve from time zero to infinity (AUCinf ) increased to 6.4-fold and 38-fold, respectively. Following co-administration with the 3D regimen, the everolimus Cmax and AUCinf increased to 4.7-fold and 27-fold, respectively. Sirolimus and everolimus half-lives increased from 96 to 249 h, and 42 to 118 h, respectively. There were no major safety or tolerability issues in this study. The ritonavir-containing 3D regimen resulted in a significant increase in sirolimus or everolimus exposure, consistent with the known strong inhibitory effect of ritonavir on CYP3A requiring dose and/or frequency modification when co-administered with each other.

Inhibition of CYP2C8 by Acyl Glucuronides of Gemfibrozil and Clopidogrel: Pharmacological Significance, Progress and Challenges

The lipid-regulating drug gemfibrozil is a useful medication for reducing high cholesterol and triglycerides in the blood. In addition to oxidation, it undergoes extensive glucuronidation to produce gemfibrozil acyl glucuronide, which is a known mechanism-based inactivator of cytochrome P450 (CYP) 2C8. Such selective and time-dependent inhibition results in clinically important drug–drug interactions (DDI) with the drugs metabolized by CYP2C8. Similarly, the acyl glucuronide of clopidogrel, a widely used antiplatelet agent, is a potent time-dependent inhibitor of CYP2C8 that demonstrated significant DDI with the substrates of CYP2C8. Current progress in atomic-level understanding mostly involves studying how different drugs bind and undergo oxidation in the active site of CYPs. It is not clear how an acyl glucuronide metabolite of the drug gemfibrozil or clopidogrel interacts in the active site of CYP2C8 and selectively inhibit the enzyme. This mini-review summarizes the current knowledge on some of the important clinical DDI caused by gemfibrozil and clopidogrel due to the inhibition of CYP2C8 by acyl glucuronide metabolites of these drugs. Importantly, it examines recent developments and potential applications of structural biology tools to elucidate the binding and orientation of gemfibrozil acyl glucuronide and clopidogrel acyl glucuronide in the active site near heme that contributes to the inhibition and inactivation of CYP2C8.

Alternatives to rifampicin: A review and perspectives on the choice of strong CYP3A inducers for clinical drug-drug interaction studies

N-Nitrosamine (NA) impurities are considered genotoxic and have gained attention due to the recall of several marketed drug products associated with higher-than-permitted limits of these impurities. Rifampicin is an index inducer of multiple cytochrome P450s (CYPs) including CYP2B6, 2C8, 2C9, 2C19, and 3A4/5 and an inhibitor of OATP1B transporters (single dose). Hence, rifampicin is used extensively in clinical studies to assess drug-drug interactions (DDIs). Despite NA impurities being reported in rifampicin and rifapentine above the acceptable limits, these critical anti-infective drugs are available for therapeutic use considering their benefit-risk profile. Reports of NA impurities in rifampicin products have created uncertainty around using rifampicin in clinical DDI studies, especially in healthy volunteers. Hence, a systematic investigation through a literature search was performed to determine possible alternative index inducer(s) to rifampicin. The available strong CYP3A inducers were selected from the University of Washington DDI Database and their in vivo DDI potential assessed using the data from clinical DDI studies with sensitive CYP3A substrates. To propose potential alternative CYP3A inducers, factors including lack of genotoxic potential, adequate safety, feasibility of multiple dose administration to healthy volunteers, and robust in vivo evidence of induction of CYP3A were considered. Based on the qualifying criteria, carbamazepine, phenytoin, and lumacaftor were identified to be the most promising alternatives to rifampicin for conducting CYP3A induction DDI studies. Strengths and limitations of the proposed alternative CYP3A inducers, the magnitude of in vivo CYP3A induction, appropriate study designs for each alternative inducer, and future perspectives are presented in this paper.

Clinically Relevant Interactions Between Ritonavir-Boosted Nirmatrelvir and Concomitant Antiseizure Medications: Implications for the Management of COVID-19 in Patients with Epilepsy

Ritonavir-boosted nirmatrelvir (RBN) has been authorized recently in several countries as an orally active anti-SARS-CoV-2 treatment for patients at high risk of progressing to severe COVID-19 disease. Nirmatrelvir is the active component against the SARS-CoV-2 virus, whereas ritonavir, a potent CYP3A inhibitor, is intended to boost the activity of nirmatrelvir by increasing its concentration in plasma to ensure persistence of antiviral concentrations during the 12-hour dosing interval. RBN is involved in many clinically important drug–drug interactions both as perpetrator and as victim, which can complicate its use in patients treated with antiseizure medications (ASMs). Interactions between RBN and ASMs are bidirectional. As perpetrator, RBN may increase the plasma concentration of a number of ASMs that are CYP3A4 substrates, possibly leading to toxicity. As victims, both nirmatrelvir and ritonavir are subject to metabolic induction by concomitant treatment with potent enzyme-inducing ASMs (carbamazepine, phenytoin, phenobarbital and primidone). According to US and European prescribing information, treatment with these ASMs is a contraindication to the use of RBN. Although remdesivir is a valuable alternative to RBN, it may not be readily accessible in some settings due to cost and/or need for intravenous administration. If remdesivir is not an appropriate option, either bebtelovimab or molnupiravir may be considered. However, evidence about the clinical efficacy of bebtelovimab is still limited, and molnupiravir, the only orally active alternative, is deemed to have appreciably lower efficacy than RBN and remdesivir.

Structural Analysis of Human Serum Albumin in Complex with the Fibrate Drug Gemfibrozil

Gemfibrozil (GEM) is an orally administered lipid-regulating fibrate derivative drug sold under the brand name Lopid^®, among others. Since its approval in the early 80s, GEM has been largely applied to treat hypertriglyceridemia and other disorders of lipid metabolism. Though generally well tolerated, GEM can alter the distribution and the free, active concentration of some co-administered drugs, leading to adverse effects. Most of them appear to be related to the ability of GEM to bind with high affinity human serum albumin (HSA), the major drug-carrier protein in blood plasma. Here, we report the crystal structure of HSA in complex with GEM. Two binding sites have been identified, namely Sudlow’s binding sites I (FA7) and II (FA3–FA4). A comparison of the crystal structure of HSA in complex with GEM with those of other previously described HSA–drug complexes enabled us to appreciate the analogies and differences in their respective binding modes. The elucidation of the molecular interaction between GEM and HSA might offer the basis for the development of novel GEM derivatives that can be safely and synergistically co-administered with other drugs, enabling augmented therapeutic efficacies.

Quantitative prediction of pharmacokinetic properties of drugs in humans: Recent advance in in vitro models to predict the impact of efflux transporters in the small intestine and blood-brain barrier

Efflux transport systems are essential to suppress the absorption of xenobiotics from the intestinal lumen and protect the critical tissues at the blood-tissue barriers, such as the blood-brain barrier. The function of drug efflux transport is dominated by various transporters. Accumulated clinical evidences have revealed that genetic variations of the transporters, together with coadministered drugs, affect the expression and/or function of transporters and subsequently the pharmacokinetics of substrate drugs. Thus, in the preclinical stage of drug development, quantitative prediction of the impact of efflux transporters as well as that of uptake transporters and metabolic enzymes on the pharmacokinetics of drugs in humans has been performed using various in vitro experimental tools. Various kinds of human-derived cell systems can be applied to the precise prediction of drug transport in humans. Mathematical modeling consisting of each intrinsic metabolic or transport process enables us to understand the disposition of drugs both at the organ level and at the level of the whole body by integrating a variety of experimental results into model parameters. This review focuses on the role of efflux transporters in the intestinal absorption and brain distribution of drugs, in addition to recent advances in predictive tools and methodologies.

A Quantitative Approach to the Prediction of Drug-Drug Interactions Mediated by Cytochrome P450 2C8 Inhibition

BACKGROUND

Ohno and Colleagues proposed an approach for predicting drug-drug interactions (DDIs) mediated by cytochrome P450 (CYP) 3A4 based on the use of the ratio of the inhibited to non-inhibited area under the plasma concentration time curve (AUC) of substrates to estimate the fraction of the dose metabolized via CYP3A4 (contribution ratio, CR) and the in vivo inhibitory potency of a perpetrator (inhibition ratio, IR). This study evaluated the performance of this approach on DDIs mediated by CYP2C8 inhibitors.

RESEARCH DESIGN AND METHODS

Initial estimates of CR and IR of CYP2C8 substrates and inhibitors were calculated for 33 DDI in vivo studies. The approach was externally validated with 17 additional studies. Bayesian orthogonal regression was used to refine the estimates of the parameters. Assessment of prediction success was conducted by plotting observed versus predicted AUC ratios.

RESULTS

Final estimates of CRs and IRs were obtained for 19 CYP2C8 substrates and 23 inhibitors, respectively. The method demonstrated good predictive capacity, with only two values outside of the prespecified limits.

CONCLUSIONS

The approach may help to adapt dose regimens for CYP2C8 substrates when given in combination with CYP2C8 inhibitors and to map the potential DDIs of new molecular entities.

Mechanism of dasabuvir inhibition of acetaminophen glucuronidation

OBJECTIVES

Acetaminophen (APAP) (paracetamol) is a widely used non-prescription drug for pain relief and antipyretic effects. The clearance of APAP is mainly through phase-2 biotransformation catalysed by UDP-glucuronosyl transferases (UGT). Dasabuvir is an anti-hepatitis C drug reported to inhibit several UGT isoforms. The study evaluated the in-vitro inhibitory capacity of dasabuvir versus APAP glucuronidation.

METHODS

Procedures included human liver microsomal incubations with APAP and isoform-selective probe substrates.

KEY FINDINGS

Dasabuvir inhibited APAP metabolism by a reversible, mixed-type (competitive and non-competitive) partial inhibition, with an inhibition constant Ki = 3.4 µM. The index constant 'a' was 6.7, indicating the relative contribution of competitive and non-competitive inhibition. The enzyme-inhibitor complex was still able to catalyse the reaction by 12% of the control capacity. Dasabuvir produced strong partial inhibition effect of UGT1A1 and UGT1A9 and relatively complete inhibition of UGT1A6.

CONCLUSIONS

Consistent with previous reports, dasabuvir inhibits the activity of 3 UGT isoforms associated with APAP metabolism. In-vitro to in-vivo scaling by 2 different approaches showed identical results, predicting an increased AUC of APAP by a factor of 1.3-fold with coadministration of dasabuvir. Until the findings are confirmed in clinical drug interaction studies, APAP dosage should not exceed 3 g per day in dasabuvir-treated patients to avoid potentially hepatotoxic APAP exposures.

Evaluation of Pharmacokinetics, Safety, and Drug-Drug Interactions of an Oral Suspension of Edaravone in Healthy Adults

Intravenous (IV) edaravone is approved as an amyotrophic lateral sclerosis (ALS) treatment. Because IV administration places a burden on patients, development of orally administered ALS treatments is needed. Therefore, 2 phase 1 studies of oral formulations of edaravone in healthy subjects examined the pharmacokinetics (PK), safety, racial differences, and drug‐drug interactions (DDIs) and investigated the dose of the oral formulation considered to be bioequivalent to the approved dose of the IV formulation. Study 1 was a placebo‐controlled, randomized, single‐blind study of single‐ascending‐dose oral edaravone with the dose range of 30 to 300 mg (n = 56). Study 2 was conducted in 2 cohorts (n = 84); the first assessed DDIs with multiple‐dose edaravone 120 mg/day given over 5 or 8 days (coadministered with single‐dose rosuvastatin, sildenafil, or furosemide), and the second evaluated PK and racial (Japanese/White) differences in PK parameters with doses of 100‐mg edaravone. The oral formulation of edaravone was well absorbed, and plasma concentrations of unchanged edaravone increased more than dose proportionally within the dose range of 30 to 300 mg. No effect of race on oral edaravone PK and no notable DDI effects possibly caused by orally administered edaravone were observed. The oral edaravone formulations were safe and tolerable under the assessed conditions. Mathematical modeling determined that equivalent exposures in plasma with the approved dose of the IV edaravone formulation, as reported previously, could be achieved when the oral edaravone formulation was administered at a dose of  ≈100 mg, with an absolute bioavailability of ≈60%.

Bioinformatics Approaches for Anti-cancer Drug Discovery

Drug discovery is important in cancer therapy and precision medicines. Traditional approaches of drug discovery are mainly based on in vivo animal experiments and in vitro drug screening, but these methods are usually expensive and laborious. In the last decade, omics data explosion provides an opportunity for computational prediction of anti-cancer drugs, improving the efficiency of drug discovery. High-throughput transcriptome data were widely used in biomarkers' identification and drug prediction by integrating with drug-response data. Moreover, biological network theory and methodology were also successfully applied to the anti-cancer drug discovery, such as studies based on protein-protein interaction network, drug-target network and disease-gene network. In this review, we summarized and discussed the bioinformatics approaches for predicting anti-cancer drugs and drug combinations based on the multi-omic data, including transcriptomics, toxicogenomics, functional genomics and biological network. We believe that the general overview of available databases and current computational methods will be helpful for the development of novel cancer therapy strategies.

Population pharmacokinetic modelling to quantify the magnitude of drug-drug interactions between amlodipine and antiretroviral drugs

PURPOSE

Drug-drug interactions (DDIs) with antiretroviral drugs (ARVs) represent an important issue in elderly people living with HIV (PLWH). Amlodipine is a commonly prescribed antihypertensive drug metabolized by CYP3A4, thus predisposed to a risk of DDIs. Guidance on the management of DDIs is mostly based on theoretical considerations derived from coadministration with other CYP3A4 inhibitors. This study aimed at characterizing the magnitude of DDIs between amlodipine and ARV drugs in order to establish dosing recommendations.

METHODS

A population pharmacokinetic analysis was developed using non-linear mixed effect modelling (NONMEM) and included 163 amlodipine concentrations from 55 PLWH. Various structural and error models were compared to characterize optimally the concentration-time profile of amlodipine. Demographic and clinical characteristics as well as comedications were tested as potential influential covariates. Model-based simulations were performed to compare amlodipine exposure (i.e. area under the curve, AUC) between coadministered ARV drugs.

RESULTS

Amlodipine concentration-time profile was best described using a one-compartment model with first-order absorption and a lag-time. Amlodipine apparent clearance was influenced by both CYP3A4 inhibitors and efavirenz (CYP3A4 inducer). Model-based simulations revealed that amlodipine AUC increased by 96% when coadministered with CYP3A4 inhibitors, while efavirenz decreased drug exposure by 59%.

CONCLUSION

Coadministered ARV drugs significantly impact amlodipine disposition in PLWH. Clinicians should adjust amlodipine dosage accordingly, by halving the dosage in PLWH receiving ARV with inhibitory properties (mainly ritonavir-boosted darunavir), whereas they should double amlodipine doses when coadministering it with efavirenz, under appropriate monitoring of clinical response and tolerance.

Clinically Significant Drug Interactions Between Psychotropic Agents and Repurposed COVID-19 Therapies

As many patients with underlying psychiatric disorders may be infected with COVID-19, and COVID-19-affected subjects may frequently experience a new onset of psychiatric manifestations, concomitant use of psychotropic medications and COVID-19 therapies is expected to be highly likely and raises concerns of clinically relevant drug interactions. In this setting, four major mechanisms responsible for drug interactions involving psychotropic agents and COVID-19 therapies may be identified: (1) pharmacokinetic drug-drug interactions mainly acting on cytochrome P450; (2) pharmacodynamic drug-drug interactions resulting in additive or synergistic toxicity; (3) drug-disease interactions according to stage and severity of the disease; and (4) pharmacogenetic issues associated with polymorphisms of cytochrome P450 isoenzymes. In this review, we summarise the available literature on relevant drug interactions between psychotropic agents and COVID-19 therapies, providing practical clinical recommendations and potential management strategies according to severity of illness and clinical scenario.

Multi-factorial pharmacokinetic interactions: unraveling complexities in precision drug therapy

Introduction: Precision drug therapy requires accounting for pertinent factors in pharmacokinetic (PK) inter-individual variability (i.e., pharmacogenetics, diseases, polypharmacy, and natural product use) that can cause sub-therapeutic or adverse effects. Although each of these individual factors can alter victim drug PK, multi-factorial interactions can cause additive, synergistic, or opposing effects. Determining the magnitude and direction of these complex multi-factorial effects requires understanding the rate-limiting redundant and/or sequential PK processes for each drug.Areas covered: Perturbations in drug-metabolizing enzymes and/or transporters are integral to single- and multi-factorial PK interactions. Examples of single factor PK interactions presented include gene-drug (pharmacogenetic), disease-drug, drug-drug, and natural product-drug interactions. Examples of multi-factorial PK interactions presented include drug-gene-drug, natural product-gene-drug, gene-gene-drug, disease-natural product-drug, and disease-gene-drug interactions. Clear interpretation of multi-factorial interactions can be complicated by study design, complexity in victim drug PK, and incomplete mechanistic understanding of victim drug PK.Expert opinion: Incorporation of complex multi-factorial PK interactions into precision drug therapy requires advances in clinical decision tools, intentional PK study designs, drug-metabolizing enzyme and transporter fractional contribution determinations, systems and computational approaches (e.g., physiologically-based pharmacokinetic modeling), and PK phenotyping of progressive diseases.

Drug-drug interaction prediction with Wasserstein Adversarial Autoencoder-based knowledge graph embeddings

An interaction between pharmacological agents can trigger unexpected adverse events. Capturing richer and more comprehensive information about drug-drug interactions (DDIs) is one of the key tasks in public health and drug development. Recently, several knowledge graph (KG) embedding approaches have received increasing attention in the DDI domain due to their capability of projecting drugs and interactions into a low-dimensional feature space for predicting links and classifying triplets. However, existing methods only apply a uniformly random mode to construct negative samples. As a consequence, these samples are often too simplistic to train an effective model. In this paper, we propose a new KG embedding framework by introducing adversarial autoencoders (AAEs) based on Wasserstein distances and Gumbel-Softmax relaxation for DDI tasks. In our framework, the autoencoder is employed to generate high-quality negative samples and the hidden vector of the autoencoder is regarded as a plausible drug candidate. Afterwards, the discriminator learns the embeddings of drugs and interactions based on both positive and negative triplets. Meanwhile, in order to solve vanishing gradient problems on the discrete representation-an inherent flaw in traditional generative models-we utilize the Gumbel-Softmax relaxation and the Wasserstein distance to train the embedding model steadily. We empirically evaluate our method on two tasks: link prediction and DDI classification. The experimental results show that our framework can attain significant improvements and noticeably outperform competitive baselines. Supplementary information: Supplementary data and code are available at https://github.com/dyf0631/AAE_FOR_KG.

Factors Associated With Serum Estradiol Levels Among Postmenopausal Women Using Hormone Therapy

OBJECTIVE

To identify factors associated with serum estradiol (E2) levels among healthy postmenopausal women using hormone therapy (HT).

METHODS

This is an unplanned post hoc analysis of data from ELITE (Early versus Late Intervention Trial with Estradiol), a randomized controlled trial of 1 mg oral E2 with or without vaginal progesterone in healthy early compared with late (<6 years compared with 10 or more years since menopause) postmenopausal women. We included results from visits when women reported at least 80% compliance with HT. Mixed-effects linear models identified factors associated with serum E2 levels while participants were taking HT, assessed every 6 months over a median follow-up of 4.8 years and adjusted for baseline E2 level, visit, and reduced E2 dose. Possible correlates evaluated included demographics, clinical characteristics, medication use, and biomarkers of liver and kidney metabolic function.

RESULTS

The analysis included 2,160 E2 measurements in 275 postmenopausal women. Mean±SD age was 55.4±3.9 vs 64.4±5.5 years, and mean±SD time since menopause was 3.6±1.8 vs 16.0±5.6 years for early vs late postmenopausal women. Adjusted for pretreatment E2 level, visit, and reduced dose indicator, higher serum E2 levels were associated with higher body mass index (BMI), higher weight, surgical menopause, alcohol use, and antihypertensive medication use. Current and past smoking and antifungal medication use were associated with lower serum E2 levels. In the multivariable model, higher BMI and alcohol use were associated with higher serum E2 levels, whereas current and past smoking were associated with lower serum E2 levels. These factors were similar between early and late postmenopausal women.

CONCLUSION

Factors associated with serum E2 levels among postmenopausal women taking HT include BMI, alcohol use, and smoking. As serum E2 levels relate to HT effect, achievement of desirable E2 levels may be maximized through personalized intervention.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, NCT00114517.

An updated review of pharmacokinetic drug interactions and pharmacogenetics of statins

INTRODUCTION

Hydroxymethylglutaryl-coenzyme A reductase inhibitors (statins) lower cholesterol synthesis in patients with hypercholesterolemia. Increased statin exposure is an important risk factor for skeletal muscle toxicity. Potent inhibitors of cytochrome P450 (CYP) 3A4 significantly increase plasma concentrations of the active forms of simvastatin, lovastatin, and atorvastatin. Fluvastatin is metabolized by CYP2C9, whereas pravastatin, rosuvastatin, and pitavastatin are unaffected by inhibition by either CYP. Statins also have different affinities for membrane transporters involved in processes such as intestinal absorption, hepatic absorption, biliary excretion, and renal excretion.

AREAS COVERED

In this review, the pharmacokinetic aspects of drug-drug interactions with statins and genetic polymorphisms of CYPs and drug transporters involved in the pharmacokinetics of statins are discussed.

EXPERT OPINION

Understanding the mechanisms underlying statin interactions can help minimize drug interactions and reduce the adverse side effects caused by statins. Since recent studies have shown the involvement of drug transporters such as OATP and BCRP as well as CYPs in statin pharmacokinetics, further clinical studies focusing on the drug transporters are necessary. The establishment of biomarkers based on novel mechanisms, such as the leakage of microRNAs into the peripheral blood associated with the muscle toxicity, is important for the early detection of statin side effects.

Population Pharmacokinetics of Paritaprevir, Ombitasvir, Dasabuvir, Ritonavir, and Ribavirin in Hepatitis C Virus-Infected Cirrhotic and Non-cirrhotic Patients: Analyses Across Nine Phase III Studies

BACKGROUND

The clinical development program of the direct-acting antiviral (DAA) combination therapy of paritaprevir (coadministered with ritonavir) and ombitasvir, with and without dasabuvir (3-DAA [3D] and 2-DAA [2D] regimens, respectively) used in the treatment of chronic hepatitis C infection has generated a robust dataset across various dosing regimens and patient populations.

OBJECTIVE

The current analysis aimed to characterize the population pharmacokinetics in patients without cirrhosis ('non-cirrhotic') and with compensated cirrhosis ('cirrhotic'), while accounting for differences across hepatitis C virus (HCV) genotypes (GT) 1, 2, and 4, multiple regimens (3D regimen ± ribavirin for GT1 in global studies, 2D regimen for subgenotype 1b in Japan, 2D regimen + ribavirin for GT2 in Japan, and 2D regimen + ribavirin for GT4), and ethnicities.

METHODS

Pharmacokinetic data from nine clinical studies (~ 1850 patients) were used to model the population pharmacokinetics of each component of the DAA regimens. Model development was performed in stages, starting with an initial base model. Covariate-parameter relationships were then assessed using forward inclusion/backward elimination procedures. Model development was guided by goodness-of-fit plots, likelihood ratio tests, plausibility of parameter estimates, and knowledge of DAA, ritonavir, and ribavirin pharmacokinetics. Paritaprevir, ombitasvir, and ritonavir pharmacokinetics were described by a one-compartment model, while dasabuvir and ribavirin pharmacokinetics were characterized by a two-compartment model.

RESULTS

The analysis showed generally overlapping exposures between compensated cirrhotic and non-cirrhotic patients or between subgroups of the identified significant covariates. The largest differences were the approximately 30-60% higher dasabuvir and paritaprevir exposures in compensated cirrhotic patients.

CONCLUSION

These differences did not warrant dose adjustments for the DAAs when used in HCV-infected patients with compensated cirrhosis.

Decreased warfarin sensitivity among patients treated with elbasvir and grazoprevir for hepatitis C infection

PURPOSE

We previously reported an interaction with warfarin anticoagulation when initiating treatment with direct-acting antiviral agents for hepatitis C infection. A decreased warfarin sensitivity led to subtherapeutic anticoagulation. To study this interaction further, we expanded our research to include patients treated with the combination of elbasvir and grazoprevir concurrent with warfarin anticoagulation and investigated changes in warfarin sensitivity during and after treatment.

METHODS

Using electronic health records of the Veterans Health Administration, patients starting treatment with elbasvir-grazoprevir for hepatitis C infection concurrent with warfarin anticoagulation were identified. Inclusion required stable warfarin anticoagulation prior to 12 weeks of treatment with elbasvir-grazoprevir. A warfarin sensitivity index (WSI) was calculated at the start of treatment, after 12 weeks after treatment, and at the end of treatment. The primary endpoint was the difference in WSI from pre- to end-treatment. The secondary endpoint was the WSI difference from before treatment to Changes in International Normalized Ratio, warfarin doses, and time in therapeutic range were measured.

RESULTS

In the final sample of 43 patients, the mean WSI decreased during treatment from 0.53 to 0.40, or 25.2%. After treatment, the mean WSI rose to 0.51. Although the mean weekly warfarin dose increased from 40.3 to 44.6 mg during treatment, the mean International Normalized Ratio decreased from 2.40 to 1.96, recovering to 2.59 after treatment. The time spent in therapeutic range decreased from 74.1% before treatment to 39.8% during treatment and back to 64.9% 12 weeks posttreatment.

CONCLUSION

When elbasvir-grazoprevir was added to stable warfarin anticoagulation, warfarin sensitivity decreased significantly during treatment and returned to baseline after treatment.

Critical Differences between Enzyme Sources in Sensitivity to Detect Time-Dependent Inactivation of CYP2C8

Clopidogrel acyl-β-d-glucuronide is a mechanism-based inhibitor of cytochrome P450 2C8 in human liver microsomes (HLMs). However, time-dependent inactivation (TDI) of CYP2C8 could not be detected in an earlier study in human recombinant CYP2C8 (Supersomes). Here, we investigate whether different enzyme sources exhibit differences in detection of CYP2C8 TDI under identical experimental conditions. Inactivation of CYP2C8 by amiodarone (100 μM), clopidogrel acyl-β-d-glucuronide (100 μM), gemfibrozil 1-O-β-glucuronide (100 μM), and phenelzine (100 μM) was investigated in HLMs and three recombinant human CYP2C8 preparations (Supersomes, Bactosomes, and EasyCYP Bactosomes) using amodiaquine N-deethylation as the marker reaction. Furthermore, the inactivation kinetics of CYP2C8 by clopidogrel glucuronide (5-250 μM) was determined in Supersomes and Bactosomes. Amiodarone caused weak TDI in all enzyme preparations tested, while the extent of inactivation by clopidogrel glucuronide, gemfibrozil glucuronide, and phenelzine varied markedly between preparations, and even different Supersome lots. Both glucuronides caused strong inactivation of CYP2C8 in HLMs, Bactosomes and in one Supersome lot (>50% inhibition), but significant inactivation could not be reliably detected in other Supersome lots or EasyCYP Bactosomes. In Bactosomes, the concentration producing half of kinact (KI) and maximal inactivation rate (kinact) of clopidogrel glucuronide (14 μM and 0.054 minute-1) were similar to those determined previously in HLMs. Phenelzine caused strong inactivation of CYP2C8 in one Supersome lot (91% inhibition) but not in HLMs or other recombinant CYP2C8 preparations. In conclusion, different enzyme sources and different lots of the same recombinant enzyme preparation are not equally sensitive to detect inactivation of CYP2C8, suggesting that recombinant CYPs should be avoided when identifying mechanism-based inhibitors.

Pharmacokinetics of Ombitasvir, Paritaprevir, Ritonavir, and Dasabuvir in Healthy Chinese Subjects and HCV GT1b-Infected Chinese, South Korean and Taiwanese Patients

BACKGROUND/PURPOSE

The 3 direct-acting antiviral (3D) regimen of ombitasvir/paritaprevir/ritonavir plus dasabuvir has recently been approved in several Asian geographic regions for the treatment of hepatitis C virus (HCV) genotype (GT) 1 infection. The pharmacokinetics of the components of the 3D regimen with or without ribavirin were evaluated in healthy Chinese subjects and HCV GT1b-infected Chinese, South Korean, and Taiwanese patients, with or without cirrhosis, to determine how the drug exposures in Asian populations compare with historical data in Western populations.

METHODS

Participants received ombitasvir/paritaprevir/ritonavir 25/150/100 mg once daily plus dasabuvir 250 mg twice daily for 14 days (healthy subjects, n = 36) or 12 weeks (HCV patients, n = 754). Patients with compensated cirrhosis also received ribavirin 1000 or 1200 mg divided twice daily, per the local label. Intensive or sparse pharmacokinetic sampling was performed for assessments of plasma drug concentrations.

RESULTS

The exposures [maximum plasma concentration (C_max) and area under the plasma concentration-time curve (AUC)] of the components of the 3D regimen were comparable (< 20% difference) in healthy Chinese subjects residing in China or the United States. In addition, the trough plasma concentrations (C_trough) in HCV GT1b-infected Asian patients were either similar to (ombitasvir) or within 75% of (paritaprevir and dasabuvir) those in Western patients without cirrhosis, or similar to (ombitasvir and paritaprevir) or within 100% of (dasabuvir) those in Western patients with cirrhosis, with widely overlapping ranges of individual values. Generally comparable drug exposures were observed among Chinese, South Korean, and Taiwanese ethnicities for noncirrhotic and cirrhotic patients.

CONCLUSION

Collectively, the results of these pharmacokinetic analyses support the use of the same dose of the 3D regimen for Asian and Western patients. CLINICALTRIALS.GOV: NCT02534870, NCT02517515, NCT02517528.

ABCG2/BCRP: variants, transporter interaction profile of substrates and inhibitors

INTRODUCTION

ABCG2 has a broad substrate specificity and is one of the most important efflux proteins modulating pharmacokinetics of drugs, nutrients and toxicokinetics of toxicants. ABCG2 is an important player in transporter-mediated drug-drug interactions (tDDI). Areas covered: The aims of the review are i) to cover transporter interaction profile of substrates and inhibitors that can be utilized to test interaction of drug candidates with ABCG2, ii) to highlight main characteristics of in vitro testing and iii) to describe the structural basis of the broad substrate specificity of the protein. Preclinical data utilizing Abcg2/Bcrp1 knockouts and clinical studies showing effect of ABCG2 c.421C>A polymorphism on pharmacokinetics of drugs have provided evidence for a broad array of drug substrates and support drug - ABCG2 interaction testing. A consensus on using rosuvastatin and sulfasalazine as intestinal substrates for clinical studies is in the formation. Other substrates relevant to the therapeutic area can be considered. Monolayer efflux assays and vesicular transport assays have been extensively utilized in vitro. Expert opinion: Clinical substrates display complex pharmacokinetics due to broad interaction profiles with multiple transporters and metabolic enzymes. Substrate-dependent inhibition has been observed for several inhibitors. Harmonization of in vitro and in vivo testing makes sense. However, rosuvastatin and sulfasalazine are not efficiently transported in either MDCKII or LLC-PK1-based monolayers. Caco-2 monolayer assays and vesicular transport assays are potential alternatives.

Tamoxifen-induced hepatotoxicity caused by drug interaction with direct-acting antiviral agents for hepatitis C

A 68-year-old man develops acute hepatocellular injury during treatment with direct-acting antiviral agents (DAA) for hepatitis C. Medical history reveals the intake of tamoxifen as adjuvant treatment for breast cancer, currently in remission. After stopping tamoxifen, despite the continuation of the anti-HCV agents, a complete resolution of liver injury occurs. This interesting case illustrates tamoxifen hepatotoxicity induced by CYP3A4 interaction with direct anti-HCV agents. It stresses the importance of checking for interactions before starting treatment for hepatitis C.

Effects of chronic kidney disease stage 4, end-stage renal disease, or dialysis on the plasma concentrations of ombitasvir, paritaprevir, ritonavir, and dasabuvir in patients with chronic HCV infection: pharmacokinetic analysis of the phase 3 RUBY-I and RUBY-II trials

PURPOSE

To characterize the pharmacokinetics of ombitasvir, paritaprevir, ritonavir, dasabuvir, and ribavirin in hepatitis C virus (HCV)-infected patients with chronic kidney disease stage 4 (CKD4) or end-stage renal disease (ESRD), including those on dialysis, in the open-label phase 3 RUBY-I and RUBY-II studies.

METHODS

Patients (n = 18 CKD4, n = 68 ESRD) received ombitasvir/paritaprevir/ritonavir 25/150/100 mg once daily ± dasabuvir 250 mg twice daily ± ribavirin 200 mg once daily for 12 or 24 weeks. Intensive pharmacokinetic samples were collected from ten patients; sparse samples were collected from all patients. Arterial and venous samples were collected from three patients during hemodialysis. Area under the plasma concentration-time curve (AUC) was estimated using noncompartmental analyses for intensive data, and steady-state trough concentrations (C_trough) were obtained from the sparse data. Pharmacokinetic results from RUBY-I and RUBY-II were compared empirically to historical data.

RESULTS

The AUC values of ombitasvir, paritaprevir, ritonavir, and dasabuvir were comparable between CKD4 and ESRD patients and were within the range of values observed in historical studies; dialysis had no effect on drug exposures. Ribavirin was extracted during hemodialysis but had similar exposures on dialysis and non-dialysis days. Individual steady-state C_trough values for each drug overlapped between CKD4 and ESRD patients, and values in both groups were similar to historical values.

CONCLUSION

Plasma concentrations of ombitasvir, paritaprevir, ritonavir, and dasabuvir were not altered by renal impairment or dialysis, suggesting these agents can be administered to HCV-infected CKD4 or ESRD patients, including those on dialysis, without dose adjustment.

TRIAL REGISTRATION

Clinicaltrials.gov identifiers: NCT02207088 (RUBY-I) and NCT02487199 (RUBY-II).

Methadone Metabolism and Drug-Drug Interactions: In Vitro and In Vivo Literature Review

Methadone is utilized for the treatment of individuals with opiate dependence. Methadone undergoes N-demethylation by multiple cytochrome P450 (CYP) enzymes including CYP3A4, CYP2B6, CYP2C19, CYP2D6, CYP2C9, and CYP2C8. In vivo, polymorphism effects on methadone systemic exposure have been noted for CYP2B6, CYP3A4, and CYP2D6. Clinical drug interaction studies with antiviral drugs in methadone maintenance treatment patients yield varying results on methadone pharmacokinetics and pharmacodynamics. In general, CYP inhibitors altered methadone exposure with no adverse effects. CYP inducers generally decreased methadone exposure with some reports of withdrawal symptoms in the subjects. Interaction studies with antiviral drug combinations yielding differing results depend on the enzyme(s) affected. For certain antiviral medicines which are dual inhibitor(s) and inducer(s) for CYP enzymes, their effect on methadone pharmacokinetics can change with time since the effect of induction is usually delayed compared to the effect of inhibition.

Clopidogrel Increases Dasabuvir Exposure With or Without Ritonavir, and Ritonavir Inhibits the Bioactivation of Clopidogrel

Dasabuvir is mainly metabolized by cytochrome P450 (CYP) 2C8 and is predominantly used in a regimen containing ritonavir. Ritonavir and clopidogrel are inhibitors of CYP3A4 and CYP2C8, respectively. In a randomized, crossover study in 12 healthy subjects, we examined the impact of clinical doses of ritonavir (for 5 days), clopidogrel (for 3 days), and their combination on dasabuvir pharmacokinetics, and the effect of ritonavir on clopidogrel. Clopidogrel, but not ritonavir, increased the geometric mean AUC_0‐∞ of dasabuvir 4.7‐fold; range 2.0–10.1‐fold (P = 8·10⁻⁷), compared with placebo. Clopidogrel and ritonavir combination increased dasabuvir AUC_0‐∞ 3.9‐fold; range 2.1–7.9‐fold (P = 2·10⁻⁶), compared with ritonavir alone. Ritonavir decreased the AUC_0‐4h of clopidogrel active metabolite by 51% (P = 0.0001), and average platelet inhibition from 51% without ritonavir to 31% with ritonavir (P = 0.0007). In conclusion, clopidogrel markedly elevates dasabuvir concentrations, and patients receiving ritonavir are at risk for diminished clopidogrel response.

Glycyrrhizin has a high likelihood to be a victim of drug-drug interactions mediated by hepatic organic anion-transporting polypeptide 1B1/1B3

BACKGROUND AND PURPOSE

Intravenous glycyrrhizin, having anti-inflammatory and hepatoprotective properties, is incorporated into the management of liver diseases in China. This investigation was designed to elucidate the molecular mechanism underlying hepatobiliary excretion of glycyrrhizin and to investigate its potential for drug-drug interactions on organic anion-transporting polypeptide (OATP)1B.

EXPERIMENTAL APPROACH

Human transporters mediating hepatobiliary excretion of glycyrrhizin were characterized at the cellular and vesicular levels and compared with rat hepatic transporters. The role of Oatp1b2 in glycyrrhizin's elimination and pharmacokinetics was evaluated in rats using the inhibitor rifampin. A physiologically based pharmacokinetic (PBPK) model for glycyrrhizin, incorporating transporter-mediated hepatobiliary excretion, was established and applied to predict potential drug-drug interactions related to glycyrrhizin in humans.

KEY RESULTS

Hepatobiliary excretion of glycyrrhizin involved human OATP1B1/1B3 (Oatp1b2 in rats)-mediated hepatic uptake from blood and human multidrug resistance-associated protein (MRP)2/breast cancer resistance protein (ABCP)/bile salt export pump (BSEP)/multidrug resistance protein 1 (Mrp2/Abcp/Bsep in rats)-mediated hepatic efflux into bile. In rats, rifampin impaired hepatic uptake of glycyrrhizin significantly increasing its systemic exposure. Glomerular-filtration-based renal excretion of glycyrrhizin was slow due to extensive protein binding in plasma. Quantitative analysis using the PBPK model demonstrated that OATP1B1/1B3 have critical roles in the pharmacokinetics of glycyrrhizin, which is highly likely to be a victim of drug-drug interactions when co-administered with potent dual inhibitors of these transporters.

CONCLUSIONS AND IMPLICATIONS

Transporter-mediated hepatobiliary excretion governs glycyrrhizin's elimination and pharmacokinetics. Understanding glycyrrhizin's potential drug-drug interactions on OATP1B1/1B3 should enhance the therapeutic outcome of glycyrrhizin-containing drug combinations on liver diseases.

Clinical Pharmacokinetics of Paritaprevir

Paritaprevir is a potent hepatitis C virus (HCV) nonstructural (NS) protein 3/4A protease inhibitor that is used in combination with other direct-acting antivirals (DAAs) for the treatment of chronic HCV infection. Paritaprevir is primarily metabolized by cytochrome P450 (CYP) 3A4 and is administered with a low dose of ritonavir to achieve drug concentrations suitable for once-daily dosing. Coadministration of paritaprevir with ritonavir increases the half-life of single-dose paritaprevir from approximately 3 h to 5-8 h, doubles the time to maximum plasma concentration (T _max) from 2.3 to 4.7 h, and increases exposures 30-fold for maximum observed plasma concentration (C _max), 50-fold for area under the plasma concentration-time curve (AUC), and >300-fold for trough concentration (C ₂₄). Paritaprevir displays highly variable, nonlinear pharmacokinetics, with C _max and AUC increasing in a greater than dose proportional manner when administered with or without ritonavir. In the presence of ritonavir, paritaprevir is excreted mostly unchanged in feces via biliary excretion. Paritaprevir exposures are higher in Japanese subjects compared with Caucasian subjects; however, no dose adjustment is needed for Japanese patients as the higher exposures are safe and well tolerated. The pharmacokinetic characteristics of paritaprevir are similar between healthy subjects and HCV-infected patients, and are not appreciably altered by mild or moderate hepatic impairment or mild, moderate, or severe renal impairment, including those on dialysis. Paritaprevir exposures are increased in patients with severe hepatic impairment. Although the presence of a low dose of ritonavir in paritaprevir-containing regimens increases the likelihood of drug-drug interactions, results from several drug interaction studies demonstrated that paritaprevir-containing regimens can be coadministered with many comedications that are commonly prescribed in HCV-infected patients.

Clinical Pharmacokinetics of Dasabuvir

Dasabuvir is a nonstructural (NS) 5B non-nucleoside inhibitor of the hepatitis C virus (HCV) used in combination with ombitasvir/paritaprevir/ritonavir for the treatment of chronic HCV infection. It is primarily metabolized by cytochrome P450 (CYP) 2C8, with a minor contribution from CYP3A. Biotransformation of dasabuvir forms the M1 metabolite, which retains antiviral activity. Dasabuvir exhibits linear pharmacokinetics with a terminal half-life of approximately 5-8 h, allowing for twice-daily dosing. The M1 metabolite of dasabuvir is the major metabolite in plasma and has a half-life similar to that of dasabuvir. Dasabuvir exposures in Asian subjects are comparable with Caucasian subjects. The pharmacokinetic characteristics of dasabuvir are similar between healthy subjects and HCV-infected patients, and are not appreciably altered by mild, moderate, or severe renal impairment or dialysis. Dasabuvir pharmacokinetic parameters were not significantly altered in subjects with mild or moderate hepatic impairment; however, exposures were significantly increased in subjects with severe hepatic impairment. Dasabuvir should be administered with food to maximize absorption. Coadministration of dasabuvir with a strong CYP2C8 inhibitor increased dasabuvir exposures by greater than tenfold, whereas coadministration with strong CYP3A inhibitors increased dasabuvir exposures by less than 50%. Furthermore, coadministration of dasabuvir with a CYP3A inducer decreased dasabuvir exposures by 55-70%. Coadministration of dasabuvir with strong CYP2C8 inhibitors or strong CYP3A/CYP2C8 inducers is contraindicated. Results from several drug interaction studies demonstrated that dasabuvir in combination with ombitasvir/paritaprevir/ritonavir can be coadministered with most comedications that are commonly prescribed in HCV-infected patients.

Clinical Pharmacokinetics of Ombitasvir

Ombitasvir is a potent, nonstructural protein 5A inhibitor of the hepatitis C virus (HCV) that is used in combination with other direct-acting antivirals for the treatment of chronic HCV infection. Ombitasvir is predominantly metabolized by amide hydrolysis followed by oxidative metabolism and is a substrate of P-glycoprotein. Ombitasvir displays linear pharmacokinetics with minimal accumulation and is eliminated via metabolism and biliary excretion. A negligible amount of unchanged drug is excreted in urine. Exposures are comparable across Chinese, Japanese, and non-Asian subjects. The pharmacokinetic characteristics of ombitasvir are similar in healthy subjects and HCV-infected patients, and are not appreciably altered by hepatic or renal impairment. Results from several drug interaction studies demonstrated that ombitasvir has a low potential for drug interactions.

Guiding dose adjustment of amlodipine after co-administration with ritonavir containing regimens using a physiologically-based pharmacokinetic/pharmacodynamic model

Amlodipine, a commonly prescribed anti-hypertensive drug, shows increased systemic exposure with cytochrome P450 (CYP) 3A inhibitors. Ritonavir (RTV) is a potent mechanism-based and reversible CYP3A inhibitor and moderate inducer that is used as a pharmacokinetic enhancer in several antiviral treatment regimens. Drug-drug interaction (DDI) between RTV and amlodipine is due to mixed inhibition and induction of CYP3A4, which is challenging to predict without a mechanistic model that accounts for the complexity of both mechanisms occurring simultaneously. A novel physiologically-based pharmacokinetic (PBPK) model was developed for amlodipine, and the model was verified using published clinical PK and DDI data. The verified amlodipine PBPK model was linked to a pharmacodynamics model that describes changes in systolic blood pressure (SBP) during and after co-administration with RTV. The magnitude and time course of RTV effects on amlodipine plasma exposures and SBP were evaluated, to provide guidance on dose adjustment of amlodipine during and after co-administration with RTV-containing regimens. Model simulations suggested that the increase in amlodipine's plasma exposure by RTV diminishes by approximately 80% within 5 days after the last dose of RTV. PBPK simulations suggested that resuming a full dose of amlodipine [5 mg once daily (QD)] immediately after RTV's last dose would decrease daily average SBP by a maximum of 3.3 mmHg, while continuing with the reduced dose (2.5 mg QD) for 5 days after the last dose of RTV would increase daily average SBP by a maximum of 5.8 mmHg. Based on these results, either approach of resuming amlodipine's full dose could be appropriate when combined with appropriate clinical monitoring.

Treatment of Chronic Hepatitis C in Patients Receiving Opioid Agonist Therapy: A Review of Best Practice

Injection drug use is the most common transmission route for hepatitis C. High rates of infection are observed among individuals on opioid agonist therapy. Although people who inject drugs carry the highest burden, few have initiated treatment. We present a comprehensive review of the evidence on the efficacy of HCV medications, drug-drug interactions, and barriers to and models of care. Studies have demonstrated comparable efficacy for individuals who are on opioid agonist therapy compared with those who are not. We propose that a strategy of treatment and cure-as-prevention is imperative in this population to curb the hepatitis C epidemic.

An update on the toxicological considerations for protease inhibitors used for hepatitis C infection

INTRODUCTION

Hepatitis C virus protease inhibitors (PIs) are important components of many direct acting antiviral regimens. Many clinical trials and real-world studies have described the safety data for individual PIs. We aimed to review the safety of both the first and second generation PIs in patients with chronic hepatitis C (CHC). Areas covered: The unique pharmacokinetic properties of PIs partly explain their toxicities. Second generation PIs, when used without interferon and ribavirin, are well-tolerated. Use of PIs in renal impaired patients or those on dialysis appears to be safe. Decompensated cirrhosis is a contraindication for PIs use due to increased drug exposure and risk of liver decompensation. Drug-drug interactions are common and should be always monitored; some drugs should not be co-administered with PIs. In patients with co-infected hepatitis B virus, reactivation after DAA (whether PI-containing or not) is a concern. Expert opinion: Second generation PIs are key players in the current DAA era. Post-marketing surveillance is essential to monitor unknown adverse events and drug-drug interactions. Non-PI based DAA should be used in decompensated liver disease. The use of these drugs should also be explored in the paediatric population.

Potential drug-drug interactions of OMBITASVIR, PARITAPREVIR/ritonavir ± DASABUVIR ± ribavirin in clinical practice

BACKGROUND & AIMS

Drug-drug interactions (DDIs) with ombitasvir/paritaprevir/ritonavir with or without dasabuvir and with or without ribavirin (OBV/PTV/r ± DSV ± RBV) are common in clinical trials. Our aim was to analyze the prevalence and management of potential DDIs and adverse events (AEs) related to DDIs in patients with chronic hepatitis C (CHC) receiving OBV/PTV/r ± DSV ± RBV in clinical practice.

METHODS

177 CHC patients started OBV/PTV/r ± DSV ± RBV in 4 Spanish hospitals and were screened for potential DDIs using the University of Liverpool database. Patients were classified according to the most serious potential DDIs at baseline and AEs during therapy.

RESULTS

At least one potential DDI was found in 110 (62.1%) patients: 100 (56.5%) had at least one manageable potential DDI and 10 (5.6%) at least one contraindicated. Patients with potential DDIs were receiving a higher number of concomitant drugs (4 vs. 2, P < 0.001). Routine medication was modified at baseline due to potential DDIs in 49 (27.7%) patients. During antiviral treatment, 67 (37.9%) patients presented at least one AE. In 9 (4.5%) patients, a DDI was suspected between OBV/PTV/r ± DSV ± RBV and the concomitant drug, requiring antiviral discontinuation in 4 patients.

CONCLUSIONS

Potential DDIs are frequent with OBV/PTV/r ± DSV ± RBV, although a change in baseline medication is made in only one-quarter of patients. More than half of potential DDIs were only followed, and only 5% of patients developed AEs in which the implication of DDIs could not be excluded.

Gadoxetic acid-enhanced magnetic resonance imaging to predict paritaprevir-induced hyperbilirubinemia during treatment of hepatitis C

Background

Paritaprevir inhibits organic anion–transporting polypeptide (OATP)1B1 and OATP1B3, which transport bilirubin. Hyperbilirubinemia is an adverse event reported during hepatitis C treatment. Gadoxetic acid is also transported by OATP1B1/1B3. We evaluated whether the enhancement effect in gadoxetic acid–enhanced magnetic resonance (MR) imaging could predict the plasma concentration of paritaprevir and might anticipate the development of hyperbilirubinemia.

Methods

This prospective study evaluated 27 patients with hepatitis C who underwent gadoxetic acid–enhanced MR imaging prior to treatment with ombitasvir, paritaprevir, and ritonavir. The contrast enhancement index (CEI), a measure of liver enhancement during the hepatobiliary phase, was assessed. Plasma trough concentrations, and concentrations at 2, 4, and 6 h after dosing were determined 7 d after the start of treatment.

Results

Seven patients (26%) developed hyperbilirubinemia (≥ 1.6 mg/dl). Paritaprevir trough concentration (C_trough) was significantly higher in patients with hyperbilirubinemia than in those without (p = 0.022). We found an inverse relationship between CEI and C_trough (r = 0.612, p = 0.001), while there was not a significantly weak inverse relationship between AUC_{0–6 h} and CEI (r = −0.338, p = 0.085). The partial correlation coefficient between CEI and C_trough was −0.425 (p = 0.034), while excluding the effects of albumin and the FIB-4 index. Receiver operating characteristic (ROC) curve analysis showed that the CEI was relatively accurate in predicting hyperbilirubinemia, with area under the ROC of 0.882. Multivariate analysis showed that the CEI < 1.61 was the only independent predictor related to the development of hyperbilirubinemia, with an odds ratio of 9.08 (95% confidence interval 1.05–78.86, p = 0.046).

Conclusions

Hepatic enhancement with gadoxetic acid was independently related to paritaprevir concentration and was an independent pretreatment factor in predicting hyperbilirubinemia. Gadoxetic acid–enhanced MR imaging can therefore be useful in determining the risk of paritaprevir-induced hyperbilirubinemia.

Predicting drug interactions in addiction treatment

It is not uncommon to be treating people with addiction who also have significant other health problems, including heart, renal or liver failure, diabetes and vascular disease. These conditions require regular medications to be taken. This can be a problem for people living with addiction and difficult social circumstances affecting compliance, among other issues. Our perspective provides a summary of general pharmacological factors affecting medicine taking in people with addiction problems, to provide a guide for hospital doctors in this setting.

The Drug-Drug Interaction Potential of Antiviral Agents for the Treatment of Chronic Hepatitis C Infection

Several safe and highly effective direct-acting antiviral (DAA) drugs for chronic hepatitis C virus (HCV) have been developed and greatly increase the number of therapeutic options available to successfully treat HCV infection. However, because treatment regimens contain at least two drugs (e.g., elbasvir and grazoprevir, glecaprevir and pibrentasvir, or sofosbuvir with daclatasvir, simeprevir, ledipasvir, or velpatasvir) and up to five drugs (ombitasvir/paritaprevir/ritonavir plus dasabuvir with or without ribavirin), the potential for drug-drug interactions (DDIs) becomes an important consideration for HCV-infected individuals with comorbidities that require concomitant medications, such as human immunodeficiency virus/HCV coinfection or immunosuppression after liver transplantation. This review details the pharmacokinetics and DDI potential of approved DAAs for the treatment of HCV infection.

Real-world efficacy and safety of ombitasvir, paritaprevir/r+dasabuvir+ribavirin in genotype 1b patients with hepatitis C virus cirrhosis

BACKGROUND

Direct antiviral agents (DAA) showed very good results in terms of efficacy and safety in clinical trials, but real-life data are still needed in order to confirm this profile.

MATERIAL AND METHODS

In Romania, through a nationwide government-funded programme in 2015-2016, approx.5800 patients with virus C cirrhosis received fully reimbursed DAA therapy with OBV/PTV/r+DSV+RBV for 12 weeks. We analysed a national prospective cohort enrolling the first 2070 patients, all with genotype 1b. The only key inclusion criteria was advanced fibrosis (Metavir stage F4) confirmed by Fibromax testing (or liver biopsy/Fibroscan). Efficacy was assessed by the percentage of patients achieving SVR 12 weeks post-treatment (SVR12).

RESULTS

Forty patients stopped the treatment because of hepatic decompensation (1.9%), 21 stopped because of other adverse events and one was lost to follow-up. This cohort was 51% females, mean age 60 years (25÷82), 67% pretreated, 70% associated NASH, 67% with severe necro-inflammation (severity score 3-Fibromax), 37% with comorbidities, 10.4% with Child Pugh A6, 0.5% B7. The median MELD score was 8.09 (6 ÷ 22). SVR by intention-to-treat was reported in 1999/2070(96.6%), 55/2070 failed to respond. Liver decompensation was statistically associated in multivariate analysis with platelets< 10⁵ /mm³ (P = .03), increased total bilirubin (P < .001), prolonged INR (P = .02), and albumin<3.5 g/dL (P = .03).

CONCLUSIONS

OBV/PTV/r+DSV+RBV proved to be highly efficient in our population of cirrhotics with a 96.6% SVR. Serious adverse events related to therapy were reported in 61/2070(2.9%), most of them liver decompensation (1.9%), related to hepatic dysfunction, and lower platelet count.

Drug Interactions Between Peficitinib, an Orally Administered, Once-Daily Janus Kinase Inhibitor, and Rosuvastatin in Healthy Subjects

BACKGROUND AND OBJECTIVE

Peficitinib is an orally administered, once-daily Janus kinase inhibitor in development for the treatment of rheumatoid arthritis. Peficitinib and its major metabolite H2 inhibit the hepatic uptake transporter organic anion transporting polypeptide 1B1 (OATP1B1) in vitro. This article reports a clinical study evaluating the effects of peficitinib on the pharmacokinetics of rosuvastatin, a substrate for the OATP1B1 transporter, and vice versa.

METHODS

In an open-label, single-sequence clinical study, 24 healthy adults of East Asian and non-East Asian origin received a single dose of rosuvastatin 10 mg on days 1 and 10. On days 5-13, subjects received a daily dose of 150 mg peficitinib. Serial blood samples for pharmacokinetic assessment of rosuvastatin were collected up to 96 h post-dose on days 1 and 10, and for peficitinib were collected up to 24 h post-dose on days 9 and 10.

RESULTS

Co-administration of peficitinib with rosuvastatin increased rosuvastatin area under the concentration-time curve (AUC) and maximum plasma concentration (C _max) by 18 and 15%, respectively and increased peficitinib AUC and C _max by 16 and 28%, respectively. In East Asian (n = 6) vs. non-East Asian subjects (n = 18), peficitinib mean AUC for a dosing interval was 45 and 21% higher, and mean C _max was 67 and 34% higher, when administered alone or with rosuvastatin. Peficitinib was well tolerated with few adverse events overall.

CONCLUSION

In this study, once-daily oral administration of peficitinib had no clinically significant effect on the pharmacokinetics of rosuvastatin, a probe substrate for OATP1B1. Therefore, it is unlikely that peficitinib will have a clinically significant effect on the exposure of other substrates for OATP1B1. CLINICALTRIALS.

GOV NUMBER

NCT01959399.

Regulation of Organic Anion Transporting Polypeptides (OATP) 1B1- and OATP1B3-Mediated Transport: An Updated Review in the Context of OATP-Mediated Drug-Drug Interactions

Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important hepatic transporters that mediate the uptake of many clinically important drugs, including statins from the blood into the liver. Reduced transport function of OATP1B1 and OATP1B3 can lead to clinically relevant drug-drug interactions (DDIs). Considering the importance of OATP1B1 and OATP1B3 in hepatic drug disposition, substantial efforts have been given on evaluating OATP1B1/1B3-mediated DDIs in order to avoid unwanted adverse effects of drugs that are OATP substrates due to their altered pharmacokinetics. Growing evidences suggest that the transport function of OATP1B1 and OATP1B3 can be regulated at various levels such as genetic variation, transcriptional and post-translational regulation. The present review summarizes the up to date information on the regulation of OATP1B1 and OATP1B3 transport function at different levels with a focus on potential impact on OATP-mediated DDIs.

Efficacy of Interferon-Free Therapies for Chronic Hepatitis C: A Systematic Review of All Randomized Clinical Trials

BACKGROUND AND OBJECTIVES

Second-generation direct-acting antivirals (DAAs) have recently arisen as more effective and safer treatments for chronic hepatitis C. These drugs can be combined into treatments without interferon (IFN), and are therefore called IFN-free therapies.

OBJECTIVE

The objective of this study systematic review was to evaluate the efficacy of IFN-free therapies for the treatment of chronic hepatitis C, and thus increase the clinical evidence for these therapies.

METHODS

A systematic review was conducted in accordance with Cochrane Collaboration recommendations. A search was performed in six different electronic databases using 'clinical trials', 'hepatitis C' and 'interferon-free' as the main descriptors, and studies that conformed to the inclusion criteria had their data extracted, including study information, baseline characteristics, and efficacy outcomes (sustained virologic response, rapid virologic response, and virologic failure).

RESULTS

Sixty-four randomized clinical trials including 15 different therapies were included in a total of 15,731 patients infected with the hepatitis C virus, mostly with genotype 1, and mainly treated for 12 or 24 weeks. The sustained virologic response rate after 12 weeks of treatment was approximately 89%, while the virologic failure rate was below 5%.

CONCLUSIONS

Second-generation DAAs presented several advantages: virologic response values higher than the average achieved by previous IFN-based therapies, reduced treatment duration, and the possibility of different combinations of therapies to meet patient needs. Thus, IFN-free therapies appear to be valuable alternatives for the treatment of chronic hepatitis C.