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.

Clinical Pharmacology in Sarcoidosis: How to Use and Monitor Sarcoidosis Medications

When sarcoidosis needs treatment, pharmacotherapy is usually required. Although glucocorticoids work reliably and relatively quickly for sarcoidosis, these drugs are associated with numerous significant side effects. Such side effects are common in sarcoidosis patients, as the disease frequently has a chronic course and glucocorticoid treatment courses are often prolonged. For these reasons, corticosteroid-sparing and corticosteroid-replacing therapies are often required for sarcoidosis. Unfortunately, many healthcare providers who care for sarcoidosis patients are not familiar with the use of these agents. In this manuscript, we provide a review of the pharmacotherapy of sarcoidosis. We discuss the mechanism of action, dosing, side-effect profile, approach to monitoring and patient counselling concerning glucocorticoids, and the common alternative drugs recommended for use in the recent European Respiratory Society (Lausanne, Switzerland) Sarcoidosis Treatment Guidelines. We also discuss the use of these agents in special situations including hepatic insufficiency, renal insufficiency, pregnancy, breastfeeding, vaccination, and drug-drug interactions. It is hoped that this manuscript will provide valuable practical guidance to clinicians who care for sarcoidosis patients.

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.

Pharmacological and clinical evaluation of deferasirox formulations for treatment tailoring

Deferasirox (DFX) is the newest among three different chelators available to treat iron overload in iron-loading anaemias, firstly released as Dispersible Tablets (DT) and more recently replaced by Film-Coated Tablets (FCT). In this retrospective observational study, pharmacokinetics, pharmacodynamics, and safety features of DFX treatment were analyzed in 74 patients that took both formulations subsequently under clinical practice conditions. Bioavailability of DFX FCT compared to DT resulted higher than expected [C_max: 99.5 (FCT) and 69.7 (DT) μMol/L; AUC: 1278 (FCT) and 846 (DT), P < 0.0001]. DFX FCT was also superior in scalability among doses. After one year of treatment for each formulation, no differences were observed between the treatments in the overall iron overload levels; however, DFX FCT but not DT showed a significant dose–response correlation [Spearman r (dose-serum ferritin variation): − 0.54, P < 0.0001]. Despite being administered at different dosages, the long-term safety profile was not different between formulations: a significant increase in renal impairment risk was observed for both treatments and it was reversible under strict monitoring (P < 0.002). Altogether, these data constitute a comprehensive comparison of DFX formulations in thalassaemia and other iron-loading anaemias, confirming the effectiveness and safety characteristics of DFX and its applicability for treatment tailoring.

Inhibition and induction of CYP enzymes in humans: an update

The cytochrome P450 (CYP) enzyme family is the most important enzyme system catalyzing the phase 1 metabolism of pharmaceuticals and other xenobiotics such as herbal remedies and toxic compounds in the environment. The inhibition and induction of CYPs are major mechanisms causing pharmacokinetic drug–drug interactions. This review presents a comprehensive update on the inhibitors and inducers of the specific CYP enzymes in humans. The focus is on the more recent human in vitro and in vivo findings since the publication of our previous review on this topic in 2008. In addition to the general presentation of inhibitory drugs and inducers of human CYP enzymes by drugs, herbal remedies, and toxic compounds, an in-depth view on tyrosine-kinase inhibitors and antiretroviral HIV medications as victims and perpetrators of drug–drug interactions is provided as examples of the current trends in the field. Also, a concise overview of the mechanisms of CYP induction is presented to aid the understanding of the induction phenomena.

Clopidogrel, a CYP2C8 inhibitor, causes a clinically relevant increase in the systemic exposure to the active metabolite of selexipag in healthy subjects

Aims

Selexipag is a prostacyclin receptor agonist approved for the treatment of pulmonary arterial hypertension. Cytochrome P450 (CYP) 2C8 is involved in the metabolism of selexipag and its active metabolite, ACT‐333679. This study evaluated the interaction of selexipag and clopidogrel, a CYP2C8 inhibitor.

Methods

The study had a 2‐treatment, 1‐sequence, crossover design. Pharmacokinetics (PK) and CYP2C8 genotype were assessed in healthy male subjects administered selexipag (200 μg twice daily [b.i.d.]) alone or with clopidogrel (300 mg single dose or 75 mg once daily [o.d.]). PK modelling and simulation were conducted to support dosing recommendations.

Results

Clopidogrel had a comparatively small effect on selexipag (<1.5‐fold difference in any PK variable). For ACT‐333679, the major contributor to the drug effect, the area under the plasma concentration–time curve during a dose interval and the maximum plasma concentration increased 2.25‐fold (90% confidence interval [CI] 2.06, 2.46) and 1.69‐fold (90% CI 1.55, 1.84), respectively with clopidogrel 300 mg and 2.70‐fold (90% CI 2.45, 2.96) and 1.90‐fold (90% CI 1.72, 2.11), respectively with clopidogrel 75 mg. The effect of clopidogrel on selexipag and ACT‐333679 exposure was comparable for all identified CYP2C8 genotypes. PK simulations predicted comparable exposure to ACT‐333679 following selexipag 400 μg b.i.d., 400 μg o.d. in combination with clopidogrel 75 mg o.d and 200 μg b.i.d. with clopidogrel 75 mg o.d.

Conclusion

Results suggest that ACT‐333679 exposure can be maintained within the therapeutic range by reducing selexipag dosing frequency to o.d. or dose to half, when selexipag is coadministered with clopidogrel.

Progress in the Consideration of Possible Sex Differences in Drug Interaction Studies

Background:

Anecdotal evidence suggests that there may be sex differences in Drug-drug Interactions (DDI) involving specific drugs. Regulators have provided general guidance for the inclusion of females in clinical studies. Some clinical studies have reported sex differences in the Pharmacokinetics (PK) of CYP3A4 substrates, suggesting that DDI involving CYP3A4 substrates could potentially show sex differences.

Objective:

The aim of this review was to investigate whether recent prospective DDI studies have included both sexes and whether there was evidence for the presence or absence of sex differences with the DDIs.

Methods:

The relevant details from 156 drug interaction studies within 124 papers were extracted and evaluated.

Results:

Only eight studies (five papers) compared the outcome of the DDI between males and females. The majority of the studies had only male volunteers. Five studies had females only while 60 had males only, with 7.7% of the studies having an equal proportion of both sexes. Surprisingly, four studies did not specify the sex of the subjects.

:

Based on the limited number of studies comparing males and females, no specific trends or conclusions were evident. Sex differences in the interaction were reported between ketoconazole and midazolam as well as clarithromycin and midazolam. However, no sex difference was observed with the interaction between clarithromycin and triazolam or erythromycin and triazolam. No sex-related PK differences were observed with the interaction between ketoconazole and domperidone, although sex-related differences in QT prolongation were observed.

Conclusion:

This review has shown that only limited progress had been made with the inclusion of both sexes in DDI studies.

Drug interactions of meglitinide antidiabetics involving CYP enzymes and OATP1B1 transporter

Meglitinides such as repaglinide and nateglinide are useful to treat type 2 diabetes patients who follow a flexible lifestyle. They are short-acting insulin secretagogues and are associated with less risk of hypoglycemia, weight gain and chronic hyperinsulinemia compared with sulfonylureas. Meglitinides are the substrates of cytochrome P450 (CYP) enzymes and organic anion transporting polypeptide 1B1 (OATP1B1 transporter) and the coadministration of the drugs affecting them will result in pharmacokinetic drug interactions. This article focuses on the drug interactions of meglitinides involving CYP enzymes and OATP1B1 transporter. To prevent the risk of hypoglycemic episodes, prescribers and pharmacists must be aware of the adverse drug interactions of meglitinides.

Effect of gemfibrozil and rifampicin on the pharmacokinetics of selexipag and its active metabolite in healthy subjects

AIMS

Based on in vitro data, there is evidence to suggest that cytochrome P450 (CYP) 2C8 is involved in the metabolism of selexipag and its active metabolite, ACT-333679. The present study evaluated the possible pharmacokinetic interactions of selexipag with gemfibrozil, a strong CYP2C8 inhibitor, and rifampicin, an inducer of CYP2C8.

METHODS

The study consisted of two independent parts, each conducted according to an open-label, randomized, crossover design. The pharmacokinetics and safety of selexipag and ACT-333679 were studied following single-dose administration either alone or in the presence of multiple-dose gemfibrozil (part I) or rifampicin (part II) in healthy male subjects.

RESULTS

Gemfibrozil had comparatively small effects on selexipag (less than 2-fold difference in any pharmacokinetic variable) but, with respect to ACT-333679, increased the maximum plasma concentration (C_max ) 3.6-fold [90% confidence interval (CI) 3.1, 4.3] and the area under the plasma concentration-time curve from zero to infinity (AUC_0-∞ ) 11.1-fold (90% CI 9.2, 13.4). The marked increased exposure to ACT-333679, which mediates the majority of the pharmacological activity of selexipag, was accompanied by significantly more adverse events such as headache, nausea and vomiting. Coadministration of rifampicin increased the C_max of selexipag 1.8-fold (90% CI 1.4, 2.2) and its AUC0_-∞ 1.3-fold (90% CI 1.1, 1.4); its effects on ACT-333679 were to increase its C_max 1.3-fold (90% CI 1.1, 1.6), shorten its half-life by 63% and reduce its AUC0_-∞ by half (90% CI 0.45, 0.59).

CONCLUSION

Concomitant administration of selexipag and strong inhibitors of CYP2C8 must be avoided, whereas when coadministered with inducers of CYP2C8, dose adjustments of selexipag should be envisaged.

Role of Cytochrome P450 2C8 in Drug Metabolism and Interactions

During the last 10-15 years, cytochrome P450 (CYP) 2C8 has emerged as an important drug-metabolizing enzyme. CYP2C8 is highly expressed in human liver and is known to metabolize more than 100 drugs. CYP2C8 substrate drugs include amodiaquine, cerivastatin, dasabuvir, enzalutamide, imatinib, loperamide, montelukast, paclitaxel, pioglitazone, repaglinide, and rosiglitazone, and the number is increasing. Similarly, many drugs have been identified as CYP2C8 inhibitors or inducers. In vivo, already a small dose of gemfibrozil, i.e., 10% of its therapeutic dose, is a strong, irreversible inhibitor of CYP2C8. Interestingly, recent findings indicate that the acyl-β-glucuronides of gemfibrozil and clopidogrel cause metabolism-dependent inactivation of CYP2C8, leading to a strong potential for drug interactions. Also several other glucuronide metabolites interact with CYP2C8 as substrates or inhibitors, suggesting that an interplay between CYP2C8 and glucuronides is common. Lack of fully selective and safe probe substrates, inhibitors, and inducers challenges execution and interpretation of drug-drug interaction studies in humans. Apart from drug-drug interactions, some CYP2C8 genetic variants are associated with altered CYP2C8 activity and exhibit significant interethnic frequency differences. Herein, we review the current knowledge on substrates, inhibitors, inducers, and pharmacogenetics of CYP2C8, as well as its role in clinically relevant drug interactions. In addition, implications for selection of CYP2C8 marker and perpetrator drugs to investigate CYP2C8-mediated drug metabolism and interactions in preclinical and clinical studies are discussed.

Clinical pharmacology of deferasirox

Iron accumulation is a consequence of regular red cell transfusions, and can occur as a result of ineffective erythropoiesis secondary to increased intestinal iron absorption, in patients with various anemias. Without appropriate treatment, iron overload can lead to increased morbidity and mortality. Deferasirox is an oral iron chelator effective for reduction of body iron in iron-overloaded patients with transfusion-dependent anemias and non-transfusion-dependent thalassemia, with a well-established safety profile. This review summarizes the clinical pharmacokinetics, pharmacodynamics, and drug-drug interaction profile of deferasirox, and the claims supporting once-daily dosing for effective chelation. Sustained labile plasma iron suppression is observed with no rebound between doses, protecting organs from potential tissue damage. Increased iron excretion positively correlates with increased deferasirox exposure; to optimize iron removal transfusional iron intake, body iron burden and safety parameters should also be considered. Deferasirox dispersible tablets should be taken ≥30 min before food due to an effect of food on bioavailability. Dosing is consistent across pediatric and adult patients and there is no ethnic sensitivity. Dose adjustment is required for patients with hepatic impairment and may be considered upon coadministration with strong uridine diphosphate glucuronosyltransferase inducers or bile acid sequestrants (coadministration should be avoided where possible), and patients should be monitored upon coadministration with cytochrome P450 (CYP) 3A4/5, CYP2C8, or CYP1A2 substrates. Coadministration with hydroxyurea, a fetal hemoglobin modulator, does not appear to impact deferasirox pharmacokinetics. In summary, a substantial body of clinical and pharmacokinetic data are available for deferasirox to guide its optimal use in multiple patient populations and clinical circumstances.

Use of deferasirox in transfusion-dependent myelodysplastic syndromes with iron overload

SUMMARY 

In myelodysplastic syndromes (MDS), transfusion-dependent anemia has been established as an independent risk factor for decreased survival. Although evidence from prospective studies is still lacking, several guidelines recommend iron-chelating therapy in MDS patients with a longer life expectancy. With the recent introduction of deferasirox, an oral active iron-chelating drug, which has shown dose-dependent efficacy and acceptable tolerability, this therapeutic option has become feasible even in the elderly. Several retrospective and prospective studies showed that in MDS patients deferasirox is effective in reducing iron burden and in maintaining the circulating toxic iron fraction within the normal range. Moreover, in a substantial fraction of patients treated with deferasirox a significant improvement of peripheral cytopenias may occur.

Deferasirox for the treatment of iron overload in non-transfusion-dependent thalassemia

Non-transfusion-dependent thalassemia (NTDT) defines a group of patients who do not require regular transfusions for survival, but are at significant risk of iron accumulation from underlying disease-related mechanisms distinct from transfusional iron overload. Management of iron overload in NTDT has received little attention compared with that of β-thalassemia major, despite evidence of significant iron-induced complications with advancing age. The efficacy and safety of the iron chelator deferasirox in NTDT has been evaluated in two pilot studies and the first prospective, randomized, placebo-controlled study (THALASSA) of any chelator in NTDT. Treatment with deferasirox for up to 2 years yielded a sustained reduction in iron burden, with a clinically manageable safety profile. Following these trial data, deferasirox is the first iron chelator approved for use in NTDT patients, and with NTDT guidelines now available, physicians are better equipped to achieve effective monitoring and management of iron burden in NTDT.

Mechanistic modeling to predict the transporter- and enzyme-mediated drug-drug interactions of repaglinide

PURPOSE

Quantitative prediction of complex drug-drug interactions (DDIs) is challenging. Repaglinide is mainly metabolized by cytochrome-P-450 (CYP)2C8 and CYP3A4, and is also a substrate of organic anion transporting polypeptide (OATP)1B1. The purpose is to develop a physiologically based pharmacokinetic (PBPK) model to predict the pharmacokinetics and DDIs of repaglinide.

METHODS

In vitro hepatic transport of repaglinide, gemfibrozil and gemfibrozil 1-O-β-glucuronide was characterized using sandwich-culture human hepatocytes. A PBPK model, implemented in Simcyp (Sheffield, UK), was developed utilizing in vitro transport and metabolic clearance data.

RESULTS

In vitro studies suggested significant active hepatic uptake of repaglinide. Mechanistic model adequately described repaglinide pharmacokinetics, and successfully predicted DDIs with several OATP1B1 and CYP3A4 inhibitors (<10% error). Furthermore, repaglinide-gemfibrozil interaction at therapeutic dose was closely predicted using in vitro fraction metabolism for CYP2C8 (0.71), when primarily considering reversible inhibition of OATP1B1 and mechanism-based inactivation of CYP2C8 by gemfibrozil and gemfibrozil 1-O-β-glucuronide.

CONCLUSIONS

This study demonstrated that hepatic uptake is rate-determining in the systemic clearance of repaglinide. The model quantitatively predicted several repaglinide DDIs, including the complex interactions with gemfibrozil. Both OATP1B1 and CYP2C8 inhibition contribute significantly to repaglinide-gemfibrozil interaction, and need to be considered for quantitative rationalization of DDIs with either drug.

Update on rifampin, rifabutin, and rifapentine drug interactions

BACKGROUND

Rifampin is a potent inducer of both cytochrome P-450 oxidative enzymes and the P-glycoprotein transport system. Among numerous well documented, clinically significant interactions, examples include warfarin, oral contraceptives, itraconazole, digoxin, verapamil, simvastatin, and human immunodeficiency virus-related protease inhibitors. Rifabutin reduces serum concentrations of antiretroviral agents, but less so than rifampin. Rifapentine is also an inducer of drug metabolism.

METHODS

A literature search of English language journals from 2008 to March 2012 was completed using several databases, including PubMed, EMBASE, and SCOPUS. Search terms included rifampin, rifabutin, rifapentine AND drug interactions.

FINDINGS

Examples of clinically relevant interactions with rifampin demonstrated by recent reports include posaconazole, voriconazole, oxycodone, risperidone, mirodenafil, and ebastine.

CONCLUSIONS

To avoid a reduced therapeutic response, therapeutic failure, or toxic reactions when rifampin, rifabutin, or rifapentine are added to or discontinued from medication regimens, clinicians need to be aware of these interactions. Recent studies have indicated that other transporter systems play a role in these drug interactions. As reports of rifampin drug interactions continue to grow, this review is a reminder to clinicians to be vigilant.

Iron overload and toxicity: implications for anesthesiologists

Conditions leading to iron overload range from rare hereditary disorders to more common medical conditions associated with chronic blood transfusions. Iron overload has deleterious effects on various vital organs (eg, liver, heart, and endocrine glands). Serum ferritin (in conjunction with transferrin saturation) is the most widely used test to evaluate iron burden and to screen for iron overload. The management plan should be adjusted to account for iron overload and potential consequences of liver, heart, and other organ involvement.

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.