Effects of Cytochrome P450 Inhibition and Induction on the Phenotyping Metrics of the Basel Cocktail: A Randomized Crossover Study

Building Confidence in Physiologically Based Pharmacokinetic Modeling of CYP3A Induction Mediated by Rifampin: An Industry Perspective

Physiologically-based pharmacokinetic (PBPK) modeling offers a viable approach to predict induction drug-drug interactions (DDIs) with the potential to streamline or reduce clinical trial burden if predictions can be made with sufficient confidence. In the current work, the ability to predict the effect of rifampin, a well-characterized strong CYP3A4 inducer, on 20 CYP3A probes with publicly available PBPK models (often developed using a workflow with optimization following a strong inhibitor DDI study to gain confidence in fraction metabolized by CYP3A4, fm,CYP3A4, and fraction available after intestinal metabolism, Fg), was assessed. Substrates with a range of fm,CYP3A4 (0.086-1.0), Fg (0.11-1.0) and hepatic availability (0.09-0.96) were included. Predictions were most often accurate for compounds that are not P-gp substrates or that are P-gp substrates but that have high permeability. Case studies for three challenging DDI predictions (i.e., for eliglustat, tofacitinib, and ribociclib) are presented. Along with parameter sensitivity analysis to understand key parameters impacting DDI simulations, alternative model structures should be considered, for example, a mechanistic absorption model instead of a first-order absorption model might be more appropriate for a P-gp substrate with low permeability. Any mechanisms pertinent to the CYP3A substrate that rifampin might impact (e.g., induction of other enzymes or P-gp) should be considered for inclusion in the model. PBPK modeling was shown to be an effective tool to predict induction DDIs with rifampin for CYP3A substrates with limited mechanistic complications, increasing confidence in the rifampin model. While this analysis focused on rifampin, the learnings may apply to other inducers.

Effect of protein binding on the pharmacokinetics of the six substrates in the Basel phenotyping cocktail in healthy subjects and patients with liver cirrhosis

Phenotyping serves to estimate enzyme activities in healthy persons and patients in vivo. Low doses of enzyme-specific substrates are administered, and activities estimated using metabolic ratios (MR, calculated as AUCmetabolite/AUCparent). We administered the Basel phenotyping cocktail containing caffeine (CYP1A2 substrate), efavirenz (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), metoprolol (CYP2D6) and midazolam (CYP3A) to 36 patients with liver cirrhosis and 12 control subjects and determined free and total plasma concentrations over 24 h. Aims were to assess whether MRs reflect CYP activities in patients with liver cirrhosis and whether MRs calculated with free plasma concentrations (MRfree) provide better estimates than with total concentrations (MRtotal). The correlation of MRtotal with MRfree was excellent (R2 >0.910) for substrates with low (<30 %, caffeine and metoprolol) and intermediate protein binding (≥30 and <99 %, midazolam and omeprazole) but weak (R2 <0.30) for substrates with high protein binding (≥99 %, efavirenz and flurbiprofen). The correlations between MRtotal and MRfree with CYP activities were good (R2 >0.820) for CYP1A2, CYP2C19 and CYP2D6. CYP3A4 activity was reflected better by midazolam elimination than by midazolam MRtotal or MRfree. The correlation between MRtotal and MRfree with CYP activity was not significant or weak for CYP2B6 and CYP2C9. In conclusion, MRs of substrates with an extensive protein binding (>99 %) show high inter-patient variabilities and do not accurately reflect CYP activity in patients with liver cirrhosis. Protein binding of the probe drugs has a high impact on the precision of CYP activity estimates and probe drugs with low or intermediate protein binding should be preferred.

The Use of Microdosing for In vivo Phenotyping of Cytochrome P450 Enzymes: Where Do We Stand? A Narrative Review

Cytochrome P450 (CYP) enzymes play a central role in the elimination of approximately 80% of all clinically used drugs. Differences in CYP enzyme activity between individuals can contribute to interindividual variability in exposure and, therefore, treatment outcome. In vivo CYP enzyme activity could be determined with phenotyping. Currently, (sub)therapeutic doses are used for in vivo phenotyping, which can lead to side effects. The use of microdoses (100 µg) for in vivo phenotyping for CYP enzymes could overcome the limitations associated with the use of (sub)therapeutic doses of substrates. The aim of this review is to provide a critical overview of the application of microdosing for in vivo phenotyping of CYP enzymes. A literature search was performed to find drug-drug interaction studies of CYP enzyme substrates that used microdoses of the respective substrates. A substrate was deemed sensitive to changes in CYP enzyme activity when the pharmacokinetics of the substrate significantly changed during inhibition and induction of the enzyme. On the basis of the currently available evidence, the use of microdosing for in vivo phenotyping for subtypes CYP1A2, CYP2C9, CYP2D6, and CYP2E1 is not recommended. Microdosing can be used for the in vivo phenotyping of CYP2C19 and CYP3A. The recommended microdose phenotyping test for CYP2C19 is measuring the omeprazole area-under-the-concentration-time curve over 24 h (AUC0-24) after administration of a single 100 µg dose. CYP3A activity could be best determined with a 0.1-75 µg dose of midazolam, and subsequently measuring AUC extrapolated to infinity (AUC∞) or clearance. Moreover, there are two metrics available for midazolam using a limited sampling strategy: AUC over 10 h (AUC0-10) and AUC from 2 to 4 h (AUC2-4).

Assessment of the Effects of Abrocitinib on the Pharmacokinetics of Probe Substrates of Cytochrome P450 1A2, 2B6 and 2C19 Enzymes and Hormonal Oral Contraceptives in Healthy Individuals

BACKGROUND AND OBJECTIVE

Abrocitinib is an oral small-molecule Janus kinase (JAK)-1 inhibitor approved for the treatment of moderate-to-severe atopic dermatitis. In vitro studies indicated that abrocitinib is a weak time-dependent inhibitor of cytochrome P450 (CYP) 2C19/3A and a weak inducer of CYP1A2/2B6/2C19/3A. To assess the potential effect of abrocitinib on concomitant medications, drug-drug interaction (DDI) studies were conducted for abrocitinib with sensitive probe substrates of these CYP enzymes. The impact of abrocitinib on hormonal oral contraceptives (ethinyl estradiol and levonorgestrel), as substrates of CYP3A and important concomitant medications for female patients, was also evaluated.

METHODS

Three Phase 1 DDI studies were performed to assess the impact of abrocitinib 200 mg once daily (QD) on the probe substrates of: (1) 1A2 (caffeine), 2B6 (efavirenz) and 2C19 (omeprazole) in a cocktail study; (2) 3A (midazolam); and (3) 3A (oral contraceptives).

RESULTS

After multiple doses of abrocitinib 200 mg QD, there is a lack of effect on the pharmacokinetics of midazolam, efavirenz and contraceptives. Abrocitinib increased the area under the concentration time curve from 0 to infinity (AUCinf) and the maximum concentration (Cmax) of omeprazole by approximately 189 and 134%, respectively. Abrocitinib increased the AUCinf of caffeine by 40% with lack of effect on Cmax.

CONCLUSIONS

Based on the study results, abrocitinib is a moderate inhibitor of CYP2C19. Caution should be exercised when using abrocitinib concomitantly with narrow therapeutic index medicines that are primarily metabolized by CYP2C19 enzyme. Abrocitinib is a mild inhibitor of CYP1A2; however, the impact is not clinically relevant, and no general dose adjustment is recommended for CYP1A2 substrates. Abrocitinib does not inhibit CYP3A or induce CYP1A2/2B6/2C19/3A and does not affect the pharmacokinetics of contraceptives.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov registration IDs: NCT03647670, NCT05067439, NCT03662516.

Measurement of CYP1A2 and CYP3A4 activity by a simplified Geneva cocktail approach in a cohort of free-living individuals: a pilot study

Introduction: The cytochrome P450 enzyme subfamilies, including CYP3A4 and CYP1A2, have a major role in metabolism of a range of drugs including several anti-cancer treatments. Many factors including environmental exposures, diet, diseaserelated systemic inflammation and certain genetic polymorphisms can impact the activity level of these enzymes. As a result, the net activity of each enzyme subfamily can vary widely between individuals and in the same individual over time. This variability has potential major implications for treatment efficacy and risk of drug toxicity, but currently no assays are available for routine use to guide clinical decision-making. Methods: To address this, a mass spectrometry-based method to measure activities of CYP3A4, CYP1A2 was adapted and tested in free-living participants. The assay results were compared with the predicted activity of each enzyme, based on a self-report tool capturing diet, medication, chronic disease state, and tobacco usage. In addition, a feasibility test was performed using a low-volume dried blood spots (DBS) on two different filter-paper supports, to determine if the same assay could be deployed without the need for repeated standard blood tests. Results: The results confirmed the methodology is safe and feasible to perform in free-living participants using midazolam and caffeine as test substrates for CYP3A4 and CYP1A2 respectively. Furthermore, though similar methods were previously shown to be compatible with the DBS format, the assay can also be performed successfully while incorporating glucuronidase treatment into the DBS approach. The measured CYP3A4 activity score varied 2.6-fold across participants and correlated with predicted activity score obtained with the self-report tool. The measured CYP1A2 activity varied 3.5-fold between participants but no correlation with predicted activity from the self-report tool was found. Discussion: The results confirm the wide variation in CYP activity between individuals and the important role of diet and other exposures in determining CYP3A4 activity. This methodology shows great potential and future cross-sectional and longitudinal studies using DBS are warranted to determine how best to use the assay results to guide drug treatments.

Circulating Biomarkers Instead of Genotyping to Establish Metabolizer Phenotypes

Pharmacogenomics (PGx) enables personalized treatment for the prediction of drug response and to avoid adverse drug reactions. Currently, PGx mainly relies on the genetic information of absorption, distribution, metabolism, and excretion (ADME) targets such as drug-metabolizing enzymes or transporters to predict differences in the patient's phenotype. However, there is evidence that the phenotype-genotype concordance is limited. Thus, we discuss different phenotyping strategies using exogenous xenobiotics (e.g., drug cocktails) or endogenous compounds for phenotype prediction. In particular, minimally invasive approaches focusing on liquid biopsies offer great potential to preemptively determine metabolic and transport capacities. Early studies indicate that ADME phenotyping using exosomes released from the liver is reliable. In addition, pharmacometric modeling and artificial intelligence improve phenotype prediction. However, further prospective studies are needed to demonstrate the clinical utility of individualized treatment based on phenotyping strategies, not only relying on genetics. The present review summarizes current knowledge and limitations.

Cytochrome P450 activity in rheumatoid arthritis patients during continuous IL-6 receptor antagonist therapy

BACKGROUND

Inflammation suppresses cytochrome P450 (CYP) enzyme activity, and single-dose interleukin 6 receptor antagonists (anti-IL-6R) reverse this effect. Here, we assess the impact of continuous anti-IL-6R therapy in patients with rheumatoid arthritis.

METHODS

In a clinical pharmacokinetic trial, the Basel cocktail was administered before and after 3 and 12 weeks of anti-IL-6R therapy to assess CYP enzyme activity (registered in the ClinicalTrials.gov database (identifier NCT04842981) on April 13th, 2021). In a retrospective study, the 4β-hydroxycholesterol/cholesterol ratio was measured as a biomarker for CYP3A4 activity before and after 3 and 6 months of anti-IL-6R therapy. The control group was patients initiating a tumor necrosis factor alfa (TNF-α) inhibitor.

RESULTS

In the clinical pharmacokinetic trial (n = 3), midazolam metabolic ratio (CYP3A4) was inconclusive due to the limited sample size. Midazolam AUC and Cmax indicate a weak impact on CYP3A4 activity after 3 weeks of anti-IL-6R therapy compared to baseline (AUC geometric mean ratio (GMR): 0.80, 95% CI: 0.64-0.99 and Cmax GMR: 0.58, 95% CI: 0.37-0.91), which returns to baseline levels after 12 weeks of therapy (AUC GMR 1.02, 95% CI: 0.72-1.46 and Cmax GMR 1.03, 95% CI 0.72-1.47). No effect on the 4β-hydroxycholesterol/cholesterol ratio was observed in the retrospective study.

CONCLUSION

Based on sparse data from three patients, continuous anti-IL-6R therapy seems to cause an acute but transient increase in CYP3A4 activity in rheumatoid arthritis patients, which may be due to a normalization of the inflammation-suppressed CYP activity. Further studies are warranted to understand the mechanism behind this putative transient effect. Trial registration Registered in the ClinicalTrials.gov database (identifier NCT04842981) on April 13th, 2021.

In vitro evaluation of tropolone absorption, metabolism, and clearance

Tropolone compounds can inhibit hepatitis B virus (HBV) replication at sub-micromolar levels and are synergistic upon co-treatment with nucleos(t)ide analog drugs. However, only a few compounds within this chemotype have been screened for their pharmacological properties. Here, we chose 36 structurally diverse tropolones from six subclasses to characterize their in vitro pharmacological parameters. All compounds were more soluble in pHs that reflect the gastrointestinal tract (pH 5 and 6.5) than plasma (pH 7.4). Those compounds that had solubility limits >100 μM were tested in a passive permeability assay, and there was no general trend in the compounds' passive permeability at any pH. Twenty-nine compounds with the best absorption parameters were tested in HEK293 cells to assess potential cytotoxicity; measured toxicities were similar to those in the hepatic HepDES19 cells used for screening (R2 = 0.55). Sixteen representative compounds were tested against five major CYP450 isoforms and there was no substantial inhibition by any compound against any of the enzymes tested (<50%). The t1/2 values of 15 compounds were determined in the microsome stability assay and 12 compounds were evaluated in plasma protein binding assays to assess factors affecting their rate of clearance. All compounds with detectable analyte peaks had t1/2 > 30 min, and while 4 of 12 had statistically significant decreased potency in conditions with increased albumin concentrations, only one compound's potency was biologically significant. These data indicate that the tropolones have pharmacological characteristics that reflect approved drugs and inform future structure activity relationships during drug design.

Effect of nivasorexant (ACT-539313), a selective orexin-1-receptor antagonist, on multiple cytochrome P450 probe substrates in vitro and in vivo using a cocktail approach in healthy subjects

Nivasorexant, a selective orexin-1-receptor antagonist, has recently been assessed in the treatment of humans with binge-eating disorder. Herein, the inhibitory potential of nivasorexant on cytochromes P450 (CYPs) 2C9, 2C19, and 3A4 was evaluated. Human liver microsomes/recombinant CYP enzymes were evaluated in vitro. In vivo, a single-center, open-label, fixed-sequence study was performed in healthy adults to explore the effect of 100 mg nivasorexant administered twice daily (b.i.d.) on the pharmacokinetics (PK) of flurbiprofen (50 mg, CYP2C9), omeprazole (20 mg, CYP2C19), midazolam (2 mg, CYP3A4) making use of a cocktail approach. Plasma PK sampling was performed over 24 h on Day 1 (Cocktail alone), 8 (Cocktail + nivasorexant), and 15 (Cocktail + nivasorexant at steady state). Genotyping of subjects' CYPs was performed while safety and tolerability were also assessed. In vitro, nivasorexant inhibited CYP2C9, 2C19, and 3A4 in competitive inhibition assays with IC50 values of 8.6, 1.6, and 19-44 μM, respectively, while showing a significant time-dependent CYP2C19 inhibition. In 22 subjects, exposure to flurbiprofen, omeprazole, and midazolam was generally higher during concomitant single- (i.e., area under the plasma concentration-time curve [AUC] ratio increased by 1.04-, 2.05-, and 1.56-fold, respectively) and repeated-dose (i.e., AUC ratio increased by 1.47-, 6.84-, and 3.71-fold, respectively) nivasorexant administration compared with the cocktail substrates administered alone. The most frequently reported adverse event was somnolence. According to regulatory guidance, nivasorexant is classified as a moderate CYP2C19 and weak CYP3A4 inhibitor after 1 day and as a weak CYP2C9, strong CYP2C19, and moderate CYP3A4 inhibitor after 8 days of 100 mg b.i.d. administration. Clinicaltrials.gov ID: NCT05254548.

Evaluation of the Cytochrome P450 3A and P-glycoprotein Drug-Drug Interaction Potential of Futibatinib

Futibatinib, a selective, irreversible fibroblast growth factor receptor 1-4 inhibitor, is being investigated for tumors harboring FGFR aberrations and was recently approved for the treatment of FGFR2 fusion/rearrangement-positive intrahepatic cholangiocarcinoma. In vitro studies identified cytochrome P450 (CYP) 3A as the major CYP isoform in futibatinib metabolism and indicated that futibatinib is likely a P-glycoprotein (P-gp) substrate and inhibitor. Futibatinib also showed time-dependent inhibition of CYP3A in vitro. Phase I studies investigated the drug-drug interactions of futibatinib with itraconazole (a dual P-gp and strong CYP3A inhibitor), rifampin (a dual P-gp and strong CYP3A inducer), or midazolam (a sensitive CYP3A substrate) in healthy adult participants. Compared with futibatinib alone, coadministration of futibatinib with itraconazole increased futibatinib mean peak plasma concentration and area under the plasma concentration-time curve by 51% and 41%, respectively, and coadministration of futibatinib with rifampin lowered futibatinib mean peak plasma concentration and area under the plasma concentration-time curve by 53% and 64%, respectively. Coadministration of midazolam with futibatinib had no effect on midazolam pharmacokinetics compared with midazolam administered alone. These findings suggest that concomitant use of dual P-gp and strong CYP3A inhibitors/inducers with futibatinib should be avoided, but futibatinib can be concomitantly administered with other drugs metabolized by CYP3A. Drug-drug interaction studies with P-gp-specific substrates and inhibitors are planned.

The Activity of Members of the UDP-Glucuronosyltransferase Subfamilies UGT1A and UGT2B is Impaired in Patients with Liver Cirrhosis

BACKGROUND AND OBJECTIVE

The impact of liver cirrhosis on the activity of UDP-glucuronosyltransferases (UGTs) is currently not well characterized. We investigated the glucuronidation capacity and glucuronide accumulation in patients with liver cirrhosis.

METHODS

We administered the Basel phenotyping cocktail (caffeine, efavirenz, flurbiprofen, omeprazole, metoprolol, midazolam) to patients with liver cirrhosis (n = 16 Child A, n = 15 Child B, n = 5 Child C) and n = 12 control subjects and obtained pharmacokinetic profiles of substrates and primary metabolites and their glucuronides.

RESULTS

Caffeine and its metabolite paraxanthine were only slightly glucuronidated. The metabolic ratio (AUCglucuronide/AUCparent, MR) was not affected for caffeine but decreased by 60% for paraxanthine glucuronide formation in Child C patients. Efavirenz was not glucuronidated whereas 8-hydroxyefavirenz was efficiently glucuronidated. The MR of 8-hydroxyefavirenz-glucuronide formation increased three-fold in Child C patients and was negatively correlated with the glomerular filtration rate. Flurbiprofen and omeprazole were not glucuronidated. 4-Hydroxyflurbiprofen and 5-hydroxyomeprazole were both glucuronidated but the corresponding MRs for glucuronide formation were not affected by liver cirrhosis. Metoprolol, but not α-hydroxymetoprolol, was glucuronidated, and the MR for metoprolol-glucuronide formation dropped by 60% in Child C patients. Both midazolam and its metabolite 1'-hydroxymidazolam underwent glucuronidation, and the corresponding MRs for glucuronide formation dropped by approximately 80% in Child C patients. No relevant glucuronide accumulation occurred in patients with liver cirrhosis.

CONCLUSIONS

Detailed analysis revealed that liver cirrhosis may affect the activity of UGTs of the UGT1A and UGT2B subfamilies according to liver function. Clinically significant glucuronide accumulation did not occur in the population investigated.

CLINICAL TRIAL REGISTRATION

NCT03337945.

Stereoisomers of octahydrocurcumin, the hydrogenated metabolites of curcumin, display stereoselective activity on the CYP2E1 enzyme in L-02 cells

As the final hydrogenated metabolite of curcumin, octahydrocurcumin (OHC) exhibits increased powerful bioactivities. The chiral and symmetric chemical structure indicated that there were two OHC stereoisomers, (3R,5S)-octahydrocurcumin (Meso-OHC) and (3S,5S)-octahydrocurcumin ((3S,5S)-OHC), which may induce different effects on metabolic enzymes and bioactivities. Thus, we detected OHC stereoisomers from rat metabolites (blood, liver, urine and feces) after oral administration of curcumin. In addition, OHC stereoisomers were prepared and then their different influences on cytochrome P450 enzymes (CYPs) and UDP-glucuronyltransferases (UGTs) in L-02 cells were tested to explore the potential interaction and different bioactivities. Our results proved that curcumin could be metabolised into OHC stereoisomers first. In addition, Meso-OHC and (3S,5S)-OHC exhibited slight induction or inhibition effects on CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP3A4 and UGTs. Furthermore, Meso-OHC exhibited more intensive inhibition toward CYP2E1 expression than (3S,5S)-OHC, ascribed to the different mode of binding to the enzyme protein (P < 0.05), which finally induced more effective liver protection effects in acetaminophen-induced L-02 cell injury.

Phenotyping Indices of CYP450 and P-Glycoprotein in Human Volunteers and in Patients Treated with Painkillers or Psychotropic Drugs

Drug-metabolizing enzymes and drug transporters are key determinants of drug pharmacokinetics and response. The cocktail-based cytochrome P450 (CYP) and drug transporter phenotyping approach consists in the administration of multiple CYP or transporter-specific probe drugs to determine their activities simultaneously. Several drug cocktails have been developed over the past two decades in order to assess CYP450 activity in human subjects. However, phenotyping indices were mostly established for healthy volunteers. In this study, we first performed a literature review of 27 clinical pharmacokinetic studies using drug phenotypic cocktails in order to determine 95%,95% tolerance intervals of phenotyping indices in healthy volunteers. Then, we applied these phenotypic indices to 46 phenotypic assessments processed in patients having therapeutic issues when treated with painkillers or psychotropic drugs. Patients were given the complete phenotypic cocktail in order to explore the phenotypic activity of CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A, and P-glycoprotein (P-gp). P-gp activity was evaluated by determining AUC_0-6h for plasma concentrations over time of fexofenadine, a well-known substrate of P-gp. CYP metabolic activities were assessed by measuring the CYP-specific metabolite/parent drug probe plasma concentrations, yielding single-point metabolic ratios at 2 h, 3 h, and 6 h or AUC_0-6h ratio after oral administration of the cocktail. The amplitude of phenotyping indices observed in our patients was much wider than those observed in the literature for healthy volunteers. Our study helps define the range of phenotyping indices with "normal" activities in human volunteers and allows classification of patients for further clinical studies regarding CYP and P-gp activities.

Developmental Pharmacokinetics of Antibiotics Used in Neonatal ICU: Focus on Preterm Infants

Neonatal Infections are among the most common reasons for admission to the intensive care unit. Neonatal sepsis (NS) significantly contributes to mortality rates. Empiric antibiotic therapy of NS recommended by current international guidelines includes benzylpenicillin, ampicillin/amoxicillin, and aminoglycosides (gentamicin). The rise of antibacterial resistance precipitates the growth of the use of antibiotics of the Watch (second, third, and fourth generations of cephalosporines, carbapenems, macrolides, glycopeptides, rifamycins, fluoroquinolones) and Reserve groups (fifth generation of cephalosporines, oxazolidinones, lipoglycopeptides, fosfomycin), which are associated with a less clinical experience and higher risks of toxic reactions. A proper dosing regimen is essential for effective and safe antibiotic therapy, but its choice in neonates is complicated with high variability in the maturation of organ systems affecting drug absorption, distribution, metabolism, and excretion. Changes in antibiotic pharmacokinetic parameters result in altered efficacy and safety. Population pharmacokinetics can help to prognosis outcomes of antibiotic therapy, but it should be considered that the neonatal population is heterogeneous, and this heterogeneity is mainly determined by gestational and postnatal age. Preterm neonates are common in clinical practice, and due to the different physiology compared to the full terms, constitute a specific neonatal subpopulation. The objective of this review is to summarize the evidence about the developmental changes (specific for preterm and full-term infants, separately) of pharmacokinetic parameters of antibiotics used in neonatal intensive care units.

Population Pharmacokinetic/Pharmacodynamic Modeling of the Effect of Abrocitinib on QT Intervals in Healthy Volunteers

Abrocitinib is a selective Janus kinase 1 inhibitor for the treatment of moderate to severe atopic dermatitis (AD). To assess the relationship between abrocitinib plasma concentrations and heart rate (HR)-corrected QT (QTc) and HR and calculate the effect of abrocitinib on these parameters at supratherapeutic concentrations, 36 healthy volunteers received single doses of abrocitinib 600 mg, placebo, and moxifloxacin 400 mg in a 3-period crossover study. The relationship between change from baseline in Fridericia-corrected QTc (∆QTcF) values and abrocitinib plasma concentrations was modeled using a prespecified linear mixed-effects model. The 90%CIs for time-matched placebo-corrected ∆QTcF (∆∆QTcF) were calculated from model parameter estimates and assessed against the regulatory threshold (10 millisecond) at the predicted supratherapeutic concentration in patients with atopic dermatitis (2156 ng/mL). Mean (90%CI) time-matched placebo-corrected change from baseline in HR (∆∆HR) was calculated similarly. At the supratherapeutic concentration, mean (90%CI) estimates for ∆∆QTcF and ∆∆HR were 6.00 (4.52-7.49) milliseconds and 6.51 (5.23-7.80) bpm, respectively. Despite a concentration-dependent effect on ∆QTcF and ∆HR, with statistically significant slopes (90%CI) of 0.0026 (0.0018-0.0035) milliseconds/(ng/mL) and 0.0031 (0.0024-0.0038) bpm/(ng/mL), respectively, abrocitinib does not have a clinically significant effect on QTc interval or HR at supratherapeutic exposures.

Liver Cirrhosis Affects the Pharmacokinetics of the Six Substrates of the Basel Phenotyping Cocktail Differently

BACKGROUND

Activities of hepatic cytochrome P450 enzymes (CYPs) are relevant for hepatic clearance of drugs and known to be decreased in patients with liver cirrhosis. Several studies have reported the effect of liver cirrhosis on CYP activity, but the results are partially conflicting and for some CYPs lacking.

OBJECTIVE

In this study, we aimed to investigate the CYP activity in patients with liver cirrhosis with different Child stages (A-C) using the Basel phenotyping cocktail approach.

METHODS

We assessed the pharmacokinetics of the six compounds and their CYP-specific metabolites of the Basel phenotyping cocktail (CYP1A2: caffeine, CYP2B6: efavirenz, CYP2C9: flurbiprofen, CYP2C19: omeprazole, CYP2D6: metoprolol, CYP3A: midazolam) in patients with liver cirrhosis (n = 16 Child A cirrhosis, n = 15 Child B cirrhosis, n = 5 Child C cirrhosis) and matched control subjects (n = 12).

RESULTS

While liver cirrhosis only marginally affected the pharmacokinetics of the low to moderate extraction drugs efavirenz and flurbiprofen, the elimination rate of caffeine was reduced by 51% in patients with Child C cirrhosis. For the moderate to high extraction drugs omeprazole, metoprolol, and midazolam, liver cirrhosis decreased the elimination rate by 75%, 37%, and 60%, respectively, increased exposure, and decreased the apparent systemic clearance (clearance/bioavailability). In patients with Child C cirrhosis, the metabolic ratio (ratio of the area under the plasma concentration-time curve from 0 to 24 h of the metabolite to the parent compound), a marker for CYP activity, decreased by 66%, 47%, 92%, 73%, and 43% for paraxanthine/caffeine (CYP1A2), 8-hydroxyefavirenz/efavirenz (CYP2B6), 5-hydroxyomeprazole/omeprazole (CYP2C19), α-hydroxymetoprolol/metoprolol (CYP2D6), and 1'-hydroxymidazolam/midazolam (CYP3A), respectively. In comparison, the metabolic ratio 4-hydroxyflurbiprofen/flurbiprofen (CYP2C9) remained unchanged.

CONCLUSIONS

Liver cirrhosis affects the activity of CYP isoforms differently. This variability must be considered for dose adjustment of drugs in patients with liver cirrhosis.

CLINICAL TRIAL REGISTRATION

NCT03337945.

Prediction of the Area under the Curve Using Limited-Point Blood Sampling in a Cocktail Study to Assess Multiple CYP Activities

A cocktail study is an in vivo evaluation method to assess multiple CYP activities via a single trial and single administration of a cocktail drug that is a combination of multiple CYP substrates. However, multiple blood samples are required to evaluate the pharmacokinetics of a CYP probe drug. A limited-point sampling method is generally beneficial in clinical studies because of the simplified protocol and reduced participant burden. The aim of this study was to evaluate whether a limited-point plasma concentration analysis of CYP substrates in a cocktail drug could predict their area under the curve (AUC). We created prediction models of five CYP substrates (caffeine, losartan, omeprazole, dextromethorphan, and midazolam) using multiple linear regressions from the data of two cocktail studies, and then performed predictability analysis of these models using data derived from data in the co-administration with inducer (rifampicin) and inhibitors (fluvoxamine and cimetidine). For the administration of inhibitors, the AUC prediction accuracy (mean absolute error (MAE)) were <39.5% in Model 1 and <26.2% in Model 2 which were created using 1- and 4-point sampling data. MAE shows larger values in the administration of inducer in compared with the administration of inhibitors. The accuracy of the prediction in Model 2 could be acceptable for screening of inhibitions. MAE for caffeine, dextromethorphan, and midazolam were acceptable in the model that used 4 sampling points from all data. The use of this method could reduce the burden on the subject and make it possible to evaluate each AUC in a minimally invasive manner.

Effect of deglucuronidation on the results of the Basel phenotyping cocktail

We investigated the effect of deglucuronidation on the plasma concentration of the constituents of the Basel phenotyping cocktail and on the interpretation of the phenotyping results under basal conditions and after cytochrome P450 (CYP) induction with metamizole. The cocktail containing caffeine (CYP1A2), efavirenz (CYP2B6), flurbiprofen (CYP2C9), omeprazole (CYP2C19), metoprolol (CYP2D6) and midazolam (CYP3A4) was administered to 12 healthy subjects before (basal) and after treatment with metamizole for 1 week. In the basal state, deglucuronidation caused an increase in the plasma concentrations and area under the curve (AUC) of metoprolol, 8'-hydroxyefavirenz, 4'-hydroxyflurbiprofen and 1'-hydroxymidazolam. This effect could be visualized in Bland-Altman plots, where the values for 8'-hydroxyefavirenz, 4'-hydroxyflurbiprofen and 1'-hydroxymidazolam were mostly above the +20% threshold. As a result, the metabolic ratio (MR), calculated as AUC_{parent drug} /AUC_metabolite , decreased with deglucuronidation for CYP2B6, CYP2C9 and CYP3A4 and increased for CYP2D6. Treatment with metamizole, a constitutive androstane receptor-dependent inducer of CYP2B6, CYP2C9, CYP2C19 and CYP3A4, accentuated the effect of deglucuronidation on AUC and MR. The correlation of MRs calculated as the plasma concentration ratio parent drug/metabolite with the MR calculated as the AUC ratio showed that 1 sample obtained between 2 and 6 hours after cocktail ingestion and analysed with and without deglucuronidation is sufficient to obtain reliable phenotyping results. Importantly, CYP2C9 and 3A4 induction would have been missed without deglucuronidation of the plasma samples. In conclusion, deglucuronidation of the plasma samples improves the stability of the phenotyping results of the Basel phenotyping cocktail and is necessary to reliably detect CYP induction.

Metamizole is a Moderate Cytochrome P450 Inducer Via the Constitutive Androstane Receptor and a Weak Inhibitor of CYP1A2

Metamizole is an analgesic and antipyretic drug used intensively in certain countries. Previous studies have shown that metamizole induces cytochrome (CYP) 2B6 and possibly CYP3A4. So far, it is unknown whether metamizole induces additional CYPs and by which mechanism. Therefore, we assessed the activity of 6 different CYPs in 12 healthy male subjects before and after treatment with 3 g of metamizole per day for 1 week using a phenotyping cocktail approach. In addition, we investigated whether metamizole induces CYPs by an interaction with the constitutive androstane receptor (CAR) or the pregnane X receptor (PXR) in HepaRG cells. In the clinical study, we confirmed a moderate induction of CYP2B6 (decrease in the efavirenz area under the plasma concentration time curve (AUC) by 79%) and 3A4 (decrease in the midazolam AUC by 68%) by metamizole. In addition, metamizole weakly induced CYP2C9 (decrease in the flurbiprofen AUC by 22%) and moderately CYP2C19 (decrease in the omeprazole AUC by 66%) but did not alter CYP2D6 activity. In addition, metamizole weakly inhibited CYP1A2 activity (1.79‐fold increase in the caffeine AUC). We confirmed these results in HepaRG cells, where 4‐MAA, the principal metabolite of metamizole, induced the mRNA expression of CYP2B6, 2C9, 2C19, and 3A4. In HepaRG cells with a stable knockout of PXR or CAR, we could demonstrate that CYP induction by 4‐MAA depends on CAR and not on PXR. In conclusion, metamizole is a broad CYP inducer by an interaction with CAR and an inhibitor of CYP1A2. Regarding the widespread use of metamizole, these findings are of substantial clinical relevance.

Effects of Hypericum perforatum (St John's wort) on the pharmacokinetics and pharmacodynamics of rivaroxaban in humans

AIMS

To investigate the influence of a cytochrome P450 CYP3A4 and efflux transporter P-glycoprotein (P-gp) inducing Hypericum perforatum extract on the pharmacokinetics and pharmacodynamics of rivaroxaban.

METHODS

Open-label, nonrandomized, sequential treatment interaction study. Following CYP3A4 and P-gp phenotyping using low-dose midazolam and fexofenadine, 12 healthy volunteers received a single oral dose of 20 mg rivaroxaban and rivaroxaban plasma concentrations and inhibition of the activated coagulation factor X (factor Xa) activity were measured prior to and up to 48 h postdosing. The procedures were repeated after 2 weeks' treatment with the H. perforatum extract.

RESULTS

The geometric mean ratios for the area under the concentration-time curve and C_max of rivaroxaban after/before induction with the H. perforatum extract were 0.76 (90% confidence interval [CI] 0.70, 0.82) and 0.86 (90% CI 0.76, 0.97), respectively. Inhibition of factor Xa activity was reduced with a geometric mean area under the effect-time curve ratio after/before induction of 0.80 (90% CI 0.71, 0.89). No clinically significant differences were found regarding T_max (median 1.5 vs 1 h, P = .26) and terminal elimination half-life (mean 10.6 vs 10.8 h, P = .93) of rivaroxaban. The H. perforatum extract significantly induced CYP3A4 and P-gp activity, as evidenced by phenotyping.

CONCLUSION

The CYP3A4/P-gp inducing H. perforatum extract caused a decrease of rivaroxaban exposure with a proportional decrease of the pharmacodynamic effect. Although the data do not justify a contraindication for the combination or a systematic adjustment of rivaroxaban dosage, avoidance of the combination or laboratory monitoring should be considered in patients taking hyperforin-containing H. perforatum extracts with rivaroxaban.

The Development and Validation of a Novel "Dual Cocktail" Probe for Cytochrome P450s and Transporter Functions to Evaluate Pharmacokinetic Drug-Drug and Herb-Drug Interactions

This study was designed to develop and validate a 10 probe drug cocktail named "Dual Cocktail", composed of caffeine (Cyp1a2 in rat and CYP1A2 in human, 1 mg/kg), diclofenac (Cyp2c11 in rat and CYP2C9 in human, 2 mg/kg), omeprazole (Cyp2c11 in rat and CYP2C19 in human, 2 mg/kg), dextromethorphan (Cyp2d2 in rat and CYP2D6 in human, 10 mg/kg), nifedipine (Cyp3a1 in rat and CYP3A4 in human, 0.5 mg/kg), metformin (Oct1/2 in rat and OCT1/2 in human, 0.5 mg/kg), furosemide (Oat1/3 in rat and OAT1/3 in human, 0.1 mg/kg), valsartan (Oatp2 in rat and OATP1B1/1B3 in human, 0.2 mg/kg), digoxin (P-gp in rat and human, 2 mg/kg), and methotrexate (Mrp2 in rat and MRP2 in human, 0.5 mg/kg), for the evaluation of pharmacokinetic drug-drug and herb-drug interactions through the modulation of a representative panel of CYP enzymes or transporters in rats. To ensure no interaction among the ten probe substrates, we developed a 2-step evaluation protocol. In the first step, the pharmacokinetic properties of five individual CYP probe substrates and five individual transporter substrates were compared with the pharmacokinetics of five CYP cocktail or five transporters cocktails in two groups of randomly assigned rats. Next, a pharmacokinetic comparison was conducted between the CYP or transporter cocktail group and the dual cocktail group, respectively. None of the ten comparison groups was found to be statistically significant, indicating the CYP and transporter substrate sets or dual cocktail set could be concomitantly administered in rats. The "Dual Cocktail" was further validated by assessing the metabolism of nifedipine and omeprazole, which was significantly reduced by a single oral dose of ketoconazole (10 mg/kg); however, no changes were observed in the pharmacokinetic parameters of other probe substrates. Additionally, multiple oral doses of rifampin (20 mg/kg) reduced the plasma concentrations of nifedipine and digoxin, although not any of the other substrates. In conclusion, the dual cocktail can be used to characterize potential pharmacokinetic drug-drug interactions by simultaneously monitoring the activity of multiple CYP isoforms and transporters.

Predicting Interactions between Rifampin and Antihypertensive Drugs Using the Biopharmaceutics Drug Disposition Classification System

STUDY OBJECTIVE

Lack of blood pressure control is often seen in hypertensive patients concomitantly taking antituberculosis medications due to the complex drug-drug interactions between rifampin and antihypertensive drugs. Therefore, it is of clinical importance to understand the underlying mechanisms of these interactions to help formulate recommendations on the use of antihypertensive drugs in patients taking these medications concomitantly. Our objective was to assess the reliability of the Biopharmaceutics Drug Disposition Classification System (BDDCS) to predict potential interactions between rifampin and antihypertensive drugs and thus provide recommendations on the choice of antihypertensive drugs in patients receiving rifampin.

DESIGN

Evidence-based in vitro and in vivo predictions of drug-drug interactions.

MEASUREMENTS AND MAIN RESULTS

We systematically evaluated interactions between rifampin and antihypertensive drugs using the theory of the BDDCS, taking into consideration the role of drug transporters and metabolic enzymes involved in these interactions. We provide recommendations on the selection of antihypertensive drugs for patients with tuberculosis. Antihypertensive drugs approved by the U.S. Food and Drug Administration and the China National Medical Products Administration were included in this study. The drugs were classified into four categories under the BDDCS classification. Detailed information on cytochrome P450 (CYP) enzymes and drug transporters for each antihypertensive drug was searched in PubMed and other electronic databases. This information was combined with the effects of rifampin on CYP enzymes and drug transporters, and the direction and relative extent of the potential interactions between rifampin and antihypertensive drugs were predicted. Recommendations were then made using the theory of BDDCS. A thorough systematic literature review was performed, and data from all published human studies and case reports were summarized for the validation of our predictions. Interventional and observational studies published in PubMed and two Chinese databases (CNKI and WanFang) through December 16, 2019, were included, and data were extracted for validation of the predictions. Using the BDDCS theory, class 3 active drugs were predicted to exhibit minimal interactions with rifampin. On reviewing case reports and pre-post studies, the predictions we made were found to be reliable. When antituberculosis medications that include rifampin are started in patients with hypertension, it is recommended that the use of calcium channel blockers and classes 1 and 2 β-blockers be avoided. Angiotensin-converting enzyme inhibitors, olmesartan, class 3 β-blockers, spironolactone, and hydrochlorothiazide would be preferable because clinically relevant interactions would not be expected.

CONCLUSION

Application of the BDDCS to predict interactions between rifampin and antihypertensive drugs for patients with both tuberculosis and hypertension was found to be reliable. It should be noted, however, that based on the CYP enzyme and drug transporter information we reviewed, the mechanisms of all of the interactions could not be elucidated, and the predictions are only based on theory. The real effects of rifampin on antihypertensive drugs need to be further observed. More studies in both animals and humans are needed in the future.

Impact of the Selective Orexin-1 Receptor Antagonist ACT-539313 on the Pharmacokinetics of the CYP3A Probe Drug Midazolam in Healthy Male Subjects

ACT-539313 is a potent and selective orexin-1 receptor antagonist. CYP3A is the major cytochrome P450 (CYP) enzyme involved in the metabolism and clearance of ACT-539313 in man. The main objective of this study was to investigate the effect of ACT-539313 on the pharmacokinetics of orally administered midazolam. Thereby, this single-center, open-label, fixed-sequence study investigated the CYP3A interaction potential of ACT-539313 following single- (on day 2) and repeated-dose (on day 11) twice-daily administration of 200 mg ACT-539313. Exposure to midazolam was higher during concomitant administration of single as well as after repeated doses of ACT-539313 over 10 days compared to midazolam alone (day 1). In the presence of ACT-539313, the geometric mean ratio of the maximum plasma concentration and the area under the plasma concentration-time curve from time 0 to 24 hours increased by 1.18- and 1.79-fold on day 2, and by 2.13- and 4.54-fold on day 11, respectively. A similar outcome was also shown in the additionally evaluated urinary 6β-hydroxycortisol/cortisol ratio (6β-CR), as the geometric mean ratio of the 6β-CR showed a decrease to 0.78 on day 2 and to 0.61 on day 11. The most commonly reported adverse events (AEs) included somnolence and headache. All AEs were transient and of mild intensity. No treatment-related effects on vital signs, clinical laboratory, and electrocardiogram were observed. In summary, the observed corresponding decrease of both the validated, exogenous (midazolam/1-hydroxymidazolam ratio) and a frequently used endogenous (6β-CR) marker of CYP3A activity is indicative of CYP3A inhibition occurring after ACT-539313 treatment.

Use of Cocktail Probe Drugs for Indexing Cytochrome P450 Enzymes in Clinical Pharmacology Studies - Review of Case Studies

BACKGROUND

The cocktail approach of probing drug metabolizing enzymes, in particular cytochrome P450 (CYP) enzymes, is a cornerstone in clinical pharmacology studies. The first report of the famous "Pittsburg cocktail" has led the way for the availability of numerous cocktail substrate mixtures that provide options for indexing of CYP enzymes and/or evaluating the perpetrator capacity of the drug.

OBJECTIVE

The key objectives were: 1) To collate, tabulate, and discuss the various cocktail substrates to determine specific CYP enzyme activity in clinical pharmacology studies with specific case studies; 2) To introspect on how the cocktail approach has withstood the test of time and evolved for enabling key decision(s); 3) To provide some futuristic views on the use of cocktail in drug discovery and development.

METHOD

The review was compiled after consultation with databases such as PubMed (NCBI database) and Google scholar to source various published literature on cocktail approaches in drug development.

RESULTS

In the reviewed case studies, CYP indexing was achieved using a single time point (differing for specific CYP enzyme) plasma determination of the metabolite to parent ratio for all CYP enzymes with the exception of CYP3A4/5, where multiple time points were required for exposure measurement of midazolam and its metabolite. Likewise, a single void of urine, for a specific time duration, has been utilized for the recovery measurements of parent and metabolite for CYP indexing purposes.

CONCLUSION

The review provides a comprehensive list of various types of cocktail approaches and discusses some key considerations including the evolution of the cocktail approaches over time, perspectives and futuristic views for the use of probe drugs to aid the execution of clinical pharmacology studies and data interpretation.

Pharmacokinetics and phenotyping properties of the Basel phenotyping cocktail combination capsule in healthy male adults

AIMS

We compared the phenotyping metrics of a combination capsule formulation to its individual components of the newly composed Basel phenotyping cocktail. Moreover, we investigated a reduced sampling regimen for clinical applications.

METHODS

We performed in vitro experiments and a crossover pharmacokinetic study in twelve healthy male subjects to compare the Basel phenotyping cocktail capsule containing 6 cytochrome P450 (CYP) probe drugs with individual administration of the same drugs. Parent compounds and selected metabolites were determined by liquid chromatography-tandem mass spectrometry. Metabolic ratios (MR) for are under the curve (AUC) and single time point measurements and their correlation were determined.

RESULTS

Experiments with human liver microsomes and primary human hepatocytes in 3D co-culture confirmed that flurbiprofen is a suitable CYP2C9 substrate. Both cocktail formulations (capsule and individual probe drug administration) were well-tolerated and yielded reproducible MRs, which were almost identical. Correlations between single time point ratios and the corresponding AUC ratios depended on the sampling time point and the concentration time curve of the probe drugs. The MR of the capsule (Spearman rank correlation coefficient, R_s : 0.77-0.97) as well as the individual components (R_s : 0.69-0.99) correlated best at 6 h post-treatment considering all 6 CYPs. Moreover, the 2-h time points of the capsule agreed suitably with the AUC; however, the MR of omeprazole could not be determined for 10 out of 12 subjects.

CONCLUSION

The capsule is easy to swallow, well tolerated and provides reliable estimates for CYP activity. The optimal sampling point for the capsule formulation is 6 h after intake.

Validation of in vitro methods for human cytochrome P450 enzyme induction: Outcome of a multi-laboratory study

CYP enzyme induction is a sensitive biomarker for phenotypic metabolic competence of in vitro test systems; it is a key event associated with thyroid disruption, and a biomarker for toxicologically relevant nuclear receptor-mediated pathways. This paper summarises the results of a multi-laboratory validation study of two in vitro methods that assess the potential of chemicals to induce cytochrome P450 (CYP) enzyme activity, in particular CYP1A2, CYP2B6, and CYP3A4. The methods are based on the use of cryopreserved primary human hepatocytes (PHH) and human HepaRG cells. The validation study was coordinated by the European Union Reference Laboratory for Alternatives to Animal Testing of the European Commission's Joint Research Centre and involved a ring trial among six laboratories. The reproducibility was assessed within and between laboratories using a validation set of 13 selected chemicals (known human inducers and non-inducers) tested under blind conditions. The ability of the two methods to predict human CYP induction potential was assessed. Chemical space analysis confirmed that the selected chemicals are broadly representative of a diverse range of chemicals. The two methods were found to be reliable and relevant in vitro tools for the assessment of human CYP induction, with the HepaRG method being better suited for routine testing. Recommendations for the practical application of the two methods are proposed.

The Effects of Caffeine on Metabolomic Responses to Muscle Contraction in Rat Skeletal Muscle

Exercise has beneficial effects on our health by stimulating metabolic activation of skeletal muscle contraction. Caffeine is a powerful metabolic stimulant in the skeletal muscle that has ergogenic effects, including enhanced muscle power output and endurance capacity. In the present study, we aim to characterize the metabolic signatures of contracting muscles with or without caffeine stimulation using liquid chromatography-mass spectrometry and capillary electrophoresis coupled to mass spectrometry. Isolated rat epitrochlearis muscle was incubated in the presence or absence or of 3 mM caffeine for 30 min. Electrical stimulation (ES) was used to induce tetanic contractions during the final 10 min of incubation. Principal component analysis and hierarchical clustering analysis detected 184 distinct metabolites across three experimental groups—basal, ES, and ES with caffeine (ES + C). Significance Analysis of Microarray identified a total of 50 metabolites with significant changes in expression, and 23 metabolites significantly changed between the ES and ES + C groups. Changes were observed in metabolite levels of various metabolic pathways, including the pentose phosphate, nucleotide synthesis, β-oxidation, tricarboxylic acid cycle, and amino acid metabolism. In particular, D-ribose 5-phosphate, IMP, O-acetylcarnitine, butyrylcarnitine, L-leucine, L-valine, and L-aspartate levels were higher in the ES + C group than in the ES group. These metabolic alterations induced by caffeine suggest that caffeine accelerates contraction-induced metabolic activations, thereby contributing to muscle endurance performance and exercise benefits to our health.

Clinical Studies on Drug-Drug Interactions Involving Metabolism and Transport: Methodology, Pitfalls, and Interpretation

Many drug-drug interactions (DDIs) are based on alterations of the plasma concentrations of a victim drug due to another drug causing inhibition and/or induction of the metabolism or transporter-mediated disposition of the victim drug. In the worst case, such interactions cause more than tenfold increases or decreases in victim drug exposure, with potentially life-threatening consequences. There has been tremendous progress in the predictability and modeling of DDIs. Accordingly, the combination of modeling approaches and clinical studies is the current mainstay in evaluation of the pharmacokinetic DDI risks of drugs. In this paper, we focus on the methodology of clinical studies on DDIs involving drug metabolism or transport. We specifically present considerations related to general DDI study designs, recommended enzyme and transporter index substrates and inhibitors, pharmacogenetic perspectives, index drug cocktails, endogenous substrates, limited sampling strategies, physiologically-based pharmacokinetic modeling, complex DDIs, methodological pitfalls, and interpretation of DDI information.

Clinical consequences related to a defective elimination of clobazam caused by homozygous mutated CYP2C19 allele

Introduction: Voluntary drug intoxication with benzodiazepines is common and in most cases without consequences. We report an interesting case of voluntary drug intoxication with clobazam (CLB) in a patient with a homozygous mutated CYP2C19 genotype. Case report: A 63-year-old Caucasian man was admitted to an intensive care unit for voluntary drug intoxication with CLB (1200 mg) complicated by prolonged hospitalization (46 days). The levels of CLB and N-desmethylclobazam (NCLB) in plasma were initially 8.3 and 14.8 mg/L. The persistence of a high concentration of NCLB (14.3 mg/L on day 30) suggested a lack of elimination. A homozygous mutated allele of CYP2C19*2 without enzyme activity was discovered. To overcome this phenotype, NCLB metabolism was induced by administering 100 mg of phenobarbital for 10 days, allowing patient improvement. Discussion: NCLB is the major active metabolite of CLB with a longer half-life and much higher steady-state plasma concentrations compared to the parent drug. The half-life elimination of CLB is 18 h that of NCLB is between 40 and 50 h. However, there is considerable inter-individual variation in the metabolism of CLB and of the report NCLB/CLB under the dependence of genotype of CYP2C19. These polymorphisms are not generally well-known by physicians and may lead to severe poisoning.

Effects of Common CYP1A2 Genotypes and Other Key Factors on Intraindividual Variation in the Caffeine Metabolic Ratio: An Exploratory Analysis

The caffeine metabolic ratio is an established marker for cytochrome P450 (CYP) 1A2 activity. Optimal sample size calculation for clinical pharmacokinetic xenobiotic–caffeine interaction studies requires robust estimates of interindividual and intraindividual variation in this ratio. Compared with interindividual variation, factors contributing to intraindividual variation are less defined. An exploratory analysis involving healthy nonsmoking non‐naïve caffeine drinkers (1–3 cups/day; 12 men, 12 women) administered caffeine (160 mg) on five occasions evaluated the effects of CYP1A2 induction status (based on genotype) and other factors on intraindividual variation in CYP1A2 activity. Results were compared with those from previous studies. Regardless of whether a hyperinducer (CYP1A2*1A/*1F or CYP1A2*1F/*1F) or normal metabolizer (CYP1A2*1A/*1A,CYP1A2*1C/*1F, or CYP1A2*1C*1F/*1C*1F), sex, age, oral contraceptive use by women, and smoking status, intraindividual variation was ≤30%. A value of 30% is proposed for optimal design of pharmacokinetic xenobiotic–caffeine interaction studies. Prospective studies are needed for confirmation.

CYP3A4-mediated effects of rifampicin on the pharmacokinetics of vilaprisan and its UGT1A1-mediated effects on bilirubin glucuronidation in humans

AIMS

The primary aim of the present study was to quantify the effects of rifampicin, a strong cytochrome P450 (CYP) 3A4 inducer, on the pharmacokinetics of the new selective progesterone receptor modulator, vilaprisan. In addition, the effects of rifampicin on the glucuronidation of bilirubin, an endogenous UDP-glucuronosyltransferase family 1 member A1 (UGT1A1) substrate, were explored.

METHODS

This was an open-label, two-period study in 12 healthy postmenopausal women. Subjects received a single oral dose of vilaprisan 4 mg in each period. In period 2, administration of vilaprisan was preceded and followed by rifampicin 600 mg day^-1 . A subtherapeutic dose of midazolam (1 mg) was coadministered with vilaprisan to monitor CYP3A4 induction. Details of the administration and sampling schedule were optimized by means of a physiologically based pharmacokinetic model. Plasma concentrations of vilaprisan, midazolam, and 1'- hydroxy-midazolam were measured and rifampicin-associated changes in the glucuronidation of bilirubin were determined.

RESULTS

As predicted by our model, the coadministration of rifampicin was associated with a substantial decrease in exposure to vilaprisan and midazolam - indicated by the following point estimates (90% confidence intervals) for the area under the plasma concentration-time curve from zero to the time of the last quantifiable concentration ratio with or without rifampicin: 0.040 (0.0325, 0.0505) for vilaprisan and 0.144 (0.117, 0.178) for midazolam. Further, it was associated with an increase in bilirubin glucuronidation, indicating that UGT1A1 was induced.

CONCLUSIONS

The exposure to vilaprisan was reduced by 96%. Such a reduction is likely to render the drug therapeutically ineffective. Therefore, it is recommended that the use of strong CYP3A4 inducers is avoided when taking vilaprisan.

Assessment of Pharmacokinetic Drug-Drug Interactions in Humans: In Vivo Probe Substrates for Drug Metabolism and Drug Transport Revisited

Pharmacokinetic parameters of selective probe substrates are used to quantify the activity of an individual pharmacokinetic process (PKP) and the effect of perpetrator drugs thereon in clinical drug-drug interaction (DDI) studies. For instance, oral caffeine is used to quantify hepatic CYP1A2 activity, and oral dagibatran etexilate for intestinal P-glycoprotein (P-gp) activity. However, no probe substrate depends exclusively on the PKP it is meant to quantify. Lack of selectivity for a given enzyme/transporter and expression of the respective enzyme/transporter at several sites in the human body are the main challenges. Thus, a detailed understanding of the role of individual PKPs for the pharmacokinetics of any probe substrate is essential to allocate the effect of a perpetrator drug to a specific PKP; this is a prerequisite for reliably informed pharmacokinetic models that will allow for the quantitative prediction of perpetrator effects on therapeutic drugs, also in respective patient populations not included in DDI studies.

Cytochrome P450 Enzymes Involved in Metoprolol Metabolism and Use of Metoprolol as a CYP2D6 Phenotyping Probe Drug

Metoprolol is used for phenotyping of cytochrome P450 (CYP) 2D6, a CYP isoform considered not to be inducible by inducers of the CYP2C, CYP2B, and CYP3A families such as rifampicin. While assessing CYP2D6 activity under basal conditions and after pre-treatment with rifampicin in vivo, we surprisingly observed a drop in the metoprolol/α-OH-metoprolol clearance ratio, suggesting CYP2D6 induction. To study this problem, we performed in vitro investigations using HepaRG cells and primary human hepatocytes (before and after treatment with 20 μM rifampicin), human liver microsomes, and CYP3A4-overexpressing supersomes. While mRNA expression levels of CYP3A4 showed a 15- to 30-fold increase in both cell models, mRNA of CYP2D6 was not affected by rifampicin. 1'-OH-midazolam formation (reflecting CYP3A4 activity) increased by a factor of 5-8 in both cell models, while the formation of α-OH-metoprolol increased by a factor of 6 in HepaRG cells and of 1.4 in primary human hepatocytes. Inhibition studies using human liver microsomes showed that CYP3A4, 2B6, and 2C9 together contributed 19.0 ± 2.6% (mean ± 95%CI) to O-demethylation, 4.0 ± 0.7% to α-hydroxylation, and 7.6 ± 1.7% to N-dealkylation of metoprolol. In supersomes overexpressing CYP3A4, metoprolol was α-hydroxylated in a reaction inhibited by the CYP3A4-specific inhibitor ketoconazole, but not by the CYP2D6-specific inhibitor quinidine. We conclude that metoprolol is not exclusively metabolized by CYP2D6. CYP3A4, 2B6, and 2C9, which are inducible by rifampicin, contribute to α-hydroxylation, O-demethylation, and N-dealkylation of metoprolol. This contribution is larger after CYP induction by rifampicin but is too small to compromise the usability of metoprolol α-hydroxylation for CYP2D6 phenotyping.

N-demethylation of N-methyl-4-aminoantipyrine, the main metabolite of metamizole

Metamizole is an old analgesic used frequently in some countries. Active metabolites of metamizole are the non-enzymatically generated N-methyl-4-aminoantipyrine (4-MAA) and its demethylation product 4-aminoantipyrine (4-AA). Previous studies suggested that 4-MAA demethylation can be performed by hepatic cytochrome P450 (CYP) 3A4, but the possible contribution of other CYPs remains unclear. Using human liver microsomes (HLM), liver homogenate and HepaRG cells, we could confirm 4-MAA demethylation by CYPs. Based on CYP induction (HepaRG cells) and CYP inhibition (HLM) we could identify CYP2B6, 2C8, 2C9 and 3A4 as major contributors to 4-MAA demethylation. The 4-MAA demethylation rate by HLM was 280 pmol/mg protein/h, too low to account for in vivo 4-MAA demethylation in humans. Since peroxidases can perform N-demethylation, we investigated horseradish peroxidase and human myeloperoxidase (MPO). Horse radish peroxidase efficiently demethylated 4-MAA, depending on the hydrogen peroxide concentration. This was also true for MPO; this reaction was saturable with a K_m of 22.5 μM and a maximal velocity of 14 nmol/min/mg protein. Calculation of the entire body MPO capacity revealed that the demethylation capacity by granulocyte/granulocyte precursors was approximately 600 times higher than the liver capacity and could account for 4-MAA demethylation in humans. 4-MAA demethylation could also be demonstrated in MPO-expressing granulocyte precursor cells (HL-60). In conclusion, 4-MAA can be demethylated in the liver by several CYPs, but hepatic metabolism cannot fully explain 4-MAA demethylation in humans. The current study suggests that the major part of 4-MAA is demethylated by circulating granulocytes and granulocyte precursors in bone marrow.

Effect of codeine on CYP450 isoform activity of rats

CONTEXT

Codeine, also known as 3-methylmorphine, is an opiate used to treat pain, as a cough medicine and for diarrhoea. No study on the effects of codeine on the metabolic capacity of CYP enzyme is reported.

OBJECTIVE

In order to investigate the effects of codeine on the metabolic capacity of cytochrome P450 (CYP) enzymes, a cocktail method was employed to evaluate the activities of CYP2B1, CYP2D1, CYP1A2, CYP3A2 and CYP2C11.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into codeine group (low, medium, high) and control group. The codeine group rats were given 4, 8, 16 mg/kg (low, medium, high) codeine by continuous intragastric administration for 14 days. Five probe drugs bupropion, metroprolol, phenacetin, midazolam and tolbutamide were given to rats through intragastric administration, and the plasma concentrations were determined by UPLC-MS/MS.

RESULTS AND CONCLUSION

The pharmacokinetic parameters of bupropion and metroprolol experienced obvious change with AUC_(0-t), C_max increased and CL decreased for bupropion in medium dosage group and midazolam low dosage group. This result indicates that the 14 day-intragastric administration of codeine may inhibit the metabolism of bupropion (CYP2B1) and midazolam (CYP3A2) in rat. Additional, there are no statistical differences for albumin (ALB), alkaline phosphatase (ALP), creatinine (Cr) after 14 intragastric administration of codeine, while alanine aminotransferase (ALT), aspartate aminotransferase (AST), uric acid (UA) increased compared to control group. The biomedical test results show continuous 14 day-intragastric administration of codeine would cause liver damage.

Considerations from the IQ Induction Working Group in Response to Drug-Drug Interaction Guidance from Regulatory Agencies: Focus on Downregulation, CYP2C Induction, and CYP2B6 Positive Control

The European Medicines Agency (EMA), the Pharmaceutical and Medical Devices Agency (PMDA), and the Food and Drug Administration (FDA) have issued guidelines for the conduct of drug-drug interaction studies. To examine the applicability of these regulatory recommendations specifically for induction, a group of scientists, under the auspices of the Drug Metabolism Leadership Group of the Innovation and Quality (IQ) Consortium, formed the Induction Working Group (IWG). A team of 19 scientists, from 16 of the 39 pharmaceutical companies that are members of the IQ Consortium and two Contract Research Organizations reviewed the recommendations, focusing initially on the current EMA guidelines. Questions were collated from IQ member companies as to which aspects of the guidelines require further evaluation. The EMA was then approached to provide insights into their recommendations on the following: 1) evaluation of downregulation, 2) in vitro assessment of CYP2C induction, 3) the use of CITCO as the positive control for CYP2B6 induction by CAR, 4) data interpretation (a 2-fold increase in mRNA as evidence of induction), and 5) the duration of incubation of hepatocytes with test article. The IWG conducted an anonymous survey among IQ member companies to query current practices, focusing specifically on the aforementioned key points. Responses were received from 19 companies. All data and information were blinded before being shared with the IWG. The results of the survey are presented, together with consensus recommendations on downregulation, CYP2C induction, and CYP2B6 positive control. Results and recommendations related to data interpretation and induction time course will be reported in subsequent articles.

Comparison of Liver Cell Models Using the Basel Phenotyping Cocktail

Currently used hepatocyte cell systems for in vitro assessment of drug metabolism include hepatoma cell lines and primary human hepatocyte (PHH) cultures. We investigated the suitability of the validated in vivo Basel phenotyping cocktail (caffeine [CYP1A2], efavirenz [CYP2B6], losartan [CYP2C9], omeprazole [CYP2C19], metoprolol [CYP2D6], midazolam [CYP3A4]) in vitro and characterized four hepatocyte cell systems (HepG2 cells, HepaRG cells, and primary cryopreserved human hepatocytes in 2-dimensional [2D] culture or in 3D-spheroid co-culture) regarding basal metabolism and CYP inducibility. Under non-induced conditions, all CYP activities could be determined in 3D-PHH, CYP2B6, CYP2C19, CYP2D6, and CYP3A4 in 2D-PHH and HepaRG, and CYP2C19 and CYP3A4 in HepG2 cells. The highest non-induced CYP activities were observed in 3D-PHH and HepaRG cells. mRNA expression was at least four-fold higher for all CYPs in 3D-PHH compared to the other cell systems. After treatment with 20 μM rifampicin, mRNA increased 3- to 50-fold for all CYPs except CYP1A2 and 2D6 for HepaRG and 3D-PHH, 4-fold (CYP2B6) and 17-fold (CYP3A4) for 2D-PHH and four-fold (CYP3A4) for HepG2. In 3D-PHH at least a two-fold increase in CYP activity was observed for all inducible CYP isoforms while CYP1A2 and CYP2C9 activity did not increase in 2D-PHH and HepaRG. CYP inducibility assessed in vivo using the same phenotyping probes was also best reflected by the 3D-PHH model. Our studies show that 3D-PHH and (with some limitations) HepaRG are suitable cell systems for assessing drug metabolism and CYP induction in vitro. HepG2 cells are less suited to assess CYP induction of the 2C and 3A family. The Basel phenotyping cocktail is suitable for the assessment of CYP activity and induction also in vitro.