Potent CYP3A4 Inhibitor Research Articles

Pharmacokinetic Interaction Between Prasugrel and Ritonavir in Healthy Volunteers

The new anti-aggregating agent prasugrel is bioactivated by cytochromes P450 (CYP) 3A and 2B6. Ritonavir is a potent CYP3A inhibitor and was shown in vitro as a CYP2B6 inhibitor. The aim of this open-label cross-over study was to assess the effect of ritonavir on prasugrel active metabolite (prasugrel AM) pharmacokinetics in healthy volunteers. Ten healthy male volunteers received 10 mg prasugrel. After at least a week washout, they received 100 mg ritonavir, followed by 10 mg prasugrel 2 hr later. We used dried blood spot sampling method to monitor prasugrel AM pharmacokinetics (Cmax, t1/2, tmax, AUC0–6 hr) at 0, 0.25, 0.5, 1, 1.5, 2, 4 and 6 hr after prasugrel administration. A ‘cocktail’ approach was used to measure CYP2B6, 2C9, 2C19 and 3A activities. In the presence of ritonavir, prasugrel AM Cmax and AUC were decreased by 45% (mean ratio: 0.55, CI 90%: 0.40–0.7, p = 0.007) and 38% (mean ratio: 0.62, CI 90%: 0.54–0.7, p = 0.005), respectively, while t1/2 and tmax were not affected. Midazolam metabolic ratio (MR) dramatically decreased in presence of ritonavir (6.7 ± 2.6 versus 0.13 ± 0.07) reflecting an almost complete inhibition of CYP3A4, whereas omeprazole, flurbiprofen and bupropion MR were not affected. These data demonstrate that ritonavir is able to block prasugrel CYP3A4 bioactivation. This CYP-mediated drug–drug interaction might lead to a significant reduction of prasugrel efficacy in HIV-infected patients with acute coronary syndrome.

Effect of Cobicistat on Glomerular Filtration Rate in Subjects With Normal and Impaired Renal Function

This study evaluated the effect of cobicistat (COBI) on glomerular filtration rate in subjects with normal renal function (RF) or with mild/moderate renal impairment, by comparing creatinine clearance [estimated glomerular filtration rate (eGFR)] with actual GFR (aGFR) using iohexol, a probe drug excreted by glomerular filtration. COBI is a potent CYP3A inhibitor (pharmacoenhancer) currently in phase 3 testing with elvitegravir, atazanavir, and darunavir. Normal RF subjects received COBI 150 mg QD, ritonavir (RTV) 100 mg QD, or placebo for 7 days; subjects with mild/moderate renal impairment received COBI 150 mg QD. The eGFR and aGFR were measured on days 0, 7, and 14 and within-subject changes calculated relative to day 0. COBI and RTV pharmacokinetics were analyzed on day 7. All 36 subjects in cohort 1 and 17 of 18 subjects in cohort 2 completed all study treatments. Study treatments were well tolerated. Small increases in serum creatinine with corresponding mean decreases in eGFR (∼10 mL/min or mL/min per 1.73 m) were observed on day 7 relative to day 0 in subjects receiving COBI (P < 0.05). The decreases were reversible on COBI discontinuation; mean eGFR values returned to baseline on day 14 (P > 0.05). No statistically significant changes in aGFR on days 7 or 14 relative to day 0 were seen with COBI (P > 0.05). No statistically significant decreases in aGFR or eGFR were observed with RTV or placebo. COBI affects eGFR but not the actual GFR. The time to onset, magnitude, and time to resolution of changes in eGFR are consistent with altered proximal tubular secretion of creatinine through inhibition of drug transporters.

Impact of Low-Dose Ritonavir on Danoprevir Pharmacokinetics

Danoprevir, a potent, selective inhibitor of the hepatitis C virus (HCV) NS3/4A protease, is metabolized by cytochrome P450 (CYP) 3A. Clinical studies in HCV patients have shown a potential need for a high danoprevir daily dose and/or dosing frequency. Ritonavir, an HIV-1 protease inhibitor (PI) and potent CYP3A inhibitor, is used as a pharmacokinetic enhancer at subtherapeutic doses in combination with other HIV PIs. Coadministering danoprevir with ritonavir as a pharmacokinetic enhancer could allow reduced danoprevir doses and/or dosing frequency. Here we evaluate the impact of ritonavir on danoprevir pharmacokinetics. The effects of low-dose ritonavir on danoprevir pharmacokinetics were simulated using Simcyp, a population-based simulator. Following results from this drug-drug interaction (DDI) model, a crossover study was performed in healthy volunteers to investigate the effects of acute and repeat dosing of low-dose ritonavir on danoprevir single-dose pharmacokinetics. Volunteers received a single oral dose of danoprevir 100 mg in a fixed sequence as follows: alone, and on the first day and the last day of 10-day dosing with ritonavir 100 mg every 12 hours. The initial DDI model predicted that following multiple dosing of ritonavir 100 mg every 12 hours for 10 days, the danoprevir area under the plasma concentration-time curve (AUC) from time zero to 24 hours and maximum plasma drug concentration (C(max)) would increase by about 3.9- and 3.2-fold, respectively. The clinical results at day 10 of ritonavir dosing showed that the plasma drug concentration at 12 hours postdose, AUC from time zero to infinity and C(max) of danoprevir increased by approximately 42-fold, 5.5-fold and 3.2-fold, respectively, compared with danoprevir alone. The DDI model was refined with the clinical data and sensitivity analyses were performed to better understand factors impacting the ritonavir-danoprevir interaction. DDI model simulations predicted that danoprevir exposures could be successfully enhanced with ritonavir coadministration, and that a clinical study confirming this result was warranted. The clinical results demonstrate that low-dose ritonavir enhances the pharmacokinetic profile of low-dose danoprevir such that overall danoprevir exposures can be reduced while sustaining danoprevir trough concentrations.

Abiraterone acetate in the treatment of metastatic castration-resistant prostate cancer: review of clinical data

Abiraterone acetate (AA), after metabolization to abiraterone, is an oral inhibitor of the cytochrome P450C17 (CYP17) complex. It inhibits the production of androgens by interfering with the enzymes C17α hydroxylase and C17-C20 lyase. It was tested in patients with metastatic castration-resistant prostate cancer and showed promising results in Phase I and II studies with prostate specific antigen and radiological responses. In a randomized Phase III trial, AA in combination with prednisone increased median overall survival compared with prednisone alone in progressive docetaxel-pretreated patients with metastatic castration-resistant prostate cancer. Side effects of AA were mild with urinary tract infections, edema and hypokalemia when used in combination with prednisone. There was an influence on pharmacokinetic parameters in patients with renal and moderate hepatic failure without severe clinical complications and no dose adjustments are necessary. AA is a potent inhibitor of CYP2D6 and CYP1A2, and can ...

Erratum to: Computer-Assisted HPLC Method Development for Determination of Tolmetin and Possible Kinetic Modulators of Its Oxidative Metabolism in Vivo

Following administration of the acidic drug tolmetin (TOL) anaphylactic reactions occurred, which have been hypothesized to be related to the formation of reactive acyl glucuronides. Recently, glutathione adducts have been detected upon incubation of TOL with human liver microsomal preparations, which proved that oxidative activation might also be a pathway of formation of reactive—possibly toxic—glutathione metabolites of TOL. The aim of this work was to develop a new and robust HPLC method to investigate the in vivo effect of 2 coadministered drugs/nutritional supplements on the kinetics of TOL in rats (cimetidine; CIM) known to be a potent inhibitor of CYP3A4, an enzyme that catalyzes the oxidative metabolism and Quercetin; and QUE which induces UGT1A6, an enzyme involved in glucuronidation of acidic drugs. DryLab®, a computer simulation software package, was used to assist in the development and optimization of the HPLC method used for separation of TOL and the two potential kinetic modulators together with three potential internal standards (zomepirac, carvedilol and fexofenadine). The method was validated in biological samples obtained from rats. Non-compartmental pharmacokinetic analysis of data obtained from plasma and rat liver tissue showed significantly higher concentrations of TOL in the presence of CIM; and significantly longer elimination half-life lives in presence of QUE, which implies that drugs or food components interacting with CYP3A4 cause alteration in the metabolic oxidative biotransformation of TOL in vivo leading to accumulation of TOL in the body through a decrease of its clearance. These findings might account for to the side-effects associated with TOL when co-administered with such kinetic modulators.

The Effect of CYP3A4 Inhibition or Induction on the Pharmacokinetics and Pharmacodynamics of Orally Administered Ruxolitinib (INCB018424 Phosphate) in Healthy Volunteers

Ruxolitinib, a selective Janus kinase (JAK) 1&2 inhibitor in development for the treatment of myeloproliferative neoplasms, is primarily metabolized by CYP3A4. The effects of inhibition or induction of CYP3A4 on single oral dose ruxolitinib pharmacokinetics (PK) and pharmacodynamics (PD) were evaluated in healthy volunteers. Coadministration of ketoconazole (a potent CYP3A4 inhibitor) and erythromycin (a moderate CYP3A4 inhibitor) increased total ruxolitinib plasma exposure (AUC(0-∞)) by 91% and 27%, respectively, and ruxolitinib PD, as measured by the inhibition of interleukin (IL)-6-stimulated STAT3 phosphorylation in whole blood, was generally consistent with the PK observed. Pretreatment with rifampin, a potent CYP3A4 inducer, decreased ruxolitinib AUC(0-∞) by 71% while resulting in only a 10% decrease in the overall PD activity. This apparent PK/PD discrepancy may be explained, in part, by an increase in the relative abundance of ruxolitinib active metabolites with the rifampin coadministration. The collective PK/PD data suggest that starting doses of ruxolitinib should be reduced by 50% if coadministered with a potent CYP3A4 inhibitor, whereas adjustments in ruxolitinib starting doses may not be needed when coadministered with inducers or mild/moderate inhibitors of CYP3A4. All study doses of ruxolitinib were generally safe and well tolerated when given alone and in combination with ketoconazole, erythromycin, or rifampin.

Effects of furanocoumarins in Kampo extract-based medicines on rat intestinal absorption of CYP3A and P-glycoprotein substrate drugs in vivo

While a great deal of information of drug-drug interactions is known, most concern Western drugs. Relatively little is known of the interactions between Western drugs and traditional drugs such as Kampo extract medicines (Japanese medicines modified from traditional Chinese medicines). This study investigated the effects of the marketed Kampo extract medicines, Senkyu-cha-cho-san and Sokei-kakketsu-to, on the intestinal absorption of CYP or P-glycoprotein (P-gp) in vivo. Midazolam, a CYP3A substrate drug, or talinolol, a P-gp substrate drug, was orally administered to rats with each of these Kampo extract medicines. Senkyu-cha-chosan or Sokei-kakketsu-to administered as a standard regimen did not obviously affect Cmax and area under the curve (AUC) of midazolam, although both Kampo extract medicines contained notopterol, a potent CYP3A4 inhibitor in vitro. The results implied a lack of potent drug-drug interactions between both Kampo extract medicines and CYP3A substrate drugs. Concomitant administration of each Kampo extract medicine unexpectedly showed the tendency to decrease Cmax and AUC of talinolol. Decreased intestinal absorption of talinolol might be caused, not by the inhibition of P-gp, but by the inhibition of organic anion transporting peptides by both Kampo extract medicines.

Blockbuster interactions: are they bad for the patient?

This editorial refers to ‘Accelerated platelet inhibition by switching from atorvastatin to a non-CYP3A4-metabolized statin in patients with high platelet reactivity (ACCEL-STATIN) study’, by Y. Park et al. , doi:10.1093/eurheartj/ehs083 Variability in individual responsiveness to clopidogrel has been widely acknowledged and investigated in these last few years. Clopidogrel inhibits platelet activation and aggregation by directly inhibiting the platelet P2Y12 adenosine diphosphate (ADP) receptor. It has become established that a significant proportion of patients display high platelet reactivity on clopidogrel treatment and thus are exposed to a greater risk of death, myocardial infarction, and stent thrombosis.1 One source of the variability is the hepatic metabolism of clopidogrel, which is a prodrug that requires metabolic activation to generate its active thiol metabolite.2 Specifically, clopidogrel activation requires two oxidative steps involving a variety of hepatic enzymes from the cytochrome P450 (CYP) system, the major catalyst of oxidative biotransformation reactions involved in drug metabolism.3 CYP2C19 is involved in both steps and contributes to an estimated 45% of the 2-oxo-clopidogrel and 21% of active metabolite generation.4 CYP3A4/5, another CYP isoenzyme, is also a significant contributor to clopidogrel bioactivation. Loss-of-function CYP2C19 genetic variants have been associated with reduced concentrations of active drug metabolite, diminished platelet inhibition, and higher rates of adverse cardiovascular events.5 On the other hand, there is no common genetic polymorphism associated with alteration in CYP3A4 activity. Among the non-genetic sources of variability, drug–drug interaction (DDI) is one of major concern; DDI may inhibit or induce the function of CYP isoenzymes and consequently affect the response to CYP-metabolized drugs including clopidogrel.3 Hence, CYP3A4 inhibitors and inducers are considered as important candidates to interfere with clopidogrel response (Figure 1). The antifungal agents ketoconazole and itraconazole are potent inhibitors of CYP3A4. In a study conducted in healthy subjects, ketoconazole co-administration resulted …

Eribulin mesylate pharmacokinetics in patients with solid tumors receiving repeated oral ketoconazole

Purpose To study the influence of repeated oral administration of ketoconazole, a potent CYP3A4 inhibitor, on the plasma pharmacokinetics of eribulin mesylate administered by single-dose intravenous infusion. Eribulin mesylate is a non-taxane microtubule dynamics inhibitor that is currently under development in phase I-III trials for the treatment of solid tumors. Experimental design A randomized, open-label, two treatments, two sequences, crossover phase I study was performed in patients with advanced solid tumors. Treatments were given on day 1 and day 15 and consisted of 1.4mg/m(2) eribulin mesylate alone or 0.7mg/m(2) eribulin mesylate plus 200mg ketoconazole on the day of eribulin mesylate administration and the following day. Pharmacokinetic sampling for determination of eribulin plasma concentration was performed up to 144h following administration of eribulin mesylate. Also safety and anti-tumor activity were determined. Results Pharmacokinetic sampling and analysis was completed in ten patients. Statistical analysis of dose-normalized log-transformed AUC0-∞ and Cmax indicated that single-dose exposure of eribulin was not statistically different when co-administered with ketoconazole (ratio of geometric least square means: 0.95 (90%CI: 0.80-1.12) and 0.97 (90%CI: 0.83-1.12), respectively) in patients with solid tumors. Ketoconazole had no effect on eribulin clearance and elimination half-life. The most frequently reported treatment related adverse events were fatigue and nausea, each reported in 8/12 patients. Seven patients (58.3%) achieved stable disease as best overall response. Conclusions The results indicate that eribulin mesylate can be safely co-administered with ketoconazole. Drug-drug interactions are not expected with other CYP3A4 inhibitors.

Potent inhibition of CYP1A2 by Frutinone A, an active ingredient of the broad spectrum antimicrobial herbal extract from P. fruticosa

Frutinone is an active ingredient extracted from the lipophilic fraction of the Polygala Fruticosa demonstrating various antibacterial and fungal properties. The aim of this study was to characterize its metabolism in an effort to understand metabolism based drug–herb interactions.In vitro metabolic clearance and metabolite identification studies were done using cryopreserved hepatocytes. Reaction phenotyping and inhibition studies were done using human liver microsomes and recombinant cytochrome P450s (CYPs). Frutinone A-CYP1A2 interactions were rationalized using docking simulations.Hepatic clearance was predicted to be low (7.17 mL/min/kg), with reaction phenotyping studies indicating no clearance by the enzymes tested. Frutinone was identified as a potent inhibitor of CYP1A2 with moderate effects on CYP2C19, 2C9, 2D6 and 3A4. CYP1A2 inhibition was reversible and characterised by an IC50 of 0.56 µM. Inhibition was differential showing mixed (Ki = 0.48 µM) and competitive (Ki = 0.31 µM) inhibition with 3-cyano-7-ethoxycoumarin and ethoxyresorufin, respectively. Two binding sites, one for inhibitors and the other for substrates were identified in silico.The potent CYP1A2 inhibition by Frutinone A could be predictive of the potential drug–herb interaction risk in the use of herbal extracts from P. fruticosa. The data suggest future pharmacological research on this chromocoumarin should take metabolic properties into account.

Effects of Ketoconazole and Rifampicin on the Pharmacokinetics of Gemigliptin, a Dipeptidyl Peptidase-IV Inhibitor: A Crossover Drug–Drug Interaction Study in Healthy Male Korean Volunteers

BackgroundGemigliptin (LC15-0444) is a newly developed selective and competitive inhibitor of dipeptidyl peptidase (DPP)-4 and has potential for the treatment of type 2 diabetes mellitus. Gemigliptin is metabolized by the cytochrome P450 (CYP) 3A4 isozyme to yield the active major metabolite LC15-0636. ObjectiveThe effects of multiple oral doses of ketoconazole (a potent CYP3A4 inhibitor) and multiple oral doses of rifampicin (a potent CYP3A4 inducer) on the pharmacokinetic properties of a single oral dose of gemigliptin were evaluated in fasting healthy male Korean volunteers. MethodsIn this open-label, 2-part, 3-treatment, 1-sequence, 2-period crossover drug–drug interaction study, 1 group of subjects received a single 50-mg oral dose of gemigliptin on 2 separate occasions—once as monotherapy and again after pretreatment with 400 mg of oral ketoconazole once daily for 7 days. The other group of subjects received a single 50-mg oral dose of gemigliptin on 2 separate occasions—once without pretreatment and again after pretreatment with 600 mg of oral rifampicin once daily for 10 days. Blood samples were obtained at 0 (predose), 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 12, 24, 48, and 72 hours after gemigliptin dosing. Plasma concentrations were determined using LC-MS/MS. Pharmacokinetic parameters were estimated via noncompartmental methods. Tolerability was assessed using measurements of vital signs, clinical chemistry tests, and interviews. ResultsTwenty-four subjects were enrolled (12 per group). Concurrent administration of ketoconazole was associated with increased total gemigliptin plasma exposure (AUC0–∞; 2.36-fold [90% CI, 2.19–2.54]) and decreased metabolism of gemigliptin until negligible concentrations of LC15-0636 were detected. Pretreatment with rifampicin was associated with decreased AUC0–∞ of gemigliptin (by 80% [90% CI, 78%–82%]) and a 2.9-fold increase (mean [SD], 0.18 [0.08] to 0.52 [0.10]) in the metabolic ratio of gemigliptin to LC15-0636. The treatments were well-tolerated, with no severe adverse events reported. Six of the 24 subjects (25%) experienced AEs during the first period of gemigliptin monotherapy administration. Six of 12 subjects (50%) each experienced AEs during concurrent administration with ketoconazole and rifampicin. ConclusionsIn this select group of healthy male Korean volunteers, concurrent administration of gemigliptin with ketoconazole or rifampicin was associated with significantly increased or decreased systemic exposure to gemigliptin, respectively. These findings suggest that gemigliptin may require a dose adjustment when concurrently administered with drugs that alter CYP3A4 activity. Concurrent administration of gemigliptin with ketoconazole or rifampicin was well tolerated. ClinicalTrials.gov identifier: NCT01426906.

RETRACTED: Preclinical metabolism of LB42908, a novel farnesyl transferase inhibitor, and its effects on the cytochrome P450 isozyme activities

Metabolism of LB42908, a novel farnesyl transferase inhibitor, was investigated for preclinical development. In vitro hepatic metabolism of LB42908 gave rise to at least 9 metabolites via phase I biotransformation pathways, which were characterized by HPLC-UV, LC-MS, and LC-MS/MS analyses. N-Dealkylation was shown to be a major phase I metabolic pathway. Species-specific in vitro metabolism of LB42908 was studied in liver fractions of rat, dog, monkey, and human. Order of metabolic stability is human≈dog>rat≈monkey in both S9 and microsomal fractions. Tissue-specific metabolism of LB42908 in various tissue homogenates of rats demonstrated that the liver was the major organ responsible for phase I metabolism of LB42908. The results from both qualitative and quantitative metabolism studies such as metabolic profiling and metabolic clearance indicated that dog would be the animal model of choice for preclinical toxicology studies. In addition, LB42908 was a potent CYP3A4 inhibitor in human liver microsomes and induced the activities of several CYP isozymes, implying that it has the potential for drug–drug interactions. Repeated dosing of LB42908 in rats did not significantly affect its own metabolism, indicating that long-term administration of LB42908 would not alter its pharmacokinetic profiles.

Safety, Pharmacokinetic, and Pharmacodynamic Phase I Dose-Escalation Trial of PF-00562271, an Inhibitor of Focal Adhesion Kinase, in Advanced Solid Tumors

PF-00562271 is a novel inhibitor of focal adhesion kinase (FAK). The objectives of this study were to identify the recommended phase II dose (RP2D) and assess safety and tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and antitumor activity of PF-00562271. Part 1 was a dose escalation without and with food. Part 2 enrolled specific tumor types in an expansion at the RP2D and also assessed the effect of PF-00562271 on single-dose midazolam PK in a subgroup of patients. Ninety-nine patients (median age, 60 years; 98% with Eastern Cooperative Oncology Group performance status of 0 or 1) were treated in 12 fasting and three fed cohorts. The 125-mg twice-per-day fed dose was deemed the maximum-tolerated dose (MTD) and RP2D. Grade 3 dose-limiting toxicities included headache, nausea/vomiting, dehydration, and edema. Nausea was the most frequently observed toxicity (60% of patients, all grades 1 or 2 at RP2D). PF-00562271 exposure increased with increasing dose; serum concentration-time profiles showed characteristic nonlinear disposition. Steady-state exposures were reached within 1 week. On coadministration, geometric mean values of midazolam maximal observed serum concentration and area under the serum concentration-time curve increased by 60% and more than two-fold, respectively. Of 14 patients evaluable by [(18)F]fluorodeoxyglucose positron emission tomography in the expansion cohorts, seven metabolic responses were observed. With conventional imaging, 31 patients had stable disease at first restaging scans, and 15 of these remained stable for six or more cycles. The MTD and RP2D of PF-00562271 is 125 mg twice per day with food. PF-00562271 displayed time- and dose-dependent nonlinear PK and is likely a potent CYP 3A inhibitor. This first-in-class study supports further investigation of FAK as a promising therapeutic target.

Potent mechanism‐based inhibition of CYP3A4 by imatinib explains its liability to interact with CYP3A4 substrates

Imatinib, a cytochrome P450 2C8 (CYP2C8) and CYP3A4 substrate, markedly increases plasma concentrations of the CYP3A4/5 substrate simvastatin and reduces hepatic CYP3A4/5 activity in humans. Because competitive inhibition of CYP3A4/5 does not explain these in vivo interactions, we investigated the reversible and time-dependent inhibitory effects of imatinib and its main metabolite N-desmethylimatinib on CYP2C8 and CYP3A4/5 in vitro. Amodiaquine N-deethylation and midazolam 1'-hydroxylation were used as marker reactions for CYP2C8 and CYP3A4/5 activity. Direct, IC(50) -shift, and time-dependent inhibition were assessed with human liver microsomes. Inhibition of CYP3A4 activity by imatinib was pre-incubation time-, concentration- and NADPH-dependent, and the time-dependent inactivation variables K(I) and k(inact) were 14.3 µM and 0.072 in(-1) respectively. In direct inhibition experiments, imatinib and N-desmethylimatinib inhibited amodiaquine N-deethylation with a K(i) of 8.4 and 12.8 µM, respectively, and midazolam 1'-hydroxylation with a K(i) of 23.3 and 18.1 µM respectively. The time-dependent inhibition effect of imatinib was predicted to cause up to 90% inhibition of hepatic CYP3A4 activity with clinically relevant imatinib concentrations, whereas the direct inhibition was predicted to be negligible in vivo. Imatinib is a potent mechanism-based inhibitor of CYP3A4 in vitro and this finding explains the imatinib-simvastatin interaction and suggests that imatinib could markedly increase plasma concentrations of other CYP3A4 substrates. Our results also suggest a possibility of autoinhibition of CYP3A4-mediated imatinib metabolism leading to a less significant role for CYP3A4 in imatinib biotransformation in vivo than previously proposed.

Modeling Chemical Interaction Profiles: II. Molecular Docking, Spectral Data-Activity Relationship, and Structure-Activity Relationship Models for Potent and Weak Inhibitors of Cytochrome P450 CYP3A4 Isozyme

Polypharmacy increasingly has become a topic of public health concern, particularly as the U.S. population ages. Drug labels often contain insufficient information to enable the clinician to safely use multiple drugs. Because many of the drugs are bio-transformed by cytochrome P450 (CYP) enzymes, inhibition of CYP activity has long been associated with potentially adverse health effects. In an attempt to reduce the uncertainty pertaining to CYP-mediated drug-drug/chemical interactions, an interagency collaborative group developed a consensus approach to prioritizing information concerning CYP inhibition. The consensus involved computational molecular docking, spectral data-activity relationship (SDAR), and structure-activity relationship (SAR) models that addressed the clinical potency of CYP inhibition. The models were built upon chemicals that were categorized as either potent or weak inhibitors of the CYP3A4 isozyme. The categorization was carried out using information from clinical trials because currently available in vitro high-throughput screening data were not fully representative of the in vivo potency of inhibition. During categorization it was found that compounds, which break the Lipinski rule of five by molecular weight, were about twice more likely to be inhibitors of CYP3A4 compared to those, which obey the rule. Similarly, among inhibitors that break the rule, potent inhibitors were 2–3 times more frequent. The molecular docking classification relied on logistic regression, by which the docking scores from different docking algorithms, CYP3A4 three-dimensional structures, and binding sites on them were combined in a unified probabilistic model. The SDAR models employed a multiple linear regression approach applied to binned 1D 13C-NMR and 1D 15N-NMR spectral descriptors. Structure-based and physical-chemical descriptors were used as the basis for developing SAR models by the decision forest method. Thirty-three potent inhibitors and 88 weak inhibitors of CYP3A4 were used to train the models. Using these models, a synthetic majority rules consensus classifier was implemented, while the confidence of estimation was assigned following the percent agreement strategy. The classifier was applied to a testing set of 120 inhibitors not included in the development of the models. Five compounds of the test set, including known strong inhibitors dalfopristin and tioconazole, were classified as probable potent inhibitors of CYP3A4. Other known strong inhibitors, such as lopinavir, oltipraz, quercetin, raloxifene, and troglitazone, were among 18 compounds classified as plausible potent inhibitors of CYP3A4. The consensus estimation of inhibition potency is expected to aid in the nomination of pharmaceuticals, dietary supplements, environmental pollutants, and occupational and other chemicals for in-depth evaluation of the CYP3A4 inhibitory activity. It may serve also as an estimate of chemical interactions via CYP3A4 metabolic pharmacokinetic pathways occurring through polypharmacy and nutritional and environmental exposures to chemical mixtures.

Suivi thérapeutique pharmacologique du stiripentol

Stiripentol is a third generation antiepileptic, marketed since 2007 under the name of Diacomit(®). It is indicated, always in combination, in the treatment of severe myoclonic epilepsy in infancy or Dravet syndrome. Its pharmacokinetics is not linear. It is a potent inhibitor of CYP3A4, 1A2 and 2C19 and increases the plasma concentrations of many other antiepileptic drugs. Without this being considered as a validated therapeutic range, the trough plasma concentrations at steady-state, corresponding to the usual doses are between 10 and 15 mg/L. The concentration-efficacy relationship is not established, but there is some evidence for a concentration-related toxicity. However, because of its non-linear kinetics, stiripentol should be a good candidate for therapeutic drug monitoring (TDM). Nonetheless, the current level of evidence for the advantage of TDM is "remains to be estimated".

From preclinical to human – prediction of oral absorption and drug–drug interaction potential using physiologically based pharmacokinetic (PBPK) modeling approach in an industrial setting: a workflow by using case example

A case example is presented in which the physiologically based modeling approach has been used to model the absorption of a lipophilic BCS Class II compound predominantly metabolized by CYP3A4, and to assess the interplay of absorption related parameters with the drug-drug interaction (DDI) potential. The PBPK model was built in the rat using Gastroplus® to study the absorption characteristics of the compound. Subsequently relevant model parameters were used to predict the non-linear human PK observed during first-in-human study after optimizing the absorption model for colonic absorption, bile micelle solubilization and unbound fraction in gut enterocytes (fu(gut)) using SIMCYP® simulator. The model fitted absorption parameters were then used to assess the drug-drug interaction (DDI) potential of the test compound when administered along with multiple doses of a potent CYP 3A4 inhibitor, ketoconazole. The impact of fu(gut) in the extent of DDI was assessed using parameter sensitivity analysis. After optimizing the preclinical model and taking into consideration bile micelle solubilization and colonic absorption, the non-linear pharmacokinetics of the test compound was satisfactorily predicted in man. Sensitivity analysis performed with the absorption parameter fu(gut) indicated that it could be an important parameter in predicting oral absorption. In addition, DDI simulations using SIMCYP® suggest that C(max) and AUC ratios may also be sensitive to the fu(gut) input in the model. Since fu(gut) cannot be measured experimentally, sensitivity analysis may help in assessing the importance of fu(gut) in human PK and DDI prediction using SIMCYP®.

Towards Safer and More Predictable Drug Treatment - Reflections from Studies of the First BCPT Prize Awardee

This MiniReview is a personal recollection of selected research topics, which the author in collaboration with colleagues has studied, aiming to improve the predictability of drug therapy. In early studies, we found bi- and trivalent cations to reduce the absorption of various tetracyclines and fluoroquinolones. Certain antacids elevated the bioavailability of some non-steroidal anti-inflammatory drugs and sulphonylureas. Various brands of phenytoin tablets revealed great differences in their bioavailability, causing clinical consequences. Numerous factors affecting the antidotal effect of activated charcoal were also studied, with charcoal compared to other gastrointestinal decontamination methods, including ipecac and gastric lavage. Effect of age and diseases on the pharmacokinetics of drugs was a research topic. Acute sotalol intoxications revealed its QT-prolonging properties, and even small mixed overdoses of moclobemide with serotonergic drugs proved fatal. Itraconazole and other potent inhibitors of CYP3A4 could drastically increase exposure to drugs like midazolam, triazolam, buspirone, lovastatin, simvastatin and oxycodone, whereas rifampicin greatly reduced their plasma concentrations. A change from potent inhibition to induction caused a 400-fold change in the exposure to oral midazolam. CYP2C8 was revealed to be crucial in the metabolism and interactions of several drugs. Many interactions affecting statins are CYP3A4-mediated, but transporters are important in certain interactions. Tizanidine is very susceptible to CYP1A2 inhibition. Fruit juices such as grapefruit juice can raise or lower exposure to different drugs. Both drug interactions and pharmacogenetics can modify the activity of cell membrane transporters and cause variability in the pharmacokinetics of and response to their substrate drugs.

Cardiac safety, drug‐induced QT prolongation and torsade de pointes (TdP)

Torquere is Latin for ‘to twist’ and gave rise to ‘torque’ in English and, in French, to ‘torsade’ a ‘twisted fringe, cord or ribbon’. Torsade de pointes (TdP) is a ballet sequence in which the dancer twists around her ‘pointes’ (dancing en pointe means ‘on the tip’ and is a classical ballet technique, usually performed using special shoes called pointes). Dessertenne used this phrase to describe a distinctive form of ventricular tachycardia in an elderly woman, because the electrical axis of the ventricular complexes varied cyclically giving the electrocardiogram (ECG) a twisted appearance (Figure 1) [1]. Similar polymorphic ventricular tachycardia had previously been identified as the cause of loss of consciousness during quinidine therapy (‘quinidine syncope’) [2]. TdP can be fatal and occurs in several clinical settings associated with prolongation of the ventricular action potential, notably drug treatment and inherited abnormalities of cardiac ion channels [3]. Prolongation of the ventricular action potential is recognized non-invasively by QT segment prolongation on the ECG (a useful but tricky surrogate end-point for risk of clinically important TdP – see below).We have commented previously on druginduced QT prolongation and its importance in drug development [4–7]. Several antidysrhythmic drugs, for example disopyramide and procainamide, as well as quinidine, cause TdP including some (flecainide, encainide and D-sotalol) that have increased mortality in randomized controlled trials [8, 9].Several non-cardiac drugs can also, albeit less frequently cause TdP. These include domperidone (in high dose intravenously – see below), methadone, arsenic trioxide, and several antihistamines, antipsychotic drugs and antiinfective drugs [3]. Not only do drugs differ in their potential to cause TdP, but several patient factors also strongly influence the risk [3]. One of the strongest of these is female sex [10] perhaps because testosterone, which shortens QT interval [11], is lower in women than in men. Several other susceptibility factors can be understood in terms of their influence on cardiac repolarization. These include poor left ventricular function, hypokalaemia, severe hypomagnesaemia and genetic polymorphisms in cardiac ion channels associated with inherited long QT syndromes (LQTS). Drug–drug interactions are clinically important, notably the interaction between ketoconazole (a potent inhibitor of CYP3A) and terfenadine [12], which contributed to the withdrawal of terfenadine from the market after several years of use, including over the counter sales. Diet (especially fruit juice consumption) also influences drug disposition in complex ways [13] underscoring the difficulties for regulators concerned about the potential for low frequency but severe drug harms.

Effect of Pomegranate Juice on Intestinal Transport and Pharmacokinetics of Nitrendipine in Rats

Pomegranate juice (PJ) is known to be a potent inhibitor of human cytochromes (CYP), particularly CYP2C9 and CYP3A4. The purpose of this study was to investigate the effect of oral PJ on the pharmacokinetics of nitrendipine (10 mg/kg) in rats. The effect of PJ was also investigated on the absorption kinetics of nitrendipine in rats using a single-pass intestinal perfusion model. There was a significant increase in effective permeability, absorption rate constant and fraction of drug absorbed in the pretreated group when compared with the control group, probably due to inhibition of the P-glycoprotein-mediated efflux of the drug by PJ. In comparison with control, PJ treatment significantly increased the area under the concentration-time curve of oral nitrendipine. The peak plasma concentration of nitrendipine was also significantly increased by PJ. However, elimination half-life of nitrendipine was not altered significantly in both PJ co-administered and pretreated groups. These results suggest that PJ inhibits the intestinal metabolism of nitrendipine without inhibiting the hepatic metabolism in rats. Therefore, the concomitant use of PJ, as food supplement, and nitrendipine should be avoided, although further clinical studies need to be undertaken in order to confirm this finding.