Cytochrome P450 3A4 Inhibitors Research Articles

Pharmacokinetic drug interactions of the non-vitamin K antagonist oral anticoagulants (NOACs).

The use of warfarin, the most commonly prescribed oral anticoagulant, is being questioned by clinicians worldwide due to warfarin several limitations (a limited therapeutic window and significant variability in dose-response among individuals, in addition to a potential for drug-drug interactions). Therefore, the need for non-vitamin K antagonist oral anticoagulants (NOACs) with a rapid onset of antithrombotic effects and a predictable pharmacokinetic (PK) and pharmacodynamic (PD) profile led to the approval of five new drugs: the direct factor Xa (F-Xa) inhibitors rivaroxaban, apixaban, edoxaban and betrixaban (newly approved by FDA) and the direct thrombin (factor-IIa) inhibitor dabigatran etexilate. The advantages of NOACs over warfarin are a fixed-dosage, the absence of the need for drug monitoring for changes in anti-coagulation and fewer clinically significant PK and PD drug-drug interactions. NOACs exposure will likely be increased by the administration of strong P-glycoprotein (P-gp) and cytochrome P450 (CYP) 3A4-inhibitors and may increase the risk of bleeds. On the contrary, P-gp inducers could significantly decrease the NOACs plasma concentration with an associated reduction in their anticoagulant effects. This manuscript gives an overview of NOACs PK profiles and their drug-drug interactions potential. This is meant to be of help to physicians in choosing the best therapeutic approach for their patients.

Therapeutic Agents with AHR Inhibiting and NRF2 Activating Activity for Managing Chloracne.

Chloracne is the major skin symptom caused by dioxin intoxication. Dioxin activates the aryl hydrocarbon receptor (AHR)–cytochrome p450 1A1 (CYP1A1) system, generates oxidative stress, and induces hyperkeratinization of keratinocytes and sebocytes leading to chloracne. Nuclear factor-erythroid 2-related factor-2 (NRF2) is a master switch that induces the expression of various antioxidative enzymes, such as heme oxygenase-1. Cinnamaldehyde is an antioxidant phytochemical that inhibits AHR–CYP1A1 signaling and activates the NRF2–antioxidative axis. The cinnamaldehyde-containing Kampo herbal medicine Keishibukuryogan is capable of improving chloracne in Yusho patients who are highly contaminated with dioxin. Agents with dual functions in promoting AHR–CYP1A1 inhibition and NRF2 activation may be useful for managing dioxin-related health hazards.

Reverse Hydroxamate Inhibitors of Bone Morphogenetic Protein 1.

Bone Morphogenetic Protein 1 (BMP1) inhibition is a potential method for treating fibrosis because BMP1, a member of the zinc metalloprotease family, is required to convert pro-collagen to collagen. A novel class of reverse hydroxamate BMP1 inhibitors was discovered, and cocrystal structures with BMP1 were obtained. The observed binding mode is unique in that the small molecule occupies the nonprime side of the metalloprotease pocket providing an opportunity to build in metalloprotease selectivity. Structure-guided modification of the initial hit led to the identification of an oral in vivo tool compound with selectivity over other metalloproteases. Due to irreversible inhibition of cytochrome P450 3A4 for this chemical class, the risk of potential drug-drug interactions was managed by optimizing the series for subcutaneous injection.

Formulation and in-vivo Evaluation of Novel Topical Gel of Lopinavir for Targeting HIV.

Background: Lopinavir is a specific reversible inhibitor of the enzyme HIV protease with mean oral bioavailability of less than 20% due to extensive hepatic metabolism by cytochrome P450 3A4. The reported half-life of Lopinavir is 5-6 hours and the maximum recommended daily dose is 400 mg/day. All the marketed tablet and capsule formulations of lopinavir are generally combined with Ritonavir, a potent inhibitor of cytochrome P450 3A4, to minimize presystemic metabolism of lop-inavir. Hence, to overcome limitations associated with oral administration of lopinavir and to promote single drug administration, utilization of vesicular nanocarriers through topical route could prove to be effective, as the approach combines the inherent advantages of topical route and the drug-carrying po-tential of vesicular nanocarriers across the tough and otherwise impervious skin barrier layer, i.e., stra-tum corneum.Objective: The objective was to develop solid lipid nanoparticles (SLN) of lopinavir and formulate a topical gel for improved systemic bioavailability of lopinavir.Method: SLNs were prepared using high-pressure homogenization technique and optimized. The na-noparticles were characterized by SEM to confirm their spherical shape. Differential Scanning Calo-rimetry (DSC) analysis was carried out to ensure the entrapment of drug inside the SLNs. A comparative evaluation was done between SLN based gel and plain gel of drug by performing ex-vivo skin permeation studies using Franz diffusion cell. To explore the potential of topical route, in-vivo bi-oavailability study was conducted in male Wistar rats.Results: The optimized formulation composed of Compritol 888ATO (0.5%) as a lipid, Poloxamer 407 (0.25%) as a surfactant and Labrasol (0.25%) as a co-surfactant gave the maximum entrapment of 69.78% with mean particle size of 48.86nm. The plain gel of the drug gave a release of 98.406 ± 0.007% at the end of 4hours whereas SLN based gel gave a more sustained release of 71.197 ±0.006% at the end of 12hours ex-vivo. As observed from the results of in-vivo studies, highest Cmax was found with SLN based gel (20.3127 ± 0.6056) µg/ml as compared to plain gel (8.0655 ± 1.6369) µg/ml and oral suspension (4.2550 ± 16.380) µg/ml of the drug. Also, the AUC was higher in the case of SLN based gel indicating good bioavailability as compared to oral suspension and plain gel of drug.Conclusion: Lopinavir SLN based gel was found to have modified drug release pattern providing sustained release as compared to plain drug gel. This indicates that Lopinavir when given topically has a good potential to target the HIV as compared to when given orally.

Quantitative Evaluation of Cytochrome P450 3A4 Inhibition and Hepatotoxicity in HepaRG 3-D Spheroids.

Predicting drug-drug interactions (DDIs) is an important step during drug development to avoid unexpected side effects. Cytochrome P450 (CYP) 3A4 is the most abundant human hepatic phase I enzyme, which metabolizes >50% of therapeutic drugs. Therefore, it is essential to test the potential of a drug candidate to induce CYP3A4 expression or inhibit its activity. Recently, 3-dimensional (3-D) mammalian cell culture models have been adopted in drug discovery research to assess toxicity, DDIs, and pharmacokinetics. In this study, we applied a human 3-D spheroid culture protocol using HepaRG cells combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS) to assess its ability to predict CYP3A4 inhibition. Levels of midazolam, a specific substrate of CYP3A4, were used to determine the long-term metabolic capacity of CYP3A4. Midazolam was decreased in the 3-D HepaRG culture system by ∼80% over 7 days, whereas its primary metabolite, 1-hydroxymidazolam, increased by ∼40%. Next, we assessed hepatotoxicity by determining the cytotoxicity of known hepatotoxicants in HepaRG spheroids, HepG2 cells, and primary human hepatocytes. Significant differences in cytotoxicity were detected in the system using 3-D HepaRG spheroids. These results suggest that 3-D HepaRG spheroids are a good model for prediction of CYP inhibition and hepatotoxicity in screening of early drug candidates.

Population Pharmacokinetic/Pharmacodynamic Analyses of Avatrombopag in Patients With Chronic Liver Disease and Optimal Dose Adjustment Guide With Concomitantly Administered CYP3A and CYP2C9 Inhibitors.

Avatrombopag, a c-Mpl agonist, has been developed to provide an alternative therapy to standard platelet transfusion care for the treatment of thrombocytopenia. The main objectives of this article were to describe the pharmacokinetics (PK) of avatrombopag, to characterize the pharmacokinetic/pharmacodynamic (PK/PD) relationship between plasma avatrombopag concentrations and platelet count, and to identify potential intrinsic and extrinsic factors affecting PK or PK/PD in patients with chronic liver disease (CLD). Platelet count following avatrombopag administration with and without concomitant medication was further simulated using the final population PK/PD model to explore potential dose adjustments. Avatrombopag PK was described by a 1-compartment model with combined first- and zero-order absorption and linear elimination. The relationship between the plasma avatrombopag concentrations and platelet count was well described by a 6-compartment life-span model with a linear drug effect. The final PK and PK/PD models included statistically significant but not clinically relevant effects of body weight and CLD on apparent volume distribution and East Asian ethnicity, albumin, and thrombopoietin level on the slope parameter in the PK/PD relationship. PK/PD simulations showed comparable elevation in platelet count with and without concomitant cytochrome P450 (CYP) 3A and CYP2C9 inhibitors for the dosing regimens of 40 and 60 mg for 5 days, with predictions of <10% of CLD patients exceeding platelet count >200 × 109 /L. Dose adjustment is therefore not necessary with concomitant use of CYP3A and CYP2C9 interacting drugs considering the limited treatment duration (ie, 5 days) and lack of significant safety concerns in CLD patients.

Clinical Pharmacokinetics and Pharmacodynamics of Bortezomib.

Proteasome inhibitors disrupt multiple pathways in cells and the bone marrow microenvironment, resulting in apoptosis and inhibition of cell-cycle progression, angiogenesis, and proliferation. Bortezomib is a first-in-class proteasome inhibitor approved for the treatment of multiple myeloma and mantle cell lymphoma after one prior therapy. It is also effective in other plasma cell disorders and non-Hodgkin lymphomas. The main mechanism of action of bortezomib is to inhibit the chymotrypsin-like site of the 20S proteolytic core within the 26S proteasome, thereby inducing cell-cycle arrest and apoptosis. The pharmacokinetic profile of intravenous bortezomib is characterized by a two-compartment model with a rapid initial distribution phase followed by a longer elimination phase and a large volume of distribution. Bortezomib is available for subcutaneous and intravenous administration. Pharmacokinetic studies comparing subcutaneous and intravenous bortezomib demonstrated that systemic exposure was equivalent for both routes; pharmacodynamic parameters of 20S proteasome inhibition were also similar. Renal impairment does not influence the intrinsic pharmacokinetics of bortezomib. However, moderate or severe hepatic impairment causes an increase in plasma concentrations of bortezomib. Therefore, patients with moderate or severe hepatic impairment should start at a reduced dose. Because bortezomib undergoes extensive metabolism by hepatic cytochrome P450 3A4 and 2C19 enzymes, certain strong cytochrome P450 3A4 inducers and inhibitors can also alter the systemic exposure of bortezomib. This article critically reviews and summarizes the clinical pharmacokinetics and pharmacodynamics of bortezomib at various dosing levels and routes of administration as well as in specific patient subsets. In addition, we discuss the clinical efficacy and safety of bortezomib.

Persistence of a Posaconazole-Mediated Drug-Drug Interaction With Ranolazine After Cessation of Posaconazole Administration: Impact of Obesity and Implications for Patient Safety.

The antianginal agent ranolazine (Ranexa®) is metabolized primarily by cytochrome P450-3A (CYP3A) enzymes. Coadministration with strong CYP3A inhibitors, such as ketoconazole and posaconazole, is contraindicated due to risk of QT prolongation from high levels of ranolazine. This study evaluated the time course of recovery from the posaconazole drug interaction in normal-weight and otherwise healthy obese subjects. Subjects received single doses of ranolazine in the baseline control condition, again during coadministration of posaconazole, and at 4 additional time points during the 2 weeks after posaconazole discontinuation. With posaconazole coadministration, the geometric mean ratio of ranolazine area under the concentration curve (AUC) increased by a factor of 3.9 in normals and by 2.8 in obese subjects. Posttreatment washout of posaconazole was slow in normals (mean half-life 36 hours) and further prolonged in obese subjects (64 hours). Recovery of ranolazine AUC toward baseline was delayed. AUC remained significantly elevated above baseline in normal-weight and obese subjects for 7-14 days after stopping posaconazole. Current product labeling does not address the need for delay or a reduced dose of ranolazine after discontinuation of a strong CYP3A inhibitor before ranolazine can be safely administered. We recommend that administration of ranolazine should be limited to 500 mg twice daily for 7 days after posaconazole discontinuation in patients with body mass index 18.5-24.9 kg/m2 and for 12 days in patients with body mass index ≥35 kg/m2 after ranolazine is resumed.

Pharmacokinetic Properties of a Sufentanil Sublingual Tablet Intended to Treat Acute Pain.

Desirable product attributes for treatment of moderate-to-severe acute pain in many medically supervised settings are rapid onset and a route of administration not requiring intravenous access. The pharmacokinetic characteristics of sublingually administered tablets containing 15 or 30 µg of sufentanil are described. Blood was sampled from healthy subjects (four studies, 122 subjects) and patients (seven studies, 944 patients). Studies in healthy subjects determined bioavailability, effect of inhibition of cytochrome P450 3A4, and the plasma concentration profile with single and hourly sublingual doses. Studies in patients evaluated effects of weight, age, sex, and organ impairment on apparent clearance. Noncompartmental and mixed-effect population methods were used. Bioavailability of a single sublingual tablet was 52%, decreasing to 35% with repeat dosing. Ketoconazole (CYP3A4 inhibitor) increased maximum plasma concentration 19% and increased the area under the curve 77%. After a single 30-µg dose, plasma concentrations reached the published sufentanil analgesic threshold (24 pg/ml) within 30 min, peaked at 1 h, and then decreased below therapeutic concentrations by ~3 h. With hourly administration, plasma concentrations plateaued by the fifth dose. Time for concentrations to decrease 50% from maximal values was similar after 1 dose (2.5 ± 0.85 h) and 12 doses (2.5 ± 0.72 h). Clearance increased with weight, decreased with age, and was not affected by renal or hepatic impairment. The time course of a single 30-µg dose was consistent with onset of analgesia and redosing frequency observed in clinical trials. Sublingual sufentanil tablets provide the opportunity to noninvasively and rapidly treat moderate-to-severe pain in a monitored setting.

Evaluation of 4β-Hydroxycholesterol and 25-Hydroxycholesterol as Endogenous Biomarkers of CYP3A4: Study with CYP3A-Humanized Mice.

Cytochrome P450 3A (CYP3A) enzymes metabolize approximately half of all drugs on the market. Since the endogenous compounds 4β-hydroxycholesterol (4β-HC) and 25-hydroxycholesterol (25-HC) are generated from cholesterol via CYP3A enzymes, we examined whether the plasma levels of 4β-HC and 25-HC reflect hepatic CYP3A4 activity by using a CYP3A-humanized mouse model, in which the function of endogenous Cyp3a was genetically replaced by human CYP3A. CYP3A-humanized mice have great advantages for evaluation of the relationship between hepatic CYP3A protein levels and plasma and hepatic levels of 4β-HC and 25-HC. Levels of CYP3A4 protein in the liver microsomes of CYP3A-humanized mice were increased by treatment with pregnenolone-16α-carbonitrile, a CYP3A inducer. Hepatic and plasma levels of 4β-HC and 25-HC normalized by cholesterol were significantly correlated with hepatic CYP3A4 protein levels. In addition, in vitro studies using human liver microsomes showed that the formation of 4β-HC was strongly inhibited by a CYP3A inhibitor, while the inhibitory effect of the CYP3A inhibition on the formation of 25-HC was weak. These results suggested that CYP3A mainly contributed to the formation of 4β-HC in human liver microsomes, whereas other factors may be involved in the formation of 25-HC. In conclusion, the in vivo studies using CYP3A-humanized mice suggest that plasma 4β-HC and 25-HC levels reflect hepatic CYP3A4 activity. Furthermore, taking the results of in vitro studies using human liver microsomes into consideration, 4β-HC is a more reliable biomarker of hepatic CYP3A activity.

Midazolam Hydroxylation Assay as a Marker for Endogenous CYP3A4‐mediated Metabolism: Metabolic Interaction with Natural Health Supplements

BackgroundEndogenous substances (endobiotics) such as vitamin D3 and estrogen are metabolized by cytochrome P450 3A4 (CYP3A4). However, measurement of endobiotic metabolites is often technology‐limited and expensive. Because of structural similarity of midazolam with vitamin D3, midazolam metabolic profile could present valuable information in identifying potential interaction of drugs or natural health supplements (NHS) with endogenous substances. Polyphenols (quercetin, raspberry ketone, gallic acid, rutin), furanocoumarin (imperatorin) and terpenoids (ursolic acid) are the biologically active human dietary constituents from grapes, berry fruits, pomegranate, and olive oil, but are also widely ingested as over‐the‐counter natural health supplements (NHS) in United States. NHS have the ability to inhibit CYP3A4‐mediated metabolism, possibly causing the plasma concentrations of the midazolam as well as vitamin D3 to increase. The objective of the present study was to develop a simple and effective metabolism assay to measure CYP3A4‐mediated midazolam hydroxylation and to screen certain NHS (polyphenols, furanocoumarin, terpenoids) for their potential to cause CYP3A4 related herb‐endobiotic interactions in humans.MethodsThe hydroxylation of midazolam to 1′‐hydroxymidazolam assay was developed and optimized. Reaction mixtures containing potassium phosphate buffer (pH 7.4), recombinant CYP3A4 protein (30 pmol/ml), NADPH‐regenerating system, and midazolam (5 uM or 2 uM) were incubated for 15 min. Substrate, metabolites and internal standard were analyzed with a reverse phase assay by a Shimadzu Prominence high‐performance liquid chromatography (HPLC) coupled to a photodiode array detector set at 220 nm using a C18 column. SigmaPlot enzyme kinetics module (version 13; Systat Software, Inc., San Jose, CA) and GraphPad Prism software (GraphPad Software Inc., San Diego, CA) were used to determine the kinetics parameters and inhibitory constants, respectively.ResultsThe Km and Vmax values for rCYP3A4‐mediated 1′‐hydroxymidazolam formation were 1.9±0.3 uM and 75.4±3.7 pmol/min/mg, respectively. Imperatorin inhibited 1′‐hydroxymidazolam formation to undetectable levels at both 2 uM and 5 uM concentrations of midazolam, whereas quercetin inhibited the formation by 31–44%. The IC50 values of imperatorin for 1′‐hydroxymidazolam and 4‐hydroxymidazolam were 7.7 uM and 2.6 uM, respectively. Ketoconazole, a known potent inhibitor of CYP3A4, yielded IC50 concentrations of 0.16–0.20 uM for midazolam hydroxylation.ConclusionsA midazolam hydroxylation assay was developed to screen potential metabolic interactions. Imperatorin was identified as an inhibitor of rCYP3A4. Quercetin showed low rCYP3A4 inhibition potential. This research further shows that NHS studied here can potentially inhibit one of the most ubiquitous enzymes responsible for inactivation of endobiotics and may provide additional health benefits. Vitamin D3 is metabolized by CYP3A4 and midazolam could potentially be used as a marker for interaction of commonly used NHS with vitamin D3. The cost‐effective HPLC method developed in this study provides a useful tool in predicting NHS‐endobiotic interactions.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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

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

Daclatasvir: A Review of Preclinical and Clinical Pharmacokinetics.

Daclatasvir is a first-in-class, highly selective, hepatitis C virus, non-structural protein 5a polymerase replication complex inhibitor with picomolar potency and broad genotypic coverage in vitro. Daclatasvir undergoes rapid absorption, with a time to reach maximum plasma concentration of 1-2h and an elimination half-life of~10 to 14h observed in single-ascending dose studies. Steady state was achieved by day 4 in multiple-ascending dose studies. Daclatasvir can be administered without regard to food or pH modifiers. Daclatasvir exposure is similar between healthy subjects and subjects infected with hepatitis C virus. Intrinsic factors such as age, race, or sex do not impact daclatasvir exposure. No dose adjustment is necessary for patients with any degree of hepatic or renal impairment. Daclatasvir has low-to-moderate clearance with the predominant route of elimination via cytochrome P450 3A4-mediated metabolism and P-glycoprotein excretion and intestinal secretion. Renal clearance is a minor route of elimination for daclatasvir. As a result, the dose of daclatasvir should be reduced from 60 to 30mg once daily when co-administered with strong inhibitors of cytochrome P450 3A4. No dose adjustment is required when daclatasvir is co-administered with moderate inhibitors of cytochrome P450 3A4. The dose of daclatasvir should be increased from 60 to 90mg once daily when co-administered with moderate inducers of cytochrome P450 3A4. Co-administration of daclatasvir with strong inducers of cytochrome P450 3A4 is contraindicated. Concurrent medications with inhibitory effects on P-glycoprotein without concurrent inhibition of cytochrome P450 3A4 are unlikely to cause marked changes in daclatasvir exposure, as the clearance of daclatasvir is through both cytochrome P450 3A4 and P-glycoprotein. The potential for daclatasvir to affect the pharmacokinetics of concomitantly administered drugs that are substrates of the cytochrome P450 enzyme system is low. In vitro, daclatasvir is a weak-to-moderate inhibitor of transporters including organic cation transporter 1, P-glycoprotein, organic transporting polypeptide 1B1, organic transporting polypeptide 1B3, and breast cancer resistance protein, although in clinical studies, daclatasvir has not altered the pharmacokinetics of concomitantly administered drugs that are substrates of these transporters to an appreciable degree, except for rosuvastatin. In summary, daclatasvir is a hepatitis C virus, non-structural protein 5a-selective inhibitor with a well-characterized pharmacokinetic profile that forms part of potent and well-tolerated all-oral treatment regimens for chronic hepatitis C virus infection.

Case Series Analysis of New Zealand Reports of Rapid Intense Potentiation of Warfarin by Roxithromycin.

IntroductionWe undertook an analysis of all the reports to the New Zealand Centre for Adverse Reactions Monitoring of a roxithromycin/warfarin interaction after two recent reports described intense rapid warfarin potentiation. The interaction was first published in 1995. Cytochrome P450 3A4 inhibition has been the proposed mechanism but has limited biologic plausibility. There are suggestions that the clinical significance of the interaction may be increased by severe illness, polypharmacy, renal dysfunction, older age and increased warfarin sensitivity.MethodsTo investigate the potentiating effect of warfarin on roxithromycin in this New Zealand case series, the reports were reviewed to identify patients at risk, compare the reporting pattern with published Australian data and evaluate the appropriateness of current prescribing advice.ResultsThirty patient reports were identified. The age range was 23–88 years, mean 66.8, median 73.0 (standard deviation 17.7) and the international normalised ratios after roxithromycin commencement ranged from 3.6 to 16.7 (mean 7.6, median 7.6, standard deviation 3.6). For eight patients with measurements on day 3, international normalised ratios were 4.3–16.7 (mean 10.4, median 8.8, standard deviation 4.4). Four patients had serious haemorrhage. Indications for roxithromycin were a range of respiratory tract infections. Anticoagulation was stable for most patients prior to acute infection. Serious infection occurred in 54.5% (12 of 22 patients with information). Polypharmacy (five or more medicines daily) was used by 36.7% of patients long term, increasing acutely to 83.3%, including additional potentially interacting medicines. Warfarin daily dose (1.5–13.0 mg, mean 4.4, median 4.0, standard deviation 2.2) was moderate to low. Pre-roxithromycin international normalised ratio values ranged from 1.4 to 3.7, mean and median 2.5, standard deviation 0.5. A high proportion of interactions were observed between warfarin and roxithromycin compared with other macrolides and compared with cytochrome P450 3A4-related macrolide interactions. The pattern was similar to published Australian data.ConclusionIn this case series, the high prevalence of acute polypharmacy, including potentially interacting medicines, and serious infection suggests that they may have contributed to warfarin potentiation and increased the clinical significance of a roxithromycin/warfarin interaction.

Screening of cytochrome P450 3A4 inhibitors via in silico and in vitro approaches.

Cytochrome P450 3A4 (CYP3A4) is an important member of the CYP family and responsible for metabolizing a broad range of drugs. Potential drug–drug interactions (DDIs) caused by CYP3A4 inhibitors could lead to increasing risk of side-effects/toxicity or decreasing effectiveness. The evaluation of CYP3A4 inhibitory activity is time-consuming, labor-intensive, and costly, and it is necessary to establish virtual screening models for predicting CYP3A4 inhibitors. In this study, 4 classifier algorithms, including support vector machine (SVM), naive Bayesian (NB), recursive partitioning (RP), and K-nearest neighbor (KNN), were applied to discriminate CYP3A4 inhibitors from the non-inhibitors. Correlation analysis and stepwise linear regression methods were used for descriptor selection and optimization. The performance of classifiers was measured by 5-fold cross-validation, Y-scrambling and test set validation. Finally, the optimal NB model with Matthews correlation coefficients of 0.894 for the test set was developed to screen FDA-approved drugs and natural products database. As a result, 90 compounds from FDA-approved drug databases were predicted as inhibitors, and 46% of them were identified as known CYP3A4 inhibitors. 6 natural products were selected for further bioactivity assay and molecular docking. 2 of them with good docking score also exerted significant CYP3A4 inhibitory activities with IC50 values of 0.052 and 1.120 μM, respectively. This study proved the feasibility of a new method for predicting CYP3A4 inhibitory activity and preventing the occurrence of DDIs at early stage in drug development.

Metabolism of PF-04958242: Substrate concentration-dependent impact of cytochrome P4503A4 inhibitors as an explanation for a lack of clinical drug–drug interaction at very low substrate doses

Metabolism of PF-04958242: Substrate concentration-dependent impact of cytochrome P4503A4 inhibitors as an explanation for a lack of clinical drug–drug interaction at very low substrate doses

CYP3A4 inducer and inhibitor strongly affect the pharmacokinetics of triptolide and its derivative in rats.

Triptolide is the most active ingredient of Tripterygium wilfordii Hook F, which is used to treat rheumatoid arthritis. (5R)-5-Hydroxytriptolide is a hydroxylation derivative of triptolide with a reduced toxicity. To investigate the metabolic enzymes of the two compounds and the drug-drug interactions with enzyme inducers or inhibitors, a series of in vitro and in vivo experiments were conducted. In vitro studies using recombinant human cytochrome P450 enzyme demonstrated that cytochrome P450 3A4 (CYP3A4) was predominant in the metabolism of triptolide and (5R)-5-hydroxytriptolide, accounting for 94.2% and 64.2% of the metabolism, respectively. Pharmacokinetics studies were conducted in male SD rats following administration of triptolide or (5R)-5-hydroxytriptolide (0.4 mg/kg, po). The plasma exposure to triptolide and (5R)-5-hydroxytriptolide in the rats was significantly increased when co-administered with the CYP3a inhibitor ritonavir (30 mg/kg, po) with the values of AUC0-∞ (area under the plasma concentration-time curve from time zero extrapolated to infinity) being increased by 6.84 and 1.83 times, respectively. When pretreated with the CYP3a inducer dexamethasone (50 mg·kg-1·d-1, for 3 d), the AUC0-∞ values of triptolide and (5R)-5-hydroxytriptolide were decreased by 85.4% and 91.4%, respectively. These results suggest that both triptolide and (5R)-5-hydroxytriptolide are sensitive substrates of CYP3a. Because of their narrow therapeutic windows, clinical drug-drug interaction studies should be carried out to ensure their clinical medication safety and efficacy.

Inhibition of Human CYP3A4 by Rationally Designed Ritonavir-Like Compounds: Impact and Interplay of the Side Group Functionalities.

Structure-function relationships of nine rationally designed ritonavir-like compounds were investigated to better understand the ligand binding and inhibitory mechanism in human drug-metabolizing cytochrome P450 3A4 (CYP3A4). The analogs had a similar backbone and pyridine and tert-butyloxycarbonyl (Boc) as the heme-ligating and terminal groups, respectively. N-Isopropyl, N-cyclopentyl, or N-phenyl were the R1-side group substituents alone (compounds 5a-c) or in combination with phenyl or indole at the R2 position (8a-c and 8d-f subseries, respectively). Our experimental and structural data indicate that (i) for all analogs, a decrease in the dissociation constant (Ks) coincides with a decrease in IC50, but no relation with other derived parameters is observed; (ii) an increase in the R1 volume, hydrophobicity, and aromaticity markedly lowers Ks and IC50, whereas the addition of aromatic R2 has a more pronounced positive effect on the inhibitory potency than the binding strength; (iii) the ligands' association mode is strongly influenced by the mutually dependent R1-R2 interplay, but the R1-mediated interactions are dominant and define the overall conformation in the active site; (iv) formation of a strong H-bond with Ser119 is a prerequisite for potent CYP3A4 inhibition; and (v) the strongest inhibitor in the series, the R1-phenyl/R2-indole containing 8f (Ks and IC50 of 0.08 and 0.43 μM, respectively), is still less potent than ritonavir, even under conditions that prevent the mechanism based inactivation of CYP3A4. Crystallographic data were essential for better understanding and interpretation of the experimental results, and suggested how the inhibitor design could be further optimized.

QTc prolongation during ciprofloxacin and fluconazole combination therapy: prevalence and associated risk factors.

Ciprofloxacin and fluconazole combination therapy is frequently used as prophylaxis for, and treatment of, infections in patients with haematological malignancies. However, both drugs are known to prolong the heart rate-corrected QT (QTc) interval, which is a serious risk factor for torsade de pointes (TdP). Therefore, the aim of the current study was to assess the prevalence of QTc prolongation during ciprofloxacin and fluconazole use. The secondary objective was to determine associated risk factors of QTc prolongation in these patients. A prospective observational study was performed in patients admitted to the Erasmus University Medical Centre and treated with ciprofloxacin and fluconazole. A 12-lead electrocardiogram (ECG) was recorded at the estimated time to peak concentration (Tmax ) for the last added drug. The main outcome was the proportion of patients with QTc prolongation during treatment. Data on the following potential risk factors were collected: patient characteristics, serum electrolyte levels, dosage of ciprofloxacin and fluconazole, renal and liver function and concomitant use of other QTc-prolonging drugs and cytochrome P450 3A4 inhibitors. A total of 170 patients were included, of whom 149 (87.6%) were treated for haematological malignancies. The prevalence of QTc prolongation was 4.7%. No risk factors were found to be associated with QTc prolongation. The QTc interval increased by 10.7ms [95% confidence interval (CI) 7.2, 14.1ms] during ciprofloxacin and fluconazole combination therapy. The prevalence of QTc prolongation in patients using ciprofloxacin and fluconazole is low compared with the prevalence in the general population, which varies from 5% to 11%. In addition, no risk factors were found. Given the low prevalence, routine ECG monitoring in patients on this therapy should be reconsidered.

Concomitant nevirapine impacts pharmacokinetic exposure to the antimalarial artemether-lumefantrine in African children.

BackgroundThe antiretroviral drug nevirapine and the antimalarial artemisinin-based combination therapy artemether-lumefantrine are commonly co-administered to treat malaria in the context of HIV. Nevirapine is a known inhibitor of cytochrome P450 3A4, which metabolizes artemether and lumefantrine. To address the concern that the antiretroviral nevirapine impacts the antimalarial artemether-lumefantrine pharmacokinetics, a prospective non-randomized controlled study in children presenting with uncomplicated malaria and HIV in sub-Saharan Africa was carried out.MethodsParticipants received artemether-lumefantrine (20/120 mg weight-based BID) for 3 days during nevirapine-based antiretroviral therapy (ART) co-administration (158–266 mg/m2 QD). HIV positive participants who were not yet on ART drugs were also enrolled as the control group. The target enrollment was children aged 3–12 years (n = 24 in each group). Intensive pharmacokinetics after the last artemether-lumefantrine dose was assessed for artemether, its active metabolite dihydroartemisinin, and lumefantrine. Pharmacokinetic parameters (area under the plasma concentration vs. time curve (AUC), maximum concentration and day 7 lumefantrine concentrations) were estimated using non-compartmental methods and compared to controls.ResultsNineteen children (16 on nevirapine and three not on ART) enrolled. Fifteen of the 16 (aged 4 to 11 years) on nevirapine-based ART were included in the pharmacokinetic analysis. Due to evolving WHO HIV treatment guidelines, insufficient children were enrolled in the control group (n = 3), so the pharmacokinetic data were compared to a historical control group of 20 HIV-uninfected children 5–12 years of age who also presented with malaria and underwent identical study procedures. Decreases of pharmacokinetic exposure [as estimated by AUC (AUC0-8hr)] were marginally significant for artemether (by -46%, p = 0.08) and dihydroartemisinin (-22%, p = 0.06) in the children on nevirapine-based ART, compared to when artemether-lumefantrine was administered alone. Similarly, peak concentration was decreased by 50% (p = 0.07) for artemether and 36% (p = 0.01) for dihydroartemisinin. In contrast, exposure to lumefantrine increased significantly in the context of nevirapine [AUC0-120hr:123% (p<0.001); Cday7:116% (p<0.001), Cmax: 95% (p<0.001)].ConclusionsNevirapine-based ART increases the exposure to lumefantrine in pre-pubescent children with a trend toward diminished artemether and dihydroartemisinin exposure. These findings contrast with other studies indicating NVP reduces or results in no change in exposure of antimalarial drugs, and may be specific to this age group (4–12 years). Considering the excellent safety profile of artemether-lumefantrine, the increase in lumefantrine is not of concern. However, the reduction in artemisinin exposure may warrant further study, and suggests that dosage adjustment of artemether-lumefantrine with nevirapine-based ART in children is likely warranted.