Hepatic Cytochrome P450 System Research Articles

Contemplating cannabis? The complex relationship between cannabinoids and hepatic metabolism resulting in the potential for drug-drug interactions.

The majority of states have fully legalized the use of medical cannabis (MC), and nearly all other states allow limited access to cannabidiol (CBD), a non-intoxicating constituent of cannabis often touted for a range of therapeutic indications. Further, the Agricultural Improvement Act of 2018 legalized hemp-derived products in all 50 states; typically high in CBD, these products are derived from cannabis varieties containing ≤0.3% delta-9-tetrahydrocannabinol (THC) by weight. The recent "green rush" has resulted in a striking increase in cannabis use among patients and consumers who often use a wide variety of novel product types, each with a unique blend of cannabinoid constituents. Importantly, however, several cannabinoids have the potential to cause drug-drug interactions (DDI) with other medications, primarily due to their involvement with the hepatic cytochrome P450 (CYP450) system. This article examines the potential for individual cannabinoids, particularly CBD, to interact with the hepatic metabolic system, which is concerning given its involvement in the metabolism of commonly-prescribed medications. CBD and other cannabinoids are metabolized extensively by the CYP450 system, and also inhibit many of these enzymes, potentially leading to variable serum levels of other medications, as well as variable levels of cannabinoids when other medications modify the system. As access and interest in cannabinoid-based products continues to increase, critical questions remain unanswered regarding their safety. The complex relationship between cannabinoids and the hepatic metabolic system, including common potential DDI resulting from cannabinoid exposure, are explored along with the clinical significance of these potential interactions and monitoring or mitigation strategies.

Basic Aspects and the Overview on Pharmacokinetics and Studies on Drug Distribution- A Panoramic Review

Patients who are in critical condition display a variety of organ dysfunctions and frequently need to be treated with a range of medications, such as sedatives, analgesics, neuromuscular blockers, antibiotics, inotropes, and gastric acid suppressants. A crucial component of treatment for this patient population is comprehending how organ dysfunction might change the pharmacokinetics of medications. Due to gastrointestinal failure, many medications will need to be administered intravenously. When the oral route is an option, hypomotility, changes in gut pH, and enteral feeding may affect bioavailability. The main factors affecting medication clearance, and consequently steady-state drug concentrations, efficacy, and toxicity in a given patient, are hepatic and renal dysfunction. Many medications are cleared from the body primarily through oxidative metabolism, and it is becoming increasingly understood how important it is for critically ill patients to have diminished hepatic cytochrome P450 system activity. Both filtration and secretion clearance pathways are necessary for the elimination of parent medications and their active metabolites, making renal failure equally crucial. Renal failure is frequently a secondary cause of changes in the steady-state volume of distribution, which can lower the body's effective medication concentrations. Failure of the endocrine, endothelium, muscular, or central neurological systems may also have an impact on how a medication is metabolized. For some medications, there is strong evidence that changes in pharmacokinetic characteristics depend on time. To maximize the pharmacodynamic response and result, it is essential to understand the underlying pathophysiology in the critically sick and utilize pharmacokinetic principles in the selection of drug and dosing regimen.

Modern views on the metabolism and biological effects of vitaminD

VitaminD is a steroid hormone that plays a crucial role in maintaining normal bone condition and calcium homeostasis. In recent years, vitaminD has become a hot topic of endocrinological research, largelyDue to the COVID-19 pandemic and the likely correlation between hypovitaminosisD and a high risk of chronic lung disease and associated mortality. Recent studies have shown that vitaminD exhibits a complex multistage metabolism and acts as a hormone on many extracellular targets. This review examines some new intriguing and as yet unclear aspects of vitaminD metabolism, such as new concepts of enzyme regulation, new pleiotropic effects of vitaminD receptor activation (VDR), and epigenetic effects. The mechanisms of vitaminD synthesis in the skin, its metabolism in the hepatic cytochrome P450 system, catabolism, metabolites and transport, gene control and epigenetic modulation are considered inDetail. In addition to the well-known role of vitaminD in calcium and bone metabolism, it has many pleiotropic extraskeletal effects, including potent effects on the immune system, cardiovascular system, adipose tissue and glucose/lipid metabolism, muscle and more. Experimental studies have shown that VDRs are expressed by cancer cell lines. Recent studies have shown a link between low levels of vitaminD and almost all aspects of the metabolic syndrome, such as type 2 diabetes, fasting blood glucose, hypertension, dyslipidemia, obesity and insulin resistance. Several studies have focused on the role of vitaminD in adipose tissue biology. In particular, a negative correlation between vitaminD and leptin or resistin is shown, as well as an inverse correlation with adiponectin. Recent studies in vitaminD-deficient mice have shown impaired secretion of glucose-stimulated insulin by pancreatic islets. VitaminD is thought to play a role in the pathogenesis and progression of cancer, and vitaminD analogues can slow cancer progression and metastasis. It is concluded that vitaminD is a molecule with several endocrine, paracrine and autocrine effects on many tissues and organs, in addition to maintaining skeletal homeostasis. Research in this area, which aims to clarify the pleiotropy of many effects of vitaminD and its metabolites, continues.

Concomitant Filled Prescriptions of Oxymorphone or Oxycodone with CYP3A Inhibitors and Inducers.

Oxymorphone's metabolism does not involve the hepatic cytochrome P450 (CYP) system. The effect of this pharmacokinetic feature of oxymorphone on opioid prescribing is unknown. To assess the relative frequency with which oxymorphone and oxycodone (a CYP3A-metabolized opioid analgesic) were each prescribed to patients concomitantly receiving CYP3A-modifying drugs (i.e., inducers and inhibitors) to characterize opioid-prescribing patterns in patients at risk for CYP3A-related drug interactions. We analyzed the Sentinel Distributed Database from January 1, 2013, to December 31, 2016, to identify the proportion of patients with concomitant dispensing of selected CYP3A modifiers among initiators of oxymorphone. We then repeated the analysis using oxycodone instead of oxymorphone. We conducted sensitivity analyses that varied the washout periods for each opioid to account for potential opioid switching. In the primary analysis, the proportion of patients with concomitant incident dispensings of oxymorphone and selected CYP3A modifiers was 3.26% (95% CI = 3.09%-3.43%), and the proportion of patients with incident dispensings of oxycodone and selected CYP3A modifiers was 2.82% (95% CI = 2.79%-2.85%). The difference between proportions was 0.43% (95% CI = 0.26%-0.60%). Sensitivity analyses that varied the washout periods for each opioid with respect to the other opioid to account for switching yielded similar results. We observed similar proportions of patients using selected CYP3A modifiers concomitantly with both oxymorphone and oxycodone. While the CIs of the point estimates did not overlap, the absolute differences between the proportions were small. This project was supported by Task Order HHSF22301001T under Master Agreement HHSF223201400030I from the U.S. Food and Drug Administration (FDA). The FDA approved the study protocol, including the statistical analysis plan, and reviewed and approved the manuscript. Coauthors from the FDA participated in the results interpretation and in the preparation and decision to submit the manuscript for publication. Coyle, Money, Staffa, Meyer, and Woods are employed by the FDA. The other authors have no financial conflicts of interest to report. The views expressed are those of the authors and not necessarily those of the U.S. Department of Health and Human Services, U.S. Food and Drug Administration.

Thromboembolic and neurologic sequelae of discontinuation of an antihyperlipidemic drug during ongoing warfarin therapy

Warfarin and antihyperlipidemics are commonly co-prescribed. Some antihyperlipidemics may inhibit warfarin deactivation via the hepatic cytochrome P450 system. Therefore, antihyperlipidemic discontinuation has been hypothesized to result in underanticoagulation, as warfarin metabolism is no longer inhibited. We quantified the risk of venous thromboembolism (VTE) and ischemic stroke (IS) due to statin and fibrate discontinuation in warfarin users, in which warfarin was initially dose-titrated during ongoing antihyperlipidemic therapy. Using 1999–2011 United States Medicaid claims among 69 million beneficiaries, we conducted a set of bidirectional self-controlled case series studies—one for each antihyperlipidemic. Outcomes were hospital admissions for VTE/IS. The risk segment was a maximum of 90 days immediately following antihyperlipidemic discontinuation, the exposure of interest. Time-varying confounders were included in conditional Poisson models. We identified 629 study eligible-persons with at least one outcome. Adjusted incidence rate ratios (IRRs) for all antihyperlipidemics studied were consistent with the null, and ranged from 0.21 (0.02, 2.82) for rosuvastatin to 2.16 (0.06, 75.0) for gemfibrozil. Despite using an underlying dataset of millions of persons, we had little precision in estimating IRRs for VTE/IS among warfarin-treated persons discontinuing individual antihyperlipidemics. Further research should investigate whether discontinuation of gemfibrozil in warfarin users results in serious underanticoagulation.

The usage of a three-compartment model to investigate the metabolic differences between hepatic reductase null and wild-type mice.

The Cytochrome P450 (CYP) system is involved in 90% of the human body's interactions with xenobiotics and due to this, it has become an area of avid research including the creation of transgenic mice. This paper proposes a three-compartment model which is used to explain the drug metabolism in the Hepatic Reductase Null (HRN) mouse developed by the University of Dundee (Henderson, C. J., Otto, D. M. E., Carrie, D., Magnuson, M. A., McLaren, A. W., Rosewell, I. and Wolf, C. R. (2003) Inactivation of the hepatic cytochrome p450 system by conditional deletion of hepatic cytochrome p450 reductase. J. Biol. Chem. , 13480-13486). The model is compared with a two-compartment model using experimental data from studies using wild-type and HRN mice. This comparison allowed for metabolic differences between the two types of mice to be isolated. The three sets of drug data (Gefitinib, Midazolam and Thalidomide) showed that the transgenic mouse has a decreased rate of metabolism.

CYP2C19 LOF alleles confer no risk for HTPR but higher risk for recurrent ischemic events in clopidogrel treated elderly ACS patients

Dual antiplatelet therapy (DAPT), combining aspirin with P2Y12 inhibitor of clopidogrel, has been recommended with compelling evidence for the treatment of acute coronary syndrome (ACS) or the prevention of stent thrombosis in patients who underwent percutaneous coronary intervention (PCI) [ [1] Amsterdam E.A. Wenger N.K. Brindis R.G. et al. 2014 AHA/ACC Guideline for the management of patients with non-ST-Elevation acute coronary syndromes: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J. Am. Coll. Cardiol. 2014; 64: e139-e228 Abstract Full Text Full Text PDF PubMed Scopus (1907) Google Scholar ]. As an inactive pro-drug, clopidogrel requires the activation by the hepatic cytochrome P450 (CYP) system to generate its active metabolite, which exerts its antiplatelet effects by irreversibly inhibiting the P2Y12 receptor on platelets. Due to the variability of active metabolite generation, there is marked inter-individual variability (~30%) in the antiplatelet effects of clopidogrel, and a reduced response to this drug may be a risk factor for cardiovascular events [ [2] Mallouk N. Labruyere C. Reny J.L. et al. Prevalence of poor biological response to clopidogrel: a systematic review. Thromb. Haemost. 2012; 107: 494-506 Crossref PubMed Scopus (71) Google Scholar ]. Accumulated pharmacogenetic evidence verified that carriers of CYP2C19 loss-of-function (LOF) alleles have decreased clopidogrel active transformation and diminished platelet inhibition. Genotyping of CYP2C19 may offer a promising clue for a personalized approach of antiplatelet treatments [ [3] Scott S.A. Sangkuhl K. Stein C.M. et al. Clinical Pharmacogenetics Implementation Consortium guidelines for CYP2C19 genotype and clopidogrel therapy: 2013 update. Clin. Pharmacol. Ther. 2013; 94: 317-323 Crossref PubMed Scopus (663) Google Scholar ]. Elderly individuals represent a growing population of patients diagnosed with ACS and treated by PCI. Complex with more comorbidity and concomitant medications, as well as the difficulties for the balance between ischemic and bleeding events, elderly patients should be of priority for personalized antiplatelet therapy [ [4] Silvain J. Cayla G. Hulot J.S. et al. High on-thienopyridine platelet reactivity in elderly coronary patients: the SENIOR-PLATELET study. Eur. Heart J. 2012; 33: 1241-1249 Crossref PubMed Scopus (126) Google Scholar ]. By far, the contribution of CYP2C19 LOF alleles to clopidogrel responsiveness in the elderly, and its implication for personalized antiplatelet treatment in this population remain unknown. In the present study, we aimed to evaluate the effects of CYP2C19 LOF alleles on platelet reactivity and clinical outcomes in elderly ACS patients treated by clopidogrel.

The effect of acenocoumarol on the antiplatelet effect of clopidogrel.

Patients exhibiting high on-clopidogrel platelet reactivity (HPR) are at an increased risk of atherothrombotic events following percutaneous coronary interventions (PCI). The use of concomitant medication which is metabolised by the hepatic cytochrome P450 system, such as phenprocoumon, is associated with HPR. We assessed the level of platelet reactivity on clopidogrel in patients who received concomitant treatment with acenocoumarol (another coumarin derivative). Patients scheduled for PCI were included in a prospective, single centre, observational registry. Patients who were adequately pre-treated with clopidogrel were eligible for this analysis, which included 1,582 patients, of whom 104 patients (6.6%) received concomitant acenocoumarol treatment. Platelet reactivity, as measured with the VerifyNow P2Y12 assay and expressed in P2Y12 Reaction Units (PRU), was significantly higher in patients on concomitant acenocoumarol treatment (mean PRU 229 ± 88 vs 187 ± 95; p < 0.001). In patients with concomitant acenocoumarol use, the proportion of patients with HPR was higher, defined as PRU > 208 (57.7% vs 41.1%; p=0.001) and PRU ≥ 236 (49.0% vs 31.4%; p< 0.001). In multivariable analysis, concomitant acenocoumarol use was independently associated with a higher PRU and the occurrence of HPR defined as PRU ≥ 236 (OR 2.00, [1.07-3.79]), but not with HPR defined as PRU > 208 (OR 1.37, [0.74-2.54]). PRU also was significantly increased after 1:1 propensity matching (+28.2; p < 0.001). As this was an observational study, confounding by indication cannot be excluded, although multivariable analyses and propensity matching were performed. The impact of the findings from this hypothesis-generating study on clinical outcome requires further investigation.

Antiplatelet Effect of Clopidogrel Can Be Reduced by Calcium-Channel Blockers

PurposeClopidogrel is metabolized by the hepatic cytochrome P450 (CYP) system into its active thiol metabolite. CYP3A4 is involved in the metabolism of both clopidogrel and dihydropyridine calcium channel blockers (CCBs). A few reports have suggested an inhibitory interaction between CCBs and clopidogrel. Accordingly, the aim of this study was to determine the effect of CCBs on the antiplatelet activity of clopidogrel by serial P2Y12 reaction unit (PRU) measurements.Materials and MethodsWe assessed changes in antiplatelet activity in patients receiving both clopidogrel and CCBs for at least 2 months prior to enrollment in the study. The antiplatelet activity of clopidogrel was measured by VerifyNow P2Y12 assay in the same patient while medicated with CCBs and at 8 weeks after discontinuation of CCBs. After discontinuation of the CCBs, angiotensin receptor blockers were newly administered to the patients or dosed up for control of blood pressure.ResultsThirty patients finished this study. PRU significantly decreased after discontinuation of CCBs (238.1±74.1 vs. 215.0±69.3; p=0.001). Of the 11 patients with high post-treatment platelet reactivity to clopidogrel (PRU≥275), PRU decreased in nine patients, decreasing below the cut-off value in seven of these nine patients after 8 weeks. Decrease in PRU was not related to CYP2C19 genotype.ConclusionCCBs inhibit the antiplatelet activity of clopidogrel.

On the possible interaction between vaccines and drugs

Dear Sirs, Reduction in the hepatic cytochrome P450 system activity has been described after a vaccination in previous studies [1, 2]. While the mechanism behind such reduction was explained as the consequence of the activity of inflammatory cytokines on the mRNA level of hepatic cytochromes [3], it is unclear what effect this interaction may have in the clinical practice. To date, only few reports describe significant changes in drug pharmacokinetics after the administration of a vaccine [4, 5], and small cohort studies reported contrasting results in patients treated with drugs that may be influenced by this interaction [6, 7, 10–12]. Moreover, it is unclear how the effects of vaccines on hepatic cytochrome P450 system activity affect patients who present risk factors such as age or genetic predisposition [1, 2]. To explore this issue further, we used the Vaccine Adverse Event Reporting System (VAERS) database, which collects information about adverse events following the administration of vaccines and is useful to detect rare vaccine-related adverse events [8]. We carried out a search of all reports consistent with a vaccine–drug interaction resulting in an adverse drug reaction, in a detectable increase of drug serum level, or in a change of drug-related biomarkers such as the International Normalized Ratio (INR). As the patients were treated with more than a single drug in many of the cases, we considered only those cases in which there was no mention of recent therapy variation, or there was an explicit statement about the absence of variations. As highlighted in Table 1, we retrieved and validated 28 reports. Among these, 12 were related to an increase of INR, and ten described an increase of serum level of phenytoin, carbamazepine and theophylline (Table 1). The remaining six cases described an adverse drug reaction attributed to an interaction between the vaccine and the drugs (Table 1). As expected, considering previous observations [1], we found that most of the cases occurred in elderly patients and within the first weeks after vaccine administration. Aitken et al. recently observed that human CYP2C8, 2C9, 2C18, 2C19, 2B6, and 3A4 mRNA expression is downregulated by inflammatory cytokines [3], which are also released as result of a vaccination [1, 2]. As one or more of these hepatic cytochromes metabolizes phenytoin, theophylline and carbamazepine, a reduction in their expression due to vaccination may explain the increased level of these drugs that we observed after vaccination. In agreement, other studies showed an increase in phenytoin serum level after vaccination with pertussis vaccine [10] and successive studies confirmed this finding in other drugs such as theophylline [11, 12]. The increased INR we observed with warfarin may also be explained by the vaccination. Warfarin is metabolized primarily by CYP2C9, and a reduction in the activity of this hepatic cytochrome may result in an increase of INR [9]. The reduced activity of this enzyme due to genetic polymorphisms [9], as well as the presence of other variants that may affect the cytokines response to vaccination, may create a subgroup of patients at higher risk for this interaction than the ones observed in our analysis. Paolo Pellegrino and Carla Carnovale contributed equally to this work.

P.5.c.001 An experimental study of the effects of rivastigmine and memantine alone and in combination on learning and memory in rats

Rivastigmine (ENA 713, or carbamoylatine) is an acetylcholinesterase (AChE) inhibitor with brain-region selectivity and a long duration of action. Both preclinical studies and studies in human volunteers have shown that rivastigmine induces substantially greater inhibition of AChE in the central nervous system (CNS) compartment than in the periphery (40% inhibition of central AChE compared with 10% inhibition of plasma butylcholinesterase in healthy volunteers). Moreover, rivastigmine preferentially inhibits the G1 enzymatic form of AChE, which predominates in the brains of patients with Alzheimer's disease (AD). Evidence from animal studies also suggests that rivastigmine is a more potent inhibitor of AChE in the cortex and hippocampus, the brain regions most affected by AD. Absorption of rivastigmine is rapid and almost complete (>96% of the administered dose). Extensive, saturable first-pass metabolism, however, leads to bioavailability of approximately 35% of the administered dose and nonlinear pharmacokinetics. The principal metabolite of rivastigmine has at least 10-fold lower activity against AChE compared with the parent drug. Rivastigmine is completely metabolized; the major route of elimination of the metabolites is renal. Although patients with AD demonstrate 30% to 50% higher plasma concentrations of rivastigmine and its principal metabolite than do healthy elderly patients, there is no evidence of drug accumulation, which is consistent with rivastigmine's short pharmacokinetic half-life. Distribution of rivastigmine into the CNS is extensive, and inhibition of AChE in the cerebrospinal fluid is detectable 1.2 hours after oral dosing in both healthy volunteers and patients with AD. Peak activity is reached somewhat more slowly in AD patients than in healthy subjects, and the inhibitory effects have a longer duration (6.0 vs 2.4 hours and 12.0 vs 8.5 hours, respectively). Rivastigmine is inactivated during the process of interacting with and inhibiting AChE, and, in contrast to other AChE inhibitors, the hepatic cytochrome P-450 (CYP-450) system is not involved in the metabolism of rivastigmine. This reduces its propensity to interact with drugs metabolized by specific CYP-450 isoenzymes. Consistent with rivastigmine's pharmacokinetic and pharmacodynamic profiles, Phase II and III trials have demonstrated that the drug is a well-tolerated and effective treatment for AD.

Effect of age on hepatic cytochrome P450 of Ross 708 broiler chickens

Age has significant impact on hepatic cytochrome P450 (CYP450) systems in animals. Ross 708 broiler chicken is a breed of chicken with fast growth characteristics. Cytochrome P450 in the livers of Ross 708 broiler chicken of different ages has been investigated. The birds were raised under standard husbandry conditions. A certain number of chickens was randomly sampled weekly for liver collection from d 1 to 56 posthatch. The chicken body and liver weights were recorded. The chicken livers were processed for liver microsomes though a multiple-step procedure at low temperature. Total CYP450 content in chicken liver homogenates and liver microsomes was measured using a UV/visible spectroscopic method. The enzymatic activities of CYP450 in the chicken liver microsomes were determined through incubation of CYP450 isoform substrates followed by measurement of formation of their metabolites. The chicken showed an opposite age pattern in hepatic CYP450 content and activities compared with most mammals. The hepatic CYP450 content and activities of chicken at d 1 posthatch were higher than at other ages. The total hepatic CYP450 content in chickens at d 1 posthatch was more than twice the average hepatic value of the chickens at d 7 to 28. This high CYP450 fell quickly in the first week posthatch and slightly rose from d 28 to 56. Hepatic CYP450 activities of CYP1A, 3A, 2C, 2D, and 2H were much higher in the chicken at d 1 posthatch. The differences of these enzymatic activities between d 1 and other ages of chicken were CYP450 isoform dependent. This result suggests that embryonic development of chicken livers has a significant impact on the age profile of hepatic CYP450 content and activities of posthatch chickens.

Differential induction of cytochrome P450 isoforms and peroxisomal proliferation by cyfluthrin in male Wistar rats

Cyfluthrin effects on in vivo drug metabolizing enzymes were evaluated using the oxidative substrate antipyrine. Antipyrine pharmacokinetics in plasma and urinary excretion of its major metabolites with and without cyfluthrin oral treatment (20mg/kg/day for 6 days) were investigated in rats. Cyfluthrin increased the apparent intrinsic clearance and decreased the antipyrine half-life at β phase. Cyfluthrin also increased the clearance of the antipyrine metabolites, norantipyrine, 4-hydroxyantipyrine and 3-hydroxymethylantipyrine and the formation rate constants for each of the three metabolites measured in urine. These results suggest that cyfluthrin affects hepatic cytochrome P450 (CYP) system. In order to confirm, a second experiment was carried out. We evaluated the effects of repeated exposure to cyfluthrin on hepatic and renal CYP2E, CYP1A and CYP4A subfamilies and peroxisomal proliferation in rats following oral administration (10 and 20mg/kg/day for 6 days). At the highest dose, cyfluthrin increased renal and hepatic O-deethylation of ethoxyresorufin and O-demethylation of methoxyresorufin, metabolism mediated by the CYP1A subfamily. Liver and kidney were susceptible to cyfluthrin-dependent induction of 12- and 11-hydroxylation of lauric acid, suggesting CYP4A subfamily induction. Also cyfluthrin increased the β-oxidation of palmitoyl-coenzyme A and carnitine acetyltransferase activity, supporting cyfluthrin as a peroxisome proliferator. In conclusion, the demonstration that cyfluthrin induced hepatic CYP1A, CYP4A subfamilies and peroxisomal proliferation raises the possibility of cyfluthrin could produce changes in oxidative stress.

In vitro evaluation of the effects of 4-aminopyridine on cytochrome P450 enzymes

Background:Dalfampridine extended release tablets (dalfampridine-ER, known as prolonged-, modified, or sustained-release fampridine tablets in some countries) are approved for the improvement of walking in patients with multiple sclerosis (MS). Dalfampridine-ER is an extended release formulation of 4-aminopyridine (4-AP). Dalfampridine-ER is incorporated into MS management strategies that may include disease-modifying and symptomatic therapies. Since several symptomatic therapies are partially or fully metabolized by enzymes of the hepatic cytochrome P450 system (CYP450) it is important to evaluate drug–drug interactions through potential effects of dalfampridine-ER on CYP450.Methods:The ability of 4-AP to inhibit CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4/5 in a direct and time-dependent manner was evaluated using pooled human liver microsomes. 4-AP concentrations were 0.03, 0.1, 0.3, 1, 3, 10, and 30 μM, representing 0.1–100-times the average plasma 4-AP concentration (30 ng/mL; 0.32 μM) at therapeutic dosing; the concentration inhibiting 50% of each enzyme activity (IC50) was determined. The ability of 4-AP (0.025, 0.25, 2.5, and 25 μM) to induce the expression of CYP1A2, 2B6, 2C9, 2C19, 2E1, and 3A4/5 enzymes was evaluated using primary cultures of freshly isolated human hepatocytes from non-transplantable livers. The enzyme-inducing effects of 4-AP were compared with the prototypical inducers. Metabolites were assayed using high-performance liquid chromatography-tandem mass spectrometry techniques. All inhibition and induction assays included positive controls.Results:4-AP did not directly inhibit CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, or CYP3A4/5, but at a concentration of 30 μM, CYP2E1 was inhibited by 12%, resulting in an estimated IC50 value of 125 μM. None of the enzymes demonstrated time-dependent inhibition by 4-AP. There was little or no effect by 4-AP on enzyme induction, with enzyme activities approximately equivalent to vehicle control. A main limitation was the inability to estimate effectiveness of 4-AP relative to prototypical CYP450 inducers.Conclusion:The likelihood of drug–drug interactions is remote in patients with MS who may be taking dalfampridine-ER concomitantly with medications that are metabolized by CYP450 pathways.

Evidence That Cytochromeb5and Cytochromeb5Reductase Can Act as Sole Electron Donors to the Hepatic Cytochrome P450 System

We previously described the development of genetic models to study the in vivo functions of the hepatic cytochrome P450 (P450) system, through the hepatic deletion of either cytochrome P450 oxidoreductase [POR; HRN (hepatic reductase null) line] or cytochrome b(5) [HBN (hepatic cytochrome b(5) null) line]. However, HRN mice still exhibit low levels of mono-oxygenase activity in spite of the absence of detectable reductase protein. To investigate whether this is because cytochrome b(5) and cytochrome b(5) reductase can act as the sole electron donor to the P450 system, we crossed HRN with HBN mice to generate a line lacking hepatic expression of both electron donors (HBRN). HBRN mice exhibited exacerbation of the phenotypic characteristics of the HRN line: liver enlargement, hepatosteatosis, and increased expression of certain P450s. Also, drug metabolizing activities in vitro were further reduced relative to the HRN model, in some cases to undetectable levels. Pharmacokinetic studies in vivo demonstrated that midazolam half-life, C(max), and area under the concentration-time curve were increased, and clearance was decreased, to a greater extent in the HBRN line than in either the HBN or HRN model. Microsomal incubations using NADPH concentrations below the apparent K(m) of cytochrome b(5) reductase, but well above that for POR, led to the virtual elimination of 7-benzyloxyquinoline turnover in HRN samples. These data provide strong evidence that cytochrome b(5)/cytochrome b(5) reductase can act as a sole electron donor to the P450 system in vitro and in vivo.

Exposure to Potentially Dangerous Drug-Drug Interactions Involving Antipsychotics

Antipsychotic drug therapy is the cornerstone of treatment of persons with schizophrenia. Because most antipsychotics are metabolized by the hepatic cytochrome P450 system, concomitant use of an antipsychotic and medications that are competitively metabolized by the same system may cause a potentially harmful drug-drug interaction. This study used a large state's Medicaid claims database to examine the proportion of patients exposed to such interactions and the risk factors associated with exposure. Claims from January 2000 through December 2003 for adult patients with a diagnosis of schizophrenia and at least one prescription for an antipsychotic (N=27,909) were examined for pairs of medications identified as potentially causing moderate or severe adverse drug effects. Logistic regression models were estimated to determine potential risk factors associated with exposure to the interaction pairs. A total of 6,417 (23%) patients were exposed to 14,213 potentially harmful interactions; 4,725 patients had at least one exposure from the same pharmacy, and 4,032 patients were exposed by the same physician. The greatest number of exposures (N=1,353) to potentially harmful combinations involved olanzapine and haloperidol. Patients prescribed risperidone were most likely to be exposed to an interaction (13.1%), followed by patients prescribed olanzapine (10.3%), quetiapine (3.3%), and clozapine (3.2%). A higher risk of exposure was associated with being female (odds ratio [OR]=.94), being white (OR=1.43), having depression (OR=1.21), or having impulse-control disorder (OR=1.98). Interventions by physicians and pharmacies to reduce the prescribing and dispensing of potentially harmful pairs of medications to patients with schizophrenia are recommended.

Antioxidant activity of new aramide nanoparticles containing redox-active N-phthaloyl valine moieties in the hepatic cytochrome P450 system in male rats.

We report the synthesis of aramide nanoparticles containing a chiral N-phthaloyl valine moiety and their antioxidant activities on hepatic contents of cytochrome P450, amidopyrene N-demethylase, aniline-4-hyroxylase and induced the hepatic content of cytochrome b5 and nicotinamide adenine dinucleotide phosphate (NADPH) cytochrome C-reductase. Polymers were obtained as well-separated spherical nanoparticles while highly aggregated particles via H-bonding organization of the aramide-containing pyridine led to a thin layer formation. The effects of the nanoparticles and CCl4 on enzyme activities and thiobarbituric acid reactive substances (TBARS) levels of male rat liver were studied. Pretreatments of rats with the polyamides prior to the administration of CCl4 decreased the hepatic content of the tested enzymes. Doses reduced the toxic effects exerted by (•CCl3) upon the liver through inhibition of the cytochrome P450 system. Inhibition of such metabolizing enzymes could reduce the carcinogenic effects of chemical carcinogens.

CYP2C19 Genetic Testing Should Not Be Done in All Patients Treated With Clopidogrel Who Are Undergoing Percutaneous Coronary Intervention

Clopidogrel when added to aspirin reduces major vascular events in patients undergoing percutaneous coronary intervention (PCI).1 Recent reports have suggested that common genetic variants involving hepatic cytochrome P450 system enzymes that convert clopidogrel to its active metabolite are associated with an increased risk of cardiovascular events. Specifically, patients who are carriers of 1 or more loss-of-function CYP2C19 alleles (including the *2 and *3 alleles) have reduced conversion of clopidogrel to its active metabolite, decreased platelet inhibition, and an increased risk of myocardial infarction, death, and stent thrombosis compared with noncarriers. Based on these findings and on related pharmacokinetic and pharmacodynamic data (NCT01123824), the United States Food and Drug Administration (FDA) has issued a “black box” warning of reduced effectiveness of clopidogrel in patients who are carriers of 2 loss-of-function alleles (so-called poor metabolizers) and has suggested that affected individuals receive a higher dose of clopidogrel or an alternative antiplatelet agent. This warning has led some investigators to conclude that all patients undergoing PCI with planned clopidogrel therapy should undergo CYP2C19 genetic testing. Response by Sibbing, Bernlochner, and Kastrati on p 521 In this report, we critically review the evidence for routine CYP2C19 testing in patients undergoing PCI according to established criteria for the implementation of a screening test in clinical practice. ### Summary of the Evidence Linking CYP2C129 Loss-of-Function Alleles to Clopidogrel Response and Cardiovascular Risk Clopidogrel is a prodrug that must undergo 2-step hepatic metabolism by enzymes of the CYP system to form the active moiety that inhibits the platelet P2Y12 receptor.2–4 Common loss-of-function variants involving the CYP2C19 gene have been conclusively demonstrated to influence clopidogrel active metabolite levels and levels of platelet inhibition5–7 (Figure 1), and an increasing number of clinical reports link loss-of-function alleles with adverse clinical outcomes.7–12 Figure 1. Hypothesized causal chain leading from loss-of-function (LOF) allele carriage to increased ischemic events …

Lack of impact of calcium-channel blockers on the pharmacodynamic effect and the clinical efficacy of clopidogrel after drug-eluting stenting

Clopidogrel is a prodrug that is metabolized to its active metabolite by the hepatic cytochrome P450 system. Calcium-channel blockers (CCBs) are metabolized by the same pathway and may therefore attenuate the antiplatelet effect of clopidogrel. The aim of this study was to assess the impact of CCB therapy on the pharmacodynamic effect and the clinical efficacy of clopidogrel after drug-eluting stent placement. A total of 1,608 consecutive patients were previously enrolled in a study that aimed to assess the relation between platelet reactivity and outcomes after coronary stenting. Here, this cohort was analyzed according to concomitant CCB therapy at admission. The primary pharmacodynamic end point was adenosine diphosphate-induced platelet aggregation (in AU · min) with multiple electrode platelet aggregometry after loading with 600 mg clopidogrel. The primary clinical end point was combination of death or definite stent thrombosis (ST) at 30 days. Secondary end points included definite ST alone, myocardial infarction, stroke, and death. Two hundred thirty-two patients (14.4%) were on CCBs on admission. Compared with patients with CCB medication, patients without CCB medication showed no significant difference in median [interquartile range] platelet aggregation values (232 [142-365] vs 223 [141-368] AU · min, P = .53). There was also no significant difference regarding the clinical end point of death or ST (2 [0.9%] vs 16 [1.2%], odds ratio 0.74, 95% CI 0.17-3.2, P = .69) between both groups. In our population, concomitant CCB therapy did not alter clopidogrel-mediated platelet aggregation and did not have a measurable impact on ST and mortality after coronary stenting.

Carbamazepine coadministration with an oral contraceptive: Effects on steroid pharmacokinetics, ovulation, and bleeding

Antiepileptic drugs (AEDs) are widely used in reproductive-age women. The AED carbamazepine (CBZ) induces the hepatic cytochrome P450 system, thereby accelerating hormone metabolism. We sought to assess the pharmacodynamic effects of CBZ on breakthrough bleeding and ovulation during oral contraceptive (OC) use. A double-blind, randomized, crossover study of healthy women ages 18-35 years. Participants took an OC containing 20 μg ethinyl estradiol (EE) and 100 μg levonorgestrel (LNG) for 4 months. Concurrently, participants took 600 mg CBZ or a matching placebo for 2 months each, administered in random order. During the second month of CBZ or placebo, we measured EE and LNG levels 12 times over 24 h, ovarian follicular diameters with eight biweekly vaginal ultrasounds, weekly progesterone levels, and bleeding (using a diary). We enrolled 25 women; 10 completed the study. Five women discontinued because of reversible CBZ side effects. Mean area under the curve (AUC) measurements were lower during CBZ use compared to placebo for EE (1,778 vs. 986 pg*h/ml, p < 0.001) and LNG (24.8 vs. 13.8 pg*h/ml, p = 0.04). Ovulation occurred in 5 of 10 CBZ cycles compared to 1 of 10 placebo cycles (p = 0.06). Three or more days of breakthrough bleeding occurred during 8 of the 10 CBZ cycles compared to 2 of the 10 placebo cycles (p = 0.07). A commonly used dose of CBZ decreased levels of contraceptive steroids, increased breakthrough bleeding, and permitted ovulation during use of a low-dose OC. Women treated with CBZ are not adequately protected from pregnancy by low-dose OCs.