CYP2D6 Substrates Research Articles

Impact of Tetrahydropalmatine on the Pharmacokinetics of Probe Drugs for CYP1A2, 2D6 and 3A Isoenzymes in Beagle Dogs.

Tetrahydropalmatine (Tet) exhibit multiple pharmacological activities and is used frequently by clinical practitioners. In this study, we evaluate the in vivo effects of single and repeated oral Tet administrations on CYP1A2, 2D6 and 3A activities in six beagle dogs in a randomized, controlled, open-label, crossover study. A cocktail approach, with dosages of the probe drugs caffeine (3.0 mg/kg), metoprolol (2.33 mg/kg) and midazolam (0.45 mg/kg), was used to measure cytochrome P450 (CYP) metabolic activities. The cocktail was administered orally as a single dose (12 mg/kg) 1 day prior to and 4 days after repeated oral Tet administrations (12 mg/kg three times daily). The probe drugs and their metabolites in plasma were quantified simultaneously by a validated HPLC technique, and non-compartmental parameters were used to evaluate metabolic variables for assessment of CYP inhibition or induction. Tet had no or minor impact on the pharmacokinetics and metabolism of the probe drugs caffeine and metoprolol, CYP1A2 and CYP2D6 substrates, respectively. However, Tet increased AUC0-24 h and decreased AUCratio(0-24 h) (1-hydroxymidazolam/midazolam ratio) for midazolam statistically significant, both in single or multiple dosing of Tet, with up to 39 or 57% increase for AUC0-24 h and 29% or 22 decrease for AUCratio(0-24 h), respectively, in line with previous in vitro findings for its CYP3A4 inhibition. The extensive use of Tet and herbal medicines containing Tet makes Tet a candidate for further evaluation of CYP3A-mediated herb-drug interactions. Copyright © 2016 John Wiley & Sons, Ltd.

Treatment of metastatic castration-resistant prostate cancer : Drug interaction potentials of abiraterone acetate and enzalutamide

With an ageing population and associated increasing multimorbidity and polypharmacy, the potential for drug-drug interactions (DDIs) becomes increasingly important. In general, DDIs are more likely to be clinically significant for drugs with anarrow therapeutic index, necessitating dosage adjustments or replacement of co-administered drugs. Many DDIs are aresult of pharmacokinetic interactions of the cytochrome P450 enzymes. In particular, the CYP3A4 isoenzyme is involved in the metabolism of about 50 % of currently used drugs. Accordingly, many commonly used drugs in patients with prostate cancer are substrates of Cyp3A4. Hence enzalutamide, astrong Cyp3A4 inductor, has the potential to substantially decrease plasma concentrations and the effects of many co-medications in this patient population, whereas abiraterone acetate, astrong Cyp2D6 inhibitor, is less of aconcern with respect to Cyp450 inhibition, since the Cyp2D6-mediated metabolism is much smaller and Cyp2D6 substrates are prescribed to alesser extent in patients with prostate cancer.

Role of Pharmacogenetics in Improving the Safety of Psychiatric Care by Predicting the Potential Risks of Mania in CYP2D6 Poor Metabolizers Diagnosed With Bipolar Disorder

One of the main concerns in psychiatric care is safety related to drug management. Pharmacogenetics provides an important tool to assess causes that may have contributed the adverse events during psychiatric therapy. This study illustrates the potential of pharmacogenetics to identify those patients for which pharmacogenetic-guided therapy could be appropriate. It aimed to investigate CYP2D6 genotype in our psychiatric population to assess the value of introducing pharmacogenetics as a primary improvement for predicting side effects.A broad series of 224 psychiatric patients comprising psychotic disorders, depressive disturbances, bipolar disorders, and anxiety disorders was included. The patients were genotyped with the AmpliChip CYP450 Test to analyzing 33 allelic variants of the CYP2D6 gene.All bipolar patients with poor metabolizer status showed maniac switching when CYP2D6 substrates such as selective serotonin reuptake inhibitors were prescribed. No specific patterns were identified for adverse events for other disorders.We propose to utilize pharmacogenetic testing as an intervention to aid in the identification of patients who are at risk of developing affective switching in bipolar disorder treated with selective serotonin reuptake inhibitors, CYP2D6 substrates, and inhibitors.

JSH Guidelines for the Management of Hepatitis C Virus Infection: A 2016 update for genotype 1 and 2.

JSH Guidelines for the Management of Hepatitis C Virus Infection: A 2016 update for genotype 1 and 2.

Worsening Psychosis in an Adolescent Female Chronically Abusing Dextromethorphan when Benztropine was added to the Treatment Regimen

Recently, there has been an increase in the use of overthe- counter (OTC) medications as recreational drugs of abuse in adolescents. It is important to recognize that some of these medications, such as Dextromethorphan (DXM) at doses beyond recommended, have detrimental effects to mental health. The symptoms DXM precipitates appear as a mental illness in acute exacerbation rather than intoxication and/or overdose. Having sufficient knowledge on how to treat adequately those patients who abuse OTCs such as DXM is of utmost importance in determining an assertive treatment intended to subside and recuperate successfully. Using the example of DXM, which is a substrate of CYP2D6 and metabolized by the enzyme, we must have awareness that many other medications are affected by this route as well. This case illustrates how Benztropine precipitated symptoms of psychosis and euphoric mood on a 14 year old Hispanic female, which was assumed to be effectively responding with Risperidone treatment. We theorize that chronic DXM abuse evoked an induction of the CYP2D6, which ultimately hindered the antipsychotic treatment efficacy. Risperidone dose was increased whereas Benztropine discontinued on the subsequent day which corresponded to the rapid subside of her psychosis. We recommend caution when adding Benztropine to antipsychotic treatment for a patient having psychotic symptoms precipitated by chronic DXM abuse, as well as considering the use of neuroleptics that are minimally or not metabolized by the CYP2D6 P450 metabolic pathway.

ADME studies and preliminary safety pharmacology of LDT5, a lead compound for the treatment of benign prostatic hyperplasia.

This study aimed to estimate the absorption, distribution, metabolism and excretion (ADME) properties and safety of LDT5, a lead compound for oral treatment of benign prostatic hyperplasia that has previously been characterized as a multi-target antagonist of α1A-, α1D-adrenoceptors and 5-HT1A receptors. The preclinical characterization of this compound comprised the evaluation of its in vitro properties, including plasma, microsomal and hepatocytes stability, cytochrome P450 metabolism and inhibition, plasma protein binding, and permeability using MDCK-MDR1 cells. De-risking and preliminary safety pharmacology assays were performed through screening of 44 off-target receptors and in vivo tests in mice (rota-rod and single dose toxicity). LDT5 is stable in rat and human plasma, human liver microsomes and hepatocytes, but unstable in rat liver microsomes and hepatocytes (half-life of 11 min). LDT5 is highly permeable across the MDCK-MDR1 monolayer (Papp ∼32×10-6 cm/s), indicating good intestinal absorption and putative brain penetration. LDT5 is not extensively protein-bound and is a substrate of human CYP2D6 and CYP2C19 but not of CYP3A4 (half-life >60 min), and did not significantly influence the activities of any of the human cytochrome P450 isoforms screened. LDT5 was considered safe albeit new studies are necessary to rule out putative central adverse effects through D2, 5-HT1A and 5-HT2B receptors, after chronic use. This work highlights the drug-likeness properties of LDT5 and supports its further preclinical development.

1529 Low risk of drug interactions when rolapitant is coadministered with CYP2D6 or BCRP substrates: Integrated safety results

1529 Low risk of drug interactions when rolapitant is coadministered with CYP2D6 or BCRP substrates: Integrated safety results

Asunaprevir: A Review of Preclinical and Clinical Pharmacokinetics and Drug-Drug Interactions.

Asunaprevir is a tripeptidic acylsulfonamide inhibitor of the hepatitis C virus (HCV) NS3/4A protease. Asunaprevir undergoes rapid absorption, with a time to reach maximum plasma concentration (T max) of 2-4h and an elimination half-life (t ½) of ≈15-20h observed in single-ascending dose studies. Steady state was achieved by day 7 in multiple-ascending dose studies. The large food effect observed with earlier formulations was mitigated by the soft-gel capsule. Asunaprevir demonstrates high apparent oral clearance and minimal renal elimination, and is eliminated primarily via cytochrome P450 (CYP) 3A4-mediated hepatic oxidative metabolism and faecal excretion. Highly preferential distribution of asunaprevir to the liver occurs via organic anion-transporting polypeptide (OATP)-mediated transport and results in low plasma concentrations. The condition of the liver affects disposition, as higher asunaprevir plasma exposures are observed in patients infected with HCV and/or hepatic impairment. Japanese patients also have higher exposure relative to North American/European patients, but comparable safety at the registrational dose. Asunaprevir has a low potential to perpetrate drug-drug interactions via CYP3A4, P-glycoprotein and OATP, but is a moderate CYP2D6 inhibitor; concomitant drugs that are substrates of CYP2D6 or P-glycoprotein and have a narrow therapeutic index should be used with care. Asunaprevir plasma exposure is strongly affected by inhibitors of OATP transport. No clinically significant interactions were observed between asunaprevir and daclatasvir or daclatasvir/beclabuvir. Asunaprevir has a complex pharmacokinetic profile and forms part of potent and well-tolerated all-oral regimens for the treatment of chronic HCV infection.

Screening for endogenous substrates reveals that CYP2D6 is a 5-methoxyindolethylamine O-demethylase.

The objective of this investigation was to screen for potential endogenous substrates for CYP2D6. Using recombinant CYP2D6, together with hepatic microsomes from CYP2D6-transgenic mice, human liver microsomes, and a specific anti-CYP2D6 monoclonal antibody, it was ascertained that CYP2D6 does not significantly metabolize the endogenous phenylethylamines 2-phenylethylamine, octopamine, synephrine, 3-methoxy-p-tyramine, 4-methoxy-m-tyramine, metanephrine, and normetanephrine, nor the indolethylamines tryptamine, serotonin, 6-methoxytryptamine, and melatonin, nor the beta-carbolines harman, norharman and tryptoline. However, the indolethylamines 5-methoxy-N,N-dimethyltryptamine (5-MDMT) and pinoline (6-methoxy-1,2,3,4-tetrahydro-beta-carboline) showed relatively high affinity for CYP2D6 in a spectral binding assay (K(s) 28 +/- 5, and 0.5 +/- 0.3 microm (mean +/- SEM), respectively) and were O-demethylated only by CYP2D6 in a panel of 15 recombinant common human P450s. Pinoline and 5-MDMT O-demethylase activities were 35- and 11-fold greater in liver microsomes from CYP2D6-humanized mice, respectively, than those in liver microsomes from control mice. Moreover, the increased activities were completely inhibited by an anti-CYP2D6 monoclonal antibody. Kinetic analysis with recombinant CYP2D6 gave K(m) and k(cat) values for 5-MDMT and pinoline O-demethylations of 12 +/- 1 microm and 65 +/- 1 min(-1) and 1.8 +/- 0.3 microm and 26 +/- 1 min(-1), respectively. These two substrates can be added to 5-methoxytryptamine, which we have recently reported to be an endogenous CYP2D6 substrate. CYP2D6 is therefore a relatively highly specific, high-affinity, high-capacity 5-methoxyindolethylamine O-demethylase. Polymorphic cytochrome CYP2D6 may therefore exert an influence on mood and behavior by the O-demethylation of these 5-methoxyindolethylamines found in the brain and pineal gland. These processes may also impact on mental and neurological health. The findings may open new vistas for the determination of CYP2D6 phenotype.

Differential cytochrome P450 2D metabolism alters tafenoquine pharmacokinetics.

Cytochrome P450 (CYP) 2D metabolism is required for the liver-stage antimalarial efficacy of the 8-aminoquinoline molecule tafenoquine in mice. This could be problematic for Plasmodium vivax radical cure, as the human CYP 2D ortholog (2D6) is highly polymorphic. Diminished CYP 2D6 enzyme activity, as in the poor-metabolizer phenotype, could compromise radical curative efficacy in humans. Despite the importance of CYP 2D metabolism for tafenoquine liver-stage efficacy, the exact role that CYP 2D metabolism plays in the metabolism and pharmacokinetics of tafenoquine and other 8-aminoquinoline molecules has not been extensively studied. In this study, a series of tafenoquine pharmacokinetic experiments were conducted in mice with different CYP 2D metabolism statuses, including wild-type (WT) (reflecting extensive metabolizers for CYP 2D6 substrates) and CYPmouse 2D knockout (KO) (reflecting poor metabolizers for CYP 2D6 substrates) mice. Plasma and liver pharmacokinetic profiles from a single 20-mg/kg of body weight dose of tafenoquine differed between the strains; however, the differences were less striking than previous results obtained for primaquine in the same model. Additionally, the presence of a 5,6-ortho-quinone tafenoquine metabolite was examined in both mouse strains. The 5,6-ortho-quinone species of tafenoquine was observed, and concentrations of the metabolite were highest in the WT extensive-metabolizer phenotype. Altogether, this study indicates that CYP 2D metabolism in mice affects tafenoquine pharmacokinetics and could have implications for human tafenoquine pharmacokinetics in polymorphic CYP 2D6 human populations.

How the Probability and Potential Clinical Significance of Pharmacokinetically Mediated Drug-Drug Interactions Are Assessed in Drug Development: Desvenlafaxine as an Example.

The avoidance of adverse drug-drug interactions (DDIs) is a high priority in terms of both the US Food and Drug Administration (FDA) and the individual prescriber. With this perspective in mind, this article illustrates the process for assessing the risk of a drug (example here being desvenlafaxine) causing or being the victim of DDIs, in accordance with FDA guidance. DDI studies for the serotonin-norepinephrine reuptake inhibitor desvenlafaxine conducted by the sponsor and published since 2009 are used as examples of the systematic way that the FDA requires drug developers to assess whether their new drug is either capable of causing clinically meaningful DDIs or being the victim of such DDIs. In total, 8 open-label studies tested the effects of steady-state treatment with desvenlafaxine (50-400 mg/d) on the pharmacokinetics of cytochrome (CYP) 2D6 and/or CYP 3A4 substrate drugs, or the effect of CYP 3A4 inhibition on desvenlafaxine pharmacokinetics. The potential for DDIs mediated by the P-glycoprotein (P-gp) transporter was assessed in in vitro studies using Caco-2 monolayers. Changes in area under the plasma concentration-time curve (AUC; CYP studies) and efflux (P-gp studies) were reviewed for potential DDIs in accordance with FDA criteria. Desvenlafaxine coadministration had minimal effect on CYP 2D6 and/or 3A4 substrates per FDA criteria. Changes in AUC indicated either no interaction (90% confidence intervals for the ratio of AUC geometric least-squares means [GM] within 80%-125%) or weak inhibition (AUC GM ratio 125% to < 200%). Coadministration with ketoconazole resulted in a weak interaction with desvenlafaxine (AUC GM ratio of 143%). Desvenlafaxine was not a substrate (efflux ratio < 2) or inhibitor (50% inhibitory drug concentration values > 250 μM) of P-gp. A 2-step process based on FDA guidance can be used first to determine whether a pharmacokinetically mediated interaction occurs and then to assess the potential clinical significance of the DDI. In the case of the drug tested in this series of studies, the potential for clinically meaningful DDIs mediated by CYP 2D6, CYP 3A4, or P-gp was found to be low.

Inhibitory Mechanisms of Human CYPs by Three Alkaloids Isolated from Traditional Chinese Herbs.

The three purified herbal compounds tetrahydropalmatine (Tet), neferine and berberine (Ber) were explored in vitro for basic inhibition mechanisms towards recombinant human CYP1A2, CYP2D6 and CYP3A4 metabolic activities. Phenacetin, dextromethorphan and testosterone, respectively, were used as CYP1A2, CYP2D6 and CYP3A4 substrates, and their metabolites were determined by validated HPLC methodologies. Positive inhibition controls were used. Mechanism-based (irreversible) inhibition was assessed by time-dependent and nicotinamide adenine dinucleotide phosphate-dependent and reversible inhibition by Lineweaver-Burk plot assessments. Inhibition mechanisms were also assessed by computerized interaction prediction by using the Discovery Studio CDOCKER software (Accelrys, San Diego, CA, USA). Tetrahydropalmatine showed a mechanism-based inhibition of both CYP1A2 and CYP2D6, and Ber of CYP2D6. Neferine and Ber both showed a nonmechanistic inhibition of CYP1A2. All compounds showed a similar and significant mechanism-based inhibition of CYP3A4. Tetrahydropalmatine and Ber demonstrated both reversible and irreversible inhibition of CYP2D6 and CYP3A4. Tetrahydropalmatine and Ber displayed H-bond and several Pi-bond connections with specific amino acid residues of CYP1A2, CYP2D6 and CYP3A4, giving further knowledge to the identified reversible and irreversible herb-drug interactions. Tetrahydropalmatine and Ber should be considered for herb-drug interactions in clinical therapy until relevant clinical studies are available.

Modulation of the pentose phosphate pathway alters phase I metabolism of testosterone and dextromethorphan in HepG2 cells.

The pentose phosphate pathway (PPP) is involved in the activity of glucose-6-phosphate dehydrogenase (G6PD) and generation of NADPH, which plays a key role in drug metabolism. The aim of this study was to investigate the effects of modulation of the PPP on drug metabolism capacity in vitro. A pair of hepatic cell lines, ie, the cancerous HepG2 cells and normal L02 cells, was used. The expression of CYP450 enzymes, p53 and G6PD in the cells were analyzed. The metabolism of testosterone (TEST, 10 μmol/L) and dextromethorphan (DEM, 1 μmol/L), the two typical substrates for CYP3A4 and CYP2D6, in the cells was examined in the presence of different agents. Both the expression and metabolic activities of CYP3A4 and CYP2D6 were considerably higher in HepG2 cells than in L02 cells. The metabolism of TEST and DEM in HepG2 cells was dose-dependently inhibited by the specific CYP3A4 inhibitor ketoconazole and CYP2D6 inhibitor quinidine. Addition of the p53 inhibitor cyclic PFT-α (5, 25 μmol/L) in HepG2 cells dose-dependently enhanced the metabolism of DEM and TEST, whereas addition of the p53 activator NSC 66811 (3, 10, 25 μmol/L) dose-dependently inhibited the metabolism. Furthermore, addition of the G6PD inhibitor 6-aminonicotinamide (5, 15 μmol/L) in HepG2 cells dose-dependently inhibited the metabolism of DEM and TEST, whereas addition of the PPP activity stimulator menadione (1, 5, 15 μmol/L) dose-dependently enhanced the metabolism. Modulation of p53 and the PPP alters the metabolism of DEM and TEST, suggesting that the metabolic flux pattern of PPP may be closely involved in drug metabolism and the individual variance.

Phenotypic differences in nebivolol metabolism and bioavailability in healthy volunteers.

IntroductionNebivolol, a third-generation β-blocker, is subject to extensive first-pass metabolism and produces active β-blocking hydroxylated metabolites, like 4-OH-nebivolol. It is primarily a substrate of CYP2D6, a metabolic pathway that is under polymorphic genetic regulation. The objective of this study was to assess the metabolizer phenotype and to evaluate the interphenotype bioavailability and metabolism of nebivolol.Material and methodsForty-three healthy volunteers were included in this open-label, non-randomized clinical trial and each volunteer received a single dose of 5 mg nebivolol. Non-compartmental pharmacokinetic analysis was performed to determine the pharmacokinetic parameters of nebivolol and its active metabolite. The phenotypic distribution was assessed based on the AUC (aria under the curve) metabolic ratio of nebivolol/4-OH-nebivolol and statistical analysis. An interphenotype comparison of nebivolol metabolism and bioavailability was performed based on the pharmacokinetic parameters of nebivolol and its active metabolite.ResultsNebivolol/4-OH-nebivolol AUC metabolic ratios were not characterized by a standard normal distribution. The unique distribution emphasized the existence of two groups and the 43 healthy volunteers were classified as follows: poor metabolizers (PMs)=3, extensive metabolizers (EMs)=40. The phenotype had a marked impact on nebivolol metabolism. The exposure to nebivolol was 15-fold greater for PMs in comparison to EMs.Conclusion40 EMs and 3 PMs were differentiated by using the pharmacokinetic parameters of nebivolol and its active metabolite. The study highlighted the existence of interphenotype differences regarding nebivolol metabolism and bioavailability.

Influence of the CYP2D6 isoenzyme in patients treated with venlafaxine for major depressive disorder: clinical and economic consequences.

BackgroundAntidepressant drugs are the mainstay of drug therapy for sustained remission of symptoms. However, the clinical results are not encouraging. This lack of response could be due, among other causes, to factors that alter the metabolism of the antidepressant drug. Objective: to evaluate the impact of concomitant administration of CYP2D6 inhibitors or substrates on the efficacy, tolerability and costs of patients treated with venlafaxine for major depressive disorder in clinical practice.MethodsWe designed an observational study using the medical records of outpatients. Subjects aged ≥18 years who started taking venlafaxine during 2008–2010 were included. Three study groups were considered: no combinations (reference), venlafaxine-substrate, and venlafaxine-inhibitor. The follow-up period was 12 months. The main variables were: demographic data, comorbidity, remission (Hamilton <7), response to treatment, adverse events and costs. The statistical analysis included logistic regression models and ANCOVA, with p values <0.05 considered significant.ResultsA total of 1,115 subjects were recruited. The mean age was 61.7 years and 75.1% were female. Approximately 33.3% (95% CI: 30.5 to 36.1) were receiving some kind of drug combination (venlafaxine-substrate: 23.0%, and venlafaxine-inhibitor: 10.3%). Compared with the venlafaxine-substrate and venlafaxine-inhibitor groups, patients not taking concomitant drugs had a better response to therapy (49.1% vs. 39.9% and 34.3%, p<0.01), greater remission of symptoms (59.9% vs. 50.2% and 43.8%, p<0.001), fewer adverse events (1.9% vs. 7.0% and 6.1%, p<0.05) and a lower mean adjusted cost (€2,881.7 vs. €4,963.3 and €7,389.1, p<0.001), respectively. All cost components showed these differences.ConclusionsThe patients treated with venlafaxine alone showed a better response to anti-depressant treatment, greater remission of symptoms, a lower incidence of adverse events and lower healthcare costs.

Evaluation of 89 compounds for identification of substrates for cynomolgus monkey CYP2C76, a new bupropion/nifedipine oxidase.

Cynomolgus monkeys are widely used in preclinical studies during drug development because of their evolutionary closeness to humans, including their cytochrome P450s (P450s). Most cynomolgus monkey P450s are almost identical (≥90%) to human P450s; however, CYP2C76 has low sequence identity (approximately 80%) to any human CYP2Cs. Although CYP2C76 has no ortholog in humans and is partly responsible for species differences in drug metabolism between cynomolgus monkeys and humans, a broad evaluation of potential substrates for CYP2C76 has not yet been conducted. In this study, a screening of 89 marketed compounds, including human CYP2C and non-CYP2C substrates or inhibitors, was conducted to find potential CYP2C76 substrates. Among the compounds screened, 19 chemicals were identified as substrates for CYP2C76, including substrates for human CYP1A2 (7-ethoxyresorufin), CYP2B6 (bupropion), CYP2D6 (dextromethorphan), and CYP3A4/5 (dextromethorphan and nifedipine), and inhibitors for CYP2B6 (sertraline, clopidogrel, and ticlopidine), CYP2C8 (quercetin), CYP2C19 (ticlopidine and nootkatone), and CYP3A4/5 (troleandomycin). CYP2C76 metabolized a wide variety of the compounds with diverse structures. Among them, bupropion and nifedipine showed high selectivity to CYP2C76. As for nifedipine, CYP2C76 formed methylhydroxylated nifedipine, which was not produced by monkey CYP2C9, CYP2C19, or CYP3A4, as identified by mass spectrometry and estimated by a molecular docking simulation. This unique oxidative metabolite formation of nifedipine could be one of the selective marker reactions of CYP2C76 among the major CYP2Cs and CYP3As tested. These results suggest that monkey CYP2C76 contributes to bupropion hydroxylation and formation of different nifedipine oxidative metabolites as a result of its relatively large substrate cavity.

Genotype-based treatment approved for type 1 Gaucher disease.

FDA and Sanofi on August 19 announced the approval of eliglustat, or Cerdelga, for the long-term treatment of adults with type 1 Gaucher disease who have a certain drug-metabolizing-enzyme genotype. Eliglustat, a glucosylceramide analog, was designed to partially inhibit the enzyme that synthesizes glucocerebroside, the company said. Patients with Gaucher disease do not adequately catabolize glucocerebroside, which is a lipid molecule in the cell membrane of the brain, nervous tissue, and other tissues. Insufficient activity by the enzyme responsible for breaking down glucocerebroside, FDA said, causes fatty materials to accumulate in the spleen, liver, and bone marrow. Patients can have spleen and liver enlargement, anemia, low blood platelet counts, and bone problems. The labeling for eliglustat instructs clinicians to select patients with type 1 Gaucher disease for treatment with the drug on the basis of their genotype for cytochrome P-450 (CYP) isoenzyme 2D6. Eliglustat is a substrate of CYP2D6. The drug’s labeling recommends dosages for patients who are extensive, intermediate, or poor metabolizers of CYP2D6 substrates but not dosages for ultrarapid metabolizers or patients whose CYP2D6 genotype cannot be determined.

The effect of CYP2D6 drug-drug interactions on hydrocodone effectiveness.

The hepatic cytochrome 2D6 (CYP2D6) is a saturable enzyme responsible for metabolism of approximately 25% of known pharmaceuticals. CYP interactions can alter the efficacy of prescribed medications. Hydrocodone is largely dependent on CYP2D6 metabolism for analgesia, ondansetron is inactivated by CYP2D6, and oxycodone analgesia is largely independent of CYP2D6. The objective was to determine if CYP2D6 medication coingestion decreases the effectiveness of hydrocodone. This was a prospective observational study conducted in an academic U.S. emergency department (ED). Subjects were included if they had self-reported pain or nausea and were excluded if they were unable to speak English, were less than 18 years of age, had liver or renal failure, or carried diagnoses of chronic pain or cyclic vomiting. Detailed drug ingestion histories for the preceding 48 hours prior to the ED visit were obtained. The patient's pain and nausea were quantified using a 100-mm visual analog scale (VAS) at baseline prior to drug administration and following doses of hydrocodone, oxycodone, or ondansetron. We used a mixed model with random subject effect to determine the interaction between CYP2D6 drug ingestion and study drug effectiveness. Odds ratios (ORs) were calculated to compare clinically significant VAS changes between CYP2D6 users and nonusers. A total of 250 (49.8%) of the 502 subjects enrolled had taken at least one CYP2D6 substrate, inhibitor, or inducing pharmaceutical, supplement, or illicit drug in the 48 hours prior to ED presentation. CYP2D6 drug users were one-third as likely to respond to hydrocodone (OR = 0.33, 95% confidence interval [CI] = 0.1 to 0.8) and more than three times as likely as nonusers to respond to ondansetron (OR = 3.4, 95% CI = 1.3 to 9.1). There was no significant difference in oxycodone effectiveness between CYP2D6 users and nonusers (OR = 0.53, 95% CI = 0.3 to 1.1). CYP2D6 drug-drug interactions appear to change effectiveness of commonly prescribed drugs in the ED. Drug-drug interaction should be considered prior to prescribing CYP2D6 drugs.

Evaluation of the Pharmacokinetic Interaction Between Ticagrelor and Venlafaxine, a Cytochrome P-450 2D6 Substrate, in Healthy Subjects

PurposeTicagrelor is a reversibly binding P2Y12 receptor antagonist used clinically for the prevention of atherothrombotic events in patients with acute coronary syndromes (ACS). Ticagrelor has been shown in vitro to be a weak inhibitor of cytochrome P-450 (CYP) 2D6, a clinically important enzyme for the metabolism of many drugs. This study assessed the effects of coadministration of ticagrelor on the pharmacokinetics of the CYP2D6 substrate venlafaxine. The impact of venlafaxine on ticagrelor pharmacokinetic parameters was also investigated. MethodsHealthy subjects (N = 22) received a single 180-mg oral dose of ticagrelor on days 1 and 9 and oral doses of venlafaxine on day 4 (37.5 mg BID) and days 5 through 10 (75 mg BID). Plasma concentrations of ticagrelor, venlafaxine, and their metabolites (AR-C124910XX and O-desmethylvenlafaxine [ODV], respectively) were quantified for pharmacokinetic analyses. Safety and tolerability were assessed throughout the study. FindingsOverall, 19 of 25 subjects were male; 14 were white, 10 were black, and 1 was Asian. Mean (SD) age was 26 (6) years, and mean (SD) body mass index was 24.3 (2.9) kg/m2. Ticagrelor had no effect on overall exposure to venlafaxine, as assessed by the AUC0–τ (geometric least squares mean ratio, 110.32 ng · h/mL [90% CI, 106.27–114.52]). Venlafaxine Cmax was increased by 22% in the presence of ticagrelor (121.83 ng/mL [90% CI, 111.80–132.75]). ODV AUC0–τ and Cmax were unaffected by coadministration with ticagrelor (98.71 ng · h/mL [90% CI, 96.61–100.85] and 101.44 ng/mL [90% CI, 98.34–104.65], respectively). Venlafaxine had no effect on the Cmax or AUC0–∞ of ticagrelor (96.54 ng/mL [90% CI, 85.03–109.61] and 89.67 ng · h/mL [90% CI, 82.78–97.14]) or AR-C124910XX (106.39 ng/mL [90% CI, 96.10–117.78] and 106.32 ng · h/mL [90% CI, 97.28–116.21], respectively). Ticagrelor and venlafaxine were well tolerated whether given alone or in combination. ImplicationsTicagrelor had no clinically relevant effect on the plasma levels of venlafaxine and its CYP2D6-generated active metabolite, ODV. On the basis of these data, ticagrelor is not expected to affect CYP2D6-mediated drug metabolism to a clinically relevant extent. Venlafaxine had no effect on the pharmacokinetics of ticagrelor.

Polymorphisms of CYP2D17 in Cynomolgus and Rhesus Macaques: an Evidence of the Genetic Basis for the Variability of CYP2D-Dependent Drug Metabolism

Cynomolgus macaques and rhesus macaques are nonhuman primate species widely used in drug metabolism studies. Cynomolgus CYP2D17, highly homologous to human CYP2D6, metabolizes human CYP2D6 substrates such as bufuralol and dextromethorphan, and the gene is expressed predominantly in liver. Although human CYP2D6 variants account for the variability of the enzyme properties among individuals and populations, genetic variants have not been investigated in CYP2D17. In the present study, CYP2D17 from 87 cynomolgus and 40 rhesus macaques was resequenced. The analysis found a total of 36 nonsynonymous variants, among which 5 were located in substrate recognition sites, the region important for protein function. Twenty-two variants were unique to cynomolgus macaques, of which 11 and 9 were found only in Indochinese and Indonesian cynomolgus macaques, respectively. Eight variants were unique to rhesus macaques. The functional characterization showed that two variant proteins (S188Y and V227I) heterologously expressed in Escherichia coli did not show substantial differences in the rate of bufuralol 1'-hydroxylation as compared with wild-type. However, measuring catalytic activities of the genotyped liver microsomes revealed that I297M and N337D were together significantly associated with higher rates, approximately 2.3- and 11.5-fold, of bufuralol 1'-hydroxylation and dextromethorphan O-demethylation, respectively, in the homozygotes than wild-type animals. The present study provided the first evidence that variability of a CYP2D-dependent metabolism in macaque liver is partly accounted for by CYP2D genotypes.