Patients' perspectives of telemedicine appointments for psoriatic arthritis during the COVID-19 pandemic: results of a patient-driven pilot survey.

BACKGROUND: Over recent years the lack of patient involvement in the design, set-up and implementation of clinical research studies has been well recognised; as such there has been a drive within research communities to increase patient participation. Patient perspectives on telemedicine differ widely, with variation in whether patients feel remote consultations are beneficial. By means of a patient-driven survey, we aimed to formally evaluate patient perspectives on its benefits and pitfalls, focusing on patients with psoriatic arthritis (PsA). METHODS: An e-survey was developed by two patient representatives on the BritPACT steering committee, with a view to determining unmet needs and the perceived impact on clinical care of virtual consultations amongst patients with PsA. RESULTS: 128 patients responded to the e-survey. 109 patients rated the effectiveness of their telemedicine appointment and, of these, 18% felt their virtual consultation was very/extremely effective compared to an in-clinic consultation and 49% felt it was somewhat/equally as effective; furthermore, 48% (51/107) felt that such virtual consultations would be of benefit to them after the pandemic. 36% of respondents felt their virtual consultation was not as effective as an in-clinic review. Themes identified from open-ended questions included the lack of visual cues, lack of physical examination and effect on rapport and ease of open communication as the main pitfalls of virtual consultations. Patients with well-controlled symptoms appeared more satisfied with remote reviews compared to those with active disease, though on the whole respondents recognised the benefits, such as saving travel time and costs. Those who had an established relationship with their health professional appeared less concerned regarding virtual consultations though a recurring view was that newly diagnosed patients should have in-clinic appointments to build rapport and improve symptom control at an early stage. CONCLUSIONS: Overall patients' perspectives on virtual consultations varied widely though patients with well-controlled symptoms and those who had a previously established relationship with their healthcare professionals and well-controlled disease appeared more satisfied with remote reviews.

Treatment of psoriatic arthritis with biologic and targeted synthetic DMARDs: British Society for Rheumatology guideline scope.

The aim of this guideline is to provide an update on evidence-based recommendations for treatment of adult patients with PsA. The previous BSR guidelines for PsA were published in 2012 and since that time, there have been many new advanced therapies licensed for PsA. This update will provide practical guidance for clinicians on the optimal selection of advanced therapies taking into account different domains of PsA (arthritis, enthesitis, dactylitis, axial disease and psoriasis) and key associated comorbidities. It will also update guidance on treatment strategy including the use of a treat-to-target approach. The guideline will be developed using the methods and processes outlined in Creating Clinical Guidelines: Our Protocol. (1) This development process to produce guidance, advice and recommendations for practice has National Institute for Health and Care Excellence (NICE) accreditation.

An Assessment of the In Vitro Inhibition of Cytochrome P450 Enzymes, UDP-Glucuronosyltransferases, and Transporters by Phosphodiester- or Phosphorothioate-Linked Oligonucleotides.

Oligonucleotides represent an expanding class of pharmacotherapeutics in development for various indications. Typically, oligonucleotides are developed with phosphorothioate linkages for the improvement of biologic stability; however, limited data are available on the potential of these molecules to cause drug-drug interactions (DDIs). In this study, four nontherapeutic oligonucleotides with either a phosphodiester or phosphorothioate linkage and partial sequences towards glutathione peroxidase or ß-actin (PD-GP and PD-Ac or PT-GP and PT-Ac, respectively) were evaluated in vitro for their potential to inhibit cytochrome P450 (P450) enzymes and UGP-glucuronosyltransferases (UGTs) in both human liver microsomes (HLMs) and cryopreserved human hepatocytes (CHHs) and to inhibit select transporters in expression systems. PD-GP and PD-Ac had little to no inhibitory effect on any P450 or UGT enzymes in HLMs and CHHs, except for PD-Ac in HLMs for CYP2C19 (IC50 = 29 µM). Conversely, PT-GP and PT-Ac caused direct inhibition of almost all P450 and UGT enzymes, with CYP1A2 (IC50 values of 0.8-4.2 µM), CYP2C8 (IC50 values of 1.1-12 µM), and UGT1A1 (IC50 values of 4.5-5.4 µM) inhibited to the greatest extent. There was evidence of possible time-dependent inhibition (TDI) of P450 enzymes with PT-GP and PT-Ac for CYP2B6, CYP2C8, CYP2C19, CYP2C9, CYP2D6, and CYP3A4/5; however, this TDI was reversible. In contrast to HLMs, there was little to no direct P450 inhibition by any oligonucleotide in CHHs [except for PD-Ac with CYP2C19 (IC50 = 36 µM) and TDI by PT-GP with CYP2C8], demonstrating test system-dependent outcomes. Inhibition was observed for the organic anion uptake transporters, including organic anion-transporting polypeptide OATP1B1 and OATP1B3, organic anion transporters OAT1 and OAT3, and organic cation transporter OCT2 (IC50 values of 12-29 µM), but not OCT1 or the efflux transporters breast cancer resistance protein and P-glycoprotein by the phosphorothioate oligonucleotides.

Let's Talk about Inclusion: A Report on Patient Research Partner Involvement in the GRAPPA 2015 Annual Meeting.

Members of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) have worked since 2012 to include the patient perspective in their psoriatic arthritis (PsA) research as well as in their annual meetings. Herein, patient research partners (PRP) report the progress made in their experience at these GRAPPA meetings and discuss their perception of the challenges that remain in ensuring that patients have a voice in PsA outcome research.

Group for Research and Assessment of Psoriasis and Psoriatic Arthritis 2015 Treatment Recommendations for Psoriatic Arthritis.

OBJECTIVE: To update the 2009 Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) treatment recommendations for the spectrum of manifestations affecting patients with psoriatic arthritis (PsA). METHODS: GRAPPA rheumatologists, dermatologists, and PsA patients drafted overarching principles for the management of PsA, based on consensus achieved at face-to-face meetings and via online surveys. We conducted literature reviews regarding treatment for the key domains of PsA (arthritis, spondylitis, enthesitis, dactylitis, skin disease, and nail disease) and convened a new group to identify pertinent comorbidities and their effect on treatment. Finally, we drafted treatment recommendations for each of the clinical manifestations and assessed the level of agreement for the overarching principles and treatment recommendations among GRAPPA members, using an online questionnaire. RESULTS: Six overarching principles had ≥80% agreement among both health care professionals (n = 135) and patient research partners (n = 10). We developed treatment recommendations and a schema incorporating these principles for arthritis, spondylitis, enthesitis, dactylitis, skin disease, nail disease, and comorbidities in the setting of PsA, using the Grading of Recommendations, Assessment, Development and Evaluation process. Agreement of >80% was reached for approval of the individual recommendations and the overall schema. CONCLUSION: We present overarching principles and updated treatment recommendations for the key manifestations of PsA, including related comorbidities, based on a literature review and consensus of GRAPPA members (rheumatologists, dermatologists, other health care providers, and patient research partners). Further updates are anticipated as the therapeutic landscape in PsA evolves.

Further Characterization of the Metabolism of Desloratadine and Its Cytochrome P450 and UDP-glucuronosyltransferase Inhibition Potential: Identification of Desloratadine as a Relatively Selective UGT2B10 Inhibitor.

Desloratadine (Clarinex), the major active metabolite of loratadine (Claritin), is a nonsedating antihistamine used for the treatment of seasonal allergies and hives. Previously we reported that the formation of 3-hydroxydesloratadine, the major human metabolite of desloratadine, involves three sequential reactions, namely N-glucuronidation by UGT2B10 followed by 3-hydroxylation by CYP2C8 followed by deconjugation (rapid, nonenzymatic hydrolysis of the N-glucuronide). In this study we assessed the perpetrator potential of desloratadine based on in vitro studies of its inhibitory effects on cytochrome P450 and UDP-glucuronosyltransferase (UGT) enzymes in human liver microsomes (HLM). Desloratadine (10 µM) caused no inhibition (<15%) of CYP1A2, CYP2C8, CYP2C9, or CYP2C19 and weak inhibition (32-48%) of CYP2B6, CYP2D6, and CYP3A4/5. In cryopreserved human hepatocytes (CHH), which can form the CYP2C8 substrate desloratadine N-glucuronide, desloratadine did not inhibit the CYP2C8-dependent metabolism of paclitaxel or amodiaquine. Assessment of UGT inhibition identified desloratadine as a potent and relatively selective competitive inhibitor of UGT2B10 (Ki value of 1.3 µM). Chemical inhibition of UGT enzymes in HLM demonstrated that nicotine (UGT2B10 inhibitor) but not hecogenin (UGT1A4 inhibitor) completely inhibited the conversion of desloratadine (1 µM) to 3-hydroxydesloratadine in HLM fortified with both NADPH and UDP-glucuronic acid. 3-Hydroxydesloratadine formation correlated well with levomedetomidine glucuronidation (UGT2B10 marker activity) with a panel of individual CHH (r(2) = 0.72). Overall, the results of this study confirm the role of UGT2B10 in 3-hydroxydesloratadine formation and identify desloratadine as a relatively selective in vitro inhibitor of UGT2B10.

A long-standing mystery solved: the formation of 3-hydroxydesloratadine is catalyzed by CYP2C8 but prior glucuronidation of desloratadine by UDP-glucuronosyltransferase 2B10 is an obligatory requirement.

Desloratadine (Clarinex), the major active metabolite of loratadine (Claritin), is a nonsedating long-lasting antihistamine that is widely used for the treatment of allergic rhinitis and chronic idiopathic urticaria. For over 20 years, it has remained a mystery as to which enzymes are responsible for the formation of 3-hydroxydesloratadine, the major active human metabolite, largely due to the inability of any in vitro system tested thus far to generate this metabolite. In this study, we demonstrated that cryopreserved human hepatocytes (CHHs) form 3-hydroxydesloratadine and its corresponding O-glucuronide. CHHs catalyzed the formation of 3-hydroxydesloratadine with a Km of 1.6 µM and a Vmax of 1.3 pmol/min per million cells. Chemical inhibition of cytochrome P450 (P450) enzymes in CHHs demonstrated that gemfibrozil glucuronide (CYP2C8 inhibitor) and 1-aminobenzotriazole (general P450 inhibitor) inhibited 3-hydroxydesloratadine formation by 91% and 98%, respectively. Other inhibitors of CYP2C8 (gemfibrozil, montelukast, clopidogrel glucuronide, repaglinide, and cerivastatin) also caused extensive inhibition of 3-hydroxydesloratadine formation (73%-100%). Assessment of desloratadine, amodiaquine, and paclitaxel metabolism by a panel of individual CHHs demonstrated that CYP2C8 marker activity robustly correlated with 3-hydroxydesloratadine formation (r(2) of 0.70-0.90). Detailed mechanistic studies with sonicated or saponin-treated CHHs, human liver microsomes, and S9 fractions showed that both NADPH and UDP-glucuronic acid are required for 3-hydroxydesloratadine formation, and studies with recombinant UDP-glucuronosyltransferase (UGT) and P450 enzymes implicated the specific involvement of UGT2B10 in addition to CYP2C8. Overall, our results demonstrate for the first time that desloratadine glucuronidation by UGT2B10 followed by CYP2C8 oxidation and a deconjugation event are responsible for the formation of 3-hydroxydesloratadine.

Patient participation in psoriasis and psoriatic arthritis outcome research: a report from the GRAPPA 2013 Annual Meeting.

For the first time, 8 patients with psoriatic arthritis (PsA) participated as full delegates at the 2013 Annual Meeting of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA). Patients were invited to provide their perspective for different sessions of the conference program. Before the conference, the patient delegates had a separate meeting to familiarize themselves with the conference program and to gain a better understanding of the vision and objectives of GRAPPA. During the conference, the patient group discussed options for increased involvement in research projects. Herein we summarize the presentations on patient participation in research, the experiences of the patient group, and plans to enhance the patient perspective in psoriasis and PsA research.

A patient-derived and patient-reported outcome measure for assessing psoriatic arthritis: elaboration and preliminary validation of the Psoriatic Arthritis Impact of Disease (PsAID) questionnaire, a 13-country EULAR initiative.

INTRODUCTION: The objective was to develop a questionnaire that can be used to calculate a score reflecting the impact of psoriatic arthritis (PsA) from the patients' perspective: the PsA Impact of Disease (PsAID) questionnaire. METHODS: Twelve patient research partners identified important domains (areas of health); 139 patients prioritised them according to importance. Numeric rating scale (NRS) questions were developed, one for each domain. To combine the domains into a single score, relative weights were determined based on the relative importance given by 474 patients with PsA. An international cross-sectional and longitudinal validation study was performed in 13 countries to examine correlations of the PsAID score with other PsA or generic disease measures. Test-retest reliability and responsiveness (3 months after a treatment change) were examined in two subsets of patients. RESULTS: Two PsAID questionnaires were developed with both physical and psychological domains: one for clinical practice (12 domains of health) and one for clinical trials (nine domains). Pain, fatigue and skin problems had the highest relative importance. The PsAID scores correlated well with patient global assessment (N=474, Spearman r=0.82-0.84), reliability was high in stable patients (N=88, intraclass correlation coefficient=0.94-0.95), and sensitivity to change was also acceptable (N=71, standardised response mean=0.90-0.91). CONCLUSIONS: A questionnaire to assess the impact of PsA on patients' lives has been developed and validated. Two versions of the questionnaire are available, one for clinical practice (PsAID-12) and one for clinical trials (PsAID-9). The PsAID questionnaires should allow better assessment of the patient's perspective in PsA. Further validation is needed.

The effect of ionizing gamma radiation on natural and synthetic fibers and its implications for the forensic examination of fiber evidence.

Circumstances of criminal activities involving radioactive materials may mean fiber evidence recovered from a crime scene could have been exposed to materials emitting ionizing radiation. The consequences of radiation exposed fibers on the result of the forensic analysis and interpretation is explored. The effect of exposure to 1-1000 kGy radiation doses in natural and synthetic fibers was noticeable using comparative forensic examination methods, such as optical microscopy, microspectrophotometry, and thin-layer chromatography. Fourier transform infrared spectroscopy analysis showed no signs of radiation-induced chemical changes in any of the fiber structures. The outcome of the comparative methods highlights the risk of "false negatives" associated in comparing colors of recovered fibers that may have been exposed to unknown radiation doses. Consideration of such results supports the requirement to know the context, including the environmental conditions, as much as possible before undertaking a forensic fiber examination.

System-dependent outcomes during the evaluation of drug candidates as inhibitors of cytochrome P450 (CYP) and uridine diphosphate glucuronosyltransferase (UGT) enzymes: human hepatocytes versus liver microsomes versus recombinant enzymes.

The ability of a drug to cause clinically significant drug-drug interactions due to direct or metabolism-dependent inhibition of cytochrome P450 (CYP) can generally be predicted from in vitro studies with human liver microsomes (HLM) or recombinant CYP enzymes, as recommended by the FDA and other regulatory agencies. This review highlights some examples of system-dependent inhibition of CYP and uridine diphosphate glucuronosyltransferase (UGT) enzymes. In the case of CYP enzymes, examples are presented where in vitro studies with HLM under-predict or over-predict the degree of inhibition observed in the clinic and where the correct prediction comes from studies with human hepatocytes. Studies with HLM under-predict the ability of gemfibrozil and bupropion to cause clinically significant inhibition of CYP2C8 and CYP2D6, respectively, and over-predict the ability of ezetimibe to cause clinically significant inhibition of CYP3A4. Gemfibrozil and bupropion represent examples of glucuronidation-dependent and reduction-dependent activation to metabolites that inhibit CYP2C8 and CYP2D6, respectively, whereas ezetimibe represents an example of glucuronidation-dependent protection against metabolism-dependent inhibition of CYP3A4. This article illustrates why, when drug candidates are extensively metabolized by non-CYP enzymes, it would be prudent to use human hepatocytes in addition to HLM or recombinant enzymes to evaluate their ability to inhibit CYP enzymes.

Construction of triple-transfected cells [organic anion-transporting polypeptide (OATP) 1B1/multidrug resistance-associated protein (MRP) 2/MRP3 and OATP1B1/MRP2/MRP4] for analysis of the sinusoidal function of MRP3 and MRP4.

Multidrug resistance-associated protein (MRP) 3/ABCC3 and MRP4/ABCC4 are ATP-binding cassette (ABC) transporters expressed in the sinusoidal membrane of hepatocytes. The purpose of the present study was to establish organic anion-transporting polypeptide (OATP) 1B1/MRP2/MRP3 and OATP1B1/MRP2/MRP4 triple transfectants as in vitro model of the hepatobiliary transport of anionic drugs. To find in vivo relevant Mrp3 probes, wild-type and Mrp3(-/-) mice were given gemfibrozil, 6-hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridymethyl)benzothiazole (E3040), troglitazone, bisphenol A, and 4-methylumbelliferone orally. Plasma concentrations of the glucuronide conjugates were significantly lower in Mrp3(-/-) mice than in wild-type mice. The systemic exposure of gemfibrozil, E3040, and troglitazone were similar in wild-type and Mrp3(-/-) mice. 4-Methylumbelliferone and bisphenol A were undetectable in the plasma. In MRP3-expressing membrane vesicles, ATP-dependent uptakes of the glucuronide conjugates of estradiol, gemfibrozil, E3040, and troglitazone were markedly greater than those in controls, whereas MRP4-expressing membrane vesicles exhibited significant ATP-dependent uptake of gemfibrozil glucuronide and estradiol glucuronide. MRP3 or MRP4 was expressed in the OATP1B1/MRP2 double transfectants using adenovirus. The expression levels of OATP1B1 and MRP2 proteins were maintained both in the OATP1B1/MRP2/MRP3 and OATP1B1/MRP2/MRP4 triple transfectants, whereas MRP3 and MRP4 were localized in the basal membrane. Significant reductions in the basal-to-apical flux of the glucuronide conjugates of estradiol, gemfibrozil, E3040, and troglitazone were observed in the OATP1B1/MRP2/MRP3 triple transfectants compared with those in the double transfectants, whereas significant reduction was observed only for gemfibrozil glucuronide and estradiol glucuronide in the OATP1B1/MRP2/MRP4 triple transfectants. These results suggest that MRP3- or MRP4-triple transfectants provide a simple and useful in vitro system for evaluating their importance in the hepatobiliary transport of drugs.

An in vitro evaluation of the victim and perpetrator potential of the anticancer agent laromustine (VNP40101M), based on reaction phenotyping and inhibition and induction of cytochrome P450 enzymes.

Laromustine (VNP40101M, also known as Cloretazine) is a novel sulfonylhydrazine alkylating (anticancer) agent. Laromustine generates two types of reactive intermediates: 90CE and methylisocyanate. When incubated with rat, dog, monkey, and human liver microsomes, [(14)C]laromustine was converted to 90CE (C-8) and seven other radioactive components (C-1-C-7). There was little difference in the metabolite profile among the species examined, in part because the formation of most components (C-1-C-6 and 90CE) did not require NADPH but involved decomposition and/or hydrolysis. The exception was C-7, a hydroxylated metabolite, largely formed by CYP2B6 and CYP3A4/5. Laromustine caused direct inhibition of CYP2B6 and CYP3A4/5 (the two enzymes involved in C-7 formation) as well as of CYP2C19. K(i) values were 125 microM for CYP2B6, 297 muM for CYP3A4/5, and 349 microM for CYP2C19 and were greater than the average clinical plasma C(max) of laromustine (25 microM). There was evidence of time-dependent inhibition of CYP1A2, CYP2B6, and CYP3A4/5. Treatment of primary cultures of human hepatocytes with up to 100 microM laromustine did not induce CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, or CYP3A4/5, but the highest concentration of laromustine decreased the activity and levels of immunoreactive CYP3A4. The results of this study suggest the laromustine has 1) negligible victim potential with respect to metabolism by cytochrome P450 enzymes, 2) negligible enzyme-inducing potential, and 3) the potential in some cases to cause inhibition of CYP2B6, CYP3A4, and possibly CYP2C19 during and shortly after the duration of intravenous administration of this anticancer drug, but the clinical effects of such interactions are likely to be insignificant.

The recovery of latent fingermarks from evidence exposed to ionizing radiation*.

Continual reports of illicit trafficking incidents involving radioactive materials have prompted authorities to consider the likelihood of forensic evidence being exposed to radiation. In this study, we investigated the ability to recover latent fingermark evidence from a variety of substrates that were exposed to ionizing radiation. Fingermarks deposited on common surfaces, including aluminum, glass, office paper, and plastic, were exposed to doses ranging from 1 to 1000 kGy, in an effort to simulate realistic situations where evidence is exposed to significant doses of radiation from sources used in a criminal act. The fingermarks were processed using routine fingermark detection techniques. With the exception of glass and aluminum substrates, radiolysis had a considerable effect on the quality of the developed fingermarks. The damage to ridge characteristics can, in part, be attributed to chemical interactions between the substrate and the components of the fingermark secretions that react with the detection reagents.

On the mechanism of hepatocarcinogenesis of benzodiazepines: evidence that diazepam and oxazepam are CYP2B inducers in rats, and both CYP2B and CYP4A inducers in mice.

The aim of this study was to evaluate diazepam and oxazepam as cytochrome P450 inducers at doses previously shown to cause liver tumors in mice but not rats. In rats, diazepam and oxazepam induced CYP2B, and were as effective as phenobarbital despite lacking phenobarbital's tumor-promoting effect in rats. In mice, diazepam and oxazepam induced both CYP2B and CYP4A at dietary doses associated with liver tumor formation. It remains to be determined why diazepam and oxazepam induce CYP4A in mice but not rats and whether this difference accounts for the apparent species difference in the tumor-promoting activity of diazepam and oxazepam.

Anabolic androgenic steroids: a survey of 500 users.

PURPOSE: The use of anabolic androgenic steroids (AAS) to increase muscle size and strength is widespread. Information regarding self-administered AAS used nonmedically to enhance athletic performance or improve physical appearance is sparse and poorly documented. The purpose of this study is to identify current trends in the drug-taking habits of AAS users. METHODS: An anonymous self-administered questionnaire was posted on the message boards of Internet Web sites popular among AAS users. RESULTS: Of the 500 AAS users who participated in the survey, 78.4% (392/500) were noncompetitive bodybuilders and nonathletes; 59.6% (298/500) of the respondents reported using at least 1000 mg of testosterone or its equivalent per week. The majority (99.2%) of AAS users (496/500) self-administer injectable AAS formulations, and up to 13% (65/500) report unsafe injection practices such as reusing needles, sharing needles, and sharing multidose vials. In addition to using AAS, 25% of users admitted to the adjuvant use of growth hormone and insulin for anabolic effect, and 99.2% (496/500) of users reported subjective side effects from AAS use. CONCLUSIONS: This survey reveals several trends in the nonmedical use of AAS. Nearly four out of five AAS users are nonathletes who take these drugs for cosmetic reasons. AAS users in this sample are taking larger doses than previously recorded, with more than half of the respondents using a weekly AAS dose in excess of 1000 mg. The majority of steroid users self-administer AAS by intramuscular injection, and approximately 1 in 10 users report hazardous injection techniques. Polypharmacy is practiced by more than 95% of AAS users, with one in four users taking growth hormone and insulin. Nearly 100% of AAS users reported subjective side effects.

The effect of fenbuconazole on cell proliferation and enzyme induction in the liver of female CD1 mice.

Fenbuconazole, a triazole fungicide, has been associated with an increase in the incidence of liver adenomas in female mice following long-term dietary exposure. The aim of this study was to evaluate whether the mode of action for liver tumor formation by fenbuconazole is similar to that of phenobarbital. Treatment of CD1 mice with 0, 20, 60, 180 or 1300 ppm fenbuconazole for up to 4 weeks caused a dose-dependent increase in liver weight that was associated with centrilobular hepatocellular hypertrophy, cytoplasmic eosinophilia and panlobular hepatocellular vacuolation, as well as an initial increase in the cell proliferation labeling index. Fenbuconazole also caused a dose-dependent increase in liver microsomal cytochromes b(5) and P450 and the levels of immunoreactive CYP2B10 and its associated activity 7-pentoxyresorufin O-dealkylation (PROD). Treatment of mice with 1000 ppm phenobarbital elicited the same effects as treatment of mice with 1300 ppm fenbuconazole, except that phenobarbital was more effective than fenbuconazole at inducing PROD activity, even though fenbuconazole induced CYP2B10 to the same extent as did phenobarbital. This difference was attributed to the ability of fenbuconazole to bind tightly to CYP2B10 and partially mask its catalytic activity in liver microsomes, which is characteristic of several azole-containing drugs. All hepatocellular changes and induced enzyme activity returned to control levels within 4 weeks of discontinuing treatment with fenbuconazole or phenobarbital, indicating that the observed changes were fully reversible. We conclude that fenbuconazole is a phenobarbital-type inducer of mouse liver cytochrome P450, and the mode of action by which fenbuconazole induces liver adenomas in mice is similar to that of phenobarbital.

Glucuronidation converts gemfibrozil to a potent, metabolism-dependent inhibitor of CYP2C8: implications for drug-drug interactions.

Gemfibrozil more potently inhibits CYP2C9 than CYP2C8 in vitro, and yet the opposite inhibitory potency is observed in the clinic. To investigate this apparent paradox, we evaluated both gemfibrozil and its major metabolite, an acyl-glucuronide (gemfibrozil 1-O-beta-glucuronide) as direct-acting and metabolism-dependent inhibitors of the major drug-metabolizing cytochrome P450 enzymes (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4) in human liver microsomes. Gemfibrozil most potently inhibited CYP2C9 (IC50 of 30 microM), whereas gemfibrozil glucuronide most potently inhibited CYP2C8 (IC50 of 24 microM). Unexpectedly, gemfibrozil glucuronide, but not gemfibrozil, was found to be a metabolism-dependent inhibitor of CYP2C8 only. The IC50 for inhibition of CYP2C8 by gemfibrozil glucuronide decreased from 24 microM to 1.8 microM after a 30-min incubation with human liver microsomes and NADPH. Inactivation of CYP2C8 by gemfibrozil glucuronide required NADPH, and proceeded with a K(I) (inhibitor concentration that supports half the maximal rate of enzyme inactivation) of 20 to 52 microM and a k(inact) (maximal rate of inactivation) of 0.21 min(-1). Potent inhibition of CYP2C8 was also achieved by first incubating gemfibrozil with alamethicin-activated human liver microsomes and UDP-glucuronic acid (to form gemfibrozil glucuronide), followed by a second incubation with NADPH. Liquid chromatography-tandem mass spectrometry analysis established that human liver microsomes and recombinant CYP2C8 both convert gemfibrozil glucuronide to a hydroxylated metabolite, with oxidative metabolism occurring on the dimethylphenoxy moiety (the group furthest from the glucuronide moiety). The results described have important implications for the mechanism of the clinical interaction reported between gemfibrozil and CYP2C8 substrates such as cerivastatin, repaglinide, rosiglitazone, and pioglitazone.