Investigating errors in medical imaging: medical malpractice cases in Finland.

OBJECTIVE: The objectives of the study were to survey patient injury claims concerning medical imaging in Finland in 1991-2017, and to investigate the nature of the incidents, the number of claims, the reasons for the claims, and the decisions made concerning the claims. MATERIALS AND METHODS: The research material consisted of patient claims concerning imaging, sent to the Finnish Patient Insurance Centre (PVK). The data contained information on injury dates, the examination code, the decision code, the description of the injury, and the medical grounds for decisions. RESULTS: The number of claims included in the study was 1054, and the average number per year was 87. The most common cause was delayed diagnosis (404 claims, 38.3%). Most of the claims concerned mammography (314, 29.8%), radiography (170, 16.1%), and MRI (162, 15.4%). According to the decisions made by the PVK, there were no delays in 54.6% of the examinations for which claims were made. About 30% of all patient claims received compensation, the most typical reason being medical malpractice (27.7%), followed by excessive injuries and injuries caused by infections, accidents and equipment (2.7%). CONCLUSION: Patient injury in imaging examinations and interventions cannot be completely prevented. However, injury data are an important source of information for health care. By analysing claims, we can prevent harm, increase the quality of care, and improve patient safety in medical imaging.

CYP-associated drug-drug interactions: A mission accomplished?

On the basis of official Finnish Medicines Authority (Fimea)-approved drug monographs, less than half of the approved small-molecule drugs between 2007 and 2016 were substrates, inhibitors or inducers of CYP enzymes, predominantly of CYP3A4. No significant unexpected, life-threatening, CYP-associated drug-drug interactions (CYP-DDIs) of newly approved drug entities have been observed in the last 10-15 years. The present analysis seems to suggest that tools to study and predict potentially significant CYP-DDIs are working and efficient.

Inhibition and induction of CYP enzymes in humans: an update.

The cytochrome P450 (CYP) enzyme family is the most important enzyme system catalyzing the phase 1 metabolism of pharmaceuticals and other xenobiotics such as herbal remedies and toxic compounds in the environment. The inhibition and induction of CYPs are major mechanisms causing pharmacokinetic drug-drug interactions. This review presents a comprehensive update on the inhibitors and inducers of the specific CYP enzymes in humans. The focus is on the more recent human in vitro and in vivo findings since the publication of our previous review on this topic in 2008. In addition to the general presentation of inhibitory drugs and inducers of human CYP enzymes by drugs, herbal remedies, and toxic compounds, an in-depth view on tyrosine-kinase inhibitors and antiretroviral HIV medications as victims and perpetrators of drug-drug interactions is provided as examples of the current trends in the field. Also, a concise overview of the mechanisms of CYP induction is presented to aid the understanding of the induction phenomena.

Single-Arm Clinical Trials as Pivotal Evidence for Cancer Drug Approval: A Retrospective Cohort Study of Centralized European Marketing Authorizations Between 2010 and 2019.

The traditional drug development paradigm, consisting of sequential phases and randomized studies, has been challenged in oncology and hemato-oncology. In the regulatory context, a number of new products have been authorized based on nonrandomized efficacy and safety data. We retrospectively analyzed the European public assessment reports for anticancer treatments authorized between 2010 and 2019 to describe the data behind such approvals. Twenty-two initial marketing authorizations, mainly conditional, were identified. Fifty percent of the products had an orphan indication, and 77% had received previous scientific advice. Conclusions of clinical benefit were based on tumor responses, ranging between 15.8 and 88%. Our data shows that single-arm clinical studies leading to positive regulatory outcomes share common methodological approaches and end points, mostly comparing the overall response rate with a fixed success threshold as the primary analysis. The clinical indications in these approvals are clustered in late-line settings, hematological malignancies, and lung cancer. Our findings underline the need to reflect on the current practice, the methodological aspects, and end points in single-arm studies, and develop specific regulatory guidance on nonrandomized and novel study designs.

Oral diabetes medications other than dipeptidyl peptidase 4 inhibitors are not associated with bullous pemphigoid: A Finnish nationwide case-control study.

BACKGROUND: Dipeptidyl peptidase 4 inhibitors (DPP4is) used to treat diabetes have been reported to be associated with an increased risk of bullous pemphigoid (BP). There are no previous reports analyzing the risk of BP in patients who are using other diabetes medications. OBJECTIVE: To evaluate the association between diabetes medications other than DPP4i and development of BP. METHODS: We investigated the prevalence of diabetes among patients with BP and the association between the use of diabetes drugs (excluding DPP4i, metformin, and insulin) and BP by analyzing national Finnish registry data for 3397 patients with BP and 12,941 patients with basal cell carcinoma as controls. RESULTS: Our results show that 19.6% of patients with BP have type 2 diabetes. Use of none of the investigated medications was associated with an increased risk of BP. LIMITATIONS: Because this was a registry-based study, it was not possible to verify the accuracy of the diagnoses. The risk of BP in users of glucagon-like peptide 1 receptor agonists could not be analyzed. CONCLUSION: Our study shows that the investigated diabetes drugs are not associated with an increased risk of BP in a Finnish patient database, indicating they can be safely used in this population. Generalization of these results to other populations will require further study.

Hospitalizations Due to Adverse Drug Events in the Elderly-A Retrospective Register Study.

Adverse drug events (ADEs) are more likely to affect geriatric patients due to physiological changes occurring with aging. Even though this is an internationally recognized problem, similar research data in Finland is still lacking. The aim of this study was to determine the number of geriatric medication-related hospitalizations in the Finnish patient population and to discover the potential means of recognizing patients particularly at risk of ADEs. The study was conducted retrospectively from the 2014 emergency department patient records in Oulu University Hospital. A total number of 290 admissions were screened for ADEs, adverse drug reactions (ADRs) and drug-drug interactions (DDIs) by a multi-disciplinary research team. Customized Naranjo scale was used as a control method. All admissions were categorized into "probable," "possible," or "doubtful" by both assessment methods. In total, 23.1% of admissions were categorized as "probably" or "possibly" medication-related. Vertigo, falling, and fractures formed the largest group of ADEs. The most common ADEs were related to medicines from N class of the ATC-code system. Age, sex, residence, or specialty did not increase the risk for medication-related admission significantly (min p = 0.077). Polypharmacy was, however, found to increase the risk (OR 3.3; 95% CI, 1.5-6.9; p = 0.01). In conclusion, screening patients for specific demographics or symptoms would not significantly improve the recognition of ADEs. In addition, as ADE detection today is largely based on voluntary reporting systems and retrospective manual tracking of errors, it is evident that more effective methods for ADE detection are needed in the future.

Tandem mass spectrometric analysis of S- and N-linked glutathione conjugates of pulegone and menthofuran and identification of P450 enzymes mediating their formation.

RATIONALE: Menthofuran is a hepatotoxin and a major metabolite of pulegone, a monoterpene found in the essential oils of many mint species. It is bioactivated by cytochrome P450 (CYP) enzymes to reactive metabolites, which may further react with glutathione to form S-linked and N-linked conjugates. The tandem mass spectrometric (MS/MS) fragmentation pathways of rarely observed N-linked conjugates, and the differences to fragmentation of S-linked conjugates, have not been reported in the literature previously, although this information is essential to enable comprehensive MS/MS-based screening methods covering the both types of conjugates. METHODS: (R)-(+)-Pulegone, (S)-(-)-pulegone, and menthofuran were incubated with a human liver S9 fraction with glutathione (GSH) as the trapping agent. Conjugates were searched with ultra-performance liquid chromatography (UPLC)/orbitrap MS and their MS/MS spectra were measured both in the negative and positive ionization polarities. Menthofuran was also incubated with recombinant human CYP enzymes and GSH to elucidate the CYPs responsible for the formation of the reactive metabolites. RESULTS: Four GSH conjugates of menthofuran were detected and identified as S- and N-linked conjugates based on MS/MS spectra. N-linked conjugates lacked the characteristic fragments of S-linked conjugates and commonly produced fragments that retained parts of glutamic acid. CYP1A2, 2B6 and 3A4 were observed to produce more GSH conjugates than other CYP isoforms. CONLUSIONS: Furans can form reactive aldehydes that react in Schiff-base fashion with the free glutamyl-amine of GSH to form N-linked conjugates that have distinct MS/MS spectra from S-linked adducts. This should be taken into account when setting up LC/MS/MS-based detection of glutathione conjugates to screen for reactive metabolites, at least for compounds with a furan moiety. Neutral loss scanning of 178.0412 Da and 290.0573 Da in the positive ionization mode, or neutral loss scanning of 256.0695 Da and 290.0573 Da and precursor ion scanning of m/z 143.0462 in the negative ionization mode, is recommended. Copyright © 2016 John Wiley & Sons, Ltd.

Metabolism and metabolite profiles in vitro and in vivo of ospemifene in humans and preclinical species.

BACKGROUND: Metabolite profiles of ospemifene, a novel nonsteroidal selective estrogen receptor modulator, were surveyed as part of its development. METHODS: The pharmacokinetics of ospemifene and its two major, pharmacologically active metabolites 4-hydroxyospemifene and 4'-hydroxyospemifene, was elucidated in studies of volunteer humans given various doses of ospemifene and in experiments of several animal species (rat, mouse, dog, and cynomolgus monkey), which had been used either for pharmacological or toxicological studies of ospemifene. Metabolites produced in in vitro human and animal liver preparations were compared between species and with the metabolite profiles in the in vivo investigations. RESULTS: Considerable interspecies differences were observed in the metabolite profiles and quantities. The major human metabolite, 4-hydroxyospemifene, was produced in substantial amounts both in vitro and in vivo in most animal species, except dog, and thus the exposure to this metabolite seems adequate in the most important toxicology species, the rat and the cynomolgus monkey. 4'-Hydroxyospemifene was equally abundant in vitro and in vivo metabolite in mice and dogs, and consequently, its contribution to the total exposure of ospemifene-related activity would be adequately covered in animal experiments. Other ospemifene metabolites were variably detected in different species, but probably they are not of consequence to pharmacology or toxicology of ospemifene. CONCLUSIONS: Overall, there are quantitative and also some qualitative differences in the metabolism of ospemifene in different species. Generally, in vitro metabolite profiles were predictive for in vivo profiles. The contribution of two major hydroxyl metabolites to activity and toxicity of ospemifene is adequately covered by at least some animal species.

Formation of GSH-trapped reactive metabolites in human liver microsomes, S9 fraction, HepaRG-cells, and human hepatocytes.

The objective was to compare several in vitro human liver-derived subcellular and cellular incubation systems for the formation of GSH-trapped reactive metabolites. Incubations of pooled human liver microsomes, human liver S9 fractions, HepaRG-cells, and human hepatocytes were performed with glutathione as a trapping agent. Experiments with liver S9 were performed under two conditions, using only NADPH and using a full set of cofactors enabling also conjugative metabolism. Ten structurally different compounds were used as a test set, chosen as either "positive" (ciprofloxacin, clozapine, diclofenac, ethinyl estradiol, pulegone, and ticlopidine) or "negative" (caffeine, citalopram, losartan, montelukast) compounds, based on their known adverse reactions on liver or bone marrow. GSH conjugates were observed for seven of the ten compounds; while no conjugates were observed for caffeine, citalopram, or ciprofloxacin. Hepatocyte and HepaRG assays produced a clearly lower number and lower relative abundance of GSH conjugates compared to assays with microsomes and S9 fractions. The major GSH conjugates were different for many compounds in cellular subfractions and cell-based systems. Hepatocytes generally produced a higher number of GSH conjugates than HepaRG cells, although the differences were minor. The results show that the hepatic enzyme system used for screening of GSH-trapped reactive metabolites do have a high impact on the results, and results between different systems are comparable only qualitatively.

Glutathione trapping of reactive drug metabolites produced by biomimetic metalloporphyrin catalysts.

RATIONALE: Metalloporphyrins can be useful in the production of drug metabolites, as they enable easier production of oxidative metabolites usually produced by the cytochrome P450 enzymes. Our aim was to test metalloporphyrin-based biomimetic oxidation (BMO) methods for production and S-glutathione trapping of reactive drug metabolites in addition to phase I metabolites. METHODS: Clozapine, ticlopidine and citalopram were selected as model compounds. These were incubated with the BMO assay and the incubations were analyzed with high-resolution liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (LC/MS/MS). Additionally, incubations with human liver S9 fraction were performed to compare the results with the BMO assay. RESULTS: Six glutathione conjugates were identified for clozapine from the S9 incubation, while the BMO assay produced four of these. Four out of the five phase I metabolites produced by S9 were detected using the BMO assay. For ticlopidine, four glutathione conjugates were detected from the S9 incubation, but none of these were observed using the BMO assay. Eight of the nine phase I metabolites produced by S9 incubation were detected in the BMO assay. As expected, no glutathione conjugates were detected for citalopram, and the same three phase I metabolites were detected in both S9 and BMO incubations. CONLUSIONS: Differences in formation of GSH-trapped reactive metabolites by BMO assay between clozapine and ticlopidine are probably due to different reactive intermediates and reaction mechanisms. The reactive intermediate of clozapine, the nitrenium ion was generated, but the reactive intermediates of ticlopidine, S-oxide and epoxide, were not detected from the incubations. However, the results show that for selected cases the use of biomimetic assays can be used to produce high amounts of S-glutathione conjugates identical to those from liver subfraction incubations, on a scale that is relevant for purification and subsequent identification by NMR spectroscopy; which is often difficult using incubations with liver subfractions.

Effects of cytochrome P450 inhibitors and inducers on the metabolism and pharmacokinetics of ospemifene.

PURPOSE: The objectives were to determine the cytochrome P450 (CYP) enzymes involved in the metabolism of ospemifene and its main hydroxylated metabolites and to examine the effects of CYP inhibitors and inducers on ospemifene pharmacokinetics. METHODS: In vitro metabolism studies were conducted using human liver microsomes; CYP-selective inhibitors and CYP-specific substrates were used to determine the roles of nine CYP isoforms in ospemifene metabolism. Two Phase 1 clinical trials were conducted in healthy postmenopausal women; crossover designs examined the effects of pretreatment with the CYP modulators rifampicin, ketoconazole, fluconazole and omeprazole on ospemifene pharmacokinetics. RESULTS: Although several CYP inhibitors decreased the in vitro formation of ospemifene metabolites, none of them completely blocked metabolism. Roles for CYP3A4, CYP2C9, CYP2C19 and CYP2B6 in the metabolism of ospemifene and its two main metabolites, 4--hydroxyospemifene and 4'-hydroxyospemifene, were confirmed. The in vivo experiments demonstrated that ospemifene serum concentrations were decreased by rifampicin pretreatment, increased by ketoconazole or fluconazole pretreatment, and minimally affected by omeprazole pretreatment. CONCLUSIONS: The clinical pharmacokinetic findings and in vitro data suggest that CYP3A4 is important for ospemifene metabolism, but other CYP isoforms and metabolic pathways also contribute. Strong CYP3A or CYP2C9 inducers (e.g. rifampicin) would be expected to decrease the exposure to ospemifene. Ospemifene should be used with caution when coadministered with the modest CYP3A inhibitor ketoconazole and should not be coadministered with the potent CYP3A/CYP2C9/CYP2C19 inhibitor fluconazole. The potent CYP2C19 inhibitor omeprazole is unlikely to cause clinically significant changes in ospemifene pharmacokinetics.

Effects of ospemifene on drug metabolism mediated by cytochrome P450 enzymes in humans in vitro and in vivo.

The objective of these investigations was to determine the possible effects of the novel selective estrogen receptor modulator, ospemifene, on cytochrome P450 (CYP)-mediated drug metabolism. Ospemifene underwent testing for possible effects on CYP enzyme activity in human liver microsomes and in isolated human hepatocytes. Based on the results obtained in vitro, three Phase 1 crossover pharmacokinetic studies were conducted in healthy postmenopausal women to assess the in vivo effects of ospemifene on CYP-mediated drug metabolism. Ospemifene and its main metabolites 4-hydroxyospemifene and 4'-hydroxyospemifene weakly inhibited a number of CYPs (CYP2B6, CYP2C9, CYP2C19, CYP2C8, and CYP2D6) in vitro. However, only CYP2C9 activity was inhibited by 4-hydroxyospemifene at clinically relevant concentrations. Induction of CYPs by ospemifene in cultured human hepatocytes was 2.4-fold or less. The in vivo studies showed that ospemifene did not have significant effects on the areas under the plasma concentration-time curves of the tested CYP substrates warfarin (CYP2C9), bupropion (CYP2B6) and omeprazole (CYP2C19), demonstrating that pretreatment with ospemifene did not alter their metabolism. Therefore, the risk that ospemifene will affect the pharmacokinetics of drugs that are substrates for CYP enzymes is low.

Ospemifene metabolism in humans in vitro and in vivo: metabolite identification, quantitation, and CYP assignment of major hydroxylations.

BACKGROUND: The metabolism of ospemifene, a novel nonsteroidal selective estrogen receptor modulator, was investigated as part of its development. METHODS: Metabolite identification, tentative quantitation, and CYP assignment of ospemifene were performed in human liver microsomes or homogenate incubations and in plasma samples from volunteer humans. The potential contributions of CYP enzymes were determined by recombinant human CYPs. Metabolite identification and tentative quantification were performed by liquid chromatography-mass spectrometry. RESULTS: The relative abundances of metabolites produced were dependent on ospemifene concentration and liver preparation, but the largest quantities of 4- and 4'-hydroxy-ospemifene (and their glucuronides in smaller quantities) were produced in human liver microsomes at low ospemifene concentrations. Other metabolites were detected in in vitro incubation with human liver including a direct glucuronide of ospemifene and some metabolites with only minor abundance. In human plasma samples, 4-hydroxy-ospemifene was the most abundant metabolite, representing about 25% of the abundance of the parent compound. All the other metabolites detected in plasma, including 4'-hydroxy-ospemifene, represented <7% of the abundance of ospemifene. Several CYP enzymes participated in 4-hydroxylation, including CYP2C9, CYP2C19, CYP2B6, and CYP3A4, whereas CYP3A enzymes were the only ones to catalyze 4'-hydroxylation. CONCLUSIONS: In vitro incubations with liver preparations provided a rather reliable starting point in the search for potential metabolites in clinical settings. The in vitro metabolite profile is informative for the in vivo metabolite profile, especially regarding the major hydroxylated metabolites. However, it is anticipated that extended in vivo exposures may result in an increased production of more distal metabolites from major metabolites.

Genetic polymorphism of cytochrome P450 2D6 determines oestrogen receptor activity of the major infertility drug clomiphene via its active metabolites.

Clomiphene citrate is the most used drug for the treatment of female infertility, a common condition in western societies and developing countries. Despite dose escalation, up to 30% of women do not respond. Since clomiphene shares structural similarities with tamoxifen, which is predominantly bioactivated by the polymorphic cytochrome P450 (CYP) 2D6, we systematically explored clomiphene metabolism and action in vitro and in vivo by pharmacogenetic, -kinetic and -dynamic investigations. Human liver microsomes were incubated with clomiphene citrate and nine metabolites were identified by mass spectrometry and tested at the oestrogen receptor for their antagonistic capacity. (E)-4-hydroxyclomiphene and (E)-4-hydroxy-N-desethylclomiphene showed strongest inhibition of the oestrogen receptor activity with 50% inhibitory concentrations of 2.5 and 1.4 nm, respectively. CYP2D6 has been identified as the major enzyme involved in their formation using recombinant CYP450 isozymes as confirmed by inhibition experiments with CYP monoclonal antibodies. We correlated the CYP2D6 genotype of 30 human liver donors with the microsomal formation rate of active metabolites and observed a strong gene-dose effect. A healthy female volunteer study confirmed our in vitro data that the CYP2D6 polymorphism substantially determines the formation of the active clomiphene metabolites. Comparison of the C(max) of (E)-4-hydroxyclomiphene and (E)-4-hydroxy-N-desethylclomiphene showed 8 and 12 times lower concentrations in subjects with non-functional CYP2D6 alleles. Our results highlight (E)-4-hydroxyclomiphene and (E)-4-hydroxy-N-desethylclomiphene as the active clomiphene metabolites, the formation of which strongly depends on the polymorphic CYP2D6 enzyme. Our data provide first evidence of a biological rationale for the variability in the response to clomiphene treatment.

Transfer of repaglinide in the dually perfused human placenta and the role of organic anion transporting polypeptides (OATPs).

OBJECTIVES: Our aim was to investigate the placental transfer of repaglinide by ex vivo placental perfusion experiment. In addition, the involvement of the active organic anion transporters (OATP1B1, OATP1B3 and OATP2B1) was studied by assessing the single nucleotide polymorphisms (SNPs) in genes (SLCO1B1, SLCO1B3 and SLCO2B1) encoding OATPs. STUDY DESIGN: Fifteen placentas were obtained after delivery and a 2-h non-recirculating perfusion of a single placental cotyledon was performed to study maternal-to-fetal and fetal-to-maternal transport of repaglinide by using antipyrine as a reference of passive-diffusion transfer compound. Genotyping was performed for all placentas. RESULTS: Maternal-to-fetal transfer of repaglinide and antipyrine were 1.5% and 13.2%, respectively, and fetal-to-maternal transfers were 6.7% and 40.3%, respectively. Fetal-to-maternal transfer of repaglinide was statistically significantly higher than maternal-to-fetal transfer (P<0.0001). The number of placentas was not sufficient for proper statistical analysis, but the fetal-to-maternal transfer seemed to be affected by the SLCO1B3 polymorphism. CONCLUSIONS: The placental transfer of repaglinide from mother to fetus was low. Since a higher transfer rate of repaglinide was observed in fetal-to-maternal than maternal-to-fetal direction, active transport by OATP-transporters may be an important factor in fetal exposure to repaglinide.

Stable expression, activity, and inducibility of cytochromes P450 in differentiated HepaRG cells.

HepaRG cells possess the unique property to differentiate in vitro and to express various functions of mature hepatocytes, including the major cytochromes P450 (P450s). In the present study, we carefully analyzed mRNA expression and activity of the major P450s and their responsiveness to three prototypical inducers, phenobarbital, rifampicin, and omeprazole, in differentiated HepaRG cell cultures over a 4-week period after low and high seeding. Only minor differences were observed in P450 activities when measured by two cocktails of probe substrates, probably related to the choice and/or concentration of substrates. Similar results were obtained from the two cell seeding conditions. Expression and activities of several P450s were dimethyl sulfoxide-dependent. However, basal P450 expression and activities as well as their responsiveness to the prototypical inducers were well maintained over the 4-week period, and a good correlation was observed between transcript levels and corresponding activities. Thus, CYP1A2, CYP2B6, and CYP3A4 were found to accurately respond to their respective prototypical inducers, i.e., omeprazole, phenobarbital, and rifampicin. Likewise, basal expression of several phase II enzymes, transporters, and nuclear receptors, and response to inducers were also well preserved. More genes were found to be induced in HepaRG cells than in primary human hepatocytes, and no marked variation was noticed between the different passages. Taken together, these data support the conclusion that HepaRG cells represent a promising surrogate to primary human hepatocytes for xenobiotic metabolism and toxicity studies.

An evaluation of the cytochrome P450 inhibition potential of selected pesticides in human hepatic microsomes.

The goal of this work was to study the ability of 18 pesticides to inhibit selective model activities for all major xenobiotic-metabolizing enzymes, namely CYP1A1/2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4. Generally organophosphorus insecticides were the most potent and extensive inhibitors, especially towards CYP1A1/2 (IC(50) values of chlorpyrifos, fenitrothion and profenofos approximately 3 micro M), CYP2B6 (IC(50) values of chlorpyrifos and fenitrothion 2.5 micro M), CYP2C8 (fenitrothion 4.3 micro M), CYP2C9 (fenitrothion and malathion 4.8 and 2.5 micro M, respectively), CYP2D6 (chlorpyrifos and phenthoate approximately 3 micro M) and CYP3A4 (chlorpyrifos, fenitrothion and phenthoate 3-4 micro M). Otherwise there were quite considerable differences in potency and extent of inhibition between different organophosphates. Pyrethroids were in general very weak or inactive. Deltamethrin and fenvalerate were potent inhibitors of CYP2D6 (IC(50) values of approximately 3 micro M) while lambda-cyhalothrin potently inhibited both CYP2D6 and CYP3A4-mediated activities (IC(50)'s about 3-4 micro M). Some pesticides caused relatively potent inhibitions sporadically (carbendazim, CYP2D6, IC(50) = 12 micro M; atrazine, CYP3A4, IC(50) = 2.8 micro M; glyphosate, CYP2C9, IC(50) = 3.7 micro M; hexaflumuron, IC(50) = 6.0 micro M). With the exceptions of alpha-cypermethrin, cypermethrin, isoproturon, carbaryl and abamectin, most pesticides inhibited relatively potently at least one CYP-selective activity, which may have relevance for potential interactions in occupational exposures and for further studies on the CYP-associated metabolism of respective pesticides.

Identification of bupropion urinary metabolites by liquid chromatography/mass spectrometry.

Human urinary metabolism of the antidepressant bupropion was studied using liquid chromatography/time-of-flight mass spectrometry (LC/TOFMS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS). A total of 20 metabolites were detected and identified. The phase I metabolism included formation of morpholinohydroxybupropion, threo- and erythrohydrobupropion, aromatic hydroxylation, butyl group hydroxylation with ketone hydrogenation and dihydroxylation. These metabolites were detected either as the free form or as glucuronide and/or sulphate conjugates. In addition also m-chlorohippuric acid was detected. Of the phase I metabolites, a dihydroxylation to the aromatic ring and to the methyl group in the middle of the substrate molecule was reported here for the first time, as well as eight of the glucuronide conjugates (to hydroxy, dihydroxy, hydroxy and hydrogenation metabolites) and three of the sulphate conjugates (to aromatic hydroxy and hydroxy and hydrogenation metabolites).

Characterization of diuron N-demethylation by mammalian hepatic microsomes and cDNA-expressed human cytochrome P450 enzymes.

Diuron, a widely used herbicide and antifouling biocide, has been shown to persist in the environment and contaminate drinking water. It has been characterized as a "known/likely" human carcinogen. Whereas its environmental transformation and toxicity have been extensively examined, its metabolic characteristics in mammalian livers have not been reported. This study was designed to investigate diuron biotransformation and disposition because metabolic routes, metabolizing enzymes, interactions, interspecies differences, and interindividual variability are important for risk assessment purposes. The only metabolic pathway detected by liquid chromatography/mass spectometry in human liver homogenates and seven types of mammalian liver microsomes including human was demethylation at the terminal nitrogen atom. No other phase I or phase II metabolites were observed. The rank order of N-demethyldiuron formation in liver microsomes based on intrinsic clearance (V(max)/K(m)) was dog > monkey > rabbit > mouse > human > minipig > rat. All tested recombinant human cytochrome P450s (P450s) catalyzed diuron N-demethylation and the highest activities were possessed by CYP1A1, CYP1A2, CYP2C19, and CYP2D6. Relative contributions of human CYP1A2, CYP2C19, and CYP3A4 to hepatic diuron N-demethylation, based on average abundances of P450 enzymes in human liver microsomes, were approximately 60, 14, and 13%, respectively. Diuron inhibited relatively potently only CYP1A1/2 (IC(50) 4 microM). With human-derived and quantitative chemical-specific data, the uncertainty factors for animal to human differences and for human variability in toxicokinetics were within the range of the toxicokinetics default uncertainty/safety factors for chemical risk assessment.

Effect of renal impairment on the pharmacokinetics of bupropion and its metabolites.

AIMS: To investigate the effect of kidney disease on bupropion pharmacokinetics and on cytochrome P450 (CYP) 2B6 activity as measured by bupropion hydroxylation. METHODS: In an open parallel group study, 17 healthy, nonsmoking subjects and 10 patients with impaired kidney function received a single 150 mg oral dose of sustained release bupropion. Plasma concentrations of bupropion and its metabolites were measured for up to 72 h. Subjects were genotyped for the CYP2B6 SNPs 1459 C>T, 785 A>G and 516 G>T. RESULTS: Bupropion AUC was 126% higher (P < 0.0001, 95% CI +72%, +180%), C(max) 86% higher (P = 0.001, 95% CI +40%, +131%), CL/F 63% lower (P = 0.001, 95% CI -29%, -96%), and t(1/2) 140% longer (P = 0.001, 95% CI +76%, +204%) in renally impaired patients. However, only minor changes were detected in the concentrations of the metabolites. In renally impaired subjects the hydroxybupropion : bupropion AUC ratio was decreased by 66% (P = < 0.0001, 95% CI -19%, -114%) and the hydrobupropion : bupropion AUC ratio by 69% (P = 0.001, 95% CI +8%, -146%) compared with controls. CONCLUSIONS: The CL/F of bupropion was significantly lower in subjects with renal impairment. Because the principal metabolites of bupropion possess similar pharmacological activity to the parent compound, dosage recommendations for patients with renal impairment cannot be given. A direct effect of renal impairment on CYP2B6 activity could not be demonstrated by the present study design.