Medetomidiinin glukuronidaation inhibitio

Lääkeainemetabolialla tarkoitetaan entsymaattisia reaktioita, jotka muuttavat lääkeaineita paremmin elimistöstä poistuvaan muotoon. Lääkeaineet voivat vaikuttaa toistensa metaboliaan inhiboimalla tai indusoimalla metaboloivia entsyymejä. Tällaisten interaktioiden seurauksena lääkeaineen pitoisuus elimistössä voi kasvaa jopa toksiseksi tai vähentyä merkittävästi. Tämä on erityisesti ongelmana silloin, kun käytössä on useita lääkkeitä samanaikaisesti. Lääketutkimuksessa onkin keskitytty tällaisten interaktioiden ennustamiseen ja niitä yritetään välttää tai ainakin vähentää. Työssä tutkittiin medetomidiinia, jonka on äskettäin havaittu metaboloituvan UDP-glukuronosyylitransferaasien (UGT) välityksellä. Työn tarkoituksena oli löytää medetomidiinin glukuronidaatiota inhiboivia yhdisteitä. Lisäksi haluttiin selvittää mahdollisen inhibition mekanismeja. On yleistä tutkia tietyn entsyymin substraatin interaktioita muiden saman perheen entsyymien kanssa. On kuitenkin harvinaisempaa tutkia tällaisia interaktioita kahden eri entsyymiperheen välillä. Tässä työssä tutkittiin inhiboivatko mahdolliset sytokromi P450 -entsyymiä (CYP) inhiboivat yhdisteet myös medetomidiinia glukuronoivia UDP-glukuronosyylitransferaaseja. Glukuronidaation inhibitiota tutkittiin HPLC-menetelmällä, joka on kehitetty aiemmin medetomidiinin glukuronidaation tutkimiseen. Aluksi glukuronidaatiota tutkittiin ilman inhibiittoreita. Tämän jälkeen tutkittiin kolmen mahdollisen inhibiittoriyhdisteen vaikutuksia medetomidiinin glukuronidaatioon ja tuloksia verrattiin ilman inhibiittoria saatuihin tuloksiin. Kolmen tutkitun yhdisteen havaittiin inhiboivan medetomidiinin glukuronidaatiota. Tutkimuksessa havaittiin myös mielenkiintoinen ilmiö, jossa inhibiittoriyhdisteen sitoutuminen aiheutti entsyymikineettisiä muutoksia UDP-glukuronosyylitransferaasin toiminnassa. On mielenkiintoista, että samat yhdisteet inhiboivat sekä CYP- että UGT-metaboliaa. Tulosten perusteella voidaan päätellä, että jos CYP ja UGT metaboloivat samaa yhdistettä, on mahdollista että yhdisteen rakenteelliset analogit aiheuttavat interaktioita molempien entsyymien kanssa. Uusia lääkeaineita kehitettäessä onkin otettava huomioon yleisesti tunnettujen CYP-entsyymien lisäksi myös UGT:t ja niiden mahdolliset yhteisvaikutukset.

EFEITO DE SURFACTANTES NA ESTABILIDADE DE COMPOSTOS DE USO TERAPEUTICO

A critical revision of literature as regards to the drug stability in the presence of surfactants were realized. The functional groups envolved in the drug decomposition were used to the development of the discussion. The analysis indicated that the detergent effect can be used to control the rates and mechanisms of drug decomposition and to obtain specific information about the drug reactivity in the environment of pharmacological action.

Photodegradation of sparfloxacin and isolation of its degradation products by preparative HPLC

Sparfloxacin, a third generation fluoroquinolone derivative, is a potent antibacterial agent active against a wide range of Gram-positive and Gram-negative organisms including Streptococcus pneuinoniae, Staphylococcus aureus, methicillin resistant S. aureus, Legionella spp., Mycoplasina spp., Chlamydia spp. and Mycobacterium spp. A drawback of fluoroquinolones is their photoreactivity. Sparfloxacin has been studied in terms of therapeutic activities. However, there are few published of analytical methods being applied to sparfloxacin. The aim in this study was to determine the photodegradation products of sparfloxacin, when submitted to UV light, and to characterize two of these products, designated SPAX-PDP1 and SPAX-PDP2. An accelerated study of stability in methanol solution was carried out by exposing a solution of sparfloxacin to UV light (peak wavelength 290 nm) for 36 hours at room temperature. The products were analyzed by NMR spectrophotometry, IR spectrometry and mass spectrophotometry. The results suggest that the products isolated here could be used to estimate the degradation of sparfloxacin in a stability study. However, the low activity exhibited by UV-irradiated sparfloxacin is a source of concern that demands further investigation of the mechanism of its photodegradation mechanism.

Bioprospecção de atividade antioxidante e antimicrobiana da casca de Stryphnodendron adstringens (Mart.) Coville (Leguminosae-Mimosoidae)

The aim of this work was to evaluate the class of secondary metabolites responsible for the antioxidant and antimicrobial activities of bark extracts of Stryphnodendron adstringens (Mart.) Coville (Leguminosae-Mimosoidae), a plant widely used in folk medicine in Brazil. Extracts of the bark were prepared with 50% ethanol, 70% ethanol, acetone:water (7:3, v/v) and chloroform. Antioxidant activity was prospected by spraying thin-layer chromatographs of the extracts with 2,2-diphenyl-1-picryl-hydrazyl (DPPH) and measuring the DPPH radical scavenging capacity by spectrophotometry. Antibacterial activity was revealed by the agar diffusion method and bioautography. TLC spots assigned to tannins in the polar extracts showed antioxidant activity by DPPH radical scavenging and the chloroform extract showed the least scavenging activity. Antimicrobial activity was indicated by the bacterial growth inhibition haloes around polar extracts and bioautography showed activity in the TLC spots assigned to tannins. It was concluded that polar extracts of the bark of S. adstringens possessed antioxidant and antimicrobial activities which were due to secondary metabolite derived from the tannin class, which are the main constituent of these bark extracts, according to the literature.

Activation of T cells by carbamazepine and carbamazepine metabolites

BACKGROUND: T-cell-mediated hypersensitivity is a rare but serious manifestation of drug therapy. OBJECTIVES: To explore the mechanisms of drug presentation to T cells and the possibility that generation of metabolite-specific T cells may provoke cross-sensitization between drugs. METHODS: A lymphocyte transformation test was performed on 13 hypersensitive patients with carbamazepine, oxcarbazepine, and carbamazepine metabolites. Serial dilution experiments were performed to generate drug (metabolite)-specific T-cell clones to explore the structural basis of the T-cell response and mechanisms of antigen presentation. 3-Dimensional energy-minimized structures were generated by using computer modeling. The role of drug metabolism was analyzed with 1-aminobenzotriazole. RESULTS: Lymphocytes and T-cell clones proliferated with carbamazepine, oxcarbazepine, and some (carbamazepine 10,11 epoxide, 10-hydroxy carbamazepine) but not all stable carbamazepine metabolites. Structure activity studies using 29 carbamazepine (metabolite)-specific T-cell clones revealed 4 patterns of drug recognition, which could be explained by generation of preferred 3-dimensional structural conformations. T cells were stimulated by carbamazepine (metabolites) bound directly to MHC in the absence of processing. The activation threshold for T-cell proliferation varied between 5 minutes and 4 hours. 1-Aminobenzotriazole, which inhibits cytochrome P450 activity, did not prevent carbamazepine-related T-cell proliferation. Substitution of the terminal amine residue of carbamazepine with a methyl group diminished T-cell proliferation. CONCLUSION: These data show that carbamazepine and certain stable carbamazepine metabolites stimulate T cells rapidly via a direct interaction with MHC and specific T-cell receptors. CLINICAL IMPLICATIONS: Some patients with a history of carbamazepine hypersensitivity possess T cells that cross-react with oxcarbazepine, providing a rationale for cross-sensitivity between the 2 drugs.

Interaction of small molecules with specific immune receptors: the p-i concept and its consequences

Drugs may stimulate the immune system by forming stable new antigenic complexes consisting of the drug or drug metabolite which is covalently bound to a protein or peptide (hapten-carrier complex). Both, B- and T-cell immunity may arise, the latter directed to hapten modified peptides presented by HLA molecules. Beside this immunological stimulation, drugs can also stimulate the immune system through binding by non-covalent bonds to proteins like immune receptors. This so-called “pharmacological interaction with immune receptors” concept (“p-i concept”) may occur with HLA or TCR molecules themselves (p-i HLA or p-i TCR), and not the immunogenic peptide. It is a type of “off-target” activity of the drug on immune receptors, but more complex as various cell types, cell interactions and functionally different T cells are involved. In this review the conditions which lead to activation of T cells by p-i are discussed: important factors for a functional consequence of drug binding is the location of binding (p-i HLA or p-i TCR); the exact site within these immune receptors; the affinity of binding and the finding that p-i HLA can stimulate the immune system like an allo-allele. The p-i concept is able to solve some puzzles of drug hypersensitivity reactions and are a basis to better treat and potentially avoid drug hypersensitivity reactions. Moreover, the p-i concept shows that in contrast to previous beliefs small molecules do interact with immune receptors with functional consequence. But these interactions are not based on “immune recognition”, are at odds with some immunological concepts, but may nevertheless open new possibilities to understand and even treat immune reactions

The development of an objective methodology to measure medication adherence to oral thiopurines in paediatric patients with acute lymphoblastic leukaemia - an exploratory study

Aims - To develop a method that prospectively assesses adherence rates in paediatric patients with acute lymphoblastic leukaemia (ALL) who are receiving the oral thiopurine treatment 6-mercaptopurine (6-MP). Methods - A total of 19 paediatric patients with ALL who were receiving 6-MP therapy were enrolled in this study. A new objective tool (hierarchical cluster analysis of drug metabolite concentrations) was explored as a novel approach to assess non-adherence to oral thiopurines, in combination with other objective measures (the pattern of variability in 6-thioguanine nucleotide erythrocyte concentrations and 6-thiouric acid plasma levels) and the subjective measure of self-reported adherence questionnaire. Results - Parents of five ALL patients (26.3%) reported at least one aspect of non-adherence, with the majority (80%) citing “carelessness at times about taking medication” as the primary reason for non-adherence followed by “forgetting to take the medication” (60%). Of these patients, three (15.8%) were considered non-adherent to medication according to the self-reported adherence questionnaire (scored ≥ 2). Four ALL patients (21.1%) had metabolite profiles indicative of non-adherence (persistently low levels of metabolites and/or metabolite levels clustered variably with time). Out of these four patients, two (50%) admitted non-adherence to therapy. Overall, when both methods were combined, five patients (26.3%) were considered non-adherent to medication, with higher age representing a risk factor for non-adherence (P < 0.05). Conclusions - The present study explored various ways to assess adherence rates to thiopurine medication in ALL patients and highlighted the importance of combining both objective and subjective measures as a better way to assess adherence to oral thiopurines.

Drug metabolism in human brain: high levels of cytochrome P4503A43 in brain and metabolism of anti-anxiety drug alprazolam to its active metabolite.

Cytochrome P450 (P450) is a super-family of drug metabolizing enzymes. P450 enzymes have dual function; they can metabolize drugs to pharmacologically inactive metabolites facilitating their excretion or biotransform them to pharmacologically active metabolites which may have longer half-life than the parent drug. The variable pharmacological response to psychoactive drugs typically seen in population groups is often not accountable by considering dissimilarities in hepatic metabolism. Metabolism in brain specific nuclei may play a role in pharmacological modulation of drugs acting on the CNS and help explain some of the diverse response to these drugs seen in patient population. P450 enzymes are also present in brain where drug metabolism can take place and modify therapeutic action of drugs at the site of action. We have earlier demonstrated an intrinsic difference in the biotransformation of alprazolam (ALP) in brain and liver, relatively more alpha-hydroxy alprazolam (alpha-OHALP) is formed in brain as compared to liver. In the present study we show that recombinant CYP3A43 metabolizes ALP to both alpha-OHALP and 4-hydroxy alprazolam (4-OHALP) while CYP3A4 metabolizes ALP predominantly to its inactive metabolite, 4-OHALP. The expression of CYP3A43 mRNA in human brain samples correlates with formation of relatively higher levels of alpha-OH ALP indicating that individuals who express higher levels of CYP3A43 in the brain would generate larger amounts of alpha-OHALP. Further, the expression of CYP3A43 was relatively higher in brain as compared to liver across different ethnic populations. Since CYP3A enzymes play a prominent role in the metabolism of drugs, the higher expression of CYP3A43 would generate metabolite profile of drugs differentially in human brain and thus impact the pharmacodynamics of psychoactive drugs at the site of action.

Drug metabolism in human brain: high levels of cytochrome P4503A43 in brain and metabolism of anti-anxiety drug alprazolam to its active metabolite.

Cytochrome P450 (P450) is a super-family of drug metabolizing enzymes. P450 enzymes have dual function; they can metabolize drugs to pharmacologically inactive metabolites facilitating their excretion or biotransform them to pharmacologically active metabolites which may have longer half-life than the parent drug. The variable pharmacological response to psychoactive drugs typically seen in population groups is often not accountable by considering dissimilarities in hepatic metabolism. Metabolism in brain specific nuclei may play a role in pharmacological modulation of drugs acting on the CNS and help explain some of the diverse response to these drugs seen in patient population. P450 enzymes are also present in brain where drug metabolism can take place and modify therapeutic action of drugs at the site of action. We have earlier demonstrated an intrinsic difference in the biotransformation of alprazolam (ALP) in brain and liver, relatively more alpha-hydroxy alprazolam (alpha-OHALP) is formed in brain as compared to liver. In the present study we show that recombinant CYP3A43 metabolizes ALP to both alpha-OHALP and 4-hydroxy alprazolam (4-OHALP) while CYP3A4 metabolizes ALP predominantly to its inactive metabolite, 4-OHALP. The expression of CYP3A43 mRNA in human brain samples correlates with formation of relatively higher levels of alpha-OH ALP indicating that individuals who express higher levels of CYP3A43 in the brain would generate larger amounts of alpha-OHALP. Further, the expression of CYP3A43 was relatively higher in brain as compared to liver across different ethnic populations. Since CYP3A enzymes play a prominent role in the metabolism of drugs, the higher expression of CYP3A43 would generate metabolite profile of drugs differentially in human brain and thus impact the pharmacodynamics of psychoactive drugs at the site of action.

Phenytoin metabolism by human cytochrome P450 : involvement of P450 3A and 2C forms in secondary metabolism and drug-protein adduct formation

The anticonvulsant phenytoin (5,5-diphenylhydantoin) provokes a skin rash in 5 to 10% of patients, which heralds the start of an idiosyncratic reaction that may result from covalent modification of normal self proteins by reactive drug metabolites. Phenytoin is metabolized by cytochrome P450 (P450) enzymes primarily to 5-(p-hydroxyphenyl-),5-phenylhydantoin (HPPH), which may be further metabolized to a catechol that spontaneously oxidizes to semiquinone and quinone species that covalently modify proteins. The aim of this study was to determine which P450s catalyze HPPH metabolism to the catechol, proposed to be the final enzymatic step in phenytoin bioactivation. Recombinant human P450s were coexpressed with NADPH-cytochrome P450 reductase in Escherichia coli. Novel bicistronic expression vectors were constructed for P450 2C19 and the three major variants of P450 2C9, i.e., 2C9*1, 2C9*2, and 2C9*3. HPPH metabolism and covalent adduct formation were assessed in parallel. P450 2C19 was the most effective catalyst of HPPH oxidation to the catechol metabolite and was also associated with the highest levels of covalent adduct formation. P450 3A4, 3A5, 3A7, 2C9*1, and 2C9*2 also catalyzed bioactivation of HPPH, but to a lesser extent. Fluorographic analysis showed that the major targets of adduct formation in bacterial membranes were the catalytic P450 forms, as suggested from experiments with human liver microsomes. These results suggest that P450 2C19 and other forms from the 2C and 3A subfamilies may be targets as well as catalysts of drug-protein adduct formation from phenytoin.

Novel Mass Spectrometric Analysis Methods for Anabolic Androgenic Steroids in Sports Drug Testing

The feasibility of different modern analytical techniques for the mass spectrometric detection of anabolic androgenic steroids (AAS) in human urine was examined in order to enhance the prevalent analytics and to find reasonable strategies for effective sports drug testing. A comparative study of the sensitivity and specificity between gas chromatography (GC) combined with low (LRMS) and high resolution mass spectrometry (HRMS) in screening of AAS was carried out with four metabolites of methandienone. Measurements were done in selected ion monitoring mode with HRMS using a mass resolution of 5000. With HRMS the detection limits were considerably lower than with LRMS, enabling detection of steroids at low 0.2-0.5 ng/ml levels. However, also with HRMS, the biological background hampered the detection of some steroids. The applicability of liquid-phase microextraction (LPME) was studied with metabolites of fluoxymesterone, 4-chlorodehydromethyltestosterone, stanozolol and danazol. Factors affecting the extraction process were studied and a novel LPME method with in-fiber silylation was developed and validated for GC/MS analysis of the danazol metabolite. The method allowed precise, selective and sensitive analysis of the metabolite and enabled simultaneous filtration, extraction, enrichment and derivatization of the analyte from urine without any other steps in sample preparation. Liquid chromatographic/tandem mass spectrometric (LC/MS/MS) methods utilizing electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) were developed and applied for detection of oxandrolone and metabolites of stanozolol and 4-chlorodehydromethyltestosterone in urine. All methods exhibited high sensitivity and specificity. ESI showed, however, the best applicability, and a LC/ESI-MS/MS method for routine screening of nine 17-alkyl-substituted AAS was thus developed enabling fast and precise measurement of all analytes with detection limits below 2 ng/ml. The potential of chemometrics to resolve complex GC/MS data was demonstrated with samples prepared for AAS screening. Acquired full scan spectral data (m/z 40-700) were processed by the OSCAR algorithm (Optimization by Stepwise Constraints of Alternating Regression). The deconvolution process was able to dig out from a GC/MS run more than the double number of components as compared with the number of visible chromatographic peaks. Severely overlapping components, as well as components hidden in the chromatographic background could be isolated successfully. All studied techniques proved to be useful analytical tools to improve detection of AAS in urine. Superiority of different procedures is, however, compound-dependent and different techniques complement each other.

Liquid Chromatography-Mass Spectrometry in Studies of Drug Metabolism and Permeability

Poor pharmacokinetics is one of the reasons for the withdrawal of drug candidates from clinical trials. There is an urgent need for investigating in vitro ADME (absorption, distribution, metabolism and excretion) properties and recognising unsuitable drug candidates as early as possible in the drug development process. Current throughput of in vitro ADME profiling is insufficient because effective new synthesis techniques, such as drug design in silico and combinatorial synthesis, have vastly increased the number of drug candidates. Assay technologies for larger sets of compounds than are currently feasible are critically needed. The first part of this work focused on the evaluation of cocktail strategy in studies of drug permeability and metabolic stability. N-in-one liquid chromatography-tandem mass spectrometry (LC/MS/MS) methods were developed and validated for the multiple component analysis of samples in cocktail experiments. Together, cocktail dosing and LC/MS/MS were found to form an effective tool for increasing throughput. First, cocktail dosing, i.e. the use of a mixture of many test compounds, was applied in permeability experiments with Caco-2 cell culture, which is a widely used in vitro model for small intestinal absorption. A cocktail of 7-10 reference compounds was successfully evaluated for standardization and routine testing of the performance of Caco-2 cell cultures. Secondly, cocktail strategy was used in metabolic stability studies of drugs with UGT isoenzymes, which are one of the most important phase II drug metabolizing enzymes. The study confirmed that the determination of intrinsic clearance (Clint) as a cocktail of seven substrates is possible. The LC/MS/MS methods that were developed were fast and reliable for the quantitative analysis of a heterogenous set of drugs from Caco-2 permeability experiments and the set of glucuronides from in vitro stability experiments. The performance of a new ionization technique, atmospheric pressure photoionization (APPI), was evaluated through comparison with electrospray ionization (ESI), where both techniques were used for the analysis of Caco-2 samples. Like ESI, also APPI proved to be a reliable technique for the analysis of Caco-2 samples and even more flexible than ESI because of the wider dynamic linear range. The second part of the experimental study focused on metabolite profiling. Different mass spectrometric instruments and commercially available software tools were investigated for profiling metabolites in urine and hepatocyte samples. All the instruments tested (triple quadrupole, quadrupole time-of-flight, ion trap) exhibited some good and some bad features in searching for and identifying of expected and non-expected metabolites. Although, current profiling software is helpful, it is still insufficient. Thus a time-consuming largely manual approach is still required for metabolite profiling from complex biological matrices.

Genome-wide association study identifies novel genetic variants contributing to variation in blood metabolite levels

Metabolites are small molecules involved in cellular metabolism, which can be detected in biological samples using metabolomic techniques. Here we present the results of genome-wide association and meta-analyses for variation in the blood serum levels of 129 metabolites as measured by the Biocrates metabolomic platform. In a discovery sample of 7,478 individuals of European descent, we find 4,068 genome- and metabolome-wide significant (Z-test, P<1.09 × 10−9) associations between single-nucleotide polymorphisms (SNPs) and metabolites, involving 59 independent SNPs and 85 metabolites. Five of the fifty-nine independent SNPs are new for serum metabolite levels, and were followed-up for replication in an independent sample (N=1,182). The novel SNPs are located in or near genes encoding metabolite transporter proteins or enzymes (SLC22A16, ARG1, AGPS and ACSL1) that have demonstrated biomedical or pharmaceutical importance. The further characterization of genetic influences on metabolic phenotypes is important for progress in biological and medical research.

Studies on CYP2C8-mediated drug interactions

Useiden lääkkeiden yhtäaikainen käyttö on nykyään hyvin yleistä, mikä lisää lääkeaineiden haitallisten yhteisvaikutusten riskiä. Lääkeaineiden poistumisessa elimistöstä ovat tärkeässä osassa niitä hajottavat (metaboloivat) maksan sytokromi P450 (CYP) entsyymit. Vasta aivan viime vuosina on havaittu, että CYP2C8-entsyymillä voi olla tärkeä merkitys mm. lääkeaineyhteisvaikutuksissa. Eräät lääkeaineet voivat estää (inhiboida) CYP2C8-entsyymin kautta tapahtuvaa metaboliaa. Tässä työssä selvitettiin CYP2C8-entsyymiä estävien lääkkeiden vaikutusta sellaisten lääkeaineiden pitoisuuksiin, joiden aikaisemman tiedon perusteella arveltiin metaboloituvan CYP2C8-välitteisesti. Näiden lääkeaineiden metaboliaa tutkittiin myös koeputkiolosuhteissa (in vitro -menetelmillä). Lisäksi CYP2C8-entsyymiä estävän lipidilääke gemfibrotsiilin yhteisvaikutusmekanismia tutkittiin selvittämällä interaktion säilymistä koehenkilöillä gemfibrotsiilin annostelun lopettamisen jälkeen. Yhteisvaikutuksia tutkittiin terveillä vapaaehtoisilla koehenkilöillä käyttäen vaihtovuoroista koeasetelmaa. Koehenkilöille annettiin CYP2C8-entsyymiä estävää lääkitystä muutaman päivän ajan ja tämän jälkeen kerta-annos tutkimuslääkettä. Koehenkilöiltä otettiin useita verinäytteitä, joista määritettiin lääkepitoisuudet nestekromatografisilla tai massaspektrometrisillä menetelmillä. Gemfibrotsiili nosti ripulilääke loperamidin pitoisuudet keskimäärin kaksinkertaiseksi. Gemfibrotsiili lisäsi, mutta vain hieman, kipulääke ibuprofeenin pitoisuuksia, eikä sillä ollut mitään vaikutusta unilääke tsopiklonin pitoisuuksiin toisin kuin aiemman kirjallisuuden perusteella oli odotettavissa. Toinen CYP2C8-estäjä, mikrobilääke trimetopriimi, nosti diabeteslääke pioglitatsonin pitoisuuksia keskimäärin noin 40 %. Gemfibrotsiili nosti diabeteslääke repaglinidin pitoisuudet 7-kertaiseksi ja tämä yhteisvaikutus säilyi lähes yhtä voimakkaana vielä 12 tunnin päähän viimeisestä gemfibrotsiiliannoksesta. Tehdyt havainnot ovat käytännön lääkehoidon kannalta merkittäviä ja ne selvittävät CYP2C8-entsyymin merkitystä useiden lääkkeiden metaboliassa. Gemfibrotsiilin tai muiden CYP2C8-entsyymiä estävien lääkkeiden yhteiskäyttö loperamidin kanssa voi lisätä loperamidin tehoa tai haittavaikutuksia. Toisaalta CYP2C8-entsyymin osuus tsopiklonin ja ibuprofeenin metaboliassa näyttää olevan pieni. Trimetopriimi nosti kohtalaisesti pioglitatsonin pitoisuuksia, ja kyseisten lääkkeiden yhteiskäyttö voi lisätä pioglitatsonin annosriippuvaisia haittavaikutuksia. Gemfibrotsiili-repaglinidi-yhteisvaikutuksen päämekanismi in vivo näyttää olevan CYP2C8-entsyymin palautumaton esto. Tämän vuoksi gemfibrotsiilin estovaikutus ja yhteisvaikutusriski säilyvät pitkään gemfibrotsiilin annostelun lopettamisen jälkeen, mikä tulee ottaa huomioon käytettäessä sitä CYP2C8-välitteisesti metaboloituvien lääkkeiden kanssa.