Population pharmacokinetics of tacrolimus whole blood and peripheral blood mononuclear cell concentrations in stable kidney-transplanted patients.

AIM: Therapeutic drug monitoring of tacrolimus based on whole blood drug concentrations is routinely performed. The concentration of tacrolimus in peripheral blood mononuclear cells (PMBCs) is likely to better reflect drug exposure at the treatment target site. We aimed to describe the relationship between tacrolimus whole blood and PBMC concentrations, and the influence of patient characteristics on this relationship by developing a population pharmacokinetic model. METHODS: We prospectively enrolled 63 stable adult kidney-transplanted patients and collected dense (12-h, n = 18) or sparse (4-h, n = 45) pharmacokinetic profiles of tacrolimus. PBMCs were isolated from whole blood (Ficoll density gradient centrifugation), and drug concentrations in whole blood and PBMCs were analysed using liquid chromatography-mass spectrometry. Patient genotype (CYP3A4/5, ABCB1, NR1I2) was assessed with PCR. Population pharmacokinetic modelling and statistical evaluation was performed using NONMEM. RESULTS: Tacrolimus whole blood concentrations were well described using a two-compartment pharmacokinetic model with a lag-time and first-order absorption and elimination. Tacrolimus PBMC concentrations were best estimated from whole blood concentrations with the use of a scaling factor, the ratio of whole blood to PBMC concentrations (RC:PBMC), which was the extent of tacrolimus distribution into PBMC. CYP3A5*1 non-expressors and NR1I2-25 385T allele expressors demonstrated higher RC:PBMC ratios of 42.4% and 60.7%, respectively. CONCLUSION: Tacrolimus PBMC concentration could not be accurately predicted from whole blood concentrations and covariates because of significant residual unexplained variability in the distribution of tacrolimus into PBMCs and may need to be measured directly if required for future studies.

Dicloxacillin is an inducer of intestinal P-glycoprotein but neither dicloxacillin nor flucloxacillin increases the risk of stroke/systemic embolism in direct oral anticoagulant users.

AIM: We aimed to assess if dicloxacillin/flucloxacillin reduces the therapeutic efficacy of direct oral anticoagulants (DOACs) and the underlying molecular mechanism. METHODS: In a randomized, crossover study, we assessed whether dicloxacillin reduces oral absorption of drugs through P-glycoprotein (P-gp) during 10 and 28 days of treatment. To study the impact of dicloxacillin/flucloxacillin on intestinal and hepatic expression of P-gp in vitro, we usd LS174T cells and 3D spheroids of primary human hepatocytes. Finally, we used nationwide Danish health registries and the UK's Clinical Practice Research Datalink to estimate hazard ratios (HRs) for the risk of stroke and systemic embolism following dicloxacillin/flucloxacillin exposure among DOAC users, using phenoxymethylpenicillin and amoxicillin as active comparators. RESULTS: Dicloxacillin reduced the area under the curve of dabigatran to a geometric mean ratio 10 days of 0.67 (95% confidence interval [CI]: 0.42-1.1) and geometric mean ratio 28 days of 0.72 (95% CI: 0.39-1.4), suggesting reduced oral absorption via increased P-gp expression. In vitro, dicloxacillin raised P-gp expression in both intestinal and liver cells, while flucloxacillin only affected liver cells. In the pharmacoepidemiologic study, dicloxacillin and flucloxacillin were not associated with increased risk of stroke/systemic embolism (dicloxacillin vs. phenoxymethylpenicillin HR: 0.93, 95% CI: 0.72-1.2; flucloxacillin vs. amoxicillin HR: 0.89, 95% CI: 0.51-1.5). CONCLUSIONS: Dicloxacillin increases expression of intestinal P-gp, leading to reduced oral absorption of dabigatran. However, concomitant use of dicloxacillin/flucloxacillin was not associated with stroke and systemic embolism among DOAC users, suggesting no clinical impact from the drug-drug interaction between dicloxacillin/flucloxacillin and DOACs.

Flucloxacillin Is a Weak Inducer of CYP3A4 in Healthy Adults and 3D Spheroid of Primary Human Hepatocytes.

Flucloxacillin is a widely used antibiotic. It is an agonist to the nuclear receptor PXR that regulates the expression of cytochrome P450 (CYP) enzymes. Treatment with flucloxacillin reduces warfarin efficacy and plasma concentrations of tacrolimus, voriconazole, and repaglinide. We conducted a translational study to investigate if flucloxacillin induces CYP enzymes. We also investigated if flucloxacillin induces its own metabolism as an autoinducer. We performed a randomized, unblinded, two-period, cross-over, clinical pharmacokinetic cocktail study. Twelve healthy adults completed the study. They ingested 1 g flucloxacillin 3 times daily for 31 days, and we assessed the full pharmacokinetics of the Basel cocktail drugs on days 0, 10, and 28, and plasma concentrations of flucloxacillin on days 0, 9, and 27. The 3D spheroid of primary human hepatocytes (PHHs) were exposed to flucloxacillin (concentration range: 0.15-250 µM) for 96 hours. Induction of mRNA expression, protein abundance, and enzyme activity of CYP enzymes were assessed. Flucloxacillin treatment reduced the metabolic ratio of midazolam (CYP3A4), (geometric mean ratio (GMR) 10 days (95% confidence interval (CI)): 0.75 (0.64-0.89)) and (GMR 28 days (95% CI): 0.72 (0.62-0.85)). Plasma concentrations of flucloxacillin did not change during 27 days of treatment. Flucloxacillin caused concentration-dependent induction of CYP3A4 and CYP2B6 (mRNA, protein, and activity), CYP2C9 (mRNA and protein), CYP2C19 (mRNA and activity), and CYP2D6 (activity) in 3D spheroid PHH. In conclusion, flucloxacillin is a weak inducer of CYP3A4, which may lead to clinically relevant drug-drug interactions for some narrow therapeutic range drugs that are substrates of CYP3A4.

Does ethnicity impact CYP2D6 genotype-phenotype relationships?

Polymorphism of the CYP2D6 gene leads to substantial interindividual variability in CYP2D6 enzyme activity. Despite improvements in prediction of CYP2D6 activity based on genotype information, large interindividual variability within CYP2D6 genotypes remains and ethnicity could be a contributing factor. The aim of this study was to investigate interethnic differences in CYP2D6 activity using clinical datasets of three CYP2D6 substrates: (i) brexpiprazole (N = 476), (ii) tedatioxetine (N = 500), and (iii) vortioxetine (N = 1073). The CYP2D6 activity of all individuals in the dataset was estimated through population pharmacokinetic analyses as previously reported. Individuals were assigned a CYP2D6 phenotype and CYP2D6 genotype group based on their CYP2D6 genotype and interethnic differences were investigated within each group. Among individuals categorized as CYP2D6 normal metabolizers, African Americans had a lower CYP2D6 activity compared to Asians (p < 0.01) and in the tedatioxetine and vortioxetine analyses also compared to Whites (p < 0.01). Among CYP2D6 intermediate metabolizers, interethnic differences were also observed, but the findings were not consistent across the substrates. Asian carriers of CYP2D6 decreased function alleles tended to exhibit higher CYP2D6 activity compared to Whites and African Americans. The observed interethnic differences within the CYP2D6 phenotype and genotype groups appeared to be driven by differences in CYP2D6 allele frequencies across ethnicities rather than interethnic differences in enzyme activity for individuals carrying identical CYP2D6 genotypes.

Estimating the In Vivo Function of CYP2D6 Alleles through Population Pharmacokinetic Modeling of Brexpiprazole.

Accurate prediction of CYP2D6 phenotype from genotype information is important to support safe and efficacious pharmacotherapy with CYP2D6 substrates. To facilitate accurate CYP2D6 genotype-phenotype translation, there remains a need to investigate the enzyme activity associated with individual CYP2D6 alleles using large clinical data sets. This study aimed to quantify and compare the in vivo function of different CYP2D6 alleles through population pharmacokinetic (PopPK) modeling of brexpiprazole using data from 13 clinical studies. A PopPK model of brexpiprazole and its two metabolites, DM-3411 and DM-3412, was developed based on plasma concentration samples from 826 individuals. As the minor metabolite, DM-3412, is formed via CYP2D6, the metabolic ratio of DM-3412:brexpiprazole calculated from the PopPK parameter estimates was used as a surrogate measure of CYP2D6 activity. A CYP2D6 genotype-phenotype analysis based on 496 subjects showed that the CYP2D6*2 allele (n = 183) was associated with only 10% enzyme activity relative to the wild-type allele (CYP2D6*1) and a low enzyme activity was consistently observed across genotypes containing CYP2D6*2. Among the decreased function alleles, the following enzyme activities relative to CYP2D6*1 were estimated: 23% for CYP2D6*9 (n = 20), 32% for CYP2D6*10 (n = 62), 64% for CYP2D6*14 (n = 1), 4% for CYP2D6*17 (n = 37), 4% for CYP2D6*29 (n = 13), and 9% for CYP2D6*41 (n = 64). These findings imply that a lower functional value would more accurately reflect the in vivo function of many reduced function CYP2D6 alleles in the metabolism of brexpiprazole. The low enzyme activity observed for CYP2D6*2, which has also been reported by others, suggests that the allele exhibits substrate-specific enzyme activity.

No significant influence of OCT1 genotypes on the pharmacokinetics of morphine in adult surgical patients.

We investigated the impact of genetic variants in OCT1 (SLC22A1) on morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) pharmacokinetics in adult patients scheduled for major surgery. Blood samples were taken before and 5, 10, 15, 30, 45, 60 and 90 min after a bolus of morphine (0.15 mg/kg). Patients were genotyped for the genetic variants (rs12208357, rs34059508, rs72552763 and rs34130495) in OCT1. Eighty-six patients completed the trial. The mean difference (95% confidence interval) for dose adjusted morphine, M3G and M6G AUC was 0.9 (-0.7-2.4), -5.9 (-11.8 to -0.03) and -1.1 (-2.5-0.4) h/L*10-6 , respectively, in patients with two reduced function alleles compared to patients with no reduced function alleles in OCT1. Accordingly, the (AUCM3G/Dose )/(AUCmorphine/Dose ) and (AUCM6G/Dose )/(AUCmorphine/Dose ) ratio was reduced, -1.8 (-3.2 to -0.4) and -0.4 (-0.7 to -0.03), respectively, when comparing the same groups. OCT1 variants had no influence on the experience of pain, adverse events or the number of PCA doses used. In conclusion, genetic variants in OCT1 had a small and clinically unimportant impact on the exposure of morphine after intravenous administration. Our results do not support pre-emptive genotyping for OCT1 prior to morphine administration in patients scheduled for major surgery.

Oral and intravenous pharmacokinetics of metformin with and without oral codeine intake in healthy subjects: A cross-over study.

The aim of the study was to investigate if there is a clinically relevant drug interaction between metformin and codeine. Volunteers were randomized to receive on four separate occasions: (A) orally administered metformin (1 g), (B) intravenously administered metformin (0.5 g), (C) five doses of tablet codeine 25 mg; the last dose was administered together with oral metformin (1 g), and (D) five doses of tablet codeine 25 mg; the last dose was administered together with metformin (0.5 g) intravenously. Blood samples were drawn for 24 h after administration of metformin, and for 6 h after administration of codeine and analyzed using liquid chromatography and tandem mass spectrometry. Healthy volunteers genotyped as CYP2D6 normal metabolizers (*1/*1) without known reduced function variants in the OCT1 gene (rs12208357, rs34130495, rs34059508, and rs72552763) were invited. The median absorption fraction of metformin was 0.31 and was not influenced by codeine intake. The median time to maximum concentration ( T max ) after oral intake of metformin was 2 h without, and 3 h with codeine (p = 0.06). The geometric mean ratios of the areas under the plasma concentration time-curve (AUCs) for morphine and its metabolites M3G and M6G for oral intake of metformin-to-no metformin were 1.21, 1.31, and 1.27, respectively, and for i.v. metformin-to-no metformin 1.28, 1.34, and 1.30, respectively. Concomitant oral and i.v. metformin increased the plasma levels of morphine, M3G and M6G. These small pharmacokinetic changes may well contribute to an increased risk of early discontinuation of metformin. Hence, a clinically relevant drug-drug interaction between metformin and codeine seems plausible.

Metformin Stimulates Intestinal Glycolysis and Lactate Release: A single-Dose Study of Metformin in Patients With Intrahepatic Portosystemic Stent.

The pharmacodynamic effects of metformin remain elusive, but several lines of evidence suggest a critical role of direct effects in the gastrointestinal (GI) tract. We investigated if metformin stimulates intestinal glucose metabolism and lactate release in the prehepatic circulation. We included eight patients with transjugular intrahepatic portosytemic stent in an open label study. Portal and arterialized peripheral blood was obtained before and 90 minutes after ingestion of 1,000 mg metformin. Metformin increased lactate concentrations by 23% (95% confidence interval (CI): 6-40) after 90 minutes in the portal vein. The plasma concentration of glucose, insulin, and C-peptide was higher in the portal vein compared with arterialized blood (P < 0.05, all) and was lowered at both sampling sites following metformin ingestion (P < 0.01, all). Plasma concentration of GLP-1 was 20% (95% CI: 2-38) higher in the portal vein at baseline and metformin increased the concentration with 11% (1.5 pM, P = 0.05). The median concentration of growth differentiation factor 15 was 10% (95% CI: 1-19) higher in the portal vein compared with arterialized blood. Ninety minutes after metformin administration, the median portal vein concentration increased to around 3,000 ng/mL with a mean portal/arterial ratio of 1.5 (95% CI: 1.2-1.8). Non-targeted metabolomics showed that metformin acutely affected benzoate-hippurate metabolism. A single-dose of metformin directly affects substrate metabolism in the upper GI tract in humans with direct stimulation of nonoxidative glucose metabolism. These data suggest glucose lowering effects of metformin can be intrinsically linked with the GI tract without hepatic uptake of the drug.

Cytochrome P450 2D6 genotype-phenotype characterization through population pharmacokinetic modeling of tedatioxetine.

The cytochrome P450 (CYP) 2D6 enzyme exhibits large interindividual differences in metabolic activity. Patients are commonly assigned a CYP2D6 phenotype based on their CYP2D6 genotype, but there is a lack of consensus on how to translate genotypes into phenotypes, causing inconsistency in genotype-based dose recommendations. The aim of this study was to quantify and compare the impact of different CYP2D6 genotypes and alleles on CYP2D6 metabolism using a large clinical data set. A population pharmacokinetic (popPK) model of tedatioxetine and its CYP2D6-dependent metabolite was developed based on pharmacokinetic data from 578 subjects. The CYP2D6-mediated metabolism was quantified for each subject based on estimates from the final popPK model, and CYP2D6 activity scores were calculated for each allele using multiple linear regression. The activity scores estimated for the decreased function alleles were 0.46 (CYP2D6*9), 0.34 (CYP2D6*10), 0.01 (CYP2D6*17), 0.65 (CYP2D6*29), and 0.21 (CYP2D6*41). The CYP2D6*17 and CYP2D6*41 alleles were thus associated with the lowest CYP2D6 activity, although only the difference to the CYP2D6*9 allele was shown to be statistically significant (p = 0.02 and p = 0.05, respectively). The study provides new in vivo evidence of the enzyme function of different CYP2D6 genotypes and alleles. Our findings suggest that the activity score assigned to CYP2D6*41 should be revisited, whereas CYP2D6*17 appears to exhibit substrate-specific behavior. Further studies are needed to confirm the findings and to improve the understanding of CYP2D6 genotype-phenotype relationships across substrates.

Metformin Lowers Body Weight But Fails to Increase Insulin Sensitivity in Chronic Heart Failure Patients without Diabetes: a Randomized, Double-Blind, Placebo-Controlled Study.

PURPOSE: The glucose-lowering drug metformin has recently been shown to reduce myocardial oxygen consumption and increase myocardial efficiency in chronic heart failure (HF) patients without diabetes. However, it remains to be established whether these beneficial myocardial effects are associated with metformin-induced alterations in whole-body insulin sensitivity and substrate metabolism. METHODS: Eighteen HF patients with reduced ejection fraction and without diabetes (median age, 65 (interquartile range 55-68); ejection fraction 39 ± 6%; HbA1c 5.5 to 6.4%) were randomized to receive metformin (n = 10) or placebo (n = 8) for 3 months. We studied the effects of metformin on whole-body insulin sensitivity using a two-step hyperinsulinemic euglycemic clamp incorporating isotope-labeled tracers of glucose, palmitate, and urea. Substrate metabolism and skeletal muscle mitochondrial respiratory capacity were determined by indirect calorimetry and high-resolution respirometry, and body composition was assessed by bioelectrical impedance analysis. The primary outcome measure was change in insulin sensitivity. RESULTS: Compared with placebo, metformin treatment lowered mean glycated hemoglobin levels (absolute mean difference, - 0.2%; 95% CI - 0.3 to 0.0; p = 0.03), reduced body weight (- 2.8 kg; 95% CI - 5.0 to - 0.6; p = 0.02), and increased fasting glucagon levels (3.2 pmol L-1; 95% CI 0.4 to 6.0; p = 0.03). No changes were observed in whole-body insulin sensitivity, endogenous glucose production, and peripheral glucose disposal or oxidation with metformin. Equally, resting energy expenditure, lipid and urea turnover, and skeletal muscle mitochondrial respiratory capacity remained unaltered. CONCLUSION: Increased myocardial efficiency during metformin treatment is not mediated through improvements in insulin action in HF patients without diabetes. CLINICAL TRIAL REGISTRATION: URL: https://clinicaltrials.gov . Unique identifier: NCT02810132. Date of registration: June 22, 2016.

Quantification of In Vivo Metabolic Activity of CYP2D6 Genotypes and Alleles Through Population Pharmacokinetic Analysis of Vortioxetine.

Assignment of CYP2D6 phenotype from genotype data can be challenging and despite efforts to standardize translation, there is currently no universally accepted method. To facilitate standardization, there remains a need to precisely quantify the in vivo function of different CYP2D6 genotypes. Vortioxetine is metabolized to its major metabolite, Lu AA34443, primarily via CYP2D6. The aim of this study was to quantify the in vivo CYP2D6 activity of different CYP2D6 alleles and genotypes through population pharmacokinetic (PopPK) modeling of vortioxetine and Lu AA34443. Plasma concentration data of vortioxetine and Lu AA34443 from 1,140 subjects originating from 29 clinical pharmacology studies were pooled for the analysis. A joint PopPK model described the pharmacokinetics of vortioxetine and Lu AA34443 simultaneously and provided estimates of the CYP2D6-mediated metabolism for each subject. Subjects normally classified as CYP2D6 intermediate metabolizers (IMs) showed different levels of CYP2D6 activity with carriers of one fully functional allele and one null function allele having 77% higher CYP2D6 activity compared with carriers of two decreased function alleles (P < 0.0001). The decreased function alleles were associated with different levels of reduction of CYP2D6 activity. Fixing the activity of fully functional alleles to 1.0, the relative activities of CYP2D6*9, CYP2D6*10, CYP2D6*17, and CYP2D6*41 were 0.22, 0.37, 0.17, and 0.21, respectively. The activity of CYP2D6*10 was shown to be significantly greater than that of CYP2D6*17 (P = 0.01) and CYP2D6*41 (P = 0.02). These results warrant further discussion of current CYP2D6 genotype-phenotype classification systems particularly regarding decreased function alleles and the IM phenotype.

Using a limited sampling strategy to investigate the interindividual pharmacokinetic variability in metformin: A large prospective trial.

AIMS: Recently a limited sampling strategy (LSS) for determination of metformin' pharmacokinetics was developed. The LSS utilizes the plasma concentration of metformin 3 and 10 hours after oral intake of a single dose to estimate the area under the concentration-time curve up to 24 hours (AUC0-24h ). The main purpose of this study was to support the feasibility of this strategy in a large prospective trial. METHODS: Volunteers orally ingested two 500-mg tablets of metformin hydrochloride. A blood sample was drawn three and ten hours after the ingestion. Urine was collected for 0-10 and 10-24 hours and urine volumes recorded. The AUC0-24h was calculated using the equation AUC0-24h = 4.779 * C3 + 13.174 * C10 . Additionally, all participants were genotyped for the single-nucleotide polymorphism A270S in OCT2, g.-66 T > C in MATE1, R61C, G465R, G401S and the deletion M420del in OCT1. RESULTS: In total, 212 healthy volunteers participated. The median (25th - 75th interquartile range) AUC0 - 24h , CLrenal , C3 and C10 , were 10 600 (8470-12 500) ng* hr* mL-1 , 29 (24-34) L* hour-1 , 1460 (1180-1770) and 260 (200-330) ng* mL-1 , respectively, which is in agreement with our previous results. GFRi was correlated with metformin AUC and CLrenal (P < .001). As expected, we found a great pharmacokinetic interindividual variability among the volunteers and no effect of the OCT1 genotype on the AUC0 - 24h . We were unable to reproduce our previous finding of a gene-gene interaction (OCT2 and MATE1) effect on CLrenal in this cohort. CONCLUSION: This study further supports the use of the 2-point LSS algorithm in large pharmacokinetic trials.

A randomised, double-blind, placebo-controlled trial of metformin on myocardial efficiency in insulin-resistant chronic heart failure patients without diabetes.

AIMS: The present study tested the hypothesis that metformin treatment may increase myocardial efficiency (stroke work/myocardial oxygen consumption) in insulin-resistant patients with heart failure and reduced ejection fraction (HFrEF) without diabetes. METHODS AND RESULTS: Thirty-six HFrEF patients (ejection fraction 37 ± 8%; median age 66 years) were randomised to metformin (n = 19) or placebo (n = 17) for 3 months in addition to standard heart failure therapy. The primary endpoint was change in myocardial efficiency expressed as the work metabolic index (WMI), assessed by 11 C-acetate positron emission tomography and transthoracic echocardiography. Compared with placebo, metformin treatment (1450 ± 550 mg/day) increased WMI [absolute mean difference, 1.0 mmHg·mL·m-2 ·106 ; 95% confidence interval (CI) 0.1 to 1.8; P = 0.03], equivalent to a 20% relative efficiency increase. Patients with above-median plasma metformin levels displayed greater WMI increase (25% vs. -4%; P = 0.02). Metformin reduced myocardial oxygen consumption (-1.6 mL O2 ·100 g-1 ·min-1 ; P = 0.014). Cardiac stroke work was preserved (-2 J; 95% CI -11 to 7; P = 0.69). Metformin reduced body weight (-2.2 kg; 95% CI -3.6 to -0.8; P = 0.003) and glycated haemoglobin levels (-0.2%; 95% CI -0.3 to 0.0; P = 0.02). Changes in resting and exercise ejection fraction, global longitudinal strain, and exercise capacity did not differ between groups. CONCLUSION: Metformin treatment in non-diabetic HFrEF patients improved myocardial efficiency by reducing myocardial oxygen consumption. Measurement of circulating metformin levels differentiated responders from non-responders. These energy-sparing effects of metformin encourage further large-scale investigations in heart failure patients without diabetes.

A phase I study of the PARP inhibitor niraparib in combination with bevacizumab in platinum-sensitive epithelial ovarian cancer: NSGO AVANOVA1/ENGOT-OV24.

BACKGROUND: Combining poly(ADP-ribose) polymerase (PARP) inhibitors with antiangiogenic agents appeared to enhance activity vs PARP inhibitors alone in a randomized phase II trial. MATERIALS AND METHODS: In AVANOVA (NCT02354131) part 1, patients with measurable/evaluable high-grade serous/endometrioid platinum-sensitive ovarian cancer received bevacizumab 15 mg/kg every 21 days with escalating doses of niraparib capsules (100, 200, or 300 mg daily) in a 3 + 3 dose-escalation design. Primary objectives were to evaluate safety and tolerability and to determine the recommended phase II dose (RP2D). RESULTS: Three of 12 enrolled patients had germline BRCA2 mutations. In cycle 1, nine patients experienced grade 3 toxicities: five with hypertension, three with anemia, and one with thrombocytopenia. There was one dose-limiting toxicity (grade 4 thrombocytopenia with niraparib 300 mg), thus the RP2D was bevacizumab 15 mg/kg with niraparib 300 mg. The response rate was 50%; disease was stabilized in a further 42%. Median progression-free survival was 11.6 (95% confidence interval 8.4-20.1) months. Niraparib pharmacokinetics were consistent with historical single-agent data. Overlapping exposure was observed across the dose ranges tested on days 1 and 21. CONCLUSIONS: There was one dose-limiting toxicity; other adverse events were typical PARP inhibitor and antiangiogenic class effects. Niraparib-bevacizumab showed promising activity; Part 2 (vs bevacizumab) was recently reported and phase III comparison with standard-of-care therapy is planned.

Metformin increases endogenous glucose production in non-diabetic individuals and individuals with recent-onset type 2 diabetes.

AIMS/HYPOTHESIS: Metformin is the endorsed first-line glucose-lowering drug for treating patients with type 2 diabetes but despite more than 50 years of use, no consensus has been reached on its mechanisms of action. In this study, we investigated the glucose-lowering effects of metformin in individuals with type 2 diabetes and non-diabetic individuals. METHODS: We performed a randomised, placebo-controlled trial in 24 individuals with recent-onset type 2 diabetes (diabetes duration 50 [48] months) who had good glycaemic control (HbA1c 48 mmol/mmol [6.5%]). The studies were conducted at Aarhus University Hospital between 2013 and 2016. Participants were randomised to receive either metformin (2000 mg/day, n = 12, MET group) or placebo (n = 12, PLA group) for 90 days, using block randomisation set up by an unblinded pharmacist. Two participants withdrew from the study prior to completion and were replaced with two new participants receiving the same treatment. In addition, we recruited a group of non-diabetic individuals with similar age and BMI (n = 12, CONT group), who were all treated with 2000 mg metformin daily. Before and after treatment all individuals underwent studies of whole-body glucose metabolism by non-steady-state [3-3H]glucose kinetics, hyperinsulinaemic-euglycaemic clamping, indirect calorimetry, metabolomics, dual x-ray absorptiometry and muscle biopsies. The primary study endpoint was the effect of metformin treatment on lipid kinetics as well as glucose rate of disappearance (Rd) and endogenous glucose production (EGP). RESULTS: One participant from the CONT group withdrew due to intolerable gastrointestinal side-effects and was excluded from analysis. As expected, metformin treatment lowered fasting plasma glucose (FPG) in the MET group (~1.5 mmol/l, p < 0.01), whereas no effect was observed in the PLA and CONT groups. Body weight and composition did not change in any of the groups. In both of the metformin-treated groups (MET and CONT), basal glucose Rd, EGP and glucagon levels increased by ~30% (p < 0.05) whereas this was not the case in the PLA group. CONCLUSIONS/INTERPRETATION: Ninety days of metformin treatment resulted in similar increases in EGP and glucose Rd in individuals with recent-onset type 2 diabetes and in non-diabetic control individuals. These results challenge the existing paradigm that metformin primarily acts in the liver by inhibiting EGP, at least in individuals with type 2 diabetes of short duration and who have discretely affected glycaemic status. Whether metformin increases basal glucose Rd by facilitating glucose uptake in other tissues such as the intestines remains to be further clarified. TRIAL REGISTRATION: ClinicalTrials.gov NCT01729156 FUNDING: This study was supported by grants from The Danish Council for Independent Research | Medical Sciences, Aase Danielsen Fund, the Novo Nordisk Foundation, the Danish Diabetes Association and the Danish Diabetes Academy supported by the Novo Nordisk Foundation.

Hepatic exposure of metformin in patients with non-alcoholic fatty liver disease.

AIMS: Metformin is first-line treatment of type 2 diabetes mellitus and reduces cardiovascular events in patients with insulin resistance and type 2 diabetes. Target tissue for metformin action is thought to be the liver, where metformin distribution depends on facilitated transport by polyspecific transmembrane organic cation transporters (OCTs). Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease in the western world with strong associations to insulin resistance and the metabolic syndrome, but whether NAFLD affects metformin biodistribution to the liver is not known. In this study, the primary aim was to investigate in vivo hepatic uptake of metformin dynamically in humans with variable degrees of liver affection. As a secondary aim, we wished to correlate hepatic metformin distribution with OCT gene transcription determined in diagnostic liver biopsies. METHODS: Eighteen patients with biopsy-proven NAFLD were investigated using 11C-metformin PET/CT technique. Gene transcripts of OCTs were determined by real-time polymerase chain reaction (PCR). RESULTS: We observed similar hepatic volume of distribution of metformin between patients with simple steatosis and non-alcoholic steatohepatitis (NASH) (Vd 2.38 ± 0.56 vs. 2.10 ± 0.39, P = 0.3). There was no association between hepatic exposure to metformin and the degree of inflammation or fibrosis, and no clear correlation between metformin distribution and OCT gene transcription. CONCLUSION: Metformin is distributed to the liver in patients with NAFLD and the distribution is not impaired by inflammation or fibrosis. The findings imply that metformin action in liver in patients with NAFLD may be preserved.

Using a semi-mechanistic model to identify the main sources of variability of metformin pharmacokinetics.

Metformin pharmacokinetics (PK) is highly variable, and researchers have for years tried to shed light on determinants of inter-individual (IIV) and inter-occasion variability (IOV) of metformin PK. We set out to identify the main sources of PK variability using a semi-mechanistic model. We assessed the influence of subject characteristics, including seven genetic variants. Data from three studies of healthy individuals with PK measurements of plasma and urine after single dose or at steady-state were used in this study. In total, 87 subjects were included (16 crossover subjects). Single nucleotide polymorphisms in ATM, OCT1, OCT2, MATE1 and MATE2-K were investigated as dominant, recessive or additive. A three-compartment model with transit absorption and renal elimination with a proportional error was fitted to the data using NONMEM 7.3. Oral parameters were separated from disposition parameters as dose-dependent absolute bioavailability was determined with support from urine data. Clearance was expressed as net renal secretion and filtration, assuming full fraction unbound and fraction excreted. Mean transit time and peripheral volume of distribution were identified as the main sources of variability according to estimates, with 94% IOV and 95% IIV, respectively. Clearance contributed only with 16% IIV. Glomerular filtration rate and body-weight were the only covariates found to affect metformin net secretion, reducing IIV to 14%. None of the genetic variants were found to affect metformin PK. Based on our analysis, finding covariates explaining absorption of metformin is much more valuable in understanding variability and avoiding toxicity than elimination.