Uptake and dispersion of metformin in the isolated perfused rat liver

Biowaiver Monographs for Immediate Release Solid Oral Dosage Forms: Metformin Hydrochloride

Data are examined regarding possible waiver of in vivo bioequivalence testing (i.e. biowaiver) for approval of metformin hydrochloride (metformin) immediate-release solid oral dosage forms. Data include metformin's Biopharmaceutics Classification System (BCS) properties, including potential excipient interactions. Metformin is a prototypical transporter-mediated drug and is highly soluble, but only 50% of an orally administered dose is absorbed from the gut. Therefore, metformin is a BCS Class III substance. A BCS-based approval approach for major changes to marketed products and new generics is admissible if test and reference dosage forms have the identical active pharmaceutical ingredient and if in vitro dissolution from both are very rapid (i.e. at least 85% within 15 min at pH 1.2, 4.5, and 6.8). Recent International Council for Harmonisation BCS guidance indicates all excipients for Class III biowaivers are recommended to be qualitatively the same and quantitatively similar (except for preservatives, flavor agents, colorant, or capsule shell or film coating excipients). However, despite metformin being a prototypical transporter-mediated drug, there is no evidence that commonly used excipients impact metformin absorption, such that this restriction on excipients for BCS III drugs merits regulatory relief. Commonly used excipients in usual amounts are not likely to impact metformin absorption.

In Vivo Imaging of Human 11C-Metformin in Peripheral Organs: Dosimetry, Biodistribution, and Kinetic Analyses

Metformin is the most widely prescribed oral antiglycemic drug, with few adverse effects. However, surprisingly little is known about its human biodistribution and target tissue metabolism. In animal experiments, we have shown that metformin can be labeled by ¹¹C and that ¹¹C-metformin PET can be used to measure renal function. Here, we extend these preclinical findings by a first-in-human ¹¹C-metformin PET dosimetry, biodistribution, and tissue kinetics study.

METHODS

Nine subjects (3 women and 6 men) participated in 2 studies: in the first study, human radiation dosimetry and biodistribution of ¹¹C-metformin were estimated in 4 subjects (2 women and 2 men) by whole-body PET. In the second study, ¹¹C-metformin tissue kinetics were measured in response to both intravenous and oral radiotracer administration. A dynamic PET scan with a field of view covering target tissues of metformin (liver, kidneys, intestines, and skeletal muscle) was obtained for 90 (intravenous) and 120 (oral) min.

RESULTS

Radiation dosimetry was acceptable, with effective doses of 9.5 μSv/MBq (intravenous administration) and 18.1 μSv/MBq (oral administration). Whole-body PET revealed that ¹¹C-metformin was primarily taken up by the kidneys, urinary bladder, and liver but also to a lesser extent in salivary glands, skeletal muscle, and intestines. Reversible 2-tissue-compartment kinetics was observed in the liver, and volume of distribution was calculated to be 2.45 mL/mL (arterial input) or 2.66 mL/mL (portal and arterial input). In the kidneys, compartmental models did not adequately fit the experimental data, and volume of distribution was therefore estimated by a linear approach to be 6.83 mL/mL. Skeletal muscle and intestinal tissue kinetics were best described by 2-tissue-compartment kinetics and showed only discrete tracer uptake. Liver ¹¹C-metformin uptake was pronounced after oral administration of the tracer, with tissue-to-blood ratio double what was observed after intravenous administration. Only slow accumulation of ¹¹C-metformin was observed in muscle. There was no elimination of ¹¹C-metformin through the bile both during the intravenous and during the oral part of the study.

CONCLUSION

¹¹C-metformin is suitable for imaging metformin uptake in target tissues and may prove a valuable tool to assess the impact of metformin treatment in patients with varying metformin transport capacity.

Age-dependent effects in fathead minnows from the anti-diabetic drug metformin

The anti-diabetic drug metformin is thought to be the pharmaceutical most deposited into the aquatic environment by mass at up to 6tons per year from individual WWTPs in urban areas. Recent studies have shown that exposure to 40ug/L of metformin increased the relative expression of the egg yolk precursor protein vitellogenin in adult male fathead minnows (Pimephales promelas) (FHM). For this study, the expression of several other genes involved in estrogen biosynthesis, clearance and downstream effects were assessed in FHM after treatment to three concentrations of metformin, to better understand the estrogenic effects of metformin on FHM. In contrast to the previous study, although upward trends were observed, metformin failed to significantly alter the expression of VTG, ERα, GnRH3, and CYP3A126 in adult male FHM. However, a concentration-dependent response to metformin was observed in younger 80-90day juvenile FHM. A 17.7-, 22-, and 22-fold increase in the relative expression of VTG mRNA in juvenile FHM exposed to 1, 10, and 100μg/L as compared to the control was observed. There was also a 3.3-, 4.7-, and 5.5-fold increase in GnRH3 in juvenile FHM exposed to 1, 10, and 100μg/L as compared to the control. Similarly, a 14-, 16-, and 24-fold increase in the relative expression of CYP3A126 mRNA was measured in juvenile FHM exposed to 1, 10 and 100μg/L metformin as compared to the control. These results indicate that juvenile FHM were more susceptible to the estrogenic effects of metformin during a 7-d exposure than older, sexually mature male FHM.

Emerging wastewater contaminant metformin causes intersex and reduced fecundity in fish

The occurrence of intersex fish, where male reproductive tissues show evidence of feminization, have been found in freshwater systems around the world, indicating the potential for significant endocrine disruption across species in the ecosystem. Estrogens from birth control medications in wastewater treatment plant effluent have been cited as the likely cause, but research has shown that endocrine disruption is not solely predictable based on hormone receptor interactions. Many other non-hormone pharmaceuticals are found in effluent at concentrations orders of magnitude higher than estrogens, yet there is little data indicating the impacts of these other medications. The widely prescribed anti-diabetic metformin is among the most abundant of pharmaceuticals found in effluent and is structurally dissimilar from hormones. However, we show here that exposing fathead minnows (Pimephales promelas) to a concentration of metformin found in wastewater effluent causes the development of intersex gonads in males, reduced size of treated male fish, and reduction in fecundity for treated pairs. Our results demonstrate that metformin acts as an endocrine disruptor at environmentally relevant concentrations.

Population pharmacokinetic modeling and noncompartmental analysis demonstrated bioequivalence between metformin component of metformin/vildagliptin fixed-dose combination products and metformin immediate-release tablet sourced from various countries

Metformin is the first-line pharmacotherapy choice for treating type-2 diabetes mellitus, alone or in combination with other antidiabetic drugs. During the development of immediate-release (IR) metformin containing novel fixed-dose combination (FDC) products, several health-authorities require sponsors to demonstrate bioequivalence between FDC products and the country-sourced metformin for market approval. Eight bioequivalence studies that compared metformin/vildagliptin FDC product (test) to metformin IR tablet sourced from various countries (reference) were conducted. A population pharmacokinetic (PPK) analysis of pooled metformin concentration-time data was performed to evaluate whether country-sourced metformin is a significant covariate. The PPK analysis demonstrated that there was no clinically relevant effect of metformin source or race/ethnicity on metformin pharmacokinetics. Also, noncompartmental analysis conducted showed that 90%CI of geometric mean ratios of test to reference metformin formulations, calculated for maximum-concentration and exposure parameters, were within the 80%-125% criteria, indicating comparable metformin exposure regardless of the country-sourced metformin IR formulation. These results are consistent with the biopharmaceutics properties of metformin and provide scientific evidence that after assessing in vitro dissolution of novel FDC formulation, additional bioequivalence studies with multiple countries' reference products may not be required once bioequivalence is established with 1 country-sourced IR metformin formulation.

Inhibitory effect of atenolol on urinary excretion of metformin via down-regulating multidrug and toxin extrusion protein 1 (rMate1) expression in the kidney of rats

Renal tubular secretion is an important pathway for the elimination of many clinically used drugs. Metformin, a commonly prescribed first-line antidiabetic drug, is secreted primarily by the renal tubule. Many patients with type 2 diabetes mellitus (T2DM) receiving metformin may together be given selective β1 blockers (e.g., atenolol). Therefore, it is of great use to evaluate the effect of atenolol on metformin urinary excretion for exploring drug interactions and predicting the adverse effect of drugs. The aim of this study was to investigate the effect of atenolol on the pharmacokinetic of metformin and plasma lactate (LCA) level in rats, for high LCA is a serious adverse reaction of metformin after long-term metformin treatment. In this study, rats were treated with metformin alone or in combination with atenolol. Plasma, urine and tissue concentration of metformin was determined by HPLC method, while Western blotting and immunohistochemical analysis were used to evaluate the renal expression of rat organic cation transporter 2 (rOct2) and multidrug and toxin extrusion protein 1 (rMate1). The results showed that, after 7 days drug treatment, the AUC0 → t of metformin in atenolol and metformin co-administration group was significantly increased by 19.5% compared to that in metformin group, while the 24h cumulative urinary excretion of metformin was significantly decreased by 57.3%. In addition, atenolol treatment significantly decreased the renal expression of rMate1, but had no effect on rOct2 expression, renal blood perfusion and glomerular filtration. Moreover, plasma LCA level in atenolol and metformin co-administration group was significantly increased by 83.3% compared to that in metformin group after 60 days drug treatment. These results indicated that atenolol can inhibit urinary excretion of metformin via decreasing renal rMate1 expression, and long-term atenolol and metformin co-administration may induce potential lactic acidosis. Our results, for the first time, provided an important experimental evidence that rMate1 is the target of transporter-mediated drug interactions concerning metformin and atenolol.

Effects of metformin on glucose metabolism of perfused rat livers

Although metformin has been used to treat type 2 diabetes for several decades, the mechanism of its action on glucose metabolism remains controversial. To further assess the effect of metformin on glucose metabolism this work was undertaken to investigate the acute actions of metformin on glycogenolysis, glycolysis, gluconeogenesis, and ureogenesis in perfused rat livers. Metformin (5 mM) inhibited oxygen consumption and increased glycolysis and glycogenolysis in livers from fed rats. In perfused livers of fasted rats, the drug (concentrations higher than 1.0 mM) inhibited oxygen consumption and glucose production from lactate and pyruvate. Gluconeogenesis and ureogenesis from alanine were also inhibited. The cellular levels of ATP were decreased by metformin whereas the AMP levels of livers from fasted rats were increased. Taken together our results indicate that the energy status of the cell is probably compromised by metformin. The antihyperglycemic effect of metformin seems to be the result of a reduced oxidative phosphorylation without direct inhibition of key enzymatic activities of the gluconeogenic pathway. The AMP-activated protein kinase cascade could also be a probable target for metformin, which switches on catabolic pathways such as glycogenolysis and glycolysis, while switches off ATP consuming processes.

Determination of norfloxacin in rat liver perfusate using capillary electrophoresis with laser-induced fluorescence detection

A capillary zone electrophoresis method has been developed for the direct determination of norfloxacin in the physiological perfusate of isolated rat liver. Norfloxacin and the internal standard triamterene were detected using laser-induced fluorescence (LIF) detection with the excitation and emission wavelength of 325 and 435 nm, respectively. The background electrolyte (BGE) was 50 mM phosphate buffer (pH 4.6). The effect of pH and concentration of BGE on the electrophoretic migration and fluorescence response of analytes were examined. Calibration curves were linear over a wide range of 0.01-100 microg/mL. The limit of quantitation was 0.01 microg/mL. The intra- and inter-day relative standard deviation was 3.7%, or less, and the accuracy was 93.2% of the nominal concentration. No endogenous substances were found to interfere. The method was used to characterize the steady-state and transient pharmacokinetics of norfloxacin in the rat liver.

Biowaiver extension potential to BCS Class III high solubility-low permeability drugs: bridging evidence for metformin immediate-release tablet

The biopharmaceutics classification system (BCS) allows biowaiver for rapid dissolving immediate-release (IR) products of Class I drugs (high solubility and high permeability). The possibility of extending biowaivers to Class III high solubility and low permeability drugs is currently under scrutiny. In vivo bioequivalence data of different formulations of Class III drugs would support such an extension. The objective of this work was to demonstrate the bioequivalence of two marketed IR tablet products of a Class III drug, metformin hydrochloride, that are rapidly dissolving and have similar in vitro dissolution profiles. The effect of race on the systemic exposure of metformin was also explored. A randomized, open-label, two-period crossover study was conducted in 12 healthy Chinese male volunteers. Each subject received a single-dose of 500 mg of each product after an overnight fasting. The plasma concentrations of metformin were followed for 24 h. No significant formulation effect was found for the bioequivalence metrics: areas under concentration-time curve (AUC0-t, AUC0-infinity) and maximal concentration (Cmax). The 90% confidence intervals for the ratio of means were found within the acceptance range of 80-125% for the log-transformed data. Based on these results, it was concluded that the two IR products are bioequivalent. The pharmacokinetic parameters of metformin in Chinese for both products were similar and were in good agreement with those reported for metformin IR tablets in other ethnic populations. This study serves as an example for supporting biowaiver for BCS Class III drugs.

Determination of metformin in human plasma by high-performance liquid chromatography with spectrophotometric detection

A simple, selective, sensitive and precise high-performance liquid chromatographic plasma assay for the hypoglycemic agent metformin is described. Acidified samples of plasma were deproteinated with acetonitrile, washed with dichloromethane and the resulting supernatant injected. Chromatography was performed at 40 degrees C by pumping a mobile phase of acetonitrile (250 ml) in pH 7, 0.03 M diammonium hydrogen phosphate buffer (750 ml) at a flow-rate of 1 ml/min through a silica column. Metformin and the internal standard (atenolol) were detected at 240 nm and were eluted 7.8 and 6.8 min, respectively, after injection. No endogenous substances were found to interfere. Calibration curves were linear (r>0.999) from 10 to 2000 ng/ml. The absolute recovery of both metformin and atenolol was greater than 76%. The detection limit and limit of quantitation were 2.5 and 10 ng/ml, respectively. The intra- and inter-day precision (C.V.) was 12%, or less, and the accuracy was within 6.2% of the nominal concentration. This method is suitable for clinical investigation and monitoring metformin concentration.