Pharmacokinetics of metformin in the rat: assessment of the effect of hyperlipidemia and evidence for its metabolism to guanylurea.

Metformin pharmacokinetics are highly dependent upon organic cationic transporters. There is evidence of a change in its renal clearance in hyperlipidemic obese patients, and no information on its metabolic fate. To study some of these aspects, the influence of poloxamer 407 (P407)-induced hyperlipidemia on metformin pharmacokinetics was assessed. Control and P407-treated adult male rats were administered 30 mg/kg metformin intravenously (i.v.). The pharmacokinetic assessments were performed at 2 time points, 36 and 108 h, following the intraperitoneal dose of P407 (1 g/kg). mRNA and protein expressions of cationic drug transporters were also measured. There was no evidence of a change in metformin pharmacokinetics after i.v. doses as a consequence of short-term hyperlipidemia, and a change in transporter mRNA but not protein expression was observed in the P407- treated rats 108 h after P407 injection. Urinary recovery of unchanged drug was high (>90%) but incomplete. Presumed metabolite peaks were detected in chromatograms of hepatocytes and microsomal protein spiked with metformin. Comparative chromatographic elution times and mass spectra suggested that one of the predominant metabolites was guanylurea. Hyperlipidemia by itself did not affect the pharmacokinetics of metformin. Guanylurea is a putative metabolite of metformin in rats.

Role of Environmental Factors in the Development of Pediatric Eosinophilic Esophagitis.

BACKGROUND: Despite accumulating data on the pathogenesis of eosinophilic esophagitis, not much is known about risk factors for the development of the disease. The role of factors such as smoking, breastfeeding, early antibiotic exposure and other factors that have been associated with other allergic diseases has not been well studied in children with eosinophilic esophagitis. AIM: To explore the role of environmental and medication exposures in the development of pediatric eosinophilic esophagitis. METHODS: We conducted a cross-sectional case-control study, utilizing a parent and child questionnaire and medical chart review. Urine cotinine levels, measured by high-performance liquid chromatography, were obtained as objective evidence for smoking exposure. RESULTS: One hundred and two children with eosinophilic esophagitis and 167 controls were recruited. The controls were mainly diagnosed with functional gastrointestinal disorders (33%) and gastroesophageal reflux disease (29%). Food allergy, specifically for peanuts and tree nuts, and allergy to pollen, tree, and grass were significantly higher among eosinophilic esophagitis children. Smoking exposure, both primary and secondary, was not associated with pediatric eosinophilic esophagitis when compared to controls (odds ratio 0.96, 95% confidence interval 0.58-1.59). Furthermore, early smoking exposure in the first year of life was higher among controls. Common accepted risk factors for allergy and atopy, such as breastfeeding practices, antibiotics exposure, animals' exposure, and others, were not found to be associated with eosinophilic esophagitis in our study. CONCLUSION: Common risk factors in other allergic and atopic conditions were not found to be associated with eosinophilic esophagitis.

Pharmacokinetics of dronedarone in rat using a newly developed high-performance liquid chromatographic assay method.

A sensitive and selective high-performance liquid chromatographic method for the determination of dronedarone in rat plasma was developed. Dronedarone was extracted using one-step liquid-liquid extraction. The separation of dronedarone was accomplished using a C18 analytical column. The mobile phase was composed of a combination of monobasic potassium phosphate and acetonitrile. The UV detection was at 254 nm for ethopropazine, the internal standard, and after its elution, changed to 290 nm for dronedarone detection. The total analytical run time was 20 min. Mean recovery was >80%; the assay had excellent linear relationships (>0.999) between peak height ratios and plasma concentrations; the lower limit of quantification 25 was ng/mL, based on 100 µL of rat plasma. Accuracy and precision were <18% over the concentration range of 25-500 ng/mL. The assay was applied successfully to the measurement of dronedarone plasma concentrations in rats given the drug orally.

A liquid chromatography-mass spectrometry method for nicotine and cotinine; utility in screening tobacco exposure in patients taking amiodarone.

A liquid chromatographic mass spectrometric (LC-MS) assay for the quantification of nicotine and cotinine in human specimens was developed. Human serum and urine (100 µL) were subjected to liquid-liquid extraction. For glucuronidated cotinine, serum was alkalinized and hydrolyzed before extraction. The dried samples were reconstituted and run using gradient flow reverse-phase liquid chromatography with MS detection. The ions utilized for quantification of nicotine, cotinine and milrinone (internal standard) were 162.8, 176.9 and 211.9 m/z, respectively. The mean recoveries were over 80% for cotinine and nicotine with excellent linearity between nominal concentrations and peak area ratios, over a wide concentration range. The percentage coefficient of variation and mean error of the inter- and intra-day validations were <15% for nicotine and cotinine. Analysis of serum from cardiac patients receiving amiodarone suggested that a number of patients were either active smokers or exposed to second-hand smoke. Significant concentrations of nicotine and cotinine were measured in the urine of a known smoking volunteer. The method was highly specific, sensitive and applicable as a tool in detecting and monitoring the passive exposure to tobacco smoke using small specimen volumes (0.1 mL).

Determination of metformin in human plasma and urine by high-performance liquid chromatography using small sample volume and conventional octadecyl silane column.

PURPOSE: To develop a selective and sensitive high-performance liquid chromatographic method for the determination of metformin in human plasma and urine, using a conventional reverse phase column and low specimen volume. METHODS: Extraction of metformin and ranitidine (as internal standard) from plasma and urine samples (100 µL) was performed with a 1-butanol-hexane (50:50, v/v) mixture under alkaline conditions followed by back-extraction into diluted acetic acid. Chromatography was carried out using a C18 column (250 mm×4.6 mm, 5 µm). A mobile phase consisting of acetonitrile and KH2PO4 (34:66, v/v) and sodium dodecyl sulphate (3 mM) was pumped at an isocratic flow rate of 0.7 mL/min. RESULTS: The calibration curves were linear (>0.995) in the concentration ranges of 10-5000 and 2-2000 µg/mL for metformin in plasma and urine respectively. .The mean absolute recoveries for 100 and 1000 ng/mL metformin in plasma using the present extraction procedure were 93.7 and 88.5%, respectively. The intra- and inter-day coefficients of variation in plasma and urine were <20% at the lowest, and <16% at other concentrations. The percent error values were less than 2% in plasma while it reached ~9% in urine. The lower limits of quantification were 7.8 ng/mL and 1.6 µg/mL of metformin base in plasma and urine respectively. CONCLUSION: The method showed high calibers of sensitivity and selectivity for monitoring therapeutic concentrations of metformin in both plasma and urine based on a 0.1 ml sample size._____________________________________________________________________________________

Dietary-Induced Obesity and Changes in the Biodistribution and Metabolism of Amiodarone in the Rat.

The metabolism and biodistribution of the antiarrhythmic drug amiodarone (AM) was assessed in male Sprague-Dawley rats given either normal chow or high-fat and high-fructose diets for 14 weeks. After the feeding period, microsomes were prepared from liver and intestine, and the metabolism of AM to desethylamiodarone was determined. Intrinsic clearance (CL) was reduced by hepatic microsomes isolated from rats given high-calorie diets. In intestinal microsomes, there was no change or a small increase in metabolic rate in obese rats. A biodistribution study was also undertaken in a group of control and high-fat + high fructose-fed rats. Excess calories led to a significant increase in plasma AM compared to normal chow-fed control animals. A population pharmacokinetic analysis of AM confirmed that its oral CL was reduced. In plasma, there was a decrease in the metabolite to drug ratio. Some tissue:plasma ratios of AM in high calorie-fed rats were aligned with a decrease in plasma unbound fraction. It is concluded that the findings reinforced those of a recent report where we found decreases in expressions of enzymes involved in AM dealkylation, in showing greater exposure and lower oral CL, and generally decreases in liver microsomal metabolism of AM after high-calorie diets.

Glycemic and Metabolic Effects of Two Long Bouts of Moderate-Intensity Exercise in Men with Normal Glucose Tolerance or Type 2 Diabetes.

BACKGROUND: The glycemic and insulinemic responses following 30-60 min of exercise have been extensively studied, and a dose-response has been proposed between exercise duration, or volume, and improvements in glucose tolerance or insulin sensitivity. However, few studies have examined the effects of longer bouts of exercise in type 2 diabetes (T2D). Longer bouts may have a greater potential to affect glucagon, interleukin-6 (IL-6) and incretin hormones [i.e., glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP)]. AIM: To examine the effect of two bouts of long-duration, moderate-intensity exercise on incretins, glucagon, and IL-6 responses before and after exercise, as well as in response to an oral glucose tolerance test (OGTT) conducted the following day. METHODS: Twelve men, six with and six without T2D, participated in two separate conditions (i.e., exercise vs. rest) according to a randomized crossover design. On day 1, participants either rested or performed two 90 min bouts of treadmill exercise (separated by 3.5 h) at 80% of their ventilatory threshold. All participants received standardized meals on day 1. On day 2 of each condition, glucose and hormonal responses were measured during a 4-h OGTT. RESULTS: On day 1, exercise increased IL-6 at the end of the first bout of exercise (exercise by time interaction p = 0.03) and GIP overall (main effect of exercise p = 0.004). Glucose was reduced to a greater extent in T2D following exercise (exercise by T2D interaction p = 0.03). On day 2, GIP and active GLP-1 were increased in the fasting state (p = 0.05 and p = 0.03, respectively), while plasma insulin and glucagon concentrations were reduced during the OGTT (p = 0.01 and p = 0.02, respectively) in the exercise compared to the rest condition for both healthy controls and T2D. Postprandial glucose was elevated in T2D compared to healthy control (p < 0.05) but was not affected by exercise. CONCLUSION: Long-duration, moderate-intensity aerobic exercise can increase IL-6. On the day following exercise, fasting incretins remained increased but postprandial insulin and glucagon were decreased without affecting postprandial glucose. This long duration of exercise may not be appropriate for some people, and further research should investigate why next day glucose tolerance was unchanged.

The effects of gastric bypass surgery on drug absorption and pharmacokinetics.

INTRODUCTION: Being overweight is widespread in most societies and represents a major health threat. Gastric bypass surgery offers a highly effective mode of treatment for the morbidly obese patients. The procedures cause an alteration in normal gastrointestinal anatomy and physiology, with consequences not only on nutrient absorption, but also possibly on orally administered drugs. Bypass of the acidic environment of the stomach, partial impairment of bile salts-drug interactions and reduced absorptive surface, all create the potential for reduced absorption of drugs. AREAS COVERED: This article provides an overview of the effects of obesity and the most prevalent type of gastric bypass (Roux-en-Y) on pharmacokinetics. Articles for review were searched using Pubmed. EXPERT OPINION: The absorption of those drugs with known bioavailability issues generally seem to be most affected by bypass surgery. It is important to consider the effect of obesity on pharmacokinetics independent of the bypass procedure, because it leads to a dramatic drop in body mass over a relatively short period of time. This may be associated with reversals in the influence of obesity on drug disposition to characteristics more in line with leaner patients. Drugs will differ in their pharmacokinetic response to surgery, limiting any general conclusions regarding the impact of the surgery on drug disposition.

Effect of gastric bypass surgery on the absorption and bioavailability of metformin.

OBJECTIVE: Use of gastric bypass surgery is common and increasing. Over 40% of patients in diabetes remission after gastric bypass surgery may redevelop diabetes within 5 years. Metformin, the first-line drug for diabetes, has low bioavailability and slow, incomplete gastrointestinal absorption. We hypothesized that gastric bypass would further reduce the absorption and bioavailability of metformin. RESEARCH DESIGN AND METHODS: In a nonblinded, single-dose pharmacokinetic study, 16 nondiabetic post-gastric bypass patients and 16 sex- and BMI-matched control subjects (mean age 40 years and BMI 39.2 kg/m(2)) were administered two 500-mg metformin tablets. Plasma metformin levels were sampled at 0.5, 1, 1.5, 2, 3, 4, 6, 8, and 24 h. Metformin absorption, estimated by the area under the curve (AUC) of the plasma drug concentrations from time 0 to infinity (AUC(0-∞)), was the primary outcome, and metformin bioavailability, assessed by measuring 24-h urine metformin levels, was a secondary outcome. RESULTS: Compared with control subjects, metformin AUC(0-∞) was increased in gastric bypass subjects by 21% (13.7 vs. 11.4 µg/mL/h; mean difference 2.3 [95% CI -1.3 to 5.9]) and bioavailability was increased by 50% (41.8 vs. 27.8%; 14.0 [4.1-23.9]). Gastric bypass patients had significantly lower AUC glucose levels over 8 h compared with control subjects (35.8 vs. 41.7 µg/mL/h; 5.9 [3.1-8.8]), but this was likely a result of differences in baseline fasting glucose and not metformin absorption. CONCLUSIONS: Metformin absorption and bioavailability seem to be higher after gastric bypass, and this may have implications on dosing and toxicity risk. Studies are needed to confirm these findings and delineate potential mechanisms.

Metformin and exercise in type 2 diabetes: examining treatment modality interactions.

OBJECTIVE: To determine the effect of metformin on the acute metabolic response to submaximal exercise, the effect of exercise on plasma metformin concentrations, and the interaction between metformin and exercise on the subsequent response to a standardized meal. RESEARCH DESIGN AND METHODS: Ten participants with type 2 diabetes were recruited for this randomized crossover study. Metformin or placebo was given for 28 days, followed by the alternate condition for 28 days. On the last 2 days of each condition, participants were assessed during a nonexercise and a subsequent exercise day. Exercise took place in the morning and involved a total of 35 min performed at three different submaximal intensities. RESULTS: Metformin increased heart rate and plasma lactate during exercise (both P≤0.01) but lowered respiratory exchange ratio (P=0.03) without affecting total energy expenditure, which suggests increased fat oxidation. Metformin plasma concentrations were greater at several, but not all, time points on the exercise day compared with the nonexercise day. The glycemic response to a standardized meal was reduced by metformin, but the reduction was attenuated when exercise was added (metformin×exercise interaction, P=0.05). Glucagon levels were highest in the combined exercise and metformin condition. CONCLUSIONS: This study reveals several ways by which metformin and exercise therapies can affect each other. By increasing heart rate, metformin could lead to the prescription of lower exercise workloads. Furthermore, under the tested conditions, exercise interfered with the glucose-lowering effect of metformin.