Rapid and sensitive high-performance liquid chromatographic assay for metformin in plasma and urine using ion-pair extraction techniques

Development, Validation and Application of HPLC Method for Metformin in Rabbit Plasma

Objective:

This study was aimed at conducting a pharmacokinetic evaluation of metformin in rabbit plasma samples using rapid and sensitive HPLC method and UV detection.

Methods:

Acetonitrile was used for protein precipitation in the preparation of plasma samples. Reverse phase chromatography technique with silica gel column (250 mm × 4.6 mm, 5 μm) at 30°was used for the separation purpose. Methanol and phosphate buffer (pH 3.2) mixture was used as a mobile phase with flow rate 0.8 ml/min. The wavelength of UV detector was adjusted at 240 nm.

Results:

The calibration curve was linear in a range of 0.1-1 µg/ml with R² = 0.9982. The precision (RSD, %) values were less than 2%, whereas, accuracy of method was higher than 92.37 %. The percentage recovery values ranged between 90.14 % and 94.97 %. LOD and LOQ values were 25 ng/ml and 60 ng/ml, respectively. Cmax and AUC0-t values were found to be 1154.67 ± 243.37 ng/ml and 7281.83 ± 210.84 ng/ml.h, respectively after treating rabbits with a formulation containing 250 mg metformin.

Conclusion:

Based on the above findings, it can be concluded that present method is simple, precise, rapid, accurate and specific and thus, can be efficiently used for the pharmacokinetic study of metformin.

Comprehensive study of the antidiabetic drug metformin and its transformation product guanylurea in Greek wastewaters

Many pollutants such as pharmaceuticals and their transformation products (TPs) are not efficiently removed from wastewater treatment plants and enter into surface waters. The aim of this study was to investigate the occurrence and behavior of metformin, one of the most prescribed drugs worldwide, and its biological transformation product guanylurea, in eight wastewater treatment plants (WWTPs) of Greece. All WWTPs were equipped with conventional activated sludge treatment and the samples were taken from the influents and the effluents, over the four seasons of one year. The analytical method developed based on SPE followed by LC-UV/Vis-ESI/MS analysis, while positive findings were confirmed also by means of LTQ Orbitrap mass spectrometer. High polarity of both compounds led to the extraction with Oasis HLB and the use of the anionic surfactant SDS. The results showed that metformin dominated in the influents (bql-1167 ng/L), while guanylurea in the effluents (bql-627 ng/L) of the wastewater treatment plants, with Metformin/Guanylurea ratio ranging between 0.88 and 81.3 in the influents and between 0.005 and 0.78 in the effluents. Lack of a clear seasonal tendency in the occurrence and removal or formation was observed. Finally, an ecotoxicological risk assessment of metformin in effluent wastewaters took place by calculating the ratio between the environmental concentrations (MEC) and the predicted no effect concentrations (PNEC). Despite the fact that metformin presented low risk in all cases, an environmental concern is suspected for guanylurea since it is continuously released into the aquatic environment.

Hydrophilic interaction chromatography-tandem mass spectrometry based on an amide column for the high-throughput quantification of metformin in rat plasma

A simple, highly sensitive, specific, reproducible, and high-throughput Amide-HILIC-MS/MS assay to quantify metformin in rat plasma was established and successfully applied for sample analysis to support pharmacokinetic studies.

HPLC-UV determination of metformin in human plasma for application in pharmacokinetics and bioequivalence studies

In this study, a simple, rapid and sensitive HPLC method with UV detection is described for determination of metformin in plasma samples from bioequivalence assays. Sample preparation was accomplished through protein precipitation with acetonitrile and chromatographic separation was performed on a reversed-phase phenyl column at 40 degrees C. Mobile phase consisted of a mixture of phosphate buffer and acetonitrile at flow rate of 1.0 ml/min. Wavelength was set at 236 nm. The method was applied to a bioequivalence study of two drug products containing metformin, and allowed determination of metformin at low concentrations with a higher throughput than previously described methods.

Liquid chromatography tandem mass spectrometry method for simultaneous determination of antidiabetic drugs metformin and glyburide in human plasma

A simple and rapid liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the simultaneous quantitation of antidiabetic drugs metformin and glyburide in human plasma using glimepiride as internal standard (IS). After acidic acetonitrile-induced protein precipitation of the plasma samples, metformin, glyburide and IS were chromatographed on reverse phase C18 (50 mm x 4.6 mm i.d., 5 microm) analytical column. Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization technique and operating in multiple reaction monitoring (MRM) and positive ion mode. The total chromatographic run time was 3.5 min and calibration curves were linear over the concentration range of 20-2500 ng/ml for metformin and 5-500 ng/ml for glyburide. The method was validated for selectivity, sensitivity, recovery, linearity, accuracy and precision, dilution integrity and stability studies. The recoveries obtained for the analytes and IS (>or=69%) were consistent and reproducible. Inter-batch and intra-batch coefficient of variation across four validation runs (LLOQ, LQC, MQC and HQC) was less than 8%. The accuracy determined at these levels was within +/-8% in terms of relative error (RE). The method was applied to a bioequivalence study of 500 mg metformin and 5mg of glyburide tablet after oral administration to 28 healthy human subjects under condition of fasting.

Dried blood spot liquid chromatography assay for therapeutic drug monitoring of metformin

The use of blood spot collection cards is a simple way to obtain specimens for analysis of drugs for the purpose of therapeutic drug monitoring, assessing adherence to medications and preventing toxicity in routine clinical setting. We describe the development and validation of a microanalytical technique for the determination of metformin from dried blood spots. The method is based on reversed phase high-performance liquid chromatography with ultraviolet detection. Drug recovery in the developed method was found to be more than 84%. The limits of detection and quantification were calculated to be to be 90 and 150 ng/ml, respectively. The intraday and interday precision (measured by CV%) was always less than 9%. The accuracy (measured by relative error, %) was always less than 12%. Stability analysis showed that metformin is stable for at least 2 months when stored at -70 degrees C. The small volume of blood required (10 microL), combined with the simplicity of the analytical technique makes this a useful procedure for monitoring metformin concentrations in routine clinical settings. The method is currently being applied to the analysis of blood spots taken from diabetic patients to assess adherence to medications and relationship between metformin level and metabolic control of diabetes.

Determination of antihyperglycemic biguanides in serum and urine using an ion-pair solid-phase extraction technique followed by HPLC-UV on a pentafluorophenylpropyl column and on an octadecyl column

An HPLC-UV method was established for the determination of metformin and buformin in biological fluids. Metformin was not retained on particles packed in conventional solid-phase extraction cartridges; in contrast, buformin was retained too firmly and not eluted with a solvent for recovery. However, both drugs were retained on particles that had been treated with an ion-pair reagent of heptanesulfonate or dodecylsulfate and recovered almost completely. The recovered fraction was subjected to HPLC on a pentafluorophenylpropyl column which was suitable for the determination of both biguanides in serum and in urine. Limits of quantitation were low enough for clinical use, and reproducibility was high with an RSD of 0.9-2.3%. HPLC on a conventional octadecyl column was suitable only for the determination of buformin in serum since interfering peaks appeared on the chromatograms of urine samples. The method was applied to analysis of some clinical specimens.

Development and validation for high selective quantitative determination of metformin in human plasma by cation exchanging with normal-phase LC/MS/MS

An assay based on cation exchange solid-phase extraction and liquid chromatography-tandem mass spectrometry (LC/MS/MS) has been developed for the quantitative determination of metformin in human plasma. The analytical method consists of cation exchange solid-phase extraction (VersaPlate CBA) without any further evaporation/dissolution steps and cation exchange-based HPLC separation (Capcell Pak SCX column) with a normal-phase gradient system followed by semi-micro LC/MS/MS in positive ion selected reaction monitoring mode using electrospray ionization. The method exhibited excellent performance in terms of selectivity, robustness, short run time (7 min/sample) and simplicity of sample preparation. The calibration range was 10-1000 ng/ml with 0.2 ml of plasma. Intra- and inter-day mean accuracies were within the ranges of 100.3-105.0% and 101.2-105.3%, respectively. Intra- and inter-day precisions were within the ranges of 0.8-1.9% and 1.5-8.6%, respectively. Mean absolute recovery was 67.0% for metformin. No apparent loss of metformin after extraction was observed in an autosampler at 10 degrees C for 24 h. Dilution of metformin by blank human plasma up to 20-fold was tested and revealed no impact on the results of determination. Furthermore, the method exhibited high selectivity, since no effect on metformin analysis was observed on comparison of samples with or without nateglinide and other agents in plasma. Results obtained with the method were also comparable to a published LC-UV method on cross-validation. This method can be applied to various clinical pharmacokinetic studies of metformin.

Fast liquid chromatographic-tandem mass spectrometric (LC–MS–MS) determination of metformin in plasma samples

Liquid chromatographic-tandem mass spectrometric (LC-MS-MS) methods for the determination of metformin in plasma from different species are presented. The first method employed a YMC cyano 2mm x 50 mm, 3 microm analytical column. For minimum sample preparation direct injection of samples after protein precipitation was performed. The polar column used with highly organic mobile phases provided a normal phase retention mechanism. The elution conditions were optimized to obtain reproducible peak areas and good peak shape. A step gradient from 100% acetonitrile to acetonitrile-water 80:20 (v/v) containing 10mM ammonium acetate and 1% acetic acid was applied, leading to a sample-to-sample cycle time of 2 min. In a second method, a column-switching LC-MS-MS assay for on-line trapping was developed. The analyte and internal standard were trapped on a YMC cyano 2 mm x 10 mm, 5 microm column using acetonitrile-methanol 95:5 (v/v). Elution was performed isocratically in back-flush mode on to the analytical column (YMC cyano 2 mm x 50 mm, 3 microm) using 10 mM ammonium acetate in acetonitrile-water 80:20 (v/v) with 1% formic acid. With this approach, the signal-to-noise ratio was improved and the run time could be shortened to 1 min. Calibration samples were prepared in the matrix to be assayed in the range of 10-10,000 ng/ml. Quality control (QC) samples were prepared at 40, 400 and 4000 ng/ml and interspersed with the unknown study samples in the assays. Deviations for precision and accuracy were less than 20% for the lower limit of quantification (LLOQ) and low QC sample and less than 15% for other calibrators and QCs.

Determination of metformin in plasma using a new ion pair solid phase extraction technique and ion pair liquid chromatography

This article describes the development of the first ion pair solid phase extraction technique (IPSPE), which has been applied to the extraction of metformin from plasma samples. In addition an ion pair chromatographic method was developed for the specific HPLC determination of metformin. Several extraction and HPLC methods have been described previously for metformin, however, most of them did not solve the problems associated with the high polarity of this drug. Drug recovery in the developed method was found to be more than 98%. The limit of detection and limit of quantification was 3 and 5 ng/ml, respectively. The intraday and interday precision (measured by coefficient of variation, CV%) was always less than 9%. The accuracy (measured by relative error, R.E.%) was always less than 6.9%. Stability analysis showed that metformin is stable for at least 3 months when stored at -70 degrees C. The method has been applied to 150 patient samples as part of a medication adherence study.

Rapid determination of metformin in human plasma using ion-pair HPLC

A rapid, simple and sensitive ion-pair HPLC method has been developed for quantification of metformin in plasma. The assay enables the measurement of metformin for therapeutic drug monitoring with a minimum detectable limit of 20 ng/ml. The method involves simple, one-step extraction procedure and analytical recovery was complete. The separation was performed on an analytical 150 x 4.6 mm i.d. mubondapak C(18) column. The wavelength was set at 235 nm. The mobile phase was 40% acetonitrile, 0.01 M sodium dodecyl sulphate, 0.01 M sodium dihydrogen phosphate, and distilled water to 100%, adjusted to pH 5.1 at a flow rate of 1.5 ml/min. The calibration curve was linear over the concentration range 0.2-2.5 microg/ml. The coefficients of variation for inter-day and intra-day assay were within the range of clinical usefulness.

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.

Determination of plasma metformin by a new cation-exchange HPLC technique

Metformin is an oral antihyperglycemic agent used in the therapy of noninsulin-dependent diabetic patients. This biguanide can induce dangerous complications such as lactic acidosis when its plasma concentration is too high. For this reason, the determination of plasma metformin should always be done during treatment. We developed a new HPLC method, for the routine determination of plasma metformin, with good reliability, rapid execution, and low costs. Sample preparation involved precipitation of the plasma proteins containing the internal standard buformin with a mixture of methanol, zinc sulfate, and ethylene glycol; the diluted supernatant was injected into a cation-exchange column. The mobile phase was potassium dihydrogenphosphate buffer-containing acetonitrile. The eluent was monitored at 236 nm. The calibration curve is linear within the range of 20-4000 ng/mL; the within-day coefficients of variation were less than 2.2% for metformin and 1.5% for buformin; the day-to-day coefficients of variation were less than 2.5% for metformin and 1.9% for buformin. The mean recoveries obtained from supplemented samples were included between 99.4 and 104.2% for metformin. Many characteristics make this method useful and easily accessible to all clinical laboratories equipped with HPLC instrumentation.

Determination of metformin in plasma by capillary electrophoresis using field-amplified sample stacking technique

A capillary electrophoresis method was described for the determination of metformin in human plasma based on the extraction of the ion-pair with bromothymol blue into chloroform. Phenformin was used as internal standard. Field-amplified sample stacking injection was employed with an electrokinetic injection voltage of 10 kV for 10 s. The running buffer was 0.1 M phosphate buffer (pH 2.5), running voltage was 20 kV and the UV absorbance detection was set at 195 nm. The limit of quantitation was 0.25 microg/ml. Linearity range of calibration curve was 0.25 to 3.5 microg/ml. Recoveries for three levels (0.25, 1 and 2 microg/ml) were 80.24%, 67.44% and 58.97% (n = 5 for each level), respectively. The intra-day precisions for the three levels were 11.9%, 3.09% and 4.33% and the inter-day precisions were 12.4%, 4.57% and 4.94%, respectively. The concentrations of metformin hydrochloride in human plasma of eight volunteers were measured after orally administrating metformin enteric-capsule and tablet.

Short administration of metformin improves insulin sensitivity in android obese subjects with impaired glucose tolerance

In a double-blind, randomized, cross-over study, the metabolic effects of a short treatment with metformin (2 x 850 mg day-1 for 2 days and 850 mg 1 h before evaluation) were compared to those of placebo in 15 obese subjects (BMI: 33.2 +/- 0.9 kg m-2), with abdominal distribution of adipose tissue and impaired glucose tolerance. An intravenous glucose tolerance test (0.3 g glucose kg-1) was performed after each period of treatment. Areas under the curve (AUC0-180 min) were calculated for plasma glucose, insulin, and C-peptide levels. Glucose tolerance was estimated by the coefficient of glucose assimilation (KG). Insulin sensitivity (SI) and glucose effectiveness (SG) indices were calculated using Bergman's minimal model. Insulin secretion rate (ISR) was determined by deconvolution of plasma C-peptide levels and insulin metabolic clearance rate (MCR) was estimated by dividing AUC 1SR by AUC insulin. Fasting plasma insulin levels were reduced after metformin (89.3 +/- 15.9 vs 112.4 +/- 24.3 pmol l-1; p = 0.04). AUC glucose, KG and SG were similar in both tests. However, AUC insulin was reduced (39.7 +/- 6.5 vs 51.8 +/- 10.4 nmol min l-1; p = 0.02), while SI (6.98 +/- 1.14 vs 4.61 +/- 0.42 10(-5) min-1 pmol-1 l; p = 0.03) and insulin MCR (715 +/- 116 vs 617 +/- 94 ml min-1 m-2; p = 0.03) were increased after metformin. The demonstration that metformin rapidly improves insulin sensitivity should encourage further research to evaluate the long-term effects of metformin in android obese subjects with impaired oral glucose tolerance.

Reduction of the acute bioavailability of metformin by the alpha-glucosidase inhibitor acarbose in normal man

In a double-blind cross-over study, we investigated a possible influence of the alpha-glucosidase inhibitor acarbose on the bioavailability of the biguanide compound metformin. Each of the six healthy young male volunteers was randomly allocated during two consecutive 7 day periods to either acarbose (days 1-3: 3 x 50 mg day-1; days 4-7: 3 x 100 mg day-1) or placebo. At day 7 and 14 of the study, the overnight-fasted subjects ingested 1000 mg metformin with the first bite of a standardized breakfast (500 kcal; 60 g carbohydrates) and together with either placebo or 100 mg acarbose. Acarbose significantly (P < 0.05) reduced the meal-induced increase in blood glucose and plasma insulin levels. Acarbose induced a significant (P < 0.05) reduction in early (90, 120, 180 min) serum levels, peak concentrations (Cmax: 1.22 +/- 0.14 vs. 1.87 +/- 0.60 mg l-1) and area under the curve of metformin (AUC 0-540 min: 423 +/- 55 vs. 652 +/- 55 mg min l-1), but did not diminish its 24 h urinary excretion. In conclusion, acarbose significantly reduces the acute bioavailability of metformin in normal subjects.

Analysis of drugs and other toxic substances in biological samples for pharmacokinetic studies

The importance of the role of analysis of drugs and other toxic substances in biological samples (bioanalysis) in medicine, toxicology, pharmacology, forensic science, environmental research and other biomedical disciplines is self-evident. Among these disciplines, bioanalysis plays a special pivotal role in pharmacokinetics. The pharmacokinetic parameters, such as half-life, volume of distribution, clearance and bioavailability, of drugs and other compounds are derived from the concentrations of these analytes assayed in the biological samples collected at specified time points. The capability of analysts to develop sensitive and specific analytical methods for the assay of low concentrations of drugs and other toxic compounds in small amounts of biological samples has contributed significantly to the theoretical advances in pharmacokinetics and its applications in clinical pharmacology and the management of drug therapy in patients. The increased demands for pharmacokinetic applications in turn have stimulated the innovation and improvement in bioanalytical technologies. The reliability of the pharmacokinetic conclusions depends on the accuracy and precision of the analytical methods employed to assay the biological samples. Factors that affect the integrity of the bioanalytical data should therefore be controlled in analysis of biological samples for pharmacokinetics studies. The biological samples for drug concentration determination should be collected as specified in the study protocol with respect to the time and site of sampling. These samples should be processed to avoid extraneous interactions between the analytes and sampling devices or additives resulting in the redistribution of the analytes between components of the biological samples, such as displacement of drug binding and changes in the distribution of the analytes between plasma and red blood cells. The stability of the drugs and other analytes in the samples should also be evaluated to establish the conditions suitable for the transportation and storage of the samples to avoid chemical, photochemical and enzymatic degradation of the analytes. Various technologies have been utilized to assay biological samples for pharmacokinetic studies. The most frequently used are chromatography (high-performance liquid chromatography, gas chromatography and thin-layer chromatography), immunoassays and mass spectrometry.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetic-pharmacodynamic relationships of oral hypoglycaemic agents. An update

Oral hypoglycaemic drugs, sulphonylureas and biguanides, occupy an important place in the treatment of Type II (non-insulin-dependent) diabetic patients who fail to respond satisfactorily to diet therapy and physical exercise. Although the precise mechanisms of action of these compounds are still poorly understood, there is sufficient agreement that sulphonylureas have both pancreatic and extrapancreatic effects, whereas biguanides have predominantly extrapancreatic actions. By using labelled compounds or measuring the circulating concentrations, the main pharmacokinetic properties of oral hypoglycaemic agents have been assessed and, in some cases, their pharmacokinetic-pharmacodynamic relationships have been evaluated. A correlation between diabetes control and plasma sulphonylurea or biguanide concentrations is generally lacking at the steady-state, with the possible exception of long-acting agents; after either oral or intravenous dosing, the reduction of plasma glucose is usually related to the increased circulating drug concentrations. The toxic effects of oral hypoglycaemic drugs are more frequent in the elderly and in the presence of conditions that may lead to drug accumulation or potentiation (increased dosage, use of long-acting compounds, hepatic and renal disease, interaction with other drugs); however, a relationship between toxic effects and drug plasma levels has been reported only for biguanides.

Reduction of metformin renal tubular secretion by cimetidine in man

To determine whether cimetidine altered the renal handling of metformin, seven subjects took 0.25 g metformin daily with and without cimetidine 0.4 g twice daily. Blood and urine samples were collected and assayed for metformin, cimetidine and creatinine by h.p.l.c. Cimetidine significantly increased the area under the plasma metformin concentration-time curve by an average of 50% and reduced its renal clearance over 24 h by 27% (P less than 0.008). There was no alteration in the total urinary recovery of metformin when cimetidine was co-administered. The effect of cimetidine on the renal clearance of metformin was time dependent, being significantly reduced up to 6 h following cimetidine. These results appeared to be consistent with competitive inhibition of renal tubular secretion. Cimetidine had no effect on the renal clearance of creatinine, but time-dependent variations in both metformin and creatinine renal clearance were observed. Metformin had no effect on cimetidine disposition. It is concluded that cimetidine inhibits the renal tubular secretion of metformin in man, resulting in higher circulating plasma concentrations. Because of its propensity for causing dose and concentration-dependent adverse effects, the dose of metformin should be reduced when cimetidine is co-prescribed.