Determination of metformin and phenformin in human plasma and urine by reversed-phase high-performance liquid chromatography

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.

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.

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.

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.

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.

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 high-performance liquid chromatography after ultrafiltration

A rapid high-performance liquid chromatography (HPLC) method was developed for determination of metformin, an oral antidiabetic agent, in plasma. Sample preparation entailed a 30-min centrifugation of plasma through a micron filter with direct injection of the protein-free ultrafiltrate into an HPLC system consisting of a cation-exchange extraction column (7.5x4.6 mm), a column switching valve, and a cation-exchange analytical column (250x4.6 mm). The eluent was monitored at 232 nm. Metformin was well resolved at a retention time of about 5 min. There was less than 2% loss of metformin during ultrafiltration and good linearity was established from 0.10 to 40 mg/l of metformin hydrochloride. The lower limit of quantitation was about 0.05 mg/l, at which concentration the signal-to-noise was above 10. The intra- and inter-assay coefficients of variation at plasma concentrations of metformin hydrochloride between 0.25 and 25 mg/l were typically 0.8-1.4% and 3.5-6.4%, respectively. This method offers a rapid sample preparation time and achieves excellent sensitivity without resorting to extraction and evaporation techniques.

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.

Meformin, plasma glucose and free fatty acids in type II diabetic out-patients: results of a clinical study

Abnormalities in free fatty acid (FFA) metabolism are an intrinsic feature of type II diabetes mellitus and may even play a role in the development of glycaemic imbalance. This study investigated whether the anti-diabetic drug metformin can reduce FFA levels in clinical practice and whether this correlates with its anti-diabetic effect. For 6 months metformin was added to sulfonylurea therapy in 68 type II diabetic outpatients with poor glycaemic control, being administered before meals and at bed-time. Basal and daily area-under-the-curve (AUC) glucose levels dropped (both P < 0.0005) like basal and daily AUC FFA levels (P < 0.004 and P < 0.001 respectively) reductions were all correlated (P < 0.001 and P < 0.003 respectively). Reductions in fasting and daily AUC glucose correlated more closely with body fat distribution, expressed by waist-hip ratio (WHR) (P < 0.006 and P < 0.004 respectively), than with the body mass index (BMI) (P < 0.02 and P < 0.04 respectively). Similarly fasting and daily AUC FFA correlated with WHR (P < 0.007 and P < 0.01 respectively) but not with BMI (both P = ns). Subdividing male and female diabetic patients into groups with low and high WHRs, fasting and daily AUC glucose were reduced in men (P < 0.01 and P < 0.02) and in women (P < 0.02 and P < 0.04 respectively) with low WHRs less than in men and in women with higher WHRs (for each gender P < 0.0001 and P < 0.0002, respectively). Decreases in fasting and daily AUC FFA, which did not reach significance in either men or women with low WHRs, were statistically significant in men (P < 0.03 and P < 0.01 respectively) and in women (P < 0.02 and P < 0.005 respectively) with high WHRs. These findings suggest that an improvement in FFA plasma levels might contribute to metformin's anti-diabetic activity which appears to be more marked in patients with high WHRs. Moreover adding a bed-time dosage to the standard administration at meal times seems to be an effective therapeutical strategy.

Low dose metformin in the treatment of type II non-insulin-dependent diabetes: clinical and metabolic evaluations

Low doses of metformin (500 mg twice daily) were administered to 20 diabetic patients, combined with the original sulfonylurea treatment which had become ineffective even at full dosage. After 1 and 5 weeks, the effects of the drug on glycemic control, blood intermediate metabolites and monocyte insulin receptors were monitored. Metformin clearly improved glycemic control by reducing both fasting blood glucose from 189.88 +/- 21.11 mg/dl to 131.12 +/- 16.02 mg/dl after 1 week and to 130.11 +/- 13.29 mg/dl after 5 weeks (p less than 0.025 both after 1 and 5 weeks); the diurnal blood glucose average fell from 235.33 +/- 24.11 mg/dl to 174.66 +/- 23.45 mg/dl (p less than 0.0025) after 1 week and to 177.65 +/- 21.71 mg/dl (p less than 0.0005) after 5 weeks. Consequently both blood glycosylated hemoglobin (p = n.s. after 1 week, p less than 0.025 after 5 weeks) and serum fructosamine (p less than 0.0025 after both 1 and 5 weeks) also decreased after metformin treatment. No change in plasma insulin and C-peptide levels was reported and no modification in diurnal rhythms of blood lactate, pyruvate, alanine glycerol and beta-OH-butyrate was detected at any time during metformin treatment. All the changes documented in the binding values were already complete at the end of the first week; insulin binding to monocytes increased slightly but significantly (p less than 0.05) and the number of receptors per cell rose (p less than 0.05) but could not be correlated to any index of glycemic control. These data suggest that the antidiabetic action of metformin is neither related to its lactate-increasing activity nor does it depend upon its inducing an increase in insulin binding values. This metformin-related hypoglycemic effect might be the result, at least in part, of a reduced oxidative phosphorylation without inhibition of hepatic gluconeogenesis and/or of decreased hepatic glucose output. Moreover, our data are also consistent with the hypothesis that metformin might affect insulin action at a post-receptor level.

Effect of plasma metformin concentrations on serum lipid levels in type II diabetic patients

In this study we evaluated the relationships between plasma metformin levels, measured by reverse-phase high-performance liquid chromatography, and serum lipid levels in 20 metformin-treated, type II diabetic patients. Mean fasting plasma metformin concentration was 490 +/- 188 ng/ml. No correlation was found between daily dose of drug and lipid parameters. A significant correlation emerged between circulating metformin concentration and serum triglycerides (r = -0.574, p less than 0.01), HDL-cholesterol (r = 0.583, p less than 0.01) and HDL2-cholesterol (r = 0.670, p less than 0.05). Multiple linear regression analysis showed that the correlation between plasma metformin concentration and serum triglycerides still remained significant after correction for other clinical and metabolic parameters. Total cholesterol and HDL3-cholesterol were not correlated with metformin concentrations. These results demonstrate the clinical usefulness of measuring plasma metformin concentrations and indicate that some effects of metformin on lipid metabolism depend on the drug plasma levels.