Stability indicating RP-HPLC method development and validation of metformin hydrochloride and glimepiride in bulk and pharmaceutical dosage form

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1 World Journal of Pharmaceutical Sciences ISSN (Print): ; ISSN (Online): Published by Atom and Cell Publishers All Rights Reserved Available online at: Original Article Stability indicating RP-HPLC method development and validation of metformin hydrochloride and glimepiride in bulk and pharmaceutical dosage form Srinivasa Rao Atla, Baby Nalanda R., Natraj S. K. Department of Pharmaceutical Analysis and Quality Assurance, Shri Vishnu College of Pharmacy (Affiliated to Andhra University), Vishnupur, Bhimavaram , West Godavari-D.t., Andhra Pradesh, India. ABSTRACT Received: / Revised: / Accepted: / Published: A stability indicating RP-HPLC method was developed and validated for the determination of Metformin HCl and Glimepiride in tablet dosage form. The method was carried out using Agilent C 18 column (250 mm 4.6 mm, 5 μ) with mobile phase consisting 25 mm Hexane-1-sulphonic acid buffer adjusted to ph 2.5 with ortho-phosphoric acid and acetonitrile (45:55 v/v), at a flow rate of 1.0 ml/min and the effluent monitored at 229 nm. The retention time of Metformin HCl and Glimepiride were found to be and min respectively. Linearity was observed over the concentration range of µg/ml for Metformin HCl and µg/ml for Glimepiride. The percentage recoveries of Metformin HCl and Glimepiride in the marketed dosage form found to be and 99.9 respectively. The reliability and analytical performance of the proposed method were statistically validated for specificity, linearity, precision, accuracy, and ruggedness, detection, and quantification limits. The drug was subjected to stress conditions including acidic, alkaline, oxidation, photolysis and humidity degradation. The drug is more sensitive towards oxidation degradation. The method was validated as per ICH guidelines. Keywords: Metformin hydrochloride, Glimepiride, RP-HPLC, Stressed degradation, Validation. INTRODUCTION Diabetes is a chronic disease in which there are high levels of sugar in the blood. It will be classified into three major types namely, type I, II, and gestational diabetes. Approximately 90% of the people suffered with diabetes of type II. It usually begins as an insulin resistance, a disorder in which the cell do not use insulin properly. Type II diabetes associated with older age, obesity, family history of gestational diabetes, impaired glucose metabolism, physical inactivity and race/ethnicity [1]. If the glycemic target level is not achieved with one oral agent, combination of oral and/or insulin therapy is recommended [2]. Combination of oral therapy becomes an obvious choice when glycemic control is not achieved with conventional monotherapy [3]. The advantages of oral dose combinations as compared to their components which are taken alone are lower cost and better compliance [4]. Metformin HCl (MET) is chemically known as 1,1-dimethyl biguanide monohydrochloride, an oral anti-diabetic drug in the class of biguanides (Fig. 1). It is used for the treatment of non-insulin dependent diabetes mellitus as first-line drug, controlled by decreasing glucose absorption, hepatic glucose production and increasing the insulin-mediated uptake of glucose [5]. MET is the only anti-diabetic drug that has been conclusively shown to prevent the cardiovascular complications of diabetes. Its use in gestational diabetes has been limited by safety concerns. It is also used in polycystic ovary syndrome and also for other diseases where insulin resistance may be an important factor. It helps in reducing lowdensity lipoprotein cholesterol and triglyceride levels [6]. Glimepiride (GLI) is chemically known as 3-Ethyl- 4-methyl-N-{2-[4-({[(4-methylcyclohexyl) carbamoyl] amino}sulfonyl)phenyl]ethyl}-2-oxo- 2,5-dihydro-1H-pyrrole-1-carboxamide [7] (Fig. 1). It is a third generation sulfonyl urea, which is very potent with long duration of action. It acts by stimulating insulin secretions from beta cells of pancreas and is also known to increase peripheral *Corresponding Author Address: Dr. Srinivasa Rao Atla, Department of Pharmaceutical Analysis and Quality Assurance, Shri Vishnu College of Pharmacy (Affiliated to Andhra University), Vishnupur, Bhimavaram , West Godavari-D.t., Andhra Pradesh, India; E- mail: drasrpharma@gmail.com

2 insulin sensitivity thereby decreasing insulin resistance. MET and GLI have been co-formulated as a fixed dose combination (FDC) and have been commonly employed for the management of Type II diabetes. This combination has been proven to result in superior glycemic control compared to monotherapy of either drug. Furthermore, FDCs show better patient compliance and are costeffective compared to administration of individual drugs. Formulation of a combination of drugs in an individual dosage form calls for the need to develop a simultaneous analytical method for the routine and stability testing of the product. Literature revealed that, several methods are reported individually and combination with other anti-diabetic drugs such as spectrophotometry [8,9], Reversed Phase high performance liquid chromatography (HPLC) [10-12], Liquid chromatography in biological fluids [13], Liquid chromatography coupled with Tandem mass spectroscopy [14], novel validated RP-HPLC-DAD method with forced degradation studies [15], HPLC and HPTLC [16], stability indicating HPTLC densitometric method [17], Gas chromatographymass spectrometry in human plasma [18], Capillary electrophoresis [19]. Literature for glimepiride revealed several methods which include spectrophotometry [20, 21], HPLC [22-24], Liquid chromatography in biological fluids [25], HPTLC [26, 27], Multivariate analysis [28] method for GLI alone as well as with other drugs in different pharmaceutical formulations. Although various methods are reported in the literature for estimation of MET and GLI, there is no simple, sensitive, stability indicating method for the estimation of both drugs. The objective of this study is to develop a simple, rapid, precise and accurate liquid chromatographic method for determination of Metformin HCl and Glimepiride in bulk and pharmaceutical dosage form as an alternative method. The method was validated as per the procedures and acceptance criteria of ICH guidelines. MATERIALS AND METHODS Chemicals and Reagents: Pharmaceutical grade Metformin HCl and Glimepiride obtained as gift sample by Dr. Reddy s Laboratories Ltd., Hyderabad, India, and tablet formulation (Amaryl- M 2) was procured from local pharmacy store and used within their shelf-life period. Methanol, water, acetonitrile are of HPLC grade and Hexane-1- sulphonic acid, ortho-phosphoric acid (Analytical 434 grade) are obtained from Sd-Fine chemicals, Mumbai. Milli Q water and 0.45 µm nylon membrane filters were obtained from Spincotech Private Limited, Hyderabad, India. Acetonitrile and buffer as a mixture, in the ratio of v/v, were used as diluent to prepare working solutions of required concentrations. All the stock and working solutions were protected from sunlight and stored in a refrigerator at 4 ºC. Instrumentation: The separation was carried out on HPLC system with waters 2695 Alliance with binary pumps and photo diode array detector (PDA) module equipped with auto-sampler with injection volume 20 µl. Data integration is carried out using Empower-2 software. Samples are injected into Agilent C 18 column (250 x 4.6 mm, 5 µ). Chromatographic conditions: Chromatographic separation was carried out on Agilent C 18 column (250 x 4.6 mm, 5 µ) using mobile phase 25 mm Hexane-1-sulphonic acid buffer adjusted to ph 2.5 using ortho-phosphoric acid and acetonitrile (45:55 v/v) was operated on isocratic mode. The chromatograms were recorded and the peaks were quantified using an automatic integrator. In this method, 1.0 ml/min flow rate was used for the separation and detection was performed at 229 nm. The injection volume was 20 µl. Preparation of stock solutions: The standard stock solutions were prepared separately by transferring 500 mg of metformin, 2 mg of glimepiride into 100 ml of standard volumetric flask. To that about 50 ml of diluent was added, the solution was sonicated to dissolve and the volume is made upto the mark and filtered through 0.45 µm membrane filter. Further dilutions were made with diluent to get the final concentrations of metformin ( µg/ml) and glimepiride ( µg/ml). Preparation of sample solution: Twenty tablets each containing 500 mg of metformin and 2 mg of glimepiride were weighed. Finely powder the tablet in a mortar, a quantity of powder equivalent to one tablet content was accurately weighed and transferred into 100 ml of standard volumetric flask containing 50 ml of diluent, sonicate for 20 min and made up to the volume. Further secondary dilutions were made with diluent to final concentrations of metformin 500 µg/ml and glimepiride 2 µg/ml. Quantification was achieved by peak area ratio method with reference to the standards. Method validation: Validation of the analytical method is the process that was established by

3 laboratory studies in which the performance characteristics of the method meet the requirements for the intended analytical application. The developed HPLC method was validated according to International Conference on Harmonization (ICH) guidelines [29]. The method was validated for the parameters like linearity, accuracy, precision, and ruggedness, limit of detection (LOD) and limit of quantification (LOQ). estimated from both linearity calibration curve method and signal to noise ratio method. These two parameters were calculated using the formula based on the standard deviation of the response and the slope. LOD and LOQ were calculated by following equations: System suitability: System suitability test is used to verify that the resolution and reproducibility were adequate for the analysis performed. Based on the fact that the equipment, electronics, samples to be analyzed constitute an integral system that can be evaluated as such. Parameters calculated for system suitability were % RSD (relative standard deviation) of retention time, area, number of theoretical plates and resolution. Linearity: The purpose of the test for linearity is to demonstrate that the entire analytical system (including detector and data acquisition) exhibits a linear response and is directly proportional over the relevant concentration range for the target concentration of the analyte. A linear relationship was evaluated across the range of the analytical procedure with minimum of six concentrations. A series of combination of standard dilutions were prepared over a concentration range of µg/ml and µg/ml of metformin and glimepiride respectively. The linearity was evaluated by linear regression analysis, which was calculated by least square method. Precision and Accuracy: Precision is the measure of closeness of the data values to each other for a number of measurements under the same analytical conditions. Precision of the assay was determined by repeatability (intra-day) and intermediate precision (inter-day). Repeatability refers to the use of the analytical procedure within the laboratory over the shorter period of the time that was evaluated by assaying the QC (quality control) samples during the same day. Intermediate precision was assessed by comparing the assays on different days. Accuracy is the degree of agreement between a measured value and the accepted reference value. The accuracy was determined by recovery studies of MET and GLI, known amount of standard was added to the pre-analyzed sample and subjected to the proposed HPLC analysis. Limit of Detection and Limit of Quantification: The sensitivity of measurement of metformin and glimepiride by use of the proposed method was estimated in terms of the Limit of quantification (LOQ) and Limit of Detection (LOD). Limit of detection (LOD) and quantification (LOQ) were Where, σ = standard deviation from the response S = Mean slope of the calibration curve Robustness and Ruggedness: The robustness of the method was studied by small but deliberate variations from the optimized conditions in wavelength (± 2 nm) and flow rate (± 0.2 ml/min). One factor at a time was changed at a concentration level of 500 µg/ml of MET and 2 µg/ml of GLI, the peak area obtained with each solution was measured and % RSD was calculated. Ruggedness was evaluated by performing assay of the formulations by different analyst, keeping the other parameters unchanged and in parallel; the chromatographic profile was observed and recorded. Solution stability: To determine the solution stability, all active sample solutions were spiked and the spiked sample solutions (20 µg/ml) were capped tightly and kept at room temperature for 24 hr. The contents of MET and GLI were determined at 0, 6, 12, 18 and 24 hr intervals by following the procedure, as described earlier. Forced degradation studies: The specificity of the method was demonstrated through forced degradation studies conducted on the sample using acid, alkaline, oxidative, reductive, thermal and photolytic degradation. The sample was exposed to these conditions and the main peak was studied for the peak purity, thus indicating that the method effectively separated the degradation products from the pure active ingredient. For each study, samples were prepared, the blank subjected to stress in the same manner for the drug solution, working standard solution of MET and GLI subjected to stress degradation. Dry heat and photolytic degradation were carried out in a solid state. Acid degradation: The MET and GLI mixture was treated with 1 ml of 0.1N HCl and heated on water bath and kept aside at 25 C for 24 hr. The mixture was cooled to room temperature and volume was made up to 20 ml with diluent. Base degradation: The MET and GLI mixture was treated with 1 ml of 0.1N NaOH and heated on 435

4 water bath and kept aside at 25 C for 24 hr. The mixture was cooled to room temperature and solution was filtered using 0.45 µ syringe filter and sonicated for 5 min and diluted to volume with 20 ml of diluent and mixed. Oxidation degradation: The MET and GLI mixture was treated with 1 ml of 3% H 2O 2 and heated on boiling water bath to remove the excess of hydrogen peroxide. The mixture was cooled to room temperature and diluted to volume with diluent and mixed. Photolytic degradation: Sample mixture of MET and GLI was exposed to sunlight for 24 hr. Sample was withdrawn, dissolved in mobile phase and volume was made up to 20 ml with diluent. Humidity degradation: The MET and GLI mixture was treated at 75% relative humidity for 24 hr. The volume was made up to 20 ml with diluent. RESULTS AND DISCUSSION The aim of the present investigation is to develop a sensitive, precise and accurate high performance liquid chromatographic method for the determination of metformin and glimepiride in pharmaceutical formulations. For developing the method [23, 27, 30], a systematic study of the effect of various factors was undertaken by varying one parameter at a time and keeping all other conditions constant. Method development consists of selecting the appropriate wave length and choice of stationary and mobile phases. Based on the nature and solubility characteristics of metformin and glimepiride, reverse phase mode of HPLC was selected for chromatography. Among different RP- HPLC stationary phases, Agilent C 18 column (250 x 4.6 mm, 5 µ) was found to be optimum. In order to get sharp peak with base line separation from interfering peaks carried out a number of experiments by varying the composition of mobile phase and its flow rate. To have an ideal separation of the drugs under isocratic conditions, mixtures of solvents like methanol, acetonitrile with different buffers in different combinations were tested as mobile phase. A mixture of 25 mm Hexane-1- sulphonic acid buffer adjusted to ph 2.5 using dilute ortho-phosphoric acid and acetonitrile in the ratio of 45:55 v/v was selected as optimum mobile phase at flow rate of 1.0 ml/min. Under these conditions, the analyte peaks were well resolved and free from tailing. The proposed RP-HPLC method was successfully used for the simultaneous determination of the MET and GLI in the formulation by UV detection at 229 nm. System suitability test was applied to representative chromatograms for various parameters such as 436 tailing factor and number of theoretical plates was determined. The results reported (Table 1 and Fig. 2) indicated that the asymmetrical factor was not more than 2.0, theoretical plate not less than 2000 for MET and GLI and the % RSD of peak area was not more than 2.0, which full-fills the good suitability of the proposed RP-HPLC method during all validation parameters. Thus, the system meets suitable criteria. Linearity: Linearity was established by least squares linear regression analysis of the calibration curve. The correlation coefficient (R 2 ) was calculated, and it was between which is well within the acceptance criteria. The results are shown in Table 2. The concentration was found to be proportional to the area, and the response of the detector was determined to be linear over the range for MET and GLI was found to be µg/ml and µg/ml (Fig. 3 and 4). Limit of detection and quantification were found to be 0.29 and 0.98 µg/ml for metformin and and µg/ml for glimepiride respectively, which indicates that the method is sensitive. Precision: The precision of the proposed method was tested by performing repeatability (intra-day) and intermediate precision (inter-day) studies. It was determined by injecting six times the expected operating range concentration. The precision data is summarised in the Table 3, revealed that the % RSD was less than 2 and there by indicating that the method was sufficiently precise. Accuracy: Accuracy was studied by recovery study using standard addition method. The accuracy was determined by measuring the recovery of MET and GLI at three different levels (50,100, and 150 %). The % recovery was % and % RSD was found to be less than 2. Results of recovery studies are shown in Table 4, which specified that the method was highly accurate for simultaneous determination of both the drugs. Robustness & Ruggedness: The intention of robustness is to identify critical parameters for the successful implementation of the method. Due to deliberate change in the method, no changes were found in the chromatogram, the method developed is robust. The results are shown in Table 5 and 6. Ruggedness was evaluated by performing assay of the formulations by different analyst by injecting six consecutive injections of the sample at working concentration from the same homogeneous mixture of tablets. This study showed % RSD less than 2, concerning % assay for both the drugs which indicate that the method developed is rugged.

5 Solution stability: The stability of the analytical solutions of the method was studied by analyzing the standard and sample solutions initially and at different time intervals. The % recovery of MET and GLI was found to be and after 24 hr. There was no significant change observed for the chromatograms of standard solution and the experimental solution at different time intervals. Furthermore, the absence of degradation peaks confirmed that sample is stable in the solvents used under the investigated conditions. Forced degradation studies: Forced degradation studies were performed to evaluate the stability indicating properties and specificity of the method. All forced degradation samples were analyzed by using the PDA detector to ensure the homogeneity and purity of MET and GLI. The conditions of stress degradations were optimized with respect to the strength of the reagent and exposure period so as to achieve degradation in the range of %. Forced degradation studies under acidic condition by using 0.1N HCl and product degradation was found to be 0.76 % and 4.0 % for MET and GLI for 24 hr respectively. Degradation behaviour under alkaline condition by using 0.1N NaOH and product degradation was found to be 7.78 % and 11.5 % for MET and GLI for 24 hr. Oxidation degradation was done by using hydrogen peroxide and product degradation was found to be 23 % and 18.3 % for MET and GLI for 24hr respectively. Photolytic degradation was found to be 8.21 % and 9.0 % for MET and GLI respectively. MET and GLI were almost stable in relative humidity stress conditions and showed a minimum degradation. Summary of stress degradation results is given in Table 7 and Fig. 5. The advantage of this method from the previous methods proposed for the drugs is that it gives a lesser retention time and also the detection method used is economical and easily available. 437 Assay: The proposed method was applied for the analysis of Amaryl-M 2 tablets and six replicate determinations were performed. The interference of excipients was studied by comparing the chromatograms of standards and formulation. The results of this assay yielded % and 99.9 % of the label claim for MET and GLI respectively. The results of this assay (Table 8) indicated that the developed method is selective for the analysis of both MET and GLI in formulations without interference of the excipients. CONCLUSION The study concludes that Metformin HCl and Glimepiride are most labile to oxidative stress conditions but stable enough to acid, alkaline and photolytic stress conditions. The developed RP- HPLC method was simple, reliable, economical, and found to be more precise, stability indicating, rugged and robust. Validation of this method was accomplished and the results obtained meet all requirements. The method was also found to be highly reproducible with a good accuracy and precision. The results demonstrated that the method would have a great value when applied in routine quality control analysis and stability studies for Metformin HCl and Glimepiride. ACKNOWLEDGEMENT Table 1. System suitability parameters (n = 6) Parameters Metformin Glimepiride Retention time Peak area Tailing factor Theoretical plates % RSD We are grateful to our Management, Sri Vishnu Educational Society, Bhimavaram, Andhra Pradesh, for providing required facilities to complete our work effectively. Conflict of Interest: Authors do not have any conflict of interest in this research work. Table 2. Statistical data of Linearity of MET and GLI Parameter Metformin Glimepiride Linearity range (µg/ml) µg/mL µg/mL Regression equation Y= 10685x Y=63866x Correlation coefficient R 2 = R 2 = Slope Intercept LOD ( g/ml) LOQ ( g/ml)

6 Table 3. Precision studies Repeatability precision (Intra-day) Intermediate precision (Inter-day) MET GLI MET GLI Average S.D % RSD Each mean value is the result of triplicate analysis Table 4. Accuracy studies Drugs Conc. (%) Amount of sample Amount found Recovery (%) (µg/ml) (µg/ml) MET GLI Each mean value is the result of triplicate analysis Tablet 5. Robustness studies of MET and GLI Parameters Variation Retention time (min) Tailing factor 0.8 ml/min Flow rate 1.2 ml/min MET 60 % organic phase Mobile Phase 50 % organic phase ml/min Flow rate 1.2 ml/min GLI 60 % organic phase Mobile Phase 50 % organic phase Average of three injections each Table 6. Ruggedness studies of MET and GLI Drug Retention time (time) Tailing factor Theoretical plates Analyst 1 MET GLI Analyst 2 MET GLI Average of three injections each Table 7. Forced Degradation studies Metformin Glimepiride Parameters Peak area % Active % % Active % Peak area ingredient Degradation ingredient Degradation Control Acid Alkaline Oxidation Photolytic Humidity Table 8. Assay studies Drug Label claim Amount found % Assay Metformin HCl 500 mg mg 100.2% Glimepiride 2 mg 1.98 mg 99.9% 438

7 439

8 440

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