51 CHAPTER 2 SIMULTANEOUS ESTIMATION OF PIOGLITAZONE, GLIMEPIRIDE AND GLIMEPIRIDE IMPURITIES IN COMBINATION DRUG PRODUCT BY A VALIDATED STABILITY-INDICATING RP-HPLC METHOD 2.1 INTRODUCTION OF DOSAGE FORM AND LITERATURE REVIEW Type 2 diabetes is a disorder characterized by high levels of glucose in the blood. It is the most common form of diabetes. Once affected, people have to deal with this disorder for the rest of their lives. A combination of glimepiride, pioglitazone hydrochloride and metformin hydrochloride extended release is used for the management of type 2 diabetes. The primary mechanism of glimepiride in lowering blood glucose is dependent, likely, on stimulating the release of insulin from functioning pancreatic beta cells (Sweetman 2009). Pioglitazone hydrochloride is a potent and highly selective agonist for peroxisome proliferators-activated receptor gamma (Sweetman 2009). Metformin hydrochloride helps in decreasing hepatic glucose production, decreasing intestinal absorption of glucose and improving insulin sensitivity by increasing peripheral glucose uptake and utilization. Thus, this combination helps in providing better glycaemic control in the management of type 2 diabetes. It also probably plays a role in the prevention of associated macrovascular and microvascular complications. Glimepiride estimation was in USP (2011). The HPLC method is mentioned as the main method for the determination of purity of both the raw materials and pharmaceutical formulations. The literature contains several
52 methods for the determination of glimepiride in pharmaceutical dosage forms, including liquid chromatography (Warnjari and Gaikwad 2005) and derivative spectroscopy (Bonfilio et al 2011). Bansal et al (2008), Kovařı ková et al (2004) and Khan et al (2005) have worked with glimepiride related substances and degradation pathway methods. Similarly, Ramulu et al (2010), Shirkhedkar and Surana (2009) and Smita Sharma et al (2010) have published the degradation behavior of pioglitazone and stability-indicating assay methods. Jain et al (2008), Karthik et al (2008) and Lakshmi et al (2009) have estimated the drugs in the combination drug product. 2.1.1 Target of the Work No stability-indicating HPLC method has been reported yet for the simultaneous determination of pioglitazone, glimepiride and glimepiride impurities in the combination drug product. Glimepiride and pioglitazone are highly unstable compounds. Although several pharmaceutical companies have marketed this combination drug product, no analytical method is available to determine this product through routine quality control and stability sample analysis processes. It is essential to develop a stability-indicating assay method for the unstable molecules in glimepiride and pioglitazone. Additionally, to prove the selectivity of the method, glimepiride major degradations of impurity B and impurity C were injected and estimated in the combination tablets. The aim of the present study is to develop a single HPLC method for the simultaneous estimation of pioglitazone, glimepiride, glimepiride impurity B and impurity C from the combination drug product.
53 2.2 EXPERIMENTAL 2.2.1 Materials and Reagents Pharmaceutical grade standards of pioglitazone (chemically: 5-(4-[2- (5-ethylpyridin-2-yl)ethoxy]benzyl) thiazolidine-2,4-dione) and glimepiride (chemically: 3-ethyl-4-methyl-N-(4-[N-((1r,4r)-4-methyl cyclohexylcarbamoyl) sulfamoyl]phenethyl)-2-oxo-2,5-dihydro-1h-pyrrole-1-carboxamide) were supplied by M/S Pharma Lab (Baddi, India). Glimepiride impurity B (chemically: 3-Ethyl-4-methyl-2-oxo-N-[2-(4- sulphamoylphenyl) ethyl]-2,3-dihydro-1hpyrrole-1-carboxamide ) and impurity C (chemically: Methyl [[4-[2-[[(3-Ethyl-4- methyl-2-oxo-2,3-dihydro-1h-pyrrol-1-yl) carbonyl]amino]ethyl]phenyl]- sulphonyl] carbamate) were purchased from LGC Standards (Mumbai, India). Chemical structures are shown in Figures 2.1 to 2.4. Commercially available combination tablets containing 15 mg of pioglitazone, 2 mg of glimepiride and 500 mg of metformin hydrochloride (PRICHEK GMP -manufactured by Indoco Rem) were purchased. HPLC grade acetonitrile, analytical reagent grade potassium dihydrogen phosphate and orthophosphoric acid were obtained from Rankem (India). Millipore water manufactured by the Milli-Q plus water purification system was used (Bedford, MA, USA). Figure 2.1 Chemical structure of pioglitazone (MF: C 19 H 20 N 2 O 3 S, MW: 356)
54 Figure 2.2 Chemical structure of glimepiride (MF: C 24 H 34 N 4 O 5 S, MW: 490) Figure 2.3 Chemical structure of glimepiride impurity B (MF: C 8 H 9 NO 2, MW: 151) Figure 2.4 Chemical structure of glimepiride impurity C (MF: C 18 H 23 N 3 O 6 S, MW: 409)
55 2.2.2 Instrumentation The Waters HPLC system consisting of 2695 binary pump plus auto sampler, a 2996 photo diode array and a 2487 UV detector (Waters Corporation, Milford, USA) was used for the development and validation. 2.2.3 System Suitability Solution Stock solutions of glimepiride impurity B, impurity C and glimepiride (1000 µg/ml) were prepared by dissolving appropriate amounts in methanol. System suitability solutions of 0.2 µg/ml of impurity B and impurity C and 0.5 µg/ml of glimepiride were prepared from the above mentioned stock solutions with a diluent mixture of acetonitrile and water (8:2, v/v). 2.2.4 Preparation of Standard Solution A standard solution, containing 750 µg/ml of pioglitazone and 100 µg/ml of glimepiride, was prepared by dissolving the appropriate amount of pioglitazone and glimepiride standard in diluent. 2.2.5 Preparation of Sample Solution Twenty tablets were weighed and powdered with the mortar and pestle tool. Powder tablets equivalent to 10 mg of glimepiride (equivalent to 75 mg of pioglitazone) were transferred to a 100 ml volumetric flask. About 60 ml of diluent was added and kept on a rotatory shaker for 10 min to disperse the material completely, sonicated for 10 min (during sonication, the bath temperature was maintained at 25 C) and diluted to 100 ml with diluent. The concentration of pioglitazone and glimepiride was 750 µg/ml and 100 µg/ml. The resulting solution was centrifuged at 10000 rpm for 5 min. The supernatant
56 solution was used for the estimation of pioglitazone, glimepiride and glimepiride impurities. 2.3 RESULTS AND DISCUSSION 2.3.1 Optimization of Chromatographic Method The HPLC method was optimized with a view to develop a stabilityindicating method. The stability-indicating method should accurately measure the active ingredients without any interference from degradation products and sample matrices. As pioglitazone and glimepiride have degradation qualities, the gradient method was preferred over the isocratic method to get a complete degradation product as well as a good resolution between close eluting compounds. The initial trials were taken with the pure drug forms of pioglitazone and glimepiride spiked with glimepiride impurity B and glimepiride impurity C. Different buffer ph (2-7) and solvent systems containing methanol and acetonitrile were tested. The reverse phase column chemistry of C 18 was applied for the preliminary trial. A good separation was achieved in the gradient program containing solution A (phosphate buffer at ph 3.2) and solution B (acetonitrile), with a flow rate of 0.8 ml/min. To prove the stability-indicating nature of the method, all forced degradation samples were injected in the optimized conditions. The peak purity of glimepiride and pioglitazone was not successful because of the interference of degradation compounds. To rectify this problem, a little adjustment in gradient, column temperature and flow rate was made, but these trials were not coming up with the desired results. So, different column chemistry was tried. Initially, the C 8 column was selected, and a known compound was merged. While using the phenyl column, one degradation peak came out from the glimepiride peak. The glimepiride peak purity was satisfactory, but the pioglitazone peak purity remained the same. Finally, the cyano column was used for development. The main base degradation peak came with more than 2.0 resolutions from the
57 pioglitazone peak. To our knowledge, this is the first method, where in spite of lot of degradation peaks being reported, the known compound got a very good resolution. Pioglitazone, glimepiride, glimepiride impurity B and impurity C were found with adequate response at 230 nm. In the case of a stressed sample, chromatogram was extracted with the entire range of 200-400 nm to check a new impurity at different wavelengths, but no extra peak was found except at 230 nm wavelength observed peaks. The required LOQ value of glimepiride impurity B and impurity C was found by using 100 µg/ml of glimepiride sample preparation with 25 µl injection volume. During the development, it was observed that the impurity B gets formed very fast, and to get a consistent result, a fresh sample preparation was prepared and used. Sonicator bath temperatures were maintained at less than 25 C while preparing the sample solution. The critical close eluting impurity of glimepiride impurity B and impurity C was found at a better resolution compared to the current USP monograph glimepiride tablet method. The optimized chromatographic method is shown in Table 2.1.
58 Table 2.1 Optimized chromatographic method Mobile phase-a 20 m mol/l potassium dihydrogen phosphate, ph adjusted to 3.2 using dilute ortho phosphoric acid Mobile phase-b Acetonitrile Diluent Mixture of acetonitrile and water (8:2, v/v) Column Zorbax cyano, 250 mm x 4.6 mm, 5 micron Column oven temperature 25 C Detection wavelength 230 nm Injection volume 25 µl Flow rate 0.8 ml/min Time (min) Mobile phase-a (%) Mobile phase-b (%) 0.01 80 20 13 80 20 Gradient programme 50 50 50 55 20 80 60 20 80 63 80 20 70 80 20 2.3.2 Method Validation The developed chromatographic method was validated for system suitability, selectivity, specificity, linearity, precision, accuracy, LOD, LOQ and robustness as per ICH and FDA guidelines. 2.3.2.1 System Suitability The observed analyte retention time (RT) and relative retention time (RRT) are presented in Table 2.2. The resolution between the close eluting pair of glimepiride impurity B and glimepiride impurity C was set as the system
59 suitability parameter (> 6.0). Also, the % RSD of the peak area of pioglitazone and glimepiride was calculated. The system suitability chromatogram is shown in Figure 2.5. Figure 2.5 System suitability chromatogram (Containing glimepiride, glimepiride impurity B and glimepiride impurity C) Table 2.2 System suitability results Parameter Pioglitazone Glimepiride Impurity B Impurity C % RSD 1.1 1.3 4.1 3.2 Retention time 31.93 38.73 21.99 19.82 Relative retention time - 1.00 0.57 0.51 USP resolution - - 6.50 - USP tailing factor 1.01 0.99 1.22 1.13 USP theoretical Plates 15011 18123 8012 7532
60 2.3.2.2 Specificity and Selectivity The specificity of the developed method was assessed by performing forced degradation studies. The specificity of the developed HPLC method was determined in the presence of its degradation products and other sample matrices. Forced degradation studies were performed on the tablet sample to indicate the proposed method s stability-indicating property and specificity. The sample solutions were subjected to acid and base hydrolysis (using 0.1 N HCl and 0.1 N NaOH respectively for 2 hours), oxidation (using 3 % H 2 O 2 for 2 hours) and UV radiation (254 nm for 48 hours). When the drug was exposed to acid and a peroxide condition, minor degradation was observed, but when exposed to base condition, major degradation was observed. Impurity B was increased in all acid, base and peroxide stressed samples, but impurity C was found only in the peroxide condition. The drugs were not affected by photolysis, and no degradation was observed. In all the stressed samples, peak purity was found within the acceptable limits (the purity angle is less than the purity threshold) indicating the specificity of the method. Results are shown in Table 2.3. Table 2.3 Forced degradation results Condition Unstressed sample Time - % Assay of Glimepiride 99.2 % Assay of Pioglitazone 99.0 Acid hydrolysis (0.1 N HCl) 2 hours 96.0 97.2 Base hydrolysis (0.1 N NaOH) 2 hours 91.9 82.3 Oxidation (3 % H 2 O 2 ) 2 hours 95.3 96.3 Light (254 nm) 48 hours 100.2 99.2
61 To prove the selectivity of the method, all individual compounds, i.e., pioglitazone, glimepiride, metformin, glimepiride impurity B and glimepiride impurity C were injected in the optimized method. Blank interference was checked by injecting the sample diluents. No interference was found with the discussed compounds. Specificity chromatograms are shown in Figures 2.6 to 2.15. Figure 2.6 Blank chromatogram Figure 2.7 Chromatogram of glimepiride impurity B injection
62 Figure 2.8 Chromatogram of glimepiride impurity C injection Figure 2.9 Chromatogram of metformin injection Figure 2.10 Chromatogram of glimepiride injection
63 Figure 2.11 Chromatogram of pioglitazone injection Figure 2.12 Chromatogram of unstressed sample injection
64 Figure 2.13 Chromatogram of acid degradation sample injection Figure 2.14 Chromatogram of peroxide degradation sample injection
65 Figure 2.15 Chromatogram of base degradation sample injection 2.3.2.3 Limit of Detection (LOD) and Limit of Quantification (LOQ) LOD and LOQ were determined by measuring the magnitude of analytical background. To estimate the LOD and LOQ, serial dilutions of glimepiride impurity B and impurity C solutions were used. The signal-to-noise ratio was then determined. Signal-to-noise ratios of 3 and 10 were considered as LOD and LOQ respectively. By injecting six preparations of the LOD and LOQ solutions of glimepiride impurity B and glimepiride impurity C, 0.005 % (i.e., 0.005 µg/ml) and 0.02 % (i.e., 0.02 µg/ml) for 25 µl injection volume were achieved. The precision at the LOQ concentration (six individual preparations) for glimepiride impurity B and glimepiride impurity C was less than 5.0 %. The results are shown in Table 2.4.
66 Table 2.4 LOQ level precision for impurities Peak Area Injection Impurity B Impurity C 1 2 3 4 5 6 Mean SD % RSD 16950 16985 17001 17500 16680 17100 17036 267.34 1.57 15591 15659 16000 15350 15455 15377 15572 241.71 1.55 2.3.2.4 Linearity The linearity of the assay method was evaluated by determining five concentration levels at three preparations from 50 % to 150 % of analyte concentration i.e., 750 µg/ml for pioglitazone and 100 µg/ml for glimepiride. Correlation obtained was found to be more than 0.9999 for both the compounds. For impurity B and impurity C, six concentration levels from LOQ to 200 % (LOQ, 25 %, 50 %, 100 %, 150 % and 200 %) were prepared by diluting the impurity stock solution to the required concentrations. The correlation coefficient obtained was greater than 0.9999. The results are shown in Table 2.5. The linearity plots are shown in Figures 2.16 to 2.19.
67 Table 2.5 Linearity data for drug substances and impurities Regression Parameters (n = 3) Compound Range (µg/ml) Equation of regression line R 2 value Pioglitazone 375-1125 Y = 332706x - 479991 0.9999 Glimepiride 50-150 Y = 123014x + 160007 0.9999 Impurity B 0.02-0.4 Y = 867436x - 115.18 0.9999 Impurity C 0.02-0.04 Y = 780417x - 524.47 0.9999 Glimepiride Linearity Graph Peak Area 20000000 15000000 10000000 5000000 0 y = 123014x + 160007 R 2 = 0.9999 0 20 40 60 80 100 120 140 160 Concentration (ppm) Figure 2.16 Linearity graph for glimepiride Peak Area 60000000 50000000 40000000 30000000 20000000 10000000 0 Pioglitazone Linearity Graph y = 332706x - 479991 R 2 = 0.9999 0 20 40 60 80 100 120 140 160 Concentration (ppm) Figure 2.17 Linearity graph for pioglitazone
68 Glimepiride Impurity B Linearity Graph Peak Area 60000000 50000000 40000000 y = 332706x - 479991 R 2 = 0.9999 30000000 20000000 10000000 0 0 20 40 60 80 100 120 140 160 Concentration (ppm) Figure 2.18 Linearity graph for glimepiride impurity B Glimepiride Impurity C Linearity Graph Peak Area 350000 300000 250000 200000 150000 100000 50000 0 y = 780417x - 524.47 R 2 = 0.9999 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Concentration (ppm) Figure 2.19 Linearity graph for glimepiride impurity C 2.3.2.5 Precision The % RSD of six sample preparations assay value was 1.1 for pioglitazone and 0.9 for glimepiride. The average assay was found to be 98.2 % for pioglitazone and 100.2 % for glimepiride. The intermediate precision of the assay method was evaluated by different columns, systems, and analysts. On different days, % RSDs were within 2.0 for both pioglitazone and glimepiride.
69 Assay value was found between 98 % and 102 %, confirming the ruggedness of the method. The precision of impurity B and impurity C was verified by injecting six individual preparations (in single injection) of 100 µg/ml glimepiride, spiked with 0.2 % of the above mentioned impurities. The % RSDs of impurity B and impurity C were 3.2 and 2.9 respectively. In the intermediate precision, the % RSDs for impurities were well within the limit of (<5.0). The results are shown in Tables 2.6 and 2.7. Table 2.6 Summary of method precision Injection 1 Pioglitazone (%) 98.5 Glimepiride (%) 99.0 Impurity B (%) 0.26 Impurity C (%) 0.21 2 97.5 99.2 0.27 0.22 3 97.3 100.1 0.27 0.21 4 98.0 101.0 0.27 0.21 5 97.5 101.1 0.25 0.22 6 100.5 100.5 0.27 0.22 Mean 98.22 100.15 0.27 0.21 SD 1.20 0.89 0.01 0.01 % RSD 1.22 0.89 3.16 2.87
70 Table 2.7 Summary of intermediate precision Injection 1 Pioglitazone (%) 98.9 Glimepiride (%) 97.1 Impurity B (%) 0.27 Impurity C (%) 0.20 2 99.3 98.3 0.26 0.21 3 99.1 99.2 0.26 0.20 4 98.4 99.5 0.26 0.19 5 98.0 99.8 0.27 0.20 6 100.1 99.1 0.26 0.20 Mean 98.97 98.83 0.26 0.20 SD 0.73 0.99 0.01 0.01 % RSD 0.74 1.00 1.96 3.16 2.3.2.6 Accuracy The recovery of three sample preparations at five concentration levels, i.e., 50 %, 75 %, 100 %, 125 %, and 150 % of working concentration levels for pioglitazone, glimepiride and glimepiride impurities were determined. The recovery of pioglitazone and glimepiride was obtained within the acceptable range, i.e., from 98 % to 102 %. The recovery of impurity B and impurity C ranged from 96.1 % to 101.3 % and 98.1 % to 102.1 % respectively. The recovery results are shown in Table 2.8.
71 Table 2.8 Accuracy results for developed HPLC method Compound Level (%) 50 Amount added (µg/ml) 375 Recovery (%) 98.3 % RSD (n = 3) 1.1 75 563 98.5 1.3 Pioglitazone 100 750 100.1 0.9 125 938 100.3 1.2 150 1125 99.2 0.8 50 50 98.1 0.9 75 75 99.3 1.1 Glimepride 100 100 99.1 1.2 125 125 98.7 0.8 150 150 100.2 0.5 50 0.10 100.3 1.1 75 0.15 101.2 1.4 Impurity B 100 0.20 96.1 3.1 125 0.25 100.1 0.8 150 0.30 101.3 0.9 50 0.10 99.1 1.3 75 0.15 98.1 1.2 Impurity C 100 0.20 98.7 2.0 125 0.25 102.1 1.9 150 0.30 101.5 0.9
72 2.3.2.7 Robustness Chromatographic parameters of the method were intensely altered to measure the robustness of the method. The system suitability parameters as well as the recovery for the main ingredients in the sample solution were examined. The parameters altered were the flow rate (± 0.1 ml/min), the buffer s ph (± 0.2) and the organic composition (± 5 %) in the mobile phase. The results obtained from the deliberate changes were well within the limits. The adequate resolution obtained between impurity B and impurity C in all the changes was greater than 5.0. The assay value of pioglitatone and glimepiride was obtained between 98 % and 102 %, confirming the robustness of the method. The robustness results are shown in Tables 2.9 to 2.11. Table 2.9 Robustness result for flow rate variation Compound 0.7 ml/min 0.8 ml/min 0.9 ml/min Resolution between impurity B and impurity C 6.8 6.6 6.5 Pioglitazone (%) 98.3 99.1 98.9 Gimepiride (%) 99.1 99.5 98.6 Impurity B (%) 0.06 0.07 0.07
73 Table 2.10 Robustness result for buffer ph variation Compound ph 3.0 ph 3.2 ph 3.4 Resolution between impurity B and impurity C 6.6 6.6 6.7 Pioglitazone (%) 98.8 99.1 99.2 Gimepiride (%) 99.5 99.5 98.2 Impurity B (%) 0.07 0.07 0.07 Table 2.11 Robustness result for organic concentration variation Compound Acetonitrile (95 %) Acetonitrile (100 %) Acetonitrile (105 %) Resolution between impurity B and impurity C 7.1 6.6 6.1 Pioglitazone (%) 98.2 99.1 99.7 Gimepiride (%) 99.1 99.5 98.4 Impurity B (%) 0.06 0.07 0.07
74 2.3.2.8 Application of the Developed Method to Commercial Tablets To evaluate the application of the developed method, commercial preparations (PRICHEK GMP -manufactured by Indoco Rem-Tablets containing 15 mg of pioglitazone, 2 mg of glimepiride and 500 mg of metformin hydrochloride) were analysed. The commercial samples were prepared six times, and the contents of pioglitazone, glimepiride, glimepiride impurity B and glimepiride impurity C were calculated. The average assay values of pioglitazone, glimepiride and glimepiride impurity B were 98.2 %, 100.1 % and 0.07 % respectively. Glimepiride impurity C was not detected in the analysed commercial sample. 2.3.2.9 Conclusion The single reversed phase stability-indicating RP-HPLC method has been established for the simultaneous estimation of pioglitazone, glimepiride, glimepiride impurity B and impurity C from the combination drug product. The method was fully validated and the data found to be satisfactory for all the method validation parameters tested. The developed method can be conveniently used by both quality control departments for routine analysis to determine the compound and commercial sample purity checks.