LAUSR

Type 2 diabetes mellitus (T2DM) is a disorder distinguished by resisting insulin effects and/or its reduced secretion leading to high blood sugar levels. It is fast becoming epidemic worldwide and is a major cause of death in the past years. Maintaining a correct blood sugar level is the primary target in the management of T2DM [1,2]. The biguanide class consists of metformin, which is used as the first line therapy for T2DM. It acts by reducing glucose production in the liver, and its decreased absorption in the gastrointestinal tract also increases the insulin sensitivity in the target cell [3]. Gliclazide is a sulphonylurea drug and acts on the β cell sulphonylurea receptor stimulating insulin release. It has a half-life of 11 h [4]. Pioglitazone is a Peroxisome Proliferator-Activated Receptors agonist of the Thiazolidinedione class. It acts on PPAR gamma 1, and PPAR gamma 2 receptors increasing the insulin sensitivity in diabetic patients and thus helps them maintain normal blood sugar levels [5]. Linagliptin, saxagliptin, and teneligliptin are the dipeptidyl peptidase-4 inhibitors, also called gliptins. They increase the levels of incretins in plasma (GLP-1 and GIP), leading to insulin increase and decrease in blood glucose [6,7]. Dapagliflozin and empagliflozin are sodium-glucose cotransporter-2 (SGLT2) inhibitors (Fig. 1). Two HPLC-UV methods for Metformin has been reported [8,9]. Pioglitazone, in combination with other compounds, has been analyzed by HPLC and reported [10–13]. Linagliptin HPLC quantification method, along with an application for pharmacokinetics in rat plasma and a UPLC-MS method in human plasma, has been published [14,15]. An LC-MS/MS method for simultaneous quantification of Linagliptin and Metformin and their pharmacokinetic study in humans have been published [16]. An LC-MS/MS analytical method for quantification of dapagliflozin in ZDF and normal rats have been published [17]. Bassam M. Ayoub et al. have published an LC-MS/MS method for Empagliflozin along with its pharmacokinetic (PK) study in human plasma and another for its estimation with metformin [18,19]. Saxagliptin, along with 5-OH saxagliptin (metabolite) has been analyzed along with metformin by LC-MS/MS [20]. Stability indicating LCMS method of teneligliptin along with identification of the degradation products and another LCMS method has been reported for PK studies in rats [21,22]. However, these methods were based on trial and error methodology. HPLC method development involves the determination of several factors (stationary phase type, type of organic modifier and its composition, pH, flow rate, temperature, etc.), and hence optimizing these experimental conditions for the desired responses (minimum retention time of last detected peak, low-resolution time, etc.) is a complicated process. The traditional approach was by varying each factor once at a time and maintaining others constant; the process is known as one factor at a time (OFAT) method. This approach was inefficient, time-consuming & strenuous. Hence a multicriteria decision making or a multivariate approach was needed, and statistically optimized design of experiment (DOE) method was developed [23,24]. Central composite design (CCD) is a technique of response surface method, one of design of experiments mode for the optimization of the HPLC experimental conditions. In the CCD technique, the experimental factors/variables can be analyzed in a minimum number of trials while making the experiments maximally informative [25,26]. Several fixed-dose combinations of these antidiabetic drugs (Metformin, Gliclazide, Pioglitazone, Linagliptin, Saxagliptin, Teneligliptin, Dapagliflozin, and Empagliflozin) containing two or more than two of them have been approved by US-FDA and other drug regulatory authorities of various countries. Here we have tried to develop a statistically optimized analytical method utilizing central composite design technique which is easy to operate with sufficient sensitivity and is precise with adequate accuracy and rapid and can be applied for the quality control of any of these fixed-dose combinations using a single method.