Phase Solubility Studies on Oral Antidiabetic Drugs with Β-cyclodextrin and Hp - Β Cyclodextrin

Nateglinide(NTG), Repaglinide(RPG), and Glimepiride(GMP) are antidiabetic drugs. These antidiabetic drugs are poorly soluble in water, which affect the bioavailability. In the present work, complex formation of all the three drugs with b-cyclodextrin (b-CD) and Hydroxy propyl bcyclodextrin (HPb-CD) and then the possibility of improving the solubility of NTG, RPG and GMP by complexation with b-CD, HPb-CD were investigated. The phase solubility studies indicated the formation of Nateglinide-b-CD, Repaglinide-b-CD, Glimepiride-b-CD, Nateglinide-HPb-CD, Repaglinide-HPb-CD and Glimepiride-HPb-CD inclusion complexes at 1:1 M ratio in solutions with stability constant of 345 M, 267 M,329 M, 433 M, 319 M, and 406 M respectively. The solubility was markedly enhanced by complexation with b-CD and HPb-CD. INTRODUCTION NATEGLINIDE (NTG) is a novel, effective oral drug for the treatment of type 2 diabetes. It belongs to Meglitinide class of blood glucose – lowering drugs. Chemically, it is ®-2-(4-iso propyl cyclohexane carboxamido)-3phenylpropanoic acid, having a formula C19 H27 NO3 (Fig 1). It is freely soluble in methanol, ethanol, ether and chloroform. Sparingly soluble in acetonitrile and octanol, practically insoluble in water. Its solubility is 180 μg/ml. REPAGLINIDE (RPG) is an oral blood glucose lowering drug of Meglitinide class used in management of type 2 diabetes mellitus. It is chemically S(+) 2ethoxy-4(2((3-methyl-1-(2-(1-piperidinyl) phenyl)butyl)amino)-2-oxoethyl) benzoic acid (Fig 2), *Corres author: A. Prameela Rani, C/o C. Bala Sekaran,20-3/2-5, II Floor, Ramalayam Street,Ayodhya nagar, Vijayawada – 520 003.Andhra Pradesh.India E-Mail: [email protected] Call: 91-866-2538492 ======================================== having a formula C27 H35N2O4. It is practically insoluble in water and its solubility is found to be 30.1 μg/ml. GLIMEPIRIDE (GMP) is the first third generation oral blood glucose lowering drug of sulfonylurea urea class and is used in management of type 2 diabetes, its very potent. Chemically it is 3-ethyl-4-methyl-N-(4-(N-((1r, 4r)-4-methyl cyclohexyl carbamoyl) sulfamoyl) phenethyl)-2-oxo-2, 5dihydro–1 H pyrrole -1carboxamide (Fig 3), having a formula C24H34N4O5 S. It is soluble in dimethyl sulfoxide, slightly soluble in acetone, acetonitrile and methanol. Practically insoluble in water. Its solubility is found to be 19.6 μg/ml. Fig 1: Structure of Nateglinide Prameela Rani. A.et al /Int.J. PharmTech Res.2009,1(4) 1633 CYCLODEXTRINS Cyclodextrins (CDs) are cyclic a-1,4 linked oligosaccharides of a-D-glucopyranose units that have relatively hydrophobic central cavity and hydrophilic outer surface. Thea, b and g-CDs consisting of six, seven and eight D-glycosidic bonds into a macro cycle. CDs are classical examples of compounds that form inclusion complexes. The structure of b-cyclodextrin shown in Fig 4. Each glucopyranose unit contains two secondary alcohols at C2 and C-3 and a primary alcohol at C-6 position providing 21 sites for chemical modification and derivatisation. Numerous derivatives containing the hydroxyl propyl(HP), methyl(M), sulfobutyl ether(SBE) and triethyl (TE) substitutents in b-CD (Fig 4) are in a position to be used as new pharmaceutical excipients. The characteristics of important CDs are summarized in table1. Fig 2: Structure of Repaglinide Fig 3: Structure of Glimepiride Fig 4: Structure of b-CD and its derivatives TABLE 1: CHARACTERISTICS OF IMPORTANT CDS. Property a-CD b-CD g-CD HP b-CD M b-CD SB b-CD TE b-CD Number of glucose units 6 7 8 7 7 7 7 Molecular weight 972 1135 1297 1400 * * 1723 Cavity diameter A 47.-5.3 6.0-6.5 7.5-8.3 0.60-0.65 5.0-6.7 Solubility (20C) (g/100ml) 14.5 1.85 23.2 50.70 31-57 5-10 1.8x10 * Derivatives will have different molecular weights depending on degree of substitution. Prameela Rani. A.et al /Int.J. PharmTech Res.2009,1(4) 1634 EXPERIMENTAL Apparatus: · UV Spectrophotometer (ELICO-model150) · Rotary shaker-KEMI Materials Nateglinide, Repaglinide and Glimepiride were gift samples from Divis Laboratories Pvt.Ltd, Hyderabad, Orchid Laboratories Pvt.Ltd, Chennai and Dr. Reddy Laboratories Pvt. Ltd, Hyderabad. b-cyclodextrin and HP b-cyclodextrin were obtained from SD fine chem Pvt.Ltd, Mumbai. All other materials used are of pharmacopoeial grade. Preparation of Drug solution Accurately weighed 50 mg of drug (NTG/RPG/GMP) was dissolved in 50 ml of methanol to give a concentration of 1mg/ml. METHOD Calibration of NTG / RPG / GMP. This is performed individually for all the three drugs by following similar procedures. Calibration curve for the estimation of the drug (NTG/RPG/GMP) was constructed employing distilled water (p 7). The stock solution of the drug (NTG/RPG/GMP) was subsequently diluted with distilled water to obtain a series of dilutions containing 2, 4, 6, 8 &10 μg/ml of the drug (NTG/RPG/GMP). The absorbances of the above dilutions were measured in UV spectrophotometer at 210 nm for NTG, 197 nm for RPG and 230 nm for GMP. The data is given in Table 2 and shown in Fig 5, 6 and 7. These Calibration curves were used for estimation of NTG, RPG and GMP in the present study. PHASE SOLUBILITY STUDIES Phase solubility studies on pure drug (NTG/RPG/GMP) with different concentrations of cyclodextrins (b-CD / HPb-CD) (3-15 millimoles) were performed by the method described by Higuchi and Connors. Excess amount of the drug (NTG/RPG/GMP) is added to 15ml of triple distilled water containing various concentrations of cyclodextrins (b-CD, HPb-CD) (3-15 mM) taken in a series of 25ml stopped conical flask and the mixture was shaken for 72 hours at room temperature on a rotary flask shaker. After 72 hrs of shaking to achieve equilibrium, 2ml aliquots are withdrawn at 1 hr interval and filtered through whatman no.1 filter paper. The filtered samples are diluted suitably and assayed for the drug (NTG, RPG, and GMP) content by specific UV method against blank in same concentration of CDs (bCD/HPb-CD) in water so as to cancel any absorbance that may be exhibited by the cyclodextrin molecules. Shaking is continued until the consecutive estimations are the same. The solubility experiments are conducted in triplicate. The results are given in Table 3, Table 4 and shown in Fig. 8, 9, 10, 11, 12 and 13. RESULTS AND DISCUSSION The Complexation of the selected drugs (NTG, RPG, GMP) with b-CD and HPb-CD, the effect of b-CD and HPb-CD on the solubility, the type of phase solubility diagram and the stability constant of CD complexes formed were investigated by phase solubility studies. With all the three drugs the aqueous solubility was increased linearity of b-CD and HPb-CD in each case. The phase solubility diagrams for the complex formation between NTG-b-CD, RPG-b-CD, GMP-b-CD, NTGHPb-CD, RPG-HPb-CD, GMPHPb-CD, are shown in Fig. 8, 9, 10, 11, 12 and 13 respectively. All the phase solubility diagrams can be classified as type AL according to Higuchi and cannors 3. Because the straight line had a slope less than unity in each case, the increase in solubility was due to the formation of a 1:1M complex in solution with all the three drugs. The apparent stability constnt (Kc) was calculated from the linear plot of the phase solubility diagram according to the equation Kc = Slope / So (1-slope) Where, So = solubility of the drug in absence of b-CD and HPb-CD. The apparent stability constants (Kc) obtained from the slope of the linear phase solubility diagrams are as follows: Kc values in the range of 200-500M indicated stronger interactions between the guest molecules (drug) and host molecules (b-CD,HPb-CD) and greater stability of the complex formed. Thus the value of stability constants indicated that the complexes formed between drug-b-CD and drug-HPb-CD are quite stable in all cases. CONCLUSION 1. The phase solubility studies indicated the formation of NTG-b-CD, RPG-b-CD, GMP-b-CD, NTGHPb-CD, RPG-HPb-CD and GMP-HPb-CD, inclusion complexes at a 1:1 M ratio in solution with stability constants (Kc) of 345M, 267M, 329M, 433M, 319M,and 406M respectively. 2. Thus the solubility of all the three drugs was markedly enhanced by complexation with b-CD and HPb-CD. Prameela Rani. A.et al /Int.J. PharmTech Res.2009,1(4) 1635 TABLE 2 : DATA FOR CALIBRATION CURVES OF NTG, RPG AND GMP. ABSORBANCE S.No. Concentration (μg/ml) Nateglinide (210 nm) Repaglinide (197 nm) Glimepiride (230 nm) 1 2 3 4 5 2 4 6 8 10 0.75 0.157 0.226 0.304 0.386 0.186 0.400 0.600 0.807 0.963 0.110 0.224 0.340 0.449 0.562 TABLE 3: EFFECT OF β-CD ON SOLUBILITY OF DRUGS (NTG/RPG/GMP) S.No. Concentration of bCD (mM) Concentration of NTG (mM) Concentration of RPG (mM) Concentration of GMP (mM) 1 2 3 4 5 6 0 3 6 9 12 15 0.56 1.00 1.50 1.97 2.45 2.95 0.060 0.110 0.155 0.204 0.252 0.300 0.040 0.043 0.047 0.051 0.055 0.059 TABLE 4: EFFECT OF HP β-CD ON SOLUBILITY OF DRUGS (NTG/RPG/GMP) S.No. Concentration of HPb-CD (mM) Concentration of NTG (mM) Concentration of RPG (mM) Concentration of GMP (mM) 1 2 3 4 5 6 0 3 6 9 12 15 0.56 1.15 1.74 2.32 2.90 3.50 0.060 0.115 0.170 0.226 0.280 0.341 0.040 0.045 0.050 0.055 0.060 0.065 TABLE 5: SOLUBILITY CONSTANTS OF DRUGS (NTG/RPG/GMP) S.No. Complex Kc(M) 1 2 3 4 5 6 NTG bCD RPGbCD GLM b CD NTG – HP bCD RPG– HP bCD GLM – HP b CD 345 267 329 433 319 406 Prameela Rani. A.et al /Int.J. PharmTech Res.2009,1(4) 1636 Fig 5: Calibration curve of Nateglinide CALIBRATION CURVE OF