International Journal of Pharmaceutics 478 (2015) 297–307

Contents lists available at ScienceDirect

International Journal of Pharmaceutics journal homepage: www.elsevier.com/locate/ijpharm

Matrix tablets for sustained release of repaglinide: Preparation, pharmacokinetics and hypoglycemic activity in beagle dogs Wei He a,1, Mengmeng Wu a,1, Shiqing Huang b , Lifang Yin a, * a State Key Laboratory of Natural Medicines, Department of Pharmaceutics, School of Pharmacy, China Pharmaceutical University, No. 24 Tongjiaxing, Nanjing 210009, PR China b The Third People’s Hospital of Chengdu, Chengdu 610031, PR China

A R T I C L E I N F O

A B S T R A C T

Article history: Received 2 October 2014 Received in revised form 14 November 2014 Accepted 26 November 2014 Available online 27 November 2014

Repaglinide (RG) is an efficient antihyperglycemic drug; however, due to its short half-life, patients are required to take the marketed products several times a day, which compromises the therapeutic effects. The present study was conducted to develop a hydrophilic sustained release matrix tablet for RG with the aims of prolonging its action time, reducing the required administration times and side effects and improving patient adherence. The matrix tablets were fabricated by a direct compression method, the optimized formulation for which was obtained by screening the factors that affected the drug release. Moreover, studies of the pharmacokinetics and hypoglycemic activity as measured by glucose assay kits were performed in dogs. Sustained drug releases profiles over 10 h and a reduced influence of medium pHs on release were achieved with the optimized formulation; moreover, the in vivo performance of extended release formulation was also examined, and better absorption, a one-fold decrease in Cmax, a two-fold increase of Tmax and a prolonged hypoglycemic effect compared to the marketed product were observed. In conclusion, sustained RG release and prolonged action were observed with present matrix tablets, which therefore provide a promising formulation for T2D patients who require long-term treatment. ã 2014 Elsevier B.V. All rights reserved.

Keywords: Repaglinide Sustained release tablets Pharmacokinetics In vitro/in vivo correlation Hypoglycemic effect

1. Introduction Diabetes mellitus is a chronic illness that requires continuous medical care, and it has become the seventh leading cause of death because it can induce several severe complications, including cardiovascular risk, hypertension, dyslipidemia, nephropathy, retinopathy and neuropathy (Kramer et al., 2013). Presently, approximately 92.4 million adults in China are suffering from diabetes, and 148.2 million adults have been diagnosed with pre-diabetes (Yang et al., 2010). Among the people with diabetes, more than 90% of cases are type 2 diabetes (T2D), which is a complex metabolic disorder that results from relatively decreased pancreatic insulin secretion and variable contributions of decreased insulin action or insulin resistance in target tissues, primarily the muscle and liver (Zhu et al., 2013). Thus, the prevention and treatment of T2D have become some one of the great challenges in the twenty-first century and aim to

* Corresponding author. Tel.: +86 2583271018; fax: +86 2583271018. E-mail address: [email protected] (L. Yin). He W. and Wu M.M. contributed equally to this work.

1

http://dx.doi.org/10.1016/j.ijpharm.2014.11.059 0378-5173/ ã 2014 Elsevier B.V. All rights reserved.

control the complications and reduce the mortality and health care expenditures (De Berardis et al., 2013). The currently available oral therapeutic drugs for T2D can be classified into five categories: sulfonylureas (SU), biguanides, a-glucosidase inhibitors, thiazolidinediones and non-SU secretagogues (DeFronzo, 1999). RG is a representative of non-SU secretagogues and is an efficient antihyperglycemic drug that lowers blood glucose by promoting insulin secretion from pancreatic b-cells via the closing of ATP-sensitive potassium channels in the plasma membrane, the opening of calcium channels and the mediation of the influx of calcium, which induces calcium-dependent exocytosis of insulin-containing granules (Scott, 2012). Oral marked products of RG, such as Fulaidi1, GlucoNorm1, NovoNorm1, Prandin1 and Surepost1, are effective treatment options for patients with T2D primarily because these drugs have fewer side effects and better toleration in elderly patients and those with impaired renal function. However, due to the short half-life of less than 1 h (Obach et al., 2008), patients are frequently required to take conventional tablets to maintain the plasma concentration, which incurs various disadvantages, including compromising the therapeutic benefits, that result in fluctuations in plasma concentrations, induce side-effects and cause inconvenience to the patients (Lalau et al., 2014). Moreover,

298

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

the administration of conventional tablets over long durations can cause poor adherence to the treatment schedules for chronic diseases, which generates resistance to therapy and thus produces bad health outcomes. Thus, a new formulation that could extend the action of RG is highly desirable. A hydrophilic matrix is one of the most commonly utilized sustained release systems due to advantages that include low cost, ease of manufacture, a proven record and performances that are relatively independent of the physicochemical and physiological conditions of the gastrointestinal tract (Aguilar-de-Leyva et al., 2012; Ferrero et al., 2013). This sustained release system consists of a drug and one or several skeleton excipients in which the drug (in molecules or solid particles) is homogeneously dispersed with a hydrophilic polymer such as cellulose derivatives, sodium alginate, xanthan gum, polyethylene oxide or carbopol (Maderuelo et al., 2011). Upon exposure to water, the polymer is hydrated and swells, which forms a gel barrier that controls drug release via a mechanism of erosion or diffusion (Wu et al., 2007). To overcome the drawbacks of conventional RG tablets, we herein designed a hydrophilic sustained release matrix RG tablet with the aims of prolonging the action time, reducing the required administration frequency and side effects and improving patient adherence. Thus, the present study sought to (I) prepare a hydrophilic sustained release matrix tablet and optimize its formulation in terms of drug release in release media of 0.1 M HCl and 0.1 M HCl-pH 6.8 PBS, (II) study the pharmacokinetics of the tablets in beagle dogs, (III) assess the in vitro/in vivo correlations, and finally (IV) evaluate the hypoglycemic activity in beagle dogs. 2. Materials and methods 2.1. Materials RG was obtained from Zhejiang Haixiang Pharmaceutical Co., Ltd. (Taizhou, China). The hydroxypropylmethycellulose (HPMC K100LV, K4M) and ethylcellulose (Ethocel1, EC) were gifts from Colorcon Co., Ltd. (Shanghai, China). Sodium alginate (Keltone HVCR) was purchased from JRS Pharma Co., Ltd. (Rosenberg, Germany). Magnesium stearate was purchased from Shanghai Yunhong Pharmaceutical Excipients Co., Ltd. (Shanghai, China). Octadecanol was provided by Sinopharm Chemical Reagent Co., Ltd. (Nanjing, China). Lactose (Flowlac100) was obtained from Meggle Pharmaceutical Co., Ltd. (Wasserburg, Germany). The PVP K30 was a gift from ISP Tech., Ltd. (Shanghai, China). The glucose assay kits were obtained from Shanghai Rongsheng Biological Pharmaceutical Co., Ltd. (Shanghai, China). The methanol and acetonitrile were of chromatographic grade, and the other reagents were of analytical grade. The animals were male beagle dogs (certificate no. SCXK (Shanghai) 2007–0004) that were purchased from the Agricultural Institute of Shanghai Communication University. 2.2. Preparation of the matrix tablets RG is a BCS II drug that has lower water-solubility and better membrane permeability; thus, we prepared a RG solid dispersion utilizing PVP K30 as a carrier to facilitate drug release (Yin et al., 2012). The solid dispersion was developed by a solvent evaporation method. Briefly, the mixture of drug and PVP K30 with a weight ratio of 1:10 was dissolved in ethanol. After the solvent was removed, the powder of solid dispersion was pulverized and sieved through a mesh with pores of 150 mm. The solid dispersion was formulated as the active agent in the tablets. The tablets were prepared via a direct compression method. Briefly, 33 mg of solid dispersions and a fixed amounts of matrix

material, pH adjustment agent, filler and glidant were mixed in incremental amounts and then the mixture was screened through a 40-mesh sieve. After blending with lubricant manually, the mixed powder was compressed directly into tablets with a singlepunch tablet machine (TDP, Shanghai Tianxiang and Chentai Pharmaceutical Machinery Co., Ltd., Shanghai, China) under a pressure force of 6–8 kg/cm2. The size batch was 100 tablets for each formulation. 2.3. In vitro drug release The drug release study was performed on a RCZ-8A dissolution tester (Tiandatianfa Tech., Ltd., Tianjin, China) based on the first method of the Chinese Pharmacopoeia 2010 edition two appendix XD. RG is a weakly basic drug with a pH-dependent solubility; therefore, we performed the release tests in system consisting of 0.1 M HCl to simulate the gastric fluid and 0.1 M HCl (first 2 h, pH 1.2) and PBS (second 10 h, pH 6.8) that simulated the transition of the tablet from the stomach to the intestine (Corti et al., 2008). The tablets were placed in 100 mL of degassed medium that was maintained at 37
0.5  C with a rotation speed of 50 rpm. Fivemilliliter samples were withdrawn at predetermined time intervals (1, 2, 4, 8, 10 and 12 h), and supplements of 5 mL of fresh medium were added followed by filtration through a cellulose acetate membrane (0.8 mm). Next, 20 mL of the filtrate was injected into an HPLC system for analysis, and the cumulative release percentages were calculated. The similarity of the drug release from the optimized formulation in the release media of 0.1 M HCl and 0.1 M HCl-pH 6.8 PBS was assessed with the similarity factor (f2) advocated by the FDA. This similarity factor is calculated as a logarithmic transformation of the sum squared error of the differences between the test formulation and the reference formulation according to Eq. (1): 8" 9 #0:5 n < = 1X 2 1þ ðR t  T t Þ  100 f 2 ¼ 50  log (1) : ; n i¼1

where Rt and Tt are the cumulative release rates of the reference formulation and test formulation, respectively, at each time point, and n is the number of the time points. The similarity factor is a number between 0 and 100; 100 indicates that the test and reference profiles exactly match, and this value approaches 0 as dissimilarity increases. In general, release profiles are considered to be similar if the f2 value is greater than 50, and greater f2 values indicate greater similarity. 2.4. Release kinetics To study the drug release mechanism, we fit the drug release results from the optimized formulation to the Peppas model (Siepmann and Peppas, 2012): Mt ¼ k  tn Mf

(2)

where Mt and Mf are the drug release (%) at time t and at infinite time, respectively, k is a constant incorporating the properties of the macromolecular polymeric system and the drug, and n is the release exponent that indicates the mechanism of drug release. For a cylindrical preparation, the drug release mechanism is considered to be non-Fickian diffusion when the release exponent n is between 0.45 and 0.89, Fickian diffusion when n is less than 0.45, and matrix erosion when n is greater than 0.89 (Wei et al., 2006; Wu et al., 2007, 2008).

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

2.5. Pharmacokinetics in beagle dogs The use of animals in this experiment was approved by the China Pharmaceutical University Animal Management and Ethics Committee. A randomized, two-period cross-over design was employed to study the pharmacokinetics in beagle dogs. Six dogs with a mean weight of 12.0
2.0 kg were assigned to group A and administered one sustained release tablet (3 mg RG/tablet), and the group B animals were administered six conventional tablets (0.5 mg RG/tablet). The dogs were fasted for 12 h prior to administration and were allowed to have a meal at 6 h after administration. The dogs had free access to water during the experimental period. The washout period between consecutive treatment schedules was one week. Three milliliters of blood were taken from the upper limb into heparinized tubes 0.5, 1, 1.5, 2–4, 6, 8, 12, 16, 24, and 36 h after the administration of the medication in group A and at 0.25, 0.5, 0.75, 1, 1.5, 2–4, 6, 8 and 12 h in group B. All blood samples were immediately centrifuged at 4, 250  g for 10 min. The supernatant plasmas were stored at –70  C. The plasma concentrations were assayed with the HPLC–MS/MS method that is detailed below. 2.6. Sample preparation and analytical assay The drug contents in the release media were analyzed using a LC-2010CHTHPLC system (Shimadazu, Tokyo, Japan) that was composed of a gradient flow control pump, an autosampler equipped with a 20-mL loop, and a UV–vis detector (Shimadazu, Tokyo, Japan). The separation was conducted on a Diamonsil C18 column (4.6 mm  150 mm) at 243 nm. The mobile phase was made up of 0.01 M ammonium acetate solution containing 0.1% triethylamine (adjusted pH to 5.0 with glacial acetic acid) and methanol (20:80, v/v) that was pumped at a rate of 1.0 mL/min at 30  C. Two hundred microliter of plasma samples were mixed with 50 mL of internal standard (200 ng/mL nateglinide in methanol), followed by vortexing for 30 s. Following mixing into 600 mL of acetonitrile, the sample was vortexed for 1 min and centrifuged at 12,000 rpm for 10 min. Subsequently, 10 mL of the supernatant was injected into the HPLC–ESI-MS/MS system for analysis. The HPLC–ESI-MS/MS equipment comprised a LC-20AD pump, a CBM-20 communication bus module, a SIL-20AC autosampler, a CTO-20A column oven (Shimadzu, Japan), and a TSQ Quantum Access tandem mass spectrometer (Thermo Scientific, Waltham, Massachusetts, USA) fitted with an electrospray ionization (ESI) ion source. Xcalibur 2.0.7 software (Thermo Scientific, Waltham, Massachusetts, USA) was employed for data acquisition and analysis. HPLC isolation was conducted on a VP-ODS C18 column (150 mm  2.0 mm, Shimadzu, Japan) at a column temperature of 40  C. The samples were gradient eluted with acetonitrile (A) and 5 mM ammonium acetate solution (B) at the flow rate of 0.3 mL/ min and monitored at 287 nm beginning at a composition of 55% A and 45% B. The gradient program was as follows: 0–1.00 min, 45% B; 1.00–1.50 min, 10% B; 1.50–4.00 min, 10% B; 4.00–4.50 min, 45% B; and 4.50–6.00 min, 45% B. The total run time was 6 min, and nateglinide was utilized as the internal standard. The HPLC eluent was diverted to a triple quadrupole tandem mass spectrometer equipped with an ESI ion source that operated in the negative ion mode, and selected reaction monitoring (SRM) was used in the drug quantification. The optimized parameters for mass spectrometric detection were set as follows: spray voltage, 3.5 kV; capillary temperature, 350  C; sheath gas, N2; pressure, 40 Arb; auxiliary gas, N2; pressure, 10 Arb; collision gas, Ar; pressure, 1.5 mTorr; precursor ion, m/z 451.3 ! m/z 379.3 for RG, m/z and 316.2 ! m/z 164.1 for nateglinide (internal standard); and collision

299

energies, 23 eV for RG and 21 eV for nateglinide. The regression equation used for the plasma concentration determination was y = 25.837x + 0.2418 (R2 = 0.9997), which resulted in linear concentrations from 1 to 800 ng/mL. The absolute recoveries of low (10 ng/ mL), medium (100 ng/mL) and high (400 ng/mL) quality control levels were 96.53
6.31%, 108.55
2.95% and 99.07
2.97%, respectively, and the intra-day and inter-day precision were not greater than 15%. 2.7. Hypoglycemic activity To determine the blood glucose levels, 20 mL of plasma sample and 2 mL of kit working fluid were mixed in a tube and then reacted for 15 min in a 37  C water bath (Zhang et al., 2014). After coloration, the absorbance value of the sample was assayed, followed by comparison with the calibration absorbance and calculation of the blood glucose concentration according to Eq. (3): C sample ¼

Asample  C calibration Acalibration

(3)

where Csample is the plasma glucose concentration, Ccalibration is the glucose concentration of the calibration liquid, Asample is the sample absorbance, and Acalibration is the calibration absorbance. 2.8. Data analysis and statistics The pharmacokinetic parameters of the conventional and sustained release RG tablets, including Cmax,Tmax, t1/2, MRT, and AUC0t, were calculated based on a statistical moment theory using the BAPP 2.3 program (Baikang Pharmaceutical Co., Ltd., Nanjing, China). Two-tailed t-tests were conducted for Cmax and AUC0t, and a non-parametric test was performed for Tmax. The data are expressed as the mean
standard deviation, and differences were considered statistically significant when the P values were less than 0.05. 3. Results and discussion 3.1. Preparation of the sustained release tablets RG was a weakly basic drug with lower solubility in simulated intestine conditions, such as pH 6.8 or 7.4 PBS. To facilitate drug release and absorption, an RG solid dispersion with PVP K30 as a carrier was fabricated. As expected, the drug was dispersed in an amorphous form into the polymer, and its solubility in water and oral bioavailability were increased by more than four- and twofold, respectively (Qin et al., 2014; Yin et al., 2012). Due to its well-known benefits, including fewer processing stages, the elimination of heat and moisture effects, increased productivity and reduction of the final cost of the product (Martinello et al., 2006), the direct compression method was used to prepare the sustained release tablets that were formulated with RG/PVP k30 solid dispersion as the active agent. Tablets that met all official pharmaceutical specifications were successfully prepared. To optimize the formulation, factors, such as the matrix material, the pH regulator and the filler, were studied in terms of drug release in both of 0.1 M HCl and 0.1 M HCl-pH 6.8 PBS media.The compositions for each formulation are present in Table 1. 3.2. Effects of the type of matrix material The influences of the types of matrix material (i.e., EC, HVCR (sodium alginate), octadecanol and HPMC, S1–S4) on RG release in

300

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

0.1 M HCl and 0.1 M HCl-pH 6.8 PBS are depicted in Fig. 1(A1 and A2). The drug releases from the formulations with EC or HVCR as the matrix in the two mediums were not significantly retarded because more than 80% of drug release occurred within the first 4h period. These findings are attributable to the fact that the EC

skeleton disintegrated within a short time (1 h) after immersion in water (Quinten et al., 2009), and the HVCR matrix was hydrated quickly in the aqueous environment (Sriamornsak et al., 2007, 2008), which resulted in rapid drug release. The drug release was slowed down when octadecanol, a lipid material, was used as the

Fig. 1. Effects of (A) the type of matrix material, (B) HPMC and (C) the amount of HPMC K100LV on RG release from sustained release tablets in 0.1 M HCl and 0.1 M HCl (0–2 h)pH 6.8 PBS (2–12 h).

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

matrix; however, incomplete release, (i.e., less than 70%) was obtained in 0.1 M HCl-pH 6.8 PBS after 4 h. In contrast, not only sustained but also complete release within 8 h was achieved from the tablets that incorporated HPMC K100LV as the matrix, despite a difference in the release medium. More importantly, the drug release exhibited a near zero-order rate that is for sustained release matrix formulations and common for osmotic pump systems. The influences of HPMC substitutes of different viscosity grades (i.e., K100LV, 100 cPa and K4M, 4000 cPa, S1 and S5) are shown in Fig. 1(B1 and B2). The drug releases from the formulations in the two media decreased significantly decreased due to the increase in polymer viscosity; this decrease was more profound in 0.1 M HCl-pH 6.8 PBS medium because RG, as a weakly basic drug, was solubilized in acid circumstances but poorly solubilized in the simulated intestinal conditions. As discussed elsewhere (Maderuelo et al., 2011), greater degrees of viscosity of the HPMC were associated with faster swelling of its side chains, which generated a very thick gel barrier and thus slowed down the drug release. A comparison of the drug releases from the formulations with HPMC K100LV and K4M revealed that the former achieved more complete release and a sustained release profile over 12 h; therefore, this formulation was chosen

301

as the matrix material. As expected, due to increased tortuosity due to a thicker gel barrier and decreased porosity that reduced the water uptake (Reza et al., 2003), increasing the amount of HPMC K100LV in the formulations from 60 to 80 mg (S6–S9) led to decreases in drug release (Fig. 1(C)). 3.3. Effect of pH regulators RG is a weakly basic compound with a pH-dependent solubility; for example, this solubility in acid conditions of 0.1 M HCl is more than five-fold greater than that in pH 6.8 PBS (Qin et al., 2014). An extended release system loading such a drug would exhibit reduced release in media with high pHs because the pH increases as the dosage form is transited along the gastrointestinal tract, leading to incomplete absorption and lower bioavailability. Herein, pH regulators and acid agents were added into the formulations to create a lower pH microenvironment with the aim of increasing the solubility and then achieving complete drug release in the intestinal fluid by improving the porosity and reducing the tortuosity (Dvorá9 cková et al., 2013; Varma et al., 2005). The effects of the type of acid agent (i.e., citric acid and tartaric acid, S10, S11 and S14) are shown in Fig. 2(A1 and A2). In 0.1 M HCl, the

Fig. 2. Effects of (A) the type of acid agent and (B) the amount of citric acid on RG release from sustained release tablets in 0.1 M HCl and 0.1 M HCl (0–2 h)-pH 6.8 PBS (2–12 h).

302

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

incorporation of acid agent produced no effect on drug release because its influence was overwhelmed by the higher drug solubility in 0.1 M HCl. In contrast, the drug release in 0.1 M HCl-pH 6.8 PBS medium was significantly promoted compared to that of the control formulation regardless of the type of regulator. As the high pH release medium obtained entry into the carrier systems, the acid agent maintained a low pH within the system, which helped to maintain the drug in a solubilized form that could diffuse out of the dosage form (Badawy and Hussain, 2007). Moreover, a further comparison of the two acid agents indicated that the formulation with citric acid as the pH modifier achieved a more complete drug release due to its lower pKa, which indicated greater acidity (the pKa values for tartaric acid and citric acid are of 3.07 and 2.93, respectively). The pH regulator should not leach out completely from the formulation within a short time; thus a sufficient concentration should be involved in the formulations until complete drug release has been achieved. As shown in Fig. 2(B1 and B2), the amount of citric acid (S9–S13) had little effect on drug release in the 0.1 M HCl, but the release in 0.1 M HCl-pH 6.8 PBS medium was increased significantly as the amount of citric acid in the formulations was increased from 0 to 30 mg. However, a further increase from 30 to 50 mg resulted in a significant slowing of drug release within the 8–12 h period. This finding is attributable to the fact that the citric

acid competed for the release medium of hydration also inhibited the hydration and swelling of the hydrophilic polymer and therefore affected drug release (Siepe et al., 2006). 3.4. Effect of filler The effects of the type of filler (i.e., hydrophilic lactose (flowlac 100) or hydrophobic MCC, S16 and S18) are shown in Fig. 3(A). The drug release from the formulation with flowlac 100 as the filler was faster and more complete than that of the formulation with MCC as the filler irrespective of the pH of the medium because watersoluble fillers such as lactose can facilitate pore production via faster penetration of the release fluid, which results in a more porous matrix and a decrease in the tortuosity of the diffusion path of eh drug (Lotfipour et al., 2004). In contrast, the incorporation of MCC into the matrix as the filler caused a delay of the penetration of the release medium into the system, which resulted in a retardation of the hydration and swelling of the polymer, which in turn reduced drug release. Moreover, it has also been reported that the incorporation of MCC can aid the formation of the gel barrier and the maintenance of its integrity, which could retard the release of the drug (Goncalves-Araujo et al., 2008; Lyons et al., 2006). To achieve complete release, flowlac 100 was used as the filler in the HPMC matrix, and the effects of the amount of flowlac 100

Fig. 3. Effects of (A) the type of filler and (B) the amount of flowlac 100 on RG release from sustained release tablets in 0.1 M HCl and 0.1 M HCl (0–2 h)-pH 6.8 PBS (2–12 h).

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

303

Table 1 Matrix tablet compositions (all quantities are given in gram). Formulation

S 1

S 2

S 3

S 4

S 5

S 6

S 7

S 8

S 9

S 10

S 11

S 12

S 13

S 14

S 15

S 16

S 17

S 18

RG SD HPMC K100LV HVCR EC 45cp Octadecanol HPMC K4M Citric acid Tartaric acid MCC Flowlac 100 Aerosil Magnesium stearate

33 60 – – – – – 30 50 – 3 2

33 – 60 – – – – 30 50 – 3 2

33 – – 60 – – – 30 50 – 3 2

33 – – – 60 – – 30 50 – 3 2

33 – – – – 60 – 30 50 – 3 2

33 – – – – – – 30 50 – 3 2

33 100 – – – – 20 – – 20 3 2

33 60 – – – – 20 – – 60 3 2

33 80 – – – – 20 – – 40 3 2

33 80 – – – – 30 – – 30 3 2

33 80 – – – – – – – 30 3 2

33 80 – – – – 40 – – 20 3 2

33 80 – – – – 50 – – 10 3 2

33 80 – – – – – 30 – 30 3 2

33 60 – – – – – 30 – 50 3 2

33 60 – – – – – 30 – 60 3 2

33 60 – – – – – 30 – 100 3 2

33 60 – – – – – 30 60 – 3 2

SD: solid dispersion of RG. Table 2 Optimized formulation of sustained release tablet. Components

Quantity (mg)

RG solid dispersion HPMC K100LV Citric acid Flowlac 100 Aerosil Magnesium stearate

33 (containing 3 mg RG) 60 30 50 3 2

(S15–S17)on drug release are depicted in Fig. 3(B). Surprisingly, the drug releases in 0.1 M HCl 0.1 and 0.1 M HCl-pH 6.8 PBS were not affected, also there was an increase in the flowlac 100 content from 50 to 100 mg At low drug loadings that are below the percolation threshold, the release constant (k) described by the Peppas model is not sensitive to altered water-soluble filler content that is incorporated into matrix formulations (Killen and Corrigan, 2006), which explains the unchanged drug release. 3.5. Optimized formulation and drug release The composition of the optimized formulation for the matrix tablets is shown in Table 2, and the drug releases in 0.1 M HCl and

0.1 M HCl-pH 6.8 PBS are depicted in Fig. 4. As expected, the drug release within the period in the (2–12 h) pH 6.8 PBS was lower than that during the period in the 0.1 M HCl because the solubility in aqueous conditions was pH-dependent. However, the two release profiles were similar because the value of the similarity factor f2 between the two curves was greater than 50 (63.13). Thus, the formulation, to some extent, compromised the effect of the pH change of the gastrointestinal tract fluids on the release of the weakly basic drug. 3.6. Release kinetics According to the correlation coefficient, the release data from the optimized formulation in the two media fitted the Peppas model well; moreover, the release exponent n was within the range of 0.45–0.89 which indicates a non-Fickian diffusion mechanism and that drug release was governed by both diffusion and matrix erosion (Table 3). Notably, the values of the release exponent in 0.1 M HCl and 0.1 M HCl-pH 6.8 PBS were different because the drug solubility in the former medium was markedly greater than that in the latter medium because RG release in the latter medium relied more heavily on a matrix erosion mechanism as evidenced by the larger n value.

Fig. 4. Effect of the medium pH on RG release from the optimized formulation of the sustained release tablets.

304

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

Table 3 Korsmeyer–Peppas model fitting of release data of sustained release tablets of RG (n = 3). Media

Correlation coefficient (R)

Diffusional coefficient (n)

Drug release mechanism

0.1 M HCl 0.1 M HCl-pH 6.8 PBS

0.9996 0.9976

0.7299 0.7717

Anomalous transport Anomalous transport

Fig. 5. Dog plasma concentration–time curves of RG following the administration of conventional and sustained release tablets (n = 6).

Table 4 Pharmacokinetic parameters of RG in beagle dogs after oral administration of conventional or sustained release tablets (n = 6). Formulation

Cmax (ng mL1)

Tmax (h)

t1/2 (h)

MRT (h)

AUC0t (ng h mL1)

F (%)

Conventional tablets Sustained release tablets

395.41
81.31 211.66
92.50

0.70
0.20 2.10
1.00

2.48
0.62 3.52
1.74

3.58
0.37 6.33
1.94

1071.25
429.62 1209.83
583.55

– 111.7
13.10

Fig. 6. Plots of the percentage of the dose absorbed versus the mean percentage of the dose released from the RG sustained release tablets in different media.

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

3.7. Pharmacokinetics in dogs The plasma concentration–time curves and pharmacokinetic parameters of RG following oral administration of conventional or sustained release tablets in beagle dogs are indicated in Fig. 5 and Table 4. The plasma concentration from the conventional tablets increased quickly and reached the maximum concentration within 1 h, and the drug was more quickly eliminated. In contrast, the Cmax and Tmax values for the sustained release tablets were approximately one-fold less and two-fold greater, respectively, than those of the conventional tablets as further evidenced by the significantly prolonged MRT and t1/2. Thus, sustained release of RG in vivo was obtained from the present formulation. In contrast, the AUC values were 1071.25
429.62 mg/mL h for the conventional tablets and 1209.83
583.55 mg/mL h for the

305

sustained release tablets, which indicates better absorption from the latter. RG is a BCS class II drug whose absorption is enhanced by the acceleration of drug release. Herein, the RG/PVPK30 solid dispersion from which the drug was dispersed in an amorphous form was utilized in the present formulation (Qin et al., 2014); this allowed for faster drug release and improved absorption. Indeed, the citric acid was used to adjust the microenvironment pH within the matrix system and increase the drug solubility that also contributed to the perfect in vivo performance. Due to its pH-dependent solubility, the absorption of RG was site-dependent in the gastrointestinal tract, which, in theory, discounts the benefits of sustained release formulations because incomplete absorption might occur. Moreover, our previous report confirmed that this drug is more likely to be absorbed in small intestine, particularly in the duodenum and jejunum (Yin et al.,

Fig. 7. (A) Hypoglycemic levels and (B) blood glucose reductions in beagle dogs after the oral administration of conventional and sustained release RG tablets (n = 6).

306

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307

2012). However, the drug was still well absorbed from the present sustained release matrix tablets, which indicates that this formulation was able to overcome the pH change of the gastrointestinal fluids; this notion was further confirmed by the similar drug release in the 0.1 M HCl and 0.1 M HCl pH 6.8 PBS media (Fig. 4). Thus, the present formulation might compromise a system for the delivery of other weakly basic compounds.

Acknowledgments This work was supported by the Creation of Major New Drugs national major projects (2011ZX09202-101-24, 2012ZX09202101008, and 2014ZX09507004-001) and the “333” High-Level Talents Cultivation Project of Jiangsu Province. References

3.8. In vitro–in vivo correlation The in vitro–in vivo correlation (IVIVC) is recommended by FDA for the use of a predictive mathematical model that depicts the relationships between the in vitro properties of an oral formulation and the relevant in vivo responses (Lu et al., 2011). The release of BCS class II drugs from oral dosage forms is the rate-limiting step in absorption; thus, the development of an IVIVC is required (Sjögren et al., 2014). A level A correlation that represented the point-topoint relationship was performed by comparing the fraction absorption in vivo to the fraction release in vitro. Herein, the absorption fraction was calculated with the Wagner–Nelson method because the in vivo course of RG was best fit by a onecompartment model. As shown in Fig. 6, the percentages of drug release in both 0.1 M HCl and 0.1 M HCl pH 6.8 PBS were wellcorrelated with the fraction absorption as evidenced by the good linear correlation and the correlation coefficients that were above 0.9. Therefore, the examination of in vitro drug release was able to predict the in vivo performance. 3.9. Hypoglycemic activity To further determine the hypoglycemic activity, the blood glucose levels and glucose reductions in the dogs were examined at each time point after the administration the sustained release tablet and conventional tablet formulations of RG. During the 0–6 h period, both the blood glucose level and the glucose reduction, with the exceptions of the time points of 0.5 and 1 h, were similar in the sustained release tablet and conventional tablet groups, which revealed a stronger hypoglycemic effect. However, 6 h later, the glucose level of the former was significantly lower than that of the latter, which was further confirmed by the glucose reduction results (Fig. 7(A and B)). These findings indicated that the present sustained release formulation prolonged the influence of RG on hypoglycemic activity in vivo. Notably, the blood glucose levels and the reductions at the time points of 0.5 and 1 h were significantly different between the two groups; we ascribe these differences to the dose-pumping effect of the conventional tablets. 4. Conclusions Herein, a sustained release matrix tablet was designed and successfully achieved the aims of prolonging the hypoglycemic effect of RG. This tablet was developed with direct compression technology, which has the promising benefits of low costs and ease of manufacture. The optimized formulation not only sustained drug release over 10 h but also afforded better absorption and steady plasma concentrations with a significant reduction in Cmax and a prolonged Tmax, which thereby extended the influence of RG on hypoglycemic activity in vivo. Moreover, the in vitro drug release and fractional absorption were well correlated because the formulation compromised the effect of the pH change in the gastrointestinal fluids on drug release. In summary, both sustained RG release and prolonged action were achieved with the matrix tablets designed here. Therefore, these tablets offer a promising formulation for T2D patients who require long-term treatment.

Aguilar-de-Leyva, A., Cifuentes, C., Rajabi-Siahboomi, A.R., Caraballo, I., 2012. Study of the critical points and the role of the pores and viscosity in carbamazepine hydrophilic matrix tablets. Eur. J. Pharm. Biopharm. 80, 136–142. Badawy, S.I.F., Hussain, M.A., 2007. Microenvironmental pH modulation in solid dosage forms. J. Pharm. Sci. 96, 948–959. Corti, G., Cirri, M., Maestrelli, F., Mennini, N., Mura, P., 2008. Sustained-release matrix tablets of metformin hydrochloride in combination with triacetylb-cyclodextrin. Eur. J. Pharm. Biopharm. 68, 303–309. De Berardis, G., Dttorre, A., Graziano, G., Lucisano, G., Pellegrini, F., Cammarota, S., Citarella, A., Germinario, C.A., Lepore, V., Menditto, E., Nicolosi, A., Vitullo, F., Nicolucci, A., 2013. The burden of hospitalization related to diabetes mellitus: a population-based study. Nutr. Metab. Cardiovasc. Dis. 22, 605–612. DeFronzo, R.A., 1999. Pharmacologic therapy for type 2 diabetes mellitus. Ann. Intern. Med. 131, 281–303. Dvorá9 cková, K., Doležel, P., Mašková, E., Muselík, J., Kejdušová, M., Vetchý, D., 2013. The Effect of acid pH modifiers on the release characteristics of weakly basic drug from hydrophlilic–lipophilic matrices. AAPS PharmSciTech 14, 1341–1348. Ferrero, C., Massuelle, D., Jeannerat, D., Doelker, E., 2013. Towards elucidation of the drug release mechanism from compressed hydrophilic matrices made of cellulose ethers. III. Critical use of thermodynamic parameters of activation for modeling the water penetration and drug release processes. J. Control. Release 170, 175–182. Goncalves-Araujo, T., Rajabi-Siahboomi, A.R., Caraballo, I., 2008. Application of percolation theory in the study of an extended release verapamil hydrochloride formulation. Int. J. Pharm. 361, 112–117. Killen, B.U., Corrigan, O.I., 2006. Effect of soluble filler on drug release from stearic acid based compacts. Int. J. Pharm. 316, 47–51. Kramer, C.K., Zinman, B., Gross, J.L., Canani, L.H., Rodrigues, T.C., Azevedo, M.J., Retnakaran, R., 2013. Coronary artery calcium score prediction of all cause mortality and cardiovascular events in people with type 2 diabetes: systematic review and meta-analysis. BMJ 346, f1654. Lalau, J.D., Azzoug, M.L., Kajbaf, F., Briet, C., Desailloud, R., 2014. Metformin accumulation without hyperlactataemia and metformin-induced hyperlactataemia without metformin accumulation. Diabetes Metab. 40, 220–223. Lotfipour, F., Nokhodchi, A., Saeedi, M., Norouzi-Sani, S., Sharbafi, J., Siahi-Shadbad, M.R., 2004. The effect of hydrophilic and lipophilic polymers and fillers on the release rate of atenolol from HPMC matrices. Farmaco 59, 819–825. Lu, Y., Kim, S., Park, K., 2011. In vitro–in vivo correlation: perspectives on model development. Int. J. Pharm. 418, 142–148. Lyons, J.G., Devine, D.M., Kennedy, J.E., Geever, L.M., O’sullivan, P., Higginbotham, C. L., 2006. The use of agar as a novel filler for monolithic matrices produced using hot melt extrusion. Eur. J. Pharm. Biopharm. 64, 75–81. Maderuelo, C., Zarzuelo, A., Lanao, J.M., 2011. Critical factors in the release of drugs from sustained release hydrophilic matrices. J. Control. Release 154, 2–19. Martinello, T., Kaneko, T.M., Velasco, M.V., Taqueda, M.E., Consiglieri, V.O., 2006. Optimization of poorly compactable drug tablets manufactured by direct compression using the mixture experimental design. Int. J. Pharm. 322, 87–95. Obach, R.S., Lombardo, F., Waters, N.J., 2008. Trend analysis of a database of intravenous pharmacokinetic parameters in humans for 670 drug compounds. Drug Metab. Dispos. 36, 1385–1405. Qin, C., He, W., Zhu, C., Wu, M., Jin, Z., Zhang, Q., Wang, G., Yin, L., 2014. Controlled release of metformin hydrochloride and repaglinide from sandwiched osmotic pump tablet. Int. J. Pharm. 466, 276–285. Quinten, T., Gonnissen, Y., Adriaens, E., Beer, T.D., Cnudde, V., Masschaele, B., Van Hoorebeke, L., Siepmann, J., Remon, J.P., Vervaet, C., 2009. Development of injection moulded matrix tablets based on mixtures of ethylcellulose and lowsubstituted hydroxypropylcellulose. Eur. J. Pharm. Sci. 37, 207–216. Reza, M.S., Quadir, M.A., Haider, S.S., 2003. Comparative evaluation of plastic, hydrophobic and hydrophilic polymers as matrices for controlled-release drug delivery. J. Pharm. Pharm. Sci. 6, 282–291. Scott, L.J., 2012. Repaglinide: a review of its use in type 2 diabetes mellitus. Drugs 72, 249–272. Siepe, S., Lueckel, B., Kramer, A., Ries, A., Gurny, R., 2006. Strategies for the design of hydrophilic matrix tablets with controlled microenvironmental pH. Int. J. Pharm. 316, 14–20. Siepmann, J., Peppas, N.A., 2012. Modeling of drug release from delivery systems based on hydroxypropyl methylcellulose (HPMC). Adv. Drug Deliv. Rev. 64, 163–174. Sjögren, E., Abrahamsson, B., Augustijns, P., Becker, D., Bolger, M.B., Brewster, M., Brouwers, J., Flanagan, T., Harwood, M., Heinen, C., Holm, R., Juretschke, H.-P., Kubbinga, M., Lindahl, A., Lukacova, V., Münster, U., Neuhoff, S., Nguyen, M.A., Peer, A.v., Reppas, C., Hodjegan, A.R., Tannergren, C., Weitschies, W., Wilson, C., Zane, P., Lennernäs, H., Langguth, P., 2014. In vivo methods for drug absorption-

W. He et al. / International Journal of Pharmaceutics 478 (2015) 297–307 comparative physiologies model selection, correlations with in vitro methods (IVIVC), and applications for formulation/API/excipient characterization including food effects. Eur. J. Pharm. Sci. 57, 99–151. Sriamornsak, P., Thirawong, N., Korkerd, K., 2007. Swelling: erosion and release behavior of alginate-based matrix tablets. Eur. J. Pharm. Biopharm. 66, 435–450. Sriamornsak, P., Nunthanid, J., Luangtana-anan, M., Weerapol, Y., Puttipipatkhachorn, S., 2008. Alginate-based pellets prepared by extrusion/spheronization: effect of the amount and type of sodium alginate and calcium salts. Eur. J. Pharm. Biopharm. 69, 274–284. Varma, M.V.S., Kaushal, A.M., Garg, S., 2005. Influence of micro-environmental pH on the gel layer behavior and release of a basic drug from various hydrophilic matrices. J. Control. Release 103, 499–510. Wei, X., Sun, N., Wu, B., Yin, C., Wu, W., 2006. Sigmoidal release of indomethacin from pectin matrix tablets: effect of in situ crosslinking by calcium cations. Int. J. Pharm. 318, 132–138.

307

Wu, B., Chen, Z., Wei, X., Sun, N., Lu, Y., Wu, W., 2007. Biphasic release of indomethacin from HPMC/pectin/calcium matrix tablet: I. Characterization and mechanistic study. Eur. J. Pharm. Biopharm. 67, 707–714. Wu, B., Deng, D., Lu, Y., Wu, W., 2008. Biphasic release of indomethacin from HPMC/ pectin/calcium matrix tablet: II. Influencing variables, stability and pharmacokinetics in dogs. Eur. J. Pharm. Biopharm. 69, 294–302. Yang, S.H., Dou, K.F., Song, W.J., 2010. Prevalence of diabetes among men and women in China. New Engl. J. Med. 362, 2425–2426. Yin, L.F., Huang, S.J., Zhu, C.L., Zhang, S.H., Zhang, Q., Chen, X.J., Liu, Q.W., 2012. In vitro and in vivo studies on a novel solid dispersion of repaglinide using polyvinylpyrrolidone as the carrier. Drug Dev. Ind. Pharm. 38, 1371–1380. Zhang, X., Qi, J., Lu, Y., He, W., Li, X., Wu, W., 2014. Biotinylated liposomes as potential carriers for the oral delivery of insulin. Nanomedicine 10, 167–176. Zhu, H., Zhang, X., Li, M.Z., Xie, J., Yang, X.L., 2013. Prevalence of Type 2 diabetes and pre-diabetes among overweight or obese children in Tianjin. China Diabet. Med. 30, 1457–1465.