Formulation and Evaluation of Floating Microspheres of Sitagliptin

 

A. Anka Rao*, Narender. Malothu, A. Narayana Rao, Bandaru Naga Raju,

B. Jahasultana. Mohammed

K L College of Pharmacy, Koneru Lakshmaiah Education Foundation, Vaddeswaram, Andhra Pradesh.

*Corresponding Author E-mail:

 

ABSTRACT:

Gastro retentive dosage forms have potential for use as controlled- release drug delivery systems. Gastro retentive floating drug delivery systems have a bulk density lower than that of gastric fluids and thus increase residence time of drug in stomach and provide controlled delivery of many drugs. The aim of the present study is formulation and characterization of floating microspheres using Sitagliptin as a model drug for the management of type-2 diabetes mellitus. Floating microspheres were prepared by oil-in-water emulsion solvent evaporation technique using ethyl cellulose and eudragit S-100 as release retarding polymers. The floating microspheres were evaluated for percentage yield (%), particle size, drug content, drug entrapment efficiency, in-vitro floating ability and in-vitro drug release studies. The surface morphology of prepared microspheres was characterized by scanning electron microscopy. The microspheres were found to be spherical in shape and porous in nature. Compatibility studies were performed by fourier transform infrared (FTIR) technique. The prepared microspheres showed prolonged drug release of 12 h and remain buoyant for more than 12 h. In-vitro release kinetics were studied in different release kinetics models like zero order, first order, higuchi and korsmeyer peppas model and the best fit model was found to be higuchi plot with release exponent n value less than  0.89. It was concluded that developed floating microspheres of Sitagliptin offers a suitable and practical approach for prolonged release of drug over an extended period of time and thus oral bioavailability, efficacy and patient compliance is improved.

 

KEYWORDS: Antidiabetic, Ethyl cellulose, Eudragit S-100, Gastro retentive drug delivery, Floating drug delivery system, Emulsion solvent evaporation method.

 

 

1. INTRODUCTION: 

Oral route is considered to be highly suitable route and frequently used for delivery of drug due to ease of administration, patient compliance and flexibility of formulation. The success of oral controlled delivery system depends on the fact that the drug can be better absorbed from GI tract. But the main problem with conventional delivery is to maintain the drug concentration within the therapeutic effective concentration level, which can be achieved only when taken several times a day.  It also has applications for local drug delivery to the stomach and proximal small intestines.1

 

Floating microspheres are gastroprotective drug delivery systems based on non-effervescent approach.

 

They are spherical empty particles without core. These microspheres are characteristically free flowing powders consisting of protein or synthetic polymers with diameters 1μm to 1000μm.2 Hydro dynamically controlled drug delivery systems (Floating drug delivery system) are low density systems that have sufficient buoyancy to float over the gastric contents and remain buoyant in the stomach without affecting the gastric emptying rate for a prolonged period of time.3 The sustained release of drug from floating systems improves the gastric retention of drugs and reduces the fluctuations in plasma drug concentration. Commonly used polymers to prepare floating microspheres include polycarbonate, HPMC, Cellulose acetate, calcium alginate, Eudragit S, chitosan etc. Thus floating microspheres are considered as one of most promising buoyant systems.4

 

2. MATERIALS AND METHODS:

2.1 Materials:

Sitagliptin was purchased from Yarrow chem products, Mumbai. Ethylcellulose and Eudragit S-100 were purchased from CDH laboratory reagents, New Delhi. Analytical grade ethanol, dichloromethane, tween-80 were purchased from Molychem, India. All other chemicals used were of analytical grade.

 

2.2 Methods:

2.2.1 Preformulation studies:

Preformulation studies are the first step in the rational development of dosage forms of a drug. It can be defined as the determination of physical, chemical and mechanical properties of a new drug substance alone and when combined with excipients. The overall objective of preformulation studies is to generate information useful in developing stable and bioavailable and sustained release dosage forms which can be mass produced.5

 

2.2.2 Solubility studies:

Solubility analysis was done to select a suitable solvent system to dissolve the drug and also to test its solubility in the dissolution medium which was to be used. Drug solubility study was performed by taking an excess quantity of drug in different solvents like water, ethanol, methanol, acetone and buffers.6

 

2.2.3 Preparation of microspheres:

Oil-in-water emulsion solvent evaporation technique:

Microspheres containing Sitagliptin as a core material were prepared by oil-in-water emulsion solvent evaporation technique. In this process, both the drug and the polymer should be insoluble in water while a water immiscible solvent is required for the polymer. The polymer was dissolved in an organic solvent such as dichloromethane and ethanol (1:1). The drug was dissolved into polymer solution and this solution containing the drug was emulsified into an aqueous phase containing tween 80, 0.2% v/v to make an oil-in water emulsion by using as emulsifying agent. After the formation of a stable emulsion, the organic solvent was evaporated either by increasing the temperature under pressure or by continuous stirring. Solvent removal from embryonic microspheres determines the size and morphology of the microspheres. Oil-in water emulsion is widely used  due to simplicity of the process and easy cleans up requirement for the final product.7 (Table-1)

 

3.0 EVALUATION OF SITAGLIPTIN FLOATING MICROSPHERES:

3.1 Particle Size Analysis:

Particle size analysis of drug-loaded Eudragit microspheres was performed by optical microscopy using a compound micro- scope. The slide containing Eudragit microspheres was mounted on the stage of the microscope and diameter of at least 300 particles was measured using a calibrated ocular micrometre. The average particle size of microspheres was determined by the total size of the microspheres divided by the number of microspheres.8

 

3.2 Percentage yield:

The prepared microspheres were collected and weighed. The measured weight was divided by the total amount of drug and polymers which were used for the preparation of the microspheres to obtained percentage yield9.

Results of percentage Yield was calculated using following equation.

 

% Yield = Practical yield/Theoretical yield × 100

 

 

3.3 Percentage Drug Entrapment Efficiency:

To determine the incorporation efficiency, 25mg microspheres were crushed and dispersed in 100ml 0.1 N HCl and sonicated for 10-15 min. The dispersion was stirred on a magnetic stirrer for 24h. The dispersion was filtered, and Drug content was analyzed Spectrophotometrically at 226.5nm. The percentage drug entrapment efficiency was calculated using the following equation10.

 

% DEE = Actual drug content/Theoretical drug content × 100

 

3.4 In-vitro Drug Release:

Percentage cumulative drug release studies were carried out for all formulations taking 20mg drug equivalent microspheres in USP type II dissolution test apparatus containing 900 ml of 0.1 N Hydrochloric acid (HCl) (PH 1.2) maintained at 37±0.20 C at a rotation speed of 100 rpm. The amount of the drug was determined first- derivative (D1)

                      Spectrophotometrically at 226.5 nm adopting the peak height method11.

 

Table 1: Various formulation of floating microspheres of Sitagliptin

Formulation code

Drug (mg)

Ethyl cellulose (mg)

Eudragit S-100 (mg)

Ethanol: Dichloromethane

Stirring speed (r/min)

F1

100

100

-

1:2

800

F2

100

200

-

1:2

800

F3

100

300

-

1:2

800

F4

100

400

-

1:2

800

F5

100

-

100

1:2

1000

F6

100

-

200

1:2

1000

F7

100

-

300

1:2

1000

F8

100

-

400

1:2

1000

4. RESULTS AND DISCUSSION:

4.1 Solubility analysis:

Sample of Sitagliptin was found to be soluble in ethanol,  methanol, Dichloromethane and chloroform and insoluble in water.

 

4.2 Melting point determination:

The melting point of drug sample was found to be 137º C.

 

4.3 Preparation of calibration curve by using UV spectroscopy:

Table 2: Absorbance value of Sitagliptin in 0.1 N HCl

Concentration (μg/ml)

Absorbance

0

0

2

0.068

4

0.1251

6

0.178

8

0.245

10

0.302

 

 

Figure 1: Calibration curve of Sitagliptin in 0.1 N HCl

 

FTIR Spectrophotometric analysis:

Table 3: Characterstic peaks of Sitagliptin

S. No.

Reference peak (cm-1)

Obtained peaks (cm-1)

Functional group

Stretching/Bending

1

1680-1630

1647

-C=O (carbonyl)

Stretching

2

1725-1700

1715

-C=O (COOH)

Stretching

3

1320-1210

1287

-C-O (COOH)

Stretching

4

2859-3064

2859-3064

-CH2 - (cycloalkane)

Stretching

5

3296-3310

3308

-NH

Stretching

 

 

Figure 2: FTIR spectrum of Drug and Ethyl cellulose

 

Figure 3: FTIR spectrum of Drug and Eudragit S-100

 

4.4 Characterization of microspheres:

4.4.1 Percentage yield

The Percentage yields of floating microspheres were found in the range of 75–88.2 %. It was observed that with the increase in the polymer concentration (i.e. decrease in drug to polymer ratio) in the formulation, the product yield increased. It was found that average percentage yield was greater than 50 % for all the batches which shows the suitability of this method for preparation of microspheres. The results were showed in table 4.

 

Table 4: Percentage yield, average particle size of floating microspheres

S. No.

Formulation

Percentage yield (%)

Average particle size (µm)

1

F1

75

44.598

2

F2

80

66

3

F3

79

80

4

F4

85

85

5

F5

87

70

6

F6

79.5

60

7

F7

88.2

120

 

4.4.2 Particle size:

The average particle size range for formulations F1, F2, F3 and F4 was found to be 44.598μm, 66μm, 80 μm, 85μm respectively and for formulations F5, F6, F7 and F8 was found to be 70μm, 60μm, 120μm, 80μm respectively. The results were showed in table 4. The particle size of the microspheres increases with increase in polymer concentration respectively. This is because the viscosity of polymer solution increases with increasing polymer concentration resulting in enhanced interfacial tension, which in turn decreases the stirring efficiency, which results in increased particle size.

 

4.4.3 Percentage floating:

Excellent buoyancy was shown by prepared microspheres because of their hollow nature, which can be retained for a longer period of time in the upper part of gastrointestinal tract (GIT) in order to increase gastric residence time of the drug.

 

4.4.4 Drug content and entrapment efficiency:

The drug entrapment efficiency of all formulations was found to be in the range between 70.48 to 82.8% and the drug content was found to be in the range of 66.38 to 74.52%, the results were showed in table 4. With the increase in polymer concentration, increased entrapment efficiency was seen because with increasing polymer content, more particles of drug would be coated leading to higher encapsulation efficiency as can be seen from Table 6. An increase in polymer concentration in the internal phase shows increase in drug loading. This may be due to increase in viscosity of internal phase which reduces the migration of drug in aqueous phase, thus entrapping greater amount of drug.

 

4.4.5 Surface morphology using SEM:

Morphology of floating microspheres was examined by scanning electron microscopy. The SEM images of prepared formulations were showed by figure 4. SEM analysis showed that the prepared floating microspheres were having size in micrometers and the particles were nearly spherical.

 

Table 5: Micromeritic properties of formulations

Formulation code

Angle of repose

Bulk density g/cm3

Tapped density g/cm3

Carr’s index (%)

Hausner ratio

F1

26

0.106

0.116

8.62

1.09

F2

25

0.108

0.116

6.89

1.07

F3

24

0.108

0.121

10.74

1.12

F4

29

0.119

0.129

7.75

1.08

F5

27

0.154

0.168

8.33

1.09

F6

26

0.127

0.143

11.18

1.12

F7

28

0.131

0.152

13.81

1.16

F8

30

0.106

0.121

12.39

1.14

 

Table 6: Evaluation of floating microparticulated drug delivery systems

Formulation code

Percentage floating (%)

Floating time (hours)

Drug content (%)

Drug entrapment efficiency (%)

F1

84

12

66.38

70.48

F2

78

15

71.6

85.95

F3

70

8

76.53

88.64

F4

76

14

80.79

90.17

F5

66

13

64.35

75.76

F6

72

11

73.80

85.12

F7

88

15

85.2

91.2

F8

86

10

74.52

82.8

 

 

 

(a)

 

(b)

 

(c)

Figure 4: (a), (b) and (c) SEM of microspheres of formulation F7

 

Fig 5: Graph showing % cumulative drug release vs time of the prepared formulations

 

4.4.6 In vitro drug release:

For comparison of the release rate of formulations prepared by using different ratio of polymers in vitro release study was done. In-vitro drug release studies were performed in 0.1 N HCl for 2 h and in pH 6.8 buffer for 10 h.11,12 The results of cumulative drug release were showed in table no. 7. The graph was plotted between cumulative drug release and time and showed in figure no. 8. The cumulative release of drug significantly decreased with increase in polymer concentration. The increased density of polymer matrix at higher concentration resulted in an increased diffusion path length. This may decrease the overall drug release from the polymer matrix. And it was found that as the polymer concentration was increased the release rate decreases. The selected formulation percentage of drug released was found to be initially 5.39% at 1 h and 69.49% up to 12 h.

 

Table 7: In-vitro dissolution studies of floating microspheres of Sitagliptin Cumulative % drug release for different batches of microspheres formulations

S. No.

Time (h)

Percent cumulative drug release for different batches of microspheres formulations

F1

F2

F3

F4

F5

F6

F7

F8

1

0

0

0

0

0

0

0

0

0

2

1

2.63

2.68

2.85

2.9

3.86

4.46

5.39

5.77

3

2

11.07

14.72

16.81

20.93

13.79

16.91

17.94

18.25

4

3

14.16

27.77

26.80

24.31

21.15

21.50

21.37

21.72

5

4

27.39

31.05

27.52

27.74

27.86

23.46

24.52

23.68

6

5

30.54

35.85

30.58

29.74

30.70

27.89

30.42

27.71

7

6

30.83

41.87

38.85

38.47

39.50

46.03

46.34

45.93

8

7

38.40

48.02

45.12

46.18

45.40

54.70

55.08

54.76

9

8

41.63

55.57

49.05

49.46

53.33

58.76

59.13

57.92

10

9

49.48

57.76

55.73

55.42

57.17

58.94

64.94

60.26

11

10

56.78

62.07

56.92

57.82

60.60

61.91

69.81

61.57

12

12

77.54

66.93

70.18

73.49

75.16

71.18

80.67

69.49

 

4.4.7 Release kinetic study:

In order to determine the release model which best describes the pattern of drug release, the in-vitro release data were substituted in various models such as zero order, first order, higuchi plot and korsmeyer peppas kinetics models.13,14 Model fitting release profiles of formulation were showed in table 8.  The highest regression (0.947) was obtained for higuchi equation. To explain the mechanism of drug release, korsmeyer-peppas equation was used. Value of slope (n) was calculated and found to be (0.713) which is less than 0.89 which indicates anomalous non-fickian diffusion i.e. coupling of diffusion and erosion, which indicates that the drug release is sustained by more than one process.

 

Table 8: Model fitting release profile of formulations F1 to F8

Formulation

Zero order (r2)

First order (r2)

Higuchi (r2)

Korsmeyer-Peppas

(r2)

n value

F1

0.918

0.976

0.974

0.885

0.836

F2

0.746

0.857

0.916

0.773

0.752

F3

0.812

0.926

0.949

0.791

0.727

F4

0.834

0.946

0.958

0.789

0.715

F5

0.837

0.939

0.958

0.874

0.735

F6

0.747

0.830

0.897

0.856

0.703

F7

0.827

0.944

0.947

0.904

0.713

F8

0.754

0.837

0.905

0.888

0.659

 

5. CONCLUSION:

Floating microspheres of Sitagliptin were prepared by novel oil-in-water emulsion solvent evaporation technique, using various biodegradable polymers such as ethyl cellulose and eudragit S-100 in order to retain drug in body for longer period of time. Sitagliptin is insoluble in water and has short half life of 1.5 h. It requires frequent dosing before meals due to short half life and thereby imposing side effects. The drug requires a novel gastro retentive drug delivery system which can provide an extended period of time in stomach and improve oral bioavailability. Floating microspheres were characterized for floating ability, compatibility study, particle size and shape, drug content, in vitro drug release, entrapment efficiency. Due to their low density, these multi particulate drug delivery systems showed good floating ability and remained in gastric environment for more than 12 h. Eudragit S-100 based microspheres showed its buoyancy for more than 15 h, required for sustained therapeutic activity in comparison to Ethyl cellulose-based microspheres.

 

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Received on 06.07.2020            Modified on 05.11.2020

Accepted on 05.01.2021           © RJPT All right reserved

Research J. Pharm. and Tech 2023; 16(5):2251-2256.

DOI: 10.52711/0974-360X.2023.00370