Application Of Response Surface Methodology Biology Essay

Published:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Divalproex sodium is an effective anticonvulsant, antimanic and migraine prophylaxis agent. The delayed release tablet is intended to release the drug after some delay or after tablet pass gastrointestinal tract. The enteric coating is common example of this tablet. The main aim of this work is to develop a delayed release tablet formulation of Divalproex sodium using direct compression method. Response surface methodology based on four variables central composite rotatable design was employed for optimization of preparation of direct compressible formulation for Divalproex sodium delayed released tablet. The four variables considered were amount of disintegrant, amount of glident and amount and type of filler. Powders flowability and tablets hardness were analyzed by flow meter and hardness tester respectively for prepared powder mixture and direct compressed tablets. Seven formulations which had good flowability and hardness were chosen for dissolution test with USP apparatus 2. From different coating solutions, combination with Kollicoat® which had low amount of propylene glycol had better results. The released drug was analyzed with HPLC-UV method. For reaching the flow time in the range of 10-20sec, the amount of lactose should be less than 12 g and the amount of AcDiSol should be less than 5 g. To achieve the desired hardness range between 100 to 140 Newton, the amount of used AcDiSol should be between 3.5 to 7.5g and the amount of lactose should be between 5 to 17.5g. From optimized formulations, formulations F1, F3, F11 and F22 displayed a good flowability, hardness and complete drug delivery and released more than 80% of contained drug during 10 min in alkali medium without drug releasing in acidic medium.

Keywords: Divalproex sodium, Direct compression, Delayed release, Central composite, Enteric coat.

1. INTRODUCTION

Epilepsy and bipolar disorder are two common, chronic and often disabling conditions, and effective treatment often requires long-term pharmacotherapy. Anticonvulsant agents, such as divalproex sodium (DVPX), have been recognized as therapies for the treatment of epilepsy and bipolar disorder. DVPX is an FDA-approved antiepileptic, antimanic and migraine prophylactic agent and is widely used for maintenance therapy. DVPX is a unique combination of equal proportions of sodium valproate and valproic acid, which dissociates in the gastrointestinal tract into the active valproate ion. It is generally recognized that DVPX needs to be administered two or more times a day due to its' short (6-16 h) elimination half-life. [1-10]. Due to its side effects especially gastrointestinal complaints and sensitivity to acidic area of stomach, production of delayed release (DR) formulation of DVPX has many useful advantages. Enteric coated dosage forms are mostly useful dosage forms in DR dosage forms group and are best formulations which are used for drugs that are destroyed in gastric fluids, cause gastric irritation, or are absorbed preferentially in the intestine. This dosage forms contain a core material comprising the active substance and enteric coating layer [2, 4, 11-15]. DVPX is available in several formulations including the conventional tablet, extended-release tablet, suspension, capsules and the sprinkle capsule [4, 7, 10, 16, 17]. Because DVPX is a narrow therapeutic index drug and requires chronic administration, a dosage form which provide increased clinical value over conventional formulations as a result of improved patient compliance, a decreased incidence and intensity of the side effects is required. Tablets are considered to be the most desirable dosage form for drug delivery, since it is preferred by patients and industry. The direct compression is a process more economical, reduces the cycle time of the products, and is straightforward in terms of requirements of good manufacturing practices and no pre-treatment of the powder blends by wet or dry granulation is involved [18-22]. Due to the wax nature of DVPX, it has weak flowability. Regarding to the manufacturability, a good flowability of the mixture of excipients and drug, is critical for the compression of the tablets in terms of dissolution, friability and content uniformity [18, 19, 23-26]. The traditional methods for formulation design are based on large number of experiments, time and cost. Statistical experimental design, also called design of experiments (DOE), is a well-established concept for planning and execution of informative experiments. DOE can be used in many applications. An important type of DOE application refers to the preparation and modification of mixtures. It involves the use of 'mixture designs' for changing mixture composition and exploring how such changes will affect the properties of the mixture. In particular, response surface methodologies (RSM) have been successfully applied in both drug discovery and development. In this methodology, the study of the ingredient effect on some measurable characteristics of the blend (or response) is an attempt to find the formulation (or formulations) that produce the 'best' response [27-34]. Therefore we used mixture of variable excipients to improve flowability of powder and tablet hardness. In this study due to the lack of enteric coated tablet of DVPX in Iran medicine market, and advantages of DC, central composite design (CCD) method from RSM in Minitab software was employed to optimize preparation of delayed release enteric coated formulation of DVPX by using DC method.

2. MATERIALS AND METHODS

Materials

The following raw materials were used: Aerosil 200 and Dibutylphethalate (Merck, Germany), Talc, Magnesium stearate, Avicel PH101 and Ac-Di-sol (Zahravi, Iran), Lactose Monohydrate (Alpavit, Netherlands), Kollicoat® MAE 30 DP (Basf, Germany), Eudragit RL 30 D (Rohmpharma, Germany) and Divalproex sodium (Katvijk Chemie BV, Netherlands). All other solvents and reagents were of analytical grade and were purchased from Merck (Germany).

Methods

Powder preparation

Drug and excipients were weighted and passed through a sieve with mesh size 40 and then mixed in mixer (Ika Wark) for 15 min. After additions of magnesium stearate, powder was mixed again for 5 min. Flowability of each blend was tested directly with flow meter machine (Erweka, Germany) using 100 g of each powder mixture. This process was repeated 6 times for each formulation and average flow time was calculated.

Tablet preparation

Tablets were produced in a single-punch tablet press with a compression force of 100 N for 10sec in caplet shape. The tablet properties were examined according to the USP 32th ed. specifications. The hardness of caplets was measured using a hardness tester (Erweka- TBH30MD, Germany) for each formulation. Each hardness value reported is a calculated average of three measurements.

In-vitro drug release for enteric coated tablets

Drug release studies were carried out using a USP type II dissolution test apparatus at 50 rpm for 1hr in 900mL simulated intestinal fluid (SIF, 0.1N HCL) maintained at 37±0.5oC. Then the dissolution medium was replaced with phosphate buffer, pH=7.5, 900mL) and tested for drug release for 90 min at same temperature and rotation speed. After 5, 10, 20, 30, 45, 60 and 90 min 5ml of the samples were taken out and 5mL of fresh phosphate buffer was added to kept volume of dissolution medium constant and sample was analyzed using HPLC method with ultra violet detector (Erweka, Germany) at 210nm. Mobile phase consist of citrate buffer, phosphate buffer (pH: 7.5) and acetonitrile (30:35:35) and flow rate was 2 mL/min. Column was L11 (Phenyl groups chemically bonded to porous silica particles, 150- 4.6 mm). Calibration curve was constructed using peak area and was linear in the range of 52.32 -557.62 mg/L (r2=0.9979). According to the data obtained from release study, difference (F1) and similar factor (F2) using following equations were calculated.

F1= {} 100 % and F2 = 50 log {[1+∑ wt (Rt _ Tt) 2]-0.5100}

Where Rt and Tt are the cumulative percentage of dissolved drug for a reference and test formulation at time t, respectively, n is the number of time points and wt is an optional weight factor. Two dissolution profiles are verified similar if F1 is between 0 and 15 and if F2 is between 50 to 100 [35-38].

Preparation of the coating solutions

Two type of coating solution containing different proportion of Kollicoat® MAE 30 DP, propylene glycol, water, talc and red color powder and two mixture of different proportion of Eudragit RL 30D, dibutylphetalate, talc, water and isopropyl alcohol were made and sprayed on tablets in coating pan. Before coating, tablets were heated until 40o C. After each spray time, tablets were dried using indirect heating. This process was continued until 2-3 hr to reach a homogenous coat. Formulations of coating solutions are summarized in Table 1.

Table 1. Composition of coating solutions

Solution 4

Solution 3

Solution 2

Solution 1

5.000 g

5.000 g

Kollicoat® MAE 30 DP

0.100 g

0.220 g

Propylene Glycol

1.425 g

1.425 g

4.229 g

4.229 g

Water

0.049 g

0.049 g

Red color powder

1.500 g

0.860 g

0.445 g

0.445 g

Talc

1.720 g

1.720 g

Eudragit RL 30 D

0.172 g

0.172 g

Dibuthylphetalate

24.400 g

24.400 g

Isopropyl Alcohol

Central Composite Design (CCD)

Central composite rotatable design (CCRD) was first described by Box and Wilson in 1951 and improved upon by Box and Hunter. The CCD consists of 2n factorial points with 2n axial points and Nc central points. For four factors, a CCD, consisting of 16 factorial points, 8 axial points and 6 replicates at the center points were employed. The center points are used to determine the experimental error and the reproducibility of the data. The independent variables are coded to the (−1, +1) interval where the low and high levels are coded as −1 and +1, respectively. The axial points are located at distance of α from center and make the design rotatable. For the optimization of the tablet formulation, a randomized rotatable central composite design was employed for four independent factors, amount of disintegrant, amount of glident and amount and type of filler. The dependent response variables measured were flowability and hardness. In a CCD, all factors are studied at the all plausible combinations, as it is considered to be most efficient in estimating the influence of individual variables (main effects) and their interactions, using minimum experimentation [19, 22, 25, 34, 39-46].

RESULTS AND DISSCUSION

Flowability and hardness tests

RSM is a collection of mathematical and statistical techniques that can be used for studying the effect of several factors at different level and their influence on each other, thus overcomes the shortcoming of the traditional methods. Another main advantage of RSM is the significant reduction of experimental runs in providing sufficient information for statistically valid results. In recent years, RSM has played an important role in pharmaceutics and other related fields [19, 40, 43-47]. The observed values of flow time and hardness of the 27 experiments are listed in Table 2. Three formulations of these formulations were chosen as test group randomly. Data evaluation is done using linear regression analysis with Minitab software and model predictor equations were obtained for each dependent variable separately using responses data of 24 standard formulations.

Flowability equation:

Y=(AcDiSol*6.21127)+( Lactose*-0.0791879)+( Avicel*0.753047)+( Aerosil*-0.687307)+( AcDiSol* AcDiSol*-0.434753)+( Lactose* Lactose*-0.0145434)+( Avicel* Avicel*0.00111923)+( Aerosil* Aerosil*-0.230314)+( AcDiSol* Lactose*-0.0692191)+( AcDiSol* Avicel*-0.123438)+( AcDiSol* Aerosil*0.284623)+( Lactose* Avicel*-0.00575765)+( Lactose* Aerosil*0.415384)+( Avicel* Aerosil*0.0713426)+(-4.45662)

Hardness equation:

Y=(AcDiSol*-3.88591)+(Lactose*-1.14155)+(Avicel*2.32568)+(Aerosil*9.50792)+(AcDiSol* AcDiSol*-0.386065)+( Lactose* Lactose*-0.0565931)+(Avicel* Avicel*-0.145466)+(Aerosil* Aerosil*0.315774)+(AcDiSol* Lactose*0.277790)+(AcDiSol* Avicel*-0.0437500)+(AcDiSol* Aerosil*-0.314815)+( Lactose* Avicel*0.0353922)+( Lactose* Aerosil*-0.655388)+ (Avicel* Aerosil*0.503704)+112.605

Estimated flow time and hardness value from these equations compared with observed values and percent error (PE) were calculated. The mean PE for flowability and hardness in standard group was 27.33±42.5 and 9.99± 8.24 respectively. Corresponding values for test group was 17.49 ±12.92 and 16.18±9.05 respectively.

Table 2. Flowability and hardness test results of suggested formulations

Formulation code

DVPX (%)

AcDiSol (%)

Lactose (%)

Avicel (%)

Aerosil (%)

Powder weight

Tablet weight

flow (sec)

Hardness (Newton)

F1

26.91

2

0

10

2.75

41.66

0.8332

13.97 ± 2.73

139.67± 9.29

F2

26.91

10

20

10

2.75

69.66

1.3932

11.48 ± 5.39

46.67 ± 0.58

F3

26.91

2

10

0

2.75

41.66

0.8332

7.60 ± 1.60

94.67 ± 10.69

F4

26.91

2

10

10

5

53.91

1.0782

25.96 ± 2.66

142.67 ± 11.37

F5

26.91

6

0

10

5

47.91

0.9582

19.56 ±12.28

134.33 ± 4.93

F6

26.91

6

20

0

2.75

55.66

1.1132

27.48 ± 3.22

61.33 ± 3.78

F7

26.91

10

10

20

2.75

69.66

1.3932

18.97 ± 8.69

68.33 ± 0.58

F8

26.91

10

10

10

0.5

57.41

1.1482

6.63 ± 1.81

68.67 ± 1.53

F9

26.91

6

10

20

5

67.91

1.3582

33.7 ± 4.23

137.67 ± 4.51

F10

26.91

6

20

20

2.75

75.66

1.5132

21.37 ± 4.68

102.33 ± 2.52

F11

26.91

2

10

10

0.5

49.41

0.9882

6.13 ± 1.58

118.00 ± 9.64

F12

26.91

10

0

10

2.75

49.66

0.9932

5.05 ± 0.84

65.33 ± 5.86

F13

26.91

6

10

20

0.5

63.41

1.2682

9.59 ± 3.90

59.33 ± 0.58

F14

26.91

2

20

10

2.75

61.66

1.2332

28.79 ± 3.87

88.67 ± 4.72

F15

26.91

6

10

0

0.5

43.41

0.8682

12.53 ± 1.97

59.00 ± 3.60

F16

26.91

6

20

10

5

67.91

1.3582

41.11 ± 3.93

78.33 ± 2.52

F17

26.91

6

10

10

2.75

55.66

1.1132

24.70 ± 1.41

87.00 ± 2.64

F18

26.91

2

10

20

2.75

61.66

1.2332

26.27 ± 0.98

121.67 ± 9.61

F19

26.91

6

0

0

2.75

35.66

0.7132

22.44 ± 2.90

106.00 ± 3.00

F20

26.91

6

0

20

2.75

55.66

1.1132

24.94 ± 2.47

106.00 ± 2.64

F21

26.91

6

10

10

2.75

55.66

1.1132

29.07 ± 6.60

87.00 ± 1.73

F22

26.91

6

10

10

2.75

55.66

1.1132

20.84 ± 1.16

137.33 ± 4.72

F23

26.91

10

10

10

5

61.91

1.2382

36.70 ± 4.86

82.00 ± 1.00

F24

26.91

6

10

0

5

47.91

0.9582

30.22 ± 2.85

92.00 ± 4.00

F25

26.91

10

10

0

2.75

49.66

0.9932

20.05 ± 2.08

48.33 ± 2.52

F26

26.91

6

20

10

0.5

63.41

1.2682

5.89 ± 0.92

76.67 ± 4.93

F27

26.91

6

0

10

0.5

43.41

0.8682

22.47 ± 11.05

92.00 ± 3.00

Counter plots

These plots are used to show the relationship between three variables. In contour plots three-dimensional relationship is plotted in two dimensions with the axis Y, X (as a Predictor) and response is shown as contour (like topographic maps). In these plots Hold Values are variables that have not been studied and have been consistently defined. The shaded area is called the constraint region and these areas in each of the graph indicate the range of prepared formulations [27, 41, 46].

Clearly it can be seen that in the lower ranges of AcDiSol and lactose (0-2g), flowability was very good and falling in the range of less than 12 seconds. With a little increase in the values ​​of these excipients until 3-5g respectively, flow time reaches in the range of 12-15 sec. Also with increasing in the amount of AcDiSol and lactose, flow time increases, which it is not desirable. According to these results respected to Aerosil and avicel, amount of these excipients should be less.

With a constant amount of lactose and Aerosil, to reach to the formulation of appropriate and acceptable quality flowability (less than 12 or 12-15sec) amount of used AcDiSol should be much lower, and should be about 3 g. In the designed formulations, levels of Avicel were considered as 0, 10 and 20g which in the most selective and optimized formulations amount of Avicel is 10 g.

Generally it can conclude that because of the chemical structure and specific features of AcDiSol, at lower values, flow time reduced. Thus appropriate flowability is going along with low (2-6g) amount of AcDiSol in selective formulations.

As flowability, these figures show that, desired hardness is in the case of low values of ​​AcDiSol (0-3.5g) and also if Aerosil and AcDiSol are constant, achieving to higher range of hardness, is correspond to using larger amounts of lactose (Figure 1).

.

Figure 1. Counter plot of mean flowability (top) and hardness (below) for prepared formulations with constant amount of some variables

Overlaid Contour Plot

In this type of plots, with defining desire conditions, white area in these plots shows the formulations proportionate with defined conditions. Top plots in Figure 2 are related to flowability and samples of suggested formulations. Below plots are corresponding plots for hardness.

Figure 2. Overlaid Contour Plots with defined conditions associated with flowability (top) and hardness (below) for samples of the proposed formulations

Considering to the flowability results, while the average flow time is between 10 to20sec, the optimum formulation is formulation which the amount of lactose is less than 12 g and the amount of AcDiSol is less than 5 g. Also if the amount of AcDiSol is greater than 8, lactose can be used with any value from 0 to 20g.

Also, these plots show that when the amount of AcDiSol is between 2 to4 and 2 to 8 respectively, the amount of applied Avicel and Aerosil should be considered in the range of 0-10 g and 0.5-35g respectively. According to the designed formulations and the results in tables 2 it can be concluded that the formulations F1 and F3 are optimized. Achieve to the desired hardness range between 140-100 Newton, when it is possible that, the amount of used AcDiSol is between 3.5 to 7.5g and the amount of lactose is between 5 to 17.5g. From the Hold Value conclouded that for optimization of formulation the amount of Avicel (10g) and Aerosil (2.75) should be fixed. Therefore, these results confirm previous results and show that the optimal formulations are F1, F3, F21 and F22.

Optimization plots

In these plots with defining the optimal conditions and used amounts of formulation components, the acceptable range for each of the components was suggested to obtain optimal formulations. In these plots composite desirability value (d) should be close to 1.Above plot in Figure 3 is related to flowability with optimized condition for powders and below plot is related to hardness of tablets with optimized situation. One of the proposed optimized formulations are shown in Figure 3 is consistent with the formulation of 22.

Figure 3. Optimization plot of formulation 22 for flowability (top) and hardness (below)

Dissolution test

Seven formulations which had good flowability (10-20 sec) and hardness (100-140 Newton) were chosen for dissolution test and were compared with reference formulation. Comparative release curves are illustrated in Figure 4. Similar and difference factors were calculated and illustrated in Table 3. It is apparent that release profiles of chosen formulations are similar with each other but their release profiles are different from reference formulation. It is verified with the results of difference and similarly factors which show the difference in formulation. Optimized formulations should release high percent of drug in a few times after putting in phosphate buffer medium but should not release any drug in acidic medium which included F1, F3, F11, F19 and F21. From coating formulations, solution 1 due to have high percent of propylene glycol swelled and was a little soft and some of drug, released in acidic medium. Solution 3 was sticky and coat was not uniform. Although the process was wary rapid but due to the existing of isopropyl alcohol it is harmful for operator. Solution 4 has more talc and due to this, coat was not uniform and some of drug was released in acidic medium too. Solution 2 not only had desirable characteristics in coating process, but also didn't dissolved in acidic medium and drug could released most of drug during 15-20 min in phosphate buffer medium with pH=7.5, therefore was chosen as desired coating solution.

Table 3. Difference and similarity factors for chosen formulations

Formulation code

Difference factor (F1)

Similarity factor (F2)

F1

41.31

24.10

F3

44.81

24.00

F5

37.05

28.10

F10

31.39

31.43

F11

40.75

25.30

F21

37.91

26.90

F22

39.92

24.87

Figure 4. Comparative dissolution curve of reference and seven chosen formulation

4. Conclusions

RSM is a widely practiced approach in the development and optimization of drug delivery devices. This technique requires minimum experimentation and time, thus to be more cost-effective than the conventional methods of formulating dosage forms. The flow time, hardness value and in vitro dissolution release profile indicate that response variables of the formulation are optimized by RSM in conjunction with central composite rotatable design. Good correlation between the predicted values and experimental data of the optimized formulation validated ability of RSM in optimizing enteric coated tablets of DVPX. One of the proposed optimized formulations is consistent with the formulation of 22. Considering to lack of enteric coated tablet of DVPX in Iran market, the optimization of formulation for enteric coated tablets of DVPX, a powder with a well-known bad flowability by direct compression and experimental design could be very beneficial and cost effective process.

Writing Services

Essay Writing
Service

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing
Service

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision
Service

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.