INTRODUCTION:

Drugs from BCS class 2 having poor solubility in water and less dissolution profile¹. Due to which, therapeutic effect is not achieved in the body that leads to inadequate therapy. To enhance dissolution profile of drug several solubility enhancement methods are in practice.^2,3 Spherical agglomeration is one of the proven technique adopted to increase the solubility and dissolution rate of poorly soluble drug. Spherical agglomeration process improve the flowability and compressibility of drug.⁴

Spherical agglomeration is multiple unit process in which crystallization, agglomeration and spheronization can be carried out simultaneously.⁵ Formulated crystals can be called as spherical agglomerates. Spherical crystallization technique has been successfully utilized for improving of flowability and compressibility of drug. These technique may enable crystalline forms of a drug to be converted into different polymeric form having better bioavailability.⁶

Spherical agglomeration is a novel particle design method developed by Kawashima et.al. It is also come under particle engineering technique in which crystallization and agglomeration carried out simultaneously.⁷ Many of the drugs administered by oral route because oral route administration is most convenient route for solid dosage forms. The basic requirement for commercial production of tablet is a particulate solid with good flowability, mechanical strength and compressibility.⁸ Hence is necessary to evaluate and manipulate the above said properties. To impart these properties the drugs are subjected to particle design techniques, spherical crystallization is one the techniques of particle design. Formulated agglomerates will improve the flowability and compressibility of drug which enables the direct tabletting of drug. It minimize the process in tabletting like mixing, granulation, drying and sieving etc. There are main four principle steps involved in the process of spherical crystallization like - 1) flocculation zone, 2) zero growth zone, 3) fast growth zone, 4) constant size zone.^{9, 10} Direct tabletting is preferred process for spherical agglomerates. It will minimize the cost of production and save time as compared to granule tabletting.

There are different methods of preparation of spherical agglomerates like

1) Solvent change method

2) Quasi emulsion solvent diffusion method

3) Ammonia diffusion method

4) Neutralization method

5) Traditional crystallization process

6) Crystallo-co-agglomeration

A saturated solution of drug in a good solvent is poured is bad solvent. The good solvent and poor solvent are freely miscible in each other.¹¹ In these method a third solvent bridging liquid is added in above mixture in small amount to induce and promote the formation of agglomerates. Depending upon the addition of amount of bridging liquid and speed of rotation size of agglomerates varying. There are different two type of factors will depend upon the size of the agglomerates one is rotation speed and another is amount bridging liquid. If speed of rotation in the formulation is increased then small size of agglomerates will formed and if speed will less particle size will increased.^10,11 Also if less amount of bridging liquid is added in the mixture then large size particle are formed and if more amount of bridging liquid is added then small size particle will be formed. It is always necessary to maintain the ternary phase diagram ratio at the time of addition of three solvents.

MATERIALS AND METHODS:

Candesartan cilexetil was obtained as a gift sample from Lupin Pharmaceuticals, Aurangabad. Polyvinyl-Pyrrolidone K-30, dichloromethane and methanol were procured was obtained from Research-Lab Fine Chemicals, Mumbai.

Preparation of spherical agglomerates of Candesartan cilexetil

Physical mixture of Candesartan cilexetil is prepared by dissolving 1 gm of drug in 50 ml of methanol then respective amount of PVP-K30 (as per batch) is been dissolved in 40 ml of water then first solution is poured in polymeric mixture then precipitate is formed. Then this solution is kept for stirring on mechanical stirrer for 1 hr. (as per respective rpm) at that time simultaneously 10 ml of dichloromethane (Bridging liquid) is added dropwise. It will start to form spherical agglomerates after 1 hr filter the solution and dry at room temperature for 24 hrs.

Table no. 1. Preparation of batches of spherical agglomerates

Sr. no.	Batch no.	Candesartan cilexetil (gm)	PVP-K30 (gm)	Speed (rpm)	Drug : polymer
1	B1	1	3	600	1:3
2	B2	1	1	600	1:1
3	B3	1	3	400	1:3
4	B4	1	1	400	1:1

Experimental design for the preparation of Spherical Agglomerates

In the present work, 2² factorial design (table no. 2) was used to optimize the batch. A two factor and two levels full factorial design was used and four experimental runs were performed. Two dependent and independent factors were selected. Two independent parameters Polyvinylpyrrolidone (X1) and speed (X2) were selected and particle size (Y1) and drug release (Y2) were dependent parameters selected.

Table No.2: Design layout for 2² factorial designs.

Batch no.	Coded value		Actual value
Batch no.	X1	X2	Polyvinylpyrrolidone	Speed
F1	+1	+1	3	600
F2	-1	+1	1	600
F3	+1	-1	3	400
F4	-1	-1	1	400

a. Determination of λ max

Stock solution of 100µg/ml was prepared by adding 10 mg of pure Candesartan cilexetil in 100 ml of solvent methanol. Then 1ml of stock solution was diluted to 10 ml of methanol to make 10µg/ml solution. Then this solution was filtered and scanned in UV spectrum. The scanning range was 200-400nm. The maximum absorbance was recorded.

b. Percentage practical yield

Percentage practical yields were calculated to know about percent yield or efficiency of the method, thus it helps in selection of appropriate method of production. Prepared particles were collected and weighed to determine practical yield (PY) from the following equation

Practical yield

Practical yield (%) = -----------------------X 100

Theoretical yield

c. Determination of % drug content

Spherical agglomerates equivalent to 32 mg of Candesartan cilexetil were weighed accurately and dissolved in suitable quantity of solvent mixture methanol. The drug content was determined at 217 nm by UV spectrophotometer. Each sample analyzed in triplicate. The percent drug content was determined using the following equation:

Practical Drug content

% Drug content =-------------------------------X 100

Theoretical Drug content

d. Fourier transform infrared spectroscopy (FTIR):

FTIR has been used to assess the interaction between drug and carrier molecules in the solid state. Infrared spectra of agglomerated powder were obtained using FTIR spectrometer (FTIR Jasco 4100). About 2-4 mg of moisture free agglomerated sample was mixed with dry potassium bromide and FTIR spectra were obtained by KBr pellet method. The scanning range was 400-4000 cm-1.

e. Powder X-ray diffraction :

To evaluate the crystallinity of Candesartan cilexetil the PXRD study was carried out by using X ray diffractometer. Powder X-ray diffraction patterns were recorded on Brucker D2 Phaser X-diffractometer.

f. Scanning Electron Microscopy (SEM):

SEM of Spherical agglomerates was carried out using JSM 6360, JEOL India Pvt. Ltd. to study the morphological characteristics of the optimized batch of agglomerates.

g. In-vitro dissolution studies of Prepared Spherical Agglomerates:

In-vitro dissolution studies of Spherical agglomerates of Candesartan cilexetil were carried out for 60 minutes using USP Dissolution test apparatus type II (Lab India DS8000, eight stages) at 50 rpm. Spherical agglomerates equivalent to 32 mg of Candesartan cilexetil was used for dissolution studies at 37±0.5°C in 900ml of pH 6.8 buffers as dissolution medium. Aliquots equal to 5 ml was withdrawn at regular time intervals (10, 20, 30, 40, 50, 60 mins), an equal volume of fresh dissolution medium was replaced to maintain the sink condition and aliquots were measured at 257 nm UV/Visible spectrophotometer. The dissolution studies were conducted in triplicate and the mean values were plotted versus time.⁴

RESULT AND DISCUSSION;

a. Organoleptic properties

All test for Organoleptic properties containing color, odor, taste, state, solubility are complied with the Indian pharmacopeia. The melting point of pure drug Candesartan cilexetil was found in the standard range as per Indian pharmacopeia.

b. Determination of λ max of Candesartan cilexetil

The standard solution of Candesartan cilexetil of concentration 10µg/ml showed maximum absorbance at the wavelength 217 nm.fig 1. Shows λ max of Candesartan cilexetil.⁵

Fig no.1. λ max of Candesartan cilexetil

c. Percentage practical yield

The result of percent practical yield studies are shown in table.3. The percent practical yield of the prepared spherical agglomerates by solvent change method is noted. It was found that solvent change method gives the practical yield in the range of 45 – 71%. The maximum yield was found 71.20% in batch B4 Batch.

Table no. 3. Percentage practical yield of spherical agglomerates

Sr. no.	Batch code	Percentage yield (%)
1	B1	45.55%
2	B2	65.41%
3	B3	41.87%
4	B4	71.20%

d. Determination of % drug content

The drug content in spherical agglomerates by solvent change method was found to be maximum. It is shown in table no.4. It was found to be in the range of 60% - 85%. It was suggesting that solvent change method has good encapsulation of the drug.

Table no. 4. Drug content of spherical agglomerates

Sr. no.	Batch code	% Drug content
1	B1	69.23
2	B2	75.56
3	B3	64.35
4	B4	85.11

e. FTIR spectra of Candesartan cilexetil

The IR spectra of Candesartan cilexetil shows broad peak at 2866.67 cm^-1 and 2938.98 cm^-1. It belongs to the valance vibration of the C-H bonds in the CH and CH₂ groups. It shows broad peak at 1753.94 cm^-1 it belongs to the C-O str of carboxylic acid. Spectra of Candesartan cilexetil shows some peaks at 1611.23 cm^-1 and 1472.32 cm^-1 it shows presence of aromatic ring containing C-C str bonding. Some of the peaks are visualized at 1345 cm^-1 to 1238 cm^-1 it indicates that presence of carboxylic acid esters and ethers with C-O str bonding. Last peak is visualized at 1075.12 cm^-1 it belongs to the primary and secondary amine. Fig.2. shows FTIR spectra of Candesartan cilexetil in the range of 4000 cm^-1 to 400 cm^-1.

Fig. 2. FTIR spectra of Candesartan cilexetil

The IR spectra of PVP-K30 (Fig. No.3.) shows 2857.02 cm^–1 (C-H stretching vibrations), 1609.31cm^–1 (C = O Carbonyl stretching), and 1238.08 cm^–1 (C-N stretching vibrations).

The results revealed no considerable changes in the IR peaks of Candesartan cilexetil, when mixed with polymer PVP-K30. These observations indicated the compatibility of PVPK30 with Candesartan cilexetil. The FTIR spectrum of PVP-30 and Candesartan cilexetil is in Fig. No.3. IR spectra indicated no well-defined interaction between the drug and polymer.

Fig.3. FTIR spectra of Candesartan cilexetil and PVP– k30

f. Powder X- ray diffraction study ( XRD )

The presence of numerous distinct less diffused peaks in the X-Ray diffraction spectrum indicates that Candesartan cilexetil present as a crystalline material. Sharper diffraction peaks indicate more crystallize the drug. The powder XRD of Candesartan cilexetil is shown in Fig.no.4.

Fig. no.4. XRD graph of Candesartan cilexetil

g. Scanning electron microscopy (SEM)

The optimized batch of spherical agglomerates of B1 to B4 were analyzed under optical microscopy. It shows spherical shaped agglomerates having good crystallinity as well as round and ball like shape. The smallest particle visualized under SEM was near about size 201.69µm and the largest particle size was 445.23 µm. fig no.5,6,7,8. Indicates that images of spherical agglomerated batch B1 to B4 respectively.

Fig no.5. SA batch B1

Fig no.6. SA batch B2

Fig no.7. SA batch B3

Fig no.8. SA batch B4

CONCLUSION:

Due to the poor water solubility of Candesartan cilexetil it exhibited only 20.45% dissolution rate in the 50 min. But as comparing the prepared batches of spherical agglomerates it shows increased dissolution rate as compared to the pure drug. Due to the incorporation of hydrophilic polymer all batches shows enhanced dissolution rate as well as solubility.

From these above data it was found that batch B2 gives highest % cumulative drug release i.e.73.12%. That’s why Batch B2 containing spherical agglomerates is considered as optimized batch, because of high dissolution rate as compared to the other batches.

As the particle size small dissolution will be greater and if particle size is large dissolution require more time. Also there is a large effect on the addition amount of bridging liquid in the mixture. Rotation Speed in the process is also having great effect on the size of the particle. High speed process produces small sized particles or agglomerates which is having better dissolution result which is shown in batch B4.

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Received on 08.07.2016 Accepted on 22.08.2016

Asian J. Pharm. Tech. 2016; 6(4): 217-222.

DOI: 10.5958/2231-5713.2016.00032.5

Sr. no.	Time (mins)	Pure drug	% Cumulative drug release
Sr. no.	Time (mins)	Pure drug	B1	B2	B3	B4	B5
1	0	0.00±0.00	0.00±0.00	0.00±0.00	0.00±0.00	0.00±0.00	0.00±0.00
2	10	3.54±0.001	12.65±0.02	18.28±0.02	6.3±0.061	12.65±0.04	15.21±0.01
3	20	7.65±0.021	20.39±0.01	23.90±0.03	14.76±0.08	29.53±0.03	24.65±0.03
4	30	11.24±0.4	30.23±0.04	52.30±0.05	24.60±0.04	46.40±0.02	34.35±0.04
5	40	16.80±0.21	35.85±0.02	64.68±0.04	31.64±0.03	50.64±0.04	39.87±0.02
6	50	20.54±0.101	55.54±0.03	73.12±0.01	35.15±0.02	70.31±0.02	43.50±0.01