INTRODUCTION:

In pharmaceutical dosage form development, the nature of drug like amorphous or crystalline plays a very important role in solubility, stability, dissolution, bioavailability etc. Many advantages of amorphous state of drug over crystalline state such as higher solubility, dissolution rate and bioavailability¹. Therapeutic effectiveness of a drug depends upon the bioavailability and ultimately upon the solubility of drug molecules. Mirabegron is a class of beta-3 adrenergic agonist and used to treat overactive bladder diseases. BCS class of mirabegron is class-II i. e. low soluble and high permeable, because of its poor aqueous solubility it is necessary to administered with higher doses ultimately it increases dosing frequency and therefore it may occur side effects. Hence an attempt is made to improve the solubility of mirabegron by fluidized bed processing solid dispersion technique^2,3.

MATERIALS AND METHODS:

Mirabegron was obtained as a gift sample from Dr. Reddy’s Lab. India, polyvinyl pyrrolidone K-30, polyethylene glycol- 6000, poloxamer-188 was procured from Balaji Drugs, Ahmedabad, India. All other chemical used in the study were of analytical grades.

Saturation Solubility Determination:

Saturation solubility of mirabegron and its solid dispersion were determined in distilled water. An excess amount of drug and solid dispersion were added in 10 ml of distilled water^18,19. The mixture was stirred in shaker for 24 hours, after saturation level dispersion was filtered and subjected to determination of concentration of mirabegron spectrophotometrically at 251nm^4,5.

Preparation of Solid Dispersion:

Mirabegron and different carrier (PVP K-30, PEG-6000, Poloxamer-188), BHT in various ratios (1:1, 1:2, 1:3 w/w) were mixed in methanol under continuous stirring¹⁴, these preparations were subjected for spraying on substrate i. e. anhydrous lactose in fluidized bed processor (ACG Miniquest F). the processing variables of FBP as shown in table 1. The mixture was granulated and the mass was dried till desired LOD is achieved⁴. The granules were sifted and further processed into a suitable formulation^4,5,6.

Table 2. Formulation of Solid Dispersion by FBP

Ingredients	Formulations
Ingredients	MS1	MS2	MS3	MS4	MS5	MS6	MS7	MS8	MS9
Mirabegron	50	50	50	50	50	50	50	50	50
PVP K30	50	100	150	-	-	-	-	-	-
PEG 6000	-	-	-	50	100	150	-	-	-
Poloxamer- 188	-	-	-	-	-	-	50	100	150

All above quantity in mg

Characterization of Powder Blend:

The flow properties of FBP- solid dispersion for various batches MS1 to MS9 were determined by angle of repose, carr’s index, Hausner’s ration, bulk density and tapped density⁷.

Design of Experiments:

For the optimization of mirabegron FBP solid dispersion Box-Behnken design were employed using State-Ease Design Expert 8.0.1 software. Total 17 experiments were designed by considering 3 independent variables i. e. Poloxamers 188, BHT and EC at two levels and effect was studied on one response i. e. drug content and drug release^4,8,9.

Table 3. Factors and levels for Box-Behnken design

Sr. No.	Independent Factors	Unit	Low level (-1)	High level (+1)
1	Poloxamer- 188	Mg	75	100
2	BHT	Mg	0.5	1
3	Ethyl cellulose	Mg	5	10

The level of all independent variables to be selected based on preliminary trials

In vitro Drug Release Study:

In vitro drug release study of mirabegron and FBP solid dispersion were performed using USP dissolution tester (Electrolab TDT 08 L, India) type-I basket apparatus in 900 ml phosphate buffer pH 6.8 maintained at 37 ±0.5 ℃ at 100 rpm. Samples were collected at specific intervals (1h, 2h, 3h, 5h, 7h, 9h,12 h & 24 h) and analysed at max 251 nm using UV visible spectrophotometer (Lab India 3000)^4,10,11.

RESULT AND DISCUSSION:

Saturation Solubility Determination:

Saturation solubility studies of pure mirabegron and its solid dispersion with poloxamer, PEG and PVP K-30 were performed in distilled water. Maximum enhancement of solubility of mirabegron in water was obtained for solid dispersion MS9 by fluidized bed processing as shown in fig.1. Therefore, MS9 batch was selected for further formulation studies.

Fig 1. Saturation solubility of pure mirabegron and its solid dispersion with different polymers at various weight ratios (MS1 to MS9)

Characterization of Powder Blend:

Uniform flow of the powder is necessary during production of tablets. All formulation were evaluated for different powder properties. The result is shown in table 4. All formulation of solid dispersion showed good flowability¹². Angle of repose varied from 18.65 to 23.15^o, bulk density from 0.525 to 0.597gm/cm^3,carrs index from 9.26 to 15.49 %.

Table 4. Evaluation of physical properties of powder blend

Batches	Angle of repose (ѳ)	Bulk Density (gm/cm³)	Tapped Density (gm/cm³)	Compressibility index (%)	Hausner’s Ratio
MS1	18.65±0.47	0.525	0.615	14.63	1.17
MS2	21.22±0.22	0.543	0.618	12.13	1.13
MS3	22.15±0.65	0.565	0.635	11.02	1.12
MS4	20.19±0.47	0.597	0.675	11.55	1.13
MS5	21.20±0.89	0.548	0.629	12.87	1.14
MS6	22.45±0.45	0.567	0.671	15.49	1.18
MS7	23.15±0.37	0.597	0.685	12.84	1.14
MS8	21.18±0.68	0.588	0.675	12.88	1.14
MS9	20.20±0.85	0.578	0.637	9.26	1.10

Table 5. Experimental design for Box-Behnken

Run	Independent variables			Dependent variables
Run	X1- Poloxamer-188	X2- BHT	X3- EC	Drug Content (%)	Drug release
1	100	0.50	15	97.12	96.23
2	87.50	7.75	15	98.56	97.36
3	75	0.50	15	97.36	96.56
4	87.50	7.75	15	98.13	95.69
5	100	7.75	20	98.12	93.78
6	87.50	15	10	99.33	99.45
7	87.50	7.75	15	98.36	95.96
8	87.50	15	20	99.50	94.69
9	87.50	7.75	15	98.78	95.74
10	75	7.75	10	98.32	99.32
11	100	7.75	10	98.74	99.25
12	87.50	7.75	15	98.36	95.41
13	87.50	0.50	20	97.45	93.65
14	75	15	15	99.48	95.36
15	87.50	0.50	10	97.46	99.47
16	100	15	15	99.15	94.78
17	75	7.75	20	98.29	93.56

Table 6. Experimental model for drug content and drug release responses

Response model	Sum of squares	Df	Mean square	F value	P value	R2	CV %	Adeq. Precision
Drug Content (%)	8.18	3	2.73	63.13	<0.0001	0.9338	0.21	20.884
Drug release	59.86	3	19.95	35.32	<0.0001	0.8907	0.78	16.072

Design of Experiments:

Box-Behnken design was constructed where the Poloxamer-188 (X1), BHT (X2) and Ethyl cellulose (X3) were selected as the independent variables. The levels of these variables were fixed on the basis of initial studies and observations¹³.

Full Model for Response Y1 (Drug Content):

Drug content = +98.38 – 0.040*X1 + 1.01*X2 – 0.061* X3. It was observed that the independent variables viz. X1 (Poloxamer- 188), X3 (ethyl cellulose) had a negative effect on drug content, but X2 (BHT) has positive effect as shown in fig.2.

Fig. 2. Effect of independent variables on drug content a. counter plot b. 3D surface plot

Full Model for Response Y2 (Drug Release):

Drug release = +96.25 – 0.095*X1 – 0.20*X2-2.73*X3. It was observed that the independent variables viz. X1 (Poloxamer- 188), X3 (ethyl cellulose) and X2 (BHT) had a negative effect on drug release, as shown in fig.3.

Fig. 3. Effect of independent variables on drug release a. counter plot b. 3D surface plot

3D Response Surface Plot:

Effect of poloxamer, BHT and EC on drug content and drug release of mirabegron showed in fig. 2. 3D response surface plot confirmed. From the figure of the response curve of Y1 (Drug content), it is observed that as concentration of poloxamer increases from -1(75) to +1 (100) and EC increases from -1(5) to +1 (10) drug content decreases significantly on the other hand concentration of BHT increases from -1 (0.5) to +1(1) drug content increases significantly, as shown in fig.2 response curve of Y2 (Drug release), it is observed that as concentration of poloxamer increases from -1(75) to +1 (100), EC increases from -1(5) to +1 (10) and BHT increases from -1 (0.5) to +1(1) drug relase decreases significantly, as shown in fig.3 statistical model predicted run number 6 as an optimized formulation. Three experimental trials of run 6 were performed to validate the predicted batch. The study exhibited the results of responses i. e. drug content 99.33 % and in vitro drug release 99.45 % of optimized batch^13,14,15.

In Vitro Drug Release Study:

In vitro drug release profile of mirabegron solid dispersion was compared with extended release mirabegron solid dispersion as shown in fig.4 mirabegron solid dispersion with poloxamer (MS9) and ER mirabegron SD (Run 6) were analysed for evaluating their dissolution rates^12,16,17. All samples were individually transferred in dissolution tester containing 900 ml phosphate buffer pH 6.8 at 37℃. The percent cumulative drug release of mirabegron SD (MS9) and ER Mirabegron SD (Run 6) was found to be 99.18% and 99.45% respectively. MS9 exhibited 99.18 % drug release indicated immediate release and Run 6 exhibited 99.45% drug release at 24 h indicates the addition of EC significantly extend the release of mirabegron^18,19,20.

Fig. 4. In vitro drug release from solid dispersion prepared by using Poloxamer (MS9) and ER solid dispersion prepared by using EC (Run 6)

CONCLUSION:

The solid dispersions of mirabegron with Poloxamer-188, PEG-6000 & PVP-K30 have been prepared in different weight ratios by fluidized bed processing. Saturation solubility studies showed a significant solubilizing effect of polymers on mirabegron. In the present study, mirabegron solid dispersion with poloxamer was developed which showed 198.48μg/ml solubility in water. Extended-release profile of mirabegron was obtained by addition of EC by the application of Box-Behnken optimization design. It is now possible to increase the solubility of poorly water-soluble drugs with the help of fluidized bed processing.

LIST OF ABBREVIATIONS:

FBP Fluidized Bed Processing

PEG-6000 Polyethylene Glycol-6000

EC Ethyl Cellulose

PVP K-30 Polyvinyl Pyrrolidone K-30

SD Solid Dispersion

ER Extended Release

BHT Butylated hydroxytoluene

DOE Design of Experimentation

ACKNOWLEDGEMENT:

The authors are thankful to Y. B. Chavan college of pharmacy, Aurangabad, Loknete Dr. J. D. Pawar College of Pharmacy, Kalwan, Nashik for providing facilities to carry out the research work.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 24.02.2021 Modified on 06.05.2021

Research J. Pharm.and Tech 2022; 15(4):1472-1476.

DOI: 10.52711/0974-360X.2022.00244

Parameter	Values
Spray rate (RPM)	2.75
Inlet Temperature (℃)	55
Product Temperature (℃)	40
Atomization air Pressure (MPa)	2.25
Air flow control (MPa)	1.8