INTRODUCTION:

Solubility and dissolution of drugs is a crucial prerequisite to the performance of the drug in vivo. The major share (90%) of the active pharmaceutical ingredients in the development pipeline and 40 % of the drugs in the market are poorly water soluble. Hence, solubility is still an important area of the research.^1,2. According to the Noyes-Whitney equation, the dissolution rate of a drug substance is directly proportional to its equilibrium solubility.³ However, the nature of the dissolving solid and the dissolution medium also exert strong influences on the dissolution rate.⁴ Various physical, chemical and miscellaneous approaches have been used to enhance the solubility and dissolution of the poorly water soluble drugs.^5,6

However, solid dispersion or complexation is still preferred technique to improve solubility due to its obvious advantages. The term solid dispersion refers to a drug-polymer two component system generally consisting of a hydrophilic matrix and a hydrophobic drug prepared by hot melt extrusion, melting (fusion) method or solvent evaporation method.^7,8Usage of solubilizing complexing agent can solve the poor aqueous solubility problem by forming guest (non polar region of one molecule) - host (cavity of another molecule) complexes.^9,10Small molecules or larger molecules can be taken up by supramolecular cyclic structures. This inclusion complex is possible because of the central cavity in their structure and these so formed cyclic molecules have been explored as drug delivery systems.¹¹Etodolac is a nonsteroidal anti-inflammatory agent and inhibitor of prostaglandin synthetase. Etodolac is absorbed from the gastro-intestinal tract with peak plasma concentrations being attained about 1-2 h after ingestion. Etodolac is poorly water soluble, and slightly soluble in simulated gastric fluid. The delayed onset of action is the result of limited dissolution rate due to poor solubility therefore its bioavailability is expected to be limited by its dissolution rate, which could be increased using solid dispersion and complexation technique.^12,13

MATERIALS:

Etodolac was obtained as gift sample from the IPCA Laboratories Ltd. Mumbai. All other ingredients were of analytical grade. Distilled water was used throughout the study.

METHODS:

Solubility Study:

Saturated solution of Etodolac was prepared in 10ml of distilled water and sonicated by using bath sonicator for two to three cycles with one cycle runned for the minimum duration of 15 min. The solution is then filtered and 1ml of clear solution is diluted upto 100 ml of distilled water. Solution so obtained was scanned using UV Vis spectrophotometer at 276nm by using distillled water as blank. The amount of drug solubilised is calculated by putting the value in calibartion curve equation.^14,15

Solubility Enhancement:

Solid dispersion and complexes can be prepared using a variety of carriers.¹⁶ The carriers used include PEG-6000, HPMC K4M, β - Cyclodextrin and PVPK-30. Fusion Method and Kneading method^17,18,19 were employed for the preparation of mixtures having drug: carrier in the 1:1, 1:2, 1:3 proportions.

Fusion Method:

Solid dispersions were prepared by melting the weighed amount of different carriers separately in a glazed porcelain evaporating dish on an electric heating mantle. The carrier was heated to a temperature just sufficient to melt it completely. Following the addition of drug to carrier melt the mixture was then cooled and solidified rapidly in an ice bath under rigorous stirring. The final solid mass was crushed, pulverized and sieved at room temperature and stored in desiccators at room temperature until further use.

The dispersions were made in different ratios with respect to drug and polymers as shown below in Table 1

Kneading Method:

This method is based on impregnating the carrier with little amount of water or hydro alcoholic solutions to convert into a paste. Kneading mixture was prepared by adding the drug to above paste followed by kneading over specified period of time.The kneaded mixture was then dried in oven at 40˚C and then pulverized and screened through sieve no 44. The resulting solid dispersions was then stored in dessicator until further use.

The complexes were made in different ratios with respect to drug and polymers as shown below in Table 2

Table No. 1 Formulation table of Solid dispersions

Formulation code	Drug (mg)	Polymer (mg)		Drug: Polymer	Method used
Formulation code	Drug (mg)	PEG 6000	HPMC K4M	Drug: Polymer	Method used
ES 1	500	500	---	1:1	Physical Mixture
ES 2	500	1000	---	1:2	Physical Mixture
ES 3	500	1500	---	1:3	Physical Mixture
ES 4	500	500	---	1:1	Fusion method
ES 5	500	1000	---	1:2	Fusion method
ES 6	500	1500	---	1:3	Fusion method
ES 7	500	---	500	1:1	Physical Mixture
ES 8	500	---	1000	1:2	Physical Mixture
ES 9	500	---	1500	1:3	Physical Mixture
ES 10	500	---	500	1:1	Fusion method
ES 11	500	---	1000	1:2	Fusion method
ES 12	500	---	1500	1:3	Fusion method

Table No 2 Formulation table of Complex

Formulation code	Drug (mg)	Polymer (mg)		Drug: Polymer	Method used
Formulation code	Drug (mg)	β-Cyclodextrin	PVPK-30	Drug: Polymer	Method used
EC 1	500	500	---	1:1	Physical Mixture
EC 2	500	1000	---	1:2	Physical Mixture
EC 3	500	1500	---	1:3	Physical Mixture
EC 4	500	500	---	1:1	Kneading method
EC 5	500	1000	---	1:2	Kneading method
EC 6	500	1500	---	1:3	Kneading method
EC 7	500	---	500	1:1	Physical Mixture
EC 8	500	---	1000	1:2	Physical Mixture
EC 9	500	---	1500	1:3	Physical Mixture
EC 10	500	---	500	1:1	Kneading method
EC 11	500	---	1000	1:2	Kneading method
EC 12	500	---	1500	1:3	Kneading method

Characterization of drug and formulation^20-24:

UV- Vis Scan of Drug Etodolac:

10 mg Etodolac was accurately weighed and transferred individually to 100ml volumetric flask containing methanol and 0.1 N HCl to produce 100ppm stock solution each. The working standard solutions of strength 2, 4, 6, 8 and 10ppm concentration were prepared by suitable dilution. The working standard solutions so prepared were analyzed by UV spectrophotometer at λ_max 276nm. Methanol was used as blank during spectrophotometric analysis. The standard calibration curve was obtained by plotting absorbance Vs concentration. The analytical concentration range concentration range was chosen over which the drug obeyed Beer- Lambert’s law.

Percent Production Yield:

The production yield of solid dispersions and complex of various combinations was calculated using the weight of final product after drying with respect to the initial total weight of the drug and carrier used in solid dispersion. Percent production yields were calculated as per the formula mentioned below,

P_Y= W_O/ W_T × 100

P_Y: Product yield; W_O: Practical mass (solid dispersions); W_T: Theoretical mass (carrier + drug).

Drug Content:

About 5mg drug equivalents of solid dispersions were accurately weighed and poured into 50ml volumetric flask containing 20ml methanol. The mixture is then sonicated for 15 min. Final volume was adjusted with methanol. From this stock solution (100µg/ml), 1ml was withdrawn and further diluted up to 10ml with methanol. This solution was used for the assay for drug content by UV spectrophotometer at 276nm. Concentration of drug in stock solution was calculated by using calibration curve and from which percent drug content in blend was calculated,

Percent Drug Content = W_A/W_T × 100

W_A: actual drug content; W_T: theoretical drug content.

Differential Scanning Calorimetry:

DSC analysis of drug and formulation was performed using Shimadzu- Thermal Analyzer DSC 60

Solubility study:

Saturation solubility studies were carried out for all solid dispersions and complexes prepared. This study was the basic criteria to identify and judge a formulation of choice, which would enhance the solubility and so, would show good results in In-vitro dissolution studies. The following procedure remains same for the drug and their formulations. Solubility studies were carried out in glass vials. In each of these vials, 10ml distilled water was added. An excess quantity of mixture was added into each vial. These vials were shaken continuously for 24 hours on a lab shaker and the resulting solutions were filtered, appropriate dilutions were made and UV absorbance was recorded at 276nm.

In- vitro drug release/ Dissolution studies:

The simple compressible tablets were prepared by using blend with equivalent to 200mg of Etodolac and other conventional excipients. In vitro dissolution study was carried out using USP dissolution type II apparatus. The dissolution vessels contained 900ml of 0.1 N HCl maintained at 37°C±1°C and paddle speed set at 50 rpm. Solid dispersion was added to the dissolution medium in a powder form. Then, 5ml samples were withdrawn at 10, 20, 30, 40, 50 and 60 min from the dissolution medium through a graduated pipette. The withdrawn sample was replaced with 5ml of fresh media. The withdrawn samples were analyzed for drug content by measuring the absorbance at 276nm using UV-visible spectrophotometer.

RESULTS AND DISCUSSION:

The solid dispersion and complex of Etodolac were prepared in different stoichiometric ratio by using various carriers. The various parameters used for characterization and evaluation are discussed below.

UV- Vis Scan of Etodolac:

The UV Visible scan of Etodolac shows maximum absorbance at 276 nm and 226nm in methanol and 0.1 N HCl respectively.

Figure No. 1: UV spectra of Etodolac in methanol

Table No 3 Percent production yield and Percent Drug Content

Formulation code	Production Yield (%)	Drug content (%)	Formulation code	Production Yield (%)	Drug content (%)
ES 1	64.49 ± 1.46	98.4 ± 0.23	EC 1	70.94 ± 0.6	98.9 ± 0.23
ES 2	72.23 ± 0.85	92.3 ± 0.17	EC 2	74.32 ± 0.45	93.2 ± 0.5
ES 3	74.84 ± 1.98	94.4 ± 0.65	EC 3	78.48 ± 1.24	97.5 ± 1.03
ES 4	72.82 ± 0.87	90.4 ± 0.81	EC 4	79.27 ± 0.47	99.3 ± 0.34
ES 5	64.76 ± 0.46	94.6 ± 0.64	EC 5	78.71 ± 0.62	90.6 ± 0.45
ES 6	69.47 ± 0.65	92.3 ± 0.91	EC 6	68.73 ± 1.43	96.2 ± 0.84
ES 7	76.45 ± 0.65	96.2 ± 0.34	EC 7	81.43 ± 0.26	98.5 ± 0.26
ES 8	81.26 ± 1.54	91.1 ± 0.64	EC 8	76.52 ± 0.62	99.4 ± 0.62
ES 9	84.52 ± 0.45	98.8 ± 0.74	EC 9	79.27 ± 1.51	92.9 ± 0.49
ES 10	73.56 ± 1.32	96.9 ± 0.94	EC 10	64.61 ± 1.02	91.6 ± 0.44
ES 11	69.24 ± 1.47	99.2 ± 0.38	EC 11	72.32 ± 1.24	93.3 ± 0.32
ES 12	78.61 ± 1.84	98.4 ± 0.47	EC 12	81.39 ± 0.89	91.5 ± 0.74

Differential Scanning Colorimetry:

DSC of received gift sample (Sample 1), Complex Formed (Sample 2) and Solid Dispersion (Sample 3) has been carried as per specifications mentioned in fig 5. The sharp exothermic peak is present at 150.39⁰C matching to its melting point. Thermal behavior of drug polymer combination is studied with the help of DSC and it is verified that the physical mixture so produced won’t affect the drug and its compatibility. The peaks observed in fig 5 are matching in regard with the drug i.e. near to the melting point of Etodolac confirms that there were no apparent chemical interactions between the drugs and carriers and physical blends are formed.

Figure No. 5 DSC Spectra for Drug

Solubility study:

The solubility study of pure drug Etodolac reflects poor solubility of drug in water as only 0.00032 gm of drug is soluble per ml of water.

The solubility data mentioned in table no 4 reflects changes in solubility of drug compare to the solubility of drug in water. The modification in solubility is the reflection of application of enhancement technique with the use of different carriers. As shown in fig 6 the solubility of all the formulation marked the increase having better solubility compare to the solubility in water. Among all the combinations tried for the solubility modification, formulation containing PEG 6000 and PVP K 30 has shown better solubility

Table No. 4 Solubility of Etodolac (post enhancement treatment)

Formulation code	Drug solubility (µg /ml)	Formulation code	Drug solubility (µg /ml)
ES 1	382.63 ± 0.24	EC 1	392.87 ± 0.96
ES 2	438.68 ± 0.43	EC 2	436.68 ± 0.71
ES 3	463.42 ± 0.76	EC 3	487.51 ± 0.62
ES 4	396.3 ± 0.74	EC 4	406.12 ± 0.68
ES 5	462.84 ± 0.37	EC 5	453.41 ± 1.28
ES 6	489.67 ± 0.95	EC 6	504.27 ± 0.87
ES 7	349.26 ± 0.36	EC 7	381.52 ± 0.84
ES 8	386.91 ± 0.17	EC 8	429.84 ± 0.68
ES 9	426.41 ± 0.45	EC 9	495.14 ±1.74
ES 10	368.61 ± 0.21	EC 10	395.4 ± 1.24
ES 11	418.46 ± 1.32	EC 11	458.67 ± 1.58
ES 12	442.49 ± 1.46	EC 12	524.6 ± 0.67

Fig No 6: Graphical Representation of solubility Enhancement

In- vitro drug release/Dissolution studies:

The best combinations so obtained by solubility study are further formulated and evaluated for drug release study. Drug release profile for the solubility modified optimized formulation is shown in fig 7. The percent drug release Vs Time profile justifies the impact of solubility enhancement techniques and role of carries in the process. Comparing and correlating the observation one can easily conclude the modification in solubility of drug has been achieved. Among the two modification techniques we can observe the influence of complexation technique over solid dispersion technique. Still various advancements are necessary to be studied in order to compare effectiveness among solid dispersion and complexation techniques.

Fig No 7: Drug Release profile for optimized formulation

CONCLUSION:

Etodolac is drug that belongs to BCS class II so the efforts were made to imodify its solubility by using solubilization technique such as solid dispersion and complexation. Among the various methods available in literature fusion method and kneading methods were preferred using novel carriers. Enhancement in solubility was attributed to various factors such as trapping of drug inside the carrier matrix and formation of an inclusion complex. DSC study indicates the physical state of the drug in the solid dispersions or complex, confirming that there were no apparent chemical interactions between drug and carrier. Based on the results of phase solubility studies we can conclude that the modification in solubility of Etodolac has been achieved. Complexation by kneading method was found advantageous over fusion method and same has been justified by the drug release study. However the avenues for improvement remain wide open in the wake that a number of carriers and methods are yet to be tried. Therefore, we can conclude that the aims and objectives of this dissertation were fulfilled with the solubility enhancement of Etodolac.

ACKNOWLEDGEMENT:

Authors of the paper are grateful to the IPCA Laboratories Ltd, Mumbai for contributing to the research providing gift sample of drug. We are thankful to all the researchers in the field whose findings served as reference during our study.

CONFLICT OF INTEREST:

No.

LIST OF SYMBOL AND ABBREVIATIONS:

nm: nanometer

µg/ml: micrograms per milliliter

mg: miligram

ES: Etodolac Solid Dispersion

EC: Etodolac Complex

˚C: Degree celcius

λ_max:wavelength of maximum absorbance

DSC: Differential scanning calorimetry

%: Percent

Ppm: parts per million

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Received on 23.07.2020 Modified on 29.01.2021

Research J. Pharm.and Tech 2022; 15(2):683-688.

DOI: 10.52711/0974-360X.2022.00113