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Fabrication and Comparative Charcateriztion of Antihypertensive Agent by Solid Dispersion and Complexation Techniques

 D Kapoor*, RB Vyas, M Patel, C Lad
Dr. Dayaram Patel Pharmacy College, Bardoli, Gujarat


Azilsartan medoxomil is [(5-methyl-2-oxo-1, 3-dioxol-4-yl) methyl 2-ethoxy-1-{[2′-(5-oxo-4,5-dihydro-1,2,4-oxadiazol-3-yl)biphenyl-4- yl]methyl}-1H-benzimidazole-7-carboxylate] with a molecular weight of 568.5 g/mol. It is a selective AT1 subtype angiotensin II receptor blocker and is indicated for the treatment of mild to moderate essential hypertension. It is having stumpy aqueous solubility, so the aim is to augment the solubility of azilsartan by solid dispersion and complexation methods. Further fabricate them into tablets by direct compression method. Solid dispersion and inclusion complex were fabricated following solvent evaporation method using poloxamer-407 and methyl β-cyclodextrin as a carrier.

The equipped formulations were characterized for compatibility by differential scanning calorimetry (DSC), X-ray diffraction (PXRD) studies and Fourier-transform infrared spectroscopy (FTIR). FT-IR study revealed no interaction between drug and excipients. Among all methods, solid dispersion ASD2 containing active pharmaceutical ingredient: poloxamer 407 in the ratio of 1:3 showed quick and high drug release (89.42% within 40 min).The tablets formulated using ASD2 solid dispersion and AC2 inclusion complex were characterized for both precompression and postcompression parameters. All the data gathered from the precompression and postcompression parameters accomplish the official requirements of tablets. The % drug release from the AF1 batch tablet is higher 86.85% than the AF2 batch tablets 73.56% within 40 minutes. Stability studies of AF1 batch tablets showed no noteworthy alteration in formulation during study period. Thus, it can be recapitulated that the formulation was unwavering.

Keywords: Bioavailability, Azilsartan, Poloxamer-407, Stability studies, PXRD.



Solubility and dissolution rate are the two important parameters to be considered for achieving the therapeutic effectiveness of the drug through the oral administration. Several techniques including micronization, nanonization, chemical modification, pH adjustment, solid dispersion, self emulsification, salt formation, co-solvency, complexation, etc have been defined to overcome the problems related to drug solubilization. The term solid dispersion refers to a group of solid products consisting of at least two different components, generally a hydrophilic matrix and a hydrophobic drug where matrix can be either crystalline or amorphous is dispersed molecularly, in amorphous particles (clusters) or in crystalline particles [1].

Another method to increase drug solubility is by complexation with cyclodextrin which is advantageous because of low hygroscopicity, less toxicity, high fluidity, excellent compatibility and compressibility of cyclodextrin complexation improves the stability of drugs in a formulation, resulting in longer shelf life [2]. Lipophilic drug-cyclodextrin complexes, commonly known as inclusion complexes, can be prepared simply by adding the drug and excipients together, resulting in enhanced drug solubilization. [3]

Azilsartan medoxomil appear like a white crystalline powder which is practically insoluble in water, freely soluble in methanol, soluble in acetic acid, slightly soluble in acetone and acetonitrile while it is very slightly soluble in 1-octanol. Azilsartan medoxomil has melting point 212-214 C, pKa 6.1 and log P 5.70. It is more lipophilic than candisartan. Azilsartan medoxomil (AZM) 2-thiophenepropanoic acid derivative potent antagonist of angiotensin II acting by blocking the angiotensin type I (AT1) receptor. Angiotensin II is a potent vasoconstrictor, the primary vasoactive hormone of the renin-angiotensin system and an important component in the pathophysiology of hypertension. It also stimulates aldosterone secretion by the adrenal cortex. Azilsartan blocks the vasoconstrictor and aldosterone-secreting effect of angiotensin II by selectively blocking the binding of angiotensin II to the AT1 receptor found in many tissues (e.g., vascular smooth muscle, adrenal gland). There is also an AT2 receptor found in much tissue but it is not known to be associated with cardiovascular homeostasis. Azilsartan does not exhibit any partial agonist activity at the AT1 receptor. Its affinity for the receptor is 1,000 times greater than for the AT2 receptor. [4, 5]

In present study, attempt is made for comparative study for enhancing the solubility of azilsartan by using solid dispersion and inclusion complexation methods and development of conventional tablet thereby to know which of these formulations performs the superior aqueous solubility and dissolution profile in comparison to the marketed product.

Materials and Methods  

Materials: Azilsartan medoxomil were obtained from Glenmark pharmaceuticals limited, Nashik. Poloxamer-407, β -cyclodextrin, lactose, magnesium stearate and talc were obtained from SD Fine Chem Ltd, Mumbai. All other materials used were of reagent grade.

Preparation of calibration curves:

Calibration curves of azilsartan medoxomil in 0.1 N HCl, phosphate buffer pH 6.8, water and methanol were formulated by using serial dilutions of the drug from 0.1 mg/ml stock solution for each medium. Absorbance was measured at 248 nm using ultraviolet (UV) visible spectrophotometer (JASCO V-630), and solubility was calculated. The plot of absorbance vs. concentration is done and beer’s range was determined. The results were analyzed in triplicate and standard division was represented. [6]  

Compatibility study using FT-IR:

Infrared spectroscopy was conducted using a Thermo Nicolet FTIR and the spectrum was recorded in the region of 4000 to 400 cm-1 .The procedure consisted of dispersing a sample (drug and drug-excipient mixture) in KBr (200-400 mg) and compressing into discs by applying a pressure of 5 tons for 5 min in a hydraulic press. All spectra were collected as an average of three scans at a resolution of 2 cm-1.The interaction between drug-excipients was pragmatic from IR‐ spectral studies by observing any shift in peaks of drug in the spectrum of physical mixture of drug [7].

Preparation of solid dispersion and inclusion complex of Azilsartan medoxomil:

Solvent evaporation method:

Azilsartan solid dispersion was fabricated by dissolving the azilsartan and poloxamer407 in adequate quantity of methyl alcohol in the ratios 1:1, 1:2 and 1:3w/w in a separate china dish. The solvent was evaporated at 45 ºC in a hot air oven until dried solid mass remains in the china dish. The solid mass was then pulverized and passed through sieve no.60 and kept in desiccators for further use. Whereas inclusion complex was formulated by triturating azilsartan and β-cyclodextrin in ratios 1:1, 1:2 and 1:3 w/w with addition of few drops of 40% of ethyl alcohol to form a paste in a separate china dish. Then solvent was allowed to evaporate at 400C to form a dry solid mass which was further trampled to fine particles and conceded through sieve no.60 and held in reserve in a desiccators for further use. The formulation design of solid dispersion and inclusion complex of azilsartan is shown in Table 1. [8, 9]

Table 1: Fabrication parameter of solid dispersion and inclusion complex of azilsartan  

Methods Formulation code Drug:Carrier

Solid dispersion

ASD1 1:1
ASD2 1:2
ASD3 1:3


AC1 1:1
AC2 1:2
AC3 1:3

Table 2:
Formulation design of azilsartan medoxomil tablet with solid dispersion and inclusion complexes 

Ingredients Code of formulations
Solid dispersion 75
Inclusion complex 75
Lactose 20 20
Magnesium sterate 3 3
Talc 2 2

 Evaluation of fabricated solid dispersion and inclusion complexes of azilsartan medoxomil:

Solubility studies: The solubility of Azilsartan medoxomil solid dispersions and inclusion complexes were determined in water. The solubility was determined by taking an excess amount of drug and SDs and adding them to 100 ml of water, in Teflon-facing screw-capped vials. The samples were kept at equilibrium for a period of 48 h in orbital shaker. The supernatant fraction collected from the vials was filtered through a 0.45 micron membrane filter and analyzed by UV-Visible spectrophotometer (V 630; Shimadzu, Japan) at a wavelength of 248 nm. Ratio optimization (drug: carrier) was done on the basis of the best solubility results obtained. [10]

Drug content: All the fabricated solid dispersion and inclusion complexes formulations equivalent to 20 mg of azilsartan were weighed precisely and dissolved in 100 ml of phosphate buffer pH 6.8 in a separate volumetric flask. The solution was filtered, diluted suitably with same solvent and drug content is analyzed at 248 nm by UV spectrophotometer [10].

Fabrication of azilsartan tablets using solid dispersion and inclusion complex:

Solid dispersion and inclusion complex fabricated from the drug carrier ratio of 1:3 (ASD3 and AC3) were formulated into tablets. The tablet containing 20 mg of azilsartan were fabricated by direct compression method as per the formula given in Table 2.

In vitro dissolution studies of azilsartan with solid dispersion and inclusion complexes: In vitro dissolution study of azilsartan and all fabricated formulations were carried out by using USP rotating basket apparatus for 45 min with rotation speed of 50 rpm. Phosphate buffer pH 6.8 was used as dissolution medium and temperature was maintained at 37 ± 0.5 0C. Samples equivalent to 20 mg of azilsartan medoxomil was filled in hard gelatin capsules and used for dissolution studies. Samples were collected at standard interval of time 5, 10, 15, 20, 30 and 45 min. The absorbance of the samples was measured at λ max 248 nm after appropriate dilution using suitable blank. [11]

Powder X-Ray Diffraction: PXRD analysis was done by irradiating the samples with mono-chromatized Cu Kα radiation (1.506 Å) and analyzed between 3° and 60° (2θ) employing a Bruker AXS D8 advance diffractometer with lynx eye detector. The step was at rate of 0.0200 with step time of 32.8 sec. The diffractogram was produced by using Diffract plus Software. [12]

Differential Scanning Calorimetry: The powdered sample was hermetically sealed in aluminum pans and heated at a constant rate of 10 °C/min, over a temperature range of 30–300 °C with nitrogen flow rate of 30 ml/min. Thermograms of the samples were obtained using differential scanning calorimetry (DSC-60, Shimadzu, Japan). Thermal analysis data were recorded with Shimadzu software programs. Indium standard was used to calibrate the DSC temperature and enthalpy scale. [12]

Fourier Transform-Infra Red Spectroscopy: FT-IR spectra of plain azilsartan and solid dispersions with carrier by using Cary 630 Fourier transform infrared spectrophotometer. Solid dispersion were then scanned using FT-IR spectra of mixture were compared with that of active pharmaceutical ingredient for change or shift in any principle peak of spectra of plain drug.[12]

Characterization of Tablets:

Precompression and post compression parameters: Precompression parameters such as bulk density, tapped density, Hausner’s ratio, Carr’s compressibility index and angle of repose were evaluated for blended powders. Further post compression parameters like weight variation, hardness, friability, disintegration and in vitro dissolution studies were evaluated for prepared tablets. [13]  

In vitro drug release: Dissolution study of marketed tablet as well as the tablet prepared from both formulations was carried in USP II apparatus by keeping 900 ml of 6.8 pH phosphate buffers as a dissolution medium. The paddles were operated at 100 rpm with 37 ± 10C of maintained temperature. The sample of 5 ml were withdrawn at 5, 10, 15, 20, 30, and 45 min and replaced with equal volume of dissolution medium. The withdrawn samples were suitably diluted with same dissolution medium and the amount of drug dissolved was estimated by UV spectrophotometer at 248 nm. Further the release data were fitted into various mathematical models like zero order, first order, Higuchi and Korsmeyer-Peppas. Regressional analysis was performed by using axel software on the in vitro release data to best fit into various kinetic models according to the regression coefficient ‘r’. [14]  

Stability study:

The optimized formulation were wrapped in aluminum foil and subjected to 40 ±2°C temperature and 75± 5% RH in stability chamber for the period of three months. The formulation was analyzed for organoleptic characteristics, hardness, drug-content, and disintegration time and dissolution study. In any rational design and assessment of dosage forms for drugs, the stability of the active component is the main criterion in determining their acceptance or rejection. Stability studies were carried out as per ICH Q1A guidelines. During the stability studies, the product is exposed to normal conditions of temperature and humidity. The optimized azilsartan formulations were subjected for stability studies. [15]  

Result and Discussion

Determination of λ Max:

The analysis of UV spectra of azilsartan medoxomil in, HCL buffer pH 1.2 and water with 0.5% Tween 80, and Phosphate buffer pH 6.8 shows the same λ max 248 nm while it was 248 nm in methanol which similar to the published one as shown in figure 1.

Figure 1: UV Spectrum of azilsartan medoxomil in A-phosphate buffer pH 6.8 B-0.1N HCl and C-methanol  

Fourier Transform-Infra Red Spectroscopy: FTIR analysis was performed on the optimized drug-polymer dispersions to determine what specific interactions were formed and if these interactions were related to hydrogen bond formation between drug and polymer. FTIR is a well-established technique for the evaluation of hydrogen bonding interactions in solid dispersion systems. If an interaction between the drug and polymers occurs, then a shift in the vibrational frequencies of the functional groups involved in the interaction is expected. For a group participating in a hydrogen bond, a shift to lower wave numbers usually indicates a stronger bond while a shift to higher wave numbers indicates the formation of a bond that is weaker than the original bond. Azilsartan has H-bond donor group and therefore is expected to interact with polymers which have H-bond acceptor group. FTIR spectra of azilsartan and solid dispersion are shown as follows.

Figure 2: FTIR spectrum of azilsartan medoxomil  


Figure 3: FTIR spectrum of Azilsartan+β-CD (AC2) 


Figure 4: FT-IR Spectrum of Azilsartan+Poloxamer407 (ASD2)

Figure 5: PXRD of pure Azilsartan medoxomil


Drug content:

Percentage drug content estimation of all formulations was done by UV spectrophotometer. The absorbances were measured and percentage drug content was calculated. Percentage drug content of all formulations were found in the range of 97.87% – 97.10% which was within the pharmacopoeial limits and shown in Table 5.

Table 3: % Drug content of prepared formulations 

S.No Formulation code % Drug content
01. ASD1 97.27
02. ASD2 97.87
03. ASD3 97.16
04. AC1 97.52
05. AC2 97.10
06. AC3 97.14

 In vitro dissolution studies of Azilsartan with solid dispersion and inclusion complexes:

In vitro drug release of solid dispersion and complexation formulations were compared with pure drug and data were tabulated and graphically represented in Figure 6. Dissolution studies were performed in 6.8 pH phosphate buffer. Among all, the formulations fabricated by using solid dispersion with poloxamer 407 in the ratio of 1:2 (ASD2) showed maximum drug release (89.42%) within 40 min. This showed that with increase in concentration of carrier poloxamer407 the dissolution rate of azilsartan also amplified considerably.

 Figure 6: In vitro release of fabricated solid dispersions and inclusion complexes 

The boost in dissolution rate of azilsartan from solid dispersion of poloxamer407 might be due to the lessening of crystal size of the drug, alteration of drug to amorphous or microcrystalline state and decline in wettability leading to formation of film surrounding the drug particle and hence diminishing the hydrophobicity of the drug. On the other hand complexation of azilsartan with β-cyclodextrin also reveal an raise in drug release from the inclusion complex formed compared to active pharmaceutical ingredient. With swell in concentration of β- cyclodextrin, the quantity of drug release was also appreciably augmented. This might be due to the fact that β-cyclodextrin exhibited lofty solubility in water which resulted in improved wettability and solubility of drug particles, which in turn surged its dissolution.

Characterization of Tablets:

Precompression and post compression parameters:

The pre-compression like bulk density, tapped density, Hausner’s ratio, Carr’s compressibility index, angle of repose and postcompression parameters for the prepared tablets were characterized and tabulated in Table 4. All the results obtained are within the Pharmacopoeial range. From the preformulation studies, it is apparent that the azilsartan solid dispersion and inclusion complex (ASD2 and AC2) satisfied the official requirements for compression of tablets through direct compression method and from the physiomechanical parameters it is obvious that all the tablets fulfilled official requirements of compressed tablets.

Table 4: Characterization of azilsartan medoxomil tablets

Parameters AF1 AF2
Bulk density 0.598 0.555
Tapped density (gm/cc) 0.569 0.523
Hausenr’s ratio 1.169 1.114
Carr’s compressibility index (%) 14.297 13.892
Hardness 3.58 3.96
Angle of repose 14.258 15.587
Weight variation 98.154 98.123
Disintegration time (sec) 425 514
Drug content (%) 98.47 97.98
Friability (%) 0.56 0.68

In vitro drug release:

The in vitro drug release of the tablets fabricated using ASD2 formulation of solid dispersion AF1 and AC3 formulation of inclusion complex AF2 was studied in USP II (paddle type) using 6.8 pH phosphate buffer and the percentage drug release was compared with pure drug. The % cumulative drug release data were graphically represented in Figure 7. The results showed, drug release of all prepared formulations were in the range of 15.34%-86.67% within 40min of dissolution studies which is comparatively higher than that of pure drug (27.90%). Among all, AF1 formulations prepared by using solid dispersion with poloxamer 407 in the ratio of 1:2 ASD2 showed utmost drug release (85.21%) within 40min. This showed that with amplify in concentration of carrier the dissolution rate of azilsartan also augmented significantly.  

Figure 7: In vitro drug release profile of active pharmaceutical ingredient, formulations AF1 and AF2  

Release kinetics:

The cumulative release data were subjected to various kinetics models and results obtained from release kinetics studies were depicted in Table 5. Both the formulations showed high linearity with slope (n) ranging from 1.1074 to 1.168, indicating that the drug was released from all formulations followed Super case II mechanism, as their ‘n’ values are higher than 0.89. So it was seen that all the formulations showed first order kinetics model following Super case II drug release mechanism.  

Table 5: Release exponent and rate constant values for all formulations  

Formulation code Kinetic models  
Zero order First order Higuchi Korsmeyer-peppas
  R2 R2 R2 R2 n
AF1 0.9258 0.9875 0.9821 0.9256 1.1589
AF2 0.9782 0.9856 0.9658 0.9349 1.1478

Stability study:

The optimized formulation AF1 was chosen for stability study on the basis of their lofty cumulative % drug release. The selected formulation was subjected to accelerated stability studies at 40 ºC / 75% RH and observed up to till date. The formulation reveals no noteworthy alteration in the physical parameters during the period of study.


In this present study an attempt has been made to boost the solubility and dissolution rate of poorly water soluble drug azilsartan by two approaches; solid dispersion and complexation, thereby compressing the equipped formulations into tablets by direct compression method, since both formulations procedures were simple, economical and less time consuming. FT-IR studies inveterate no possible interactions between drug and excipients. Drug content estimation for all formulations complies within the standard range. In-vitro release study of all formulations showed enhance in percentage drug release than that of active pharmaceutical ingredient and among the formulations, ASD3 showed higher % drug release. The drug release pattern showed first order kinetics model following Super case II drug release mechanism. Stability study of AF1 formulation showed no significant changes in physical properties of tablets within the study period.


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