1. INTRODUCTION:

Floating drug delivery systems are used to retain the dosage form in the stomach for several hours, increase gastric residence time, release the drug over prolonged period of time and enhance bioavailability by retaining the dosage form at the site of absorption for several hours. Drug release from these systems should be at a desired rate, predictable and reproducible. Polymers which are used as release retarding materials in the design of floating dosage forms play a vital role in retaining the dosage form in a buoyant state in stomach for several hours and delivering the drug in a controlled manner over a prolonged period of time ^[1]. Though a wide range of buoyant polymers and other effervescent agents are available, there is a continued need to develop new and effective release retarding polymers for floating drug delivery systems. Modified starches have been used in various pharmaceutical purposes such as fillers, superdisintegrants and matrix formers in tablet formulations^[2]. One of the important modified starches is calcium starch reported to have excellent matrix forming ability and suitable for controlled release applications. In the present work, calcium starch was synthesized, characterized and evaluated as rate controlling matrix former for floating tablets^3-4.

Losartan potassium, a BCS class-III drug, has taken as the model drug for the present study. Losartan potassium is used to treat high blood pressure (hypertension). It is also used to lower the risk of stroke in certain people with heart disease. It has been reported that the absolute bioavailability of Losartan potassium when given orally is 33% and biological half-life is 2 h. Following oral administration, losartan is well absorbed and undergoes substantial first-pass metabolism.

The objective of the study is to formulate and evaluate floating tablets of Losartan potassium employing calcium starch as matrix polymer in comparison to hydroxy propyl methyl cellulose K100M, a synthetic cellulose derivative.

2. MATERIALS AND METHODS:

Materials

Losartan potassium, HPMC K 100M, Potato starch, Sodium bicarbonate, Magnesium stearate, Talc, Microcrystalline cellulose, Sodium hydroxide, Calcium chloride, Hydrochloric acid were obtained from Research Lab Fine Chem Industries, Mumbai and all other ingredients used were of analytical grade.

Experimental Methods

I. Synthesis of calcium starch

Calcium starch was synthesized by gelatinizing potato starch in the presence of sodium hydroxide and cross linking by treatment with calcium chloride ⁵.

Potato starch (5 parts) was dispersed in purified water (50 parts) to form starch slurry. Sodium hydroxide (3 parts) was dissolved in water (30 parts) and the solution was added to starch slurry. Mixing was continued for 30 minutes to form a thick gelatinized mass. The mass formed was added to 300 ml of calcium chloride (20% w/v) solution contained in a vessel while stirring at 1000 rpm with a medium duty stirrer ^[6]. The stirring was continued for 1 hr to precipitate calcium starch formed. The calcium starch formed was collected by vacuum filtration, washed repeatedly with water and dried at 80ºC. The dried polymer was powdered and passed through mesh No. 100.

II. Characterization of calcium starch:

Prepared calcium starch was evaluated for various properties.

1. Solubility: Solubility of calcium starch was tested in water and organic solvents such as alcohol, dichloromethane, chloroform and acetone⁷.

2. Identification: FTIR spectroscopy was used for identification of calcium starch.

3. pH: The pH of a 1% w/v slurry was measured by using pH meter.

4. Melting Point: Melting point was determined by using melting point apparatus.

5. Viscosity: Viscosity of 1% dispersion was measured using Brookfield viscometer⁸.

6. Swelling Index:

200 mg of Calcium starch was added to 10 ml of water and light liquid paraffin taken in two different graduated test tubes and mixed. The dispersion in the tubes were allowed to stand for 12 hr. The volumes of the sediment in the tubes were recorded. The swelling index of the material was calculated as follows.

Volume of sediment in water – Volume of sediment in light liquid paraffin ×100

Volume of sediment in light liquid paraffin

7. Test for Gelling Property:

The gelling property of the starch and modified starches prepared was evaluated by heating a 7% w/v dispersion of each in water at 100°C for 30 min.

8. Moisture Absorption:

The hygroscopic nature of calcium starch was evaluated by moisture absorption studies in a closed desiccator at 84% relative humidity and room temperature.

9. Particle Size: Particle size was analyzed by optical microscopic method.

10. Density:

Density (g/cc) was determined by liquid displacement method using benzene as liquid.

11. Bulk Density:

Bulk density (g/cc) was determined by three tap method in a graduated cylinder.

12. Angle of Repose:

Angle of repose was measured by fixed funnel method.

13. Compressibility Index:

Compressibility index (CI) was determined by measuring the initial volume (Vo) and final volume (V) after hundred tapings of a sample of starch acetate and calcium starch in a measuring cylinder. CI was calculated using equation.

Compressibility index (CI) = Vo – V/ Vo × 100

III. Preformulation study:

a) Organoleptic Properties: Pure drug was evaluated for organoleptic properties such as appearance and colour.

b) Solubility Analysis:

The solubility of Losartan potassium was checked in water and organic solvents. The solubility was analyzed by quantitative determination using UV spectroscopy at a wave length of 251 nm.

c) Melting Point Determination:

Melting point determination of pure drug Losartan potassium was done by capillary tube method. The presence of small amount of impurity can be detected by lowering as well as widening in the melting point range ^[9].

d) Identification of Pure Drug:

FTIR spectroscopy was used for identification of pure drug Losartan Potassium.

e) Determination of λmax:

Preparation of Stock Solution:

An accurately weighed 100 mg of Losartan potassium was transferred in a 100 ml volumetric flask. To the flask 0.1N HCl was added in small proportion so as to dissolve Losartan potassium. The volume was made up to 100 ml with 0.1N HCl to get a concentration of 1000 μg/ml.

Determination of λmax:

20 μg/ml solution of Losartan potassium was prepared in dilution. The resulting solution was scanned in UV-Vis spectrophotometer from 200 to 400 nm to determine the λmax.

f) Construction of Standard Curve:

1. Preparation of 0.1N Hydrochloric Acid Solution:

8.5 ml of Hydrochloric acid was diluted with sufficient water to produce 1000 ml in standard measuring flask.

2. Preparation of Standard solution of Losartan potassium: Weigh accurately 100 mg of Losartan potassium and transferred to 100 ml of volumetric flask. Allow to dissolve the drug completely and then make up the volume with 0.1 N HCl to get a concentration of 1 mg/ml.

From the above stock solution take 0.2, 0.4, 0.6, 0.8 and 1.0 ml of stock solution were pipette out into 10 ml volumetric flasks. The volumes were made up to the mark with 0.1N HCl. These dilutions gave 20, 40, 60, 80 and 100 µg/ml concentration of Losartan potassium. From the above solutions further dilutions are carried to get the concentration series of 2, 4, 6, 8 and 10 µg/ml of standard Losartan potassium by using 0.1 N HCl. The absorbance of each standard solution was measured by using UV-Spectrophotometer at 251 nm. The calibration graph was plotted by taking concentration on X axis and absorbance on Y axis¹⁰.

IV. Preparation of floating tablets of Losartan potassium:

Floating tablets containing 50 mg of Losartan potassium were formulated by direct compression method employing calcium starch at 10% to 50% concentration in the formula F1 – F5. Formulation F6 was prepared by employing HPMC K 100 at 50% concentration. Sodium bicarbonate was used as gas generating agent at 20% strength in each case. Talc and magnesium stearate were used as glidant and lubricant respectively at 2% concentration in all the formulations ^[11].

Accurately weighed quantities of calcium starch and microcrystalline cellulose were taken in a mortar and mixed geometrically. To this 20 mg of Losartan potassium was added and mixed slightly with pestle. Accurately 50 mg of Sodium bicarbonate was taken separately in a mortar and powdered with pestle. The powder is passed through sieve no 40 and mixed with the drug blend which is also passed through sieve no # 40. The whole mixture was collected in a plastic bag and mixed for 3 minutes. To this 5 mg of magnesium stearate and talc were added and mixed for 5 minutes. The mixture equivalent to 250 mg was compressed into 8 mm tablets on a 10-station tablet punching machine (Karnavathi Pvt. Ltd.).

Table No - 1: Formulation of Losartan potassium Tablets

Ingredients (mg)	Formulation Code
Ingredients (mg)	F1	F2	F3	F4	F5	F6
Losartan potassium	50	50	50	50	50	50
Calcium Starch (10 – 50%)	25	50	75	100	125	---
HPMC K -100	---	---	---	---	---	125
Sodium bicarbonate (20%)	50	50	50	50	50	50
Microcrystalline Cellulose	115	90	65	40	15	15
Magnesium Stearate (2%)	5	5	5	5	5	5
Talc (2%)	5	5	5	5	5	5
Total Weight (mg)	250	250	250	250	250	250

V. Evaluation of Pre-Compression parameters:

a) Bulk density

Apparent bulk density was determined by placing pre-sieved drug excipient blend in to a graduated cylinder and measuring the volume and weight as it is ^[12]. Bulk density was determined by using following formula.

Bulk density = Weight of sample in gram / Volume occupied by the sample

b) Tapped density:

The ratio of weight of powder and tapped volume is known as Tapped Density ^[13].

Tapped density = Weight of Powder/ tapped volume of Powder.

c) Compressibility index/Carr’s index

It is an indication of the compressibility of a granule or powder. It is a ratio of Tapped density and Bulk Density.

Compressibility Index = Tapped density / Bulk Density

d) Hausner ratio:

It indicates that the flow properties of the powder and measured by the ratio of tapped density to bulk density ^[14].

Hausner’s ratio = V_O / V_f

V_O =Bulk volume, V_f = Tapped volume.

e) Angle of Repose:

The angle of repose was calculated by measuring the height and radius of the heap of granules formed ^[15-16].

Then, θ = tan^-1 (h/r)

Where, θ is the angle of repose

h is the height of the heap of powder and

r is the radius of the heap of the powder

VI. Evaluation of Post compression parameters:

a) Tablet dimensions: 10 tablets were randomly picked from each batch and their thickness and diameter were measured using a calibrated vernier calliper (± 5% is allowed).

b) Hardness: The hardness of each batch of tablet was checked by using Monsanto hardness tester ^[17-18].

c) Friability:

Friability generally refers to loss in weight of tablets in the containers due to removal of fines from the tablet surface. 10 tablets were weighed and the initial weight of these tablets was recorded and placed in Roche friabilator and rotated at the speed of 25 rpm for 100 revolutions ^[19]. Then tablets were removed from the friabilator, dusted off the fines and again weighed and the weight was recorded.

W₁-W₂

Friability = –––––––––––––––x 100

W₁

Where: w₁= weight of the tablet before test.

w₂ = weight of the tablet after test.

d) Weight variation:

Twenty tablets were weighed individually and then collectively, average weight of the tablets was calculated and compared with single tablet weight ^[20]. The percentage weight variation is computed according to Indian Pharmacopoeia.

e) Drug Content:

The tablets were tested for their drug content uniformity. At random 20 tablets were weighed and powdered. The powder equivalent to 100 mg of drug was weighed accurately and dissolved in 100 ml of 0.1N HCl. The solution was shaken thoroughly. The undissolved matter was removed by filtration through Whatman No.1 filter paper. Then transfer 1 ml of above solution into 100 ml volumetric flask and make up the volume with 0.1N HCl. The absorbance of the diluted solutions was measured at 251 nm. The concentration of the drug was computed from the standard curve of the Losartan potassium in 0.1N HCl ^[21-23].

f) Evaluation of buoyancy:

The tablets were placed in a 100 ml glass beaker containing 0.1 N HCl. The time required for the tablet to rise to the surface of the medium was determined as Floating Lag Time (FLT) or Buoyancy Lag Time (BLT). The time for which the tablet remained floating on the surface of medium was determined as total floating time ^[24].

g) In-vitro dissolution study:

In-vitro dissolution study of the floating tablets of Losartan potassium was performed according to USP Type-II dissolution apparatus employing a paddle stirrer at 50 rpm using 900 ml of 0.1N HCL as dissolution medium at 37±0.5°C. Samples of the dissolution medium (10 ml) were withdrawn at specific time intervals and replaced immediately with equal volume of fresh medium. The samples were filtered through whatman’s filter paper and diluted if necessary and then analyzed by UV-Visible spectrophotometer at 251 nm using 0.1N HCl as blank. Drug concentration was calculated from the standard curve and expressed as cumulative percent drug release ²⁵

3. RESULTS AND DISCUSSION:

I. Characterization of calcium starch

A. Physicochemical Properties:

Table No - 2: Physicochemical Properties of Calcium Starch

PROPERTY	RESULTS
Solubility	Insoluble in all aqueous and organic solvents tested
pH of a 1% w/v	6.2
Melting Point	220^°C
Viscosity of 1% w/v	1.6 cps
Swelling Index	350.4
Test for Gelling Property	No gelling was observed with calcium starch whereas in the case of potato starch, it was gelatinized and formed gel.
Moisture Absorption	4.2 %
Particle Size	5.41 μm
Density	0.794 gm/cc
Bulk Density	0.816 gm/cc
Angle of Repose	17.42
Compressibility Index	14.32

The calcium starch prepared was characterized by determining various physicochemical properties. Calcium starch prepared was found to be white, crystalline, non hygroscopic powder and can easily be ground to different sizes. This powder has an average particle size of 5.41 μm. The calcium starch prepared was insoluble in water, methanol, dichloromethane and chloroform. When tested for melting point, it was charred at 220^OC. In water it exhibited good swelling index (350.4). No gelling/pasting was observed with calcium starch when its aqueous dispersion was heated at 100^°C for 30 min, where as potato starch formed a paste/gel during the above heat treatment. In the micromeritic evaluation, the angle of repose and compressibility index values revealed the excellent flow characteristic of calcium starch prepared. All the physical properties studies indicated that calcium starch is a promising pharmaceutical excipient in tablets.

B. Identification of Calcium Starch:

The IR spectrum (Fig.4.3) of calcium starch showed the carbonyl stretching at 1795.37 cm^-1, C – H stretching at 2514.40 cm^-1,which was absent in the IR spectrum of potato starch, indicating the carbonization of the native starch.

Figure No - 1: IR Spectra of Calcium Starch

Figure No - 2: IR Spectra of Potato Starch

II. Preformulation study:

a) Organoleptic Properties:

Organoleptic properties of Losartan potassium were determined manually and was found to be white in colour without any odour and having bitter taste.

b) Solubility Studies:

Losartan potassium was found to be freely soluble in water; soluble in alcohols; slightly soluble in common organic solvents such as acetonitrile, methyl ethyl ketone.

c) Melting Point Determination:

After performing capillary method melting point of Losartan potassium found in range of 268^OC.

d) Identification of Pure Drug:

FT-IR spectroscopy was used to determine the functional group present in the pure drug sample.

Figure No - 3: IR Spectra of Pure Losartan potassium

e) Determination of λmax:

The 20 μg/ml Losartan potassium solution was scanned in UV-Vis spectrophotometer from 200 to 400 nm to determine the λmax. The λmax was found to be at 251 nm, so the calibration curve of Losartan potassium was developed at this wavelength.

f) Standard Curve of Losartan potassium:

The standard curve of Losartan potassium was done by using 0.1N HCl as the medium and making the concentrations of 2 to 10 µg/ml solutions. The absorbance of solutions was examined under UV spectrophotometer at an absorption maximum of 251 nm. The standard graph was constructed by taking the absorbance on Y-axis and concentrations on X-axis. The standard calibration curve of Losartan potassium in 0.1N HCl was shown in Figure 4. Drug Concentration and absorbance followed linear relationship. The curve obeyed Beer-Lambert’s law and the correlation coefficient value (R²) is 0.9959.

Table No - 3: Standard calibration curve of Losartan potassium

S. No	Concentration (µg/ml)	Absorbance in 0.1N HCl
1	2	0.248
2	4	0.422
3	6	0.719
4	8	0.994
5	10	1.199

Figure No - 4: Calibration curve of Losartan potassium

The angle of repose of all the formulations was within the range of 21.74 - 25.56°.The bulk density was found in the range of 0.73±0.29 to 0.84±0.14 gm/cm³. The tapped density ranged between 0.80±0.25 to 0.93±0.18 gm/cm³. The Compressibility index of all the formulations exists in the range between 5.19±0.65 to 10.0±0.55. The result of the Hausner’s ratio of all the formulations was between 1.07±0.24 to 1.12±0.13. These values indicate that the prepared blends exhibited good flow properties.

The hardness for the tablets of all formulations was adjusted to 6.8–7.2 Kg/cm² which indicate good mechanical strength with an ability to withstand physical and mechanical stress conditions while handling. The thickness was measured for the tablets of all formulations and was found to be within the acceptable range. The weight of the tablet varied between 2.3 ± 0.65 to 2.5±0.45% for all the formulations. All the tablets passed weight variation test as the ±7.5% weight variation was within the pharmacopoeial limits. In all the formulations, the friability value is less than 1% and meets the IP limits which indicate good mechanical resistance of the tablet. The drug content varied between 98.31%±0.25 to 99.79%±0.58 for all the formulations.

Evaluation of in vitro release:

The in-vitro release of Losartan potassium from floating tablet was found to vary according to the percentage of polymer used. The release of Losartan was decreased with increasing concentration of calcium starch as controlled release polymer. The formulation F5 contains highest concentration of 50% calcium starch showed better controlled release of 76.38% after 12 hrs. The formulation F5 was compared with formulation F6 containing 50% HPMC K-100 and it shown nearly similar controlled release of 73.23%. Hence the F5 was considered as optimized formulation.

Figure No - 6: Cumulative % drug release using Calcium Starch (F1 – F5)

Figure No - 7: Cumulative % drug release using Calcium Starch and HPMC K-100 (F5 and F6)

4. CONCLUSION:

Losartan potassium controlled release floating tablets were prepared by direct compression method using calcium starch as release retard polymer. Losartan release from formulation F5 containing 50% calcium starch showed better controlled release than other formulations. The formulation F5 was compared with formulation F6 containing 50% HPMC K-100 and F6 has shown nearly similar controlled release of 73.23%. From the results of experiments, the calcium starch is suitable for the design of controlled release floating tablets of Losartan potassium.

5. ACKNOWLEDGEMENT:

The authors sincerely thank Vijaya Institute of Pharmaceutical Sciences for Women for providing necessary equipments and their support in the fulfillment of the research work successfully.

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Received on 14.07.2021 Modified on 30.07.2021

Asian J. Pharm. Res. 2021; 11(4):219-226.

DOI: 10.52711/2231-5691.2021.00039

S. No	Formula Code	Angle of repose	Bulk density (gm/cm3)	Tapped density (gm/cm3)	Carr’s Index	Hausner’s Ratio
1.	F1	21.74±0.14	0.76±0.27	0.83±0.31	8.13±0.65	1.09±0.02
2.	F2	24.22±0.26	0.73±0.29	0.80±0.25	5.19±0.65	1.09±0.03
3.	F3	25.17±0.23	0.83±0.14	0.89±0.26	6.74±0.66	1.07±0.24
4.	F4	25.56±0.25	0.84±0.14	0.92±0.26	7.36±0.58	1.09±0.26
5.	F5	24.70.±0.42	0.83±0.17	0.93±0.18	10.0±0.55	1.12±0.13
6.	F6	24.22±0.18	0.76±0.14	0.84±0.28	8.00±0.27	1.10±0.16

Formulat- -ion Code	Hardness (Kg/cm²)	Friability (%)	Weight Variation (%)	Thickness (mm)	Drug Content (%)
F1	6.9±0.22	0.59±0.12	2.3±0.65	4.52±0.55	99.61±0.45
F2	6.8±0.55	0.62±0.25	2.4±0.55	4.53±0.24	99.79±0.58
F3	7.2±0.51	0.61±0.58	2.5±0.32	4.53±0.32	98.54±0.55
F4	7.1± 0.25	0.58±0.36	2.3±0.69	4.52±0.33	98.31±0.25
F5	7.1±0.69	0.62±0.64	2.5±0.45	4.55±0.85	99.62±0.54
F6	7.2± 0.25	0.63±0.58	2.4±0.28	4.53±0.55	98.69±0.58

Time (hr)	F1	F2	F3	F4	F5	F-6
0	0	0	0	0	0	0
1	32.24	27.65	21.36	18.16	16.25	16.42
2	46.42	44.21	38.12	32.35	30.56	29.42
4	58.91	55.83	50.53	45.42	41.32	38.91
6	67.24	64.26	59.84	55.61	50.21	49.24
8	78.84	73.87	70.83	64.71	58.29	57.84
10	89.78	83.38	79.22	73.25	67.21	65.78
12	97.13	92.71	87.74	81.56	76.38	73.23

S. No	Formulation	Buoyancy lag time (BLT) (minutes)	Duration of Buoyancy (DB) (hours)
1	F1	4.25	10
2	F2	3.53	10
3	F3	5.03	12
4	F4	5.12	12
5	F5	4.09	12
6	F6	2.15	12

Volume of sediment in water – Volume of sediment in light liquid paraffin ×100

Volume of sediment in light liquid paraffin

Figure No - 3: IR Spectra of Pure Losartan potassium

Figure No - 5: Buoyancy lag time and duration of buoyancy of tablet