INTRODUCTION:

The goal of any ideal drug delivery system is to provide a therapeutic quantity of drug to the proper site in the body to achieve prompt response, and thus maintain the desired drug concentration. Such a conceptualized ideal drug delivery can be possible with intravenous infusion of drug at the positioning of action over a desired period of time. In recent years, scientific and technological advancements have been made within the analysis and development of rate controlled oral drug delivery systems. These formulations are a unit designed to deliver the medicine at a controlled and planned rate, thus maintaining their therapeutically effective concentration in circulation for prolonged periods of your time.

A great majority of controlled formulations are formulated in the form of tablets. However, wide physiological and environmental variations in the gastrointestinal tract with respect to the surface area of absorption, pH, fluidity, rate of transit time, presence of food stuffs and co-administered medicine could influence gastric emptying^1-3.

If a controlled release product is formulated in the form of tablet which keeps its integrity throughout the gastrointestinal tract, then the location of the tablet will vary under different circumstances. This will result in the variation within the rate of drug delivery to the systemic circulation. Compared with single unit dosage form, multiunit controlled release drug delivery systems like micro beads, microcapsules and microspheres are becoming popular as they pass through the gut avoiding the vagaries of gastric emptying and different transit rates spread over a large area of absorbing mucosa preventing exposure to high drug concentration and release drug in a more predictable manner^4-5.

Rifaximin is used to treat traveler's diarrhea that is caused by bacteria called Escherichia coli. It is also used to prevent hepatic encephalopathy, which is a condition that occurs when your liver does not work normally. This medicine is also used to treat irritable bowel syndrome with diarrhea. Rifaximin is C₄₃H₅₁N₃O₁₁. Half Life is Approximately 6 hours. Absorption is Low in both the fasting state and when administered within 30 minutes of a high-fat breakfast. In vitro drug interactions studies have shown that rifaximin, at concentrations ranging from 2 to 200 ng/mL, did not inhibit human hepatic cytochrome P450 isoenzymes: 1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1, and 3A4. In an in vitro hepatocyte induction model, rifaximin was shown to induce cytochrome P450 3A4 (CYP3A4), an isoenzyme which rifampin is known to induce. This suggests that the absorbed Rifaximin undergoes metabolism with minimal renal excretion of the unchanged drug⁶.

MATERIALS AND METHODS:

Rifaximin was procured from Yarrow Chemicals, Sodium Alginate was supplied by Loba Pvt. Ltd., HPMC-E5 was obtained as a gift sample from Colorcon Pvt. Ltd., Goa, Liquid Paraffin and Calcium Chloride was procured from SD Fine Chemicals.

Drug –Excipient Interaction Study:

FT-IR Study of Rifaximin Alginate Microbeads:

The drug-excipient interaction study was carried out by employing FT-IR. The study by FTIR of the drug and excipient was carried out by conventional KBr plate method in order to study the interaction of the drug and polymer so as to determine the physical as well as chemical changes that can occur during the formulation. For this the physical mixture of excipient and pure drug was mixed in a ratio of 1:1 with potassium bromide and the small pellet was formed by pressing the mixture was incorporated into the disk and the FT-IR was carried out in the frequency range 400-4000 cm-1. The predominant peaks were recorded and were matched with standard FTIR^7-8.

Standard Calibration Curve:

The standard calibration curve of Rifaximin was carried out on UV spectrophotometer by using phosphate buffer of pH 7.4 as the solvent. From the solution which is now having a concentration of 100 µg/ml samples of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 and 5 ml were pipette out into 10ml volumetric flasks. The volume was made up to the mark with Phosphate buffer 7.4 to get the final concentration of 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 µg/ml respectively. The absorbance of concentration was measured at 250nm⁹.

Formulation of Microbeads:

Microbeads containing Rifaximin were prepared by ionotropic gelation technique. The polymeric solution was prepared by dispersing the weighed quantity of sodium alginate and HPMC in deionized water. Suspensions were prepared by using light liquid paraffin with drug and polymeric solution and were thoroughly mixed with help of Mechanical Stirrer at 500 rpm^10-12. To prepare homogenous suspension, the formed mixture allowed to stand for 1 h to make it bubble free. By following the same procedure the alginate beads of different ratios of drug: polymer were prepared. The resulted homogenous dispersion was extruded into 100 ml of 2% cross-linker solution (CaCl₂) through hypodermic syringe with flat tip needle (18 G) and stirred at 100 rpm at 3 hours. The formed microbeads were allowed to cure for 3 hours in the cross-linker solution to complete the gelation. The beads were removed after the gelation period and washed with ethanol to harden the beads surface and to remove liquid paraffin, finally with distilled water repeatedly to make free from un-reacted ion. The microbeads were then filtered and dried in room temperature for 24 hrs and stored in a ambered colored vials for further use¹³.

Evaluation Parameters:

Swelling Index:

The swelling index of the microbeads is an indication of the capacity of the microbeads to imbibe water and swell. For estimating swelling index, the microbeads (500 mg) were weighed initially then suspended in 25 ml of phosphate buffer(pH 7.4) and 0.1N HCL(pH 1.2). The beads were taken out at different time intervals using stainless steel grid and blotted carefully without pressing hard to remove the excess surface liquid. The swollen beads were weighed using electronic microbalance. The studies were performed in triplicate and average values were taken in data analysis^14-15.

Weight of wet microbeads

Swelling Index = –––––––––––––––––––––––– x 100

Weight of dry microbeads

Table 1: Formulation Chart of Rifaximin Alginate Bead

Sr. no.	Batch No.	Drug (mg)	Sodium Alginate (mg)	HPMC E5 (mg)	Calcium chloride (%)	Liquid Paraffin (ml)	Water (ml)
1	Fz1	250	200	1000	4%	2ml	10ml
2	Fz2	250	400	800	4%	2ml	10ml
3	Fz3	250	600	600	4%	2ml	10ml
4	Fz4	250	800	400	4%	2ml	10ml
5	Fz5	250	1000	200	4%	2ml	10ml

Drug Content Estimation:

Different batches of microbeads were checked for drug content uniformity. Accurately weighed (50 mg) amount of dried microbeads were taken in a pestle and mortar and powdered. The powdered microbeads were then separately dissolved in adequate quantity of 1.2 pH phosphate buffer and kept for 24 h. the solution was then filtered, scanned for absorbance was noted down at 250 nm using UV spectrophotometer¹⁶.

Determination of Entrapment Efficiency:

The amount of Rifaximin present in the microbeads was determined. The dried microbeads from each batch were crushed in a mortar pestle. The powdered microbeads were extracted in to 50 ml of phosphate buffer (pH 7.4) by magnetic stirring for a period of 2 h. The solution was filtered through Whatman filter paper, suitably diluted and estimated for drug content spectrophotometrically at 250 nm using UV–Visible Spectrophotometer¹⁷.

The drug entrapment efficiency was determined using following formula:

Drug Entrapment Efficiency = EQ/TQ *100

Where,

EQ= Experimental drug content, and

TQ= Theoretical drug content ^[6].

Loose surface crystal study (LSC):

The purpose of this study was to estimate the amount of un-entrapped drug present on the surface of the beads. Beads from formulations Fz1, Fz2, Fz3, Fz4 and Fz5 were suspended in 100 ml of phosphate buffer (pH 7.4), and samples were shaken vigorously for 15 min in a measuring cylinder. The amount of drug dissolving from the surface of the beads was analyzed at 250 nm using UV spectrophotometer, and the percentage of drug released with respect to entrapped drug in the sample was recorded¹⁸.

Surface Morphology:

Surface morphology of microbeads was investigated by Scanning Electron Microscopy (SEM) using JSM 6380A (JOEL, Japan). The microbeads, coated with Platinum by ion Auto fine coater JFC-1600 (JOEL, Japan), for 20 s at 1.1V under argon atmosphere were mounted onto metal stubs using double micrographs were taken¹⁹.

In-vitro Drug Release Studies:

The release profiles of Rifaximin from microbeads were examined in phosphate buffer and 0.1N HCL at ph 7.4 and 1.2 respectively by using USP type II rotating basket apparatus. The prepared microbeads were taken in the basket and were placed in a dissolution vessel containing 900ml of the dissolution medium. The study was carried out in a solution of 0.1N HCL of pH 1.2 for 3 hours, and after 3 hours the remaining study was carried out in phosphate buffer of pH 7.4. Basket was rotated at a constant speed of 75rpm at a constant temperature of 37±1^oC. At scheduled time intervals 5ml of the samples were withdrawn and replaced with fresh medium in order to maintain the sink condition. The samples were filtered by using a Whatman filter paper and then suitably diluted from which the drug release was determined by using UV spectrophotometer at 250 nm²⁰.

RESULT AND DISCUSSION:

Drug –Excipients Interaction Study:

FT-IR:

The FTIR spectra of rifaximin exhibited peaks at 3583 due to phenols, 3401 cm due to O-H (hydroxyl group) stretching variation, 2963.41-2923.66 cm due to C-H stretching variation, 2853.84 due to aldehyde stretching variation,1591.02 due to amide ,1259.34 due to alocohol, ethers, esters, carboxylic acids ,760-1025 is due to vibration of C-O (Carbonyl group) in alcohol hydroxyl groups.

Figure 1: FT-IR of Pure Drug (Rifaximin)

Figure 2: FT-IR of Optimize Formulation (Fz4)

Table 2: 0.1N HCL (1.2pH)

Sr.no.	Batch No.	Normal Weight (gm)	Swelling Weight (gm)	Difference in Weight(gm)	Swelling Index (%)
1	Fz1	3.30	4.12	0.82	80.09
2	Fz2	1.58	2.55	0.97	61.96
3	Fz3	1.20	2.01	0.81	59.7
4	Fz4	1.09	3.02	1.93	36.09
5	Fz5	0.71	1.09	0.38	65.13

Table 3: Phosphate Buffer (pH 7.4)

Sr.No.	Batch No.	Normal Weight (gm)	Swelling Weight (gm)	Difference in Weight(gm)	Swelling Index (%)
1	Fz1	1.84	3.59	1.75	51.25
2	Fz2	1.40	4.83	3.43	28.98
3	Fz3	2.29	5.32	3.03	43.04
4	Fz4	1.44	6.31	4.87	22.82
5	Fz5	1.93	7.42	5.49	26.01

Standard Calibration Curve:

Standard calibration curve of Rifaximin alginate beads: The maximum absorption of Rifaximin alginate beads in phosphate buffer of ph 7.4 was found to be 223 nm. The linear equation was found to be y= 0.015x + 0.006 the r² value were found to be 0.999 respectively.

Figure 3: Standard Calibration Curve

Swelling Index:

Swelling index of prepared batches carried out in two different media. One batch on acidic medium (pH 1.2) and another in phosphate buffer (pH 7.4). When compared both phosphate buffer and acidic buffer, swelling behavior of Rifaximin alginate beads was Lowest in acidic medium and swelling behavior was highest in phosphate buffer. This result clearly suggests that Rifaximin alginate beads slightly swell in the stomach and swell more in intestine.

Weight of wet microbeads

Swelling Index = –––––––––––––––––––––––––– x 100

Weight of dry microbeads

Loose Surface Crystal Study:

Loose surface crystal study is a important parameter giving an indication of amount of drug on the surface of the microbeads without proper entrapment. The LSC was highest at FZ5 formulation (4.82%) where as LSC was Lowest in formulation of Fz4 (1.2%). Thus in FZ5 more drug is present on the surface of the beads contributing less drug entrapment within the beads.

Table 4: LSC Study

Batch	LSC Study(%)
Fz1	2.51%
Fz2	2.32%
Fz3	3.62%
Fz4	1.2%
Fz5	4.82%

Drug Entrapment Efficiency:

Accurately weighed amount of Rifaximin loaded beads were kept in 100ml of the solution was then diluted with phosphate buffer of pH 7.4 for the spectrophotometric analysis of Rifaximin at 223nm. The drug entrapment efficiency was determined using following formula:

Drug Entrapment Efficiency = EQ/TQ *100

Where,

EQ= Experimental drug content, and

TQ Theoretical drug content

Table 5: Drug Entrapment Efficiency

Sr.no.	Formulation Code	Drug Entrapment Efficiency(%)
1	Fz1	82.23
2	Fz2	88.00
3	Fz3	92.75
4	Fz4	93.53
5	Fz5	82.46

Figure 4: Graphical Representation of Drug Entrapment Efficiency

Rifaximin Alginate Beads:

The shape of rifaximin alginate beads can be seen figure: beads prepared by the use of rifaximin and alginate (in phosphate buffer) were uniformly shaped addition of calcium chloride solution gives the best characteristics of the beads.

In-vitro Dissolution Study:

The drug release of prepared hydrogel alginate microbeads was carried out and it was found that the drug release (%) was found to be in the range of 0.81 to 4.81% for the time period of 03 hours. From the drug release data, it was seen that the batch of fz4 was having the most sustained drug release as compared with other batches the drug release pattern indicates that as the conc. of polymer increases the rate of drug release decreases.

Figure 5: Spherical shape of rifaximin alginate beads(Fz4)

Figure 6: An example of un-uniform beads (Fz1)

Figure 7: Graphical Representation of In-vitro Dissolution Study

Figure 8: Surface morphology of microbeads

Surface Electron Morphology:

The scanning electron microscopy for optimized batch FZ4 was performed and it was found that the prepared microbeads were having a spherical shape and the surface was having facture on the surface which might be due to the storage conditions.

CONCLUSION:

Rifaximin loaded alginate hydrogel beads were successfully achieved by using calcium chloride as a crosslinker, Hydroxypropyl methylcellulose (HPMC) was used to promote the Floating Drug Delivery System. In this process we have developed a drug delivery system that shows the enhanced sustained release of Rifaximin. This study revealed that the Rifaximin alginate beads could be used as potential candidate for application in antimicrobial activity. This formulation helps in prolong drug release, therefore better bioavailability can be seen and hence increase in therapeutic activity of the drug could be achieved. Therefore this developed sodium alginate micro beads with release modifier could be used as a carrier for the sustained delivery of other categories of drugs. The entire process is feasible in an industrial scale and demands pilot study.

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Received on 20.06.2022 Modified on 30.07.2022

Asian J. Res. Pharm. Sci. 2022; 12(4):285-290.

DOI: 10.52711/2231-5659.2022.00049