INTRODUCTION:

The most practical and widely used method of medicine delivery in the past has been taken by mouth. Medications with a brief half-life and easy absorption from the gastrointestinal system are rapidly removed from the bloodstream. Oral controlled release formulations have been created to circumvent these issues since they release the medication gradually into the digestive system and keep the drug's concentration in the blood steady for extended periods of time.¹

This route, however, has a number of physiological issues. Among these are a person's unique and erratic pace of stomach emptying, a short gastrointestinal transit time (8–12h), given the fact that several there is a window of absorption of drugs in the upper small intestine.² These challenges have led scientists to develop a medication delivery method that can remain in the stomach for an prolonged and consistent amount of duration. Gastro-retentive drug delivery systems are made to extend the duration that medications that are:

· Locally active in the stomach.

· Unstable the intestinal environment.

· Possess a small GIT absorption window.

· Are less soluble in areas with high pH.³

Developing strategies to extend the stomach residence duration of dose forms has been the focus of pharmaceutical scientists' efforts for almost fifty years.⁴ Gastric retention, the term for dosage forms extended stay in the stomach, has a number of medicinal and biopharmaceutical uses. Enhancement of stomach local action, higher concentrations in the stomach, better bioavailability of certain medications with windows in the upper GIT, or enhanced patient compliance as a result of dose reduction.⁵

The dose forms that are able to stay in the stomach are known as gastrointestinal drug delivery systems (GRDDS). As seen in Fig.1 controlled drug administration can enhance the absorption window. Extended gastric retention raises the solubility of medications solubility in a setting with a high pH of the gastrointestinal tract (GIT), decreases residual waste, and enhances bioavailability. This category includes applications for local delivery of the stomach and small intestine.⁶

Figure 1: Absorption of drugs from (a) traditional dose forms and (b) drug delivery systems that need stomach contraction.

A consideration of physiology for the development of GRDDS

1. Anatomy of the GIT:

There are three primary divisions under the GIT:

1. The stomach

2. The small intestine – duodenum, jejunum, and ileum

3. The large intestine⁸

Figure 2: Anatomy of human stomach⁹

From oral to appendage, the GIT is a continuous muscle tube that performs a variety of physiological functions, including motility, digestion, absorption, excretion, and secretion, to absorb nutrients and remove waste. There are four distinct anatomic parts that make up the stomach, this is the gut GIT expanded in a J shape: the cardia, fundus, body, and antrum. The stomach's primary job is to hold food and combine it with gastric secretions before emptying its contents (chime) at a controlled pace that allows for absorption and digestion past the pyloric sphincter and into the small intestine. The stomach has a capacity of roughly 50 milliliters when empty.⁷ It has the capacity to extend to one liter. The GIT's walls share a basic tissue arrangement with the stomach and large intestine. Different layers are arranged from the outside to the inside, and these layers include the serosa, Lamina propria, circular muscle, endocrine planetary, submucosa, muscular mucosa, and epithelium.¹⁰

GRDDS help these medications to improve their:

· Bioavailability

· Efficiency of therapeutics

· A possible dosage decreases.

· The minimum fluctuation in the therapeutic levels due to the upkeep of constant levels for a longer period of time.

· Minimize medication waste.

· Increases the solubility of weakly basic drugs like domperidone and papaverine that are less soluble in high pH settings.

2. Gastric PH:

Human physiologic stomach pH fluctuates between different parts of the GIT and is not always the same.¹¹Due to various physiological and biochemical parameters, as well as variations in the stomach's state during measurement (fed or fasted), it also shows significant intra- and inter-subject variability. It is reported that the average stomach pH in healthy individuals who have fasted is 1.1±0.15.¹² The pH in the fed condition first drops below 5.0 and then, over the course of a few hours, gradually rises to the values of the fasting state. It is claimed that the mean pH in the fed-state of healthy guys is 3.6±0.¹³

3. The Emptying of the Stomach:

Emptying of the stomach is the motility-driven process by which the dose form is discharged from the stomach into the small intestine. Gastric emptying controls how long a dose form stays in the stomach after drug administration. Since the primary sites of absorption for drugs with a narrow window of absorption are the stomach and proximal small intestine, this process is significant for those pharmaceuticals. The same factors that affect gastric emptying also affect how long the medication stays in contact with the target location, which influences the drug's oral bioavailability. The capacity to manage or regulate gastric emptying can increase the stomach's potential to serve as an organ for drug absorption and to enhance the design possibilities because it is a highly variable process.¹⁴

Suitable drug Candidates for GRDDS.¹⁵

· For instance, levodopa and riboflavin have a little through a GI tract window.

· It is primarily absorbed from the stomach and upper part of the GIT, as is the case with cinnarizine, chlordiazepoxide, and calcium supplements.

· Medications that work locally in the stomach, like misoprostol and antacids.

· Medications that break down in the intestines, like metronidazole and ranitidine HCl.

· Medications that disrupt typical bacteria in the colon, such as amoxicillin trihydrate.

· The DF's low-density form responsible for the stomach fluid's buoyancy.

· High-density DF that does not burst at the base of the stomach.

Floating Drug Delivery System:

Because the floating drug delivery system's bulk thickness is smaller than that of GI fluid, it can stay afloat in the abdomen for longer periods of time without affecting the stomach's natural emptying process.^[16] The material floats during this process and is expelled from the body at a critical pace after the medication is released. This raises the possibility that bacteria will infiltrate the body and makes controlling the quantities of bacterial drugs easier^17,18

The Floating Medication Delivery System's Mechanism:¹⁹

Because their bulk density is lower than that of gastric fluids, floating drug delivery systems (FDDS) float in the stomach for extended periods of time without slowing down the rate of gastric emptying. As can be seen in Figure No. 3(a), the medication is released from the body at the proper rate while the system is floating on the contents of the stomach. However, in addition to the minimal stomach content required to meet the buoyancy retention principle, a minimal amount of floating force (F) is also required to maintain the dose form's consistent buoyancy on the meal's surface. A particular technique for determining resultant weight has been developed in the literature to assess the dynamics of the floating force.

F = F buoyancy – F gravity = (Df – Ds) gv

Where,

F = total vertical force,

Df = fluid density,

Ds = object density,

v = volume,

g = acceleration due to gravity

Figure 3: The floating drug delivery system's mechanism

Classification of the floating medication delivery system²¹

The Effervescent System:

These systems were further divided into

1. Gas generating System

The reaction between sodium bicarbonate, citric acid, and tartaric acid is the main mechanism in this system, which produces CO₂ gas. The system becomes less dense due to the gas produced, allowing it to float on the stomach contents. Salts and citric/tartaric acid release CO₂, which is captured by the system's jellified hydrocolloid layer. As a result, the specific gravity of the hydrocolloid layer is lowered, causing it to float over the chime.²⁰ The seed for the system is a double-layered sustained release tablet. A frothy mixture of sodium bicarbonate and tartaric acid makes up the inner layer. PVA shellac-based swelling membrane makes up the outermost layer. (Figure No. 4: effervescent drug delivery method.)

Figure 4: Gas generating system

2. System that contains volatile liquid

These comprise an expandable stomach chamber that is filled with a liquid (cyclopentane or ether, for instance) that gasifies at body temperature. These methods use a designated hollow unit to osmotically regulate a floating system. The medication is kept in the first chamber of the system, and the volatile system (Figure No. 4: Gas Generating System) is kept in the second. These systems are divided into the following categories:

i) Intra Gastric Floating Gastrointestinal Medicated Delivery System:

This method consists of a flotation chamber that is either filled with innocuous gas or vacuum, and a micro porosity compartment that houses a pharmacological reservoir.

Figure 5: Intra gastric floating gastrointestinal medicated delivery system.

ii) Gastrointestinal Inflatable Medication Delivery system:

An malleable container filled with using gasifiers made of liquid ether to expand the stomach to body temperature. The inflatable chamber contains a bioerodible polymer filament, such as a copolymer of polyvinyl alcohol and polyethylene, which slowly dissolves in stomach juice, causing the inflated chamber to collapse and release gas.

Figure 6: Gastrointestinal inflatable medication delivery system

Non-effervescent mechanism²²

1. A Hydrodynamically Balanced System:

This is a prescription formulation designed to float in the stomach contents that contains gel-forming hydrocolloids. Because drug delivery systems have a lower bulk density than gastric fluids, they can remain in the stomach for extended periods of time without affecting the rate at which the stomach empties. The medication is removed from the system gradually while it is floating on the contents of the stomach at the appropriate rate. watching the system release gradually at the scheduled speed. When the drug is ejected, the stomach's residual system is emptied. GRT rises as a result of improved concentration fluctuation management.

Figure 8: Hydrodynamically balanced system

2. Micro balloons:

In technical terms, micro balloons, also known as hollow microspheres, are spherical particles devoid of a core. These microspheres, which are typically less than 200 micrometers in size, are particles that flow easily composed of proteins or synthetic polymers. Utilizing cutting-edge technologies like solvent evaporation, tiny balloons filled with medication within their outer polymer shell are able to form a hollow inner core. An ethanol/dichloromethane solution containing the medication and a mixture of enteric acrylic polymers is introduced to an agitated Poly Vinyl Alcohol (PVA) solution with a temperature control of 40°C. The organic solvent is eliminated from the mixture by either stirring continuously or increasing the temperature while applying pressure once the emulsion has hardened into a stable state. Within the hollow internal cavity of the polymer microsphere, dichloromethane vaporizes in the distributed polymer droplet to produce a gaseous state.

3. Microporous Compartment:

Using this technique, the pharmaceutical storage area is encased in a layer of microporous material with pores extending along both of its upper and lower sides. The delivery method dissolves the medication as it floats above the gastric fluid, which passes through the aperture and is absorbed in the stomach and the first segment of the small intestine.

Figure 10: Microporous compartment

4. Alginate Beads:

Calcium alginates that have been freeze-dried have been used to make multiple unit floating dosage forms.²³Calcium chloride-containing aqueous solution and sodium alginate solution can be dipped to form spherical beads with a diameter of around 2.5 mm. These beads are separated and dried using air. This leads to the formation of an aporous system, which keeps the stomach afloat.

Figure 11: Alginate beads

Floating Microspheres:

Types of flotation fluid have a lower bulk density than gastric fluid and are unaffected by the speed at which the stomach empties. The medication is released gradually at the intended pace when the stomach material is floating in the system, which lengthens the gastric residence and results in variations in plasma concentration. Additionally, it produces a long-lasting therapeutic effect and reduces the possibility of striking and dose dumping²⁴.

Advantages of Floating Microspheres²⁵

1. It is possible to treat upper gastrointestinal conditions more precisely.

2. The range of medication concentration variation has decreased.

3. Selectivity for receptor activation has improved.

4. Less physical resistance exists.

5. Sustained periods of significant and productive concentration.

6. The bioavailability is improved.

7. First pass biotransformation is improved.

8. Administration of medication with prolonged effects and a lower dose frequency.

9. Reduced negative behavior at the colon.

Disadvantages of Floating Microspheres²⁶

1. It would not be appropriate to use medications such as nifedipine, which passes through first pass metabolism and is highly absorbed throughout the gastrointestinal tract.

2. Additionally, drugs that irritate the stomach's mucous lining need not to be given.

3. Drug combinations that do not stabilize in the stomach's acidic environment should not be added to systems.

4. For these medication delivery systems to function well, there needs to be a large amount of stomach fluid.

5. It is not recommended to utilize medications that have issues with GIT stability or solubility.

Methods of preparation of Floating Microspheres:

There are several techniques for making gastro-retentive floating microspheres. Still, the evaporation of solvent approach and the technique of ionotropic gelation has been extensively working by researchers worldwide to investigate floating microspheres from a variety of perspectives. The right strategy needs to be chosen in order to effectively capture active components and produce floating controlled release microspheres. The drug, the polymer's makeup, and the intended usage all affect the production method selection.²⁷

Microspheres Can Be Prepared by Following Methods²⁸

1. Spray Drying Method

2. Solvent Evaporation Method

3. Single emulsion method

4. Double emulsion method

5. Phase separation coacervation method

6. Solvent extraction method

7. Quasi emulsion solvent diffusion method

Spray Drying Method:

A heated air stream is used to acquire, homogenize, and accept medication in the solid form, enabling atom-level dispersion. The medication is thus dispersed faster in the polymer solution. This facilitates the production of tiny mist or microscopic droplets. The result is the creation of microspheres, which the cyclone separator then uses hot air to help separate.^29-30

Figure 12: Spray drying Method

Solvent Evaporation Method:

The solvent evaporation process is finished once the liquid production vehicle phase is finished. To disperse the microcapsule coating, a non-soluble volatile solvent is applied to the liquid production vehicle phase. The coated polymer solution contains a microencapsulating core material that has been dissolved or distributed. To create the right-sized microcapsules, the core material combination is agitatedly distributed during the liquid production vehicle phase.³¹

Figure 13: Solvent Evaporation Technique.

Single Emulsion Technique:

Most organic polymers use this kind, which is utilized to make proteins and carbohydrates. With the aid of linking agent modification, natural polymers are dissolved or dispersed in aqueous fluids and show overdispersion in non-aqueous media.³²

Double Emulsion Technique:

This process results in the development of a double emulsion, or w/o/w, which is made up of several emulsions. This method can be used to natural polymers, mostly synthetic polymers that are best suited for water-soluble medications, peptides, proteins, and vaccinations. The primary emulsion then exhibits the effects of homogenization in the formation of a double emulsion.³²

Figure 14: Double Emulsion Technique

Phase Separation Coacervation Method:

The development of the polymer-rich phase known as coacervates is entirely dependent on the organic component, which decreases the polymer's solubility. In the first three stages, the covering polymer solution disperses one core material. Three immiscible layers are formed. The second is the polymer sheath that surrounds the heart. Third, salting out of the polymer covering to stiffen it by adding a cross-linking agent and desolving the thermal phase with a non-aqueous vehicle.²⁹

Solvent Extraction Method:

The frozen sample is crushed and powdered as part of a standard solvent extraction process. After combining the powder with anhydrous sodium sulfate, it is suspended in a solvent such diethyl ether and combined for a ew hours at room temperature.³³

Figure 15: Solvent extraction method

Quasi Emulsion Solvent Diffusion Method:

This technique makes use of an outer phase that contains polyvinyl alcohol and purified water. Polymers, drugs, and ethanol are components of the internal process. After being created at 60 degrees Celsius, the internal phase is applied to the external phase at room temperature. Once the emulsification process is complete, the mixture is constantly swirled for two hours. After that, the mixture can be filtered to facilitate separation. The object is then cleaned and dried at 40°C for a day in a vacuum oven.³⁴

Figure 16: Quasi emulsion solvent diffusion method

Characterization of Floating Microspheres:

1. Size of Particles:

The diameters of the microsphere particles were measured using an optical microscopic technique, and the mean microsphere size was ascertained by measuring 100 particles using a calibrated ocular micrometer.⁴²

2. Bulk density:

Bulk density is the term used to describe the substance's overall density.

The true volume of the intraparticle pores and interparticle gaps are included. Particle packing is particularly vulnerable to bulk. When we talk about bulk density, we mean: ⁴³

Weight of the Powder

Bulk Density = ----------------------------------------------

Bulk volume of powder

3. Tapped Density:

To measure the tapped densities, you might apply the tapping method. The volume of weighted quantities of microspheres was calculated using a tapped density device after 100 and 1000 taps, respectively.

Sample Weight

Tapped Density = ------------------------------------------

Volume Tapped

4. Efficiency of Drug Entrapment:

By dividing the amount of drugs actually present from the amount of drugs predicted, one can assess how effective floating microspheres are in drug entrapment.⁴⁴

5. Percentage Yield:

After dividing the total weight of the created microspheres by the weight of the drug and excipient, the result is multiplied by 100.⁴⁵

Weight of hollow microspheres

% Yield = --------------------------------------------- X 100

Weight of drug taken + Total polymer weight

6. Floating behavior:

The USP type II apparatus is employed to determine the floating behavior of FMs. The microspheres kept into the apparatus in gastric fluid having pH 1.2, temp 37±0.5⁰C. It is computed by ⁴⁶

Buoyancy (%) = ------------------------X 100

Qs + Qf

Qf = Quantity of floating microspheres

Qs = Mass of hollow microspheres

7. Ratio of Swelling:

To examine the swelling feature of floating microspheres, submerge a known weight of microspheres in phosphate buffer pH 6.8 or 0.1 N HCl in a glass beaker for the necessary duration at 37±0.5°C. The microspheres are taken out at various times after being given opportunity to inflate.⁴⁷

Applications of Floating Microspheres:

1. Sustained Drug Delivery System:

These systems allow the medication to be released gradually because they can remain in the stomach for long periods of time. Consequently, these techniques deal with the brief stomach dwelling period that occurs when using an oral CR formulation. Due to their bulk density of less than 1, these systems are able to float atop the contents of the stomach. These systems are quite large and cannot pass via the pyloric hole. HBS frameworks have the ability to remain in the stomach for extended periods of time, which allows the drug to be released gradually.⁴⁸

2. Site-Specific Drug Delivery System:

These systems are very beneficial for medications like furosemide and riboflavin, which are mostly absorbed from the stomach or the proximal portion of the small intestine. Floating microspheres can greatly improve stomach pharmacotherapy by encouraging local drug release and high drug concentrations at the gastric mucosa. This allows the treatment of gastritis, oesophagitis, stomach, and duodenal ulcers by getting rid of Helicobacter pylori from the stomach's submucosal tissue.⁴⁹

3. Enhancement of Absorption:

When delivering medications that are insoluble and only sporadically soluble, floating microspheres work particularly well. It is well recognized that as a medicine loses its solubility, there is less time for it to dissolve, which means that transit time has a bigger impact on drug absorption. Hollow microspheres can potentially prevent the chance that solubility will become the rate-limiting stage in release by reducing the solubility of weakly basic drugs that are poorly soluble at an alkaline pH. The positioned gastric release helps medications that are well absorbed by the stomach, such as verapamil hydrochloride. The active agent's absorption profile will be positively altered by the gastro-retentive floating microspheres, increasing its bioavailability.⁵⁰

4. Maintain The Blood Level Stable:

The tool makes it easy to administer medication and increases patient compliance by offering a convenient means of maintaining a steady blood level.

5. Decreased Variations in Drug Content:

Ongoing administration of the medication after regulated release when in contrast to dose formulations with instant release, the blood drug concentrations produced by the administration of gastro-retentive dosage forms (CRGRDF) fall into a narrower range. Consequently, Peak concentration-related negative effects that rely on concentration can be prevented, and changes in pharmacological effects are minimized.²⁸

6. Microspheres for the transfer of genes:

Viral vectors, nonionic liposomes, polycation complexes, and microcapsules are all used in the delivery of genotype technologies. Even though viral vectors are highly efficient and have a wide range of cell objectives, they are still advantageous for genotype delivery. Nevertheless, when applied in vivo, they cause harmful consequences and immunological reactions. Gene therapy has been considering nonviral delivery techniques as a solution to the limitations of viral vectors. The advantages of a nonviral delivery system include ease of preparation, the ability to target specific cells or tissues, a weakened immune system, unlimited plasmid size, and large-scale, reproducible production. Polymer will be employed in gene delivery applications as a DNA transporter.⁵¹

CONCLUSION:

GRDDS has the potential to significantly increase the therapeutic efficaciousness of medications with limited absorption windows, high acidic solubility, and alkaline pH instability. The world of pharmaceuticals has greatly advanced thanks to microspheres. The new usage of these medications makes it possible to target their delivery, which presents challenges for their regular supply. Higher doses can now be delivered as microspheres, reducing the possibility of gastrointestinal adverse effects and enabling the administration of an entire course of antibiotics in a single dosage. Microspheres have been the subject of considerable research in recent years in order to enable a wider range of uses, and these applications are clearly rather extensive. The use of floating microspheres as gastroretentive dosage forms has a significant impact on healthcare by precisely controlling the pace at which a target medicine is released to a particular place. It is anticipated that improved multi-unit floating microspheres will provide physicians an additional option for a more affordable, secure, and bioavailable formulation in the efficient treatment of a variety of illnesses. These methods enable the development of novel controlled and delayed release oral formulations, opening up new avenues for innovative pharmaceutical research. Additionally, new developments in pharmaceutical research will undoubtedly present viable opportunities for the creation of creative and efficient ways to create these prospective drug delivery systems.

ACKNOWLEDGEMENT:

We appreciate the helpful guidance we received from the Teachers and Principal of Loknete Dr. J. D. Pawar College of Pharmacy, Manur, Tal-Kalwan.

CONFLICT OF INTEREST:

There are no conflicts of interest mentioned by the author.

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Received on 03.04.2024 Revised on 19.10.2024

Accepted on 22.01.2025 Published on 23.04.2025

Available online from April 26, 2025

Asian J. Pharm. Tech. 2025; 15(2):205-214.

DOI: 10.52711/2231-5713.2025.00032

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Creative Commons License.

Sr. No	Drug	Polymers	Technique	Transporter	Reference
1.	Lamotidine	HPMCK4M	Method of ionotropic gelation	Floating beds	35
2.	Stavudine	Eudragit RS100, RL100	Method of evaporation solvent	Floating microsphere	36
3.	Roxatidine	HPMC, ethyl cellulose	Technique for diffusing solvent	Floating microsphere	37
4.	Nimodipine	Eudragit S 100, ethyl cellulose	Method of evaporation solvent	Floating microsphere	38
5.	Cimetidine	HPMC, ethyl cellulose	Method of evaporation solvent	Floating microsphere	39
6.	Esomeprazole	HPMC K4M, HPMC K15M	Diffusion of double emulsion solvent	Floating microsphere	40
7.	Nizatidine	Polymethyl methacrylate	Method of evaporation solvent	Floating microsphere	41