Floating Drug Delivery Systems: Mechanisms, Formulation Approaches, and Future Prospects

People generally find taking medication orally very convenient and painless. Sometimes, the medication moves too quickly through the stomach and the small intestines, giving the body insufficient time to process and absorb it.(1) To counter this, a special drug delivery system named Gastroretentive Drug Delivery Systems (GRDDS) was developed. Gastro-Retentive Drug Delivery System (GRDDS) is a novel oral drug delivery system with a target of maximizing the dwell-time of a dosage form in the stomach region. In standard oral drug delivery systems, dosage forms move quickly through the GI tract, which may cause suboptimal release of the drug or decreased bioavailability, especially for a drug which has a preference for absorption in the stomach or the upper part of the small intestine. [2] GRDDS overcomes these limitations by retaining the drug delivery system in the gastric region for an extended period, thereby ensuring controlled and site-specific drug release. This system is particularly beneficial for drugs that:

Have a narrow absorption window in the upper GI tract

Are locally active in the stomach (e.g., drugs for gastric ulcers or Helicobacter pylori infection)

Are unstable or poorly soluble at intestinal pH

Require prolonged therapeutic action(3,4)

Advantages of Gastro-retentive Drug Delivery System (GRDDS)

1. Improved Bioavailability: Prolonged gastric residence time increases the bioavailability of drugs that depend on the stomach or the proximal part of the small intestine for absorption.
2. Sustained Drug Delivery / Minimized Frequency of Dosing: GRDDS allows controlled and prolonged drug release, thereby reducing dosing frequency and improving patient compliance.
3. Minimal Fluctuation of Drug Concentration: The continuous release of the drug maintains steady plasma levels of the drug and minimizes peak–trough fluctuations.
4. Reduced Adverse Activity in the Colon: By limiting drug exposure to the colon, GRDDS reduces colonic irritation and side effects associated with unstable drugs or irritating drugs in the lower GI tract.(5,6)
5. Enhanced therapeutic efficacy: Prolonged drug release at the absorption site improves therapeutic effectiveness, especially for drugs with a short half-life.
6. Better Patient Compliance: Less frequent dosing and consistent therapeutic effect result in better adherence to treatment regimens.
7. Site-Specific Drug Delivery in the Stomach: GRDDS are ideal for drugs intended for local action in the stomach, such as antacids, antibiotics for Helicobacter pylori, and anti-ulcer drugs.Reduced Drug Wastage: Controlled and targeted drug release minimizes drug loss due to premature passage through the gastrointestinal tract.viii.  Better Absorption of Drugs with Narrow Absorption Window: Drugs that exhibit absorption only in the upper GI tract are greatly benefited by extended gastric retention.
8. Reduced Dose Requirement: Because of the improved bioavailability, the total drug dose can be reduced to avoid dose-related toxicity.(7)
9. Improved Solubility of Weakly Basic Drugs: The acidic environment in the stomach enhances the dissolution of weakly basic drugs, thereby promoting their absorption.
10. Suitable for Drugs Degraded in Intestinal pH: GRDDS protects drugs that are unstable in the alkaline environment of the intestine by retaining them in the stomach.(8)

Types of the gastroretentive system

Gastro-retentive drug delivery systems are designed using different formulation approaches to prolong the residence time of dosage forms in the stomach. Based on the mechanism by which gastric retention is achieved, the GRDDS can be classified into following major types:

1. Floating Drug Delivery Systems: The density of these systems is less than that of gastric fluid; thus, these systems can float on the stomach contents for a considerable period of time. The drug is released while the system is buoyant, making it suitable for drugs whose absorption takes place in the upper GI tract.(9)
2. High-Density Systems: These are formulated with materials having a density greater than that of gastric fluid. They sink to the bottom of the stomach and resist peristaltic movements, thus increasing gastric retention time.
3. Swelling and Expanding Systems: These are systems that swell or expand rapidly following contact with gastric fluid to a size that is large enough to prevent passage through the pylorus. This allows for prolonged gastric residence, thereby providing a sustained drug release.iv. Bioadhesive systems: These systems adhere to the gastric mucosal surface because of bioadhesive polymers, resisting gastric emptying and improving drug absorption.(10,11,12)
4. Raft-Forming Systems: Raft-forming systems form viscous, gel-like floating rafts in the presence of gastric fluid. They are particularly useful in the treatment of gastric reflux and ulcer conditions.
5. Carbon dioxide gas-generating systems: Upon their contact and reaction with gastric acid, a sufficient amount of carbon dioxide gas is produced; this gas gets entrapped in the dosage form, thereby reducing its density and allowing it to float.
6. Ion-exchange resin systems: Drugs complexed with ion-exchange resins are slowly released in the acidic gastric environment, resulting in prolonged gastric retention and sustained release of the drug. Hydrodynamically Balanced Systems (HBS): These are single-unit floating systems formulated with hydrophilic polymers that swell and maintain buoyancy in gastric fluid, ensuring sustained drug delivery.(13,14)

Figure 1: Types of Gastro-retentive drug delivery systems

Of the different approaches for GRDDS, FDDS is the most promising and widely investigated approach. This is because floating systems are designed such that their density is lower than that of the gastric fluid, enabling them to float on the stomach for an extended period of time without interfering with normal gastric emptying. The drug is released in a controlled manner at the desired site while floating on the gastric contents.

The reasons that floating systems represent the most promising GRDDS approach include:

1. Simplicity of Design and Formulation Floating systems can be formulated using conventional polymers and excipients; hence they are more practical and cost-effective compared to complex expandable or bioadhesive systems.(15)
2. Prolonged Gastric Residence Time: Since the floating systems maintain buoyancy, they can stay in the stomach for many hours, allowing extended drug release and enhancement of therapeutic efficacy.(16)
3. Better Patient Compliance: Floating dosage forms are generally well tolerated and do not cause any gastric irritation or obstruction, unlike some swelling or expandable systems.
4. Wide Applicability: Floating systems are suitable for many drugs, especially those that are absorbed in the stomach or upper small intestine, have a narrow absorption window, or are unstable at intestinal pH.(17, 18)
5. Reduced Risk of Gastric Obstruction: Unlike expandable systems, floating systems do not depend on heavy swelling to achieve retention, hence diminishing risks for gastric blockage.
6. Steady-state and controlled drug delivery: floating systems can keep steady plasma drug concentrations by providing sustained drug release while remaining in the gastric region.
7. Clinical and commercial success: Various floating formulations have reached clinical development and commercialization, thus exhibiting practical feasibility and regulatory acceptance.(19)

FDDS basically stand for Floating Drug Delivery Systems, a specialized gastro-retentive drug delivery system. This is designed to stay afloat in the stomach for an extended time. These systems exhibit less density compared to that of gastric fluid, thus these can float on the gastric contents and may not impede the normal process of gastric emptying. The floating may cause the release of the drug in a controlled and sustained manner, allowing prolonged therapeutic action. The prolonged gastric residence time of FDDS increases absorption, mainly of those drugs that are preferentially absorbed from the stomach or the upper part of the small intestine. This approach highly improves bioavailability, therapeutic efficacy, and patient compliance.(20)

Principle of Floating Drug Delivery Systems

FDDS works based on the principle of buoyancy.FDDS is based on the principle of buoyancy. When this dosage form comes in contact with gastric fluids, it is too:

• Producing gas which accumulates in the system and reduces its density, or
• Swell to form a low-density, gel-like consistency that will float.

This leads to a dosage form remaining in the stomach for a couple of hours and releasing the drug at a desired site.(21,22,23)

Suitability Of Floating Drug Delivery Systems

Floating Drug Delivery Systems are specifically beneficial in:

• Drugs absorbed primarily from the upper GI tract, including the stomach and the upper parts of the small intestine
• Drugs that lack good solubility or stability in intestinal fluids
• Drugs with a short biological half-life, which need frequent administration
• Drugs for topical administration within the stomach, for instance, antulcer medications and antacids

By holding the dosage form in the stomach, FDDS helps increase the absorption of the drug and reduce the loss of the drug by rapid gastric emptying.

Benefits of Floating Drug Delivery Systems

• Prolonged Gastric Residence Time: The floating tablets or capsules are retained in the gastric phase for an extended period, thus ensuring a prolonged drug release.
• Increased Drug Absorption and Bioavailability: FDDS increase the absorption of drugs, which are better absorbed under acidic pH or in the upper gastrointestinal region.
• Decreased Dosage Intervals: The need for frequent dosing is reduced due to sustained drug releases.
• Minimized Side Effects: The controlled release of the drug helps to minimize the peak level of the drug in the plasma and thereby the side effects of the drug.
• Effective in Diarrhea and Gastric Motility: In cases of diarrhea and increased gastric motility, FDDS may preserve the retention of the drug in the gastrointestinal tract.
• Increased Patient Compliance: Lower doses of the drug and higher effectiveness of therapy reduce the chances of patient noncompliance.
• Suitable for Local Gastric Action: FDDS are best suited for catering to medications which are designed for local action in the stomach, for example, antibiotics and anti-ulcer medications.(23)

Factors Affecting the Floating and Floating Time of FDDS

The factors affecting floating and floating time of FDDS are as follows: The performance of FDDS largely depends on their ability to remain buoyant in the gastric fluid and retain a position in the stomach for a longer period. Several physiological, formulation-related, and patient-specific factors influence the floating behavior and gastric retention time.

• Density of the Dosage Form: The most critical factor affecting floating behavior is the density of the dosage form. For effective floating, the density of the system should be lower compared to that of the gastric fluid (approximately 1.004 g/cm³). Dosage forms of lower density remain buoyant for a longer time, while systems of higher density tend to sink and are rapidly emptied from the stomach.
• Dosage Form Shape: The shape of the dosage form significantly affects gastric retention and floating stability. It has been observed that tetrahedral and ring-shaped dosage forms possess more excellent floating behaviour and longer gastric residence time as compared to spherical or flat shapes since they can better resist peristaltic movements of the stomach.

Size of Dosage Form: The size of the dosage form is also very significant in determining gastric retention. Dosage forms that are larger than 9.5mm in size will tend to reside in the stomach for a relatively longer time, whereas smaller dosage forms will readily pass into the intestines due to the pyloric sphincter during gastric emptying.(24)

• Gender, Posture, and Age: Various physical properties such as gender, posture, and age demonstrate the effects on gastric emptying time.
• Gastric emptying is slower in females than in males.
• The elderly, especially those above 70 years old, tend to have slow gastric emptying.
• Body position, whether erect or supine, might influence gastric contractions and the flotation process.
• Effect of Concomitant Drugs: Some drugs can cause a change in gastric motility, which can have a subsequent effect on the
• Atropine, glycopyrrolate, metoclopramide, and domperidone can
• But then again, medications such as neostigmine may cause the slowing down of gastric motility, resulting in the prolongation of gastric retention for the floating system.

Disease State: There are numerous diseases that may adversely influence gastric emptying:

• Diabetes mellitus and Crohn’s disease could affect gastric motility and emptying.
• There is a relation of depression to delayed gastric emptying.
• Certain conditions such as stress or anxiety may contribute to faster gastric emptying by increasing gastric motility. Stress and anxiety can also cause faster gastric emptying(25)

Types of floating Drug Delivery System

There are different types of floating systems depending on the floating mechanism:

1. Effervescent (Gas-Generating)

Effervescent-floating systems produce buoyancy by the production of carbon dioxide gas when they come into contact with gastric fluid. The produced gas gets entrapped in the polymer matrix, causing the density of the dosage form to decrease and resulting in the production of a floating system.

Effervescent Floating System Composition Such systems always comprise:

• Gas-producing substances: Sodium bicarbonate, Calcium carbonate
• Acidic parts: Citric acid or tartaric acid (optional, for the purpose of gas evolution
• Hydrophilic polymers: HPMC, Carbopol,
• Excipients: Binders, Lub

Table No. 1: Types of Effervescent (Gas-Generating) Floating Drug Delivery Systems(22,23,24,25,26)

Mechanism of Effervescent (Gas-Generating) Floating Drug Delivery Systems (FDDS):

1. Effervescent or gas-producing : floating systems are designed to generate gas in response to the gastric fluid to which the dosage form is exposed. The gas helps reduce the density of the drug, which then allows it to float along with the gastric fluids in the stomach for an extended period, thus releasing the drug in a regulated fashion.
2. Hydration and Polymer Swelling: The hydrophilic polymers in the formulation start to swell by absorbing the gastric fluid, creating a kind of barrier around the dosage form due to the formation of a gel-like structure.
3. Effervescent Reaction (Gas Generation): The gas-generating reagent (for example, sodium bicarbonate) reacts with gastric acid (or organic acids), resulting in the evolution of carbon dioxide gas according to the following reaction:
4. Gas Entrapment in a Polymer Matrix: The produced CO? is trapped in the swelled polymeric matrix, leading to an expansion in the dosage form and a reduction in its density.
5. Buoyancy and Floating Phenomena: With a density difference in favor of gastric fluids (approximating 1.004 g/cm³), the drug particles float on top of the gastric liquor.
6. Prolonged Gastric Retention: The final property of floating is its role in prolonging gastric
7. Controlled Drug Release: While floating, the drug is released gradually through diffusion and/or erosion of the polymer matrix, maintaining sustained plasma drug levels.(27,28)

Figure 2: Mechanism of Effervescent (Gas-Generating) Floating Drug Delivery Systems

2.Non-Effervescent Floating Systems

Non-effervescent floating systems are a form of gastro-retentive drug delivery systems (GRDDS). These systems work by being buoyant without the production of gas. The primary function of non-effervescent floating systems is carried out by swellable and gelation polymers such as hydroxypropyl methylcellulose (HPMC).

In contrast to effervescent systems, non-effervescent systems do not include gas-releasing agents but rely on the hydration and gelation processes of polymers for lightness and floatation.

Principle of Non-Effervescent Floating Systems

The principle on which non-effervescent floating systems lie is that of hydrodynamic balance. When the dosage form is exposed to gastric fluid:

• hydrophilic polymers: Quickly hydrate and
• A gel barrier is formed around the drug formulation
• The swollen system has a bulk density below that of gastric fluid
• The dosage form remains Buoyant for an Extended Period
• Drug is delivered in a controlled and sustained fashion(29,30)

Table No. 2: Types of Non-Effervescent Floating Drug Delivery Systems(28,29,30,31)

• Oral Dosage: The non-effervescent floating tablet or capsule is taken orally.
• Contact with Gastric Fluid: On arrival at the stomach, the drug form comes into contact with the gastric fluid.
• Polymer Hydration: The hydrophilic polymer Hydroxyzine absorbs gastric fluids and hydrates.
• Swelling and Gelation: The polymer absorbs water to form a viscous hydrogel enveloping the drug product.
• Buoyancy Achievement: The buoyant system has a density that is less than that of gastric fluid; therefore, it floats.
• Prolonged Gastric Retention: The floating drug reduces the risk of rapid gastric emptying
• Controlled Drug Release: The release of the drug is achieved slowly through the process of diffusion and erosion of the gel layer.(32,33)

Figure 3: Mechanism of Non-Effervescent Floating Drug Delivery Systems

Polymer used for a floating drug delivery system

Polymers are also important constituents in the design and development of Floating Drug Delivery Systems (FDDS). These polymers are mainly responsible for providing buoyancy, drug release, and the strength of the drug delivery system in the gastric environment. However, the choice of the appropriate polymer is contingent on factors such as swelling properties, gelation capacity, density, viscosity, and drug compatibility. In FDDS, the polymers absorb the gastric fluid and increase in size to form a thick gel layer around the drug delivery system, making it float as well as preventing the release of the drug quickly. Certain polymers are also responsible for gas entrapment in effervescent systems or for maintaining the entrapped air in non- effervescent systems, thus decreasing the overall system density. In FDDS, the polymers can be either natural, semi-synthetic, or synthetic in nature. (34)Natural polymers like sodium alginate, guar gum, or chitosan are more desirable due to their biocompatible and biodegradable properties. Amongst the semi-synthetic polymers, derivatives such as cellulose are more desirable as hydroxypropyl methylcellulose (HPMC) because of its optimal swelling and drug release capacity. Other synthetic polymers such as Eudragit, polyvinyl alcohol, or biodegradable polymers like PLGA, are used to provide exact drug release along with precise control over drug release and mechanical strength.(35,36)

Table No. 3: Polymers used for a floating drug delivery system (36,37)

Characterization of Floating Drug Delivery Systems (FDDS) is essential to ensure adequate buoyancy, prolonged gastric retention, controlled drug release, and formulation stability. Evaluation of FDDS involves the assessment of floating behavior, swelling characteristics, drug content uniformity, and drug release profile. These studies help in predicting the in vivo performance of the system and confirm its suitability for gastro-retentive drug delivery. The various characterization parameters of FDDS are summarized in the table(38)

Table No.4: Characterization of Floating Drug Delivery Systems (FDDS)

Recent Advancements in Floating Drug Delivery Systems (FDDS)

Floating Drug Delivery Systems (FDDS) have been recognized and identified as one of the most promising areas in gastro retentive drug delivery systems for improving oral bioavailability of drugs with a narrow absorption window, short half-life, and/or preferring stomach and upper GI tract for absorption. Although conventional FDDS have offered a wide range of applications with many advantages, contemporary pharmaceutical research has concentrated on addressing drawbacks, including dependence on gastric emptying patterns, gastric pH, and difficulty in controlling drug release in conventional FDDS. Consequently, new approaches have been introduced to optimize FDDS and make it more efficient and successful.

The progress of FDDS is motivated by:

• unpredictable gastric retention because of physiological variations
• Short duration of floating in conventional systems
• Performance in fasted state scenarios
• Need for better control over drug release kinetics
• Patient-friendly drug delivery systems that target specific needs.

Such challenges have motivated the emergence of the next-next-generation solar floaters with enhanced efficiency and reproducing abilities.(39)

• Advanced Polymer-Based Floating Systems

Current studies also highlight the application of new and multi-functioning polymers for enhanced buoyancy and drug release.

Major Break-Through

• High-viscosity and blend polymers (such as combinations of HPMC and natural gums) to enhance the strength of gels
• Stimuli-sensitive polymers that are sensitive to either pH, ion strength, or gastric motility.
• Combination of bioadhesive polymers and floating polymers to enhance dual gastro-retention properties.

Benefits

• Improved floating stability
• Longer gastric residence time
• Enhanced drug release predictability
• Floating Microspheres & Micro

One of the most important developments in FDDS is the creation of microballoons, or floating microspheres.

Key Features

The

• Hollow spherical structures with low density
• By solvent diffusion or emulsion methods
• Offer advantages over multiple-unit dosage forms

Advantages

• Lower risk of dose dumping
• Uniform distribution in stomach
• Increased patient safety and adherence

It would seem that drug delivery systems are most beneficial for use in chronic therapy, where a drug needs to release slowly for

1. Raft-Forming Advanced Systems

Raft forming systems today embody an evolved form of conventional floating systems. Innovations

• Enhanced alginate raft systems with better mechanical strength
• Calcium release agents for rapid gelation
• Improved floating lag time and rafting stability

Applications

• Managing gastroesophageal reflux disease (GERD
• Localized gastric drug delivery
• Nanotechnology-Based Floating

Nanotechnology has brought forth new possibilities in FDDS development.

Controversial Issues

• Floating nanoparticles and nanospheres within polymeric matrices
• Floating beads and capsules nano-enabled
• Solubility of poorly soluble drugs using nanocarriers

Advantages

• Enhanced solubility and dissolution rate
• Improved Bio
• Controlled and Targeted Drug Delivery
• Dual Mechanism Floating

More recently, two or more gastro-retentive systems are combined for performance improvement.

Examples

• Floating + bioadhesive systems
• Floating + swelling designs
• Floating + Controlled Release Matrix Systems

Significance

• Dependence on singular retention systems decreased
• Advances in gastric retention under different physiological conditions
• 3D Printing and FDDS

Additive manufacturing has recently emerged for FDDS designs.

Major Break-Through

• 3D Printed Floating Tablets w/ Programmable Density
• Customizable drug release profiles
• Individual dosage forms

Impact

• A high degree of control over the geometry and porosity of tablets
• Patient specific
• Smart and Responsive Floating Systems

The Smart FDDS adjusts itself to physiological conditions.

Innovations

• pH-responsive floating systems
• Enzymatic activation
• Time-controlled floating behavior

They are capable of site-specific as well as time-dependent drug release.

Table No. 5: Recent Advancements in Floating Drug Delivery Systems(40,41)

Floating Drug Delivery Systems (FDDS) are a continually expanding domain of research in oral controlled drug delivery systems; they offer many advantages for drugs that have a small window of absorption, a short biological half-life, or for which site-specific entry in the upper GI tract is desired. In view of advances in material science, formulation, and processing methods, FDDS are expected to assume considerable importance in the development of pharmaceuticals in the years to come. One of the key areas that research in FDDS is expected to explore is the development of "smart" and "stimulus-responsive" FDDS. These systems would utilize novel polymers which could respond to changes in gastric pH values, temperature, ion concentrations, as well as gastric contractions. This would enable these systems to ensure desired floating as well as drug release profiles regardless of changes in physiological conditions. Another promising area that is expected to assume importance is that of "nanotechnology" and FDDS coupled together. The addition of nanospheres, Nano-emulsions to FDDS would enable a marked increase in the solubility and availability of sparingly soluble actives. Nano-based advances in FDDS would be particularly useful for a wide range of actives that need to be delivered via the oral geometry, porosity, density, and drug distribution, enabling the design of customized Floating Dosage Forms. This technology is enabling personalized medicine therapies where drug dosage and delivery profiles can be designed specifically for different patients. The future studies are also emphasizing multi-mechanism Gastro-Retentive Systems, combining Floating Mechanism with other retention techniques such as Bioadhesion, Swelling, Expandable Systems, and Muco-Adhesion. The hybrid systems provide improved and consistent gastric retention, overcoming obstacles linked with Single Mechanism FDDS. The expanding application base of Biodegradable, Biocompatible, and Natural Polymers is another significant area. The use of natural polymers is ensuring enhanced safety profiles, lowering toxicity issues, and enabling sustainable drug development. Natural Polymers are also improving patient acceptability and compliance, particularly for long-term drug therapies. In clinical and regulatory contexts, future innovations in In Vitro-In Vivo Correlation (IVIVC) Methods, Imaging Modalities, and Predictive Modeling will enable a seamless transition between lab research studies and real-world drug performance. Future studies will ease faster approvals and launches related to Floating Dosage Form Design.(42)

Key Future Prospects of FDDS

Development of smart, pH- and stimuli-responsive floating systems

• Integration of nanotechnology-based carriers for improved bioavailability
• Application of 3D printing for personalized and customizable FDDS
• Design of multi-mechanism gastro-retentive systems-floatation plus bioadhesion/ swelling
• More usage of biodegradable and natural polymers
• Improved IVIVC and Advanced In-Vivo Imaging Techniques
• Improving the clinical translation and commercialization of FDDS(43)

Table No.6: Marketed Approved Floating Formulations