AN OVERVIEW ON FLOATING DRUG DELIVERY SYSTEM

IRJMST Vol 5 Issue 6 [Year 2014] ISSN 2250 – 1959 (0nline) 2348 – 9367 (Print)

International Research Journal of Management Science & Technology http://www.irjmst.com 24

AN OVERVIEW ON FLOATING DRUG DELIVERY SYSTEM

Author - Avinash Jiddewar

Principal

Navjivan Shikshan Prasarak Madal,

College of Pharmacy, Darva, Maharashtra, India

Mobile no. – 09527597232

E-mail i.d. – [email protected]

ABSTRACT

The purpose this review on floating drug delivery systems (FDDS) was to compile the

recent literature with special focus on the principal mechanism of floatation to achieve

the physiological and formulation variables affecting gastric retention, approaches to

design Effervescent and Noneffervescent floating systems, and their classification and

formulation aspects. It is known that differences in gastric physiology (such as, gastric

pH, motility) exhibit both intra- as well as inter-subject variability demonstrating

significant impact on gastric retention time and drug delivery behavior The floating or

hydrodynamically controlled drug delivery systems are useful in such application. From

the formulation and technological point of view, the floating drug delivery system is

comparatively easy and logical approaches are discussed.

KEY WORD:-

Floating drug delivery system, Effervescent, Noneffervescent, Evaluation, gastric

physiology.

INTRODUCTION

In 1968, Davis firstly discovered the concept of floating drug delivery system (FDDS)

after experience gagging or choking by some persons while swallowing medicinal pills.

The GI-tract is the most important route for the delivery of drugs to the systemic

circulation.1 Effective oral drug delivery process depends upon the factors such as gastric


International Research Journal of Management Science & Technology http://www.irjmst.com Page 125

emptying process, gastrointestinal transit time of dosage form, drug release from the

dosage form and site of absorption of drugs First it would be single dose, which releases

the active ingredient over an extended period of time. Floating drug delivery system

(FDDS) have a bulk density less than gastric fluids and so remain buoyant in the stomach

without affecting the gastric emptying rate for a prolonged period of time (Yie W. Chein

et al, 1992). While the system is floating on the gastric contents, the drug is released

slowly at the desired rate from the system. After release of drug, the residual system is

emptied from the stomach. This results in an increased GRT and a better control of

fluctuations in plasma drug concentration.2 Oral administration is the most versatile,

convenient and commonly employed route of drug delivery for systemic action. Indeed,

for controlled release system, oral route of administration has received the more attention

and success because gastrointestinal physiology offers more flexibility in dosage form

design than other routes. Development of a successful oral controlled release drug

delivery dosage form requires an understanding of three aspects:

Gastrointestinal (GI) physiology

Physiochemical properties of the drug and

Dosage form characteristics.3

CLASSIFICATION:

Floating Oral Drug Delivery System (FDDS) are retained in the stomach and are useful

for drugs that are poorly soluble or unstable in intestinal fluids. Floating drug delivery

system (FDDS) have a bulk density less than gastric fluids and so remain buoyant in the

stomach without affecting the gastric emptying rate for a prolonged period of time. While

the system is floating on the gastric contents, the drug is released slowly at the desired

rate from the system. After release of drug, the residual system is emptied from the

stomach. This results in an increased GRT and a better control of fluctuations in plasma

drug concentration. Floating drug Delivery systems are classified depending on the use of

2 formulation variables:

EFFERVESCENT and NON-EFFERVESCENT SYSTEMS: -

A. Effervescent Floating Dosage Forms:-

1) Volatile liquid containing system: -

The GRT of a drug delivery system can be sustained by incorporating an inflatable

chamber, which contains a liquid e.g. ether, cyclopentane, that gasifies at body

temperature to cause the infatuation of the chamber in the stomach. The device may also

consist of a bioerodible plug made up of PVA, Polyethylene, etc. that gradually dissolves

causing the inflatable chamber to



Release gas and collapse after a predetermined time to permit the spontaneous ejection of

the inflatable systems from the stomach. developed floating capsules composed of a

plurality of granules that have different residence times in the stomach and consist of an

inner foamable layer of gas-generating agents. This layer was further divided into 2

sublayers, the outer containing sodium bicarbonate and the inner containing tartaric acid.

This layer was surrounded by an expansive polymeric film (composed of poly vinyl

acetate [PVA] and shellac), which allowed gastric juice to pass through, and was found to

swell by foam produced by the action between the gastric juices and the gas-generating

agents. It was shown that the Swellable membrane layer played an important role in

maintaining the buoyancy of the pills for an extended period of time.

2) Gas-generating Systems:

These buoyant delivery systems utilize effervescent reactions between

carbonate/bicarbonate salts and citric/tartaric acid to liberate CO2, which gets entrapped

in the gellified hydrocolloid layer of the systems thus decreasing its specific gravity and

making it to float over chyme.5, 6.

B. Non-effervescent systems:

1. Colloidal gel barrier systems Hydrodymamically balance system (HBSTM) was first

design by Sheth and Tossounian in 1975.Such systems contains drug with gel forming

hydrocolloids meant to remain buoyant on stomach contents. This system incorporate a

high level of one or more gel forming highly swellable cellulose type

hydrocolloids.e.g.HEC, HPMC, NaCMC, Polysacchacarides and matrix forming polymer

such as polycarbophil, polyacrylates and polystyrene, incorporated either in tablets or in

capsule. On coming in contact with gastric fluid, the hydrocolloid in the system hydrates

and forms a colloidal gel barrier around the gel surface. The air trapped by the swollen

polymer maintains a density less than unity and confers buoyancy to this dosage forms. 7

2. Microporous Compartment System This technology is based on the encapsulation of

drug reservoir inside a Microporous compartment with aperture along its top and bottom

wall. The peripheral walls of the drug reservoir compartment are completely sealed to

prevent any direct contact of the gastric mucosal surface with the undissolved drug. In

stomach the floatation chamber containing entrapped air causes the delivery system to

float over the gastric contents. Gastric fluid enters throughthe apertures, dissolves the

drug, and carries the dissolve drug for continuous transport across the intestine for

absorption.

3. Alginate beads Multiple unit floating dosage forms have been developed from freeze-

dried calcium alginate. Spherical beads of approximately 2.5 mm in diameter can be

prepared by dropping a sodium alginate solution in to aqueous solutions of calcium

chloride, causing precipitation of calcium alginate. The beads are then separated snap and



frozen in liquid nitrogen, and freeze dried at - 40°C for 24 hours, leading to the formation

of porous system, which can maintain a floating fource over 12 hours.

4. Hollow Microspheres Hollow microspheres (microballons), loaded with ibuprofen in

their outer polymer shells were prepared by a novel emulsion-solvent diffusion method.

The ehanol: dichloromethane solution of the drug and an enteric acrylic polymer was

poured in to an agitated aqueous solution of PVA that was thermally controlled at

40°C.The gas phase generated in dispersed polymer droplet by

evaporation of dichloromethane formed in internal cavity in microspheres of the polymer

with drug. The microballons floated continuously over the surface of acidic dissolution

media containing surfactant for greater than 12 hours in vitro.

Mechanism of floating systems:

Various attempts have been made to retain the dosage form in the stomach as a way of

increasing the retention time. These attempts include introducing floating dosage forms

(gas-generating systems and swelling or expanding systems), mucoadhesive systems,

high-density systems, modified shape systems, gastric-emptying delaying devices and co-

administration of gastric emptying delaying drugs. Among these, the floating dosage

forms are the most commonly used. Floating drug delivery systems (FDDS) have a bulk

density less than gastric fluids and so remain buoyant in the stomach without affecting

the gastric emptying rate for a prolonged period of time. While the system is floating on

the gastric contents (given in the Fig. 2A), the drug is released slowly at the desired rate

from the system. After release of drug, the residual system is eliminated from the

stomach. This results in an increased GRT and a better control of the fluctuations in

plasma drug concentration. However, besides a minimal gastric content needed to allow

the proper achievement of the buoyancy retention effect, a minimal level of floating force

(F) is also required to maintain the buoyancy of the dosage form on the surface of the

meal. To measure the floating force kinetics, a novel apparatus for determination of

resultant weight has been reported in the literature. The apparatus operates by measuring

continuously the force equivalent to F (as a function of time) that is required to maintain

a submerged object. The object floats better if F is on the higher positive side (Fig. 2B).

This apparatus helps in optimizing FDDS with respect to stability and sustainability of

floating forces produced in order to prevent any unforeseeable variations in intragastric

buoyancy 8.

F = Fbuoyancy – Fgravity = (Df – Ds) g v

Where, F = total vertical force,

Df = fluid density,



Ds = object density,

v = volume and

g = acceleration due to gravity 9.

Fig. 2. Mechanism of floating systems.

Factors Affecting the Floating and Floating Time -

Density: - Floating is a function of dosage form buoyancy that is dependent on the

density.

Shape of dosage form: - Tetrahedron and ring shaped devices with flexural modules of 48

and 22.5 kilo pounds per square inch (KSI) are reported to have better floating, 90% to

100% retention at 24 hours compared with other shapes 10

.

Concomitant drug administration: - Anticholinergics like atropine and

propantheline,opiates like codeine and prokinetic agents like metoclopramide and

cisapride; can affect floating time.

Fed or unfed state: - Under fasting conditions, the GI motility is characterized by periods

of strong motor activity or the migrating myoelectric complex (MMC) that occurs every

1.5 to 2 hours 11

Nature of meal: - Feeding of indigestible polymers or fatty acid salts can change the

motility pattern of the stomach to a fed state, thus decreasing the gastric emptying rate

and prolonging drug release 12

.

Caloric content and feeding frequency: - Floating can be increased by four to 10 hours

with a meal that is high in proteins and fats. The floating can increase by over 400

minutes when successive meals are given compared with a single meal due to the low

frequency of MMC.



Age: - Elderly people, especially those over 70, have a significantly longer; floating 13

.

Disease condition such as diabetes and crohn’s disease etc also affect drug delivery.

Posture: - Floating can vary between supine and upright ambulatory states of the patient 14

.

ADVANTAGES OF FLOATING DRUG DELIVERY SYSTEM

The Gastroretentive systems are advantageous for drugs absorbed through the

stomach. E.g. Ferrous salts, antacids.

Acidic substances like aspirin cause irritation on the stomach wall when come in

contact with it. Hence HBS formulation may be useful for the administration of

aspirin and other similar drugs.

Administration of prolongs release floating dosage forms, tablet or capsules, will

result in dissolution of the drug in the gastric fluid. They dissolve in the gastric

fluid would be available for absorption in the small intestine after emptying of the

stomach contents. It is therefore expected that a drug will be fully absorbed from

floating dosage forms if it remains in the solution form even at the alkaline pH of

the intestine.15,16

The gastro retentive systems are advantageous for drugs meant for local action in

the Stomach. E.g. antacids.

When there is a vigorous intestinal movement and a short transit time as might

occur in certain type of diarrhea, poor absorption is expected. Under such

circumstances it may be advantageous to keep the drug in floating condition in

stomach to get a relatively better response.

The gastroretentive systems are advantageous for drugs absorbed through the

stomach, e.g. ferrous salts, antacids.

Acidic substances like aspirin cause irritation on the stomach wall when come in

contact with it. Hence, HBS formulation may be useful for the administration of

aspirin and other similar drugs.

Administration of prolongs release floating dosage forms, tablet or capsules, will

result in dissolution of the drug in the gastric fluid. They dissolve in the gastric

fluid would be available for absorption in the small intestine after empty-ing of

the stomach contents. It is therefore expected that a drug will be fully absorbed

from floating dosage forms if it remains in the solution form even at the alkaline

pH of the intes-tine.



The gastro retentive systems are advantageous for drugs meant for local action in

the stomach. E.g. antacids.

FDDS improves patient compliance by decreas-ing dosing frequency.

Bioavailability enhances despite first pass effect because fluctuations in plasma

drug concentration are avoided; a desirable plasma drug concentration is

maintained by continuous drug release.

Better therapeutic effect of short half-life drugs can be achieved.

Gastric retention time is increased because of buoyancy.

Enhanced absorption of drugs which solubilize only in stomach.

Avoidance of gastric irritation, because of sustained release effect, floatability and

uniform release of drug through multi particulate sys-tem.16

DISADVANTAGES OF FLOATING DRUG DELIVERY SYSTEM

Floating system is not feasible for those drugs that have solubility or stability

problem in G.I. tract.

These systems require a high level of fluid in the stomach for drug delivery to

float and work efficiently coat, water.

The drugs that are significantly absorbed through out gastrointestinal tract, which

undergo significant first pass metabolism, are only desirable candidate.

Floating system is not feasible for those drugs that have solubility or stability

problem in G.I. tract.

Some drugs present in the floating system causes irritation to gastric mucosa

APPLICATION OF FLOATING DRUG DELIVERY SYSTEMS

Floating drug delivery offers several applications for drugs having poor bioavailability

because of the narrow absorption window in the upper part of the gastrointestinal tract. It

retains the dosage form at the site of absorption and thus enhances the bioavailability.

These are summarized as follows.

1. Sustained Drug Delivery

HBS systems can remain in the stomach for long periods and hence can release the drug

over prolonged period of time. The problem of short gastric residence time encountered

with an oral CR formulation hence can be overcome with these systems. These systems



have a bulk density of <1 as a result of which they can float on the gastric contents. These

systems are relatively large in size and passing from the pyloric opening is prohibited.

Eg. Sustained release floating capsules of nicardipine hydrochloride were developed and

were evaluated in vivo. The formulation compared with commercially available

MICARD capsules using rabbits. Plasma concentration time curves showed a longer

duration for administration (16 hours) in the sustained release floating capsules as

compared with conventional MICARD capsules (8 hours).17

2. Site-Specific Drug Delivery

These systems are particularly advantageous for drugs that are specifically absorbed from

stomach or the proximal part of the small intestine, eg, riboflavin and furosemide. Eg.

Furosemide is primarily absorbed from the stomach followed by the duodenum. It has

been reported that a monolithic floating dosage form with prolonged gastric residence

time was developed and the bioavailability was increased. AUC obtained with the

floating tablets was approximately 1.8 times those of conventional furosemide tablets.18

3. Absorption Enhancement

Drugs that have poor bioavailability because of sitespecific absorption from the upper

part of the gastrointestinal tract are potential candidates to be formulated as floating drug

delivery systems, thereby maximizing their absorption. Eg. A significantly increase in the

bioavailability of floating dosage forms(42.9%) could be achieved as compared with

commercially available LASIX tablets (33.4%) and enteric coated LASIX-long product

(29.5%).19

Evaluation of Floating Drug Delivery Systems

Various parameters that need to be evaluated in gastroretentive formulations include

floating duration, dissolution profiles, specific gravity, content uniformity, hardness, and

friability in case of solid dosage forms 20

. In the case of multiparticulate drug delivery

systems, differential scanning calorimetry (DSC), particle size analysis, flow properties,

surface morphology, and mechanical properties are also performed.

A. In Vitro Methods

1) Floating lag time and floating time: The test for floating time measurement is usually

performed in stimulated gastric fluid or 0.1 N HCl maintained at 37 0C. It is determined

by using USP dissolution apparatus containing 900 ml of 0.1 N HCl as dissolution

medium at 37 0C. The time taken by the dosage form to float is termed as floating lag

time and the time for which the dosage form floats is termed as the floating or flotation

time. The system to check continuous floating behavior contains a stainless steel basket

connected to a metal string and suspended from a Sartorius electronic balance 21

.A lotus-



spread sheet could automatically pick up the reading on the balances. Test medium used

in floating kinetics measurements was 900 ml simulated gastric fluid (pH 1.2) maintained

at 37°C, data was collected at 30 sec interval; baseline was recorded and subtracted from

each measurement. Dissolution basket had a holder at the bottom to measure the

downward force.

2) Dissolution study Gohel et al proposed a more relevant in vitro dissolution method to

evaluate a floating drug delivery system (for tablet dosage form). A 100-mL glass beaker

was modified by adding a side arm at the bottom of the beaker so that the beaker can hold

70 ml of 0.1 mole.lit-1 HCl dissolution medium and allow collection of samples. A

burette was mounted above the beaker to deliver the dissolution medium at a flow rate of

2 ml/min to mimic gastric acid secretion rate. The performance of the modified

dissolution apparatus was compared with USP dissolution Apparatus 2 (Paddle). The

problem of adherence of the tablet to the shaft of the paddle was observed with the USP

dissolution apparatus 22

. The tablet did not stick to the agitating device in the proposed

dissolution method. The drug release followed zero-order kinetics in the proposed

method. The proposed test may show good in vitroin vivo correlation since an attempt is

made to mimic the in vivo conditions such as gastric volume, gastric emptying, and

gastric acid secretion rate 23

.

3) Swelling index An in vitro measuring apparatus has been conceived to determine the

real floating capabilities of buoyant dosage forms as a function of time. It operates by

measuring the force equivalent to the force F required to keep the object totally

submerged in the fluid24

.This force determines the resultant weight of the object when

immersed and may be used to quantify its floating or no floating capabilities 25

. The

magnitude and direction of the force and the resultant weight corresponds to the vectorial

sum of buoyancy (F bouy) and gravity (F grav) forces acting on the object as shown in

thee quation

F = F buoy – F grav

F = d f gV – d s gV = (d f - d s) gV

F = (df – M / V) gV

in which F is the total vertical force (resultant weight of the object), g is acceleration due

to Gravity, d f is the fluid density, d s is the object density, M is the object mass, and V is

the volume of the object. By convention, a positive resultant weight signifies that the

force F is exerted upward and that the object is able to float, whereas a negative resultant

weight means that the force F acts downward and that the object sinks 26,27

.



B. In vivo method

1) X-Ray method - X-Ray is a very popular evaluation parameter for floating dosage

form now a day. It helps to locate dosage form in the g.i.t. and by which one can predict

and correlate the gastric emptying time and the passage of dosage form in the GIT. Here

the inclusion of a radio-opaque material into a solid dosage form enables it to be

visualized by Xrays 26

.

2) gamma-Scintigraphy - Gamma -Emitting radioisotopes compounded into CR-DFs has

become the state-of-art for evaluation of gastroretentive formulation in healthy

volunteers. A small amount of a stable isotope e.g. Sm, is compounded into DF during its

preparation. The main drawbacks of gamma - scintigraphy are the associated ionizing

radiation for the patient, the limited topographic information, low resolution inherent to

the technique and the complicated and expensive preparation of radiopharmaceuticals 27

.

3) Gastroscopy - It comprises of peroral endoscopy, used with a fibereoptic and video

systems. It is suggested that gastroscopy may be used to inspect visually the effect of

prolonged stay in stomach milieu on the FDDS. Alternatively, FDDS may be drawn out

of the stomach for more detailed evaluation 28

, 29

.

4) Ultrasonography - Ultrasonic waves reflected substantially different acoustic

impedances across interface enable the imaging of some abdominal organs. Most DFs do

not have sharp acoustic mismatches across their interface with the physiological milieu.

Therefore, Ultrasonography is not routinely used for the evaluation of FDDS. The

characterization included assessment of intragastric location of the hydrogels, solvent

penetration into the gel and interactions between gastric wall and FDDS during peristalsis

30.

CONCLUSION

Recently many drugs have been formulated as floating drug delivery systems with an

objective of sustained release and restricting the region of drug release to stomach. The

principle of buoyant Preparation offers a simple and practical approach to achieve

increased gastric residence time for the dosage form and sustained drug release. The

currently available polymer‐ mediated non effervescent and effervescent FDDS,

designed on the basis of delayed gastric emptying and buoyancy principles, appear to be

a very much effective approach to the modulation of controlled oral drug delivery. The

most important criteria which has to be looked into for the productions of a floating drug

delivery system is that the density of the dosage form should be less than that of gastric

fluid. And hence, it can be concluded that these dosage forms serve the best in the

treatment of diseases related to the GIT and for extracting a prolonged action from a drug

with a short half life.



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AN OVERVIEW ON FLOATING DRUG DELIVERY SYSTEM

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