The solid oral dosage forms such as capsule, tablets gives specific drug concentration in systemic blood circulation without getting any control over drug delivery system and also cause major fluctuations in plasma drug concentrations. The most convenient and preferred means of any drug delivery to the systematic circulation is the oral Administration To achieve improved therapeutic advantages the oral controlled release drug delivery system have recently been of increasing interest in pharmaceutical field. such as ease of administration of doses, patient compliance towards the product and flexibility in formulation of drug. Those drugs are eliminated quickly from the systemic circulation who are easily absorbed from gastrointestinal tract [GIT] and have short half- life. the development of sustained -controlled release oral formulations is to avoid this limitation and it is an attempt to release the drug slowly into the gastrointestinal tract and maintain the therapeutic drug concentration in the blood circulation for a long period of time. For to get maximum gastric retention of solid dosage forms is followed by the mechanisms of muco- adhesion, sedimentation, flotation, modified shape systems, expansion or by the simultaneous administration of pharmacological agents followed by gastric emptying. The classification of floating drug delivery systems (FDDS) has been described in detail on the basis of these approaches. The diminished efficiency of the administered dose due to incomplete drug release from the DDS caused by the relatively short gastric residence time in humans through the major absorption zone such as proximal part of GIT. Thus considerations have led to the development of oral controlled release CR dosage forms possessing gastric retention capabilities are the control of location of a drug delivery system, especially for drugs exhibiting an absorption window in the GI tract or drug with a stability problem, in a specific region of the GI tract offers several advantages1. To formulate a successful stomach specific or gastro retentive drug delivery system, many approaches square measure currently utilized within the prolongation of the stomachic residence times (GRT) like hydrodynamic ally balanced systems (HBS) / floating drug delivery system, low density system, raft systems incorporating alginate gels, bioadhesive or mucoadhesive systems, high density systems, super porous

hydro gels and magnetic systems.2 

DEFINITION  

Floating systems are low – density system that have sufficient resistance to float on the stomach and stay float in gastric without creating any effect on the gastric emptying rate for a long period of time. While the system floats on the gastric contents the drug will be released slowly at the desire concentration in the system.Thus, the residue will be cleared from the stomach. Then these results will conduct to GRT elevation and be better control of flux in plasma drug concentrations.  It also useful for proximal gastrointestinal tracts local drugs for example antibiotics for Helicobacter pylori on the manage for a peptic ulcer and for drugs that difficult to dissolve or not stable in  intestinal fluids.3 

STOMACH ANATOMY 

The basic operate of the abdomen is to method and transport food in tittle intestine the duration of food is tiny and largely protein square measure digestible. Structurally the abdomen is split into 3 regions: structure, body, and pylorus. the average pH in fasted healthy person is one .1±0.15, once intake of food the PH scale rises to the level of 3.0 to 4.0.3 

Migrating myoelectric cycle (MMC) is further divide into four phases. They are 

1. Phase I  (basal phase) 

2. Phase II (pre burst phase)

3. Phase III (burst phase) 

4. Phase IV.  

Phase I 

In this phase the gastric emptying rate is slow as the onset of MMC is delayed. this phase usually lasts for 30 to 60 min. Contraction does not occur in this phase. it is also known as basal phase. 

Phase II 

In this phase bile secretion and mucus discharge take place and intermediate contraction occurs. It lasts for 20- 40 mins. It is also known as pre- burst phase. The intensity and frequency increase gradually as the phase progresses. 

Phase III 

In this phase, regular and intense contraction take place for a short time. It last usually for 1020 min.  this phase also called as housekeeper wave as it tends to empty the fasting contents of the stomach. Large objective remains in the stomach in the stomach in the fed state but passed down to the intestine during this phase.    

Phase IV 

Last for 0 -5 minutes and occur between phase III and I of 2 consecutive cycle. After the ingestion of a mixed meal, the pattern of contractions changes from fasted to that of fed state. This also known as digestive motility pattern and comprises continuous contraction as in phase II of fasted state. During the fed state onset of MMC is delayed resulting in slowdown of gastric emptying rate.4 

Need for gastric retention        

• Drugs that are absorbed from the proximal a part of the canal (GIT). Drugs that are less soluble or are degraded by the alkaline pH they encounter at the lower a part of GIT.   Drugs that are absorbed due to variable internal organ evacuation time. Local or sustained drug delivery to the abdomen and proximal bowel to treat bound conditions.  
• Mostly very useful for the treatment of peptic ulcers caused by Helicobacter pylori infections.1 

APPROACHES OF STOMACH RETENTION 

Various approaches are pursed to extended the retention of Associate in Nursing oral dose type within the abdomen for instance, bioadhesive approach during which the adhesive capability of some chemical compounds with conjugated protein is closely applied to the animal tissue surface of abdomen. 1. High density approach  For making ready such variety of formulation, the density of the pellets ought to be over the abdomen fluid. It might be a minimum of one 50 G / ml during this kind the drug will be coated or mixed with significant, nontoxic material like sulfate oxide, etc. Low density approach: floating systems come back Below tenuity approach during this approach, the density of pellets ought to be but one g/ ml thus on float the pellets or tablets within the internal organ fluid and unleash the drug slowly for a extended amount of your time. 

 FACTOR AFFECTING GASTRIC RETENTION 

Factor affecting gastric emptying. The most vital parameters touching stomachal remotion and hence, the stomachal retention time of oral indefinite quantity forms include: 

1. Density:

GRT may be operated of indefinite quantity kind buoyancy that’s obsessed with the density.  

2. Size:

Indefinite quantity kind units with a diameter of quite seven. 5mm or reportable to possess Associate in Nursing exaggerated GRT compared those with diameter of nine .9 mm 

3. Single and multiple unit formulation:

Multiple unit formulations show a lot of inevitable unharness profile and insignificant impairing of performance thanks to failure of units, permit co administration of units with totally different unharness profiles.  

4. Fed or unfed state:

Under fast conditions the GI motility is characterised by periods of study motor active or the migrating myoelectric advanced (MMC) that happens each 1.5 to 2 hours. 

5. Nature of meal:

Feeding of inedible polymer or carboxylic acid salts will modification the motility pattern of the abdomen to a fed state decreasing the stomach remotion rate and prolonging drug release  

6. Calories content:

GRT is exaggerated by four to ten hours with a meal that’s high in protein and fats. 

7. Frequency of feed:

The GRT will increase by over 400 minutes once sequent meals are given. 

8. Gender:

Mean mobile GRT in male (3.4 ± 0.6 hour) is a smaller amount compared with their age and race matched feminine counterpart (4.6 ±  8.2hours) 

9. Age:

senior individuals, particularly those  over  seventy,            have  a considerably longer GRT. 

10. Biological factor:

Polygenic disorder and Crohn’s disease, stress etc. 

11. Posture –

GRT will vary between supine and upright mobile state of the  patient.2 

FLOATING DRUG DELIVERY SYSTEMS (FDDS) 

These formulations have very low density and 

so float over gastric materials.                                                       

1. Bioadhesive systems 

They are fix with stomach mucosa and hence, give the localized retention of the system. 

2. Swelling systems 

These systems absorb water and get enlarged sized by swelling. 

3. High density systems 

These are stays in the stomach for longer period of time, by setting down to the folds of stomach1.  Floating systems are low density systems that have

maximum buoyancy to float on the gastric material and remain in the stomach for the longer period of time. A minimum stomachic content required to allow proper achievement of the bouncy retention principle, a minimum floating force (F) is also to required to keep the dosage form to be buoyant on the surface of gastric content. The force equivalent to F that is required to maintain the submerged 

dosage form force F is on higher positive  

F=F (buoyancy) -F (gravity) = (DF-Ds) g.v --------(1)

Where  

F= total vertical force  

DF = fluid density  

Ds = object density  

V= volume and g= acceleration due to gravity  

6. Mechanism of floating system

Various attempts have been made up to retain the dosage form in the stomach as a way of increasing the retention time. These attempts include introduction floating dosage forms mucoadhesive systems, high – density system, modified shape system, gastric emptying delaying drugs. Among these the floating dosage forms are the most commonly used. Floating drug delivery systems FDDS. Have bulk density less than gastric fluids and so remain buoyant in the stomach without affecting the gastric emptying rate for a prolong period of time. While the system is floating on the gastric contents the drug is released slowly at thedesired rate from the system. After release of stomach. This results in an increased GRT and a better control of the fluctuation in plasma drug concentration.  oral dosage forms (capsule or tablet) that are designed to prolong the retention time of the drug within the GI tract. The recent literature survey shows that interest increased in academics and industrial research regarding

Classification of floating drug delivery system

A. Effervescent FDDS

1. Gas generating system. 

2. Volatile liquid containing system  

B. Non – Effervescent FDDS 

1.  Colloidal gel barrier system. 

2.  Microporous compartment system 

3. Floating microspheres / micro balloons  

4. Alginate floating beads9. 

(C)Raft forming system (A)Effervescent system Effervescent systems include use of gas generating agents, carbonates (e.g Na bicarbonate) and alternative organic acid (e.g acid and salt acid) gift within the formulation to supply CO2 gas so reducing the density of system and creating it float on the gastric fluid. an alternate the incorporation of matrix containing portion of liquid that manufacture gas that evaporate at body temperature.7 

1. Gas generating systems 

These are formulated by intimately mixing the CO2 generating agents and the drug within the matrix tablet. these have a bulk density lower than gastric fluids and therefore remain floating in the stomach unflattering the gastric emptying rate for a prolonged period

the development of novel dosage forms that can be sustained in the stomach for a longer and predictable period of time. The numerous marketed FDDS are given in table. 

2. Volatile  liquid  vacuum  containing systems 

This system is created to float within the abdomen owing to floatation chamber which can be a vacuum or full of air or a harmless gas, whereas drug reservoir is encapsulated within a microporous compartment.8 

B. non-effervescent system 

This type of system when swallowing swell unrestrained via inhibitions of viscus fluid to associate extent that it prevents their exit from the abdomen. these systems could also be remarked because the plug type system since they need a bent to stay lodged close to pyloric valve. One in all formulation strategies of such indefinite quantity forms involves the blending of drug with a gel that swells involved with viscus fluid when oral administration and maintains a relative integrity of form and a bulk density of but one inside the outer jelly like barrier. the air at bay by the swollen compound confers buoyancy to the current indefinite quantity forms. The foremost normally used excipient is non effervescent floating drug delivery system area unit gel forming or extremely swell able polysaccharide sort hydrocolloids, polysaccharides and matrix forming polymers like polyacrylate, polymethacrylate and polycarbonate.9 

1. Colloidal  gel  barrier  systems (hydrodynamic balanced system) 

This system prolong gastric retention time and maximizes the amount of drug that reaches its absorption site in the solution form. It essentially contains drug with gel –forming hydrocolloids to remain buoyant on the stomach content. Such as polycarbophil, polystyrene and polyacrylate. upon contact with gastro intestinal fluid the hydrocolloid in the system hydrates to generate a colloid gel barrier to its surrounding.11 

2. Microporous compartment systems

This technology incorporates the encapsulation technique of a drug reservoir inside a microporous compartment along with pores at top and bottom walls. In the stomach the floatation chamber composed of entrapped air causes the delivery system to float over the gastric content11 

1. Floating  Microspheres  /          Micro balloons 

Hallow microspheres also are known as micro balloons are considered as a most efficient buoyant system. It is composed of central hallow space inside the microsphere. Hallow microsphere is loaded with a drug in their outer polymer shelf are fabricated by a novel solvent diffusion method for emulsion.10 

2. Alginate beads / Floating beads Multi –

Unit floating dosage forms have been developed from calcium alginate spherical beads of about 2.5 mm in diameter and can be fabricated by adding sodium alginate solution into aqueous solution of calcium chloride, resulting in the precipitation of calcium alginate, the beads are further separated, snap – frozen in liquid nitrogen and freeze – dried at 400?c for 24 hrs leads to generation of a porous system. this fabricated system would maintain a floating force for over  12hrs and these floating beads provide a longer residence time of 

more than 5.5 hrs.11 

  (C) Raft- forming systems  Raft – forming system are in much attention for the delivery of antacid and drug delivery for gastro infection and disorders. On contact with gastric fluid, a gel – forming solution swells and forms a viscous of gastric fluid thus facilities release drug slowly in the stomach.11 

ADVANTAGES OF FDDS 

1. Floating dosage form such as tablets or capsules will remains in the solution for prolonged time event alkaline pH of the intestine. 
2. FDDS are advantages for drugs meant for local action in the stomach e:g Antacids . 
3. FDDS dosage forms are advantage in case of vigorous intestinal movement and in diarrhoea to keep the drug in floating condition in stomach to get a relatively better response. 
4. Acidic substance like aspirin causes irritation on the stomach wall when come in contact with it hence FDDS formulation may be useful for the administration of aspirin and other similar drugs.  
5. The FDDS are advantages for drugs absorbed through the stomach e:g ferrous salts . 
6. Slow release of the drug into the body minimize the counter activity leading to higher drug efficacy. 
7. FDDS reduce the drug concentration fluctuation over a critical concentration and thus enhance the pharmacological effects and improves the clinical outcomes.