In recent years several advancements has been made in research and development of oral drug delivery system. Concept of novel drug delivery system arose to overcome certain aspect related to physicochemical properties of drug molecule and the related formulations. Purpose of this review is to compile the recent literature with special focus on various gastro retentive approaches that have recently become leading methodologies in the field of site-specific orally administered controlled release drug delivery. In order to understand various physiological difficulties to achieve gastric retention, we have summarized factors influencing gastric retention and also included various strategies for gastric retention. GRDDS has become leading methodology in site specific orally administered controlled release drug delivery system. Various drugs, which are unstable in alkaline pH, soluble in acidic pH, having narrow absorption window, site of action specific to stomach can be developed by using this technique.

A comprehensive review on gastro retentive drug delivery system

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Gastro Retentive Drug Delivery System is one of the novel approach and all researchers in pharma industries are focused in the same. The main aim of writing this review on Gastro Retentive floating drug delivery systems is to assemble the recent literature with special emphasis on its principal mechanism of floatation to achieve gastric retention and its recent development. Floating systems are low density systems that has density lower than gastric fluid and floats over the gastric fluid and remains buoyant in the stomach without affecting the gastric emptying rate for a prolonged period of time. Floating dosage forms can be formulated as tablets, capsule. This review article includes detailed information about its classification, advantages and in-vitro evaluation parameters. *Corresponding Author Email: arpithakharvi7411@gmail.com Received 10 January 2019, Accepted 21 January 2019 Journal home page: http://www.ajptr.com/ Kharvi et. al., Am. J. PharmTech Res. 2019; 9(01) ISSN: 2249-3387 39 www.ajptr.com INTRODUCTION Oral administration is one of the most appropriate and widely used route for drug to show the systemic effect. The drugs that are well absorbed in the GIT, gets degraded in the intestine, and have a short half-life requires the frequent dosing to achieve the specific therapeutic activity. The development of oral sustained or controlled release formulation, such as gastro retentive drug delivery system can be an attempt to release the drug slowly into GIT for prolonged period and maintain an effective drug concentration in the systemic circulation. The complete absorption of the drug in the absorption site can be prevented by the rapid gastrointestinal transit and can reduce the therapeutic efficacy of the dose that is administered. Most of the drugs are absorbed in the stomach or upper part of small intestine. Gastro-retentive Drug Delivery System (GRDDS) are the type of dosage forms that retains in the stomach. The gastric retention of solid dosage forms can be achieved by different mechanisms such as floating system, sedimentation, modified shape systems, expandable systems etc. FDDS is one of the most feasible approach for achieving the gastric retention for prolonged period. The bulk density of the floating drug delivery system is lower than the gastric fluid thus they remain buoyant in the stomach for longer period of time without affecting the gastric emptying rate. The Gastro-retentive dosage forms on contact with the gastric fluid forms the colloidal gel barrier around the surface, the gel barrier is impermeable to water and thus maintains the bulk density less than one and remains buoyant in the stomach until the entire dose is released. These type of dosage forms remains in the gastric region for several hours and hence considerably increases the gastric residence time of the drugs. The FDDS are mainly useful for drugs that are absorbed in the upper part of the gastrointestinal tract, and drugs that are less soluble in GIT or are degraded by the alkaline pH may benefit from prolonged gastric retention. The FDDS are also useful for local and sustained drug delivery to the stomach and proximal small intestine to treat certain condition, prolonged gastric retention of the drug may offer several advantages together with improved bioavailability and therapeutic efficacy, reduction in dose frequency and possible reduction of the dose size. PHYSIOLOGY OF GIT: GIT system has a complex anatomy and physiology. Variation in pH, bile contents, enzyme activity etc. can influence the dissolution, release and absorption of drug in GIT from the dosage form. The Gastro-intestinal tract is essentially a tube about nine meters long that runs through the middle of the body from the mouth to the anus and includes the throat (pharynx), esophagus, stomach, small intestine (consisting of the duodenum, jejunum and ileum) and large intestine (consisting of the Kharvi et. al., Am. J. PharmTech Res. 2019;9(01) ISSN: 2249-3387 www.ajptr.com 40 cecum, appendix, colon and rectum). Mainly the stomach is divided into three regions the Fundus, Body and Antrum (pylorus).  Body: It acts as a reservoir for undigested materials.  Fundus: Proximal part of stomach.  Antrum: It is the main site for mixing motion and act as a pump for gastric emptying propelling action. Migrating Myoelectric Cycle (MMC): Gastric emptying takes place both in fed and fasting states, the pattern of motility differs in both the states. Due to this bioavailability of drug administered orally is different, because it depends upon the state of feeding. During fasting state inter-digestive series of electrical event takes place between stomach and intestine which is called as inter-digestive myoelectric cycle or migrating myoelectric cycle (MMC). It is divided into four phases-: 1. Phase-I-: It is a basic phase, remains for 30-60 minutes, it does not have any secretory activity and contractile motion. 2. Phase-II-: It is also known as pre-burst phase, intermittent contractions occur and it last for 20-40 minute. As the phase progresses the intensity and frequency also increases gradually. 3. Phase-III-: It is known as burst phase; remains for 4-6 minutes. It includes intense and regular contractions for short time. It is due to wave that all the undigested material is moved out of the stomach down to the small intestine. It is also known as the housekeeper wave. 4. Phase-IV-: It remains for 0-5 minute, occur between Phase III and Phase I. After ingestion of the meals, the pattern of contraction changes from fasted to feed state. These contractions result in reducing the size of food particles to less than 1 mm which is then pushed in the form of suspension towards the pylorus. Kharvi et. al., Am. J. PharmTech Res. 2019; 9(01) ISSN: 2249-3387 41 www.ajptr.com Different features of stomach: Gastric pH: Fasted healthy subject 1.1 ± 0.15 Fed healthy subject 3.6 ± 0.4 Volume: Resting volume is about 25-50 ml Gastric secretion: Acid, pepsin, gastrin, mucus and some enzymes about 60 ml with approximately 4 mmol of hydrogen ions per hour. Effect of food on Gastric secretion: About 3 litres of secretions are added to the food. Gastro Intestinal transit time increase. FACTORS AFFECTING GASTRIC RETENTION: The factors that affects the gastric emptying of an oral dosage form are as follows,  Density: Gastric resident time (GRT) of dosage form buoyancy that is dependent on the density. If the dosage form is having density less than the gastric fluid which can increase the GRT.  Size: Dosage form having a diameter of 7.5 mm has reported to have an increased GRT when compared with the dosage form having diameter of 9.9 mm.  Shape: Tetrahedron and ring shaped devices remains in the stomach for longer period of time with better GRT up to 90-100% retention at 24hrs when compared with the other shapes like planar disc, planar multi lobe, continuous stick and string.  Single or multiple unit formulation: Multiple unit formulations show a more obvious release profile and minor impairing of performance due to failure of units, allow co-administration of dosage form units with different release profiles or containing incompatible substances and permit a more safety against dosage form failure compared with single unit dosage forms. Multiple unit formulations are more reliable as compared to single unit formulations, which suffer “all or none concept”. The units of multiple unit systems are freely distributed throughout the GI tract.  Fed or unfed state: Under fasting conditions, the GI motility is affected by the period of the migrating myoelectric complex (MMC) that occurs every 1.5 to 2 hours. The MMC pushes the Kharvi et. al., Am. J. PharmTech Res. 2019;9(01) ISSN: 2249-3387 www.ajptr.com 42 undigested material from the stomach, and if the time of administration of the formulation coincides with the MMC, the GRT of the dosage for unit can be expected to be very short. However, in the fed state, MMC is delayed and GRT is considerably longer.  Nature of meal: Feeding of indigestible polymers or fatty acid salts such as cellulose, starch, reffinose and poly-dextrose can delay MMC by changing motility pattern of the stomach, thus can decrease the gastric emptying rate, increases the GRT of the dosage form.  Caloric content: GRT can be increased by 4 to 10 hours with the meal containing high proteins and fats can increase the GRT to up to 4-10 hours.  Frequency of feed: The GRT can increase by 400 minutes when successive meals are given compared with a single meal due to the low frequency of MMC.  The resting volume of the stomach is 25 to 50 ml. Volume of liquids administered affects the gastric emptying time. When volume is large, the emptying is faster. Biological factors such as:  Gender: GRT in males around (3.4±0.6 hours) compared with their age and GRT of female around (4.6±1.2 hours), regardless of the weight, height and body surface.  Age: Geriatrics, especially those over 70, have a significantly longer GRT, normal adult’s men have faster gastric emptying rate when compared to women and old people.  Stress can increase the gastric emptying rate while it is decreased in case of depression.  Posture: GRT can vary between supine and upright ambulatory states of the patient. SUITABLE DRUG CANDIDATES FOR GASTRO-RETENTIVE DRUG DELIVERY SYSTEM: 1. Generally, the ideal candidates for GRDDS are molecules that have poor intestinal absorption but having the better absorption in the upper part of the GIT. 2. Acts locally in the stomach. 3. Primarily absorbed in the stomach. 4. Poorly soluble at an alkaline pH. 5. Absorbed rapidly from the stomach. 6. Degrade in the colon. 7. It should be absorbed primarily in the duodenum and upper jejunum segments. e.g. Calcium is mainly absorbed in the duodenum. 8. Drugs which have a short half-life and require frequent dosing. 9. Drugs which undergoes first pass metabolism. Kharvi et. al., Am. J. PharmTech Res. 2019; 9(01) ISS

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A Review on Gastro Retentive Drug Delivery Systems with the Special Focus on Floating Drug Delivery

Background: Rabeprazole sodium is a newer generation anti-ulcer drug with short half-life and low bioavailability. Present research work is an attempt to design novel floating beads of Rabeprazole sodium in multiparticulate dosage form to increase residence time and modulate its release behavior for stomach-specific delivery. Materials and Methods: In this present study, Rabeprazole sodium beads were formulated by ionotropic gelation method and effect of variation in sodium alginate and gellan gum concentrations alone and in combination on release properties was examined. Results: Formulated beads were analyzed for particle size, density, entrapment efficiency, swelling index, in vitro buoyancy properties, surface topography, in vitro drug release and release kinetics study. The percentage content and entrapment efficiency of Rabeprazole sodium in beads ranged from 77.06±3.612 to 92.88±5.723 and 57±1.543 to 89±1.089 respectively. In vitro drug release of Rabeprazole sodium from the beads at the end of 12 hr ranged from 69.373% to 97.0142%. The release behavior was best fitted in Korsemeyer-Peppas equation. F9 was optimized depending on entrapment efficiency, in vitro buoyancy properties and in vitro drug release. Modified formulation F9 was also subjected to a series of tests. mucoadhesive study , in vivo X-ray imaging in rabbits and stability study. Conclusion: These studies revealed that beads exihibited 84% mucoadhesion, floating up to 12 hr as well as stability at 25±2°C. Hence Floating bead formulation of Rabeprazole sodium will be a promising drug delivery system to improve drug residence time and patient compliance.

pdf/multiparticulate-floating-beads-an-aid-to-enhance-2q0udfczg8.pdf

Multiparticulate Floating Beads an Aid to Enhance Therapeutic Efficacy of Rabeprazole

This review explains the recent advances in gastro-retentive drug delivery systems with special focus on floating drug delivery systems. Oral controlled release (CR) dosage forms (DF) have been extensively used to improve therapy of many important medications. However, in the case of narrow absorption window drugs, this pharmaceutical approach cannot be utilized, as it requires sufficient colonic absorption of the drug (which contradicts the definition of narrow absorption window agents). On the other hand, incorporation of the drug into a CR delivery system, which releases its payload in the stomach over a prolonged time period, can lead to significant therapeutic advantages owing to various pharmacokinetic (PK) and pharmacodynamic aspects. Gastro-retentive dosage forms (GRDFs) are a drug delivery formulation that are designed to be retained in the stomach for a prolonged time and release there their active materials and thereby enable sustained and prolonged input of the drug to the upper part of the gastrointestinal (GI) tract. This technology has generated enormous attention over the last few decades owing to its potential application to improve the oral delivery of some important drugs for which prolonged retention in the upper GI tract can greatly improve their oral bioavailability and/or their therapeutic outcome. This article reviews some of the latest developments in GRDF technology from a pharmaceutical point of view.

Gastro-retentive drug delivery system: a review on its recent advancement

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Gastro-retentive drug delivery system: a review on its recent advancement