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A Short Review on Stomach Specific Drug Delivery System International Journal of PharmTech Research CODEN (USA): IJPRIF ISSN : 0974-4304 Vol.4, No.4, pp 1527-1545, Oct-Dec 2012 A Short Review on Stomach Specific Drug Delivery System Garima Gupta1*, Amit Singh1 1Department of Pharmaceutics, R.V. Northland Institute, Greater Noida, G. B. Nagar, U.P.,India. *Corres.author: [email protected] Abstract: Technological attempts have been made in the research and development of rate-controlled oral drug delivery systems to overcome physiological adversities, such as short gastric residence times (GRT) and unpredictable gastric emptying times (GET). Conventional oral dosage forms pose low bioavailability problems due to their rapid gastric transition from stomach, especially in case of drugs which are less soluble at alkaline pH of intestine. Similarly, drugs which produce their local action in stomach get rapidly emptied and do not get enough residence time in stomach. So, frequency of dose administration in such cases is increased. To avoid this problem, various efforts have been made to prolong the retention time of drug delivery system. In this review, we will discuss about the various approaches to produce gastro retention of drug delivery system, with current & recent developments of Stomach Specific floating drug delivery system. Key words: Gastro retention, Floating drug delivery system, Stomach specific drug delivery, gastric emptying time. INTRODUCTION:- The oral route is considered as the most promising route of drug delivery. Conventional drug delivery The oral delivery of drugs is the most preferred system achieves as well as maintained the drug route of administration due to ease of concentration within the therapeutically effective administration. Drug bioavailability of range needed for treatment, only when taken pharmaceutical oral dosage forms is influenced by several times a day.3 Drug that have narrow various factors. One important factor is the gastric absorption window in the gastrointestinal tract residence time (GRT) of these dosage forms.1 (GIT) will have poor absorption. For these drugs, Indeed, gastric retention has received significant gastroretentive drug delivery systems offer the interest in the past few decades as most of the advantages in prolonging the gastric emptying conventional oral delivery systems have shown time.4 some limitations related to fast gastric emptying Several difficulties are faced in designing time. A gastro retentive dosage form (GRDF) can controlled release systems for better absorption overcome this problem and is particularly useful and enhanced bioavailability. One of such for drugs that are primarily absorbed in the difficulties is the inability to confine the dosage duodenum and upper jejunum segments. The form in the desired area of the gastrointestinal classification of different modes of gastric tract. Drug absorption from the gastrointestinal retention is:2 tract is a complex procedure and is subject to High-density (sinking) systems. many variables. It is widely acknowledged that the Low-density (floating) systems. extent of gastrointestinal tract drug absorption is Expandable systems. related to contact time with the small intestinal Superporous hydrogel systems. mucosa.5 Gastroretentive systems can remain in Mucoadhesive systems. the gastric region for several hours and hence Magnetic systems. significantly prolong the gastric residence time of Garima Gupta et al /Int.J.PharmTech Res.2012,4(4) 1528 drugs. Prolonged gastric retention improves Drug show local effect within stomach. bioavailability, reduces drug waste, and improves In order to fulfill all these conditions, various solubility for drugs that are less soluble in a high approaches of the controlled drug delivery have pH environment. To formulate a successful been developed. One of these types of the stomach specific or gastroretentive drug delivery approaches, which ensure that a particular drug or system, several techniques are currently used such dosage form remains within stomach for longer as hydrodynamically balanced systems (HBS) / duration of time, is Gastro retentive drug delivery floating drug delivery system,6 low density system.23 system,7,8 raft systems incorporating alginate However, in certain condition gastro retention is gels,9,10 bioadhesive or mucoadhesive systems,11 considered undesirable:17 high density systems,12,13 Superporous hydrogels14 For drugs which are gastro irritant, for e.g. and magnetic systems.15,16 Diclofenac sodium, ibuprofen, acetyl salicylic Recent development in technology has provided acid etc. viable dosage alternatives that can be administered For acid labile drugs which are stable at via different routes of administration. Various gastric pH, e.g. macrolide antibiotics. routes that are used these days include oral, Drugs which get absorbed throughout the parenteral, topical, nasal, rectal, vaginal, ocular gastrointestinal tract equally. etc. But out of these routes, oral route of drug delivery is considered as the most favoured and BASIC GIT PHYSIOLOGY: GASTRIC practiced way of drug delivery, because of EMPTYING following reasons:17,18 The stomach is anatomically divided into three Ease of administration parts: More flexibility in designing - fundus Ease of production - body Low cost - antrum (pylorus) Most of the drugs given via oral route are The separation between stomach and duodenum is subjected to absorption throughout the the pylorus. The part made of fundus and body gastrointestinal tract, with major absorption from acts as a reservoir for undigested material, whereas stomach and intestine.19,20 Various processes occur the antrum is the main site for mixing motions and after the drug release from the dosage form, which act as a pump for gastric emptying by propelling affect the absorption of drugs, e.g. degradation of actions. Gastric emptying occurs during fasting as drug by enzymatic or microbial action, well as fed states. The pattern of motility is precipitation etc. however distinct for the two states. During the Drugs, which get absorb from stomach or show fasting state an interdigestive series of electrical local effect, should spend maximum time in events take place, which cycle both through stomach. This however, is found very difficult to stomach and intestine every 2–3 h.24 This is called occur, in case of conventional dosage forms like the interdigestive myloelectric cycle or migrating tablets and capsules, because of the gastric myloelectric cycle (MMC), which is further emptying. divided into four phases.25 Gastric emptying of a particular dosage form depends on various factors like volume and Following four phases as described below:26 composition of the meal, temperature and viscosity PHASE-I: (basal phase) lasts from 30-60 min of the meal, pH of stomach, body posture, with rare contractions. emotional state of the individual, diseased state, PHASE-II: (preburst phase) lasts for 20-40 min gastric motility altering drugs etc. Parameters that with the intermittent action potential and affect the process of gastric emptying can be contractions as the phase progresses, the studied by various techniques viz. scintigraphy, intensity and the frequency also increases ultrasonology, endoscopy, radiotelemetry, gradually. radiology etc.21,22 Prolonged gastric retention of PHASE-III: (burst phase) lasts for 10-20 min it drug is required in the following conditions:17, 19 includes intense and regular contractions for Drug is best absorbed from stomach e.g. short period. It is due to this wave that all the aspirin, phenylbutazone etc. undigested material is swept out of stomach to Gastric fluids facilitate and improve the small intestine. disintegration and dissolution of the drug, PHASE-IV: Lasts for 0-5 min and occurs Dissolution and absorption of drug is between phase 3 and 1 of two consecutive promoted by the food e.g. griseoflvin, cycles. Slow dissolving drugs, Garima Gupta et al /Int.J.PharmTech Res.2012,4(4) 1529 Figure No. 1 patterns of gastroretentive motility After the ingestion of a mixed meal, the pattern of pH (e.g. captopril), and the drugs for local action contractions changes from fasted to that of fed in the stomach (e.g. misoprostol). Antibiotics, state. This is also known digestive motility pattern catecholamines, sedatives, analgesics, anti and comprises of continuous contractions as in convulsants, muscle relaxants, anti hypertensives phase II of fasted state. These contractions result and vitamins can also be administered in HBS in reducing the size of food particles (less than dosage form.27 1mm), which are propelled towards the pylorus in the suspension form. During the fed state onset of FACTORS AFFECTING GASTRO mmc, is delayed resulting in slowdown of gastric RETENTION:23 emptying rate. Scintigraphic studies involving the a) Physiological factors: measurements of gastric emptying rates in healthy Size of dosage form: Dosage forms having human subjects have revealed that an orally diameter greater than the diameter of pyloric administered controlled release dosage form is sphincter escape from gastric emptying and mainly subject to two physiological adversities: remain within gastric region. 1. Short GRT Shape of dosage form: Round or Ring 2. Unpredictable GET shaped dosage form are considered better in Yet another major adversity encountered through comparison to other shapes. the oral route is the first pass effect, which leads to Density: Location of the particular gastro 26 reduced systemic bioavailability of many drugs. retentive dosage form in gastric
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