A SHORT REVIEW ON STOMACH SPECIFIC DRUG DELIVERY SYSTEM
Garima Gupta*, Amit Singh
Department of Pharmaceutics,
R.V. Northland Institute,
Greater Noida, G. B. Nagar, U.P.
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.
REFERENCE ID: PHARMATUTOR-ART-1301
The oral delivery of drugs is the most preferred route of administration due to ease of administration. Drug bioavailability of pharmaceutical oral dosage forms is influenced by various factors. One important factor is the gastric residence time (GRT) of these dosage forms.1 Indeed, gastric retention has received significant interest in the past few decades as most of the conventional oral delivery systems have shown some limitations related to fast gastric emptying time. A gastro retentive dosage form (GRDF) can overcome this problem and is particularly useful for drugs that are primarily absorbed in the duodenum and upper jejunum segments. The classification of different modes of gastric retention is:2
High-density (sinking) systems.
Low-density (floating) systems.
Superporous hydrogel systems.
The oral route is considered as the most promising route of drug delivery. Conventional drug delivery system achieves as well as maintained the drug concentration within the therapeutically effective range needed for treatment, only when taken several times a day.3 Drug that have narrow absorption window in the gastrointestinal tract (GIT) will have poor absorption. For these drugs, gastroretentive drug delivery systems offer the advantages in prolonging the gastric emptying time.4
Several difficulties are faced in designing controlled release systems for better absorption and enhanced bioavailability. One of such difficulties is the inability to confine the dosage form in the desired area of the gastrointestinal tract. Drug absorption from the gastrointestinal tract is a complex procedure and is subject to many variables. It is widely acknowledged that the extent of gastrointestinal tract drug absorption is related to contact time with the small intestinal mucosa.5 Gastroretentive systems can remain in the gastric region for several hours and hence significantly prolong the gastric residence time of drugs. Prolonged gastric retention improves bioavailability, reduces drug waste, and improves solubility for drugs that are less soluble in a high pH environment. To formulate a successful stomach specific or gastroretentive drug delivery system, several techniques are currently used such as hydrodynamically balanced systems (HBS) / floating drug delivery system,6 low density system,7,8 raft systems incorporating alginate gels,9,10 bioadhesive or mucoadhesive systems,11 high density systems,12,13 Superporous hydrogels14 and magnetic systems.15,16
Recent development in technology has provided viable dosage alternatives that can be administered via different routes of administration. Various routes that are used these days include oral, parenteral, topical, nasal, rectal, vaginal, ocular etc. But out of these routes, oral route of drug delivery is considered as the most favoured and practiced way of drug delivery, because of following reasons:17,18
* Ease of administration
* More flexibility in designing
* Ease of production
* Low cost
Most of the drugs given via oral route are subjected to absorption throughout the gastrointestinal tract, with major absorption from stomach and intestine.19,20 Various processes occur after the drug release from the dosage form, which affect the absorption of drugs, e.g. degradation of drug by enzymatic or microbial action, precipitation etc.
Drugs, which get absorb from stomach or show local effect, should spend maximum time in stomach. This however, is found very difficult to occur, in case of conventional dosage forms like tablets and capsules, because of the gastric emptying.
Gastric emptying of a particular dosage form depends on various factors like volume and composition of the meal, temperature and viscosity of the meal, pH of stomach, body posture, emotional state of the individual, diseased state, gastric motility altering drugs etc. Parameters that affect the process of gastric emptying can be studied by various techniques viz. scintigraphy, ultrasonology, endoscopy, radiotelemetry, radiology etc.21,22 Prolonged gastric retention of drug is required in the following conditions:17, 19
* Drug is best absorbed from stomach e.g. aspirin, phenylbutazone etc.
* Gastric fluids facilitate and improve the disintegration and dissolution of the drug,
* Dissolution and absorption of drug is promoted by the food e.g. griseoflvin,
* Slow dissolving drugs,
* Drug show local effect within stomach.
In order to fulfill all these conditions, various approaches of the controlled drug delivery have been developed. One of these types of the approaches, which ensure that a particular drug or dosage form remains within stomach for longer duration of time, is Gastro retentive drug delivery system.23
However, in certain condition gastro retention is considered undesirable:17
* For drugs which are gastro irritant, for e.g. Diclofenac sodium, ibuprofen, acetyl salicylic acid etc.
* For acid labile drugs which are stable at gastric pH, e.g. macrolide antibiotics.
* Drugs which get absorbed throughout the gastrointestinal tract equally.
BASIC GIT PHYSIOLOGY: GASTRIC EMPTYING
The stomach is anatomically divided into three parts:
- antrum (pylorus)
The separation between stomach and duodenum is the pylorus. The part made of fundus and body acts as a reservoir for undigested material, whereas the antrum is the main site for mixing motions and act as a pump for gastric emptying by propelling actions. Gastric emptying occurs during fasting as well as fed states. The pattern of motility is however distinct for the two states. During the fasting state an interdigestive series of electrical events take place, which cycle both through stomach and intestine every 2–3 h.24 This is called the interdigestive myloelectric cycle or migrating myloelectric cycle (MMC), which is further divided into four phases.25
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