Skip to main content

Renin Angiotensin Mechanism.

Gastroretentive Drug Delivery Systems: An Introduction.

Gastroretentive Drug Delivery Systems: An Introduction.


  • The name itself indicates that these are drug delivery systems which are retained at GIT (gastrointestinal tract) however, they are defined as follows,
  • Definition: Gastroretentive dosage forms (GRDFs) are a drug delivery formulation that is 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.

Need for Gastroretentive Drug Delivery Systems:

  • Oral drug delivery system Sustained drug delivery systems These drug delivery systems suffer from mainly two adversities:
  1. Short gastric retention time(GRT).
  2. Unpredictable short gastric emptying time (GET)
  • This leads to diminished effects of the administered dose.
  • There are certain drugs having specific absorption windows located in specific parts of the GIT, the short gastric retention time again diminishes their efficacy in administered dose. 
  • Certain conditions like peptic ulcer need local action where the drug is desired to stay for longer period of time at the site of action. 
  • So in order to cope up with the situations stated above, there was a need to design a formulation which can overcome the problem of short gastric retention time.
  • Gastro retentive drug delivery systems were developed as the remedy.

Right Candidates for Gastro retentive Drug Delivery System:



      Drugs acting locally in the stomach (active in the stomach).
Antacids
Drugs for H. Pylori.
Misoprostol
      Drugs that are primarily absorbed in the stomach.
Amoxicillin.
      Drugs that are poorly soluble at alkaline pH.
Furosemide,
Diazepam,
Verapamil,
      Drugs with a narrow window of absorption.
Cyclosporine,
Methotrexate,
Levodopa.
      Drugs which are absorbed rapidly from the GI tract.
Metronidazole,
Tetracycline.
      Drugs that degrade in the colon.
Ranitidine,
Metformin.
      Drugs that disturb normal colonic microbes
Drugs against H. Pylori.

Factors affecting Gastroretentive Systems:

  1. The density of formulation.
  2. The Size and shape of the formulation.
  3. Units in the formulation.
  4. Feeding status of the patient.
  5. Nature of meal taken by the patient.
  6. The frequency of the meals.
  7. Gender of the patient.
  8. Age of the patient.
  9. Sex of the patient.

Physiology of Stomach: 

  • The stomach is an organ with a function for storage and mixing of the food.
  • The stomach is composed of the following parts: the fundus, lying above the opening of the esophagus into the stomach; the body; the central part; and the antrum. 
  • The pylorus is an anatomical sphincter situated between the most terminal antrum and the duodenum.
  • The motility of the stomach differs remarkably between the fasted and the fed state.
  • The antrum region is responsible for the mixing and grinding of gastric contents.
  • Under fasting conditions, the stomach is a collapsed bag with a residual volume of approximately 50ml and contains a small amount of gastric fluid (pH 1–3) and air.

The ideal requirements of Dosage forms for Gastric Retention:

  • The dosage form must satisfy certain requirements: 
  • Ability to withstand the forces caused by peristaltic waves in the stomach and the constant contractions and grinding and churning mechanisms. 
  • Resist premature gastric emptying. 
  • Device should be removed from the stomach with an ease.

Approaches for Gastric Retention:

  • Increasing the GRT of DFs can be achieved in several ways. 
  • Naturally, food high in calorie value or containing fats and some amino acids can slow gastric emptying and intestinal transit. 
  • Certain drugs such as metoclopramide are known to decrease the gastric motility and thus increase the GRT of drugs that are administered concomitantly. 
  • However, it is not acceptable to add a second drug to improve bioavailability. 
  • Recently, some sophisticated technologies have been developed to increase the GRT of drug formulations utilizing different features of the stomach anatomy and physiology.
  1. Floating Drug Delivery Systems.
  2. Expandable Dosage Forms.
  3. Swelling Dosage Forms.
  4. Unfolding Dosage Forms.
  5. Bioadhesive Formulations.
  6. High-Density Formulations.

Methods To Assess Gastroretentivity Of GRDFs:

  1. Magnetic Resonance Imaging.
  2. Radiology (X-Ray).
  3. Ɣ-Scintigraphy.
  4. Gastroscopy.
Upcoming Article: Floating Drug Delivery System.

References:

  1. Encyclopedia of Pharmaceutical Technology.
  2. Lecture Notes.
  3. Ross and Wilsons "Anatomy and Physiology"


Labels:

Popular posts from this blog

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called ...
Read more

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and ...
Read more

Flash Distillation.

  Principle: When a hot mixture is allowed to enter from a high-pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization .  During this process, the chamber is cooled.  The less volatile fraction is condensed and the more volatile component remains in the vapor phase .  This process requires time, hence liquid and vapor are kept in intimate contact until equilibrium is achieved. Flash distillation is also called equilibrium distillation because separation of two liquids takes place when liquid and vapor phases are at equilibrium. Equipment used for Flash Distillation: Construction: It consists of a pump, which is connected to a feed reservoir.  Pumps help in pumping the feed into the heating chamber.  The heating chamber is heat supplied by steam.  The other end of the pipe is directly introduced into the vapor-liquid separator through a reducing valve.  The vapor outlet...
Read more