When a drug is administered in a oral dosage form, and has very less bioavailability in lower intestine, then the absorption and bioavailability of the drug very much depend on gastric emptying time, which is very much unpredictable variable.
Gastro retentive drug delivery systems are drug delivery systems which are intended increase gastric retention time of a dosage form and to deliver a drug in stomach, there are certain conditions when delivering a drug in gastric environment helps to increase its therapeutic efficiency in case a localized drug delivery in stomach is intended.
For example famotidine is used to treat peptic ulcer but it has very low bioavailability when famotidine is delivered in conventional tablet dosage form as it is less soluble in alkaline ph which is encountered in small intestine immediately after a dosage form passes out from stomach.
In order to achieve retaining of a dosage form in to gastric acid, following methods are employed
1. Floating, raft, tablets and capsules.
In this method dosage form is designed so that it floats over gastric juice , method to achieve this include formation of raft , by swelling, expanding , to impart low density to the dosage form , which can be achieved with gas forming systems , sachet systems and hollow microspheres .
2. Bioadhesive or mucoadhesive tablets and capsules:
In this method dosage form is formulated with certain mucoadhesive polymers of hydroxy propyle methyl and propyl cellulose derivatives, and their sodium salts, which up on coming in contact with water swell and stick to mucus wall of stomach, both floating and Bioadhesive or mucoadhesive approaches can also adapted , and exciepients used are Agar , sodium alginate, carbopol and polyvinyl acetate, HPMC and polyacrylate polymers.
Which are the drugs formulated in gastro retentive dosage forms
Aspirin, griseofulvin, cinnarizine, diltiazem,,chlordiazepoxideHCL , acetaminophen, verapimil hydrochloride , pepstatin, ampicillin, amoxycillin trihydrate,, fluorouracil,, benserazide,diazepam, theophylline,furosemide, misoprostol, L-Dopa, ursodeoxycholic acid, atenolol, isosorbide mononitrate, para aminobenzoic acid, piretamide.
Advantages of gastroretentive dosage form
1.Gastrict emptying time which is a major factor in case a drug has absorption window in stomach , absorption and thus bioavailability is increased , which may further reduce the subsequent required number of dosage and drug concentration in a therapy.
2.Local drug delivery to attain localized action can be achieved in stomach.
3.Drug can be formulated as a sustained release or prolonged release dosage form with Gastro retentive dosage form
4.Gastroretentive drug delivery system has good result in case lower intestinal movement is increase like in case of diarrhea .
5.Drugs with low solubility in alkaline PH and which rapidly degrade in alkaline ph or in colon when formulated as gastric floating tablets or capsules or gastroretentive dosage form they are absorbed better. Example famotidine
Disadvantages of gastroretentive dosage form
1.Some drugs like aspirin which breakdown in to salicylic acid which is also has capability of damage stomach lining and form ulceration , which can be dangerous.
2.Drug like ibuprofen , can cause sever acidity , and ulceration in case it stick to gastric lining for longer time.
What is Therapeutic Index ?