Applications of Floating Drug Delivery Systems

          Floating drug delivery offers several applications for drugs having poor bioavailability because of the narrow absorption window in the upper part of the gastrointestinal tract. It retains the dosage form at the site of absorption and thus enhances the bioavailability. These are summarized as follows.

Sustained drug delivery:

              HBS systems can remain in the stomach for long periods and hence can release the drug over a prolonged period of time. The problem of short gastric residence time encountered with an oral CR formulation hence can be overcome with these systems. These systems have a bulk density of g1 as a result of which they can float on the gastric contents. These systems are relatively large in size and passing from the pyloric opening is prohibited. Recently sustained release floating capsules of nicardipine hydrochloride were developed and were evaluated in vivo. The formulation compared with commercially available micard capsules using rabbits. Plasma concentration time curves showed a longer duration for administration (16 hours) in the sustained release floating capsules as compared with conventional micard capsules (8 hours).

    Similarly a comparative study between the madopar HBS and madopar standard formulation was done and it was shown that the drug was released up to 8 hours in vitro in the former case and the release was essentially complete in less than 30 minutes in the latter case.

Site-specific drug delivery:
               These systems are particularly advantageous for drugs that are specifically absorbed from stomach or the proximal part of the small intestine, eg, riboflavin and furosemide. Furosemide is primarily absorbed from the stomach followed by the duodenum. It has been reported that a monolithic floating dosage form with prolonged gastric residence time was developed and the bioavailability was increased. AUC obtained with the floating tablets was approximately 1.8 times those of conventional furosemide tablets. A bilayer-floating capsule was developed for local delivery of misoprostol, which is a synthetic analog of prostaglandin e1 used as a protectant of gastric ulcers caused by administration of NSAIDs. By targeting slow delivery of misoprostol to the stomach, desired therapeutic levels could be achieved and drug waste could be reduced.

Absorption enhancement
              Drugs that have poor bioavailability because of site specific absorption from the upper part of the gastrointestinal tract are potential candidates to be formulated as floating drug delivery systems, thereby maximizing their absorption. A significant increase in the bioavailability of floating dosage forms (42.9%) could be achieved as compared with commercially available lasix tablets (33.4%) and enteric coated lasix-long product (29.5%).

Enlists examples of various drugs formulated as different forms of floting tablets.

Tablets    Chlorpheniraminemaleate
Theophylline
Furosemide
Ciprofolxacin
Pentoxyfillin
Captopril
Acetylsalicylicacid
Nimodipine
Amoxycillintrihydrate
VerapamilHCl
Isosorbidedinitrate
Sotalo
Atenolol
Isosorbidemononitrate
Acetaminophen
Ampicillin
Cinnarazine
Diltiazem
Florouracil
Piretanide
Prednisolone
Riboflavin- 5′ Phosphate