Hydrogels for Oral Administration

SEONG HOON JEONG, YOURONG EU, and KINAM PARK 

Departments of Pharmaceutics and Biomedical Engineering, Purdue University, West Lafayette, Indiana, U.S.A. 

One of the unique properties of hydrogels is that due to isotropic swelling, the original shape can be maintained during and after swelling. 

Polycationic hydrogels swell less at neutral pH than at acidic pH thus they minimize drug release at higher pH. This property was applied to mask poor tastes of some drugs in the neutral pH environment of the mouth. When caffeine was loaded into hydrogels made of copol3miers of methyl methacrylate and AT -dimethylaminoethyl methacrylate (DMAEM), it was not released at neutral pH, but released with zero-order at pH 3-5 where DMAEM became ionized (18). 

Polycationic hydrogels in the form of semi-interpene-trating polymer networks (semi-IPN) have also been used for drug delivery to the stomach. Semi-IPN of crosshnked chitosan and PEO showed more swelUng imder acidic conditions. This type of hydrogels could be applied for local dehvery of antibiotics, such as amoxicillin and metronidazole, in the stomach for the treatment of Helicobacter pylori (19). 

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Commercially, pullulan is produced by a fermentation process. A fungus Aureobasidium pul-lulans grows on a carbohydrate substrate. Then A. pullulans is harvested, followed by the rupture of cell with either enzyme or physical force. Pullulan then is extracted using simple water extraction process. The process is completely eco-friendly and therefore pullulan can be used for drug delivery. Pullulan hydrogel microparticles or nanoparticles are used for oral administration of gastro-sensitive drugs. 

The pH-sensitive hydrogels have been most frequently used to develop controlled release formulations for oral administration. The pH in the stomach (<3) is quite different from the neutral pH in the intestine, and such a difference is large enough to elicit pH-dependent behavior of polyelectrolyte hydrogels [95]. These hydrogels have been investigated in a number of therapeutic oral delivery systems either as... 

Sensitivity to pH Changes. The second strategy developed for the oral administration of drugs through hydrogels is based on their sensitivity to changes in pH in different areas of the digestive which allows them to swell to acid or neutral pH and to release the bioactive compound in areas such as the stomach or intestine. 

The aim of many of the hydrogels that have been designed for controlled drug release is to have their administration through different routes, for example, oral, nasal, vaginal, subcutaneous, or transdermal. ... 

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