Mucosa adhesive systems

However, the action of saliva and the continuous swallowing thereof tends to wash away drugs applied to the mucosa, resulting in short retention time and low therapeutic efficacy. Therefore, proper design of a dosage form for use in the oral cavity is necessary [23], and to overcome some of these shortcomings, a buccal adhesive system of drug delivery has been developed and is under continued research for improvement [26,24,25]. 

More recently, increasing research attention has focused upon the use of mucoadhe-sive delivery systems in which the biopharmaceutical is formulated with/encapsulated in molecules that interact with the intestinal mucosa membranes. The strategy is obviously to retain the drug at the absorbing surface for a prolonged period. Non-specific (charge-based) interactions can be achieved by the use of polyacrylic acid, whereas more biospecihc interactions are achieved by using selected lectins or bacterial adhesion proteins. Despite intensive efforts, however, the successful delivery of biopharmaceuticals via the oral route remains some way off. 

Sustained adhesion of the dosage form (tablet, patch) to the mucosa is an important first step to successful buccal delivery. The mucus plays an important role during this mucoadhe-sive process by buccal drug delivery systems. The interaction between the mucus and mucoadhesive polymers generally used in most dosage forms can be explained by theories summarized in Table 9.1. 

The buccal mucosa comprises an expanse of smooth and relatively immobile surface and thus is ideally suited to the use of retentive delivery systems. In contrast, the sublingual mucosa is unsuitable for adhesive dosage forms for a number of reasons, including ... 

An ideal buccal deUveiy system should stay in the oral cavity for at least few hours and release the active ingredients in a unidirectional way towards the mucosa in a controlled or sustained-release fashion. Muco- and bioadhesive polymers are supposed to prolong the residence time of the device in the oral cavity. One of the experiments developed a direct staining method to visualize the polymer adhesion to human buccal cells after exposure to an aqueous dispersion of chitosan. An in vivo study was performed on a test group of human subjects, who rinsed with... 

Bioadhesive systems Drug coated with a bioadhesive polymer that selectively provides adhesion to the colonic mucosa. 

Other rectal dosage forms may be used other than fat-based suppositories. One study describes a liquid suppository that immediately after administration forms a gel with strong adhesion to the rectal mucosa [14]. The gelling at body temperature is caused by a poloxamer. Adhesion to the rectal mucosa is provided by carbomers and cellulose derivates. Compared to a fatty suppository, this delivery system is expected to spread less far into rectum and colon, thereby avoiding the hepatic portal system (see also Sect. 11.3). 

One of the problems ofbuccal delivery is that the surface of the mucous membrane is constantly washed by a stream of saliva, which will exclude a major part of the drug firom absorption and also reduce administration time. Increased residence time can be obtained by using a bioadhesive delivery system (Harris and Robinson, 1990), and such a system has been tested with insulin. A double-layered patch wi an adhesive peripheral layer that stuck to the oral mucosa for 6hr and a core consisting of insulin, sodium glycocholate, and cocoa butter was administered to dogs (Ishida etal, 1981 Nagai, 1985). Bioavailability was calculated as 0.5% as compared with intramuscular administration. 

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