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Figure 3.8 Clearance of a micronised resin from a Zydis™ formulation demonstrating trapping of resin between papillae on the tonge (mean clearance±sd)

trapped within the papillae of the tongue. There was little spread of the formulation laterally in the buccal cavity. Surprisingly, incorporation of salivary stimulants made little difference to the rate of dissolution of the formulation. Salivary stimulants increase the output of the submandibular and sublingual salivary glands, which discharge watery secretions onto the floor of the mouth, wetting the side of the tongue and cheek surfaces. The posterior third of the tongue surface contains mucus glands, but the quantity of secretion is relatively small. Thus increased salivary flow may not result in a more aqueous phase available for dissolution of the dosage form from the tongue surface. Delivery of drugs from a fast-dissolving formulation would not be expected to avoid first-pass metabolism since the unit disintegrates rapidly and the drug would be swallowed.

Bioadhesive dosage forms

Bioadhesion is a process which occurs when two materials, at least one of which is biological, are held together by interfacial forces. In pharmaceutics, bioadhesion is typically between an artificial material e.g. a polymer and/or a copolymer and a biological substrate. Where the biological substrate is covered with a mucus layer, the term "mucoadhesion" is used. It is described as a two-step process: first is the contact between two surfaces and second the formation of secondary bonds due to non-covalent bonding.

Many polymers can potentially be used in bioadhesive systems, including both water soluble and insoluble hydrocolloids, ionic and non-ionic and hydrogels. Appropriate materials for buccal delivery systems have to be mucoadhesive, have a sustained-release property and good feel in the mouth47. Bioadhesives have been formulated into tablets (e.g. Susadrin® (Pharmax Ltd.) which contains nitroglycerin48); gels and patches. Adhesive patches appear to be the most widely studied systems for buccal drug delivery. Patches vary

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