Oral dosage forms, adhesivity

Interest in the adhesion of dosage forms to epithelial surfaces has heen aroused hy the possihility of deliberate contact between oral dosage forms and the gut wall to retard the rate of transit down the gastrointestinal tract, but also by the possibility of dosage forms accidentally adhering to the oesophagus or other epithelial surfaces. Adhesive preparations have been formulated for diverse tasks such as the topical treatment of stomatitis and the administration of insulin. The adhesive nature of transdermal patches is important, as is the adhesion of film coats to tablet surfaces. Adhesion of erythrocytes and bacterial cells to polymer surfaces is also of importance in the understanding, respectively, of blood compatibility of polymers and bacterial infection mediated by catheters. 

Adhesivity of oral dosage forms may be a factor in determining their efficacy (buccal delivery) or in causing adverse events (as in oesophageal injury) adhesion of transdermal patches to the skin is clearly important. 

Povidone can be used in oral drops, oral solutions, syrups and in topical solutions to improve the solubility of active substances in the same way as in parenteral dosage forms. The medium and higher molecular weight grades, are usually used for this purpose, as they increase the viscosity of the solutions, which can be an advantage in providing a constant drip rate or improving the appearance or the adhesion to the skin. 

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]. 

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