Oral mucosa physiology

Oral mucosae are covered with mucus that serves as a link between the adhesive and the membrane. Mucin is a polyelectrolyte under neutral or slightly acidic conditions because of the terminal sialic acid residues having a pA a value of 2.6. At physiological pH (7.4), the mucin molecule is polyanionic, which contributes to bioadhesion. 

Advantages of the oral mucosal route of delivery include its capacity to bypass all the limitations associated with the oral route, ease of administration, relatively low content of enzymes, and adequate vascular drainage. As described in the following sections, most of the limitations of the oral mucosa epithelium arise from its stratified nature and its intercellular content characteristics. Nonetheless, due to its direct connection to systemic circulation, delivery systems could potentially be formulated to show either bolus-like or controlled release profiles for specific therapeutic needs. Polymers used in the development of such delivery systems play a major role in the release profile, permeation enhancement, and the localization of the active in the vicinity of the absorbing mucosa. Among the various uses of polymers in delivery systems, their mucoadhesive nature is the most prominent application in the oral mucosal route and is the main focus of this entry. After describing the physiological considerations in the oral cavity mucosa, this entry will review the literature pertinent to the use of polymers in delivery systems for the oral mucosal route. 

THE ORAL MUCOSA AS A SITE FOR DRUG DELIVERY 52.2.1 Physiology... 

Lennernas s group at Uppsala has performed extensive studies to confirm the validity of this in vivo experimental set-up at assessing the rate and the extent of drug absorption. Recovery of PEG 4000 (a non-absorbable marker) is more than 95%, which indicates that the absorption barrier is intact. In addition, maintenance of functional viability of the mucosa during perfusion has been demonstrated by the rapid transmucosal transport of D-glucose and L-leucine. Estimation of absorption half-lives from the measured Pefr agree well with half-lives derived from oral dose studies in humans (i.e. physiologically realistic half-lives). Human Peff estimates are well correlated with the fraction absorbed in humans, and served as the basis for BCS development, and hence the technique is ultimately the benchmark by which other in situ intestinal perfusion techniques are compared. The model has been extensively used to... 

There have been sustained efforts in recent years to use the carrier systems of the brush-border membrane of intestinal mucosa to increase absorption of orally administered drugs [29] [30]. One system of particular interest is the intestinal peptide carrier (hPEPTl) whose physiological function is the absorption of di- and tripeptides and whose xenobiotic substrates include /3-lactam antibiotics, renin inhibitors, and angiotensin-converting enzyme (ACE) inhibitors [31]. 

To assess the impact of drug metabolism in the gut wall on oral bioavailability and develop adequate models for gut wall metabolism, it is necessary to understand the physiology of the intestinal mucosa. 

Ci0H2iNO, Mr 171.28, mp 63 °C, is a white, crystalline powder which gives a physiological cooling sensation on skin or mucosa. It is mainly used to create cooling and freshness in oral care preparations [28b]. 

C13H24O3, Mr 228.33, [a]p max. -78°, is a white, crystalline substance giving a physiological cooling sensation on skin and mucosa [101a], It is used to create neutral cooling effects in cosmetic or oral care preparations (see p. 58). 

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