Oral mucosa secretions

While the metabolic activity of the oral cavity towards peptides and proteins is less than that of the GI tract, it should be recognized that the oral mucosa and secretions do have the ability to degrade drugs and that measures might be necessary to overcome this. 

If atropine is administered in large amounts, it can cause a number of systemic effects, for example relaxing muscular spasm in the gastrointestinal tract, gall bladder, urinary bladder and ureter. It has been used to reverse bradycardia and dry the secretions of bronchial and oral mucosa prior to surgery. 

Oral mucosae are composed of multiple layers of cells, which show various patterns of differentiation dependent on the functions of different regions in the oral cavity. The oral mucosa is covered by a stratified, squamous epithelium, and three different types of mucosa can be distinguished the masticatory, the lining, and the specialized mucosa. Blood supply to the oral cavity tissues is delivered via the external carotid artery, which branches to the maxiliary lingual and facial artery. There are no mucus-secreting goblet cells in the oral mucosa, but mucins are found in human saliva. These mucins are water-soluble and form a gel of 10-200 pm thickness. Saliva, mainly composed of water (99%), is continuously secreted in the oral cavity and exists as a film with a thickness of 0.07-0.1 mm. ... 

Nasal decongestant sprays such as phenylephrine and oxymetazoline that reduce inflammation by vasoconstriction are often used in sinusitis. Use should be limited to the recommended duration of the product to prevent rebound congestion. Oral decongestants may also aid in nasal or sinus patency. To reduce mucociliary function, irrigation of the nasal cavity with saline and steam inhalation may be used to increase mucosal moisture, and mucolytics (e.g., guaifenesin) maybe used to decrease the viscosity of nasal secretions. Antihistamines should not be used for acute bacterial sinusitis in view of their anticholinergic effects that can dry mucosa and disturb clearance of mucosal secretions. 

Unlike the skin, the mucosae of the oral cavity are constantly maintained moist by the continual secretion of saliva from the three major salivary glands (submandibular, parotid, and sublingual) and the minor salivary glands located in or beneath the mucosae. The thickness of the salivary film (pellicle) has been calculated to be between 70 /rm and 100 /./m [23] however, both the composition and amount of saliva produced can vary between individuals, with time of day, disease states, and drug therapy [33], all of which must be taken into account when considering the oral cavity as a site for drug delivery. 

Omeprazole (p. 167) can cause maximal inhibition of HCl secretion. Given orally in gastric juice-resistant capsules, it reaches parietal cells via the blood. In the acidic milieu of the mucosa, an active metabolite is formed and binds covalently to the ATP-driven proton pump (H+/K+ ATPase) that transports H+ in exchange for IC into the gastric juice. Lansoprazole and pantoprazole produce analogous effects. The proton pump inhibitors are first-line drugs for the treatment of gastroesophageal reflux disease. 

Pancreatic enemies (B) from slaughtered animals are used to relieve excretory insufficiency of the pancreas ( disrupted digestion of fats steatorrhea, inter alia). Normally, secretion of pancreatic enzymes is activated by cholecystokinin ancreozymin, the en-terohormone that is released into blood from the duodenal mucosa upon contact with chyme. With oral administration of pancreatic enzymes, allowance must be made for their partial inactivation by gastric acid (the lipases, particularly). Therefore, they are administered in acid-resistant dosage forms. 

Seventy-four percent of oral doses of PCMTB-l C were excreted in the bile by conventional rats. Most of this (50 to 70%) has been characterized to be products of the MAP (8). Neither of the mercapturates shown in fig. 3 were secreted in the bile therefore, the mercapturic acids that were excreted with the germfree rat feces had to have been formed either by metabolism of the precursors of the mercapturic acid by the intestinal mucosa, or by the tissues during enterohepatic circulation of these precursors. Comparison of the rates of excretion of oral doses of PCMTB- C given to germfree and conventional rats indicate that there was enterohepatic circulation of the in the germfree rats. Conventional rats excreted more than 80 percent of the dose in the feces within two days while it took at least eight days for the germfree rats to excrete 80 percent of the dose in the feces. 

For orally administered peptides and proteins, the gastrointestinal tract is the major site of metabolism. Presystemic metabolism is the primary reason for their lack of oral bioavailability. Parenterally administered peptides and proteins, however, may also be metabolized in the intestinal mucosa following intestinal secretion. At least 20% of the degradation of endogenous albumin takes place in the gastrointestinal tract [13]. 

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