Chemical Complexation

The sulfate esters and sulfonate derivatives of polysaccha-rides and lignin form chemical complexes with the enzyme pepsin. These complexes have no proteolytic activity. Because polysulfates and polysulfonates are poorly absorbed from the GI tract, specific chemical complexation appears to be a desirable mechanism of pepsin inhibition.77 Unfortunately, these polymers are also potent anticoagulants.

The properties of chemical complexation and anticoagulant action are separable by structural variation. In a comparison of selected sulfated saccharides of increasing number of monosaccharide units, from disaccharides through starch-derived polysaccharides of differing molecular size, three conclusions are supported by the data: (a) the anticoagulant activity of sulfated saccharide is positively related to molecular size; (b) anticoagulant activity is absent in the disaccharides; and (c) the inhibition of pepsin activity and the protection against experimentally induced ulceration depend on the degree of sulfation and not on molecular size.77 The readily available disaccharide sucrose has been used to develop a useful antiulcer agent, sucralfate.

Sucralfate. Sucralfate, 3,4,5,6-tetra-(polyhydroxyalu-minum)-a-d-glucopyranosyl sulfate-2,3,4,5-tetra-(polyhy-droxyaluminum)-jS-d-fructofuranoside sulfate (Carafate), is the aluminum hydroxide complex of the octasulfate ester of sucrose. It is practically insoluble in water and soluble in strong acids and bases. It has a pKa value between 0.43 and 1.19.

Sulcrafate Mechanis

Sucralfate R = S03[AI2(0H)5]

Sucralfate is minimally absorbed from the GI tract by design, and thus exerts its antiulcer effect through local rather than systemic action. It has negligible acid-neutralizing or buffering capacity in therapeutic doses. Although its mechanism of action has not been established, studies suggest that sucralfate binds preferentially to the ulcer site to form a protective barrier that prevents exposure of the lesion to acid and pepsin. In addition, it adsorbs pepsin and bile salts. Either would be very desirable modes of action.

The simultaneous administration of sucralfate may reduce the bioavailability of certain agents (e.g., tetracycline, phenyt-oin, digoxin, or cimetidine).78 It further recommends restoration of bioavailability by separating administration of these agents from that of sucralfate by 2 hours. Presumably, sucralfate binds these agents in the GI tract.78 The most frequently reported adverse reaction to sucralfate is constipation (2.2%). Antacids may be prescribed as needed but should not be taken within 0.5 hour before or after sucralfate.

Dosage forms: Tablets ( l g) and suspension (1 g/10 mL) Usual adult dose: 1 g (10 mL or 2 teaspoons of the oral suspension) 4 times a day on an empty stomach. Oral, 1 g 4 times a day on an empty stomach. Treatment should be continued for 4 to 8 weeks.

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