Coating Agents

Coating agents, substances (Mucilaginosa), colloidal substances which have long been used in medicine to protect tissues from external mechanical, thermal, and chemical irritations. Coating agents include various, predominantly plant-based substances: starch, gums, plant mucilages, pectin substances, etc. Coating agents form false solutions with water, i.e., they swell in it, passing into a state of ultramicroscopic division with great adsorptive capacity. Due to this, coating agents impart colloidal properties to the medium, which retard both physical diffusion processes and the absorption of substances present in the medium in dissolved form. By themselves, coating agents do not possess pharmacological action, but they retard the absorption into the blood of other substances - medicinal, nutritional, as well as water. By forming a protective layer on inflamed mucous membranes and skin, coating agents protect them from irritation and thus contribute to the more rapid resolution of the inflammatory process. Being tasteless themselves, coating agents mask the taste of substances mixed with them, mainly sour and pungent; an example is the difference in taste between raspberry and currant: in raspberry, there is less sugar per unit weight than in currant, but the sour taste of raspberry is less perceptible than that of currant, because raspberry contains thirteen times more coating agents than currant. The presence of coating agents in the gastrointestinal tract usually leads to a weakening of reflexes from the mucous membrane; irritating (absorbable) substances in this case act much more weakly; the local action of medicinal substances on the intestine extends over a greater distance and lasts longer when used together with coating agents; this is the basis, for example, of the use of opium, as containing coating agents, preferably over morphine in intestinal diseases. If irritating substances are not absorbed, their use together with coating agents leads to a longer and therefore stronger action; therefore, castor oil as a laxative acts more energetically in emulsion than when given per se. Outside the body, and possibly in the stomach, coating agents retard the digestion of proteins, and are themselves slowly digested and absorbed. As a result, in the gastrointestinal tract, conditions can be created for the microbial and enzymatic breakdown of coating agents. Coating agents are absorbed into the blood in a state of partial breakdown, lose their properties in the process, and are oxidized in the tissues. Coating agents are used: 1) in inflammation of the mucous membranes of the gastrointestinal tract, oral cavity, pharynx, and throat; 2) in poisoning with irritating and caustic substances; 3) in mixtures with irritating medicinal substances; 4) to increase the duration of local action of various substances; 5) to increase the viscosity of a saline solution injected into a vein in order to delay its elimination from the blood; 6) as corrigens and constituents in various pharmaceutical forms. In their action on mucous membranes and skin, coating agents are closely related to so-called adsorbent substances, predominantly of inorganic origin; they are insoluble in water and do not form colloidal solutions with it, but due to their very large surface, they absorb and retain other substances, including gases. The main representatives are: talc, animal and charcoal, clay, etc. They are used in inflammation and ulcers of the gastrointestinal tract, in poisoning with various substances for their adsorption, in the form of powders in skin diseases, for stabilization of medicinal substances in the stomach and intestine, for absorption of poisonous warfare gases in gas masks. Coating agents are also closely related to softening agents (Emollientia), which represent pharmacologically indifferent fats and oils of animal, plant, and mineral origin. Their action on the skin and mucous membranes is generally limited to protection from external influences; but in addition, when rubbed into the skin, they penetrate into its superficial layers, making it soft and elastic; due to this property, the access of other means mixed with softening agents into the skin is facilitated. Softening agents are used in diseases of the skin and mucous membranes either per se or in mixtures with other substances; in the latter case, they constitute constituents for thick and liquid ointments, pastes, suppositories, vaginal balls, plasters, etc.