Colloidal Preparations

Colloidal Preparations represent aqueous colloidal solutions or hydrophilic dry colloids (see), which swell upon contact with water and yield colloidal solutions or gels. Colloidal preparations make possible the introduction into the body of substances insoluble in water, which in colloidal form in many cases exhibit very strong action (for example, sols of gold and silver). In the introduction of colloidal preparations into medicine, many (largely unverified) assumptions played a role regarding the coating action of hydrophilic colloids (mucilages, glues, gelatin, tragacanth), supposedly protecting damaged or potentially damaged tissues from the action of harmful substances; regarding the absence of harmful influence of colloids on the osmotic state of cells, since colloids have low osmotic pressure and cannot penetrate cells; regarding the absence of salting-out action, characteristic of electrolytes; regarding the selective action of certain colloids (experiments on vital staining of tissues; Ehrlich); regarding the similarity (Bredig) of the action of metal colloidal solutions to the action of enzymes, etc. Methods for obtaining colloidal preparations can be divided into methods for obtaining colloidal solutions (see Colloids, colloidal chemistry) and methods for obtaining dry colloidal preparations. Methods for obtaining dry preparations: 1) precipitation from aqueous colloidal solution with alcohol or concentrated solutions of electrolytes; 2) evaporation of the colloidal solution, necessarily at low temperature in drying cabinets of the vacuum-dryer, ventilation type, as well as with moving parts (drum and belt dryers and dryers of the spray system). Drying must be rapid and under conditions preventing the transition of the gel into an irreversible modification. - To impart greater stability to colloidal preparations and protect them from "aging," stabilizing substances (see Protective action) are introduced into their composition. Storage of colloidal preparations requires the use of all possible precautions: dark and non-leaching glassware, storage in a dark and cool place, tight sealing to prevent penetration of dust and vapors (especially ammonia and acids). Main colloidal preparations used in modern therapy. 1. Water-insoluble (heavy) metals, their oxides, hydroxides of oxides, and some salts. These include preparations of gold (obtained from a solution of gold hydrochloric acid by reduction with tin chloride or formaldehyde); preparations of silver [obtained by reduction of freshly precipitated silver oxide in the presence of sodium salts of protalbuminic or lysalbuminic acids as a protective colloid (see Colyargol)]; silver oxides or proper silver oxide (AgOH) [obtained by precipitation in the presence of protective colloids (see Protargol)]; mercury [obtained by reduction of corrosive sublimate with formaldehyde or emulsification of mercury in solutions of protein substances (girgol)]; mercurous chloride (obtained by interaction of solutions of mercurous nitrate and NaCl); lead, bismuth, copper, etc. Iron oxide, peptized with ferric chloride (Liquor Ferri oxychlorati) or with protein in the presence of alkali (Liquor Ferri albuminati), -iron albuminate (see) - has been included in the Pharmacopoeia VII with preparation formulas. Most of these colloidal preparations have a positive charge of micelles. 2. Metalloids and acids. Colloidal sulfur (obtained by the action of strong sulfuric acid on hyposulfite or by interaction of hydrogen sulfide and sulfur dioxide); colloidal silicic acid (precipitated by pouring liquid glass into excess HCl, followed by dialysis); colloidal arsenic, antimony, and their oxygen and sulfur compounds, synthetic high-molecular dyes. Colloidal preparations of this group are electronegative. 3. Colloidal solutions of natural colloids (starch, mucilages, proteins), to which milk, serums, vaccines, and proteinotherapeutic preparations should also be added; their particles can be negatively, positively, or amphoterically charged. Recent research shows the colloidal nature of many solutions considered typically crystalloid (Burov's fluid, lead acetate, solution of potassium arsenite, Claproth's drops, and many others), which also explains the phenomenon of "aging" of these drugs. - Among hydrophobic colloidal preparations, mention should be made of carbon and kaolin, whose adsorption properties are often used in therapy. Testing of colloidal preparations consists of determining the amount of active substance and the degree of its dispersion (size and uniformity of particles), quality, quantity, and state of the protective colloids or other stabilizing substances present, quality and quantity of electrolytes or other crystalloids. All colloidal preparations are salted out by electrolytes - it is best to use sodium nitrate for this purpose, which does not give precipitates with crystalloids; sodium chloride, sodium sulfate or ammonium sulfate, etc. are also commonly used. Great importance is attached to determining the quality of stabilizers, since in some colloidal preparations the proteinotherapeutic action of the protective colloid is more pronounced than the specific action of the main substance in the preparation. For studying the colloid-chemical properties of the preparation, determination of viscosity (viscometers), surface tension of solutions (stalagmometer), optical properties (ultramicroscopy, Tyndall phenomenon, polarization, X-ray interference, Brownian motion), relation to ultrafiltration, electrophoresis and electrocataphoresis, rate of sedimentation of particles (when centrifuging at a very high number of revolutions), etc. are used. It is very important for substances to be administered intravenously to establish their stability to blood pH and to salts of physiological solution. Good colloidal protection is characterized by the absence of reactions usual for the given preparation in crystalloid form (for example, protargol or colyargol should not give a precipitate with a weak solution of sodium chloride, not yet capable of salting them out; "dialyzed" iron oxide should not give reactions characteristic of trivalent ionized iron with yellow blood salt or thiocyanates, etc.). - Few colloidal preparations have found application in the form of organosols, most often in the form of glues or lacquers, such as collodion (see), traumatcin, etc.