Patent GB-820495-A (GB)
Title: Improvements in or relating to enteric coatings
IPC: A61K9/28
Filed: 1956-03-15
Abstract: A coating composition for the enteric coating of medicaments comprises a hydrolysed styrenemaleic anhydride copolymer of structure (-Ra-Xb-)n where R represents polymerizable ethylenic units more than 70% of which are styrene units, the remainder being units of acrylonitrile, acrylic acid, methacrylic acid, itaconic acid, vinyl chloride or vinylidene chloride, X represents ethylenic units of which more than 50% are maleic acid units, the remainder being maleic anhydride and a/b equals from 1 to about 4, or a non-toxic water-soluble salt thereof, either alone or together with a plasticiser and/or a dusting powder, the coating materials being dissolved in a polar low-boiling solvent.  Specified solvents include methanol, ethanol, dioxane, acetone, methylethyl ketone or mixtures thereof.  Plasticisers include dibutyl, diethyl and dioctyl phthalate, polyethylene glycols and glyceryl mono-oleate.  Liquid petrolatum may also be added to increase the ease of application. Specified dusting powders include talc, barium sulphate, "dry-flo" starch, calcium stearate, styrene-maleic anhydride copolymer and hydrolysed styrene-maleic anhydride copolymer.  A detailed preparation of the hydrolysed styrene-maleic anhydride copolymer is given.ALSO:Medicaments are coated with an enteric coating comprising a hydrolysed styrene-maleic anhydride copolymer of structure (-Ra-Xb-)n, where R represents polymerizable ethylenic units more than 70% of which are styrene units the remainder being units of acrylonitrile, acrylic acid, methacrylic acid, itaconic acid, vinyl chloride or vinylidene chloride, X represents ethylenic units of which more than 50% are maleic acid units, the remainder being maleic anhydride, and a/b equals from one to about four, or a non-toxic water-soluble salt thereof, either alone or together with a plasticizer and/or a dusting powder, the coating materials being dissolved in a polar low-boiling solvent and after coating the coated medicament is coated intermittently with a dusting powder.  Solvents specified include methanol, ethanol, dioxane, acetone, methyl ethyl ketone or mixtures thereof.  Specified plasticizers are phthalic acid esters of straight and branched chain aliphatic alcohols such as p dibutyl phthalate, diethyl phthalate and dioctylphthalate, polyethylene glycols and glyceryl mono-oleate.  Liquid petrolatum may be added to the composition to increase the ease of application. Medicaments which may be coated include sodium salicylate, ammonium chloride, theophylline-sodium acetate, thyroid, erythromycin, sodium chloride, potassium chloride, magnesium sulphate, potassium nitrate, ferrous sulphate, methenamine-sodium biphosphate, mandelic acid-ammonium chloride, emetine and bismuth compounds, aminophyllin, theobromine-sodium acetate, pancreatin, bile salts, extract of bile, digitalis, gentian violet, some anthelmintics, trypsin, metallic sulphides, salts of mercury, sodium ricinoleate, delayed action medicaments such as 10[2-(1-pyrrolidyl) ethyl]-phenothiazine hydrochloride, pepsin, ammonium salicylate, potassium p-aminobenzoate and bacterial antigens.  Talc is the preferred dusting powder, but barium sulphate, "Dry-flo" starch, calcium stearate, styrene-maleic anhydride copolymer and hydrolysed styrene-maleic anhydride copolymer may also be used.  The medicament in the form of tablets or pills may be sub-coated prior to coating with the enteric coating, which may be carried out by tumbling in a coating pan or by spraying.  Examples are given.