Verfahren zur Herstellung von stabilen Tetracyclinpraeparaten

Stable, approximately neutral solutions of tetracyclines, for internal or topical use, comprise a tetracycline of formula wherein R1 is hydrogen or chlorine, R2 is hydrogen or methyl and R3 is hydrogen (i.e. tetracycline; chlortetracycline; demethyltetracycline; or demethylchlortetracycline), with approximately 2 molar equivalents of a pharmaceutically acceptable calcium salt, and 15-25% w/v of urea, in a suitable pharmaceutically acceptable polydyric alcohol. The preferred pH is 6.5-7.5, and if necessary is adjusted by a physiologically acceptable base (e.g. alkanolamines). Suitable calcium salts are the cyclohexyl sulphamate, chloride, lactate, acetate, lactobionate, levulimate, or ascorbate. Preferred polyhydric alcohols are propylene glycol, glycerol, or liquid polyethylene glycols. Other optional ingredients include antioxidants, (e.g. sodium bisulphite, monothioglycerol, distilled water up to 15% vol/vol, flavours, benzocaine, adrenocorticoids, or vitamins. The preparations are exemplified by oral preparations (syrups), otic drops, and solutions sterilised by autoclaving.