THE PROCESS OF MANUFACTURING PHARMACEUTICAL GRADE TANNATES

摘要

Antihistamines are available in the form of fee bases as well as salt i.e. hydrochloride, maleate, tannate, etc. Frequently, it is necessary to utilise antihistamines in the form of tannate salt because such salts are generally quite stable and may be administered in such from without untoward side effects. Tannic acid, also known as tannin, is a well know naturally occurring substance. Tannic acid, which is available commercially, usually contain about 5 % of water, has a molecular weight of about 1700 and is typically produced from Turkish or Chinese nutgall. Antihistamine tannates, presently manufactured commercially, are relatively impure. Such tannates are prepared by the reaction of antihistamine free base with tannic acid and using a volatile solvent, isopropanol (IPA). The yield is only fair (around 70 %) and decomposition products e.g. 2-5 % along with significant amount of volatile solvent, isopropanol (6-10 %) remains with the product, which cannot be removed. According to present invention, the tannates are made by dissolving tannic acid and amine in different compatible solvents. The solvents can be halogenated alkanes or alkanoic esters. The examples of halogenated alkane is chloroform, and that of alkanoic ester is ethyl acetate. This avoids the use of isopropanol. This method gives tannates which are lighter in colour. Ephedrine and Pseudoephredine tannates are prepared by using ethyl acetate as a medium for reactions to get pharmaceutical grade tannate.