Hot melt method for preparing diphenhydramine tannate

摘要

The invention pertains to a method for preparing diphenhydramine tannate by reacting diphenhydramine free base at a temperature of about 75 to about 150° C. with tannic acid neat or as an aqueous slurry containing up to about 20 wt. % water. The diphenhydramine free base may be obtained by reacting a commercially available diphenhydranine salt such as diphenhydramine maleate with a base such as aqueous sodium hydroxide. The resultant diphenhydramine tannate has extended release properties and is useful in pharmaceutical compositions as an antihistamine for human beings.