Procedimiento para la obtención de cimetidina polimorfo "A" a partir de cimetidina polimorfo "B" impuro

the methods allowing the crystallizations of ethyl-alcohol-water mix and the obtention of an a polymorph cimetidine from impure a and b polymorphs in compliance with the requirements set by us pharmacopeia are described. it was established that if the impurity content was equal to or lower than twice the allowable limit, then absolute ethyl alcohol with a weigth yield over 70 % could be used; however, if the impurity content doubled or tripled the said allowable level, then it would be necessary to use ethyl alcohol with a 6 % content and a weight yield from 60 to 65 %. also, results obtained from testing at an industrial scale presented.