Process for preparing amorphous rifaximin and the amorphous rifaximin thus obtained

Abstract

A process is described which enables Rifaximin in a completely amorphous form to be obtained. Said process comprises the steps of dissolving crude Rifaximin in absolute ethanol while hot and then collecting after precipitation by cooling the title compound under amorphous form.

1 . Process for preparing amorphous rifaximin in which crude rifaximin is dissolved in absolute ethanol while hot, then collected after precipitation by cooling of the solution. 
   
   
       2 . Process as claimed in  claim 1  wherein the crude rifaximin has a water content of between 4 and 7%. 
   
   
       3 . Process as claimed in  claim 1  wherein the crude rifaximin is dissolved in absolute ethanol in the presence of ascorbic acid. 
   
   
       4 . Process as claimed in  claim 1  wherein the crude rifaximin is dissolved with stirring at a temperature of 40-60° C. and then re-precipitated by cooling the solution to 8-12° C. 
   
   
       5 . Process as claimed in  claim 4  wherein the precipitated rifaximin is collected by filtration, washed with absolute ethanol and dried. 
   
   
       6 . Process as claimed in  claim 5  wherein said drying is conducted under vacuum at 60-70° C. 
   
   
       7 . Amorphous rifaximin obtained according to the process of  claim 1 .