Patent ID: 8754098

Claim:
A method for producing a polymorph Form ζ of rifaximin, comprising the steps of: forming an ethanol slurry of Form α-dry of rifaximin; maintaining the slurry at ambient temperature for about three days; and crystallizing rifaximin from the slurry; wherein the polymorph exhibits an X-ray powder diffraction pattern having characteristics peaks expressed in degrees 2θ(+/−0.20 degree θ) at: 4.7, 7.6 and 9.5; or 4.7, 7.3 and 8.2; or 7.6, 8.6, and 10.5; or 8.2, 8.6 and 9.5; or 10.2, 12.6, and 13.2; or 7.3, 10.5, and 12.9; or 7.3, 7.6, 8.2 and 8.6; or 4.7, 7.3, 7.6, 9.5, and 10.5; or 8.2, 8.6, 9.5, 10.2, and 10.5; or 8.6, 9.5, 10.2, 10.5, and 11.2; or 4.7 6.3, 6.4, 7.3, 7.6, 8.2, 8.6, 9.5, 10.2, 10.5, 11.2, 11.9, 12.2, 12.6, 12.9, and 13.2.