Minocycline base polymorphic forms and its preparation method

The present invention relates to a minocycline in V cryst. form with a X diffractogram ratio having peaks at 2.9; 5.34; 7.9; 12.94; 15.06; 16.74; 18.22; 19.78; 21.06; 22.26; 23.02; 25.42 ±> 0.2°2θ. A method preps. the new polymorphic forms IV and V by dissolving and​/or suspending minocycline on the basis of an org. solvent followed by crystn., and their use in pharmaceutical compn.