Structural Elucidation of the Neuraminidase Inhibitor Zanamivir (Relenza): Creeping and Diffusion for Polymorph Separation

Zanamivir, the active ingredient of the antiviral drug Relenza, is the most potent of the four currently approved neuraminidase inhibitors for treatment of pandemic strains of influenza. A combination of solution creeping and vapor diffusion of antisolvent was successfully applied to obtain two crystalline polymorphic dihydrates and to accomplish the first structure determination of zanamivir with X-ray diffraction.