The present invention provides for amorphous Letermovir and orally administrable solid pharmaceutical formulations thereof (immediate release formulation). Said amorphous Letermovir is suitable for immediate release formulations when isolated out of an organic solution by either roller-drying said organic solution in a volatile organic solvent, in particular acetone, at a temperature of 30° C. to 60° C., and subsequently drying the amorphous Letermovir obtained, or isolating said amorphous Letermovir by precipitation from water miscible solvents selected from acetone or acetonitrile into excess water as anti-solvent, and subsequently filtrating or centrifuging the amorphous Letermovir obtained. The immediate release formulations of amorphous Letermovir are intended for use in methods of prophylaxis or methods of treatment of diseases associated with the group of Herpesviridae, preferably associated with cytomegalovirus (CMV), even more preferably associated with human cytomegalovirus (HCMV).
