The present invention relates to novel forms of ethyl ((S)-((((2R,5R)-5-(6-amino-9H-purin-9-yl)-4-fluoro-2,5-dihydrofuran-2-yl)oxy)methyl)(phenoxy)phosphoryl)-L-alaninate, pharmaceutical formulations, and therapeutic uses thereof in treating viral infections (e.g., an HIV infection).本發明係關於((S)-((((2R,5R)-5-(6-胺基-9H-嘌呤-9-基)-4-氟-2,5-二氫呋喃-2-基)氧基)甲基)(苯氧基)磷醯基)-L-丙胺酸乙酯之新穎形式、醫藥調配物,及其在治療病毒感染(例如HIV感染)之治療用途。