The present Invention relates to sodium (2R,5S,13aR)-7,9-dioxo-10 -((2,4,6-trifluorobenzyl)carbamoyl)-2,3,4,5,7,9,13,13a-octahydro-2,5-methanopyrido[1,2:4,5] pyrazino[2,1-b][1,3]oxazepin-8-olate Form I.La présente invention concerne le (2R,5S,13aR)-7,9-dioxo-10-((2,4,6-trifluorobenzyl)carbamyl)-2,3,4,5,7,9,13,13a-octahydro-2,5-méthanopyrido[1,2:4,5]pyrazino[2,1-b][1,3]oxazépin-8-olate de sodium de forme I.