Lyophilized composition of a diazabicyclooctane compound and process of producing the same

A process for producing a lyophilized composition comprising crystals of a compound represented by the following formula (I):

• the process comprising crystallizing said compound by subjecting an aqueous solution containing said compound and a salt to lyophilization, the salt being selected from the group consisting of an inorganic salt that is amenable to be added to a parenteral injection, tetrabutyl ammonium bromide, sodium acetate, sodium citrate, sodium tartrate, sodium glutamate and potassium sodium tartrate, wherein the crystals of the compound of formula (I) are crystalline form I having characteristic peaks appearing at a lattice spacing (d) of 7.34, 5.66, 5.53, 5.30, 5.02, 4.66, 4.37, 4.28, 4.06, 3.68, 3.62, 3.47, 3.36, 3.30, 3.16, 3.11, 3.03, 2.99 and 2.50 Å in a powder X-ray diffraction pattern.