Serum levels Following an the intravenous infusion of 1 g of ceftriaxone for 30 minutes, serum levels immediately after cessation of the infusion process were at 123.2 µg/ ml, and at 94.81, 57.8, 20.2 and 4.6 µg/ ml, respectively, 1.5, 4, 12 and 24 hours after the onset of infusion.