In the present work, radiolysis of gamma irradiated sulbactam sodium (SS) was investigated through detailed ESR studies performed at low and at high temperatures on the radiolytic products induced in this drug after gamma irradiation in the dose range of 3-15 kGy. While unirradiated SS presented no ESR signal, irradiated SS exhibited an ESR spectrum with many resonance peaks. Variations of the spectrum pattern and of the intensities of resonance peaks with microwave power, applied radiation dose, storage time and temperature were followed. A radical with unpaired electron localised on the carbon atom of five membered ring directly attached to two CH3 groups and SO2- ionic radical called as species A and B, respectively, were found to be produced after gamma radiolysis of SS. The characteristic spectral and kinetic features of these species were determined by spectrum simulation calculation and by curve fitting techniques using experimental signal intensity data as input. Although, species A was fairly unstable at room and especially at high temperatures, species B were observed to be relatively stable even at high temperatures having activation energies of E-A = 46(+/-4) kJ/mol and E-B = 82(+/-3) kJ/mol, respectively, at room temperature. Four different mathematical functions were tried to explore the dosimetric features of SS and a linear function of applied dose described best the dose-response data obtained for stable species, that is, radical B, in the dose range of 0-10 kGy. An accuracy of 4% in the dose measurements was concluded to be achievable through back-projection dose calculations if SS were used as a dosimetric material. (C) 2004 Elsevier B.V. All rights reserved.