Cefazolin-13C2,15N is intended for use as an internal standard for the quantification of cefazolin by GC- or LC-MS. Cefazolin is a broad-spectrum cephalosporin antibiotic that is active in vitro against various Gram-positive and Gram-negative bacteria (MICs = 0.2-12.5 μg/ml). It also inhibits the growth of clinical isolates of S. aureus, E. coli, P. mirabilis, and K. pneumoniae (MICs = 0.1-25 μg/ml).