Third-generation cephalosporins These drugs are active against Haemophilus influenzae and some Enterobacterales (formerly Enterobacteriaceae; eg, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis) that do not produce AmpC beta-lactamase or extended-spectrum beta-lactamase (ESBL) Most 3rd-generation cephalosporins, including ceftriaxone and cefotaxime, are also active against some gram-positive species, especially streptococci including some strains with reduced penicillin susceptibility.