Treatment of Meningococcal Diseases Ceftriaxone Dexamethasone While awaiting definitive identification of the causal organism, immunocompetent adults suspected of having meningococcal infection are given a third-generation cephalosporin (eg, cefotaxime 2 g IV every 4 to 6 hours, ceftriaxone 2 g IV every 12 hours) or meropenem (2 g IV every 8 hours) plus vancomycin 15 to 20 mg / kg IV every 8 to 12 hours.