Have you ever taken care of really critical, undifferentiated patient, only later to find out that they were diagnosed with a serious, contagious illness? We are exposed to innumerable pathogens each day in the ED, but there are only a few that necessitate antimicrobial prophylaxis and even fewer that require prophylaxis from simply being very close to the patient. Neisseria meningitidis, a common cause of bacterial meningitis, is one of these pathogens.

Who gets treated? Essentially all close contacts. A close contact is defined as someone who has had prolonged (>8 hours) contact while in close proximity (<3 feet) to the patient, or someone who has been directly exposed to the patient’s oral secretions during the 7 days before the onset of patient’s symptoms and until 24 hours after antibiotic initiation.

How do you treat? Three choices:


  • Adults (non-pregnant): 600mg every 12 hours for 2 days
  • Children >1 mo: 10 mg/kg every 12 hours for 2 days
  • Children <1 mo: 5 mg/kg every 12 hours for 2 days

Ciprofloxacin (non-pregnant adults only)

  • 500mg ONCE


  • Adults: 250 mg single IM dose
  • Children <15 years old: 125 mg single IM dose

So what about the IM vs IV routes? There was some thought that ceftriaxone should be give IM in order to get the “depot effect” (slow release at the injection site ensures constant stimulation of the immune system for production of high antibody titers). However, when you look at the package insert, the average plasma concentration 24 hours after 500 mg IV and 500 mg IM is essentially identical. The only difference is that the concentration of IM appears to be lower and more steady, whereas that of IV starts high and gradually declines.

So, either way is fine. If the patient has an IV, go ahead and use that. If not, remember that the IM injection is REALLY painful. If you want to be kind, mix the ceftriaxone with some 1% lidocaine (see ALiEM post for how to do this below).

Thanks to Dr. Kathy Li for inspiring this post!


UpToDate on prophylaxis: https://www.uptodate.com/contents/treatment-and-prevention-of-meningococcal-infection

ALiEM on IV vs IM: https://www.aliem.com/2012/10/trick-of-trade-iv-ceftriaxone-for/

ALiEM on CTX + lido: https://www.aliem.com/2014/11/ceftriaxone-im-hurts-mix-lidocaine/

May 2024