This free iTunes segment is just one tiny snippet of the fully-loaded 3-hour monthly Peds RAP show. Earn CME on your commute while getting the latest practice-changing peds information: journal article breakdowns, evidence-based topic reviews, critical guideline updates, conversations with experts, and so much more. Sign up for the full show at hippoed.com/PEDSRAPPOD. Pediatric ID specialist Michael Neely, MD, and Michael Cosimini, MD discuss how cephalosporins work and which bugs they do and do not kill. Pearls: In general, cephalosporins do not cover anaerobes, enterococcus, listeria and MRSA. Oral cephalosporins are generally not first line in pediatrics.  Some exceptions include the treatment of UTIs and some skin and soft tissue infections; group A strep and sinopulmonary infections in penicillin allergic patients are other common indications. 1st generation cephalosporins do have gram positive coverage, but do not work well against strep pneumo, MRSA, enterococcus. They do cover some enteric gram negative bacteria, the “PECK” organisms.   What are cephalosporin antibiotics and how do they compare to penicillins?  Chemically, both penicillins and cephalosporins are beta-lactam antibiotics, with the beta-lactam portion responsible for bacterial killing.  The chemical portions off the beta-lactam ring make the antibiotics different. Beta-lactam antibiotics work by binding to the penicillin-binding protein on the bacterial cell wall.  These proteins have structural functions that maintain the integrity of the bacterial cell wall and therefore, when these antibiotics bind, the penicillin-binding protein is disrupted, the cell wall falls apart and the bacterial dies.       How do you keep a straight spectrum of activity for antibiotics?  To help with this, think of bacteria into big categories: gram-positive, gram-negative and “other”. Gram-positive bacteria include: Staph aureus (MSSA, MRSA), Streptococcus (Group A Strep, Group B Strep, Strep pyogenes, Strep viridans), Enterococcus, Pneumococcus, Listeria Gram-negative bacteria are a much bigger group and can be divided into: Respiratory gram-negatives include Moraxella, Haemophilus, Meningococcus Enteric gram-negatives include the “PECK” bacteria: Proteus, E.coli, Klebsiella What bacteria do cephalosporins not cover?  In general, cephalosporins do not cover anaerobic bacteria, enterococcus, listeria and MRSA.  There are a few exceptions to this rule. Cefoxitin (a second generation cephalosporin), for example, does have anaerobic coverage.  It is commonly used in the treatment of PID as it covers enteric anaerobes and Neisseria gonorrhea. There is a 5th generation cephalosporin that does cover MRSA (discussed later). Are cephalosporins well absorbed?  Generally speaking, cephalosporins in oral formulations are not as well absorbed as penicillins and are more difficult to get where they need to go outside the urinary tract. Also, generally speaking, no beta-lactam really gets into the spinal fluid in very high concentrations; all of them do have better penetration when there is inflammation.  Practically, remember that the penetration into the CSF between ampicillin and ceftriaxone is negligible. What bacteria do first generation cephalosporins cover?  Although the classic teaching is that cephalosporins are good for gram-positive coverage (staph and strep), this is not a hard and fast rule.  As stated, enterococcus is not covered by any cephalosporin and MRSA is not covered by most cephalosporins.  First generation cephalosporins are also good for coverage of the “PECK” enteric gram negative bacteria, but not good for coverage of other gram negative bacteria.  These organisms tend to cause UTIs and therefore, first generation cephalosporins (for example, cephalexin) are frequently used for UTI treatment. Of