Antibiotics 101

Categories of Antibiotics

Beta-Lactams

Common central structure with a beta lactam ring and a thiazolidine ring (penicillins and carbapenems) or a dihydrothiazine ring (cephalosporins). All bind to and inhibit PBPs, enzymes important for cross-linking bacterial cell wall peptidoglycans. Prevents cross linkage of the cell wall peptigoglycans, leading to loss of bacterial cell wall integrity. All require active bacterial growth for bacteriocidal action.

Penicillins

Penicillin Class Examples Description
Natural penicillins penicillin G Narrow spectrum, short half lives, mostly IV or IM, well-distributed through the body.
Aminopenicillins amoxicillin, ampicillin Broader spectrum then natural pcns. Can be given orally due to modifications that protect against stomach acids. Higher peak levels means longer dosing interval.
Penicillinase-resistant penicillins oxacillin, nafcillin, cloxacillin, dicloxacillin Hepatic clearance, but same short half life means q4h dosing. Very narrow spectrum.
Ureidopenicillins piperacillin Intrinsic resistance to many beta-lactamases. Short half life. Covers GN, Pseudomonas, MSSA.

Cephalosporins

Generation Examples Description
I cefazolin, cephalexin, cefadroxil Predominantly effective against Gram-positive cocci. Frequently used for MSSA/GAS soft tissue infections, surgical prophylaxis, impetigo.
II cefuroxime, cefprozil Increased activity against aerobics and anaerobic GNB. Effective against MSSA and non-enterococcal Strep.
III ceftriaxone, ceftazidime, cefotaxime, cefixime Enhanced GNB activity, does not cover SPICE organisms. Ceftazidime covers Pseudomonas.
IV cefepime, cefpirome Broadest spectrum of activity. Effective against GPB and GNB. Zwitterionic properties allow excellent penetration of body cavities. Resistant to most beta-lactamases. Cefepime covers Pseudomonas.
V ceftaroline Anti-MRSA. Superior in CAP. Excellent body space penetration.

Pathogens

MSSA

Oral options

IV options

MRSA

Pseudomonas