Beta-lactams
One-Sentence Definition
β-lactams are a family of antibiotics sharing a β-lactam ring that inhibit peptidoglycan cross-linking (PBP targets) in the Bacterial Cell Wall — including penicillins, cephalosporins, carbapenems, and monobactams.
Simple Explanation
They block wall synthesis — bacteria pop or stop dividing. Different subclasses reach different bugs and tissues.
Detailed Scientific Explanation
| Subclass | Examples | Spectrum highlights | Resistance |
|---|---|---|---|
| Penicillins | penicillin G/V, ampicillin, piperacillin | Gram-positive; some GNR with piperacillin | β-lactamases; MRSA (no PBP2a binding) |
| Cephalosporins | ceftriaxone, cefepime | Generations broaden GNR coverage | ESBL, AmpC, porin loss |
| Carbapenems | meropenem, imipenem | Broad; last-line many GNR | Carbapenemases |
| Monobactams | aztreonam | Aerobic Gram-negatives (not anaerobes) | Enzyme-specific |
Combinations: clavulanate/tazobactam/avibactam/vaborbactam/relebactam inhibit many (not all) β-lactamases.
Pharmacology: time-dependent killing — maintain %T>MIC; renal dosing adjustments common.
Mechanism
Bind penicillin-binding proteins (transpeptidases) → impaired cell wall cross-linking → lysis (often with autolysins).
Clinical Importance
- Backbone of many empiric regimens (meningitis, sepsis, UTI, skin)
- Allergy evaluation (true IgE-mediated vs intolerance) shapes choices
AMR Relevance
- Central to Mechanisms of Antibiotic Resistance — enzymes, PBP changes, porin loss
- Stewardship: narrow by culture; avoid unnecessary broad cephalosporins driving ESBL/AmpC
Related Notes
- Bacterial Cell Wall · Antimicrobial Susceptibility Testing · Antimicrobial Stewardship
- Resistance: MRSA · ESBL · AmpC · Carbapenemases
Related MOCs
Active Recall Questions
- Why don’t classic penicillins treat MRSA?
- ESBL vs AmpC — inhibitor response difference?
- Time-dependent vs concentration-dependent — β-lactams which?