What are the different types of beta-lactam (β-lactam) antibiotics?

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Beta-Lactam Antibiotics: Complete Classification

Beta-lactam antibiotics are characterized by a four-membered beta-lactam ring and include four major classes: penicillins (with or without beta-lactamase inhibitors), cephalosporins, carbapenems, and monobactams. 1

Major Classes of Beta-Lactam Antibiotics

1. Penicillins

Natural and Semisynthetic Penicillins:

  • Penicillin G 2
  • Amoxicillin 1
  • Ampicillin 1
  • Cloxacillin (semisynthetic penicillinase-resistant penicillin) 1

Penicillins with Beta-Lactamase Inhibitors:

  • Amoxicillin-clavulanate 1
  • Ampicillin-sulbactam 1
  • Piperacillin-tazobactam 1
  • Ticarcillin-clavulanate 1

2. Cephalosporins

First Generation:

  • Cephalexin 1
  • Cefazolin 1
  • Cefadroxil 1
  • Cephalothin 1
  • Cephradine 1

Second Generation:

  • Cefuroxime (cefuroxime axetil) 1
  • Cefoxitin 1
  • Cefaclor 1
  • Cefprozil 1
  • Cefamandole 1

Third Generation:

  • Ceftriaxone 1
  • Cefotaxime 1
  • Ceftazidime 1
  • Cefixime 1
  • Cefpodoxime proxetil 1
  • Cefdinir 1
  • Ceftizoxime 1

Fourth Generation:

  • Cefepime 1

3. Carbapenems

  • Ertapenem 1, 3
  • Imipenem 1, 4, 5
  • Meropenem 1, 5

4. Monobactams

  • Aztreonam 1, 6, 5

Structural Characteristics and Mechanism

All beta-lactams share a four-membered beta-lactam ring that is essential for their antibacterial activity. 1, 2

  • Penicillins have a beta-lactam ring adjacent to a five-membered thiazolidine ring 1
  • Cephalosporins have a beta-lactam ring adjacent to a six-membered dihydrothiazine ring 1
  • Carbapenems are structurally similar to penicillins but with enhanced stability against beta-lactamases 5, 2
  • Monobactams have a unique monocyclic beta-lactam nucleus, structurally different from other beta-lactams 6, 5

Mechanism of Action

Beta-lactams exert their antibacterial effect by inhibiting bacterial cell wall synthesis through binding to penicillin-binding proteins (PBPs), ultimately producing bacterial autolysis. 1, 4

Clinical Considerations

Cross-Reactivity Patterns

The true cross-reactivity between penicillins and cephalosporins is approximately 2-4.8%, far lower than the historically quoted 10%. 1

  • Cross-reactivity is primarily determined by identical R1 side chains rather than the beta-lactam ring itself 1
  • Aztreonam has no cross-reactivity with penicillins or cephalosporins, except for ceftazidime due to shared R1 side chain. 1
  • Carbapenems have very low cross-reactivity with penicillins or cephalosporins. 1

Neurotoxicity Risk

Cefazolin and cefepime have lower neurotoxicity thresholds compared to other beta-lactams, with cefazolin having the highest relative pro-convulsive activity (294 compared to penicillin G = 100). 1

The relative pro-convulsive activity ranking: Cefazolin (294) > Cefepime (160) > Penicillin G (100) > Imipenem (71) > Aztreonam (42) > Ampicillin (21) > Ceftazidime (17) > Meropenem (16) > Ceftriaxone (12) > Piperacillin (11) > Cefotaxime (8.8) > Cefoxitin (1.8) 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Research

β-lactam antibiotics: An overview from a medicinal chemistry perspective.

European journal of medicinal chemistry, 2020

3
Research

Beta-lactam antibiotics: newer formulations and newer agents.

Infectious disease clinics of North America, 2004

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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