Beta-Lactam Antibiotics

Definition and Mechanism

• Beta-lactam antibiotics are a class of antibacterial agents that inhibit cell wall synthesis in bacteria.
• They work by binding to the enzyme DD-transpeptidase, which is necessary for cell wall formation.
• This binding prevents the cross-linking of peptidoglycan chains, ultimately leading to cell lysis and death.

Types of Beta-Lactam Antibiotics

• Penicillins:
  • Natural penicillins (e.g. penicillin G, penicillin V)
  • Semi-synthetic penicillins (e.g. ampicillin, amoxicillin)
  • Beta-lactamase-resistant penicillins (e.g. methicillin, cloxacillin)
• Cephalosporins:
  • First-generation (e.g. cephalexin, cephalothin)
  • Second-generation (e.g. cefaclor, cefuroxime)
  • Third-generation (e.g. cefotaxime, ceftriaxone)
  • Fourth-generation (e.g. cefepime, cefpirome)
• Monobactams:
  • Aztreonam
• Carbapenems:
  • Imipenem, meropenem, ertapenem

Spectrum of Activity

• Beta-lactam antibiotics are effective against a wide range of Gram-positive and Gram-negative bacteria.
• They are particularly effective against:
  • Staphylococcus aureus
  • Streptococcus pneumoniae
  • Haemophilus influenzae
  • Escherichia coli
• However, they are not effective against:
  • Anaerobic bacteria (e.g. Bacteroides fragilis)
  • Mycobacteria (e.g. Mycobacterium tuberculosis)
  • Fungi

Resistance and Side Effects

• Resistance to beta-lactam antibiotics can occur due to:
  • Production of beta-lactamase enzymes
  • Alteration of the target enzyme DD-transpeptidase
  • Changes in the bacterial cell wall
• Common side effects of beta-lactam antibiotics include:
  • Allergic reactions
  • Gastrointestinal disturbances
  • Diarrhea
  • Clostridioides difficile infection