B Lactam Antibiotics General

Question 1

What AB’s are included in this group?

Answer 1

Penicillins
Carbapenems
Aztreonam
Cephalosporins

Question 2

Mechanism of action

Answer 2

• Inhibit cell wall synthesis by blocking peptidoglycan crosslinking
• The beta-lactam structure mimics the D-ala-D-ala residue of bacterial peptidoglycan
• Irreversibly binds to penicillin-binding proteins (transpeptidases responsible for peptidoglycan crosslinking), stalling the catalytic reaction because the beta-lactam cannot be cleaved
• Bacterial death as a result of an inability to synthesize new cell wall during replication
• Activate autolytic enzymes
• Beta-lactam antibiotics are bactericidal.

Question 3

CNS penetration (+ exceptions)

Answer 3

CNS penetration: only when meninges are inflamed

Exceptions: ceftriaxone and aztreonam always have good CNS penetration

Question 4

Route of elimination

Answer 4

Route of elimination:
- Primarily renal

Exceptions:
- Primarily biliary: nafcillin

Both renal and biliary: other anti-staphylococcal penicillins (e.g., oxacillin, dicloxacillin), ceftriaxone

Question 5

Adverse effects

Answer 5

General adverse effects:

• Penicillin allergy (hypersensitivity reactions)
• Jarisch-Herxheimer reaction (e.g., when treating syphilis)

Question 6

B lactamase inhibitors

Which drugs can be used to fight B lactamase inhibitors?

Answer 6

Beta-lactamase inhibitors:

• Beta-lactamases, which are usually produced by gram-negative and anaerobic organisms, can split the beta-lactam ring and render certain betalactam antibiotics ineffective.
• Beta-lactamase inhibitors increase the spectrum of antibiotic activity.

Drugs:
Clavulanic acid (combined with amoxicillin)
Sulbactam (combined with ampicillin)
Tazobactam (combined with piperacillin)
Beta-lactamase inhibitors (CAST): Clavulanic Acid, Sulbactam, Tazobactam