Beta-lactam Antibiotics Flashcards
(18 cards)
Which of the following is true for antibiotics that exhibit concentration-dependent bactericidal activity
A. Increasing their concentrations from levels slightly above the MIC to levels far above the MIC increases their rate of bactericidal activity.
B. The duration of these antibiotics’ postantibiotic effect (PAE) is time-dependent.
C. If concentrations exceed the MIC, aminoglycosides and fluoroquinolones do not have a PAE on residual bacteria.
D. Aminoglycosides and fluoroquinolones are usually most effective as continuous infusions.
A
Increasing their concentrations from levels slightly above the MIC to levels far above the MIC increases their rate of bactericidal activity. Choices B and C are incorrect; the opposite is true. D: These medications are most effective as intermittent boluses that reach peak free serum levels ≥ 10 times the MIC of the bacteria.
Production of β-lactamases that inactivate penicillins in penicillin-resistant Staphylococcus aureus, Haemophilus influenzae, and Escherichia coli is an example of which of the following mechanisms of antibiotic resistance?
A. Decreased cell wall permeability
B. Enzymatic inactivation
C. Changes in target
D. Bypass of antibiotic inhibition
B
Enzymatic inactivation. Choices A, C, and D are exemplified by other phenomena. For example, decreased affinity of penicillin-binding proteins for β-lactam antibiotics (eg, in Streptococcus pneumoniae with reduced penicillin sensitivity) is an example of choice C (changes in target).
Which of the following is NOT a beta-lactam antibiotic?
A. Penicillin
B. Ceftriaxone
C. Imipenem
D. Vancomycin
D
Vancomycin is a glycopeptide, not a beta-lactam.
What is the mechanism of action of beta-lactam antibiotics?
A. Inhibit 50S ribosomal subunit
B. Inhibit DNA gyrase
C. Inhibit peptidoglycan cross-linking by binding to PBPs
D. Increase efflux pump activity
C
Beta-lactams bind to penicillin-binding proteins (PBPs) and inhibit cell wall cross-linking.
Which beta-lactam is primarily used to treat Pseudomonas aeruginosa infections?
A. Ceftriaxone
B. Amoxicillin
C. Piperacillin-tazobactam
D. Benzylpenicillin
C
Piperacillin-tazobactam covers Pseudomonas.
Which beta-lactam class is resistant to beta-lactamase and can treat ESBL-producing organisms?
A. Penicillins
B. Cephalosporins
C. Carbapenems
D. Monobactams
C
Carbapenems are broad-spectrum and beta-lactamase resistant.
Which of the following beta-lactams is safe for use in penicillin-allergic patients due to low cross-reactivity?
A. Cefazolin
B. Imipenem
C. Aztreonam
D. Amoxicillin
C
Aztreonam has minimal cross-reactivity with penicillin allergy.
Beta-lactamase inhibitors function by:
A. Binding to bacterial ribosomes
B. Inhibiting bacterial DNA replication
C. Inactivating enzymes that degrade beta-lactams
D. Blocking efflux pumps
C
Beta-lactamase inhibitors protect the beta-lactam ring from degradation
Which of the following is true regarding beta-lactams?
A. All beta-lactams have high oral bioavailability
B. Beta-lactams are bacteriostatic
C. Their efficacy depends on time above MIC (time-dependent killing)
D. They are primarily metabolized by the liver
C
Beta-lactams are time-dependent killers.
Which combination is used for resistance reversal via synergism?
A. Vancomycin + Linezolid
B. Amoxicillin + Clavulanic Acid
C. Ceftriaxone + Rifampicin
D. Gentamicin + Ciprofloxacin
B
Amoxicillin + Clavulanic Acid = Resistance reversal through synergy.
What is the common structural feature of beta-lactam antibiotics, and why is it important?
- The beta-lactam ring is the common structure in all beta-lactam antibiotics.
- It inhibits transpeptidase (PBP) enzymes, which are essential for bacterial cell wall synthesis.
List the four major classes of beta-lactam antibiotics and give one example of each.
Penicillins – e.g., Amoxicillin
Cephalosporins – e.g., Ceftriaxone
Carbapenems – e.g., Meropenem
Monobactams – e.g., Aztreonam
Explain the mechanism of resistance via beta-lactamases and how it can be overcome.
Bacteria produce beta-lactamase enzymes that break the beta-lactam ring.
This renders the antibiotic ineffective.
Solution: Beta-lactamase inhibitors (e.g., Clavulanic acid) are co-administered to block these enzymes.
beta-lactamase inhibitors themselves have minimal/no antimicrobial activity but serve a protective role.
Describe how carbapenems differ from other beta-lactams in terms of spectrum and resistance.
Carbapenems are broadest-spectrum beta-lactams.
Effective against Gram-positive, Gram-negative, and anaerobes.
They are resistant to most beta-lactamases (but not carbapenemases).
Used in serious or resistant infections.
Define Extended-Spectrum Beta-Lactamases (ESBLs). What antibiotics can still be effective?
ESBLs are enzymes that hydrolyze extended-spectrum cephalosporins and penicillins.
Effective options: Carbapenems, ceftazidime-avibactam, and some non-beta-lactam agents.
What does “time-dependent killing” mean, and which antibiotic classes does it apply to?
Time-dependent killing means the drug is most effective when its concentration stays above MIC for a longer time.
Applies to beta-lactams (penicillins, cephalosporins, carbapenems).
Why is aztreonam considered safe in penicillin-allergic patients?
Aztreonam is a monobactam with a distinct structure, so it does not cross-react with penicillin allergies (except in rare ceftazidime allergy due to side-chain similarity).
Explain how beta-lactamase inhibitors enhance the efficacy of beta-lactam antibiotics. Provide one clinical example.
(5 marks)
Beta-lactamase inhibitors (e.g., clavulanic acid, tazobactam) protect beta-lactam antibiotics from enzymatic degradation by irreversibly binding bacterial beta-lactamases.
This potentiates the antibiotic’s effect, enabling it to reach its target (PBPs) and exert bactericidal action.
Examples:
Amoxicillin + Clavulanate = Augmentin
Piperacillin + Tazobactam = Zosyn
