Antibiotics Flashcards
(92 cards)
What aspects of bacterial machinery can be inhibited by abx?
Cell wall synthesis Protein synthesis DNA/RNA synthesis Folate synthesis Membrane integrity
Cell wall synthesis inhibitors
Beta-lactams (penicillin, cephalosporin, carbapenems, monobactams)
Glycopeptides and lipoglycopeptides
How do glycopeptides and lipoglycopeptides differ mechanistically from the beta lactams?
Beta lactams bind to and inhibit transpeptidase while glycopeptides and lipoglycopeptides bind to cell wall precursors and prevent cross linking/extension
Which abx relies on renal dipeptidase inhibitor celastatin?
Imipenem
What differentiates second generation cephalosporins from cephamycins?
The bacterial spectrum
Cephamycins are active against B.fragilis and some Serratia spp. and the purely second generation cephalosporins (cefaclor, cefprozil, and cefuroxime) are not
What is the general spectrum of coverage for the monobactam aztreonam
Gram-negative aerobes
What are the protein synthesis inhibitors that bind the 50s ribosomal subunit?
Oxazolidinones
Macrolides and ketolides
Streptogramins
What are the protein synthesis inhibitors that bind the 30s ribosomal subunit?
Tetracyclines
Aminoglycosides
Glycylcyclines
What is the difference in MOA between oxazolidinones and streptogramins?
Oxazolidinones bind to P site on ribosome and prevent initiation of protein synth
Streptogramins have 2 headed mechanism as they are given in combined ratio — quinupristin inhibits polypeptide elongation and induces early termination of protein synth; dalfopristin impedes polypeptide chain formation and induces conformational change in 50S ribosomal subunit that enhances quinupristin binding
Why are macrolides grouped with the ketolides? What distinguishes a macrolide from a ketolide?
Grouped together bc similar MOAs, chemical structure, and adverse effects
Their bacterial coverage differs; ketolides can be active in macrolide resistant strains
What antibiotic acts as a DNA/RNA synthesis inhibitor?
Fluoroquinolones
What proteins do fluoroquinolones inhibit?
Topoisomerase II (DNA gyrase) and topoisomerase IV
What are some side effects of fluoroquinolones?
Abdominal discomfort, nausea, vomiting, C.diff induced colitis, HA, dizziness
Achilles tendon rupture
QT prolongation (moxifloxacin)
What are the 2 folate synthesis inhibitors?
Sulfonamides
Benzylpyrimidines
What is the antibiotic that works as a membrane integrity inhibitor?
Polymyxins
Why are sulfonamides and benzylpyrimidines synergistic?
Trimethoprim and sulfamethoxazole inhibit subsequent steps in THF biosynthetic pathway
Are polymyxins active against gram positive bacteria? Why?
No, because they do not have an outer membrane
Major mechanisms of antibiotic synergism
Blockade of sequential steps in metabolic sequence (TMP/SMX)
Inhibition of enzymatic inactivation (beta-lactamase inhibitors)
Enhancement of antimicrobial agent uptake (penicillins and vancomycin can increase uptake of aminoglycosides)
Major mechanisms of antibiotic antagonism
Inhibition of cidal activity by static agents (tetracyclines and penicillins)
Induction of enzymatic inactivation (P.aeruginosa and some other bacteria possess inducible beta-lactamases; some beta lactam abx are potent inducers of beta-lactamase production — imipenem, cefoxitin, ampicillin)
Which of the following is a mechanism underlying the resistance of strains of S.pneumoniae to fluoroquinolones?
A. Reduced topoisomerase sensitivity to inhibitors
B. Increased synthesis of PABA
C. Formation of methyltransferases that change receptor structure
D. Structural changes in porins
E. Formation of drug-inactivating hydrolases
A. Reduced topoisomerase sensitivity to inhibitors
What is the most likely mechanism of resistance for MRSA to methicillin?
A. Methylation of the binding site
B. Active efflux of drug from bacteria
C. Beta-lactamase production
D. Phosphorylation of the drug by bacterial enzymes
E. Structural modifications of transpeptidase
E. Structural modifications of transpeptidase
37 y/o female presents to clinic with low grade fever and sore throat. PE reveals tonsillar exudate and gram stain reveals high number of bacteria. A dx is made and penicillin G is prescribed because the identified tonsillar exudate has been shown to be sensitive to penicillin G.
Which of the following bacteria is most likely to be causing this patient’s infection?
A. Klebsiella pneumoniae B. Clostridium difficile C. Staphylococcus aureus D. Streptococcus pyogenes E. Pseudomonas aeruginosa
D. Streptococcus pyogenes
67 y/o woman presents to ED with nausea, vomiting, fever, and altered consciousness. Her vitals are BP 90/50 mm Hg, pulse 115 bpm, respirations 20/min and temp 103.6 F. PE reveals pt in distress with nuchal rigidity. Empirical IV therapy is initiated with ampicillin, ceftriaxone, and vancomycin.
Which of the following best explains the common mechanism of action that all 3 of these drugs possess?
A. Inhibition of THF synthesis B. Misreading of mRNA template code C. Inhibition of peptidoglycan synthesis D. Blockade of peptidyl-transfer RNA translocation E. Enhancement of DNA gyrase activity
C. Inhibition of peptidoglycan synthesis
A 5 y/o boy presents with ear pain despite being tx with amoxicillin. Your pediatrician partner suggests changing the pt’s prescription to amoxicillin + potassium clavulanate.
Which of the following best explains the advantage of this proposed drug combo over amoxicillin monotherapy?
A. Extended antibacterial spectrum against P.aeruginosa
B. Inhibition of bacterial inactivation of amoxicillin
C. Inhibition of renal excretion of amoxicillin
D. Increased influx of amoxicillin into bacteria
E. Decreased amoxicillin hypersensitivity
B. Inhibition of bacterial inactivation of amoxicillin
