Anitbiotics Update Flashcards
What is antagonism by concurrent antibiotics?
Induction of enzymatic (β-lactamase) activity
Some gram-negative bacilli possess inducible lactamases Some β-lactam antibiotics are themselves potent inducers Combining an inducer with a susceptible lactam may result in antagonism
What is synergism?
Synergism is marked by a fourfold or greater reduction in the MIC or MBC of each drug when used in combination versus when used alone.
How can synergistic antibiotics cause increased drug uptake?
Penicillins and other cell wall-active agents can increase the uptake of aminoglycosides by a number of bacteria, including staphylococci, enterococci, streptococci, and P aeruginosa. (SEPS)
Enterococci are thought to be intrinsically resistant to _____ because of permeability barriers
aminoglycosides
What synergistic antibiotic combo can cause sequential step blockade?
Trimethoprim-sulfamethoxazole is the best-
known example of this mechanism.
Blockade of the two sequential steps in the folic acid pathway by trimethoprim- sulfamethoxazole results in a much more complete inhibition of growth than achieved by either component alone.
What synergistic antibiotic combo can cause inhibition of enzymatic inactivation?
Enzymatic inactivation of β-lactam antibiotics is a major mechanism of antibiotic resistance. Inhibition of lactamase by β-lactamase inhibitor drugs (e.g., sulbactam) results in synergism.
• Amoxicillin/Clavulanic acid [Augmentin]
• Piperacillin/Tazobactam [Zosyn]
• Ampicillin/Sulbactam [Unasyn]
– These adjunctive agents are all irreversible
inhibitors of bacterial beta-lactamases •
Imipenem/Cilastin [Primaxin]
– Cilastatin is a reversible, competitive inhibitor of renal dehydropeptidase-1 (DHP-1), an enzyme that breaks down imipenem to inactive BUT nephrotoxic metabolites
Imipenem/Cilastin [Primaxin]
– Cilastatin is a reversible, competitive inhibitor of renal dehydropeptidase-1 (DHP-1), an enzyme that breaks down imipenem to inactive BUT nephrotoxic metabolites
All protein synthesis inhibitors except _____ are bacteriostatic.
aminoglycosides
What is Linezolid?
• Protein synthesis inhibitor that binds to a unique spot on the 50S subunit
– As a result, there is no cross-resistance with other antimicrobial agents
– Resistance has been reported following mutation in drug binding site
What is Nitrofurantoin?
• Asynthetic, broad-spectrum, weakly acidic antibacterial.
– Therapeutic concentrations are achieved only in the urine.
- Reduced by bacterial flavoproteins to reactive intermediates, which inactivate or alter bacterial ribosomal proteins and other macromolecules.
- The fact that nitrofurantoin interferes with a variety of bacterial processes may explain the lack of acquired bacterial resistance to nitrofurantoin.
Is nitrofurantoin bacteriostatic or bactericidal?
bacterocidal
