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Questions and Answers
What is the characteristic of second-generation cephalosporins?
Which of the following is a third-generation cephalosporin?
What is the advantage of fourth-generation cephalosporins?
What is the mechanism of resistance to cephalosporins?
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What is the adverse effect of cephalosporins in 10-20% of patients with penicillin allergy?
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What is the characteristic of aztreonam?
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What is the characteristic of vancomycin?
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What is the characteristic of bacitracin?
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What is the characteristic of imipenem?
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What is the indication for cefixime?
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Study Notes
Penicillins
- Inhibit cell wall synthesis by preventing formation of peptidoglycan crosslinks in bacterial cell walls, especially in Gram-positive organisms
- Bactericidal, but only act on dividing cells
- Not toxic to animal cells, which have no cell wall
- Poorly lipid soluble, do not cross blood-brain barrier in appreciable concentrations unless inflamed (effective in meningitis)
- Actively excreted unchanged by the kidney, dose reduction necessary in severe renal failure
Types of Penicillins
- Benzylpenicillin (Penicillin G): acid labile, β-lactamase sensitive, only parenteral, narrow spectrum, covers Streptococcus pyogenes, S. pneumoniae, Neisseria meningitis or N. gonorrhoeae, treponemes, Listeria, Actinomycetes, Clostridia
- Phenoxymethyl penicillin (Penicillin V): acid stable, given orally for minor infections
- Ampicillin: less active against Gram-positive bacteria, but has a wider spectrum
- Amoxycillin: similar to ampicillin, better absorbed orally
- Flucloxacillin: acid stable, orally or parenterally, β-lactamase resistant, narrow spectrum, for Staphylococcus aureus infections
- Azlocillin: β-lactamase sensitive, broad spectrum, including Pseudomonas aeruginosa and Proteus species
Cephalosporins
- Also inhibit cell wall synthesis due to β-lactam ring, bactericidal
- Good alternatives to penicillins when a broad-spectrum drug is required
- Prevent cross-linkage of NAM subunits
- More stable, more easily absorbed, work on some Gram-negative bacteria
Classification of Cephalosporins
- First generation: early compounds, active against Gram-positive cocci, alternative to penicillins for staph. and strep. infections, useful in UTIs
- Second generation: resistant to β-lactamases, active against Enterobacteriaceae (e.g. E. coli, Klebsiella spp, Proteus spp), may be active against H. influenzae and N. meningitidis
- Third generation: resistant to β-lactamases, increased spectrum of activity, very broad spectrum against Gram-negative rods, less activity against Gram-positive organisms
- Fourth generation: increased spectrum of activity, better against Gram-positive organisms than third generation, better against Gram-negative bacilli, especially Enterobacteriaceae and Pseudomonas aeruginosa
Resistance and Adverse Effects of Cephalosporins
- Resistance: changes in PBP, decreased permeability, production of enzymes
- Adverse effects: allergy, nephritis, acute renal failure, superinfections, gastrointestinal upsets when given orally
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Description
Learn about the mechanism of penicillins in inhibiting bacterial cell wall synthesis, their effects on Gram-positive organisms, and their pharmacokinetics.
