Katzung 12th ed - Chapter 43 - Beta-lactams - Cephalosporins (1) Flashcards
Give two examples of each generation of cephalosporin.
1st gen – Cefazolin, Cephalexin
2nd gen – Cefuroxime, Cefaclor
3rd gen – Ceftriaxone, Cefotaxime, Ceftazidime
4th gen – Cefepime
Describe the mechanism of action of cephalosporins.
It is the same as for penicillins. Cephalosporins bind to penicillin-binding proteins and inhibit transpeptidation in peptidoglycan synthesis. This inhibits the formation of cross-links in the cell wall that confer rigidity.
What is the difference in resistance mechanisms between penicillins and cephalosporins?
Cephalosporins are not as sensitive to beta-lactamases.
In addition to gram positive cocci, 1st generation cephalosporins are active against which bacteria?
E.coli, Klebsiella, Proteus.
It is important to note that 1st generation cephalosporins are NOT active against which bacteria?
Listeria, MRSA, Haemophilus, Pseudomonas, Enterobacter, Serratia, Citrobacter
What is the excretion method of 1st and 2nd generation cephalosporins?
Renal excretion. 10% by filtration, 90% by tubular secretion.
What is the half-life of cephalosporins: 1st gen? 2nd gen? 3rd gen?
1st gen: 30 minutes. Up to 10 hours in renal failure.
2nd gen: Variable.
3rd gen: 7-8 hours.
What is the route of metabolism and excretion for 3rd generation cephalosporins?
Metabolised by the liver and excreted in bile. Therefore there is no dosing adjustment required in renal failure.
What is the difference in microbial coverage of 1st generation and 2nd generation cephalosporins?
2nd generations cover the same as 1st, the only extra they cover is Haemophilus influenza and some Serratia.
Which cephalosporins can cross the blood-brain barrier?
3rd generations, and one of the 2nd generations (cefuroxime). Not 1st generations.
Which 3rd generation cephalosporin provides good coverage of pseudomonas?
Ceftazidime.
It is important to note that 3rd generation cephalosporins are NOT active against which bacteria?
Enterobacter and Listeria.
The 4th generation cephalosporins are useful against which bacteria? Which one are they still not quite useful for?
Useful for: Pseudomonas, Enterobacter, Haemophilus, Staph aureus, Neisseria.
Still under development: MRSA
The 4th generation cephalosporins: what is their route of clearance? Half-life?
Renally cleared. Half-life 2hrs.
