Katzung 12th ed - Chapter 43 - Antibiotics: Beta-lactams - Penicillins (1)

Question 1

Name three subgroups of Beta-lactams.

Answer 1

1) Penicillins
2) Cephalosporins
3) Carbapenems (e.g. meropenem)

Question 2

What are the 3 subgroups of penicillins? Give examples for each group.

Answer 2

Natural penicillins (e.g. penicillin V, penicillin G, procaine penicillin)
Antistaphylococcal penicillins (e.g. flucloxacillin, dicloxacillin)
Extended spectrum penicillins (e.g. amoxicillin, ampicillin, ticarcillin, piperacillin)

Question 3

Describe the cell wall of gram positive bacteria.

Answer 3

Single phospholipid bilayer, surrounded by a thick layer of peptidoglycan.

Question 4

Explain the mechanism of action of beta-lactam antibiotics.

Answer 4

Penicillins bind to penicillin-binding protein and inhibit transpeptidation in peptidoglycan synthesis. This prevents the formation of cross-links in the cell wall that confer rigidity.

Question 5

Which groups of bacteria are killed by natural penicillins?

Answer 5

Gram positive cocci, Gram negative cocci, some anaerobes.

Question 6

Name four resistance mechanisms that bacteria have developed against the natural penicillins.

Answer 6

1 – Beta-lactamase
2 – Alteration of the penicillin-binding protein
3 – Impaired penetrance of penicillin through membrane
4 – Efflux

Question 7

What makes MRSA resistant to natural penicillins?

Answer 7

Altered penicillin-binding protein binding sites.

Question 8

What advice should you give to a patient for the administration of most oral penicillins?

Answer 8

With the exception of amoxicillin, most oral penicillins should be taken 1-2hrs before or after food, because absorption is impaired by food.

Question 9

How are the natural penicillins excreted?

Answer 9

By the kidneys.

Question 10

What is the half-life of natural penicillins? What if there is renal failure?

Answer 10

30 minutes. Can be up to 10 hours in renal failure.

Question 11

Name some specific bacteria that can be killed with penicillin G.

Answer 11

Streptococci, Meningococci, some Enterococci, some Pneumococci, some Staphylococci, Treponema pallidum, Clostridium.

Question 12

What is significant about the action of flucloxacillin?

Answer 12

It is a beta-lactam that is not destroyed by beta-lactamase, and is therefore effective against MRSA.

Question 13

What are the routes of metabolism and excretion of flucloxacillin?

Answer 13

Hepatic metabolism. Renal excretion.

Question 14

What dose of flucloxacillin should be given to patients with renal failure?

Answer 14

The same dose as that given to patients with no renal failure. There is no dose adjustment for renal failure.

Question 15

What is the standard dose of natural penicillins and flucloxacillin?

Answer 15

10-50mg/kg/day in 3-4 doses orally or IV.

Question 16

What is the rate of true anaphylactic reaction to penicillin?

Answer 16

0.05% of recipients. (1 in 2000)

Question 17

What are the routes of metabolism and excretion for amoxicillin, ampicillin, piperacillin and ticarcillin (the extended-spectrum penicillins)?

Answer 17

Hepatic metabolism. Renal excretion.

Question 18

What dose of the extended-spectrum penicillins should be given to patients with renal failure?

Answer 18

The same dose as that given to patients with no renal failure. There is no dose adjustment for renal failure.

Question 19

What is an adverse effect of penicillin given in high doses to patients with renal failure?

Answer 19

Hypernatraemia and Seizures.

Question 20

Name some bacteria that are covered by the extended-spectrum penicillins.

Answer 20

All of those covered by natural penicillins (streptococci, meningococci, pneumococci, staphylococci, treponema pallidum, clostridium), as well as:
Ampicillin – Shigella, Anaerobes, E.coli, Salmonella (as long as they don’t contain beta-lactamase)
Ticarcillin – Pseudomonas, Enterobacter
Piperacillin – Klebsiella

Question 21

Name the three beta-lactamase inhibitors that resemble beta-lactam molecules.

Answer 21

Clavulanic acid, Tazobactam, Sulbactam. Note that these do NOT have antibacterial activity alone.

Question 22

What is the major clinical use of carbapenems?

Answer 22

Infections due to resistant organisms, such as resistant strains of pneumococci and enterobacter. Carbapenems have the same mechanism of action as other beta-lactams, but in addition they are resistant to most beta-lactamases.

Question 23

What is another name for penicillin V?

Answer 23

Phenoxymethylpenicillin.

Question 24

Clavulanic acid is active against beta-lactamases from which bacteria?

Answer 24

Haemophilus, Neisseria, Salmonella, Shigella, E.coli, Klebsiella, Legionella, Bacteroides.

Question 25

Clavulanic acid is NOT active against beta-lactamases from which bacteria?

Answer 25

Enterobacter, Citrobacter, Serratia, Pseudomonas.

Question 26

Carbapenems: Describe their absorption in tissues.

Answer 26

Carbapenems penetrate body tissues and fluids well, including CSF.

Question 27

Carbapenems: How are they cleared?

Answer 27

Renally cleared. Dose adjustment required in renal failure.

Question 28

Carbapenems: Half-life?

Answer 28

1 hour

Question 29

What is another name for benzylpenicillin?

Answer 29

Penicillin G

Question 30

Are penicillins bacteriostatic or bacteriocidal?

Answer 30

Bacteriocidal