Penicillins

Question 1

What type of antibiotic are penicillins?

Answer 1

Beta Lactam Antibiotic

Question 2

What part of bacteria do penicillins target?

Answer 2

Target Cell wall synthesis

Question 3

How do penicillins work?

Answer 3

Penicillins work by binding to the enzymes required for peptidogylan cross linking in bacterial cell walls.
This lack of cross linking makes the bacterial wall weaker so it cannot maintain its osmotic gradient.
As a result water gets in and the bacterial cell swells causing lysis bursting and cell death.

Question 4

What spectrum does amoxicillin have?

Answer 4

Broad spectrum

Question 5

How can synthetic penicillins be made? E.g. amoxicillin

Answer 5

The beta lactam structure has different side groups which can be added e.g. amoxicillin has an amino side group on it making it more active against gram negative bacteria.

Question 6

What structure does the beta lactam ring have?

Answer 6

(C-C-C-N); Structural analogue of D-alanyl-D-alanine

Question 7

How do bacteria create resistance against penicillin antibiotics?

Answer 7

Some bacteria can produce beta lactamase enzymes which break down the beta lactam ring and inactivate the antibiotic

Question 8

What are the common indications for using amoxicillin?

Answer 8

1. Empirical treatment of pneumonia
   - Gram postive activity (strep pneumonia)
   - Gram negative activity (H. influenza)
2. Empirical treatment of UTIs
   - nitrofurantoin and trimethoprim more commonly used
3. Hospital acquired infections and Intra-abdominal sepsis
   - As a combination treatment as co-amoxiclav
   - Usually caused by G- and resistant bacteria
4. H.Pylori Eradication

Question 9

What gram positive and gram negative bacteria does amoxicillin cover?

Answer 9

Gram + : streptococcus species and staphylococcus species

Gram - : H. Influenza

Question 10

What are the contra-indications of using amoxicillin?

Answer 10

• Those at risk of C.Diff infection
• Those with previous penicillin allergy (anaphylaxis and urticaria)
• Those with severe renal impairment (can cause crystaluria)

Question 11

Name some features of a minor penicillin reaction?

Answer 11

Non confluent
Non pruitic
Small
Onset after 72 hours

Question 12

What are the treatment options if someone only has a mild penicillin reaction?

Answer 12

Cephalosporins can be used

Question 13

What are the treatment options for someone with a penicillin reaction?

Answer 13

Clarythromycin

Other beta lactams should not be used

Question 14

What are the interactions with amoxicillin?

Answer 14

• Warfarin: kills the bacteria responsible for vitamin K production so can increase bleeding risk
• Methotrexate: can reduce renal excretion causing toxicity
• OCP : can reduce effectiveness

Question 15

What are some side effects of amoxicillin?

Answer 15

• GI Upset (Nausea and diarrhoea)
• Antibiotic associated colitis e.g. c.diff: can cause perforation and death
• Hypersensitivity reactions: rash
• Anaphylactic reaction
• Cholestatic jaundice: rare effect of co-amoxiclav

Question 16

What is a rare side effect of co-amoxiclav?

Answer 16

Cholestatic Jaundice

Question 17

How many people are affected by a penicillin allergy?

Answer 17

Rashes (1-10% of exposed pts) and anaphylaxis (<0.05% pts),

Question 18

What mediates the skin rash associated with penicillin and when does it usually occur?

Answer 18

IgG
Occurs 7-10 days after first exposure
1-2 days after second exposure (delayed IgG)

Question 19

What mediated the anaphylactic reaction associated with penicillin and when does it occur?

Answer 19

Minuites to hours
IgE mediated
Life threatening

Question 20

What are some features of a penicillin anaphylactic reaction?

Answer 20

Hypotension, Bronchospasm and Angioedema

Question 21

Who are at more of a risk of having a penicillin allergy?

Answer 21

Those with the atopic triad: asthma, eczema and hay fever

Question 22

Is a macpap rash a true penicillin reaction?

Answer 22

No but used Clarithromycin instead

Question 23

What other antibiotic has a similar spectrum to amoxicillin?

Answer 23

Clarythromycin

Question 24

How is amoxicillin excreted?

Answer 24

Hepatic metabolism

Excreted in urine and bile

Question 25

When should antibiotics be switched from IV to oral?

Answer 25

For severe infection, amoxicillin is prescribed at a high dose (e.g. 1 g 8-hrly) for IV administration. Intravenous antibiotics should be switched to oral administration after 48 hours if clinically indicated and the patient is improving (e.g. resolution of pyrexia, tachycardia) and able to take oral medication.

Question 26

What are the benefits of prompt IV to oral switch?

Answer 26

Reduces complications and risks

Question 27

When should amoxicillin be given orally?

Answer 27

mild-to-moderate infection (e.g. without systemic features)

Question 28

If co-amoxiclav is prescribed as 500/125 what does this mean?

Answer 28

The relative amounts of amoxicillin (e.g. 500 mg) and clavulanic acid (e.g. 125 mg) in the preparation
In practice the dose prescribed is often these numbers combined, e.g. 625 mg

Question 29

Give an example of a small spectrum antiobitoc prescription that may be used in hospitals rather than the brodspeac amoxicillin and co-amoxiclav?

Answer 29

Pneumonia: Benzylpenicillin and clarythromycin