Penicillins Flashcards
What type of antibiotic are penicillins?
Beta Lactam Antibiotic
What part of bacteria do penicillins target?
Target Cell wall synthesis
How do penicillins work?
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.
What spectrum does amoxicillin have?
Broad spectrum
How can synthetic penicillins be made? E.g. amoxicillin
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.
What structure does the beta lactam ring have?
(C-C-C-N); Structural analogue of D-alanyl-D-alanine
How do bacteria create resistance against penicillin antibiotics?
Some bacteria can produce beta lactamase enzymes which break down the beta lactam ring and inactivate the antibiotic
What are the common indications for using amoxicillin?
- Empirical treatment of pneumonia
- Gram postive activity (strep pneumonia)
- Gram negative activity (H. influenza) - Empirical treatment of UTIs
- nitrofurantoin and trimethoprim more commonly used - Hospital acquired infections and Intra-abdominal sepsis
- As a combination treatment as co-amoxiclav
- Usually caused by G- and resistant bacteria - H.Pylori Eradication
What gram positive and gram negative bacteria does amoxicillin cover?
Gram + : streptococcus species and staphylococcus species
Gram - : H. Influenza
What are the contra-indications of using amoxicillin?
- Those at risk of C.Diff infection
- Those with previous penicillin allergy (anaphylaxis and urticaria)
- Those with severe renal impairment (can cause crystaluria)
Name some features of a minor penicillin reaction?
Non confluent
Non pruitic
Small
Onset after 72 hours
What are the treatment options if someone only has a mild penicillin reaction?
Cephalosporins can be used
What are the treatment options for someone with a penicillin reaction?
Clarythromycin
Other beta lactams should not be used
What are the interactions with amoxicillin?
- 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
What are some side effects of amoxicillin?
- 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
What is a rare side effect of co-amoxiclav?
Cholestatic Jaundice
How many people are affected by a penicillin allergy?
Rashes (1-10% of exposed pts) and anaphylaxis (<0.05% pts),
What mediates the skin rash associated with penicillin and when does it usually occur?
IgG
Occurs 7-10 days after first exposure
1-2 days after second exposure (delayed IgG)
What mediated the anaphylactic reaction associated with penicillin and when does it occur?
Minuites to hours
IgE mediated
Life threatening
What are some features of a penicillin anaphylactic reaction?
Hypotension, Bronchospasm and Angioedema
Who are at more of a risk of having a penicillin allergy?
Those with the atopic triad: asthma, eczema and hay fever
Is a macpap rash a true penicillin reaction?
No but used Clarithromycin instead
What other antibiotic has a similar spectrum to amoxicillin?
Clarythromycin
How is amoxicillin excreted?
Hepatic metabolism
Excreted in urine and bile
When should antibiotics be switched from IV to oral?
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.
What are the benefits of prompt IV to oral switch?
Reduces complications and risks
When should amoxicillin be given orally?
mild-to-moderate infection (e.g. without systemic features)
If co-amoxiclav is prescribed as 500/125 what does this mean?
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
Give an example of a small spectrum antiobitoc prescription that may be used in hospitals rather than the brodspeac amoxicillin and co-amoxiclav?
Pneumonia: Benzylpenicillin and clarythromycin
