Antimicrobial Chemotherapy Flashcards
Streptococcus pyogenes causes
Cellulitis (skin infection) and throat infections
Penicillin and all beta lactams are metabolised in the _______ and excreted from the ________ in urine
Liver
Kidney
The original penicillin was Penicillin __
Penicillin G - (Benzylpenicillin)
How does Penicillin work
Penicillin contains beta lactam ring. They bind on bacteria transpeptidase.
Transpeptidase synthesises bacterial cell wall. So Penicillin inhibits cell wall formation
Name one problem of the first penicillin (benzylpenicillin or penicillin G)
Had poor oral bioavailability.
Stomach acid digest it.
Rapid renal clearance
Penicillin V was developed after penicillin G, it was orally active and would not be digested by stomach acid. Why was amoxicillin preferred though?
Pen V has a short half live. 6 doses needed a day. Not convenient.
Amoxicillin had a longer half life (twice). Only needed 3 a day
Is amoxicillin good for pseudomonas infection ?Y or N
N
Give and example of antipseudomonal penicillin
Piperacillin
How do bacteria such as S. aureus/E. Coli develop resistance to beta-lactams
By developing beta-lactamase enzymes which hydrolyses beta-lactam rings
After resistance development through beta-lactamase enzyme. Name a antibiotic that was produced for staphylococcal beta lactamases infection
Flucloxacillin- the main antibiotic for S. aureus
What is the main antibiotics used for S. aureus
Flucloxacillin
Name a beta lactamase inhibitor drug
Co-amoxiclav
Produced from amoxicillin + clavulinic acid (protects the antibiotic from degradation)
MRSA is resistant to all penicillins. How?
Target alteration/modification mechanism - Mec A gene codes for a different enzyme (not transpeptidase) to synthesise cell wall.
It does not use the beta lactamase enzyme mechanism
E. Coli developed resistance to penicillin through 2 mechanism. List them
- Beta-lactamase enzyme degradation
2. Efflux pumps
Mycoplasma/ Chlamydia have always been resistant to penicillin. Why?
They do not possess a cell wall
List the 4 mechanisms of antibiotic resistance
- Alteration of Target site
- Reducing permeability of cell wall
- Enzyme degradation
- Antibiotics Efflux pump
Benefits of Cephalosporins antibiotics
Acts against different bacterial species
Its beta-lactam ring does not get hydrolysed by beta-lactamase enzyme
Which of the following is not a penicillin A. Penicillin G B. Penicillin V C. Amoxicillin D. Co-amoxiclav E. Cephalosporins F. Flucloxacillin
E. Cephalosporins
Streptococcus Pyogenes has not developed resistant to any penicillin, so the best drug is …
Amoxicillin
List 5 sites of target for antibiotics. With at least an enzyme of antibiotic that targets that site
- Cell wall - beta-lactams
- Protein Synthesis - macrolides/tetracyclines
- DNA replication- Quinolones
- RNA synthesis - Rifamycins
- Antimetabolites- Trimethoprim
What antibiotics work on Mycoplasma/chlamydia? and how
Macrolide
Macrolides targets protein synthesis rather than cell wall
List 5 reasons why patients might not respond to antibiotic treatment
- Wrong diagnosis
- Patient infected with Resistant strain
- Resistant strain develops after treatment
- Drug has poor tissue penetration
- Patient factors: obesity/poor blood supply
List 3 issues with antibiotics use
- Antibiotic allergy is common
- Antibiotics do not always work, despite expectation to work from lab testings
- Antibiotics can activates commensals to become opportunistic pathogens
Allergy to penicillin is common. True or False
True
Amoxicillin Mechanism of action: Standard dose: Adverse effect: Interactions:
Amoxicillin
- A penicillin
Mechanism of action: inhibition of cell wall synthesis
Standard dose: 250-1000mg 8 hourly
Adverse effect: Allergy, damage to commensal microflora
Interactions: can increase levels of other protein bound drugs
Clarythromycin Mechanism of action: Standard dose: Adverse effect: Interaction:
Clarythromycin:
- A Macrolide. Used when patient are allergic to penicillin and effect against mycoplasma/chlamydia
Mechanism of action: Inhibition of protein synthesis in bacterial ribosome (50s subunit)
Standard dose: 500mg 12 houly
Adverse effect: Nausea and diarrhoea. Arrythmias
Interaction: inhibits enzyme involved in metabolism of other drugs.
Don’t not want to give to patient with lung sclerosis as they wont metabolise it properly
Vancomycin Mechanism of action: Standard dose: Adverse effect: Interaction:
Vancomycin
A Glycopeptide. Active only against Gram positive bacteria. Active against MRSA
Mechanism of action: Inhibits bacterial cell wall (different target to beta-lactams)
Oral bioavailability : very low
Standard dose: 500-1500mg 12 hourly. Narrow therapeutic window
Adverse effect: Toxic to kidney and ears
Interaction: Other drugs
