Y Lecture 2: Anti-Microbial Agents 2

Question 1

What mnemonic can be used to help decide which antibiotic to use?

Answer 1

• CHAOS – things to consider when prescribing antimicrobials
o C Choice of correct antimicrobial depends upon the…
o H Host characteristics (i.e. renal failure, pregnancy, allergy, age, genetics, hepatic function)
o A Antimicrobial susceptibilities of the…
o O Organism itself and also the…
o S Site of infection (i.e. bone, CSF, urine)

Question 2

What is the Minimum Inhibitory Concentration and Breakpoint of an antibiotic useful for?

Answer 2

Working out sensitivity MIC > breakpoint = resistantMIC < breakpoint = sensitive

Question 3

What antibiotic should be given for gram pos cocci in clusters?

Answer 3

Flucloxacillin

Question 4

What antibiotic should be given empirically for gram neg cocci?

Answer 4

Ceftriaxone (could be meningococcus)

Question 5

What is the “eagle effect”?

Answer 5

Increasing the penicillin dose –> decreasing antibacterial activitity after a point

Question 6

How does the choice of antibiotic to treat UTI differ between community and hospital?

Answer 6

Community: nitrofurantoin/ trimethoprim
Hospital: cephalexin/ augmentin

Question 7

What factors affect the local concentration of the antimicrobial?

Answer 7

o pH at the infection site
o Lipid-solubility of the drug
o Ability to penetrate the blood-brain barrier

Question 8

What do you check for a systemic response?

Answer 8

o Fever ± raised CRP

o High WBC (mainly neutrophils; may be LOW WBC in severe infection)

Question 9

What are different routes of administration?

Answer 9

o IV - serious (or deep-seated) infection
o PO - usually easy, but avoid if poor GI function or vomiting. Different classes of antimicrobial have different oral bioavailabilities
o IM - not an option for long-term use. Avoid if bleeding tendency or drug is locally irritant
o Topical - limited application and may cause local sensitisation

Question 10

What organisms cause pneumonia?

Answer 10

• Common Organisms:
o Streptococcus pneumoniae
o Moraxella catarrhalis
o Haemophilus influenzae

Atypicals: Legionella, Mycoplasma, Chlamydia

Question 11

What is the treatment for pneumonia?

Answer 11

o Pharyngitis: Benzylpenicillin, 20 days; phenoxymethylpenicillin, 10 days
o Community-acquired pneumonia (mild): Amoxicillin
o Community-acquired pneumonia (severe): Co-amoxiclav & clarithromycin

Question 12

How do you treat UTIs?

Answer 12

• Simple cystitis- Trimethoprim 3 days
• Hospital-acquired UTI - cephalexin or augmentin
• Infected urinary catheter- change under gentamicin cover

Question 13

Treatment for c.dificile

Answer 13

• STOP the offending antibiotic (usually a cephalosporin)

If SEVERE, treat with:
o Metronidazole (PO)
o If above fails, use vancomycin (PO)

Question 14

Treatment for bacterial meningitis

Answer 14

o Neisseria, S. pneumoniae - Benzylpenicillin (high dose) or ceftriaxone/cefotaxime
o Listeria - Amoxicillin / ampicillin
o Baby <3 months - Cefotaxime + amoxicillin (covers listeria)