Anti-microbials 2

Question 1

What are the types of antibiotic misuse?

Answer 1

i) If there is no infection

ii) Incorrect Antibiotics
- > The use of excessive empirical treatment is driving antibiotic resistance

iii) Inappropriate Dose
- > Commonly inadequate than excessive

iv) Inappropriate Duration

v) Can cause Adverse effects
5% of people given an antimicrobial experience an adverse effect
-> GI, Fever & Rash, Renal Dysfunction, Acute Anaphylaxis
-> Allergies. Penicillin Allergy is the most common (PENICILLIN IS VERY ACTIVE, therefore try to give where possible i.e. mild reactions are fine)

Question 2

What are the selection considerations for antibiotics?

Answer 2

1. Host:
   - > Age of the host i.e. Tetracyclines deposit in growing bones therefore avoided in children and mothers
   - > Pregnancy i.e. Trimethoprim (Folate Antagonist) is ass. with neural tube defects
   - > Immunocompromised
   - > Renal/Liver Failure
2. Antimicrobial Susceptibility
   - > Check local guidelines for resistance patterns
   - > Regulatory bodies undergo susceptibility testing to find the MIC - Minimum Inhibitory Concentration of the Organism
3. Site of Infection
   - > Some sites are difficult to access i.e. bone, urine CSF
   - > pH and lipid solubility will affect the ability of the antimicrobial
4. Pharmacokinetics
5. Route of admin
6. Dosage

(Use narrow spectrum if possible)

Question 3

How do you carry out antimicrobial susceptibility testing?

Answer 3

Test microbe with different concentrations of antimicrobial to calculate MIC(minimum inhibitory concentration) or zone size and compare to guidance to see if it is resistant or susceptible.

Question 4

What is the difference between empirical and definitive antibiotic treatment?

Answer 4

1. Empirical is given at the start as the “best guess” for an unknown microbial using local policies etc
2. Definitive is when microbe is identified using cultures and the correct antimicrobial is chosen

Question 5

What are signs that a patient may have an infection?

Answer 5

1. Fever
2. Increased CRP
3. Increased WBCs (neutrophils), decreased WBCs

also consider:

1. Duration
2. Risk factors
3. Source of infection
4. Exclude pro-inflammatory medical diseases

Question 6

What influences the antibiotic route of administration?

Answer 6

Oral

• > This is first line as it is least invasive
• > No risk of Cannula introducing infection
• > Avoid if Poor GI function or Vomiting

IV

• > This is very effective
• > Usually switched to PO after 48 hours except CNS and Severe Infections i.e. Osteomyelitis&Endocarditis

IM

• > Tends to be painful
• > Only indicated in Gonorrhoea, IM Ceftriaxone
• > Avoid if bleeding tendency

Topical

• > Limited application
• > Local Sensitisation

Question 7

What 3 patterns of activity do antibiotics have?

Answer 7

Type 1 Antibiotics 
Concentration Dependent Killing 
-> Aminoglycosides i.e. Gentamicin
-> Daptomycin
-> Fluoroquinolones
-> Ketolides
Goal of therapy is to acheive high peaks of antibiotic concentrations (cMAX)
tends to be infrequent high doses

Type 2 Antibiotics 
Time Dependent Killing
-> Penicillins
-> Cephalosporins
-> Carbapenems
-> Erythromycin
-> Linezolid
Goal of therapy is to achieve high lengths of time above the MIC 
tends to be frequent lower doses

Type 3 Antibiotics 
Both Concentration and Time dependent 
-> Azithromycin 
-> Clindamycin
-> Oxazolidinones
-> Tetracyclines
-> Vancomycin 
Goal of therapy is to maintain high peaks of antibiotic concentrations for prolonged periods of time