General principles of anitbiotics

Question 1

What is the purpose of 1) empirical use, 2) directed use and 3) prophylactic use in the prescription of antibiotics?

Answer 1

Antimicrobial therapy may be prescribed for:

Empirical use: where therapy is aimed at the likely causative organism before the results of microbiology and antimicrobial susceptibility tests are available.

Directed use: where therapy is aimed at the specific organism following microbiology results.

Prophylactic use: where therapy is aimed to prevent infection in specific situations where either prophylaxis has been shown to be effective or where the consequences of infection would be associated with significant morbidity.

Question 2

List five examples of cephlasporins

Answer 2

Cefaclor
Cefalexin
Cefazolin
Cefepime
Cefotaxime
Cefoxitin
Ceftaroline
Ceftazidime
Ceftazidime with avibactam
Ceftolozane with tazobactam
Ceftriaxone
Cefuroxime

Question 3

What is the mechanism of a cephlasporin?

Answer 3

Interfere with bacterial cell wall peptidoglycan synthesis by binding to penicillin-binding proteins, eventually leading to cell lysis and death; bactericidal.

Question 4

Describe a circumstance where a cephlasporin would be epmirically indicated

Answer 4

Cephalosporins are rarely the drugs of first choice. Exceptions include ceftazidime for melioidosis, and cefotaxime or ceftriaxone for the empirical treatment of bacterial meningitis.

Question 5

What organism is melioidosis caused by?

Answer 5

Burkholderia pseudoallei (soil and water saphrophyte) [found in contaminated water]

Question 6

What is the clinical presentation of meilodosis?

Answer 6

It is variable; consider
- pneumonia
- higher risk if immunosupressed (CKD, chronic resp disease esp cystic firosis, ETOH abuse)
- abscess in organs (especially SPLEEN + PROSTATE)
- localised cutaneous ulcers or abscesses
- asymptomatic infection

Question 7

How do you make a definitive Dx of meilodosis?

Answer 7

culture of B.psueomallei

Question 8

In adult males, what additional Ix should be considered if suspicious for meilodosis?

Answer 8

CT abdomen - look for abscesses; note consider USS in females + children

Question 9

Where is meilodosis endemic?

Answer 9

Northern Australia and parts of Asia-Pacific

Question 10

What type of bacteria is B.pseumallei and therefore what antibiotic class is suitable?

Answer 10

• gram negative bacilli
• empirical cover with a CEPHLASPORIN (ceftazidime) or MEROPENUM

Question 11

What are the most common pathogens associated with meningitis (excluding <2months of age and >50/immunocompromised

Answer 11

1) Streptococcus pneumonia (gram positive)
2) Nisseria meningitis (gram negative)