Pathogen-Antibiotic Matching 2

Question 1

Some examples of situations that guide antibiotic choices:

Answer 1

• Allergy: 10% of patients can’t have penicillin’s
• Elderly: Avoid some drugs e.g. ciprofloxacin, with a high risk for Clostridium difficile infection
• Some patients can’t take oral antibiotics
• Some patients can’t take IV antibiotics
• Some patients have renal impairment –> avoid nephrotoxic drugs
• Microbiology culture results may allow narrowing of the spectrum of antibiotics
• Microbiology culture results may dictate a new antibiotic choice (resistance)
• Don’t want to exacerbate problems e.g. a patient with diarrhoea might not like to be given a macrolide/prokinetic
• Some antibiotics interact with drugs a patient is already on e.g. warfarin

Question 2

Antibiotic selection steps:

Answer 2

1. Determine what is the infection diagnosis (or working diagnosis, or differential diagnosis)?
2. Identify which bacteria cause this infection?
3. Identify which antibiotics are effective against these bacteria?
4. Of the antibiotics, which have the right characteristics e.g. can be given orally, to treat the infection in that patient?

Question 3

Clinical Case 1

A patient is admitted to a medical assessment unit in Leeds after being seen by a GP.

The GP referral is brief, and asks you to see a 75 year old man who has:

• symptoms of confusion and shortness of breath
• signs of fever and tachypnoea.

1. What could be wrong with this patient?
2. What could a fever indicate?
3. What are the possible causes of infection in this patient?

Answer 3

• Fever indicates infection
• Probable causes of infection listed:

Question 4

What is a pre-test probability?

Answer 4

The chance that the patient has the disease, estimated before the test result is known. It is based on the probability of the suspected disease in that person given their symptoms.

Question 5

Clinical Case 1 Continued

Clinical History:

• Central nervous system:
  
  • Confusion for 2 days
• Respiratory system:
  
  • Cough, sputum production
• Cardiovascular system: NAD
• Genitourinary system: NAD
• Skin and soft tissue: NAD
• Abdominal system: NAD
• Other:
  
  • Recent antibiotic use

Examination:

• Central nervous system
  
  • Mini mental state reduced: 28/30
• Respiratory system:
  
  • Hypoxia, tachypnoea, abnormal chest examination
• Cardiovascular system: NAD
• Genitourinary system: NAD
• Skin and soft tissue: NAD
• Abdominal system: NAD
• Other: NAD

1. What are the post-test probablities?
2. What’s still in your differential diagnosis?
3. Can your differential diagnosis include low probability infections, and why?

Answer 5

1. See table
2. Community acquired pneumonia is suspected
3. Yes include low probability infections
   
   1. These could be severe and cannot be missed e.g. meningitis

Question 6

What tests should be done for patient in clinical case 1?

Answer 6

Question 7

Undertaking difficult tests is influenced by the result of the quick and easy tests.

Example scenarios:

Answer 7

Question 8

What is diagnosis iteration?

Answer 8

A procedure in which repetition of a sequence of operations (tests) yields results successively closer to a desired result (a high diagnostic probability).

Question 9

Treatment of CAP: pathogens and antibiotics

Answer 9

Question 10

For patients with a low severity CAP (low CURB score):

1. What antibiotics are recommended?
2. What antibiotics are given if there is a penicillin allergy?

Answer 10

1. Amoxicillin
2. Doxycycline or Clarithromycin

Question 11

For patients with a medium severity CAP (medium CURB score):

1. What antibiotics are recommended?
2. What antibiotics are given if there is a penicillin allergy?

Answer 11

1. Amoxicillin + clarithromycin
2. Doxycycline or levofloxacin

Question 12

For patients with a high severity CAP (high CURB score):

1. What antibiotics are recommended?
2. What antibiotics are given if there is a penicillin allergy?

Answer 12

1. Co-amoxiclav IV + clarithromycin
2. Levofloxacin

Question 13

Guidelines for treating CAP

Answer 13

Question 14

Which antibiotic would you choose in the following pneumonia scenarios?:

1. Medium severity: Sputum culture result growing Streptococcus pneumoniae

A- Amoxicllin and clarithromycin

B-Amoxicillin

C: Clarithromycin

Answer 14

Amoxicillin or Clarithromycin –> you know what the pathogen is, targeted (gram-positive)

Question 15

Which antibiotic would you choose in the following pneumonia scenario?:

• Low severity: Respiratory PCR result with a Mycoplasma pneumoniae

A-Amoxicillin

B:Clarithromycin

C-Doxycycline

Answer 15

Clarithromycin or Doxycycline (active against mycoplasma as does not have cell wall)

Question 16

Which antibiotic would you choose in the following pneumonia scenario?:

• Low severity: Pneumonia not better on amoxicillin after 7 days?

A: Amoxicillin

B: Clarithromycin

C-Levofloxacin

Answer 16

Suggests bacteria is resistant to amoxicillin or that the infection is caused by a bacteria other than pneumoccus (despite being low severity) –> try Clarithromycin or Levofloxacin

Question 17

Which antibiotic would you choose in the following pneumonia scenario?:

• Severe pneumonia in a patient with penicillin allergy and epilepsy (so unable to take levofloxacin). Clue: Aztreonam can be used in patients with penicillin allergy)

A: Aztreonam

B: Aztreonam and amoxicillin

C: Aztreonam, teicoplanin and clarithromycin.

Answer 17

C: Aztreonam, teicoplanin and clarithromycin.

Aztreonam alone would not cover all the pathogens. Amoxicillin would result in a penicillin allergy.

Question 18

Which antibiotic would you choose in the following pneumonia scenario?:

• Moderate pneumonia and the patient had a blood culture growing an E.coli

A: E.coli does not cause community associated pneumonia, I need to look at a different guideline.

B: Amoxcillin and clarithromycin and wait for the result of the sputum culture.

Answer 18

A

Question 19

What are PO antibiotics?

Answer 19

Oral antibiotics

Question 20

In patients with known colonisation of MRSA, what antibiotics would you use to treat CAP caused by S. aureus?

• A patient who could take PO antibiotics?
• A patient who could only take IV antibiotics?

Answer 20

• Doxycycline could be prescribed. It is commonly used to treat pneumonia of mild to moderate severity.
• Vancomycin and doxycycline or ciprofloxacin

Question 21

What bacteria is cystitis caused by?

Answer 21

E. coli (or similar)

Question 22

Cystitis antibiotic options:

Answer 22

Question 23

What oral antibiotics can be prescribed for cystitis?

Answer 23

Pivmecillinam, Nitrofurantoin, trimethoprim, amoxicillin-clavulanic acid, cephalexin, ciprofloxacin or levofloxacin are all options

Question 24

Kidney infections (upper UTIs) can be misdiagnosed as cystitis (lower UTI). Lower UTI antibiotics can not be used for upper UTI infections.

What should be used instead?

Answer 24

Ciprofloxacin, IV cefuroxime, ertapenem, meropenem, gentamicin, IV amoxicillin-clavulanic acid, piperacillin-tazobactam and aztreonam are all options.

Question 25

What are ESBL enzymes?

Answer 25

enzymes in Gram-negative bacteria (e.g. E.coli) that confer resistance to most beta-lactam antibiotics, including penicillins, cephalosporins, and the monobactam aztreonam.

Question 26

Bacteria causing most urinary tract infections, and the antibiotic options you have and that are lost (in red) when the isolate is an ESBL resistant E.coli or CPE resistant E.coli

Answer 26

Question 27

What are CPEs?

Answer 27

Gram-negative bacteria that are resistant to the carbapenem class of antibiotics, considered the drugs of last resort for such infections –> carbapenemase-producing Enterobacteriaceae (CPE)