MI: Antimicrobials 2

Question 1

List some ways in which antibiotics can be misused.

Answer 1

• No infection present
• Selection of incorrect drug
• Inadequate or excessive dose
• Inappropriate use of empirical antibiotics

NOTE: about 50% of people with bacteraemia will get better by themselves

Question 2

List some common adverse events associated with antibiotics.

Answer 2

• GI upset
• Rash and fever
• Renal dysfunction
• Acute anaphylaxis
• Hepatitis

Question 3

What does the ‘CHOICE’ of correct antimicrobial depend on?

Answer 3

CHAOS

• Choice of drug - narrow spectrum where possible, considering local sensitivity patterns and cost
• Host characteristics (e.g. age, pregnancy)
• Antimicrobial susceptibility
• Organism
• Site of infection (e.g. bone, CSF)

Question 4

How is the type of drug decided upon?

Question 5

Which types of infection typically require IV antibiotics?

Answer 5

• Serious infection
• Deep/CNS infections

Question 6

What is MIC?

Answer 6

• Minimum inhibitory concentration - minimum concentration of drug required to inhibit bacterial growth
• There is a regulatory body that sets the MIC cut-off

Question 7

What is the agar diffusion method?

Answer 7

• A disc is impregnated with antibiotic
• As distance from the disc increases, the concentration of antibiotic decreases logarithmically
• The border of the clear zone is the MIC
• This is time-consuming

Question 8

What type of antibiotics should be used in nosocomial infections and severe sepsis?

Answer 8

Broad-spectrum

Question 9

Why should as large a sample as possible be sent when identifying organisms?

Answer 9

More sample means higher sensitivity

Question 10

For what samples would you do gram staining as a preliminary investigation?

Question 11

Name two methods of rapid antigen detection.

Answer 11

• PCR
• Immunofluorescence

Question 12

What factors about the site of infection can affect antibiotic choice?

Answer 12

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

Question 13

Which two types of infection require special consideration because they are difficult to penetrate with antibiotics?

Answer 13

• Osteomyelitis
• Endocarditis

Question 14

In which circumstances would you avoid IM administration of antibiotics?

Answer 14

• Bleeding tendency
• Drug is locally irritant

Question 15

What is an important predictor of efficacy?

Question 16

Describe the type I pattern of antibiotic activity. Give an example of an antibiotic of this type.

Answer 16

• Concentration-dependent killing
• Peak above the MIC (Cmax) is the most important parameter
• Example: aminoglycosides
• These drugs tend to be given as one big dose
• The benefits of achieving a higher Cmax must be balanced with the increased toxicity
• Trough concentration should also be measured to ensure that the drug is being eliminated (this determines the frequency of drug administration)

Question 17

Describe the type II pattern of antibiotic activity. Give an example of an antibiotic of this type.

Answer 17

• Time-dependent killing
• Time spent above the MIC is the most important factor
• Example: penicillins
• Therefore, penicillins need to be given frequently

Question 18

Describe the type III pattern of antibiotic activity. Give an example of an antibiotic of this type.

Answer 18

• Concentration and time-dependent
• AUC above the MIC is the most important factor
• Example: vancomycin

NOTE: infusions may be used to maintain an AUC above the MIC

Question 19

What are the main side-effects of aminoglycosides?

Answer 19

Ototoxicity and nephrotoxicity

Question 20

Name two common organisms that cause skin infections.

Answer 20

• Streptococcus pyogenes*
• Staphylococcus aureus*

Question 21

How are simple skin infections treated?

Answer 21

Flucloxacillin

NOTE: unless penicillin allergic or MRSA

Question 22

How should invasive group A streptococcal infection be treated?

Answer 22

• Aggressive and early debridement
• Early use of antibiotics (e.g. clindamycin)
• Use of IVIG

Question 23

What is the eagle effect?

Answer 23

• There is a relative lack of efficacy of beta-lactams in infections with a high bacterial burden
• This is because beta-lactams only work on dividing bacteria
• In cases of high bacterial burden, a lot of bacteria may be in the stationary phase of the cell cycle

Question 24

List some common organisms that cause bacterial respiratory tract infections.

Answer 24

• Streptococcus pneumoniae
• Haemophilus influenzae
• Moraxella catarrhalis
• Atypical: Legionella, Mycoplasma, Chlamydia

Question 25

What is used to treat: 1. Pharyngitis 2. CAP (mild) 3. CAP (severe)

Answer 25

1. **Pharyngitis =** Benzylpenicillin (10 days) **2. CAP (mild)** = Amoxicillin **3. CAP (severe)** = Co-amoxiclav and clarithromycin

Question 26

List some treatment options for hospital-acquired pneumonia.

Answer 26

* Cephalosporins * Ciprofloxacin * Tazocin * If MRSA, consider adding vancomycin

Question 27

List the main pathogens that cause meningitis.

Answer 27

* *Neisseria meningitidis* * *Streptococcus pneumoniae* * *Listeria monocytogenes* (in the very young, elderly and immunocompromised)

Question 28

What is the mainstay of treatment for bacterial meningitis?

Answer 28

Ceftriaxone NOTE: consider adding amoxicillin if *Listeria* is likely

Question 29

How is menigitis in babies \< 3 months treated?

Answer 29

Cefotaxime + amoxicillin NOTE: ceftriaxone is NOT used in neonates because it displaces bilirubin from albumin and causes biliary sludging

Question 30

What are the treatment options for *N. meningitidis* meningitis?

Answer 30

* Benzylpenicillin * Ceftriaxone or cefotaxime

Question 31

Outline the treatment of: 1. Simple cystitis 2. Hospital-acquired UTI 3. Infected urinary catheter

Answer 31

1. **Simple cystitis** - trimethoprim (3 days) 2. **Hospital-acquired UTI** - cephalexin or co-amoxiclav 3. **Infected urinary catheter** - change catheter under gentamicin cover

Question 32

How is *C. difficile* colitis treated?

Answer 32

* Stop the offending antibiotic (usually a cephalosporin) * If severe, treat with metronidazole or vancomycin

Question 33

What are some important things to consider if there is no response to antibiotics within 48 hours?

Answer 33

* Does the patient have a bacterial infection? * Is there a persitent focus of infection? * Is there a deep-seated collection that requires drainage? * Could the patient have bacterial endocarditis? * Is the dose appropriate? * Is there another infection present (consider *Candida*)?

Question 34

How should you approach lack of response after 48 hours of ABx administration?

Answer 34

* Does the patient have a bacterial infection - collected relevant cultures? * Is there a persistent focus present (e.g. an infected vascular or urinary catheter) * Is there a deep-seated collection (e.g. intra-abdominal) that requires drainage? * Could the patient have bacterial endocarditis? * Am I using the correct dose of the antimicrobial? * Is another infection present (esp consider Candida)?

Question 35

What is the recommended length of course for the following infections? 1. N. meningitidis meningitis 2. Adult osteomyelitis 3. Bacterial endocarditis 4. Grp A streptococcus pharyngitis 5. Simple cystitis

Answer 35

1. 7 days 2. 6 weeks 3. 4-6 weeks 4. 10 days 5. 3 days 6.