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PathY5 > Antimicrobials 2 > Flashcards

Antimicrobials 2 Flashcards

1
Q

How are antimicrobials commonly misused?

A

No infection present

Selection of incorrect drug

Inadequate or excessive dose

Inappropriate duration of therapy

Expensive agent used when cheaper is available

(In short: Incorrect dose, duration, diagnosis and drug/ cost)

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2
Q

What does resistance cost?

A

Suffering and money:
Re-operation, abscess, wound infection

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3
Q

What % of people in hospital suffer an adverse event and which AEs do they suffer?

A

5%

GI upset
Fever & rash
Renal dysfunction
Acute anaphylaxis
Hepatitis

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4
Q

Why are antimicrobials CHAOS?

A

CHOICE of antimicrobial based on:
HOST characteristics
ANTIMICROBIAL susceptibilities
ORGANISM itself
SITE of infection

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5
Q

How are drugs chosen?

A

Narrow and bactericidal if possible

Ideally based on bacteriological diagnosis (or best guess)

Sensitivity pattern

Patient characteristics

Cost

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6
Q

What theoretical considerations must be made to choose a drug?

A

Pharmacokinetics (absorption, distribution, elimination)

Route of administration (IV if not PO or access deep site/ CNS)

Dosage (Age (+weight), Renal/ Hepatic function, monitoring)

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7
Q

What host factors affect choice?

A

Allergy
Age
Genetics
Hepatic function
Renal function

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8
Q

What is the MIC?

A

Minimum inhibitory Concentration

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9
Q

How does the agar disc diffusion method work?

A

Antibiotic-impregnated disc absorbs moisture from the agar; antibiotic diffuses into the agar medium.

As distance from the disc increases, there is a logarathmic reduction in the [antibiotic].[diffused antibiotic] at the interface of growing and inhibited bacteria ~ MIC

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10
Q

When do we do blood cultures?

A

Prior to antibiotics

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11
Q

How do we use empirical cover?

A

broad-spectrum agent that is likely to “cover” the likely organisms, given the differential

After culture: narrow it down

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12
Q

When is an empiric antibiotic appropriate?

A

Nosocomial infections (pneumonia) and severe sepsis

The best antibiotic should be prescribed first, based on the patient’s risk factors, suspected pathogen and local resistance patterns.

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13
Q

How do we identify the infecting organism?

A

Gram stain (CSF/ joint aspirate/ pus)

Rapid antigen detection (immunofluorescence and PCR)

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14
Q

Why should we consider the site of infection?

A

The local concentration of the antimicrobial will be affected by factors such as:

pH at the infection site

Lipid-solubility of the drug

Ability to penetrate the blood-brain barrier (CNS infections)

Special considerations required for Rx endocarditis or osteomyelitis

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15
Q

How do we determine if a patient truly requires an antimicrobial?

A

Evidence of systemic response (fever, raised CRP, raised WBC or really low WBC)

Considering duration, RFs, source, exclusion of other proinflammatory disease

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16
Q

When do we use IV?

A

Serious (or deep-seated) infection

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17
Q

When do we use PO?

A

Usually easy, but avoid if poor GI function or vomiting

Different classes of antimicrobial have different oral bioavailabilities

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18
Q

When do we use IM?

A

Not an option for long-term use

Avoid if bleeding tendency or drug is locally irritant

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19
Q

When do we use Topical?

A

Limited application and may cause local sensitisation

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20
Q

When is IV to PO switch recommended?

A

i.v. to p.o. switch is recommended in hospital for most infections if the patient has stabilised after 48 hours i.v. therapy

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21
Q

What is Type I pattern of activity and which antibiotics are useful?

A

Concentration-dependent killing and Prolonged persistent effects

Aminoglycosides
Daptomycin
Fluoroquinolones
Ketolides

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22
Q

What is the goal of therapy with Type I pattern?

A

Maximise concentrations

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23
Q

What is the PK/PD parameter in Type I patterns?

A

24h-AUC/MICPeak/MIC

24
Q

What is Type 2 pattern of activity and which antibiotics are useful?

A

Time-dependent killing and Minimal persistent effects

Carbapenems
Cephalosporins
Erythromycin
Linezolid
Penicillins

25
Q

What is the goal of therapy with Type 2 pattern?

A

Maximisation of duration of exposure

26
Q

What is the PK/PD parameter in Type 2 patterns?

A

T>MIC

27
Q

What is Type 3 pattern of activity and which antibiotics are useful?

A

Time-dependent killing and Moderate to prolonged persistent effects

Azithromycin
Clindamycin
Oxazolidinones
Tetracyclines
Vancomycin

28
Q

What is the goal of therapy with Type 3 pattern?

A

Maximise amount of drug

29
Q

What is the PK/PD parameter in Type 3 patterns?

A

24h- AUC/MIC

30
Q

How long do you give Abx for?

A

Based on clinical markers

31
Q

How long should you treat N. meningitidis meningitis?

A

7 days

32
Q

How long should you treat Acute osteomyelitis?

A

6 weeks

33
Q

How long should you treat Bacterial endocarditis?

A

4-6 weeks

34
Q

How long should you treat GpA Streptococcal pharyngitis?

A

10 days

35
Q

How long should you treat Simple cystitis in women?

A

3 days

36
Q

How do you treat skin infections and why?

A

Flucloxacillin (except allergy or MRSA)

Impetigo/ cellulitis/ wound infections are normally due to Staph aureus and beta haemolytic strep which responds to penicillin

37
Q

What is iGAS treatment?

A

Aggressive and early debridement

Antibiotics – adjunctive use of protein synthesis inhibitors esp. clindamycin (also has good skin & soft tissue penetration)
Use of IVIg

38
Q

What is the Eagle effect?

A

High doses of penicillin have a worse bactericidal effect.

Originally referred to the paradoxically reduced antibacterial effect of penicillin at high doses, though recent usage generally refers to the relative lack of efficacy of beta-lactam antibacterial drugs on infections having large numbers of bacteria.

39
Q

What is the proposed mechanism of the eagle effect?

A

Penicillin is a bactericidal antibiotic (inhibiting cell wall synthesis) but this synthesis only occurs when bacteria are actively replicating (or in the log phase of growth).

In cases of extremely high bacterial burden (such as with Group A Strep), bacteria may be in the stationary phase of growth.

In this instance since no bacteria are actively replicating (presumably due to nutrient restriction) penicillin has no activity.

40
Q

How do you treat pharyngitis?

A

Benzylpenicillin 10 days

41
Q

How do you treat mild CAP?

A

Amoxicillin

42
Q

How do you treat severe CAP?

A

Co-amoxiclav and clarithromycin

43
Q

How bad is hospital acquired respiratory tract infections?

A

Second most common HAI
23% mortality
Greatest likelihood of tracheal intubation and mechanical ventilation

44
Q

How do you treat a HA RTI?

A

Cephalosporins, ciprofloxacin, piperacillin/ tazobactam

If MRSA consider Vanc addition

45
Q

What are the main pathogens of bacterial meningitis and how do we treat them?

A

N. Meningitidis
S. pneumoniae
+/- Listeria in the very young/elderly/immuno-compromised

Ceftriaxone (+/- amoxycillin if Listeria likely)

46
Q

How do you treat meningitis in babys?

A

Baby less than 3 months: Cefotaxime PLUS Amoxicillin (to cover for listeriosis)

Note: Ceftriaxone not used in neonates as displaces bilirubin from albumin and because it can cause biliary sludging

Neisseria meningitidis: Benzylpenicillin (high dose) or Ceftriaxone/Cefotaxime

47
Q

How does penicillin resistance happen in N meningitidis?

A

The mechanism of relative resistance to penicillin involves, at least in part, the production of altered forms of one of the penicillin-binding proteins.

Although treatment with penicillin is still effective against these relatively resistant strains, there is evidence that low-dose treatment regimens can fail.

Beta-Lactamase production in meningococci is extremely rare but has been reported

48
Q

How do you treat simple cystitis?

A

Trimethoprim 3 days

49
Q

How do you treat HA UTI (commonest type of HAI)?

A

Cephalexin or Augmentin

50
Q

How do you treat an infected urinary catheter?

A

Change under gentamicin cover

51
Q

How do you treat C difficile colitis

A

STOP the offending antibiotic (usually a cephalosporin);
If severe, Rx with p.o. metronidazole;
If above fails, use p.o. vancomycin

52
Q

How are antibiotics usage monitored?

A

Antibiotic policy/guidelines drawn up in consultation with other specialists in the Antibiotic Review Group

Microbiologist /pharmacist review of complex cases or inappropriate antimicrobial usage

53
Q

If there is no response within 48 hours what should you consider?

A

Is it really bacterial? Are there 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?

Correct dose?

Is another infection present (esp consider Candida)?

54
Q

Summarise antibiotic prescribing

A

Get blood culuture (or appropriate culutre)

Prescribe empirical Abx on most likely Ddx.

Monitor clinical status and response (48-72h)- re-evaluate when microbiology has got results

Tailor therapy to more narrow Abx based on Micro and pt response.

If patient has been well then evaluation may result in discontinuation of treatment.

55
Q

Is resistance increasing?

A

Yes

56
Q

How are carbapenemases changing?

A

KPC was high during an outbreak in NW England
OXA-48 is also high

57
Q

What is a MIC breakpoint and how is it used?

A

The point at which the there is therapeutic success

MIC>breakpoint - resistant
MIC

PathY5 (98 decks)

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