Principles of Infectious Disease and Antimicrobial Therapy

Question 1

Systematic approach for Selecting Antimicrobial Agents

Answer 1

1. Confirm the presence of infection
2. Determine the site of infection
3. Identify the pathogen
4. Select presumptive therapy
5. Refine therapy
6. Monitor therapeutic response

Question 2

Factors to help confirm the presence of infection

Answer 2

H&P

Predisposing factors

Signs and Sxs

• Fever
• WBC count with differential
  
  • Normal 4500-10,000
  • Inc WBC with left shift (more neutrophils= bacterial)
• Other: ESR, CRP, procalcitonin
• Pain and inflammation
• Disease specific signs and sxs

Question 3

Normal temperature

Answer 3

98.6F or 37C

Question 4

Febrile temperatures

Answer 4

100.4F 38C

102F 39C

104F 40C

Question 5

Drugs that can cause a false positive and false negative fever

Answer 5

False +

• Drug induced

False -

• ASA, APAP, NSAIDS
• Corticosteroids

Question 6

WBC Differential

Answer 6

With bacterial infection, WBC may be as high as 30,000-40,000

Presence of immature bands (neutrophils), that are >10%, is indicative of bone marrow response to bacterial infection

Question 7

Other tests of inflammation

Answer 7

ESR

CRP

Procalcitonin (PCT)–appears to reflect severity of infection

Question 8

Identification and Classification of Pathogen

Answer 8

1. Stains–Gram stain, acid fast, India ink
2. Serologies
3. Culture and activity

Question 9

Common Uses of Gram Stain

Answer 9

Empiric antimicrobial treatment

Routinely performed on:

• CSF for meningitis
• Urethral smears for UTI
• Abscesses or effusions

Question 10

Selection of Presumptive Therapy is Based On….

Answer 10

Host factors

Drug factors

Question 11

Host factors

Answer 11

Drug allergies

Age

Pregnancy

Renal and hepatic function

Site of infection

Concomitant drug therapy

Underlying disease states

Question 12

Drug factors

Answer 12

Antimicrobial activity

Spectrum of activity

Pharmacokinetics

Pharmacodynamics

Tissue penetration

Adverse effect profile

Cost and convenience

Question 13

Antimicrobial activity

Answer 13

Bactericidal

• Kills sensitive organisms so that the number of viable organisms falls rapidly after drug exposure

Bacteriostatic

• Inhibits the growth of the bacteria but does not kill them; immunologic mechanisms are required to eliminate organisms

Question 14

Most common mechanism of action of antibiotics

Answer 14

Blocks cell wall synthesis and protein synthesis

Question 15

Antimicrobial Spectrum of Activity

Answer 15

Narrow

Extended

Broad

Question 16

Minimum Inhibitory Concentration

Answer 16

The lowest antimicrobial concentration that prevents visible growth of an organism after 24hrs of incubation

Question 17

Susceptibility Testing Methods

Answer 17

Macrodilution method

Microdilution method–Multiple Abx

Kirby-Bauer disk diffusion method

E-test – strip

Automated methods

Question 18

Bacteria can be classified as

(Sensitivity and Resistance)

Answer 18

Susceptible

Intermediate

Resistant

Based on the relationship between MIC adn peak serum concentration of typical doses

Peak should be 2-4X MIC to be susceptible

Question 19

Factors that increase antibiotic resistance

Answer 19

Overuse of antibiotics

Low dose and inadequate levels

Prlonged exposure

Inappropriate antibiotics

Day Care

Resistance also varies with region, and increases with careless antibiotic use

Question 20

Requirements for antibiotic activity

Answer 20

Penetrate Cell

Reach Intracellular Target

Kill Organism

Question 21

Mechanism of Resistance

Answer 21

Decreased permeability

Drug efflux

Drug inactivation

Altered target

Question 22

Pharmacokinetic and Pharmacodynamic factors to consider when choosing presumptive therapy

Answer 22

Concentration and time dependent effects

• MIC
• CDKR: Concentration-Dependent Killing Rate
• PAE: Postantibiotic effect

Question 23

CDKR

Answer 23

Concentration-Dependent Killing Rate

More bacteria are killed at higher concentrations of antibiotics

i.e.aminoglycosides and fluoroquinolones

Not beta lactams

Question 24

PAE

Answer 24

Postantibiotic Effect

Persistent effect of an antibiotic on bacterial growth after the antibiotic is removed

Most bactericidal antibiotics exhibit PAE

Less frequent dosing allowed

Question 25

Therapeutic Steps

Answer 25

Empiric Therapy

• Likely pathogens for site of infection
• Patient Hx–travel, allergies, etc
• Local susceptibility

Refine therapy based on culture and sensitivity results

Monitor therapeutic response and adjust therapy as needed

Question 26

Gram (+) Cocci

Answer 26

• Staph *
• Strep *

Enterococcus

Question 27

Gram (-) cocci and cocci-bacilli

Answer 27

• H. flu*
• Neisseria*
• Moraxella catarrhalis*

Question 28

Enterobacteriacea

(Gram (-))

And other random Gram (-)

Answer 28

EKP: E. coli, Klebsiella, Proteus

ESP: Enterobacter, Serratia, Providencia

Pseudomonas aeruginosa

Question 29

Anaerobes

Answer 29

Bacteroides fragilis

Question 30

Acute Otitis Media

(Common pathogens causing)

Answer 30

• S. pneumoniae*
• H. flu*
• M. catarrhalis*

Question 31

Sinusitis

(Common pathogens causing)

Answer 31

• S. pneumoniae *
• H. flu*
• M. catarrhalis*

Question 32

Meningitis

(Common pathogens causing)

Answer 32

• S. pneumoniae*
• H. flu*
• N. meningitidis*

Question 33

Chronic Bronchitis (ABECB)

(Common pathogens causing)

Answer 33

• C. pneumoniae *
• M. pneumoniae *
• S. pneumoniae*
• H. flu *
• M. catarrhalis *

Question 34

Pneumonia

(Common pathogens causing)

Answer 34

• S. pneumoniae*
• M. pneumoniae*
• H. flu*
• M. catarrhalis*

Question 35

Urinary Tract Infection

(Common pathogens causing)

Answer 35

• S. pneumoniae*
• M. pneumoniae*
• H. flu*
• Psuedomonas*
• Staph aureus*

Question 36

Osteomyelitis

(Common pathogens causing)

Answer 36

Staph

Question 37

Bowel perf–Appendicitis

(Common pathogens causing)

Answer 37

• E. coli, Klebsiella* (MC)
• Enterococcus*
• Psuedomonas*
• Bacteriodes*