Antimicrobial Selection

Question 1

what are the 3 indications for antimicrobials

Answer 1

1. infection
2. prophylaxis
3. metaphylaxis

Question 2

prophylaxis

Answer 2

short term administration to prevent infection during surgery

Question 3

metaphylaxis

Answer 3

treatment of a group of animals that aren’t diseased but are in proximity to diseased animals

Question 4

what are the main considerations when choosing a specific antimicrobial

Answer 4

• susceptibility of organism
• infection site
• administration route, frequency, and adverse effects
• cost/owner compliance
• drug label and WDTs
• concurrent medications
• host factors

Question 5

broad spectrum antimicrobials

Answer 5

active against a wide spectrum of bacteria

• carbapenems
• fluoroquinolones
• chloramphenicol
• 2nd/3rd generation cephalosporins
• tetracyclines
• clavamox

Question 6

pros and cons of broad spectrum antibiotics

Answer 6

pros:
- effective against a wide variety of bacteria

cons:
- greater disruption of normal flora
- increased risk of resistance

Question 7

narrow spectrum antimicrobials

Answer 7

active against a selected group of bacteria

• erythromycin
• penicillin
• clindamycin
• aminoglycosides
• rifampin

Question 8

pros and cons of narrow spectrum antimicrobials

Answer 8

pros:
- less disruption of normal flora
- decreased risk of resistance

cons:
- may not be effective if organism is unknown

Question 9

what are limited sites

Answer 9

body sites that only certain drugs are able to reach

• abscesses
• brain/CNS
• eye
• prostate
• bronchial epithelium and secretions

Question 10

can all drugs penetrate intracellularly

Answer 10

NO - only certain drugs are able to be effective against intracellular organisms

• tetracyclines
• fluoroquinolones
• macrolides

Question 11

local factors that effect drug penetration

Answer 11

• purulent material and necrotic debris
• foreign material
• acidic environment
• anaerobic environment
• poor vascularization
• biofilms
• abscesses

Question 12

1st line drugs

Answer 12

used for empirical selection in the absence of/pending results of C&S testing
- will treat a LIKELY cause of infection

• amoxicillin
• cephalexin
• doxycycline
• TMS
• penicillin
  +/- fluoroquinolones

Question 13

2nd line drugs

Answer 13

used on the basis of C&S testing with the lack of susceptibility to 1st line drugs
- if results show susceptibility to a 1st line drug, use the 1st line drug

• piperacillin
• amikacin
• gentamicin
• 3rd generation cephalosporins
• fluoroquinolones

Question 14

3rd line drugs

Answer 14

reserved drugs - only used when absolutely necessary
- MUST have documented susceptibility
- must not be susceptible to any 1st or 2nd line drugs
- infection must be serious/life threatening
- infection should be treatable

• vancomycin
• linezoid
• carbapenems

Question 15

considerations for equine antimicrobials

Answer 15

• poor oral absorption of drugs
• requires large volume of parenteral drugs
• potential for GI upset

Question 16

considerations for food animal antimicrobials

Answer 16

• cost
• withdrawal times
• label and ELDU of drugs
• large volume required
• effect on meat/milk quality
• often parenteral drugs

Question 17

when is it indicated to use a combination of antimicrobials

Answer 17

1. resistance is rapidly generated against a single antimicrobial
2. poolymicrobial infection in which one antimicrobial will not provide wide enough spectrum
3. unknown organism w/ life threatening infection
4. mixed infections with anaerobic bacteria

Question 18

synergistic response

Answer 18

ability to kill is enhanced over the additive effect of 2 drugs

Question 19

indifferent response

Answer 19

no enhanced ability to kill bacteria, additive only

Question 20

antagonistic response

Answer 20

the drug combination is less effective than the individual drug

avoid using the two drugs together when this is the result

Question 21

when is antimicrobial prophylaxis recommended

Answer 21

risk of infection outweighs the adverse effects of the drug

Question 22

what type of antimicrobial should be used for prophylaxis

Answer 22

different antimicrobial than one used to treat the infection that would occur at the site

Question 23

should prophylactic antimicrobials be used for IV or urinary catheters

Answer 23

no - will increase the risk of infection

Question 24

goal of surgical prophylaxis

Answer 24

prevent the development of a SSI and reduce the duration of hospitalization

Question 25

indications for surgical prophylaxis

Answer 25

1. procedure has a high rate of infection
   - contaminated and clean-contaminated
2. consequence of infection is high (even if chances of getting infection are slim)

Question 26

should prophylactic antimicrobials be used in clean orthopedic surgeries without an implant

Answer 26

no

Question 27

should prophylactic antimicrobials be used in clean orthopedic surgeries with an implant

Answer 27

yes - implant can cause biofilm formation

Question 28

should prophylactic antimicrobials be used in clean-contaminated surgeries

Answer 28

yes

Question 29

should prophylactic antimicrobials be used in contaminated surgeries (ex. into the GIT)

Answer 29

yes

Question 30

should prophylactic antimicrobials be used in spays/neuters

Answer 30

no

Question 31

what is the most common antimicrobial used for surgical prophylaxis in small animals

Answer 31

cefazolin

Question 32

when should prophylactic antimicrobials be administered

Answer 32

30-60 minutes before incision

short sx: single dose prior to surgery
long sx: use throughout surgery then stop immediately after