Pharmacology - Antimicrobials

Question 1

List the five factors that determine the risk of emergence of resistant bacterial strains.

Answer 1

1. Size of the inoculum
2. Ability of the bacteria to acquire mutations
3. Ability of host defenses to eliminate resistant bacteria
4. Drug concentrations at the site of infection
5. Duration of exposure to AMDs

Question 2

Define “antibiotic”

Answer 2

A natural chemical, produced by other organisms, that is designed to suppress the growth of other organisms (including bacteria, fungi, or protozoa).

Question 3

Define “antimicrobial”

Answer 3

Any compound, natural or synthetic, that suppresses microbial growth.

Question 4

Define “antibacterial”

Answer 4

Any compound that suppresses bacterial growth.

Question 5

List major strategies that may reduce the selection for antimicrobial resistance.

Answer 5

1. Documentation of the presence of infection
2. Appropriate susceptibility testing
3. Proper identification of the infecting organism
4. The use of agents that are as specific for the pathogen as possible, at the proper dose and for the proper duration of time

Question 6

First-line antibacterial drugs are those that could be used for empirical selection in the absence of or pending the results of culture and susceptibility testing. These include:

Answer 6

1. Amoxicillin
2. Amoxicillin-clavulanate
3. Cephalexin
4. Doxycycline
5. Minocycline
6. Trimethoprim-sulfonamides (TMS)

Question 7

Second-line drugs are those to be used on the basis of culture and susceptibility testing and because of the lack of any appropriate first-line options. These include:

Answer 7

1. Piperacillin-tazobactam
2. Amikacin
3. Third-generation cephalosporins
4. Fluoroquinolones

Question 8

The use of third-line drugs, including vancomycin, linezolid, rifampin, human-labeled third-generation cephalosporins (e.g., ceftazidime), and carbapenems such as imipenem and meropenem, is usually reserved for situations when certain criteria are met. What are those criteria?

Answer 8

1. Infection must be documented based on clinical abnormalities and culture.
2. The infection is serious and has the potential to be life threatening if left untreated.
3. Resistance is documented to all other reasonable first- and second-line options.
4. The infection is potentially treatable.
5. The clinician may seek advice from an infectious disease clinician or a clinical microbiologist to discuss antimicrobial susceptibility test results, and to discuss the use of these agents if there is unfamiliarity with their use.
6. The clinician should attempt for a duration of treatment that is as short as possible.

Question 9

Answer 9

Question 10

Which two antimicrobials exhibit concentration-dependent killing?

Answer 10

Fluoroquinolones and aminoglycosides. These drugs work optimally when the peak concentration in the plasma (Cmax) or the area under the curve (AUC) exceeds the MIC by a defined index factor.

Question 11

Drugs that exhibit concentration-dependent killing also have postantibiotic effect (PAE). What is PAE?

Answer 11

A persistent antimicrobial effect after drug concentrations at the site of infection fall below the MIC.

Question 12

Which antimicrobials exhibit time-dependent killing?

Answer 12

β-lactams (penicillins and cephalosporins), macrolides, clindamycin, vancomycin, and tetracyclines. The activity of these drugs is maximized by the time above the MIC rather than the magnitude of the concentration.

Question 13

List three appropriate initial antimicrobial choices for bacterial skin infection

Answer 13

Cephalexin
Amoxicillin-clavulanate
Clindamycin

Question 14

List four appropriate initial antimicrobial choices for bacterial urinary tract infection

Answer 14

Amoxicillin
Amoxicillin-clavulanate
Cephalosporins
Trimethoprim-sulfamethoxazole

Question 15

List two appropriate initial antimicrobial choices for bacterial prostatic infection

Answer 15

Trimethoprim-sulfamethoxazole
Fluoroquinolones (enrofloxacin, marbofloxacin, orbifloxacin, levofloxacin)

Question 16

List two appropriate initial antimicrobial choices for bacterial respiratory tract infection

Answer 16

Tetracyclines (doxycycline, minocycline)
Fluoroquinolones

Question 17

List two appropriate initial antimicrobial choices for the intestinal tract for animals with hepatic encephalopathy

Answer 17

Ampicillin
Neomycin

Question 18

List three appropriate initial antimicrobial choices for bacterial biliary tract infection

Answer 18

Amoxicillin-clavulanate
Cephalosporins
Fluoroquinolones

Question 19

List three appropriate initial antimicrobial choices for bacterial infection in the brain

Answer 19

Metronidazole (anaerobes only)
Fluoroquinolones
Trimethoprim-sulfonamides

Question 20

List three appropriate initial antimicrobial choices for bacterial osteomyelitis

Answer 20

Clindamycin
Cephalosporins
Amoxicillin-clavulanate

Question 21

List two age-related factors when considering antimicrobial selection

Answer 21

1. The administration of systemic tetracyclines is contraindicated in young animals because of the potential for teeth discoloration (Doxycycline is less likely to produce this reaction if administered for a short course)
2. Fluoroquinolones have the potential to cause cartilage and joint toxicity in dogs aged between 7 and 28 weeks.

Question 22

True or False: Dogs are the species most susceptible to reactions from sulfonamides (including trimethoprim-sulfonamides) because of an inability to acetylate the parent drug for elimination.

Answer 22

True. Subsequently, some breeds of dog convert the drug to a cytotoxic metabolite that produces hypersensitivity-like reactions following trimethoprim-sulfonamide administration. Doberman pinschers may be at higher risk for this problem. Keratoconjunctivitis sicca (dry eye) is also a risk when administering sulfonamides to dogs.

Question 23

True or False: The absorption of some AMDs, such as ketoconazole and itraconazole, is impaired by medications that suppress gastric acid production.

Answer 23

True

Question 24

True or False: The single most important mechanism of antibacterial resistance is acquisition of foreign DNA by horizontal transfer, especially that carried by plasmids and transposons.

Answer 24

True

Question 25

Name three specific situations in which prophylactic antibiotic therapy is indicated

Answer 25

1. To prevent surgical infections when contamination is expected 2. Treatment of deep bite wounds 3. Following chemotherapy when moderate to severe neutropenia develops (<1000 neutrophils/μL).