Pharm LO: Lecture 2

Question 1

What is the first question you should ask yourself when selecting an antibiotic?

Answer 1

Is this a bacterial infection that needs antibiotics or is this a viral infection that will not respond to antibiotics

Question 2

If there is a bacterial infection, what do we use?

Answer 2

SPACED

Question 3

What does S stand for in SPACED

Answer 3

S: Spectrum:

• Will the infectious agent be harmed by the antibiotic I have chosen
• Related to Gram status (+/-) and oxygen tolerance
• The overuse of broad spectrum antibiotics can harm the gut

Question 4

What does P stand for in SPACED

Answer 4

P: Pharmacokinetics / Pharmakodynamic

• Will the antibiotic reach the site of infection
• If it does reach site, will the drug concentration at the site be greater than the minimum inhibitory conc. Of the bacteria
• Antibiotic with low Vd will NOT reach privileged sites

Question 5

What does A stand for in SPACED

Answer 5

adverse

• adverse effects

Question 6

What does C stand for in SPACED

Answer 6

C: Compliance

• Will the owner be able to give the drug at home or farm
• Am I complying with regulatory rules for antibiotics

Question 7

What does E stand for in SPACED

Answer 7

E: Environment

• Where is the infection?
  Bone, lung, acidic (GI), Abscess

Question 8

What does D stand for in SPACED

Answer 8

D: Diagnostics

• What does lab data show

Question 9

What are the two main parameters that dictate the spectrum (i.e., the range of bacteria harmed by a given antibiotic) of an antibiotic?

Answer 9

1. gram status of bacteria
   - positive or negative
2. Oxygen tolerance
   - aerobic or anaerobic

These influences which antibiotic is used due to cell wall structure and metabolic environment

Question 10

T/F: Spectrum and Pharmacodynamics have some overlap

Answer 10

true

Question 11

_________ antibiotics (which kill bacteria) are often preferred—especially in immunocompromised patients

Answer 11

bactericidal

Question 12

________ antibiotics (which inhibit bacterial growth)

Answer 12

bacteriostatic

Question 13

Define Bactericidal drugs

Answer 13

directly kill bacteria (e.g., aminoglycosides, penicillins).

Question 14

Define Bacteriostatic drugs

Answer 14

stop bacterial replication, allowing the immune system to clear the infection

Question 15

What can we use to remember the Bacteriostatic drugs (stop replication, allowing the immune system to clear the infection)

Answer 15

SulfTet MacChlor

• (Sulfonamides, Tetracyclines, Macrolides, Chloramphenicol) → all bacteriostatic

Question 16

T/F: fluoroquinolones are implicated in serious adverse events in two separate physiologic systems, they are one of the most important classes of antibiotics

Answer 16

TRUE

• Two
  = Skeletal system (Chondrotoxic (can damage cartilage in young animals))

= Ocular system (Retinopathies in cats)

• Clinically vital
  = Excellent tissue penetration
  = Strong against gram negative pathogens
  = Usefulness in serious or resistance infections

Question 17

What are the two facets of Compliance

Answer 17

1. owner compliance
2. regulatory compliance

Question 18

What is owner compliance

Answer 18

Will the client or caretaker be able to properly administer the antibiotic (correct dose, route, frequency, and duration)?

• Important for both small animal and large animal/farm settings.

Question 19

What is regulatory compliance

Answer 19

Are you, as the veterinarian, following all legal and regulatory rules for that antibiotic’s use (e.g., extra-label drug use, food animal restrictions)?

• Some drugs are illegal in food animals

Question 20

What are the privileged sites that are important for Environment?

Answer 20

Privileged sites are areas of the body that are difficult for many antibiotics to penetrate due to physical or physiological barrier

Question 21

Give examples of privilaged sites

Answer 21

• Central nervous system / brain
• Prostate
• Eye
• Testes and ovaries
• Joints and bones
• Abscesses

Question 22

Antibiotics with low volume of distribution (Vd) — typically water-soluble drugs — have limited access to ?

Answer 22

Privilaged sites

• Low Vd tends to stay in the plasma

Question 23

Define MIC

Answer 23

MIC (Minimum Inhibitory Concentration

• The lowest concentration of an antibiotic that inhibits visible bacterial growth in the lab

Question 24

Define Breakpoint

Answer 24

A reference value established by the CLSI (Clinical and Laboratory Standards Institute) that determines whether a bacterial isolate is classified as Sensitive (S) or Resistant (R) to an antibiotic

Question 25

If MIC < breakpoint =

Answer 25

sensitive

Question 26

If MIC > breakpoint =

Answer 26

resistant

Question 27

What is laboratory determined resistance and be prepared to identify it if given an example?

Answer 27

Laboratory-determined antibiotic resistance occurs when - The Minimum Inhibitory Concentration (MIC) of a bacterial isolate is greater than the established breakpointfor that antibiotic. MIC>BreakpointMIC>Breakpoint - This means that the maximal plasma concentration achievable in the patient is lower than the MIC, so the antibiotic will not effectively inhibit or kill the bacteria

Question 28

Example: If a bacterium’s MIC for enrofloxacin is >2 µg/mL, but the drug’s breakpoint is 1 µg/mL, the isolate is classified as =

Answer 28

resistant

Question 29

What are the active mechanisms of resistance?

Answer 29

Bacteria actively alter or remove the antibiotic through - Efflux pumps – pump the antibiotic out of the bacterial cell. - Alteration of the drug’s target – mutation or modification of the site the antibiotic binds to. - Enzymatic alteration of the antibiotic – bacterial enzymes chemically inactivate the drug. - Development of a new metabolic pathway – bypasses the pathway targeted by the antibiotic. - Altered membrane permeability – reduces antibiotic entry into the cell.

Question 30

What are the passive mechanisms of resistance?

Answer 30

These occur naturally without active bacterial changes - Lack of target – the bacterium inherently lacks the antibiotic’s target. - L-form bacteria – Gram(+) bacteria that lose their cell wall become resistant to cell wall–targeting antibiotics. - Slow-growing bacteria – less susceptible because many antibiotics act during active growth.Anaerobic bacteria – resistant to drugs that require oxygen for uptake.

Question 31

Provide three guidelines for the prevention of antibiotic resistance.

Answer 31

1. Use critically important antibiotics only when absolutely necessary. - Avoid using powerful drugs like fluoroquinolones, macrolides, or 3rd-generation cephalosporins unless no safer alternatives exist. - “You don’t need a cannon to kill a fly.” 2. Avoid metaphylaxis (mass or prophylactic treatment) except in special, justified cases (e.g., bovine respiratory disease (BRD)). 3. Avoid unnecessary combination therapy. - Use a single, targeted antibiotic when possible to limit resistance selection pressure.

Question 32

What is persistence?

Answer 32

Persistence refers to a phenomenon where a subset of bacteria temporarily go dormant during antibiotic treatment, allowing them to “hide” from the antibiotic’s effects. - These persister cells are not genetically resistant; they simply pause their metabolism so the antibiotic cannot act on them. - Once the antibiotic is removed, they reactivate and begin growing again, leading to chronic or recurring infections. - Re-administration of the antibiotic will still kill them, unlike true resistant bacteria.