Pharmacology of antimicrobials

Question 1

Give a definition of pharmokinetics

Answer 1

The action of the animal on the drug

- the absorption, distribution, metabolism, excretion/elimination

Question 2

Give a definition of pharmodynamics

Answer 2

The action of the drug on the animal

- In the case of antibiotics, it is the effect of the drug on the bacteria

Question 3

More use of antibiotics leads to what effect?

Answer 3

More selection pressure

Question 4

What is the general mechanism of action of antibiotics?

Answer 4

Aim is to prevent the growth and/or survival of invading organisms while causing minimal damage to the host

Question 5

What are the 4 ways antibiotics can work?

Answer 5

• Disrupt cell wall production of function
• DNA function inhibitors
• Protein synthesis inhibitors
• Disrupt cell membrane function

Question 6

Which factors allow antibiotics to be classified?

Answer 6

• How they affect bacteria
• If they are conc or time dependent
• Range of bacteria they affect
• Post-antibiotic effect
• Chemical structure and properties

Question 7

Define the term bacteriostatic antibiotic

Answer 7

Antibiotics that prevent replication but do not kill susceptible bacteria

Question 8

Give 2 examples of bacteriostatic antibiotics

Answer 8

Tetracycline

Macrolides

Question 9

Define the term bacteriocidal antibiotics

Answer 9

Antibiotics that kill susceptible bacteria

Question 10

Give 2 examples of bacteriocidal antibiotics

Answer 10

Beta-lactams

Fluoroquinolones

Question 11

What is prophylactic treatment?

Answer 11

Preventative treatment

- Preventing an initial infection or its reoccurrence after infection

Question 12

What is curative treatment?

Answer 12

Treatment of a sick animal/s following the diagnosis of infection and/or clinical disease

Question 13

What is control treatment?

Answer 13

Treatment of a group of animals after the diagnosis of infection in part of the group, with the aim of preventing the spread of infectious disease to those at risk

Question 14

What is the post-antibiotic effect?

Answer 14

The ability of a drug to suppress or kill bacteria after the drug conc has dropped below the MIC

Question 15

What is the importance of the post-antibiotic effect?

Answer 15

An antibiotic with a good PAE should require less frequent administration

Question 16

Describe the features of conc dependent antibiotics

Answer 16

• Rate and extent of bacterial killing increases as the drug conc increases
• Exponential curve
• Longer post antibiotic effects
• Long dosing intervals

Question 17

Describe the features of time dependant antibiotics

Answer 17

• Overall effect is strongly correlated to time above the MIC
• Bacteriocidal activity does not increase with increasing conc once the MIC has been reached
• Sigmoid curve

Question 18

What is the main aim of administration?

Answer 18

Obtain effective concentrations at the site of infection for an adequate duration

Question 19

What are the advantages and disadvantages of injectable administration?

Answer 19

Adv:
- Can be used for poorly absorbed drugs or drugs that are ineffective if given orally
- Fast onset of action
Dis:
- Painful
- Expensive
- Aseptic technique required
- Must be a soluble preparation

Question 20

How must IV preparations be administered?

Answer 20

Slowly/infusion

Question 21

Subcutaneous injection is for what desired effect?

Answer 21

Slower, more prolonged

Question 22

Intramuscular injections are best for what effect?

Answer 22

Large volumes of medication that require a fast absorption

Question 23

What factors of a drug influence the dose of an oral drug that is bioavailable?

Answer 23

• Stability in gastric contents
• Susceptibility to inactivation
• Physiochemical properties (solubility)
• Presence of food/binding to food

Question 24

Where in the body is an oral drug metabolised before it reaches the liver?

Answer 24

Gut lumen
Mucosal epithelium
Liver

Question 25

Drug distribution systemically is determined by what factors?

Answer 25

Blood flow to tissues

Ability to penetrate cellular barriers

Question 26

List 4 factors that can be affected by plasma protein binding

Answer 26

Tissue penetration
Volume of distribution
Half-life
Elimination

Question 27

What is half life?

Answer 27

The time taken for the plasma conc to half after reaching pseudo-equilibrium distribution

Question 28

What is meant by the term clearance?

Answer 28

The ability to eliminate a drug

Question 29

Describe synergism

Answer 29

Potentiation of one drug action by another

Question 30

Where are the main sites of drug elimination?

Answer 30

Kidney (eliminated) and liver (metabolised)

Question 31

Which factors can reduce elimination of a drug via the liver?

Answer 31

• Elderly have poorer blood flow
• Neonates have low liver enzyme activity
• Some drugs have reduced liver enzyme activity
• Extensive liver damage

Question 32

Which drugs are classified as Beta-lactams?

Answer 32

Penicillin

Cephalosporins

Question 33

What is the MOA of Beta-lactams

Answer 33

Interfere with the cross-linking in the cell wall during growth, the lack of cross links weakens the cell wall and eventually the bacteria lyses

Question 34

Give some bacterial protein synthesis inhibitor drug examples

Answer 34

Aminoglycosides
Macrolides
Tetracyclines

Question 35

Give some drug examples that affect the bacterial DNA metabolism

Answer 35

Sulphonamides

Fluoroquinolones

Question 36

Penicillins should not be used orally in which species?

Answer 36

Guinea pigs, rabbits, hamsters, gerbils

Question 37

How does the activity of cephalosporins change against gram +ve and -ve bacteria from the 1st to 4th generations?

Answer 37

1st - best activity against gram +ve, little against gram -ve
2nd - slightly less activity against gram +ve, but more against gram -ve
3rd - Less against gram +ve, greater for gram -ve
4th - Mostly gram -ve