Pharmacology of antimicrobials Flashcards
Give a definition of pharmokinetics
The action of the animal on the drug
- the absorption, distribution, metabolism, excretion/elimination
Give a definition of pharmodynamics
The action of the drug on the animal
- In the case of antibiotics, it is the effect of the drug on the bacteria
More use of antibiotics leads to what effect?
More selection pressure
What is the general mechanism of action of antibiotics?
Aim is to prevent the growth and/or survival of invading organisms while causing minimal damage to the host
What are the 4 ways antibiotics can work?
- Disrupt cell wall production of function
- DNA function inhibitors
- Protein synthesis inhibitors
- Disrupt cell membrane function
Which factors allow antibiotics to be classified?
- How they affect bacteria
- If they are conc or time dependent
- Range of bacteria they affect
- Post-antibiotic effect
- Chemical structure and properties
Define the term bacteriostatic antibiotic
Antibiotics that prevent replication but do not kill susceptible bacteria
Give 2 examples of bacteriostatic antibiotics
Tetracycline
Macrolides
Define the term bacteriocidal antibiotics
Antibiotics that kill susceptible bacteria
Give 2 examples of bacteriocidal antibiotics
Beta-lactams
Fluoroquinolones
What is prophylactic treatment?
Preventative treatment
- Preventing an initial infection or its reoccurrence after infection
What is curative treatment?
Treatment of a sick animal/s following the diagnosis of infection and/or clinical disease
What is control treatment?
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
What is the post-antibiotic effect?
The ability of a drug to suppress or kill bacteria after the drug conc has dropped below the MIC
What is the importance of the post-antibiotic effect?
An antibiotic with a good PAE should require less frequent administration
Describe the features of conc dependent antibiotics
- Rate and extent of bacterial killing increases as the drug conc increases
- Exponential curve
- Longer post antibiotic effects
- Long dosing intervals
Describe the features of time dependant antibiotics
- 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
What is the main aim of administration?
Obtain effective concentrations at the site of infection for an adequate duration
What are the advantages and disadvantages of injectable administration?
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
How must IV preparations be administered?
Slowly/infusion
Subcutaneous injection is for what desired effect?
Slower, more prolonged
Intramuscular injections are best for what effect?
Large volumes of medication that require a fast absorption
What factors of a drug influence the dose of an oral drug that is bioavailable?
- Stability in gastric contents
- Susceptibility to inactivation
- Physiochemical properties (solubility)
- Presence of food/binding to food
Where in the body is an oral drug metabolised before it reaches the liver?
Gut lumen
Mucosal epithelium
Liver
Drug distribution systemically is determined by what factors?
Blood flow to tissues
Ability to penetrate cellular barriers
List 4 factors that can be affected by plasma protein binding
Tissue penetration
Volume of distribution
Half-life
Elimination
What is half life?
The time taken for the plasma conc to half after reaching pseudo-equilibrium distribution
What is meant by the term clearance?
The ability to eliminate a drug
Describe synergism
Potentiation of one drug action by another
Where are the main sites of drug elimination?
Kidney (eliminated) and liver (metabolised)
Which factors can reduce elimination of a drug via the liver?
- Elderly have poorer blood flow
- Neonates have low liver enzyme activity
- Some drugs have reduced liver enzyme activity
- Extensive liver damage
Which drugs are classified as Beta-lactams?
Penicillin
Cephalosporins
What is the MOA of Beta-lactams
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
Give some bacterial protein synthesis inhibitor drug examples
Aminoglycosides
Macrolides
Tetracyclines
Give some drug examples that affect the bacterial DNA metabolism
Sulphonamides
Fluoroquinolones
Penicillins should not be used orally in which species?
Guinea pigs, rabbits, hamsters, gerbils
How does the activity of cephalosporins change against gram +ve and -ve bacteria from the 1st to 4th generations?
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
