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EOS Principles of diseases > antibiotics > Flashcards

antibiotics Flashcards

1
Q

define antibiotic and what they are broadly used for?

A
  • a chemical produced by a microorganism that kills or inhibits the growth of another microorganism
  • antibiotics are used to prevent & treat infectious diseases
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2
Q

define an antimicrobial agent

A

a chemical (microorganism or synthetic) that kills or inhibits the growth or microorganism

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3
Q

what is chemotherapy?

A
  • involves the use of chemical agents to treat or control disease
  • both antibacterial agents & anti fungal agents
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4
Q

define bacteriostatic agents

A
  • chemical agents that prevent bacterial growth by stopping cells from dividing
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5
Q

define bacteriocidal agents

A
  • chemical agents that prevent bacterial growth by killing them
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6
Q

describe the purpose of selective toxicity in antimicrobials

A
  • antimicrobials are selectively toxic for bacteria with minimal harm or side-effects for the patient
  • antimicrobials act on structures found in bacteria but not the host
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7
Q

describe the 2 categories of antimicrobials

A

bacteriostatic agents

  • reversibly inhibit growth of bacteria, allowing host immune defences to eliminate infection
  • duration of treatment must be sufficient for host defences to eradicate infection

bacteriocidal agents

  • cause irreparable damage & bacterial cell death by binding irreversibly to target structures
  • used for infections that cannot be controlled or eradicated by host (critical site of infection or immunocompetence)
  • most drugs are both bacteriostatic & bacteriocidal depending on the clinical situation
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8
Q

what are broad spectrum antimicrobials and when are they used?

A
  • are effective against a wide range or microorganisms

- used with seriously ill patients or if organism is unidentified

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9
Q

what are narrow spectrum antimicrobials and when are they used?

A
  • are effective against only a small number of microorganisms of a single taxonomic group
  • used if organism is identified as it minimises disruption to host microflora
  • decreases likelihood of resistance
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10
Q

what are the 6 problems with antimicrobials?

A
  1. not selective in their elimination of microbiota, leading to disruption of normal microflora
  2. toxicity
  3. resistance
  4. drug hypersensitivity/allergy reactions
  5. other adverse reactions
  6. residues of antimicrobials in animal products for human consumption
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11
Q

which high risk drugs should never be used on horses? what could using these cause?

A
  • lincomycin
  • clindamycin
  • oral penecillins

-> lead to pseudomembranous colitis due to overgrowth of Clostridium difficile bacteria in hindgut

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12
Q

which drugs are considered risky for horses but can be usefully employed in certain conditions?

A
  • oxytetracycline

- erythromycin

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13
Q

which drugs are fatal in guinea pigs? what could using these drugs cause?

A
  • broad spectrum antimicrobials (gram positive spectrum) -> ampicillin, penicillin, bacitracin, erythromycin, linocmycin, gentamicin, clindamycin, streptomycin, vancomycin & tetracycline are fatal
  • reduce normal GI anaerobes & gram positive bacteria -> leading to overgrowth or coliforms & clostridial bacteria
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14
Q

which drugs cannot be used orally on guinea pigs but can be used parentally?

A
  • enrofloxacin

- chloramphenicol

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15
Q

what toxicity problems can aminoglycosides cause?

A
  • nephrotoxic

- ototoxic

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16
Q

what toxicity problem can chloramphenicol cause?

A

aplastic anaemia

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17
Q

what toxicity problems does fluoroquinolones cause? Which animals should it not be used in?

A
  • inhibits cartilage growth, so it is not to be used in young animals
  • causes retinopathy in cats
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18
Q

what toxicity problems do trimethoprim / sulphonamides have?

A
  • keratoconjunctivitis sica (KCS) (dry eye) with prolonged use
  • idiosyncratic hepatotoxicity in DOGS
  • athropathies, cutaneous reactions & haemolytic anaemia
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19
Q

what toxicity problems does tetracycline have?

A
  • have effect bone growth & stain teeth in young animals

- doxycycline can cause oesophageal strictures (should follow drug with food)

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20
Q

what is antimicrobial resistance?

A
  • occurs when a micro-organism previously susceptible to the action of the antimicrobial is no longer affected by it
  • antimicrobial resistance is a serious threat
21
Q

which drugs are hypersensitivity reactions most common with?

A
  • penicillins
  • cephalosporins
  • sulphonamides
22
Q

what can drug hypersensitivity manifest as? (3)

A
  • acute anaphylaxis
  • cutaneous reaction
  • haematological disturbances
23
Q

what other adverse reactions can be induced by antimicrobials?

A
  • tissue necrosis at injection site
  • impaired host immunity
  • hepatic microsome enzyme induction or inhibition
  • adverse interactions with other drugs
24
Q

what is the mechanism of action of B-lactams, glycopeptides, bacitracin drugs?

A
  • inhibit cell wall synthesis
25
Q

what is the mechanism of action of polymixins (polypeptides)?

A
  • inhibition of cell membrane function
26
Q

what is the mechanism of action of chloramphenicol, macrolids, tetracyclines, amionglycosides & rifamycins?

A
  • inhibition of protein synthesis
  • antimicrobials of this class target the structure of prokaryotic ribosomes which is different to eukaryotic ribosomes
  • chloramphenicol & macrolides - inhibit 50S ribosome
  • tetracycline & aminoglycosides - inhibit 30S ribosome
  • rifamycins - inhibits RNA polymerase
27
Q

what is the mechanism of action of quinolones & imidazoles?

A
  • inhibition of nuclei acid synthesis

- quinolones inhibit DNA supercoiling

28
Q

what is the method of action of sulphonamides & trimethoprim

A
  • inhibition of synthesis of essential metabolites
29
Q

how do B-lactam drugs work?

A
  • B-lactams all have a 4-sided B-lactam ring which bind to penicillin binding proteins
  • stops cross-linking of bacteria cell wall
  • triggers peptidoglycan breakdown
30
Q

name the broad spectrum B-lactams in common use

A
  • ampicillin/amoxycilin

- 1st generation cephalosporins

31
Q

name 3 narrow spectrum B-lactams that target gram positive bacteria (Staphs & Streps)

A
  • methicillin
  • cloxacilin
  • penicillin
32
Q

name 3 narrow spectrum B-lactams that target gram negative bacteria (& some gram positives)

A
  • ticarcilin (targets pseudomonas)
  • 2nd, 3rd & 4th generation cephalosporins
  • carbapenems/monobactam
33
Q

which B-lactam inhibitor combination can be used against bacteria that produce B-lactamase enzyme?

A
  • clavulanic acid added to amoxillin & ticarcillin
34
Q

How do glycopeptides (vancomycin) inhibit cell wall synthesis? and what is there importance against S. aureus?

A
  • glycopeptides bind to the end to the peptidoglycan pentapeptide chain to prevent access of the end of the penta-peptide chain to the active site of enzyme that synthesises call wall
  • only effective against gram positives
  • important last line against antimicrobial resistant S.aureus
35
Q

how does bacitracin work? what type of applications does it have

A
  • bacitracin interferes with transport of peptidoglycan precursors across the cytoplasmic membrane
  • its toxicity limits its use to topical applications
  • common in non-prescription first-ad ointments
36
Q

how does polymyxins inhibit cell membrane function?

A
  • polymyxins contain cationic detergents which bind to phospholipids in the outer membrane of gram NEGATIVES
  • cationic detergents increase permeability & disrupt cell
  • only used as topical preparations
37
Q

how does chloramphenicol work? When is it used?

A
  • inhibits protein synthesis by binding to 50S ribosomal subunit & inhibiting peptidyl transferase activity
  • prevents peptide bonds from forming, blocking protein synthesis
  • good penetration through blood-brain barrier & eyes, so it is effective against a wide range of microorganisms
  • drug of last restore for life-threatening infections
  • aplastic anaemia is a rare side effect
38
Q

how does macrolides & lincomycins work?

A
  • reversibly bind to 50S ribosome to prevent continuation of protein synthesis
  • effective against gram positives & mycoplasma
  • drug of choice for penicillin allergies
39
Q

how do aminoglycosides work?

A
  • irreversibly bind to 30S ribosomal subunit causing distortion & malfunction of ribosome, blocking initiation of translation
  • bactericidal
40
Q

how do tetracyclines work?

A
  • reversibly bind to 30S ribosomal subunit
  • blocks tRNA from attaching to ribosome to prevent continuation of protein synthesis
  • effective against certain gram +ves & -ves
  • useful against intracellular bacteria
41
Q

how does Quinolones (Fluoroquniolones) work?

A
  • inhibits the action of topoisomerase DNA gyrase which normally maintains supercoiling of DNA
  • prevents supercoiling of DNA
  • well tolerated in birds, reptiles & pocket pets
  • use for gram +ve & -ve (not anaerobes except new pradofloxacin)
42
Q

how does Nitromidazoles work?

A
  • binds to DNA & fragments of DNA to inhibit nucleic acid synthesis
  • particularly effective in anaerobes
43
Q

how do sulphonamides & trimethoprim inhibit the synthesis of essential metabolites?

A
  • sulphonamides competitively inhibit the synthesis of folate
  • trimethoprim blocks enzyme in folate synthesis

(folate is required for purine synthesis in bacteria)

44
Q

how do we know whether an antimicrobial agent will work?

A
  • by using disc diffusion susceptibility testing (Kirby-Bauer procedure)
  • bacteria isolate is then classified as sensitive, intermediate or resistance
  • it is then approximated whether the plasma concentration attained by the antimicrobial is high enough to inhibit the growth of bacteria
45
Q

define the minimum inhibitory concentration (MIC) used for measuring antimicrobial sensitivity

A
  • the MIC is the lowest concentration if a drug which inhibits bacterial growth
46
Q

what are the 3 methods for determining MIC of an antimicrobial?

A
  • concentration gradient on a strip
  • agar dilution
  • broth dilution
47
Q

what are antimicrobials used for clinically?

A
  • antimicrobial drugs are used to treat or prevent disease produced by infectious bacterial agents
  • treatment should be based on clinical diagnosis
  • only use prophylactically is risk is real
48
Q

what is important to remember for antimicrobial use?

A
  • use the most appropriate antimicrobial for the case, at the right dose & only for as long as necessary

EOS Principles of diseases (12 decks)

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