antibiotics Flashcards
(48 cards)
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
2
Q
define an antimicrobial agent
A
a chemical (microorganism or synthetic) that kills or inhibits the growth or microorganism
3
Q
what is chemotherapy?
A
- involves the use of chemical agents to treat or control disease
- both antibacterial agents & anti fungal agents
4
Q
define bacteriostatic agents
A
- chemical agents that prevent bacterial growth by stopping cells from dividing
5
Q
define bacteriocidal agents
A
- chemical agents that prevent bacterial growth by killing them
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
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
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
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
10
Q
what are the 6 problems with antimicrobials?
A
- not selective in their elimination of microbiota, leading to disruption of normal microflora
- toxicity
- resistance
- drug hypersensitivity/allergy reactions
- other adverse reactions
- residues of antimicrobials in animal products for human consumption
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
12
Q
which drugs are considered risky for horses but can be usefully employed in certain conditions?
A
- oxytetracycline
- erythromycin
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
14
Q
which drugs cannot be used orally on guinea pigs but can be used parentally?
A
- enrofloxacin
- chloramphenicol
15
Q
what toxicity problems can aminoglycosides cause?
A
- nephrotoxic
- ototoxic
16
Q
what toxicity problem can chloramphenicol cause?
A
aplastic anaemia
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
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
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)
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
what is the mechanism of action of polymixins (polypeptides)?
- inhibition of cell membrane function
26
what is the mechanism of action of chloramphenicol, macrolids, tetracyclines, amionglycosides & rifamycins?
- 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
what is the mechanism of action of quinolones & imidazoles?
- inhibition of nuclei acid synthesis
| - quinolones inhibit DNA supercoiling
28
what is the method of action of sulphonamides & trimethoprim
- inhibition of synthesis of essential metabolites
29
how do B-lactam drugs work?
- 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
name the broad spectrum B-lactams in common use
- ampicillin/amoxycilin
| - 1st generation cephalosporins
31
name 3 narrow spectrum B-lactams that target gram positive bacteria (Staphs & Streps)
- methicillin
- cloxacilin
- penicillin
32
name 3 narrow spectrum B-lactams that target gram negative bacteria (& some gram positives)
- ticarcilin (targets pseudomonas)
- 2nd, 3rd & 4th generation cephalosporins
- carbapenems/monobactam
33
which B-lactam inhibitor combination can be used against bacteria that produce B-lactamase enzyme?
- clavulanic acid added to amoxillin & ticarcillin
34
How do glycopeptides (vancomycin) inhibit cell wall synthesis? and what is there importance against S. aureus?
- 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
how does bacitracin work? what type of applications does it have
- 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
how does polymyxins inhibit cell membrane function?
- 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
how does chloramphenicol work? When is it used?
- 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
how does macrolides & lincomycins work?
- reversibly bind to 50S ribosome to prevent continuation of protein synthesis
- effective against gram positives & mycoplasma
- drug of choice for penicillin allergies
39
how do aminoglycosides work?
- irreversibly bind to 30S ribosomal subunit causing distortion & malfunction of ribosome, blocking initiation of translation
- bactericidal
40
how do tetracyclines work?
- 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
how does Quinolones (Fluoroquniolones) work?
- 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
how does Nitromidazoles work?
- binds to DNA & fragments of DNA to inhibit nucleic acid synthesis
- particularly effective in anaerobes
43
how do sulphonamides & trimethoprim inhibit the synthesis of essential metabolites?
- sulphonamides competitively inhibit the synthesis of folate
- trimethoprim blocks enzyme in folate synthesis
(folate is required for purine synthesis in bacteria)
44
how do we know whether an antimicrobial agent will work?
- 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
define the minimum inhibitory concentration (MIC) used for measuring antimicrobial sensitivity
- the MIC is the lowest concentration if a drug which inhibits bacterial growth
46
what are the 3 methods for determining MIC of an antimicrobial?
- concentration gradient on a strip
- agar dilution
- broth dilution
47
what are antimicrobials used for clinically?
- 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
what is important to remember for antimicrobial use?
- use the most appropriate antimicrobial for the case, at the right dose & only for as long as necessary
