principles of antibiotics Flashcards

1
Q

what is an antibiotic

A

agents produced by micro organisms that kill or inhibit the growth of other micro organisms in high dilution

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2
Q

how do antibiotics re

A

by binding a target site on a bacteria

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3
Q

how to define the class of an antibiotic

A

the location where the antibiotic binds to the target site on the bacteria will tell you the class

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4
Q

what are antimicrobial

A

semi synthetic derivatives of antibiotics

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5
Q

examples of antimicrobial

A

anti fungal
anti bacterial
antihelminthic
antiprotozoal
antiviral agents

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6
Q

what do beta lactam antibiotics do

A

disrupt peptidoglycan production
by binding covalently and irreversibly to the penicillin binding proteins
cell wall is disrupted and lysis occurs
results in a hypo osmotic or iso osmotic environment

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7
Q

what are beta lactam antibiotics active against

A

active only against rapidly multiplying organisms

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8
Q

in order to bind to the penicillin binding proteins what must the beta lactam antibiotics do first

A

diffuse through the bacterial cell wall

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9
Q

what do gram negative organisms have that decreases antibiotic penetration

A

an additional lipopolysaccharide layer

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10
Q

which bacteria are more suspectible to B lactam

A

gram positive are more susceptible than gram negative

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11
Q

what causes differences in the spectrum and activity of b LACTAM antibiotic

A

due to their relative affinity for diff penicillin binding sites

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12
Q

why are beta lactams ineffective in the treatment of intracellular pathogens

A

because the penicillins poorly penetrate mammalian cells

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13
Q

what are we trying to achieve with antibiotics

A

they give time and support for the immune system to deal with an infection

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14
Q

describe the bacterial agenda

A
  1. attack and enter
  2. local spread
  3. multiply
  4. evade host defences
  5. shed from body
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15
Q

consequences of bacteria

A

direct - destroy phagocytes or cells in which bacteria replicate

toxins - exotoxin (protein production), endotoxin (gram negative)

indirect - inflammation, immune pathology

diarrhoea

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16
Q

describe bactericidial antibiotics

A

the agent kills the bacteria
they are antibiotics that inhibit cell wall synthesis

17
Q

when are bactericidal antibiotics useful

A
  • if poor penetration (endocarditis)
  • difficult to treat infections
  • need to eradicate infection quickly (meningitis)
18
Q

describe bacteriostatic antibiotics

A

prevent growth of bacteria - inhibitory to growth
antibiotics that inhibit protein synthesis, dna replication or metabolism
reduce toxin production and endotoxin surge less likely

19
Q

what is MBC/MIC

A

a ratio of minimum bactericidal concentration to minimum inhibitory concentration

20
Q

what must the antibiotic do to work effectively

A

it should remain at the binding site for a suffficient period of time in order for the metabolic processes of the bacteria to be sufficiently inhibited

21
Q

what is related to concentration within the microorganisms

A

the drug must not only attach to its binding target but also must occupy an adequate number of binding sites

22
Q

what are the 2 major determinants of anti bacterial effects

A

the concentration
and the time
that the antibiotic remains on these binding sites

23
Q

what is time dependent killing

A

key parameter isn’t he time that serum concentrations remain above the MIC during the dosing interval

24
Q

what is concentration dependent killing

A

key parameter is how high the concentration is above MIC

25
Q

what is the antibiotic dependent on

A

pharmacokinetics - the movement of a drug from its administration site to the place of its pharmacologic activity and then its elimination from the body

26
Q

process of pharmacokinetics

A
  1. its release from the dosage form
  2. its absorption from the site of administration into the bloodstream
  3. its distribution to various parts of the body, including the site of action
  4. its rate of elimination from the body via metabolism or excretion of unchanged drug
27
Q

how do bacteria resist antibiotics

A
  • change antibiotic target
  • destroy antibiotic
  • prevent antibiotic access
  • remove antibiotic from bacteria
28
Q

resist antibiotics - describe change antibiotic target

A

bacteria change the molecular configuration of antibiotic binding site or masks it

29
Q

resist antibiotics - describe destroy antibiotic

A

the antibiotic is destroyed or inactivated

30
Q

resist antibiotics - describe prevent antibiotic access

A

modify the bacterial membrane porin channel size, numbers and selectivity

31
Q

resist antibiotics - describe remove antibiotic from bacteria

A

proteins in bacterial membranes act as an export or efflux pumps - so level of antibiotic is reduced

32
Q

why do bacteria develop resistant?

A

intrinsic - naturally resistant
acquired - spontaneous gene mutation
- horizontal gene transfer - conjugation
- transduction
- transformation

33
Q

intrinsic resistance

A

all subpopulations of a species will be equally resistant

34
Q

acquired resistance

A

a bacterium which was previously susceptible obtains the ability to resist the activity of a particular antibiotic
only certain strains or subpopulatuons fi a species will be resistant

35
Q

2 important resistances in gram positive bacteria

A

MRSA
VR

36
Q

describe MRSA

A

methicillin resistant staphylococcus aureus bacteriophage mediated acquisition of staphylococcal cassette chromosome menc

contains resistance gene mecA encodes penicillin binding protein 2a confers resistance to all b lactam antibiotics in addition to methicillin

37
Q

describe VRE

A

vancomycin resistant enterococci
plasmid mediated acquisition of gene encoding altered amino acid on peptide chain preventing vancomycin binding

promoted by cephalosporin use

38
Q

name an important resistance in gram negative bacteria

A

ESBL

39
Q

describe ESBL

A

extended spectrum beta lactamase (ESBL) inhibition

these hydrolyse oxylimino side chains of cephalosporins: cefotaxime, ceftriaxone and ceftaidime and monobactams: aztreonam