Antimicrobials Flashcards
What is the goal of antibacterial therapy?
Help the body eliminate infectious organisms without toxicity to the host
What are three examples of natural defense mechanisms in animals?
Mucociliary escalator in the respiratory tractFlushing effect of urinationGut normal flora
What are of primary importance in preventing and/or controlling infection in patients?
Natural defence mechanisms
What are the four quadrants of the antimicrobial spectrum?
Gram positive aerobesGram negative aerobesObligate anaerobesPenicillinase producing Staph
What are the six atypical bacterial species that don’t fit into the antimicrobial spectrum quadrants?
RickettsiaMycoplasmaChlamydiaBorreliaBartonellaMycobacterium
How does bacterial resistance occur?
Antibacterial agents preferentially select for resistant populations of bacteria
When should antibacterial agents be used?
Definitively diagnosed bacterial infectionLikely diagnosis when all signs and data are consideredBelieved likely to progress without therapyWould cause critical illness if it occurred and was not treated
What is the main type of antibacterial therapy used?
Empirical therapy - don’t know for sure what bacteria is but use the best possible drug with the signs shown
What should you base your prescription of antibacterial drugs on?
Clinical problem and the most likely organisms to be pathogens in that site
What is strongly recommended if therapy fails or infection immediately recurs after therapy?
Culture and sensitivity
What could be given if you do not want to give antibacterials but owner feels something should be done?
Vitamin therapy - no resistance and little to no side effects
What are the clues that a bacterial infection is present?
Heat, redness and swellingPyrexiaNeutrophiliaBacterial cause common for signs
Is vomiting without diarrhoea indicative of antibacterial therapy?
No - no bacteria that cause this
Should antibacterial therapy be considered for a cat less than 10 with haematuria?
No - feline idiopathic cystitis - resolves in 5-7 days with no real treatment
Why is it rare for cats presenting with urine problems for the cause to be bacterial?
Have a very concentrated urine that bacteria are unable to survive well in
What seven things should be considered before providing antibacterial therapy?
Predict likely bacteria?Predict susceptibility?Is culture needed/feasible?Pharmacokinetic factors?Side effects or increased patient risk?Client compliance issues?Cost considerations?
What are the five factors that affect the success of antibacterial therapy?
What bugs live where?Bacterial susceptibilityDistribution to site of infectionLocal conditionsClient compliance
What three main places do infections come from?
EnvironmentOther animalsWithin
If a drug is not susceptible in vitrohow will it work in vivo?
Generally resistant in vivo
Why might a drug only be possibly effective in vivoif pathogen is sensitive in vitro?
Variety of pharmalogical, host and bacterial factors affect effectiveness in vivo
What is MIC?
Minimum inhibitory concentratin
Define MIC
Lowest concentration of drug that will inhibit bacterial growth
What level of MIC is used to determine therapeutic dose?
MIC90 - concentration that will inhibit 90% of isolates of a bacterial species
Which antimicrobials cause inhibition of cell wall synthesis?
PenicillinsCephalosporinsBacitracin
Which antimicrobials cause inhibition of cell membrane function?
PolymyxinsAmphotericin BImidazolesNystatin
Which antimicrobials cause inhibition of protein synthesis?
ChloramphenicolMacrolidesLincosamidesTetracyclinesAminoglycosides
Which antimicrobials cause inhibition of nucleic acid synthesis?
SulphonamidesTrimethoprimQuinolonesMetronidazoleRifampin
What do bacteriostatic antimicrobials do?
Temporarily inhibit growth of organisms though effect is reversible once drug removedDrug concentration should be maintained above the MIC throughout dosing interval
What are the five bacteriostatic antimicrobials?
ChloramphenicolLincosamidesMacrolidesTetracyclinesNon-potentiated sulphonamides
What do bactericidal antimicrobials do?
Under ideal conditions kill bacteria and are preferred when concerned about site of infection or host defences
What are the six examples of bactericidal antimicrobials?
PenicillinsCephalosporinsAminoglycosidesFluoroquinolonesPotentiated sulphonamides (TMPS)Metonidazole
What two things can bactericidal antimicrobials dependent on?
Time and concentration
What determines the therapeutic success of time dependent antimicrobials?
Time above MIC over 24hr period
What are three examples of time dependent antimicrobials?
PenicillinsCephalosporinsTMPS
What do bacteria need to be doing for time dependent antimicrobials to be effective?
Multiplying
What determines the therapeutic success of concentration dependent antimicrobials?
Peak concentration achieved or area under the concentration curve
What are three examples of concentration dependent antimicrobials?
AminoglycosidesFluoroquinolonesMetronidazole
Do bacteria need to be multiplying with concentration dependent antimicrobials?
No - can combine with bacteriostatic drugs
What is the optimal ratio for concentration dependent antimicrobials?
Maximum concentration divided by MIC is greater than 8
Which antimicrobials are not effective against gram positive aerobes?
AminoglycosidesMetronidazole
Which antimicrobials are not effective against gram negative aerobes?
MetronidazolePenicillin GLincosamidesMacrolides
Which antimicrobials are not effective against obligate anaerobes?
FluoroquinolonesAminoglycosides
Which antimicrobials are not effective agains penicillinase producing staph?
Penicillin GAminopenicillinsMetronidazole
What do aminoglycosides need to work?
Oxygen
What type of bacteria does Metronidazole not work against?
Aerobes
What are some examples of antimicrobials that are effective for treating gram positive aerobes?
Penicillin GAnimopenicillinsCephalosporinsLincosamidesMacrolidesTetracyclinesRifampin
What are some examples of antimicrobials that are effective at treating gram negative aerobes?
FluoroquinolonesAminoglycosides2nd and 3rd gen. CephalosporinsTicarcillin-clavulanate
What are some antimicrobials that are effective at treating obligate anaerobes?
Penicillin GAmoxy-clavClindamycinMetronidazoleChloramphenicolRifampin
What are some antimicrobials that are effective at treating penicillinase producing staph?
Amoxy-clav1st and 2nd gen. CephalosporinsCloxacillinFluoroquinolonesRifampin
What are the three antimicrobials that are effective treatments but some important species are resitant? Which quadrant do they work in?
Fluoroquinolones - gram positive aerobesAmoxy-clav - gram negative aerobesClindamycin - penicillinase producing staph
What are the four ‘brown’ drugs and which quadrants are they not that effective against?
1stgeneration cephalosporins, cefovicin and amoxycillin- against gram negative aerobes and obligate anaerobesLincosamides (not clindamycin)- against anaerobesTMPS- all quadrantsTetracyclines- all quadrants except gram positive aerobes
Which antimicrobial drug has excellent activity against atypical bacteria?
Tetracyclines
What limits distribution of antimicrobials in tissues with adequate blood supply?
Perfusion - free drug concentrations in plasma are directly related to or equal to concentration in interstitial space
What limits distribution of antimicrobials to tissues without adequate blood supply?
Permeability - lipid membrane forms a barrier to drug diffusion
Where do most antibacterial drugs reach therapeutically adequate concentrations?
In bone and synovial fluid
Which areas of the body is it difficult for antimicrobials to access?
BrainEyeProstateBronchusMammary glandIntracellularPoorly vascularised tissues
What are the six bacteria that are intracellular?
BartonellaBrucellaChlamydophilaMycobacteriumRickettsiaStaphylococcus
Which antimicrobials poorly penetrate barriers?
PenicillinsCephalosporinsBeta-lactamase inhibitorsPolymixinsAminoglycosides
Which antimicrobials have good penetration?
SulphonamidesTrimethoprimLincosamidesMacrolidesTetracycline
What are the antimicrobials with great penetration across barrier?
ChloramphenicolFluroquinolonesLipophilic tetracyclinesMetronidazoleRifampin
What five environmental conditions affect the success of antimicrobial therapy?
Abcess formationPusNecrotic debrisOedema fluidForeign material
How can foreign material affect effectiveness of antimicrobial therapies?
Phagocytes degranulate to destroy material depleting intracellular bactericidal substancesCan protect bacteria from antibacterial drugs and phagocytosis
How does haemoglobin affect penicillin activity?
Reduces activity
What is TMPS inactivated by?
Pus
Which drugs does a low pH cause a marked loss of activity in?
ErythromycinClindamycinFluoroquinolones
What is surgical prophylaxis?
Use of antimicrobials pre and post surgery to prevent infection occuring
What four things need to be considered when assessing post operative risk of infection?
Degree of contaminationVirulence of organismHealth of patientLocal tissue health
What seven things should be used to justify surgical prophylaxis?
Timing of surgeryHealth of patientLevel asepsisPresence of implantsSurgical timeSurgical techniqueOrgans involved
Which patients have an increased risk of post operative infection with their clinical status?
Those who are shocked or emaciated
Which procedures have a greater post operative infection risk?
Emergency procedures
How does the duration of the surgery affect the post operative risk of infection?
1.5 hours infection rate of 1.6%>1.5 hours infection rate 8%RIsk double for every 30 minutes over 1 hour procedure
What is the increase in post operative infection risk with anaesthesia?
0.5% increase in risk for every minute beyond 60 minutes
How much more at risk of post operative infection are animals receiving propofol?
3.8 times more at risk
How does clipping affect the post operative risk of infection?
Clipped surgical sites before induction 3 times more likely to develop post op infection
What six cases are surgical prophylaxis indicated in?
Dental proceduresLeukopenic patientsContaminated surgeryOrthopaedic and major abdominal/thoracic surgerySurgical time greater than 90 minsConsequences of infection would be disastrous
Why is aseptic technique so important?
Antibiotics not a substitute for aseptic technique - can’t compensate for gross contamination, local tissue trauma or compromised patient health
Describe administration of surgical prophylaxis
Administer before procedureAchieve maximum effect the drug must be present in wound at time of contaminationAdvantages of therapy minimal if commenced later than 3-5 hours after contamination
What are the most useless drugs to use for surgical prophylaxis in most small animal cases?
Amoxycillin or long acting drugs
What are generally recommended as the best drugs for surgical prophylaxis?
2ndgeneration cephalosporinsAmoxycillin-clavulanate1stgeneration cephalosporinIV at time of induction or SC or IM 1-2 hours prior to surgery
What key questions are asked to determine whether antimicrobials are indicated?
Is infection definite, probable or very possible?Could critical illness occur?Any signs of heat, redness, swelling, pyrexia or known cause for presenting signs?
What questions need to be asked if you do need to use an antibacterial?
Where is infection?What bacteria would I expect there?Do I need to maximise cure chance?What antibacterials would be effective against these bacteria?Are there any pharmacokinetic issues?Are there any side effect issues?Are there any client compliance issues?
What are the general withdrawal perios for milk and meat?
7 days for milk28 days for meat
What should enrofloxacin (Baytril) not be used in?
Birds producing eggs for human consumptionLayer replacement birds within 14 days of coming into lay
Which animals should metronidazole/phenylbutazone not be used in?
Food producing animals as carcinogenic
Whose responsibility is it to ensure residues do not enter the food chain?
Farmer/owner
What two tests are done on produce to check for residues?
Milk - beta-lactam test done at dairyMeat - kidney test done at abattoir in case of suspicion
What are the two criterion on the WHO list for the importance of antimicrobials?
- An agent which is the sole, or one of limited therapy, to treat a serious human disease2. An antimicrobial used to treat disease caused by non-human sourced organisms or organisms that may acquire resistance genes from non-human sources
What are the three levels of importance of antimicrobials on the WHO list?
Critically important - meet both criteriaHighly important - meet one of the criteriaImportant - meet neither of the criteria
Which five antibiotics cannot be given orally rabbits?
Penicillins Lincosamides Aminoglycosides Cephalosporins Erythromycins
