Antimicrobials Flashcards
define antimicrobials
Chemicals that kill or inhibit the growth of microorganisms (can include bacteria, fungi, viruses, protozoa).
define antibacterials
chemical that kills or inhibits growth of bactera
define antiseptic
biocide that reduces microbial population on living tissue
define disinfectant
biocide that reduced microbial population on inanimate objects
define minimum inhibitory concentration MIC
lowest concentration of antimicrobial that completely inhibits growth in vitro
define minimum bactericidal concentration
lowest concentration of antimicrobial that kills 99.9% isolates in vitro
_______ drugs have activity against a single pathogen or limited group of pathogens and are less likely to have adverse affects
narrow-spectrum
_____ drugs have activity against a wide range of pathogens, useful when causative agent and have serious disease
broad-spectrum
drugs with intermediate range of pathogens are sometimes called
extended spectrum
fluoroquinolone, aminoglycosides, and metronidazole have ______-dependent and bacteri_______ effects
concentration-dependent, bactericidal (there are no concentration-dependent bacteriostatic drugs)
efficacy of _______-dependent antibacterials depend on amount of time at concentration at SITE OF INFECTION is higher than MIC
time-dependent
time-dependent effects: name 5 drugs with dosage regimen goal to maximize time above MIC
penicillins, phenicols, cephalosporins, macrolides, tetracyclines
time-dependent effects: name 3 drugs that 24 hour AUC/MIC ratio (daily total exposure to drug) is a better predictor of efficacy than just time above MIC
azithromycin, clarithromycin, clindamycin (they are time-dependent technically bu have concentration-depdendent-like effects)
name 4 time-dependent bactericidal drug classes
penicillins, cephalosporins, TMS, florfenicol (only bactericidal against BRD pathogens)
name the 6 time-dependent bacteriostatic drug classes
chloramphenicol, florfenicol (except bactericidal against BRD pathogens), tetracyclines, sulfonamides, lincosamides, macrolides
give 3 tests that can be sued to determine MIC for a drug and bacterial isolate
broth dilation, Kirby-Bauer (disk diffusion), and E-test (the strip)
bacterial are classified as ________ or _____ to antibacterials based on MIC breakpoints
susceptible or resistant
Bacteria are classified as susceptible or resistant to antibacterials based on ______
MIC breakpoints (breakpoint specific to drug, MIC values specific to bacteria)
what treatment is based on knowledge of what bacteria are likely causing disease, and what antibacterial drugs re likely effective against them, is called
empirical treatment
3 questions to consider for deciding if antimicrobials are necessary
do we have a suitable antimicrobials to treat disease? will the animal recover without antimicrobials? will the use of antimicrobials greatly improve disease outcome of reduce risk to other animals?
what is prophylactic vs metaphylactic treatment
preventative treatment of an animal (prophylactic) or group of animals (metaphylactic)
what is therapeutic treatment
treatment of a diagnosed bacterial infection
what are the 4 quadrants of bacteria types and antimicrobial selection
Gram + aerobes, Gram - aerobes, Gram + anaerobes, Gram - anaerobes
there are __ categories of drugs based on importance in human medicine
4
sulfonamides: give MOA and bacteri_____
folic acid inhibitors (prevent bacteria from synthesizing folic acid from PABA); therefore bacteriostatic
why did prontosil, a sulfonamide, protect mice and rabbits from streptococcal infections but not kill/harm bacteria in a test tube?
prontosil was a prodrug [has to get metabolized to sulfanilamide]
what do all the sulfonamide class drugs have in their name
:) sulfa
sulfonamide drugs: tell me their activity against aerobic vs anaerobic and gram + vs - bacteria
limited activity against Aerobic gram +: staph, strep, Nocardia
limited activity against Aerobic gram - : Klebsiella, Pasterurella, Proteus, some E. coli (there is fair amount of resistance)
not effective for ANaerobes in vivo
not effective for abscesses because PABA and thymidine inhibits sulfonamide activity
sulfonamide drugs: are they effective against any parasites?
yes! some protozoa and coccidians: Toxoplasma, sarcocystis
sulfonamides ALONE are mainly used in what animal species
production animals. eg. in pork, may promote better growth.
but not listed on the “reasonable empirical choices for cattle” cart - we really just use potentiated sulfonamides now
sulfonamides + diaminopyrimidine, which have better antimicrobial activity than sulfonamides alone, are known as what
potentiated sulfonamides
give mechanism of action for diaminopyrimidines
folic acid synthesis inhibitors (remember, they have sulphonamides) because they inhibit dihydrofolate reductase
name the two diaminopyrimidines to know
trimethoprim and ormetoprim
PK of diaminopyrimidines: unlike sulphonamides, what do these drugs penetrate via diffusion
cell membranes (can enter prostate, CNS, milk; like sulphonamides, still not great in abscesses)
they are lipid-soluble organic bases
- this drug is delivered as a combination product in appropriate ratio
- labelled q24h but more effective given q12h
- used in companion animals for enteric bacteria, and used in cattle for streptococcus, and in horses used against a variety of aerobes because it is one of few safe oral antibacterials in horses
- category III
trimethoprim/sulfadiazine, ie. TMS (1:5 trimethoprim:sulfa formulation)
TMS is labelled for acute strangles in horses, but what should you be cautious about
not effective in abscesses bc it is a potentiated sulfonamide (reduced activity due to PABA and thymidine in the abscesses)
bacterial resistance to sulphonamides and potentiated sulphonamides is common. name 3 mechanisms of cross-resistance
efflux pumps, failure to penetrate organism, changes in target membrane
note complete cross-resistance means that resistance to one = resistance to all
the beta lactam class of drugs, which are drugs that have a beta-lactam ring, includes these three groupings
penicillins, cephalosporins, carbapenems, and “related drugs”
what is beta-lactam MOA
β‐lactams bind to penicillin binding proteins (transpeptidases) that cross‐link peptidoglycans within the cell wall, causing cell wall to be nonfunctional and cells undergo osmotic rupture (“pop”) (as such, they are bactericidal)
why do bata-lactamh generally have few adverse effects
mammals don’t have cell walls
PK of beta-lactams: excreted largely unchanged by the kidneys, so what does that tell you?
metabolism not a big part of PK for these drugs