pharmacology 3 Flashcards
minimum inhibitory concentrations (MIC)
lowest concentration of drug that inhibits visible bacterial growth
MIC90 concentration for inhibiting 90% of the bacteria
Minimum bactericidal concentration (MBC)
the lowest concentration of a drug that kills 99.9% of bacteria
mutant prevention concentration (MPC)
the concentration of the least susceptible single-step mutant
in theory, kills them all so mutant so they cant form
bacteriostatic
stop bacteria from multiplying: don’t kill them
MBC much larger than MIC
elimination of infection requires host immune response
requires an immunocompetent patient
bactericidal
kill bacteria if concentrations reach MBC for a certain period of time
MBC at or near the MIC
preferred for immunosuppressed animals
preferred for severely ill patients
bactericidal antimicrobials are not always bactericidal
static at concentration below MBC
dose dependent
bacteria dependent
bacterial must be multiplying for cidial to work
postantibiotic effect (PAE)
persistent drug effect
after plasma concentration decline below the MIC/MBC
mechanisms of PAE
decreased virulence of bacteria
development of abnormal cell wall or septum
increased susceptibility to host defenses
persistence at site of infection
only occurs with some drugs and is bacteria-dependent
pharmacokinetic-pharmacodynamic interaction
predict the success of antimicrobial therapies
relate concentration of drug to MIC of the pathogens
vary by class of drug
vary with each pathogen
drug-bug interaction
time-dependent antibiotics
T>MIC
duration plasma concentration if above the MIC over 24 hours
concentration dependent antibiotics
Cmax:MIC
ratio of the maximum plasma concentration to the MIC
Concentration/time dependent antibiotics
AUC:MIC
ratio of the AUC.24 to the MIC
narrow spectrum
implies activity against a limited subset of bacteria
broad spectrum
implies activity against a wide range of bacteria
may include mycoplasma, rickettsia, and chlamydia
spectrum of activity
tells you that the bacteria can be affected by antimicrobial
aerobic bacteria
gram +
streptococci
staphylococci
gram -
respiratory pathogens
enteric pathogens
anaerobic bacteria
gram +
gram -
penicillins
active against streptococci, but NOT staphylococci
NOT active against gm - (Cell wall blocks)
active against most gm + and gm - anaerobes
aminoglycosides
active against staphylococci but NOT streptococci
active against respiratory and enteric gm -
NO activity against anaerobes
macrolides
active against gm + aerobes
active against respiratory gm - but NOT enteric
active against most gm + anaerobes
facultative anaerobes
are aerobes
can grow in anaerobic conditions
culture as aerobes
test susceptibility in aerobic conditions
in vitro susceptibility may not equal in vivo susceptibility
additive/indifferent
2+2=4
used to extend spectrum
does not enhance activity of either
synergism
what we hope for
combination enhances activity
static alone, cidial together
2+2=6
antagonism
what we worry about
2-+2=2
activity of the combination is less than sum
first questions for antibacterial use
is an antibacterial necessary
use an antimicrobial when
bacterial infection systemic
do not use an antimicrobial when
viral infection
fungal infection
parasitic infection
maybe use an antimicrobial when
protozoal infection
bacterial infection-local
intravenous judicious use
highest concentrations
highest risk of adverse effects
severe systemic illness
owner comfort level/animal temperament
IM/SC judicious use
bioavailability is often complete
risk of drug toxicity less than IV
injection site reactions
owner comfort level/animal temperatment
oral judicious use
ileus-gi too slow
colitis-gi too fast
malabsorption
drug interaction
transdermal judicious use
not recommended no no no
others routes of administration for judicious use
topical-eye,skin, wound
inhaled
intraarticular/regional limb perfusion
site of infection
for most pathogens, the site of infection is the interstitial fluid
protein binding is a major determinant of drug distribution of ISF
low protein bound drugs have good destruction
highly protein bound drugs have limited distribution>80%
site of infection-exception to the rule
CNS, eye, prostate, bronchus, testes
protective barriers that consist of tight junction between the endothelial
limited drug movement into these areas
lipids solubility or active transport
site of infection-intracellular infection
lipophilic drugs have better penetration into cell than do hydrophilic drugs
site of infection-abscesses and granulomas
drug diffusion slow
lower cmax
slower equilibrium
lower blood supply to the area
treatment unsuccessful without draining
if you can drain and lavage the abcsess, antibacterial may not be necessary
if can not drain-choose a more lipophilic drug. treat for al long time
local tissue factors
affect the efficacy of some drugs
purulent debris
acidic environment
hemoglobin/hemorrhages
anaerobic conditions/necrotic tissue-decreased blood supply
choosing an antibiotic
empiric treatment
know which bacteria are commonly involved in which infections
choose a drug likely to treat that bacteria
