micro poop 2. Flashcards
What factors must be considered in choosing an antimicrobial agent?
identity of infecting organism, information about the susceptibility of the infecting organism, factors specific to the patient
What is empiric theory?
the application of knowledge of the organisms most likely to cause infection in a given clinical setting and its most likely susceptibility to an antibiotic
Why is knowing the susceptibility of the organism important in choosing an antibiotic?
organisms exhibit intrinsic or innate resistance to certain antibiotics so you won’t consider these, while some are universally susceptible to certain antibiotics
What factors to the patient are important to consider when choosing an antibiotic?
history of previous reactions, age (gastric acidity changes with age - important for orally ingested), pregnancy, renal/hepatic function, site of infection
pharmacokinetics
encompasses all the ways that the body manipulates a drug, including absorption, distribution, metabolism, and excretion
pharmacodynamics
describes the biochemical and physiologic effects of the drug and its metabolism of action on the bacteria
bacteriostatic
antimicrobial agents that inhibit the growth and/or reproduction of the infecting agent, but fail to actually kill the agent
Why is bacteriostatic typically better than bacteriocidal?
normal defenses typically destroy the microorganism
What are examples of bacteriostatic agents?
macrolids (erythromycin), clindamycin, sulfamethoxazole, trimethoprim, tetracyclines, chloramphenicol
bacteriocidal
antimicrobial agent that is capable of causing irreversible damage or death to the organism
What are examples of bacteriocidals?
b-lactam antibiotics (penicillins and cephalosporins), vancomycin, aminoglycosides, fluoroquinolones
What is a factor that can influence if a antimicrobial is bacteriostatic or bacteriocidal?
antimicrobial concentration at the site of action - can be bacteriostatic at low concentrations and bactericidal at high concentrations
MIB
Minimal bacteriocidal concentration - the lowest concentration which prevents the organism from multiplying
broad spectrum antibiotics
active against wide range - usually both gram positive and gram negative
When are broad spectrum typically used?
empirically prior to identifying the causative bacteria (wide differential and potentially serious illness)
narrow spectrum antibiotic
active against a select group of bacterial types
What are the five mechanisms antibiotics inhibit/kill bacteria?
interfere with cell wall synthesis, protein synthesis, cytoplasmic membrane function, nucleic acid synthesis, metabolic pathway
What are antibiotics that interfere with cytoplasmic membrane function tricky?
all organisms have a cytoplasmic membrane
What antibiotics interfere with cell wall?
beta lactams (penicillin, cephalosporin, carbapenems, monobactams), vancomycin, bacitracin
What antibiotics interfere with cell membrane?
polymyxins
What antibiotics interfere with folate synthesis?
sulfonamides, trimethoprim
What antibiotics interfere with DNA gyrase?
quinolones
What antibiotics interfere with RNA polymerase?
rifampin
What antibiotics interfere with ribosome subunits?
macrolides, clindamycin, linezolid, cholamphenicol, streptogramins, tetracyclines, aminoglycosides
What is the mechanism of action for inhibitors of cell wall synthesis?
interfere with peptidoglycan sheet synthesis and murrain assembly
What are the beta-lactams?
PCCM (P-in, C-in, C-em, M-am) penicillin, cephalosporin, carbapenem, monobactam
How do beta lactams work?
bind at the active site of the transpeptidase enzyme that cross-links the peptidoglycan strands, irreversibly inhibiting the enzyme - formation of cell wall is prevented (non toxic to human)
What is the general structure of a penicillin? What group does it belong to?
house with an attached garage, beta lactams that block cell wall synthesis
How are cephalosporins categorized?
by generation - each generation exhibiting increased spectrum of activity as well as increased resistance to destruction by beta=lactamase enzymes
What is the structure of a cephalosporin?
weird house with attached garage
What are the third and fourth generation cephalosporins more targeted towards?
gram negative bacteria
carbapenems
cell wall inhibition - active against all pathogenic organisms and resistant to destruction by the extended spectrum beta lactamases
What is the structure of a carbapenem?
house with both attached and detached garage
What is the only antibiotic that works against MRSA?
vancomycin
What is the method of action for vancomycin?
blocks residues instead of cleaving like penicillin - prevents crosslinking
What bacteria are vancomycin effective against?
gram-positive bacteria (including MRSA) - gram negative resistant due to LPS porons
What is used for people who are allergic to penicillin? What is the method of action?
inhibitors of protein synthesis - infere with formation of 30S complex, 70S ribosome, or block elongation process
aminoglycosides - method of action and danger of these drugs
inhibit protein synthesis - causes misreading of mRNA —> therapeutic level is high, near toxic level - need to stop and give kidneys a rest
linezolid - method of action and when should it be used
inhibit protein synthesis - should only be used against gram + bacteria that are resistant to other antibiotics
macrolids
bacteriostatic - block protein synthesis
lincosamides
similar to macrolids - inhibit protein synthesis
chloramphenicol - method of action and when should it be used
inhibits protein synthesis - VERY TOXIC - should only be used against salmonella
tetracyclines
inhibit protein synthesis - static in nature, immune system must be able to clear the bacteria
quinolones/fluorquinolones
inhibition of DNA synthesis - esp inhibiting DNA gyrases/topoisomerases required for supercoiling DNA
metronidazole
inhibition of DNA synthesis
rifampin
inhibition of RNA synthesis
bacitracin
inhibition of RNA transcription
What is trimethoprim used in combination with?
sulfamethoxazole
trimethoprim
prevention of synthesis of folic acid
sulfonamides and dapsone
prevents synthesis of folic acid
