Antibiotics Flashcards
(29 cards)
selective toxicity
antibiotics must be more toxic to the pathogen than to the pathogen’s host
bacteriostatic
inhibits the growth of bacteria but doesn’t otherwise kill them
bacteriocidal
level of antibiotic that kills the bacteriu
quantitative determination of antibiotic activity
E test
- use a piece of paper with antibiotic concentartions in a gradient
- look for lowest necessary to inhibit growth
qualitiative determination of antibiotic activity
- kirby bauer disc diffusion test
- measures the size of zone of inhibition
4 mechanisms of bacterial resistance to antibiotics
- naturally lack the drug target
- outer membrane of gram-negative block many meds
- spontaneous mutations
- Horizontal gene transfer
therapeutic index
lowest dose toxic to patient/therapeutic dose
clinical situations where antibiotic prophylaxais may be warranated
- bite
- meningitis
- heart valve
Beta lactam antibodies
- cell wall synthesis inhibitors
- penicillins, cephalosporins, and carbapanems
- inhibits cross linking of peptidoglycans
- Most effective against GRAM POSITIVE bacteria (they have a thick peptidoglycan layer)
Penicillins
- 5 types with varying side chains
- varying resistance to beta lactamases
cephalosporins
- resistant to some beta lactamases
- 4 generations
carbapenems
- resist most beta lactamases
- last resort antibiotics
- NDM1 are resistant
non beta lactam cell wall inhibitor
- Vancomycin
- binds to D-Ala-D-Ala subunit to prevent cross linking
- cause cell lysis
- treat Gram positve and C. Diff
- also last resort
Tx: poorly absorbed so administer IV
Cell membrane inhibitors
- Polymyxin B
- toxicity –> only apply topically
- insert into the membrane –> lysis
Gram NEGATIVE bacteria
Nucleic Acid Synthesis inhibitors
- Fluoroquinolones
- inhibit prokaryotic topoisomerase (DNA Gyrase)
- may have some toxicity, still oral
Protein synthesis inhibitors
- Clindomycin, Streptomycin, Erythromycin
- Macrolides, Aminoglycosides, Lincosamides, Tetracyclines
Macrolides
- prevent continuation of protein synthesis
- bind to 50S subunit
- Erythromycin
Lincosamides
- bind to 50S subunit
- block initiation of translation
- Clindamycin
Aminoglycosides
- bind to 30S subunit
- mRNA is misread and causes truncated proteins
- Streptomycin
Tetracyclines
- block attachment of tRNA to ribosome
- binds to 50S
Metabolic inhibitors
- Sulfonamides
- Analogs of essential metabolites used in FOLIC ACID synthesis
- mimics PABA, comp. inhibition
- can not outcompete PABA
ways of determing MIC
- Kirby bauer diffusion test
2. E test
side effects of clindamycin
- protein synthesis inhibitor
- disrupts normal gut microbiota
- proliferation of C. diff
- can lead to enterocolitis
side effects of tetracyclin
- broad spectrum antibiotic
- blocks binding of tRNA to ribosome
- inhibits lactobacillus in vagina, changing the pH, allowing C. albicans to grow into yeast infection
-also causes tooth staining, dont prescribe to children or pregnant women
