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50 Cards in this Set

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  • Back
Initiation of protein synthesis
– 30S and 50S do their thing w/ mRNA -> 70S
– Aminoglycosides block during initiation
Elongation and translocation of protein synthesis
- requires hydrolysis of GTP
- tRNA binding to the “A” site is inhibited by Chloramphenicol, Tetracycline, and Clindamycin
Translocation of protein synthesis
- requires hydrolysis of GTP
- blocked by erythromycin and spectinomycin
Aminoglycosides Mechanism of Action
- bactericidal
– go into cyto via O2, so they only get aerobes
– once inside, they inhibit protein synthesis by binding 30S and makes initaion complex break down
Aminoglycosides administration
– parenteral admin
– distribution good except to CSF
– [] dependent w/ a long post-antibiotic effect so single daily dosing to ↑ []’s is good
– excreted unchanged in urine
– 2.5 hr half life
Aminoglycosides Side effects
- Ototoxicity, nephrotoxicity, which limit usefulness
– neuromuscular blocaid also noted
Aminoglycosides Anitmicrobial activity
– aerobic (-) infections (Enterobacter, Klebsiella, E. coli, Proteus, Pseudomonas, Serratia)
– usually combo w/ B-lactam
Aminoglycosides Resistance
1) producing enzymes that that phosphorylate, adenylate, or acetylate it – 2) a ↓ in uptake
3) alteration of 30S binding site
Chloramphenicol Mechanism
- binds to the 50S subunit of the 70S ribosome and inhibits peptidyl transferase
– static
Chloramphenicol Antimicrobial activity
- for meningitis infections by H. ful or N. meningitidis if a ß-lactam is contraindicated or ineffective
– alternative to the tetracyclines in rockey mountain spotted fever
Chloramphenicol Administration
– rapdily absorved from GI and distributes everwhere
– inactivated by glucuronyl transferase, so little is excreted unchanged
– liver disease can ↑ ½ life from 3 to 10 hrs
Chloramphenicol Toxic effects
– Aplastic anemia with pancytopenia is rare but bad
– BM toxicity also seen
– grey-baby syndrome from circulatory collapse
– inhibits P450, so it can slow metabolism of P450 drugs (coumadin)
Chloramphenicol Resistance
– production of CAT which acetylates and inactivates the drug
– plasmid mediated
Tetracyclines Mechanism
– static
- binds to the acceptor site on the 30S of 70S to block binding of the A-tRNA
Tetracyclines Antimicrobial activity
– 1st choice or alternative for M pneumoniae, rickettsial Chlamydiae, V. cholera
- Brucella (w/ an aminoglycoside or rifampin)
- Borrelia infections
Tetracyclines Administration
- oral (impaired by milk, antacids, or iron) or IV
– Distribution good except for CSF
– removed by liver then circulate in enterohepatic route
– eliminated in feces and urine
– 6-15 hr ½ life
Tetracyclines Side Effects
- GI irritation most common
– Photosensitivity w/ doxy
– hepatotoxicity if OD
– it will deposit in bones and teeth, so avoided in pregnant women and children under 8
- renal toxicity if given with potentially nephrotoxic drugs or if patient already has impaired renal function
Tetracyclines Resistance
1) ↑ efflux by an active transport pump
2) production of proteins that interfere w/ binding
Erythromycin Mechanism
- static
– binds 50S of 70S and blocks translocation from the A to P site
Erythromycin Antimicrobial activity
- 1st choice for Legionnaire's disease, M. pneumoniae, and C. trachomatis
– alternative for various strep and Anthrax
Erythromycin Admin
- given orally
– C and E better absorbed than A
– well distributed except CSF
– excreted in bile
Erythromycin Toxcity
- GI effects occasionally and sometimes intolerance requires discontinuation
- Hepatotoxicity, fever, eosinophilia, and rashes also seen
– E and C inhibit P450
– don’t use > 1 b/c they are antagonistic
Clindamycin Mechanism
– static
– binds 50S of the 70S ribosomal to block peptidyl transferase
Clindamycin Antimicrobial activity
- for anaerobic infections Bacteroides, C. perfringens, Strep. anaerobic (peptostreptococcus) and Staph aureus
– C + primaquine is alternative to trimethoprim/sulfamethoxazole for PCP in AIDS patients
– also w/ pyrimethamine for AIDS-related toxoplasmosis
Clindamycin Admin
- orally or parenterally
– widely distributed except CSF
- 10% excreted unchanged b/c it is metabolized in liver and excreted in the bile
- Small quantities found in feces for up to 2 weeks (GI)
Clindamycin Toxicity
– GI irritation, skin rashes, and hepatotoxicity common
- Severe diarrhea due to outgrowth of C. difficile, which produces a necrotizing toxin
Clindamycin Resistance
1) Mutation of the ribosomal binding site
2) Production of a methylase
3) Inactivation
Streptogramins Mechanism
- binds 50S of 70S, constricting the exit channel of the nascent peptide
- cidal
Streptogramins Antimicrobial activity
- for vancomycin-resistant E. faecium (but not E. faecalis!)
– other potential uses for MRSA, penR-S. pneumoniae, and GAS, GBS
Streptogramins Administration
- 70:30 (dalfopristin : quinupristin)
- oral or parenterally
– liver elimination
- t1/2 ~ 1.5 hr
Streptogramins Toxicity
- well tolerated
- Hepatotoxicity in 1%
- also hypersensitivity, rash, diarrhea, NandV, & myalgia
Oxazolidinones Mechanism
- synthetic
– binds to the 50S and prevents 70S fromation
– usually static but can be cidal
Oxazolidinones Antimicrobial activity
– to treat MRSA, vancomycin-resistant E. faecium and E. faecalis (VRE), penR-S. pneumoniae, and GAS and GBS
- Resistance recently noted (mutations in 23S rRNA)
Oxazolidinones Administration
– IV and oral
Oxazolidinones Toxicity
– reversible MAO inhibitor, so don’t give w/ MAOIs, tricyclic antidepressants, etc
– avoid tyramine – can ↑ brady in patients taking B-blockers
– thrombocytopenia and superinfections also seen
Metronidazole Mechanism
– only taken up anaerobes – converted to active metabolite
– disrupts DNA and cidal
Metronidazole Antimicrobial activity
– 1st choice for C. difficile and Bacteroides fragilis
- has been used for acute dental infections like Vincent's gingivostomatitis
– best one for trichomonias, giardia, and amebia
Metronidazole Administration
– IV but can be given oral
- Widely distributed
– extensively metabolized & inactivated in the liver
– metabolites and unchanged drug excreted by the kidneys
Metronidazole Toxicity
– Nausea, headache, dry mouth are common
– Diarrhea, epigastric distress and insomnia more rare
– disulfiram-like action after alcohol
- Carcinogenic and teratogenic in animals and mutagenic to bacteria
– don’t take in pregnancy