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49 Cards in this Set
- Front
- Back
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Describe the bacterial ribosome
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It has a 30S and a 50S unit. The 50S subunit consists of two rRNAs, one is a 5S and the other is a 23S
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Describe how resistance against macrolides occurs
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1) efflux pump
2) mutation of the ribosomal binding site 3) methylation of the ribosomal binding site |
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Where do macrolides bind?
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They bind on the domain V of 23S rRNA of the 50S subunit
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What are the most important members of the macrolide class and how do they act?
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1) Erythromycin
2) Clarithromycin 3) Azithromycin It inhibits protein synthesis by blocking translation and binds to the 23S ribosomal subunit |
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What are four problems with erythromycin?
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1) narrow antibiotic spectrum
2) instability in acid 3) severe abdominal cramping 4) inhibition of P450s |
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When is erythromycin used and on what sort of organisms?
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It is used when a patient is allergic to penicillins and can be used to treat pneumococci, streptococci, staphylococci, mycoplasma and legionella
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How is clarithromycin different from erythromycin?
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1) It has a broader spectrum
2) less GI upset 3) prolongation of the QT interval |
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What is different about azithromycin from the other macrolides?
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It has high tissue concentrations and can be given over 5 days instead of 10
No inhibition of P450 |
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Describe the most common adverse effects associated with erythromycin
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1) Erythromycin causes cholestatic hepatitis
2) epigastric distress by stimulation of motilin receptors 3) inhibition of P450 metabolism |
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What is the member of the ketolid class and how does it work?
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Telithromycin is similar to macrolides but binds to domains II and V on the 23S rRNA
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How does telithromycin overcome resistances to which macrolides are susceptible?
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They bind to both domains II and V on the 23s rRNA, which makes them a poor ligand for the efflux pump and they can overcome methylation
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What is telithromycin used to treat and who should not receive it ?
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It is used to treat community acquired pneumonia and should not be used in patients with a history of hepatitis or jaundice associated with the use of macrolides
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What drug is in the lincosamide class and how does it work?
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Clindamycin - it has a mechanism of action similar to the macrolides, blocking peptide bond formation at the 50S rRNA subunit
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What is clindamycin used to treat?
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Anaerobic infections such as bacteroides fragilis and gram positives
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What drug often causes pseudomembranous colitis?
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Clindamycin
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What are the streptogramins and what are they used to treat? Bacterostatic or bacteriocidal?
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Quinupristin/Dalfopristin - bacteriocidal
They can treat vancomycin resistant enterococcus faecium (not faecalis) |
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What drug is referred to as an oxazolidinone and how does it work and what does it treat?
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Linezolid inhibits the 50s rRNA subunit
It can treat MRSA, VRE (all enterococci) and penicillin resistant strep pneumo |
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Describe serious side effects associated with linezolid
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1) myelosuppression
2) inhibition of monoamine oxidase leading to seratonin syndrome 3) peripheral neuropathy |
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Describe how chloramphenicol works and how resistance occurs
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It inhibits the 50s rRNA
Resistance occurs due to acteylation that converts it to an inactive metabolite |
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Describe the adverse side effects of chloramphenicol
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1) non-reversible aplastic anemia
2) dose related/reversible bone marrow suppression 3) gray baby syndrome - due to inability to glucuronidate and eliminate the drug |
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How does telithromycin overcome resistances to which macrolides are susceptible?
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They bind to both domains II and V on the 23s rRNA, which makes them a poor ligand for the efflux pump and they can overcome methylation
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What is telithromycin used to treat and who should not receive it ?
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It is used to treat community acquired pneumonia and should not be used in patients with a history of hepatitis or jaundice associated with the use of macrolides
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What drug is in the lincosamide class and how does it work?
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Clindamycin - it has a mechanism of action similar to the macrolides, blocking peptide bond formation at the 50S rRNA subunit
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What is clindamycin used to treat?
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Anaerobic infections such as bacteroides fragilis and gram positives
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What drug often causes pseudomembranous colitis?
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Clindamycin
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What are the streptogramins and what are they used to treat? Bacterostatic or bacteriocidal?
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Quinupristin/Dalfopristin - bacteriocidal
They can treat vancomycin resistant enterococcus faecium (not faecalis) |
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What drug is referred to as an oxazolidinone and how does it work and what does it treat?
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Linezolid inhibits the 50s rRNA subunit at the site of 30s binding
It can treat MRSA, VRE (all enterococci) and penicillin resistant strep pneumo (gram positive resistants) |
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Describe serious side effects associated with linezolid
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1) myelosuppression
2) inhibition of monoamine oxidase leading to seratonin syndrome 3) peripheral neuropathy |
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Describe how chloramphenicol works and how resistance occurs
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It inhibits the 50s rRNA
Resistance occurs due to acteylation that converts it to an inactive metabolite |
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Describe the adverse side effects of chloramphenicol
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1) non-reversible aplastic anemia
2) dose related/reversible bone marrow suppression 3) gray baby syndrome - due to inability to glucuronidate and eliminate the drug |
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When is chloramphenicol used?
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When no other antibacterial is effective because its side effects are so serious (aplastic anemia, bone marrow suppression, gray baby syndrome)
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What are the classes of drugs that work on the 50s rRNA subunit?
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1) macrolides (erythro, azithro, clarithro
2) telithromycin 3) clindamycin 4) streptogramins 5) linezolid 6) chloramphenicol |
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What are the agents that bind to the 30s rRNA subunit?
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1) tetracylines
2) aminoglycosides 3) glycylcylcines (e.g. tigecycline) |
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What are the tetracyclines and how do they work?
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1) tetracycline
2) doxycycline 3) minocycline 4) demeclocycline They work by binding to the 30s rRNA and inhibiting attachement of the aminoacyl-tRNA |
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Describe how the major clinical resistance to tertacyclins occurs
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A pump removes the drug from the cells
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Describe the absorption of tetracycline and agents that can alter it
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It is impaired by milk and metal ions which chelate tetracycline and prevent GI absorption
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What drug is fecally eliminated and can be used in patients with renal failure?
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doxycycline
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Describe the adverse effects of tetracyclines
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1) GI irritation
2) photosensitivity 3) teeth discoloration in children as well as bone growth inhibition 4) contraindicated in pregnancy 5) deposition of the drug in the skin |
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What is the mechanism of action of tigecycline and for what is it used to treat?
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It binds with higher affinity to the same binding site on the 30s rRNA as the tetracyclines and is used to treat multi-resistant pathogens such as MRSA, VRE, acinetobacter
prevents binding of the aminoaceyl-tRNA to the ribosome |
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What are the main side effects of tigecycline?
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nausea and vomiting
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What are the most common aminoglycosides?
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1) gentamycin
2) tobramycin 3) amikacin 4) kanamycin 5) streptomycin 6) neomycin |
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Describe the uptake of aminoglycosides into the cell
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Uptake of aminoglycosides is an energy dependent process that requires oxygen, so they are not affective against anaerobes
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How do aminoglycosides act?
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They inhibit protein synthesis by binding to the 30s rRNA subunit, inhibiting/freezing the initiation complex and cause misreading of the genetic code
They are bactericidal |
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How is resistance to aminoglycosides mediated?
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They are metabolized by acetylation, phosphorylation, ect. as well as mutations in porins and ribosomal binding sites
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Describe the absorption of aminoglycosides
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They are poorly absorbed after oral administration but rapidly absorbed after i.m. or sub Q administration
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What is important to remember about aminoglycosides and the kidney?
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They are excreted by glomerular filtration and require a dosage adjustment in patients with renal failure or poor renal function
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What are the most common adverse side effects associated with aminoglycosides?
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1) ototoxicity - auditory or vestibular
2) nephrotoxicity - acute renal insufficiency and tubular necrosis 3) neuromuscular blockade |
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What drugs are dosed on the basis of lean body mass and not actual body weight?
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aminoglycosides
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Describe the method of dosing for aminoglycosides
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The entire daily dose is given at one time because aminoglycosides use concentration-dependent killing and have a high post-antibiotic effect
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