Chloramphenicol, Tetracyclines, Macrolides, Clindamycin & Linezolid Flashcards
What antibiotics bind to the 50s ribosomal subunit and block transpeptidation?
Chloramphenicol
Macrolides
What class of antibiotics bind to the 30s subunit and block the incoming charged tRNA?
Tetracyclines
What protein synthesis inhibitors are bactericidal?
Aminoglycosides Linezolid (variable)
What is the MOA of chloramphenicol?
Binds to 50s ribosomal subunit
Blocks transpeptidation
What is the MOA of tetracyclines?
Binds to 30s ribosomal subunit
Blocks binding of charged tRNA
What is the MOA of macrolides?
Binds to 50s ribosomal subunit
Blocks transpeptidation
Chloramphenicol has limited use owing to toxicities but is often still used in developing countries because of the low cost. What toxicities are associated with chloramphenicol?
Anemia
Aplastic anemia
Gray baby syndrome
How do bacteria gain resistance to chloramphenicol?
Plasmid
Encodes acetyltransferase that inactivates the drug
What are the clinical uses of chloramphenicol?
Rocky Mountain spotted fever (Rickettsia rickettsii)
Although chloramphenicol can be used to treat Rocky Mountain spotted fever, what is the preferred agent?
Doxycycline
Is chloramphenicol bactericidal or bacteriostatic?
Bacteriostatic
List the tetracyclines.
Tetracycline
Doxycycline
Minocycline
What compounds inhibit tetracycline absorption in the gut?
Divalent cations
milk, antacids, iron
How do bacteria gain resistance against tetracyclines?
Plasmid
Decreased uptake or increased efflux by transport pumps
What is a contraindication for tetracycline use?
Pregnancy
What toxicities are associated with tetracyclines?
GI distress
Photosensitivity
Discoloration of teeth and inhibition of bone growth in children
What are indications to use tetracyclines?
Borrelia burgdorferi M. pneumoniae Ricketssia Chlamydia Acne
Why are tetracyclines very effective against Ricketssia and Chlamydia?
Accumulate intracellularly
List the macrolides.
Erythromycin
Azithromycin
Clarithromycin
Are tetracyclines bactericidal or bacteriostatic?
Bacteriostatic
Are macrolides bactericidal or bacteriostatic?
Bacteriostatic
What are the clinical uses of macrolides?
Atypical pneumonias
B. pertussis
STIs (Chlamydia)
Gram positive cocci in patients allergic to penicillin
What is the treatment for N. gonorrhea?
Ceftriaxone
Azithromycin to empirically treat for Chlamydia
How do bacteria gain resistance against macrolides?
Methylation of 23s rRNA binding site inhibits binding of drug
What effect do clarithromycin and erythromycin have on the CYP450 enzyme system?
Inhibitors
What are the toxicities associated with macrolides?
M: motility issues (GI) A: arrhythmia (QT prolongation) C: cholestasis (acute cholestatic hepatitis) R: rash O: eOsinophilia
What is the MOA of clindamycin?
Binds 50s ribosomal subunit
Blocks peptide transfer
Is clindamycin bactericidal or bacteriostatic?
Bacteriostatic
What are indications for clindamycin?
Treats anaerobic infections above the diaphragm
Group A strep
What toxicities are associated with clindamycin?
Pseudomembranous colitis
Fever
Diarrhea
What drug binds to the 50s ribosomal subunit and prevents formation of the initiation complex?
Linezolid
When in linezolid used?
MRSA
VRE
How do bacteria acquire resistance to linezolid?
Point mutation of ribosomal RNA
What toxicities are associated with linezolid?
Bone marrow suppression (especially thrombocytopenia)
Peripheral neuropathy
Serotonin syndrome
A bacteria aquires a methylase that adds a methyl group to the ribosomal binding site of azithromycin. What other drug, other than macrolides, will the bacteria be resistant to?
Clindamycin
