ANTIBIOTICS II 2

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What makes these antibiotics selective?: Bacteria have 70$ ribisomes whereas mammalian cells have 80$ ribosomes.
Where does Linezolid bind and what does it prevent?: Linezolid (an oxazoladinone) bind the 50$ and prevents formation of the initiation complex.
Where do Tetracyclines bind and what does they prevent?: Tetracyclines bind the 30$ and prevent binding of aminoacyl tRNA.
Where do aminoglycosides bind and what does they prevent?: Aminoglycosides bind the 30$ and interfere with the initiation complex and cause MISREADING of mRNA.
Where does Chloramphenicol bind and what does it prevent?: Chloramphenicol binds 50$ and inhibits PEPTIDYL TRANSFERASE.
Where do Macrolides, Lincosamides, typeB Streptogramins and Ketolides bind and what does they prevent?: These drugs bind 50$ and inhibit TRANSLOCATION.
What is one antibiotic combination to avoid?: Because of the close proximity of the binding between Chloramphenicol, Clindamycin and Macrolides, binding of one may block the binding of others.
What action does the Oxazolidinone LINEZOLID have?: Binds 50$, prevents formation of initiation complex.

Bacteriostatic for G+, also a weak nonspecific MAOI (caution in people taking seritonergics)
What action do the Tetracyclines have?: Broad Spectrum bacteriostatic activity against G +/- aerobic & anaerobic bacteria.
Name the tetracyclines.: Tetracycline, Doxycycline and Minocycline.
Whats up with doxycycline and minocycline?: They have more lipophilic substituents and are most active by weight. This is because the absorption of these drugs is not impaired by food, as in all the other tetracyclines.
What are the adverse effects of Tetracyclines?: Crosses the placenta. Tx of pregnant women or kids< 8 yo will result in discolored teeth and bone deformation.

IM administration causes painful local irritation.
What are the aminoglycosides? (8): Streptomycin
Neomycine
Gentamycin
Kanamycin
Tobramycin
Sisomycin
Amikacin
Netilmicin
What is the action of the Aminoglycosides?: They bind the 30$ subunit and interfere with the initiation complex, cause misreading and premature chain termination.
Broad bactericidal activity, primarily against G- bacteria.
What about the pharmacokinetics of the aminoglycosides?: They have a significant PAE.

In G- bacteria, the drugs cross the outer membrane via a PORIN channel and cross the inner membrane by O2 dependent active transport.
SYNERGISM occurs when administered with Beta-lactam antibiotics.
What are the adverse effects of the aminoglycosides?: Ototoxicity
Nephrotoxicity
Curare-like neuromuscular blockade w high doses
What is the action of Chloramphenicol?: Broad spectrum, bacteriostatic for most bacteria, bacterioCIDAL for meningeal pathogens.
Binds 50$ and inhibits peptidyl transferase.
What are the adverse effects of Chloramphenicol?: Direct effects on bone marrow: Dose realted normocytic anemia and idiosyncratic blood dyscrasias including APLASTIC ANEMIA!
What is Gray baby syndrome?: Gray baby syndrome- vomiting, flaccidity, hypothermia, resp distress, gray pallor and shock (40%fatality)

mechanism: inadequate glucuronic acid conjugation and inadequate renal excretion of the unconjugated drug.
What is the MLS group of antibiotics?: Macrolides, Lincosamide, and Type B Streptogramin. Ketolide was recently added to this group aswell.
What are the Macrolides?: Erythromycin, Clarithromycin, and Azithromycin
What action do the macrolides have?: They bind the 50$ subunit and inhibit the translocation step of protein synthesis.
They are usually bacteriostatic, but can be bacteriCIDAL in high concentrations.
What is the unique mechanism of macrolide resistance?: Production of a methylase (enzyme know as MLSb determinant) that modifies the ribosomal target, leading to decreased drug binding.
What about hepatic enzymes and the macrolides?: Erythro- and clarithro-(but not azithro) inhibit hepatic enzymes.
Erythro- interactions with liver p450's inhibits the metabolism of a variety of other drugs.
Adverse effects of the macrolides?: GI, hepatic and CARDIAC (arrythmias- QT prolongation w VT)
What is the only Lincosamide we study and what is its action?: Clindamycin.
a congener of lincomycin that has improved pharmacokinetics and less toxicity.
Binds 50$ and inhibits translocation step.
What is the spectrum for the Lincosamide clindamycin?: Broad spectrum, G+ cocci. Good for anaerobes like B Fragilis, clostridium.
Adverse effects of clindamycin?: GI-modification of GI flora can cause pseudomembranous colitis assoc w overgrowth of C. Difficile
NM blockiing
Skin Rashes- more common in HIV pts
What are the Type B Streptogramins?: Synecid is a combination of Streptogramin A (DALFOPRISTIN) and Streptogramin B (QUINUPRISTIN).
How do the Streptogramins work?: Strep B QUINUPRISTIN- binds 50$ inhibits translocation step.
Strep A DALFOPRISTIN- induces a conformational change in 50$ subunit, ENHANCING the binding of quinupristin (strep B)
Spectrum of Streptogramins? Side Effects?: BacteriCIDAL against G+

Pain and phlebitis at site of infusion.
What Ketolide are we studying? Whats its action?: Telithromycin

same binding to 50$ and inhibition of translocation as macrolides BUT is resistant to efflux pumps and has increased ribosomal binding affinity
Why is Telithromycin so cool?: Recently apporved (April 26 2004) it is especially useful in tx of drug resistant respiratory infections.
Used in community aquired pneumonia, acute sinusitis, acute exacerbations of chronic bronchitis and tonsillitis/pharyngitis
What are the side effects of Telithromycin?: similar to macrolides, GI sxs, dizziness and headache.
Telithromycin also inhibits p450 enzyme (CYP34A) and increased serum concentrations of certain drugs.
Which 2 MLS are resistant to efflux pumps?: Telithromycin (ketolide) and Clindamycin (lincosamide)

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