Streptogramin Antibiotics and Oxazolidinone Antimicrobial Agents

Question 1

Synercid

Answer 1

mixture containing 30% quinupristin and 70%

dalfopristin

Question 2

dalfopristin MOA

Answer 2

During peptide synthesis, when the second tRNA base pairs with the appropriate codon in the mRNA, peptidyl transferase (ribosomal RNA) catalyzes the formation of a peptide bond between the two amino acids present. Dalfopristin directly interferes with the peptidyl transferase-catalyzed step

Question 3

Quinupristin MOA

Answer 3

Quinupristin binds in the ribosomal tunnel and causes blockage of the tunnel (23S rRNA within the ribosome)

Question 4

therapeutic use of Synercid

Answer 4

1.) Vancomycin-resistant Enteroccus faecium bacteremia (it is not effective against Enterococcus faecalis infections). Certain Enteroccus faecium strains are resistant to all
other antibiotics.

2. Skin infections caused by MRSA
3. Vancomycin-resistant Enteroccus faecium urinary tract infections.

Question 5

resistance

Answer 5

The most common resistance to quinupristin is due to adenine methylation of A2058 in the
23S rRNA as in the case of erythromycin and clindamycin.
-Susceptibility of the organism to
dalfopristin is not affected by this rRNA modification

Question 6

more resistance

Answer 6

Resistance can also be due to efflux and enzymatic inactivation (metabolism) by resistant
bacteria.

Question 7

why might Streptogramin be reserved for life threatening infections?

Answer 7

treatment of vancomycin-resistant E. faecium is currently resulting in a 70% cure rate.

Question 8

continued used of Streptogramin in what will cause continued resistance?

Answer 8

animal feed

Question 9

side effects of synercid.

Answer 9

mild side effects have been reported and include inflammation and pain at the site of injection, nausea, diarrhea, muscle weakness and rash.

Question 10

have life of synercid.

Answer 10

1.5 hours

Question 11

does synercid cross BBB or placenta?

Answer 11

no

Question 12

what concentrates synercid concentrations?

Answer 12

Macrophages concentrate the drug up to 50X the extracellular fluid concentration.

Question 13

how is synercid cleared?

Answer 13

75% through biliary excretion (fecal matter) and the remainder appears in the urine

Question 14

what does Streptogramins inhibit?

Answer 14

cytochrome CYP 3A4, which metabolizes warfarin, diazepam, astemizole, terfenadine, cisapride, non-nucleoside reverse transcriptase inhibitors, and
cyclosporine

Question 15

Oxazolidinones block?

Answer 15

inhibit protein synthesis

Question 16

Oxazolidinones MOA

Answer 16

acts early by potent interaction with 50S ribosomal subunit. In the initiation step of bacterial translation, the 50S subunit
associates with fMet-tRNA and a complex composed of the 30S ribosomal subunit and mRNA to form the functional 70S initiation complex. Linezolid interacts with the 50S subunit with micromolar affinity->This interaction prevents the formation of the 70S initiation complex

Question 17

Linezolid interacts with

Answer 17

23S rRNA

-no affinity for 30S

Question 18

Linezolid treats?

Answer 18

1) Vancomycin-resistant Enterococcus faecium
2) Nosocomial pneumonia caused by methacillin–resistant strains of Staphylococcus aureus
3) Skin infections caused by methicillin-resistant strains of Staphylococcus aureus

Question 19

how is Linezolid given?

Answer 19

I.V

-great oral bioavailability

Question 20

when should Linezolid be used?

Answer 20

To reduce the development of drug-resistant bacteria and maintain the effectiveness of linezolid,
it should be used only to treat or prevent infections that are proven or strongly suspected to be
caused by multiply drug-resistant Gram-(+) bacteria.

Question 21

form of resistance to Linezolid

Answer 21

target site modification

• Resistance mutations identified in various species are associated with G to U substitution in the peptidyl transferase center of 23S rRNA at position 2576 and result in reduced affinity of linezolid to the 50S subunit
• other mutations occur near P site

Question 22

side effects of linezolid

Answer 22

GI nausea, vomiting and diarrhea, headache, tongue discoloration and oral Monilia infection

more serious side effects:thrombocytopenia, GI bleeding and anemia

Question 23

what should be monitored for when taking Linezolid

Answer 23

complete blood counts

Question 24

have life of Linezolid

Answer 24

4-6 hours

Question 25

bioavailability of Linezolid

Answer 25

100% after oral administration

Question 26

does Linezolid interact with cytochrome P450’s

Answer 26

No

Question 27

what does Linezolid inhibit?

Answer 27

reversible, nonselective inhibitor of monoamine oxidase

-potential for interaction with adrenergic and serotonergic agents

Question 28

what should patients taking Linezolid avoid?

Answer 28

large quantities of foods or beverages that are rich in tyramine in order to avoid a significant
pressor response

Question 29

difference between pristinamycin Ia and Ib

Answer 29

Ia: has CH3
Ib: has H

Question 30

pristinamycin have antibiotic activity, why aren’t pristinamycin Ia and Ib used

Answer 30

not soluble

Question 31

dalfopristin has the same mechanism has

Answer 31

chlorenphrinacol

Question 32

another name for Linezolid

Answer 32

Zyvox

Question 33

Monilla infection is seen with what?

Answer 33

Linezolid side effects

• candida albicans
• infection called thrush
• suppression of bacteria in mouth and GI tract allows fungal growth to take over

Question 34

food rich tyramine

Answer 34

stilton cheese, red wine, cheddar, camembert cheese, and many others