Streptogramin Antibiotics and Oxazolidinone Antimicrobial Agents

Question 1

Synercid is a mixture containing?

Answer 1

30% quinupristin and 70% dalfopristin

Question 2

Are quinupristin and dalfopristin useful on their own?

Answer 2

No, each of these compounds is bacteriostatic alone, but bactericidal in combination

Question 3

Dalfopristin MOA

Answer 3

directly interferes with the peptidyl transferase-catalyzed step

Question 4

What reaction does peptidyl transferase (ribosomal RNA) catalyze?

Answer 4

catalyzes the formation of a peptide bond between the two amino acids present in the ribosome

Question 5

Quinupristin MOA

Answer 5

binds in the ribosomal tunnel and causes blockage of the tunnel

Question 6

Syncercid is used IV for treatment of:

Answer 6

1. Vancomycin-resistant Enterococcus faecium bacteremia
2. Skin infections caused by MRSA
3. Vancomycin-resistant Enterococcus faecium urinary tract infections

Question 7

Most common resistance to quinupristin is due to?

Answer 7

adenine methylation of A2058 in the 23S rRNA as in the case of erythromycin and clindamycin

Question 8

What can resistance to Streptogramin also be caused by?

Answer 8

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

Question 9

What is Streptogramin likely to be reserved for?

Answer 9

reserved for serious life-threatening infections caused by gram (+) organisms

Question 10

Mild side effects of synercid?

Answer 10

inflammation and pain at the site of injection, nausea, diarrhea, muscle weakness and rash

Question 11

Drug interactions of Streptogramins

Answer 11

Streptogramins inhibit cytochrome CYP3A4

Question 12

CYP3A4 metabolizes

Answer 12

warfarin, diazepam, astemizole, terfenadine, cisapride, non-nucleoside reverse transcriptase inhibitors and cyclosporine

Question 13

Oxazolidinones are a novel class of antimicrobials that act by

Answer 13

inhibiting protein synthesis

Question 14

MOA of linezolid?

Answer 14

acts early by potent interaction with 50S ribosomal subunit

Question 15

In the initiation step of bacterial translation, the 50S subunit associates with?

Answer 15

associates with fMet-tRNA and a complex composed of the 30S ribosomal subunit and mRNA to form the functional 70S initiation complex

Question 16

What does linezolid have affinity for?

Answer 16

the 50S subunit - no affinity to the 30S subunit

Question 17

Linezolid interaction with the 50S subunit does what?

Answer 17

prevents the formation of the 70S initiation complex

Question 18

Which rRNA does linezolid specifically interact with?

Answer 18

the 23S rRNA

Question 19

Linezolid is used to treat:

Answer 19

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 20

Emergence of linezolid resistant has been reported in which species?

Answer 20

Enterococcus species, MRSA, and E. coli

Question 21

Other mild reported side effects of linezolid?

Answer 21

headache, tongue discoloration and oral Monilia (Candida) infections

Question 22

More serious side effects of linezolid?

Answer 22

thrombocytopenia, GI bleeding and anemia

Question 23

Long-term treatment of linezolid resulted in?

Answer 23

fully reversible myelosuppression and linezolid-induced neuropathy

Question 24

What should be monitored weekly in patients receiving linezolid?

Answer 24

complete blood counts

Question 25

Linezolid is a reversible, nonselective inhibitor of

Answer 25

monoamine oxidase

Question 26

Patients taking linezolid should not consume large quantities of?

Answer 26

food or beverages that are rich in tyramine (cheese, red wine) in order to avoid a significant pressor response

Question 27

Because of drug interactions, linezolid has the potential for interaction with?

Answer 27

adrenergic and serotonergic agents

Question 28

What has been observed when linezolid is administered to normotensive subjects?

Answer 28

a reversible potentiation of pressor response to pseudoepherine