antibiotics 2

Question 1

linezolid

Answer 1

an oxazoladinone
inhibits protein synthesis by binding 50S and prevents formation of initiation complex(70s complex)

effective against e faecalis (including VRE vanc resistant), s epidermidis (+MRS), S aureus (+MRSA), s haemolyticus, and s pneumoniae (+pen. resistant)

Question 2

tetracycline

Answer 2

inhibits protein synthesis by binding 30s –> prevents binding of aminoacyl tRNA (elongation)

crosses outer mem using porin channel and inner mem using active transport (mammal cells lack this)

effective for all rickettsiae (rocky mountain spotted fever)

oral; anything else impairs ingestion

penetrates CNS

Question 3

tigecycline

Answer 3

a glycylcyline that inhibits protein synthesis by binding 30s and prevents A site aminoacyl tRNA elongation

good for tetracycline resistant strains

Question 4

streptomycin

Answer 4

an aminoglycoside; inhibits protein synthesis by binding 30s (in the 16s rRNA) and interfering with initiation complex –> causes misreading of mRNA

broad bactericidal but primarily gram -
(cross outer mem via porin ch and cross inner by active transport)
transport is also oxygen dependent (inactive for anaerobes)

Give IV or IM —-has a polycationic charge –> poor absorption orally

low accumulation in CSF

synergistic with B lactams and has a post-antibiotic effect

Question 5

chloramphenicol

Answer 5

binds to 50s and inhibits peptidyl transferase step of protein synthesis

only used for infections when benefit >risk of toxicity

broad bacteriostatic
bactericidal for h influenzae, strep pneumoniae, and N meningitidis

enters CNS and crosses placenta

Question 6

erythromycin

Answer 6

a macrolide that binds 50s and inhibits the translocation step of protein synthesis

inactivated by gastic acid but absorbed by upper small intestine

Question 7

streptogramins

Answer 7

streptogramin A and B

A binds nearby and induces a conformational change in the 50s subunit –> enhances B binding
B binds 50s and inhibits translocation step (same site at macrolides)

USE FOR vancomycin resistant e faecium or multidrug resistant gram + orgs

Question 8

clindamycin

Answer 8

a lincosamide that binds the P and A sites in the 50s and suppresses protein synthesis

effective for macrolide resistant strains and against anaerobes

goes to bone and crosses placenta but not CNS

Question 9

nitrofurantoin

Answer 9

many actions: causes DNA damage, and also inhibits ribosomal proteins and bacterial enzymes

USE ONLY FOR UTI due to e coli, s aureus, and e faecalis

not effective for acinetobacter, peudomonas, or proteus

Question 10

bacteria have what type of ribosome?

Answer 10

70s

mammals have 80s

Question 11

mechanisms of tetracycline resistance

Answer 11

decreased influx or acquisition of efflux pumps

decreased access to ribosome due to protecting proteins (TetO genes)

enzymatic inactivation of the drug (TetX gene)

Question 12

side effects of tetracycline

Answer 12

GI –> pseudomembranous enterocolitis
teeth and bone issues in pregnant women and kids

Iv can cause venous thrombosis; IM can cause painful irritation

hepatic toxicity (liver accumulation)

photosensitivity

Question 13

tigecycline resistance

Answer 13

it is a substrate for TetX –> bacterial strains with tetX gene are resistant

Question 14

tigecycline is recommended for

interacts with

Answer 14

adults, not kids or pregnant women

warfarin and oral contraceptives

Question 15

streptomycin is synergistic with…

Answer 15

B lactams

Question 16

resistance against streptomycin

Answer 16

acquire inactivating enzymes (acetylases, adenylases, phosphorylases (plasmid encoded)

Question 17

side effects of streptomycin

Answer 17

ototoxicity
nephrotoxocity
curare-like NM blockade –> respiratory peralysis
dermatitis and nerve dysfunction

Question 18

chloramphenical crosses placenta…why cant infants process it?

Answer 18

it requires hepatic function for urine secretion)

Question 19

chloramphenicol side effects

Answer 19

TOXIC
anemia

inhibits mammal 70s protein synthesis

gray baby syndrome - infant toxicity = vomiting, flaccid, hypothermia, resp. distress, gray pallor, and shock due to inadequate glucuronic acid conjugation or inadequate renal excretion

inhibiting CYP3A4 –> prolong drug half lives

antagonist to macrolides and clindamycin (competes for same binding site)

Question 20

resistance to erythromycin (macrolide)

Answer 20

ATP efflux pump

methylase that modifies the ribosomal target = decreased drug binding

MLSb determinants: resistance to macrolides, lincosamides, and streptogramin B

hydrolysis by esterases

mutation of ribosome - specifically the 23 s rRNA to which the macrolides bind

Question 21

side effects of erythromycin

Answer 21

GI motility
cholestatic hepatitis
cardiac arrhythmias (long QT with VT)

inhibits CYP3A4 and p450s –> MANY drug interactions

Question 22

resistance to clindamycin

Answer 22

plasmid encoded MLSb

constitutive production of methylase

Question 23

clindamycin side effects

Answer 23

modification of GI flora can lead to life threatening pseudomembranous enterocolitis with c dificile overgrowth

can inhibit neuromuscular transmission

rashes common in HIV patients

Question 24

side effects of streptogramins

Answer 24

infusion-related pain and phlebitis
arthralgias
myalgias