protein synthesis inhibition abx

Question 1

Which antibiotics target which parts of bacterial protein synthesis? Static/cidal designation

Answer 1

30S inhibitors: A and T: aminoglycosides (bactericidal) and tetracycline (static)
50S inhibitors: CELL: chlroamphenicol, clindamycin; erythromycin (macrolides), linezolid. all static except linezolid, which is variable

Question 2

Aminoglycosides: examples, mechanism

Answer 2

gentamicin, neomycin, amikacin, tobramycin, streptomycin.
inhibit the 30S subunit and prevent formation of the initiation complex. cause misreading of mRNA. block translocation. require O2 for uptake, so they are ineffective for anaerobes.
(remember that A initiatiates the alphabet)

Question 3

Aminoglycosides: resistance

Answer 3

all anaerobes are resistant because aminoglycosides require O2 for uptake.
bacteria gain resistance by inactivating the drug: acetylation, phosphorylation, or adenylation

Question 4

Aminoglycosides: use

Answer 4

used for severe gram negative rod infection. synergy with beta lactams. give neomycin for bowel surgery

Question 5

Aminoglycosides: toxicity

Answer 5

nephrotoxicity, esp. when used with cephalosporins, neuromuscular blockade, ototoxicity (esp. when used with loop diuretics), teratogenic

Question 6

tetracycline: mechanism and resistance

Answer 6

bacteriostatic and bind the 30 S subuint. prevent attachment of aminoacyl-tRNA to ribosome (prevents elongation). limited CNS penetration. resistance: decr. uptake or incr. efflux by plasmid-encoded pumps.

Question 7

tetracycline: special considerations

Answer 7

don’t take with milk or antacids or iron-containg preps because divalent cations like Ca, Fe, Mg inhibit tetracycline absorption in the gut

Question 8

tetracycline use

Answer 8

borrelia burdoferi, mycoplasma pneumonia. Accumuates intracellularly, so it works well against rickettsia and chlamydia. used for acne

Question 9

tetracycline toxicity

Answer 9

GI distress, discoloration of teeth and inhibition of long bone growth in kids, photosensitivity. contraindicated in pregnancy

Question 10

Macrolide mechanism and resistance

Answer 10

binds 50S and blocks translocation (mac-no-slides). (binds 23S rRNA). resistance: methylation of 23S rRNA-binding site.

Question 11

Macrolide uses

Answer 11

atypical pneumonias (mycoplasma, legionella, chlamydia), STDs for chlamydia, and gram-positive cocci (step infections in ppl w/ penicillin allergies)

Question 12

Macrolide toxicity

Answer 12

clarithromycin is embryotoxic and should be avoided in pregnancy.
MACRO: GI motility issues, arrhythmia and long QT, acute cholestatic hepatitis, rash, eosiniophilia. incr. serum conc. of theophyllines, oral anticoagulants

Question 13

chloromphenicol mechanism

Answer 13

blocks peptidyl transferase at 50S ribosomal subunit. inactivated by plasmid-encoded acetyltransferace

Question 14

Chloromphenicol use

Answer 14

menigitis (esp. Hib, N. menigitidis, S. pneumo), and Rocky Mountain Spotted fever.
limited d/t toxicities

Question 15

chloramphenicol toxicities

Answer 15

anemia, aplastic anemia gray baby syndrome in premature infants b/c they lack liver UDP-glucuronyl transferase

Question 16

Clindamycin mechanism

Answer 16

blocks peptide transfer (translocation) at the 50 S subunit (much like chloromphenicol).

Question 17

Clindamycin uses

Answer 17

anaerobic infections in aspiration pneumonia, lung abscesses, and oral infections. also effective against invasive GAS infection. (anaerobes above the diaphragm)

Question 18

Clindamycin toxicity

Answer 18

pseudomembranous colitis, fever, diarrhea, C diff.