antibiotics 3

Question 1

sulfamethoxazole

Answer 1

a sulfonamide; inhibits nucleic acid synthesis
–structural analogs and competitive antagonists of PABA at dihydropteroate synthase (1st step of DNA synthesis where PABA –> dyhydropteric acid)

selectivity due to bacteria synthesize folic acid (mammals done)

broad and bacteriostatic
crosses BBB and placenta

Question 2

trimethoprim

Answer 2

a benzylpyrimidine; inhibits nucleic acid synthesis; selective inhibitor of bacterial dihydrofolate reductase (mammal form is less sensitive)

broad and bacteriostatic
oral, crosses BBB and placenta
weak base that can get stuck in prostatic and vaginal fluids

Question 3

ciprofloxacin

Answer 3

(-oxacins are fluoroquinolones)

a fluoroquinolone that inhbiits DNA gyrase –> inhibits DNA replication or transcription by preventing relaxation of supercoiled DNA

bactericidal for gram -

oral; impaired by dairy and antacids
full distribution –> GOOD FOR PROSTATITIS

Question 4

metronidazole

Answer 4

a nitroimidazole; inhibits dna replication by causing strand breaks

USE for anaerobes (anaerobic bacteria have an electron transport protein that reduces the drug to allow strand breakage)
can also use for vancomycin resistant c dificile

bactericidal
oral or IV; enters CNS

Question 5

rifampin

Answer 5

a rifamycin; inhibits RNA synthesis by noncovalently binding to the beta subunit of the DNA-dependent RNA polymerase

bactericidal
USE for gram +: neisseria and mycobacteria
USE as prophylaxis for meningitis from h influenzae or meningococci

causes red orange coloring of tears, urine, feces, and swear

Question 6

sulfonamide (sulfamethoxazole) resistance

Answer 6

decreased permeability/influx
efflux pump
increase PABA synthesis or decreased synthase sensitivity

Question 7

sulfamethoxazole side effects

Answer 7

crystalluria due to drug precipitation

anemia/agranulocytosis

hypersensitivity: rashes, fever, malaise, photosensitivity, stevens-johnson syndrome

potentiates anticoagulants, sulfonylurea hypoglycemic agents and hydantoin antizeizure drug

Question 8

trimethoprim resistance

Answer 8

increased reductase or decreased sensitivity of reductase

Question 9

trimethoprim side effects

how to prevent?

Answer 9

megaloblastic anemia, leukopenia, granulocytopenia

–can be prevented by administering folinic acid!

Question 10

trimethoprim + sulfamethoxazole (TMP/SMX)

Answer 10

synergistic from sequential blockade of folate synthesis

becomes bactericidal

full distribution including prostate and csf

associated with birth defects (not for use in pregnancy)

not recommended for AIDs patients

Question 11

DNA gyrase

Answer 11

bacterial topoisomerase II

not present in mammals

Question 12

ciprofloxacin / fluoroquinolone resistance

Answer 12

decreased affinity of DNA gyrase or topoisomerase 4

Question 13

ciprofloxacin side effects

Answer 13

not for use in pregnancy or kids due to CARTILAGE DAMAGE

N/V, pseudomembranous colitis

increased levels of theophyline drug

Question 14

metronidazole side effects

Answer 14

leukopenia
seizures and peripheral neuropathy after prolonged use

interferes with alcohol metabolicm (disulfuram like reaction = sympathetic symptoms = tachy)

barbiturates induces CPY so metronidazole half life is decreased

Question 15

examples of genetically encoded resistance to
1-glycosaminoacids 
2-beta lactams
3-tetracycline
4-oxazoladinones

Answer 15

1 - change of Dala-Dala substrate
2 - B lactamase
3 - TetO proteins block the antibiotic
4 - mutation of target (23s rRNA of 50s)

Question 16

antibiogram

Answer 16

derived from lab testing of antibiotic sensitivity of bacterial strains based on IN VITRO SENSITIVITY

reflects the sensitivity and resistance of that hospitals specific strains

Question 17

two combos to prevent the development of resistance by blocking two unrelated pathway

Answer 17

• erythromycin and sulfasoxazole (macroline and sulfonamide)

- beta lactam + aminoglycoside (beta lactam pokes holes in cell wall so aminoglycoside can get in more easily)

Question 18

trimethoprim + sulfamethoxazole

Answer 18

combo of a benzylpyrimidine and a sulfonamide)

=sequential inhibition of successive dna metabolism steps; also converts from static to bactericidal

Question 19

to inhibit the inactivating enzyme in resistant orgs, combine amoxicillin with

Answer 19

a beta lactamase inhibitor

clavulonate or sulbactam

Question 20

cilastatin

Answer 20

renal dipeptidase inhibitor

used in resistant bacteria