Introduction to Anti-Microbials

Question 1

TMP-SMX

Answer 1

Co-trimoxazole (combination of trimethoprim and sulfonamides

Broad activity- gram negatives, Staph. aureus, some protozoa and fungi, UTIs, respiratory and GI tracts

common side effects include rash, nausea, vomiting, headache
severe but rare- Stevens Johnson Syndrome

Question 2

Trimethoprim

Answer 2

inhibits Dihydrofolate Reductase to prevent dihydrofolic acid being converted to tetrahydrofolic acid

becomes resistant by acquiring a plasmid encoding alternative dhfr gene

teratogen

Question 3

Sulfonamide

Answer 3

Inhibits Dihydropteroate Synthetase which is not found in humans- prevents creation of dihydropteroic acid
rarely used alone (combine with trimethoprim)

can become resistant due to chromosomal mutation or acquiring plasmid encoding alternative alleles of gene encoding synthetase

displaces bilirubin in fetuses and can cause Kernicterus (not used in pregnancy)

Question 4

Quinolones

Answer 4

DNA inhibitors
Bactericidal
broad activity against gram negative
topo II inhibition is important for gram negative
topo IV inhibition is important for gram positive
active against “atypicals” and mycobacteria
good oral bioavailability, but needs to be taken at different times than divalent cations

Question 5

Ciprofloxacin

Answer 5

primarily targets topo II (DNA inhibitor)

poor activity against strep

Question 6

Moxifloxacin

Answer 6

DNA inhibitor

gram positive, gram negative, and anaerobic activity
poor penetration into urinary tract, so bad choice for UTI

Question 7

Fluoroquinolone adverse effects

Answer 7

common problems- nausea, headaches, vomiting, dizziness, abdominal pain
serious adverse effects- can prolong QT interval in combination with other drugs; tendon rupture

Question 8

Nitrofurantoin

Answer 8

exclusively used for UTIs
common side effect- nausea
rare- pulmonary fibrosis

damages DNA

Question 9

Rifamycin

Answer 9

RNA inhibitor
binds to beta subunit of RNA polymerase and blocks transcription
bactericidal

resistance due to mutations in binding site

metabolized by cytochrome P450 3A4

side effects:
turns secretions orange
pain, nausea, vomiting, diarrhea
hepatitis due to liver damage

Question 10

Rifampin

Answer 10

RNA inhibitor (rifamycin)

potent inducer of cyp450 3A4
can increase metabolism of many drugs

used for prophylaxis (ex: after exposure to meningitis)

Question 11

Rifabutin

Answer 11

RNA inhibitor (rifamycin)

Question 12

Rifaximin

Answer 12

RNA inhibitor (rifamycin)
not absorbed at all--> stays in GI tract

used for GI infections - such as traveler’s diarrhea

Question 13

Fidaxomicin

Answer 13

RNA inhibitor–> RNA polymerase blocker
non-absorbable oral antimicrobial
poor activity against gram negative enteric flora (including gram negative anaerobes)
used in C. difficile treatment