Flashcards in Sulfonamides and Quinolones Deck (58)
what is prontosil?
prodrug of the active sulfonamide, p-aminobenzenesulfonamide
competitively inhibit dihydropteroate synthase, preventing incorporation of PABA into folic acid nucleus
(bioisosteres of PABA)
why do sulfonamides not affect human cells?
mammal cells use preformed folates in diet, while some bacteria make their own folic acid
alternate sulfonamide MOA
antimetabolite: some strains use drug as a substrate, but then the product is not capable of the next rxn
can sulfonamide action be reversed?
yes- increase [PABA]
describe PABA vs. sulfanilamide activity at physio pH
-why is this a problem?
-how it is overcome?
PABA pKa 6.5 -> anion at physio pH
sulfanilamide pKa 10.4 -> weak acid a physio pH
fix by attaching an e- withdrawing heteroaromatic ring to acidify the sulfonamide N and increase potency (due to electronegativity of R + resonance stabilization of anion)
what side effect does the increase in acidity of sulfonamides with a more EN R group mediate?
increased acidity causes decreased incidence of crystalluria
specific names of 9 sulfonamide drugs
sulfasalizine (different MOA)
general uses of sulfonamides
G(+) and G(-)
how are sulfonamides normally given? what is one example and what is it used for
combinations: Bactrim (TMP-SMX)
-used for AIDS pneumocystis
MOA of TMP (trimethoprim)
inhibits DHFR, a sequential step in the THF synthesis pathway past where sulfamethoxazole works on DHPS
most popular sulfonamide and use?
sulfisoxazole - UTIs
what is the triple sulfas combination and what does it treat?
1:1:1 sulfabenzamide, sulfacetamide, sulfathiazole
-used for Gardnerella vaginalis
what are the triple sulfas also combined with? what does this treat?
triple sulfas + phenylpropanolamine-pheniramine p.o.
pheniramine = antihistamine to decrease inflammation
what sulfonamide is different than the rest? why and what does it treat?
prodrug is not well-absorbed by GI: bacteria metabolize it to 5-aminosalicylic acid (anti-inflammatory)
-used for ulcerative colitis and Crohn's disease
-SE: irritates gastric mucosa, but not as badly as other salicylates
long-acting: prevents/treats malaria (inhibits falciparum DHFR)
what is sulfadoxine often combined with and what is this combo called?
sulfadoxine + pyrimethamine = Fansidar
first line chemo for acute toxoplasmosis
AE of sulfonamides: general mechanisms
-these drugs used for more than abx activity:
-sulfonyurea hypoglycemic agents (tolbutamide)
most common AE of sulfonamides
allergies: rash, photosensitivity, drug fever
rare AE of sulfonamides
crystalluria and hematopoietic disturbances
three mechanisms of sulfonamide resistance
1. overproduction of PABA
2. decrease affinity of DHPS for drug
3. decrease cell permeability to drug
how common is sulfonamide resistance? implications?
common- no longer used as single-use dudes
mechanism of resistance to TMP
plasmid borne version of DHFR
-distributed more rapidly than sulfas
-T1/2 = 10-12h
-drug + inactive metabolites cleared in urine
-widely distributed, including CSF (but not as distributed as TMP b/c differences in lipophilicity)
-T1/2 = 10-12h
metabolized by N-4 N-acetylation, sometimes N-1 glucuronidation -> inactive
-hydroxylamine + nitroso metaoblites toxic
division of humans in terms of sulfonamide metabolism
fast and slow acetylators-> affects metabolism