Inhibits dihydropteroate synthase which is involved in the first step of the synthesis of folic acid.

Para-aminobenzoic (PABA)+ Pteridine --> Dihydropteroic Acid (immediate precursor of folic acid)

Glutamate is then added to make FH2 which is reduced by dihydrofolate reductase (DHFR) to make FH4. FH4 is used in a 1-carbon transfer reaction to make thymidine. If you don't have folic acid you can't do this 1-carbon transfer and can't make thymidine --> no DNA synthesis.

Doesn't affect humans because we get folic acid from our diet.

Generally used with DHFR inhibitors for a synergistic effect.

DHFR

inhibits bacterial DHFR

Side effects: blood dyscrasias

DHFR

antimalarial; inhibits protozoal DHFR

DHFR

inibits mammalian, bacterial, and protozoal DHFR

used to treat psoriasis and various cancers

Orally absorbed Sulfonamide

Available alone or with erythromycin (a macrolide) in generic forms for kids with otis media

Sulfamethoxazole

aka SMZ

Orally absorbed Sulfonamide

Available with trimethoprim (aka TMP) (Bactrim; Septra)

aka Co-Trimoxazole

only sold as TMP-SMZ

used for various urinary, respiratory, and GI infections

Topical Sulfonamide

used for:

Ulcerative blepharitis (usually S. aureus and S. epidermidis)

Bacterial conjunctivitis (S. aureus, Strep pneumoniae, H. influenzae,and Moraxella catarrhalis)

Topical Sulfonamide

Used for burns to prevent sepsis. Silver is toxic to microorganisms.

Topical Sulfonamide

Used for burns (limited use).

Can cause metabolic acidosis by inhibiting carbonic anhydrase (loss of HCO3- and thus loss of buffering capacity)

• Crystalluria - recommend drinkings lots of water with oral dose to prevent nephrotoxicity
• Kernicterus - juandice caused by displacement of bilirubin from plasma proteins. Bilirubin enters CNS and deposits in basal ganglia (avoid in last 2 months of pregnancy)
• Bloody Dyscrasias - acute hemolytic anemia, agranulocytosis, aplastic anemia.
• Hypersensitivity - by any route
  • Erythema Multiform - sudden onset of asymptomatic macules, papules, and vesicles on extremites and face
  • Stevens-Johnson Syndrome - fever, headache, cough, & conjunctivitis followed by macules on face, neck, and other areas eventually forming bullous eruptions on skin and mucous memranes
  • Drug Fever