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Folic acid inhibitors
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Folic acid inhibitors

Folic acid Inhibitors
Because humans do not synthesize folic acid, these antibiotics do not interfere with our own cellular metabolism.
Sulfonamides: Sulfamethoxazole, Sulfisoxazole, and Sulfadiazine
  • Most common uses
– Gram-positive – Gram-negative bacteria – Chlamydiae – Nocardia – Commonly used to treat infections of the urinary and lower respiratory tracts: MRSA pneumonia, Otitis media and some cases of gonorrhea – Trimethoprim is often combined with sulfamethoxazole for bactericidal effects TMP/SMX, aka, Bactrim.
  • Mechanism of Action
– Sulfonamides competitively bind dihydropteroate synthase (in place of para-aminobenzoic acid ((PABA)) Inhibit early steps in folic acid synthesis – Trimethoprim inhibits dihydrofolate reductase
  • Mechanism of Resistance
– Enzyme modification – Reduction of drug uptake – Increased drug efflux – Increased PABA synthesis
  • Adverse effects of Sulfonamides
– Hypersensitivity, with potential for Stevens-Johnson syndrome or toxic epidermal necrolysis – Drug-induced hemolytic anemia, which is more likely in individuals with G6PD deficiencies – Nephrotoxicity – Aseptic meningitis, specifically associated with TMP/SMX
Dapsone
  • Most common uses
– Mycobacteria: Leprosy, dermatitis herpetiformis, and some other skin conditions.
  • Mechanism of Action
– Inhibits Mycobacteria folic acid synthesis via inhibition of dihydropteroate synthase.
  • Adverse effects of Sulfonamides
– Hemolytic anemia, particularly in individuals with G6PD deficiencies.
para-aminosalicyclic acid (PAS)
  • Most common uses
– Mycobacterium tuberculosis
  • Mechanism of Action
– Inhibits folic acid synthesis
  • Adverse effects
– Gastrointestinal upset – Hypersensitivity

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