Antibacterials: Sulfonamides

Question 1

Trimethoprim

Answer 1

• family: sulfonamide
• mechanism: Inhibits dihydrofolate reductase–> stops folic acid reduction to tetrahydrofolate
• kinetics: oral intermediate-acting, concentrates in prostatic and vaginal fluids
• clinical: UTI, treat a variety of infections (such as MRSA) when used w/SMX
• toxicity/interactions: megaloblastic anemia, leukopenia, and granulocytopenia
• misc: when used w/SMX–>sequential blockade of folate synthesis; IV TMP-SMX is used for pneumocystis pneumonia

Question 2

Sulfamethoxazole

Answer 2

• family: sulfonamide
• mechanism: Inhibitor of folate synthesis: competitively inhibit dihydropteroate synthase b/c it’s structurally similar to PABA
• kinetics: oral short- to medium-acting
• clinical: UTI, treat a variety of infections (such as MRSA) when used w/TMP
• toxicity/interactions: hypersensitivity (allergic reactions), nausea, vomiting, diarrhea, hematotoxicity, nephrotoxicity; warfarin and methotrexate can increase plasma levels of sulfonamides
• misc: when used w/TMP–>sequential blockade of folate synthesis; IV TMP-SMX is used for pneumocystis pneumonia

Question 3

Sulfisoxazole

Answer 3

• family: sulfonamide
• mechanism: Inhibitor of folate synthesis: competitively inhibit dihydropteroate synthase b/c it’s structurally similar to PABA
• kinetics: oral short- to medium-acting
• clinical: UTI
• toxicity/interactions: hypersensitivity (allergic reactions), nausea, vomiting, diarrhea, hematotoxicity, nephrotoxicity; warfarin and methotrexate can increase plasma levels of sulfonamides

Question 4

Sulfadiazine

Answer 4

• family: sulfonamide
• mechanism: Inhibitor of folate synthesis: competitively inhibit dihydropteroate synthase b/c it’s structurally similar to PABA
• kinetics: oral intermediate-acting
• clinical: toxoplasmosis (when used with pyrimethamine)
• toxicity/interactions: hypersensitivity (allergic reactions), nausea, vomiting, diarrhea, hematotoxicity, nephrotoxicity, crystalluria; warfarin and methotrexate can increase plasma levels of sulfonamides

Question 5

Sulfasalazine

Answer 5

• family: sulfonamide
• mechanism: Inhibitor of folate synthesis: competitively inhibit dihydropteroate synthase b/c it’s structurally similar to PABA
• kinetics: oral nonabsorbable
• clinical: ulcerative colitis, enteritis, and other inflammatory bowel disease
• toxicity/interactions: hypersensitivity (allergic reactions), nausea, vomiting, diarrhea, hematotoxicity, nephrotoxicity; warfarin and methotrexate can increase plasma levels of sulfonamides

Question 6

Sulfacetamide

Answer 6

• family: sulfonamide
• mechanism: Inhibitor of folate synthesis: competitively inhibit dihydropteroate synthase b/c it’s structurally similar to PABA
• kinetics: topical
• clinical: bacterial conjunctivitis, trachoma
• toxicity/interactions: hypersensitivity (allergic reactions), nausea, vomiting, diarrhea, hematotoxicity, nephrotoxicity; warfarin and methotrexate can increase plasma levels of sulfonamides

Question 7

Sulfadoxine

Answer 7

• family: sulfonamide
• mechanism: Inhibitor of folate synthesis: competitively inhibit dihydropteroate synthase b/c it’s structurally similar to PABA
• kinetics: oral long-acting
• clinical: 2nd line treatment for malaria (used with pyrimethamine)
• toxicity/interactions: hypersensitivity (allergic reactions), nausea, vomiting, diarrhea, hematotoxicity, nephrotoxicity; warfarin and methotrexate can increase plasma levels of sulfonamides