Folic Acid

Question 1

Sulfonamides

Answer 1

1. ​Sulfamethoxazole (SMX) (short acting)
2. Sulfisoxazole (topical)
3. Sulfadiazine (short acting)

Question 2

Sulfonamide mechanism

Answer 2

Inhibit folate synthesis. Para-aminobenzoic acid (PABA) antimetabolites inhibit dihydropteroate synthase.

Bacteriostatic (bactericidal when combined with trimethoprim).

(Dapsone, used to treat lepromatous leprosy, is a closely related drug that also inhibits folate synthesis.)

Question 3

Sulfonamide clinical use

Answer 3

1. Gram-positives
2. gram-negatives
3. Nocardia
4. Chlamydia
5. Triple sulfas or SMX for simple UTI

Question 4

Sulfonamide toxicity

Answer 4

1. Hypersensitivity reactions
2. hemolysis if G6PD deficient
3. nephrotoxicity (tubulointerstitial nephritis)
4. photosensitivity
5. kernicterus in infants
6. displace other drugs from albumin (e.g., warfarin)

Question 5

Sulfonamide resistance

Answer 5

Altered enzyme (bacterial dihydropteroate synthase), ↓ uptake, or ↑ PABA synthesis.

Question 6

Trimethoprim mechanism

Answer 6

Inhibits bacterial dihydrofolate reductase.

Bacteriostatic.

Question 7

Trimethoprim clinical use

Answer 7

Used in combination with sulfonamides (trimethoprim-sulfamethoxazole [TMP- SMX]), causing sequential block of folate synthesis.

Combination used for

1. UTIs
2. Shigella
3. Salmonella
4. Pneumocystis jirovecii pneumonia treatment and prophylaxis
5. toxoplasmosis prophylaxis

Question 8

Trimethoprim toxicity

Answer 8

1. Megaloblastic anemia
2. leukopenia
3. granulocytopenia

(May alleviate with supplemental folinic acid)