Sulfonamides, Trimethoprim, Nitrofurantoin and Methanamine

Question 1

Sulfonamides MOA:

Answer 1

Competes with PABA for the enzyme dihydropteroate synthetase (PABA –> Folic Acid).

Question 2

Sulfonamides excretion:

Answer 2

Excreted via glomerular filtration.

Question 3

Sulfonamide ADRs (6):

Answer 3

• Anaphylaxis.
• Cutaneous reactions.
  > Including SJS.
• Hematologic reactions.
• Hypersensitivity reactions.
• Nephrotoxicity.
• Kernicterus.
  > When given in last months of pregnancy.

Question 4

Sulfonamides spectrum of action (11):

Answer 4

G+:
- MRSA
- Strep
- Bacillus anthracis
G-:
- Piddly
- PEK
- Citrobacter
- Enterobacter
Other:
- Chlamydia trachomatis
- Toxoplasma gondii
- Plasmodium falciparum
- Nocardia

Question 5

Sulfonamides mechanism of resistance:

Answer 5

• Overproduction of PABA.
• Structural change in dihydropteroate synthetase.
• Decreased permeability of the bacteria to the drug.

Question 6

Indications for sulfonamides (6):

Answer 6

• Acute uncomplicated UTI.
• Pneumocystis carinii.
• Nocardosis.
• Malaria.
• Rheumatic fever prophylaxis.

Question 7

Trimethoprim MOA:

Answer 7

Inhibits dihydrofolate reductase which prevents the formation of tetrahydrofolic acid.

Question 8

Trimethoprim ADRs (4):

Answer 8

• Cutaneous reactions.
• GI reactions.
• Hematologic reactions.
• Caution in pts with possible folate deficiency.

Question 9

Trimethoprim spectrum of activity

Answer 9

G+:
- Staph
- Strep
- Bacillus anthracis
G-:
- Piddly
- PEK
- Citrobacter
- Enterobacter
Other
- Pneumocystis carinii (with dapsone)

Question 10

Indications for trimethoprim:

Answer 10

• Acute uncomplicated UTI.
• Recurrent UTI prophylaxis.
• Traveler’s diarrhea.

Question 11

Trimethoprim/sulfamethoxazole (bactrim) indications:

Answer 11

• UTI.
• RTI.
• GI infections.
• STDs.

Question 12

SMZ/TMP (bactrim) drug interactions:

Answer 12

• Warfarin.

- Methotrexate.

Question 13

Nitrofurantoin ADRs (6):

Answer 13

• Hypersensitivity.
• Hematologic reactions.
• Hepatotoxicity.
• Peripheral neuropathy.
• GI reactions
• Pulmonary reactions

Question 14

Nitrofurantoin spectrum of activity

Answer 14

G+:
- Staph aureus
- Staph saprophyticus
- Enterococcus
G-:
- E. coli
- Klebsiella pneumonia
- Citrobacter spp.
- Enterobacter aerogenes

Question 15

Indications for nitrofurantoin:

Answer 15

• Acute uncomplicated UTI tx.

- UTI prophylaxis.

Question 16

Methenamine MOA:

Answer 16

At urine pH hydrolyzed to formaldehyde which kills by denaturing proteins.

Question 17

Methenamine ADRs:

Answer 17

• Hypersensitivity
• Hemorrhagic cystitis
• GI reactions
• Avoid in hepatic insufficiency
• Renal failure