Infectious Diseases I: Sulfonamides

Question 1

MOA of sulfamethoxazole (SMX)

Answer 1

inhibits folic acid synthesis by inhibiting the formation of dihydrofolic acid from PABA

Question 2

MOA of trimethoprim (TMP)

Answer 2

inhibits folic acid synthesis by blocking dihydrofolic acid reduction to tetrahydrofolate

Question 3

General coverage of Sulfonamides

Answer 3

GRAM +: 
Staph (including CA-MRSA)
S. pneumo
GRAM -:
Haemophilus
proteus
E coli
Klebsiella
and MORE
Opportunistic infections:
Nocardia
Pneumocystis
Toxoplasmosis

Question 4

What do sulfonamides NOT cover (easier to remember)

Answer 4

Pseudomonas
Entercocci
Atypicals
anaerobes
Group A strep coverage is unreliable

Question 5

Brand names for SMX/TMP

Answer 5

Bactrim
Septra
Sulfatrim

Question 6

Single strength of SMX/TMP

Answer 6

400 mg SMX
80 mg TMP

5:1 ratio

Question 7

Double strength of SMX/TMP

Answer 7

800 mg SMX
160 mg TMP

5:1 ratio

Question 8

Weight based dosing is based on which component of SMX/TMP?

Answer 8

TMP

Usually 10-20 mg/kg/day

Question 9

Typical dose of SMX/TMP for uncomplicated UTI

Answer 9

1 DS tab BID x 3 days

Question 10

SMX/TMP can be used during pregnancy (t/f)

Answer 10

FALSE

Embryofetal toxicity
CI in breastfeeding too

Question 11

SMX/TMP side effects

Answer 11

n/v/d
skin reactions (rash, --> SJS/TEN)
Crystallization in kidneys (drink plenty of water)
photosensitivity
Incr K+
hypoglycemia
Positive Coombs test (aplastic anemia)

Question 12

Common uses of SMX/TMP:

Answer 12

CA-MRSA infections
UTI
PCP treatment and prophylaxis

Question 13

SMX/TMP can significantly increase INR in pts on warfarin (t/f)

Answer 13

TRUE

SMX/TMP are inhibitors of CYP 2c8/9

Question 14

SMX/TMP can increase the levels of these drugs (6 total):

Answer 14

Sulfonylureas
metformin
phenytoin
azathioprine/mercaptopurine
dofetilide
methotrexate

Question 15

SMX/TMP renal dosing:

Answer 15

CrCL: 15-30: adjustment required

CrCL < 15: do not use