Sulfonamides/Potentiated Sulfonamides

Question 1

How do sulfonamides work?

Answer 1

Disruption of DNA synthesis by competition with PABA.. These drugs DO NOT target mammalian cells.

Question 2

Do sulfonamides work in purulent debris?

Answer 2

Purulent debris decreases activity.

Question 3

Resistance mechanisms:

Answer 3

Both chromosomal and plasma-mediated. Overwhelm mechanisms to outcompete sulfonamide.

Question 4

What groups are sulfas split into?

Answer 4

Short acting, Intermediate acting (loading dose may be given), long acting (loading dose may be given), Enteric sulfas

Question 5

What do sulfas work on?

Answer 5

There is too much resistance for empiric use of sulfas. Used against coccidia and nocardia, and also combined with other agents to enhance antimicrobial/protozoal activity.

Question 6

What are administration routes for sulfas?

Answer 6

Mostly oral with some parenteral, but too irritating to give IM or SubQ

Question 7

Do sulfas concetrate intra- or extracellularly?

Answer 7

Extracellularly, and do not cross barriers well. EXCEPT sulfadiazine!!

Question 8

How are sulfas eliminated?

Answer 8

Renal, but can be nephrotoxic due to crystalluria (biotransformation).

Question 9

Are sulfas bactericidal and bacteriostatic?

Answer 9

Bacteriostatic

Question 10

Are sulfas time or concentration dependent?

Answer 10

Time dependent.

Question 11

Adverse reactions to sulfas:

Answer 11

Type A - Crystalluria, drug interactions, hemorrhagic syndrome in chickens.
Type B - Dry eye, polyarthropathy, hepatotox, cutaneous drug eruptions, hypothyroidism. These Type B reactions occur especially in Dobermans.

Question 12

Regulatory issues may be common with sulfas.

Answer 12

Green gut syndrome in calves - stains gut for short period of time. Helps ID test tissues for residues. Feed mill cleaning is essential so healthy cows do not test positive for residues. Copraphagia in pigs may lead to positive test for residues.
NO extra label use in dairy cattle!

Question 13

Are potentiated sulfas lipid or water soluble?

Answer 13

Lipid soluble, so they cross the BBB.

Question 14

How do potentiated sulfas work?

Answer 14

They also work to inhibit DNA production, but they inhibit DHFR not PABA. Synergystic!!

Question 15

Resistance mechanisms to potentiated sulfas:

Answer 15

Plasma mediated, with resistance often developing quickly when these are used as individual agents.

Question 16

What do potentiated sulfas work on?

Answer 16

Broad spec, except anaerobes. NO special spec action. Coccidia, Nocardia (drug of choice), and Toxoplasma (pyrimethamine)

Question 17

What are some potentiated sulfas?

Answer 17

Trimethoprim + Sulfadiazine (TMS)
Trimethoprim + Sulfamethoxazole (Bactrim)
Ormethoprim + Sulfadiazine
Pyrimethamine + Sulfadiazine

Question 18

What are potentiated sulfas?

Answer 18

Sulfonamides with Diaminopyrimidines
Trimethoprim and Ormethoprim: Bacterial –> Protozoal –> Mammalian
Pyrimethamine: Protozoal –> Mammalian –> Bacterial

Question 19

How are potentiated sulfas absorbed?

Answer 19

Orally, especially in small animals. NOT in ruminants.

Injectables given IV, too irritating for IM and subQ

Question 20

How are potentiated sulfas eliminated?

Answer 20

Pyrimethamine - Hepatic

Thrimethoprim - Renal

Question 21

Are potentiated sulfas bactericidal or bacteriostatic?

Answer 21

Bactericidal

Question 22

Are potentiated sulfas time or concentration dependent?

Answer 22

Time dependent

Question 23

Adverse rxns to potentiated sulfas:

Answer 23

Similar to sulfas.

Type A - May also cause bone marrow suppression/teratogenesis. Give folinic acid as antidote.