Sulfonamide Antimicrobial Agents

Question 1

What is inhibited competitively by the sulfonamides?

Answer 1

the incorporation of p-aminobenzoic acid (PABA) into the folic acid nucleus

Question 2

The sulfonamides inhibit?

Answer 2

dihydropteroate synthase

Question 3

Why do sulfonamides have selective toxicity for bacterial cells as opposed to mammalian cells

Answer 3

mammalian cells utilize preformed folates in the diet and some bacterial cells are required to make their own folic acid

Question 4

How can the antibiotic activity of sulfonamides be reversed?

Answer 4

by adding large quantities of PABA to the diet

Question 5

Sulfonamides in general inhibit?

Answer 5

gram (+) and gram (-) bacteria
nocardia
Chlamydia trachomatis
some protozoa and fungi
enteric bacteria such as E. coli, Klebsiella, salmonella, shigella and enterobacter

Question 6

Why are sulfonamides usually used in combination

Answer 6

the resistance factors are too widespread for these drugs to be used in a single drug therapy

Question 7

What is the antifungal activity of trimethoprim-sulfamethoxazole important for?

Answer 7

the treatment of AIDS-infected patients that have developed Pneumocystis carinii (jiroveci)

Question 8

What does trimethoprim inhibit?

Answer 8

dihydrofolate reductase

so combination with sulfamethoxazole inhibits sequential steps in the biosynthesis of tetrahydrofolic acid

Question 9

Most popular sulfonamide

Answer 9

sulfisoxazole (broad spectrum antibiotic activity)

Question 10

Sulfisoxazole and sulfamethoxazole are mainly used to treat

Answer 10

simple urinary tract infections

Question 11

used as a cream to treat vaginal infections by Gardnerella vaginalis

Answer 11

1:1:1 combination of sulfabenzamide, sulfacetamide, and sulfathiazole (triple sulfas)

Question 12

Triple sulfas-phenylpropanolamine-pheniramine is also used to treat

Answer 12

used orally in tablet/suspension to treat sinus and throat infections

Question 13

What is sulfasalizine used to treat

Answer 13

ulcerative colitis and Crohn’s disease

Question 14

Direct administration of salicylates, including 5-aminosalicyclic acid is?

Answer 14

irritating to the gastric mucosa

Question 15

What is sulfadoxine?

Answer 15

long-acting sulfonamide used with pyrimethamine to prevent and treat malaria

Question 16

What is pyrimethamine

Answer 16

inhibitor of Plasmodium falciparum dihydrofolate reductase

Question 17

first-line chemotherapy to treat acute toxoplasmosis

Answer 17

sulfadiazine in combination with pyrimethamine

Question 18

All sulfonamides and their derivatives are?

Answer 18

cross-allergenic

Question 19

sulfonamide derivates in use include

Answer 19

carbonic anhydrase inhibitors, thiazides, furosemide, sulfonylurea hypoglycemic agents etc

Question 20

Most common adverse reactions of sulfonamides

Answer 20

allergic reactions - present as rash, photosensitivity, and drug fever

Question 21

potentially fatal adverse reaction of sulfonamides

Answer 21

Stevens-Johnson syndrome: rare skin and mucous membrane rash tha tis potentially fata

Question 22

Other adverse reactions of sulfonamides

Answer 22

crystalluria and hematopoietic disturbances: asplasmic anemia, granulocytopenia, and thrombocytopenia
anorexia, nausea, and vomiting occurs in 1-2%

Question 23

Resistance to sulfonamides occurs through the following mechanisms

Answer 23

1. mutations that cause overproduction of PABA
2. mutations in dihydropteroate synthase that decreases its affinity for the sulfonamides
3. mutations that result in a decrease in cell permeability to the sulfonamides

Question 24

Why do you always give sulfonamides in combination

Answer 24

resistance is very common
resistance to combination therapy targeting two enzymes in highly reduced since the microorganism wold have to carry mutations in two enzymes

Question 25

What happens when the dihydrofolate reductase (DHFR) gene is mutated

Answer 25

enables the expressed enzyme to be active in the presence of drug through a decreased binding affinity of trimethoprim