sulfonamide Flashcards
What is the definition of chemotherapy?
The drug treatment of parasitic infections in which the infective parasites are destroyed without harming the animal host. It also includes cancer therapy.
Chemotherapy targets various parasites, including bacteria, viruses, protozoa, fungi, and worms.
Who reported the antibacterial activity of prontosil?
Domagk in 1932
Prontosil was the lead drug for sulphonamides and showed activity in experimental infections caused by streptococcus.
What is sulfanilamide?
The first synthetic antibacterial agent acting on a wide range of infections.
Sulfanilamide is metabolized from prontosil and is active in vivo but inactive in vitro.
What are the essential features of sulfonamides?
- para-Amino group is essential (R1=H)
- para-Amido groups are allowed
- Inactive in vitro but active in vivo
- Act as prodrugs
- Aromatic ring is essential
- para-Substitution is essential
- Sulfonamide group is essential
- Sulfonamide nitrogen must be primary or secondary
- R2 can be varied
These features are crucial for the antibacterial activity of sulfonamides.
What effect does the amide group have on sulfonamides?
It lowers the polarity of the sulfonamide and cannot ionize.
Alkyl groups increase hydrophobic character, aiding in crossing the gut wall.
What is the role of PABA in relation to sulfonamides?
PABA is incorporated into the developing tetrahydrofolic acid molecule by enzyme-catalyzed condensation.
Sulfonamides can be classified as antimetabolites and their antimicrobial efficacy can be reversed by adding PABA.
What is the significance of dihydropteroate synthase?
It is an enzyme needed for the biosynthesis of folic acid derivatives and is not present in human cells.
Sulfonamides inhibit this enzyme, leading to selective toxicity against bacteria.
True or False: Sulfonamides are ideal for patients with weakened immune systems.
False
Sulfonamides are bacteriostatic agents and not ideal for patients with weakened immune systems.
What is the pKa of sulfonamides?
Approximately 10.4
This pKa indicates the acidity of the sulfonamide functional group.
How does the pH affect the bacteriostatic activity of sulfonamides?
Bacteriostatic activity at pH 7.8 is 1/10 that at pH 6.8.
Anion concentration has a significant effect on the activity of sulfonamides.
What are the three classes of sulfonamides based on their use?
- Oral absorbable agents for systemic distribution
- Oral nonabsorbable agents like sulfasalazine
- Topical agents like sodium sulfacetamide
Each class serves different therapeutic purposes.
What is the significance of the combination therapy of sulfamethoxazole and trimethoprim?
They inhibit different enzymes in the same biosynthetic pathway, allowing for lower, safer dose levels.
The optimum ratio for these agents in vitro is 1:20, achieved by administering a 1:5 combination orally.
What is sulfasalazine used for?
Treatment of ulcerative colitis and Crohn’s disease.
It is a pro-drug activated by gut bacteria to mesalazine and sulfapyridine.
What happens when the water solubility of sulfonamides is poor?
It can lead to crystallization in urine (crystalluria) and kidney damage.
Increased water intake is recommended to avoid crystalluria.
What is the pKa of sulfisoxazole?
Approximately 5.0
This value indicates its ionization state and solubility characteristics.
What are the chemical properties of sulfonamides?
They are amphoteric and can act as either acids or bases.
Active sulfonamides possess a free N4 amino group, which is essential for their activity.
