Classification of sulfonamides is a vital topic for B. Pharm students that covers chemical and pharmacological grouping of sulfonamide antibacterial agents. This concise introduction explains classification by chemical structure (simple aryl, heterocyclic, long‑acting, topical), by pharmacokinetics and clinical use (systemic, topical, long‑acting), and by structure‑activity relationships (para‑amino benzene sulfonamide moiety). Emphasis on mechanism of action, resistance mechanisms, adverse effects (hypersensitivity, hematologic toxicity), and important drug interactions prepares students for rational therapeutic choices and formulation considerations. Key terms: sulfonamides, classification of sulfonamides, SAR, pharmacokinetics, clinical use. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the most common primary basis for classifying sulfonamide antibacterial agents?
- Chemical structure and substituents
- Route of administration
- Cost and manufacturing method
- Brand name
Correct Answer: Chemical structure and substituents
Q2. Which sulfonamide contains a heterocyclic ring in its structure?
- Sulfadiazine
- Sulfapyridine
- Sulfamethoxazole
- Sulfanilamide
Correct Answer: Sulfapyridine
Q3. Sulfonamides exert antibacterial action primarily by inhibiting which enzyme?
- Dihydropteroate synthase (DHPS)
- Dihydrofolate reductase (DHFR)
- DNA gyrase
- Peptidoglycan transpeptidase
Correct Answer: Dihydropteroate synthase (DHPS)
Q4. Which structural feature is essential for antibacterial activity of classical sulfonamides?
- Para‑amino benzene sulfonamide moiety
- Beta‑lactam ring
- Quaternary ammonium group
- Thiourea side chain
Correct Answer: Para‑amino benzene sulfonamide moiety
Q5. Sulfonamides are generally classified as which type of antibacterial agents?
- Bactericidal
- Bacteriostatic
- Fungicidal
- Virucidal
Correct Answer: Bacteriostatic
Q6. Trimethoprim, when combined with a sulfonamide, inhibits which enzyme to produce synergistic blockade of folate synthesis?
- Dihydrofolate reductase (DHFR)
- Dihydropteroate synthase (DHPS)
- Thymidylate synthase
- RNA polymerase
Correct Answer: Dihydrofolate reductase (DHFR)
Q7. Which sulfonamide is commonly used as a topical ophthalmic agent?
- Sulfadiazine
- Sulfamethoxazole
- Sulfacetamide
- Sulfapyridine
Correct Answer: Sulfacetamide
Q8. Which sulfonamide is classified as long‑acting and is often used in antimalarial combinations?
- Sulfadiazine
- Sulfamethoxazole
- Sulfadoxine
- Sulfanilamide
Correct Answer: Sulfadoxine
Q9. A severe cutaneous adverse reaction associated with sulfonamide use is:
- Stevens‑Johnson syndrome (SJS) / Toxic epidermal necrolysis (TEN)
- Exfoliative dermatitis from sun exposure only
- Eczematous dermatitis unrelated to medication
- Nummular dermatitis
Correct Answer: Stevens‑Johnson syndrome (SJS) / Toxic epidermal necrolysis (TEN)
Q10. Sulfonamide use can precipitate hemolytic anemia in patients with which enzymatic deficiency?
- Glucose‑6‑phosphate dehydrogenase (G6PD) deficiency
- Phenylalanine hydroxylase deficiency
- Acetyl‑CoA carboxylase deficiency
- Methylmalonyl‑CoA mutase deficiency
Correct Answer: Glucose‑6‑phosphate dehydrogenase (G6PD) deficiency
Q11. Which sulfonamide is commonly used with pyrimethamine for treatment of toxoplasmosis?
- Sulfamethoxazole
- Sulfadiazine
- Sulfapyridine
- Sulfanilamide
Correct Answer: Sulfadiazine
Q12. Sulfonamides are generally avoided in late pregnancy because they can cause what neonatal complication?
- Neonatal hypoglycemia
- Kernicterus due to displacement of bilirubin
- Congenital heart defects
- Neonatal thrombocytopenia only
Correct Answer: Kernicterus due to displacement of bilirubin
Q13. The most common molecular mechanism of bacterial resistance to sulfonamides is:
- Mutation in dihydropteroate synthase producing an altered target
- Increased drug uptake via porins
- Enhanced binding to ribosomes
- Inhibition of beta‑lactamase
Correct Answer: Mutation in dihydropteroate synthase producing an altered target
Q14. Which laboratory test is essential to monitor for hematologic toxicity during prolonged sulfonamide therapy?
- Liver function test only
- Complete blood count (CBC) with differential
- Fasting blood glucose
- Serum amylase
Correct Answer: Complete blood count (CBC) with differential
Q15. Which sulfonamide formulation is widely used topically for burn wound infections?
- Sulfamethoxazole oral tablets
- Silver sulfadiazine topical cream
- Sulfapyridine oral suspension
- Sulfadiazine eye drops
Correct Answer: Silver sulfadiazine topical cream
Q16. To reduce the risk of sulfonamide crystalluria, which urinary manipulation is recommended?
- Acidify the urine
- Alkalinize the urine
- Reduce fluid intake
- Administer high dose vitamin C only
Correct Answer: Alkalinize the urine
Q17. Which drug is a prodrug that is converted by colonic bacteria to 5‑aminosalicylic acid and a sulfonamide moiety and is used in ulcerative colitis?
- Sulfamethoxazole
- Sulfasalazine
- Sulfadiazine
- Sulfapyridine
Correct Answer: Sulfasalazine
Q18. The commonly used combination marketed as co‑trimoxazole contains which sulfonamide?
- Sulfadiazine
- Sulfamethoxazole
- Sulfapyridine
- Sulfacetamide
Correct Answer: Sulfamethoxazole
Q19. The primary hepatic metabolic pathway for many sulfonamides is:
- Glucuronidation only
- N‑acetylation in the liver
- Sulfation only
- Oxidative deamination
Correct Answer: N‑acetylation in the liver
Q20. Hepatic N‑acetylation of sulfonamides generally affects water solubility how?
- Increases water solubility markedly
- Decreases water solubility and may promote crystalluria
- Has no effect on solubility
- Converts drug to an active more potent metabolite
Correct Answer: Decreases water solubility and may promote crystalluria
Q21. Which of the following drug classes contains agents that are sulfonamide derivatives used as antidiabetic drugs?
- Beta‑lactams
- Sulfonylureas
- Aminoglycosides
- Macrolides
Correct Answer: Sulfonylureas
Q22. Acetylation of the para‑amino group of classical sulfonamides inactivates antibacterial activity because it:
- Enhances binding to DHPS
- Prevents interaction with the target enzyme (loss of activity)
- Increases renal excretion making it more potent
- Promotes conversion to a bactericidal metabolite
Correct Answer: Prevents interaction with the target enzyme (loss of activity)
Q23. A clinically important drug interaction with sulfonamides is increased anticoagulant effect when combined with which agent?
- Amlodipine
- Warfarin
- Metformin
- Ranitidine
Correct Answer: Warfarin
Q24. Sulfonamides are commonly active against many urinary pathogens; which of the following is typically susceptible?
- Escherichia coli
- Pseudomonas aeruginosa universally
- Mycoplasma pneumoniae only
- Candida albicans
Correct Answer: Escherichia coli
Q25. The typical mass ratio of sulfamethoxazole to trimethoprim in the standard co‑trimoxazole formulation is approximately:
- 1:1
- 5:1 (sulfamethoxazole : trimethoprim)
- 10:1
- 1:5 (sulfamethoxazole : trimethoprim)
Correct Answer: 5:1 (sulfamethoxazole : trimethoprim)
Q26. A common photosensitivity reaction associated with sulfonamides is best described as:
- Ototoxicity with tinnitus
- Photosensitivity leading to exaggerated sunburn
- Tendon rupture
- Peripheral neuropathy only
Correct Answer: Photosensitivity leading to exaggerated sunburn
Q27. To prevent sulfonamide‑induced crystalluria and renal precipitation, recommended measures include:
- Fluid restriction and urine acidification
- Maintain good hydration and urine alkalinization
- Administer with high‑fat meals only
- Avoid monitoring urine output
Correct Answer: Maintain good hydration and urine alkalinization
Q28. Which commonly used thiazide diuretic contains a sulfonamide moiety in its chemical structure (non‑antibacterial sulfonamide derivative)?
- Sulfamethoxazole
- Hydrochlorothiazide
- Furosemide
- Acetazolamide
Correct Answer: Hydrochlorothiazide
Q29. Hemolytic anemia due to sulfonamide exposure in a susceptible patient would most likely produce which laboratory finding?
- Low reticulocyte count
- High reticulocyte count
- Marked hyperlipidemia
- Decreased indirect bilirubin
Correct Answer: High reticulocyte count
Q30. Which combination is classically used as an antimalarial intermittent preventive therapy and illustrates a long‑acting sulfonamide paired with an antiparasitic?
- Sulfamethoxazole‑trimethoprim
- Sulfadoxine‑pyrimethamine
- Sulfadiazine‑pyrimethamine
- Sulfapyridine‑chloroquine
Correct Answer: Sulfadoxine‑pyrimethamine
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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