As B. Pharm students, mastering Sulphamethizole, Sulfisoxazole, and Sulphapyridine is essential for understanding sulfonamide pharmacology. These sulfonamides act as PABA analogues that competitively inhibit dihydropteroate synthase, producing bacteriostatic effects by disrupting folate synthesis. Key concepts include pharmacokinetics (absorption, hepatic acetylation, renal excretion), clinical uses (urinary tract infections, otitis media, and historical systemic roles), adverse effects (hypersensitivity reactions, crystalluria, hemolysis in G6PD deficiency, risk of kernicterus), drug interactions, and resistance mechanisms. This focused set of MCQs emphasizes mechanism of action, PK/PD, toxicity, monitoring, and clinical decision-making relevant to B. Pharm curricula. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which enzyme is directly inhibited by Sulphamethizole, Sulfisoxazole, and Sulphapyridine in bacteria?
- Dihydrofolate reductase
- Dihydropteroate synthase
- DNA gyrase
- Peptidoglycan transpeptidase
Correct Answer: Dihydropteroate synthase
Q2. The primary antimicrobial effect of these sulfonamides is best described as:
- Bactericidal by cell wall lysis
- Bacteriostatic by inhibition of folate synthesis
- Bactericidal by membrane disruption
- Bacteriostatic by inhibiting protein synthesis
Correct Answer: Bacteriostatic by inhibition of folate synthesis
Q3. Sulphapyridine is clinically important because it is:
- A topical antifungal widely used today
- The active metabolite of sulfasalazine responsible for systemic effects
- Primarily excreted via bile with enterohepatic recycling
- An inhibitor of dihydrofolate reductase in human cells
Correct Answer: The active metabolite of sulfasalazine responsible for systemic effects
Q4. Which sulfonamide is classically associated with treatment of acute otitis media in pediatric practice?
- Sulphamethizole
- Sulfisoxazole
- Sulphapyridine
- Sulfadoxine
Correct Answer: Sulfisoxazole
Q5. The best preventive measure to reduce the risk of crystalluria with these drugs is:
- Co-administration of high-dose vitamin C
- Adequate hydration and urinary alkalinization
- Reducing dietary protein intake
- Using intramuscular rather than oral administration
Correct Answer: Adequate hydration and urinary alkalinization
Q6. A clinically significant drug interaction of sulfonamides is potentiation of the anticoagulant effect of:
- Heparin
- Warfarin
- Aspirin
- Clopidogrel
Correct Answer: Warfarin
Q7. The most common immunologic mechanism underlying sulfonamide cutaneous adverse reactions is:
- Type I IgE-mediated hypersensitivity
- Type II cytotoxic hypersensitivity
- Type III immune complex-mediated hypersensitivity
- Type IV delayed (T-cell mediated) hypersensitivity
Correct Answer: Type IV delayed (T-cell mediated) hypersensitivity
Q8. Sulfonamides can precipitate hemolytic anemia in patients with which enzymatic deficiency?
- Phenylalanine hydroxylase deficiency
- Glucose-6-phosphate dehydrogenase deficiency (G6PD)
- Thymidine kinase deficiency
- Pyruvate kinase deficiency
Correct Answer: Glucose-6-phosphate dehydrogenase deficiency (G6PD)
Q9. Use of systemic sulfonamides near term in pregnancy is contraindicated primarily because of risk of:
- Neonatal hypoglycemia
- Kernicterus due to displacement of bilirubin
- Neonatal pulmonary hypertension
- Teratogenic limb defects
Correct Answer: Kernicterus due to displacement of bilirubin
Q10. Trimethoprim is commonly combined with a sulfonamide because it inhibits which enzyme, producing sequential blockade of folate synthesis?
- Dihydropteroate synthase
- Dihydrofolate reductase
- Thymidylate synthase
- Folate synthetase
Correct Answer: Dihydrofolate reductase
Q11. A common bacterial resistance mechanism to sulfonamides involves:
- Increased permeability to sulfonamides
- Plasmid-mediated production of an altered dihydropteroate synthase
- Enhanced binding of sulfonamides to bacterial ribosomes
- Inactivation of sulfonamides by beta-lactamases
Correct Answer: Plasmid-mediated production of an altered dihydropteroate synthase
Q12. Genetic acetylation polymorphism affects sulfonamide toxicity such that slow acetylators are more likely to experience:
- Rapid drug elimination and therapeutic failure
- Higher plasma levels and increased adverse effects
- Enhanced renal clearance with low toxicity
- Complete resistance to antibacterial action
Correct Answer: Higher plasma levels and increased adverse effects
Q13. Systemic adverse effects of sulfasalazine are mainly attributed to which moiety released in the colon?
- 5-Aminosalicylic acid (5-ASA)
- Sulphapyridine
- Sulfisoxazole
- Sulphamethizole
Correct Answer: Sulphapyridine
Q14. Which sulfonamide is relatively more water-soluble and less prone to cause crystalluria?
- Sulphamethizole
- Sulfisoxazole
- Sulphapyridine
- Sulfadoxine
Correct Answer: Sulfisoxazole
Q15. Before initiating prolonged systemic therapy with these agents, which baseline laboratory tests are most appropriate to monitor for safety?
- Liver function tests and chest X-ray
- Complete blood count (CBC) and renal function tests
- Fasting lipid profile and thyroid function tests
- Blood glucose and serum amylase
Correct Answer: Complete blood count (CBC) and renal function tests
Q16. Sulfonamides should be avoided in which stage of pregnancy due to increased neonatal risk?
- First trimester only
- Second trimester only
- Third trimester (near term)
- They are safe in all trimesters
Correct Answer: Third trimester (near term)
Q17. Which of the following is a common clinical indication for Sulphamethizole or related short-acting sulfonamides?
- Severe systemic fungal infections
- Uncomplicated urinary tract infections
- Viral upper respiratory infections
- Chronic heart failure management
Correct Answer: Uncomplicated urinary tract infections
Q18. The primary metabolic pathway for sulfonamides in the liver is:
- Glucuronidation only
- Oxidative deamination
- Acetylation followed by renal excretion
- Conjugation with taurine
Correct Answer: Acetylation followed by renal excretion
Q19. The antimicrobial spectrum of sulfonamides primarily includes:
- Only anaerobic bacteria
- Both certain Gram-positive and Gram-negative organisms by folate pathway inhibition
- Only atypical organisms like Mycoplasma
- Only Pseudomonas aeruginosa and other non-fermenters
Correct Answer: Both certain Gram-positive and Gram-negative organisms by folate pathway inhibition
Q20. A rare but severe mucocutaneous adverse reaction linked to sulfonamides is:
- Acne vulgaris
- Stevens-Johnson syndrome (SJS) / Toxic epidermal necrolysis (TEN)
- Alopecia
- Melasma
Correct Answer: Stevens-Johnson syndrome (SJS) / Toxic epidermal necrolysis (TEN)
Q21. The predominant route of elimination for Sulphamethizole, Sulfisoxazole, and Sulphapyridine is:
- Fecal excretion unchanged
- Renal excretion of parent drug and metabolites
- Exhalation as volatile metabolites
- Secretion into bile without renal involvement
Correct Answer: Renal excretion of parent drug and metabolites
Q22. Historically, Sulphapyridine was widely used systemically but is now mainly of interest because:
- It has the broadest current clinical use among sulfonamides
- It is the principal component responsible for sulfasalazine’s systemic toxicity
- It is the safest sulfonamide in pregnancy
- It is an antifungal rather than antibacterial agent
Correct Answer: It is the principal component responsible for sulfasalazine’s systemic toxicity
Q23. Which property of sulfonamides underlies their potential to cause neonatal kernicterus?
- High placental metabolism to teratogens
- Strong displacement of bilirubin from albumin binding sites
- Direct inhibition of neonatal bilirubin conjugation enzymes
- Induction of fetal hemolysis through immune mechanisms
Correct Answer: Strong displacement of bilirubin from albumin binding sites
Q24. The combination of a sulfonamide with trimethoprim produces which pharmacodynamic effect?
- Antagonism resulting in reduced activity
- Synergy leading to bactericidal action
- No change compared to either agent alone
- Conversion from bacteriostatic to fungistatic activity
Correct Answer: Synergy leading to bactericidal action
Q25. Which patient population should generally avoid systemic sulfonamides because of higher risk of adverse outcomes?
- Patients with chronic hypertension
- Newborn infants and late-pregnancy fetuses
- Middle-aged adults with hyperlipidemia
- Patients with hypothyroidism
Correct Answer: Newborn infants and late-pregnancy fetuses
Q26. Inhibiting dihydropteroate synthase in bacteria ultimately reduces synthesis of which essential metabolites?
- Amino acids lysine and methionine
- Purines and thymidine required for DNA synthesis
- Cell wall N-acetylmuramic acid
- Ribosomal RNA components
Correct Answer: Purines and thymidine required for DNA synthesis
Q27. Sulfonamides are structural analogues of:
- Pteridine
- PABA (para-aminobenzoic acid)
- Folic acid
- Thymidine
Correct Answer: PABA (para-aminobenzoic acid)
Q28. A patient develops fever and a widespread morbilliform rash a week after starting a sulfonamide; this presentation most likely represents:
- Drug hypersensitivity reaction
- Drug-induced lupus erythematosus
- Idiosyncratic cholestatic hepatitis
- Primary bacterial infection unrelated to drug
Correct Answer: Drug hypersensitivity reaction
Q29. Slow acetylator phenotype affects sulfonamide disposition by:
- Increasing renal tubular secretion of parent drug
- Slowing hepatic N-acetylation leading to higher parent drug levels
- Enhancing conjugation and rapid elimination
- Preventing enterohepatic recirculation entirely
Correct Answer: Slowing hepatic N-acetylation leading to higher parent drug levels
Q30. Which monitoring sign would most promptly suggest developing sulfonamide-induced hematologic toxicity?
- Progressive thrombocytopenia or leukopenia on serial CBC
- Elevated serum cholesterol levels
- Increased serum uric acid
- Persistent hyperglycemia
Correct Answer: Progressive thrombocytopenia or leukopenia on serial CBC
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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