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sulfonamides trimethoprim current prescribing safety reference

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python -c "from pptx import Presentation; p=Presentation('/tmp/workspace/attachments/24c2d9b4-8f3c-40af-be29-fa93ad3f858f/Sulphonamides& trimethoprim.pptx'); print('Slides:',len(p.slides)); [print('\\n--- SLIDE',i,'---\\n'+'\\n'.join(s.text for s in slide.shapes if getattr(s,'has_text_frame',False) and s.text.strip())) for i,slide in enumerate(p.slides,1)]"

MCQs: Sulphonamides, Trimethoprim and Co-trimoxazole

Part A: Direct MCQs

1. Sulfonamides act primarily by inhibiting:
A. DNA gyrase
B. Dihydropteroate synthase
C. Dihydrofolate reductase
D. Peptidyl transferase

2. Sulfonamides are structural analogues of:
A. Folic acid
B. Para-aminobenzoic acid (PABA)
C. Dihydrofolic acid
D. Tetrahydrofolic acid

3. The antibacterial action of sulfonamides alone is usually:
A. Bactericidal
B. Bacteriostatic
C. Fungicidal
D. Virucidal

4. The free N4 amino group of sulfonamides is required for:
A. Renal excretion
B. Protein binding
C. Antibacterial activity
D. Placental transfer

5. Humans are relatively unaffected by sulfonamides because humans:
A. Do not require folate
B. Synthesize folate by an alternative enzyme
C. Obtain folate from the diet
D. Rapidly metabolize PABA

6. Which organism is intrinsically resistant to sulfonamides?
A. Nocardia species
B. Chlamydia trachomatis
C. Pseudomonas aeruginosa
D. Escherichia coli

7. Sulfonamides have poor activity against:
A. Gram-positive cocci
B. Anaerobes
C. Nocardia
D. Chlamydia

8. A common mechanism of sulfonamide resistance is:
A. Decreased production of PABA
B. Increased affinity of dihydropteroate synthase for sulfonamide
C. Overproduction of PABA
D. Inhibition of bacterial ribosomes

9. Which sulfonamide is commonly used in combination with pyrimethamine for acute toxoplasmosis?
A. Sulfadiazine
B. Sulfacetamide
C. Sulfasalazine
D. Sulfisoxazole

10. Sulfasalazine is mainly used in:
A. Tuberculosis
B. Inflammatory bowel disease
C. Malaria
D. Pneumocystis pneumonia

11. Silver sulfadiazine is used topically mainly for:
A. Acne vulgaris
B. Burn-wound infection prophylaxis
C. Fungal keratitis
D. Scabies

12. A serious cutaneous adverse reaction associated with sulfonamides is:
A. Erythema nodosum
B. Stevens-Johnson syndrome
C. Psoriasis
D. Vitiligo

13. Sulfonamides may cause hemolysis particularly in patients with:
A. Iron-deficiency anemia
B. Vitamin B12 deficiency
C. G6PD deficiency
D. Sickle-cell trait

14. Sulfonamides should be avoided in neonates because they may cause:
A. Gray baby syndrome
B. Kernicterus
C. Red man syndrome
D. Tooth discoloration

15. Trimethoprim selectively inhibits bacterial:
A. Dihydropteroate synthase
B. DNA-dependent RNA polymerase
C. Dihydrofolate reductase
D. Transpeptidase

16. Trimethoprim is selectively toxic because it inhibits bacterial dihydrofolate reductase much more efficiently than mammalian enzyme. This difference is approximately:
A. 5-fold
B. 50-fold
C. 500-fold
D. 50,000-fold

17. Trimethoprim may cause which hematological adverse effect?
A. Megaloblastic anemia
B. Hemolytic anemia in all patients
C. Polycythemia
D. Thalassemia

18. Co-trimoxazole consists of:
A. Sulfadiazine + pyrimethamine
B. Sulfamethoxazole + trimethoprim
C. Sulfacetamide + trimethoprim
D. Sulfadoxine + trimethoprim

19. The bactericidal action of co-trimoxazole is due to:
A. Inhibition of cell-wall synthesis
B. Inhibition of two sequential steps in folate synthesis
C. Inhibition of protein synthesis at two ribosomal sites
D. Increased renal excretion of bacteria

20. Which is the usual composition of one double-strength co-trimoxazole tablet?
A. Trimethoprim 80 mg + sulfamethoxazole 400 mg
B. Trimethoprim 160 mg + sulfamethoxazole 800 mg
C. Trimethoprim 200 mg + sulfamethoxazole 1,000 mg
D. Trimethoprim 400 mg + sulfamethoxazole 80 mg

Part B: Scenario-Based MCQs

21. A patient with HIV presents with fever, dry cough, progressive dyspnea, and diffuse bilateral interstitial infiltrates. Pneumocystis jirovecii pneumonia is diagnosed. Which drug is the preferred treatment?
A. Sulfasalazine
B. Sulfacetamide
C. Co-trimoxazole
D. Sulfadoxine alone

22. A woman with recurrent uncomplicated urinary tract infections requires prophylaxis. Which regimen from the presentation may be used for prophylaxis in selected patients?
A. One-half single-strength co-trimoxazole tablet three times weekly
B. Silver sulfadiazine cream once weekly
C. Sulfasalazine daily
D. Sulfadoxine-pyrimethamine monthly

23. A premature newborn develops jaundice. Which drug should be avoided because it can displace bilirubin from plasma proteins and contribute to kernicterus?
A. Sulfonamide
B. Trimethoprim
C. Penicillin G
D. Azithromycin

24. A patient receiving co-trimoxazole develops fever, painful oral erosions, conjunctivitis, and widespread blistering rash. What is the most likely diagnosis?
A. Erythema multiforme minor
B. Stevens-Johnson syndrome
C. Acneiform eruption
D. Serum sickness

25. A man with G6PD deficiency develops dark urine and jaundice after receiving a sulfonamide for a urinary infection. The likely adverse effect is:
A. Aplastic anemia
B. Hemolytic anemia
C. Megaloblastic anemia
D. Nephrotic syndrome

26. A patient with acute toxoplasmosis requires standard first-line therapy. Which combination is most appropriate?
A. Sulfadiazine + pyrimethamine
B. Sulfamethoxazole + trimethoprim
C. Sulfadoxine + trimethoprim
D. Sulfasalazine + folic acid

27. A patient with a large burn has a high risk of secondary bacterial infection. Which topical sulfonamide is preferred for prevention of burn-wound infection?
A. Sulfisoxazole
B. Silver sulfadiazine
C. Sulfasalazine
D. Sulfadoxine

28. A patient has bacterial conjunctivitis. Which sulfonamide preparation may be used locally?
A. Oral sulfadiazine
B. Intravenous sulfamethoxazole
C. Sodium sulfacetamide ophthalmic solution
D. Sulfasalazine tablets

29. An elderly patient with renal impairment receives trimethoprim for a UTI and later develops macrocytosis and leukopenia. These effects are best explained by:
A. Inhibition of bacterial cell-wall synthesis
B. Antifolate action of trimethoprim
C. Direct bone-marrow invasion by bacteria
D. G6PD deficiency

30. A patient has falciparum malaria and is prescribed sulfadoxine with pyrimethamine. Which additional agent helps reduce pyrimethamine-related folate toxicity?
A. Vitamin K
B. Folic acid only
C. Folinic acid (citrovorum factor)
D. Vitamin C

Answer Key with Brief Explanations

Q.	Answer	Explanation
1	B	Sulfonamides inhibit bacterial dihydropteroate synthase.
2	B	They compete with PABA in bacterial folate synthesis.
3	B	Sulfonamides alone are bacteriostatic.
4	C	A free N4 amino group is necessary for antibacterial activity.
5	C	Humans obtain preformed folate from dietary sources.
6	C	Pseudomonas aeruginosa is intrinsically resistant.
7	B	Activity against anaerobic bacteria is poor.
8	C	Increased PABA production can overcome sulfonamide inhibition.
9	A	Sulfadiazine with pyrimethamine is used for acute toxoplasmosis.
10	B	Sulfasalazine is used in ulcerative colitis and other inflammatory bowel diseases.
11	B	Silver sulfadiazine is used for burn-wound infection prevention.
12	B	Stevens-Johnson syndrome is a rare but severe sulfonamide reaction.
13	C	Oxidative hemolysis may occur in G6PD deficiency.
14	B	Sulfonamides may precipitate kernicterus in neonates.
15	C	Trimethoprim inhibits bacterial dihydrofolate reductase.
16	D	It is about 50,000 times less effective against mammalian DHFR.
17	A	Folate antagonism can cause megaloblastic anemia, leukopenia, and granulocytopenia.
18	B	Co-trimoxazole is sulfamethoxazole plus trimethoprim.
19	B	Sequential blockade of bacterial folate synthesis produces synergy.
20	B	Double-strength tablet: TMP 160 mg + SMX 800 mg.
21	C	Co-trimoxazole is a main treatment and prophylactic drug for P. jirovecii.
22	A	A low-dose intermittent co-trimoxazole regimen may prevent recurrent UTI in selected women.
23	A	Sulfonamides can displace bilirubin and increase kernicterus risk.
24	B	Fever, mucosal lesions, and blistering rash suggest Stevens-Johnson syndrome.
25	B	Sulfonamides can trigger hemolytic anemia in G6PD deficiency.
26	A	Sulfadiazine plus pyrimethamine is standard therapy for acute toxoplasmosis.
27	B	Silver sulfadiazine is used topically in burns.
28	C	Sodium sulfacetamide is used in bacterial conjunctivitis.
29	B	Trimethoprim is an antifolate and can cause bone-marrow suppression.
30	C	Folinic acid may be given with pyrimethamine to reduce folate-related toxicity.

Safety point: co-trimoxazole can also cause hyperkalemia, particularly in renal impairment or with potassium-raising medicines such as ACE inhibitors, as noted in the current FDA product labeling.

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