Question:
Longest acting sulphonamide is -
Longest acting sulphonamide is -
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Think of the agent paired with pyrimethamine for malaria.
Updated On: Jun 24, 2026
- Sulfadiazine
- Sulphadoxine
- Sulfamethoxazole
- Sulfamethiazole
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The Correct Option is B
Solution and Explanation
Step 1: Sulphonamides are classified by their duration of action, which depends on how slowly they are eliminated from the body. The slower the clearance, the longer the drug stays active.
Step 2: Among the listed agents, sulphadoxine has an extremely long elimination half-life of about 100 to 200 hours, making it the longest acting sulphonamide. Together with sulfamethopyrazine, it belongs to the ultra-long-acting group.
Step 3: Because of this prolonged action, sulphadoxine is used in combination with pyrimethamine (as Fansidar) for the treatment and prophylaxis of malaria.
Step 4: The distractors are shorter acting. Sulfadiazine is intermediate acting, while sulfamethoxazole and sulfamethiazole are short to intermediate acting and require more frequent dosing. Hence sulphadoxine is the correct answer.
Step 2: Among the listed agents, sulphadoxine has an extremely long elimination half-life of about 100 to 200 hours, making it the longest acting sulphonamide. Together with sulfamethopyrazine, it belongs to the ultra-long-acting group.
Step 3: Because of this prolonged action, sulphadoxine is used in combination with pyrimethamine (as Fansidar) for the treatment and prophylaxis of malaria.
Step 4: The distractors are shorter acting. Sulfadiazine is intermediate acting, while sulfamethoxazole and sulfamethiazole are short to intermediate acting and require more frequent dosing. Hence sulphadoxine is the correct answer.
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