Question:medium
Longest acting sulphonamide is -
Longest acting sulphonamide is -
Show Hint
Think of the agent paired with pyrimethamine for malaria.
Updated On: Jun 24, 2026
- Sulfadiazine
- Sulphadoxine
- Sulfamethoxazole
- Sulfamethiazole
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: The key to this question is matching each sulphonamide with how long it persists in plasma, since duration of action tracks the elimination half-life.
Step 2: Sulfamethiazole and sulfamethoxazole are cleared relatively quickly, so they fall into the short-to-intermediate band and need repeated dosing. Sulfadiazine sits in the intermediate range.
Step 3: Sulphadoxine stands apart because its half-life stretches to several days, placing it in the ultra-long-acting category alongside sulfamethopyrazine. This is why a single dose can cover a malaria treatment course.
Step 4: Comparing all four, sulphadoxine clearly has the slowest clearance and therefore the longest action.
\[\boxed{\text{Sulphadoxine}}\]
Step 2: Sulfamethiazole and sulfamethoxazole are cleared relatively quickly, so they fall into the short-to-intermediate band and need repeated dosing. Sulfadiazine sits in the intermediate range.
Step 3: Sulphadoxine stands apart because its half-life stretches to several days, placing it in the ultra-long-acting category alongside sulfamethopyrazine. This is why a single dose can cover a malaria treatment course.
Step 4: Comparing all four, sulphadoxine clearly has the slowest clearance and therefore the longest action.
\[\boxed{\text{Sulphadoxine}}\]
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