Question

Assertion (A): Co-trimoxazole is contraindicated in a subject with G6PD deficiency. Reason (R): Co-trimoxazole is the drug of choice in Pneumocystis carinii pneumonia.

• A. Both A and R are individually true and R is the correct explanation of A
• B. Both A and R are individually true but R is NOT the correct explanation of A
• C. A is true but R is false
• D. A is false but R is true

Hint:

Ask whether the drug's usefulness against Pneumocystis has anything to do with why it is avoided in G6PD deficiency.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question tests two separate facts about co-trimoxazole, its risk in G6PD deficiency and its use in Pneumocystis carinii pneumonia, and whether the second explains the first.

Step 2: Key Concept or Approach:
Drugs with oxidant potential, including the sulfonamide component of co-trimoxazole, precipitate acute haemolysis in G6PD-deficient red cells because these cells cannot regenerate enough NADPH and reduced glutathione to withstand oxidative stress. Separately, co-trimoxazole's antifolate, anti-Pneumocystis activity is what makes it the standard treatment and prophylaxis for Pneumocystis pneumonia in immunocompromised patients. These are two unrelated pharmacological properties of the same drug.

Step 3: Working Through the Options:
A is true, co-trimoxazole is a well-recognised trigger of haemolysis in G6PD deficiency and should be avoided in these patients. R is also true on its own, co-trimoxazole genuinely is the drug of choice for Pneumocystis carinii pneumonia. However, R does not explain A at all, the reason co-trimoxazole is avoided in G6PD deficiency is its oxidant, haemolytic effect on red cells, which has nothing to do with its effectiveness against Pneumocystis.

Step 4: Conclusion:
Both statements are true individually, but R is not the correct explanation of A, matching the option stating both are true with R not the correct explanation.