This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
What drug is used for prophylaxis against Pneumocystis jirovecii in patients on chemotherapy? 
Select and explain. 
A. Cotrimoxazole, B. Amoxicillin, C. Dexamethasone, D. Cephalosporin
A: Cotrimoxazole
Answer: A: Cotrimoxazole 
Explanation: Answer- A. CotrimoxazoleDrug of choice for prophylaxis and treatment of pneumocystis infection in both immunocompetent as well as immunocompromised is cotrimoxazole.Cyclospora, Isospora & Pneumocystis jiroveci - Cotrimoxazole