This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Integrated QBank, Subject name: Unknown
A HIV patient with CD4 count of 160 cells/ul presented with fever, cough and shoness of breath for 3 weeks. Chest X ray is shown below. Based on the x ray findings silver staining of the bronchoalveolar lavage was done and shown below. What is drug of choice for the causative organism? 
Select and explain. 
A. Azithromycin, B. Vancomycin, C. Gentamycin, D. Cotrimoxazole
D: Cotrimoxazole
Answer: D: Cotrimoxazole 
Explanation: Chest X ray depicts bilateral widespread interstitial pneumonia and Gomori Methenamine silver staining shows cysts with crushed ping pong balls appearance and are present in aggregate of 2-8. This is characteristic of Pneumocystis Pneumonia which is typically seen in AIDS patient in which CD4 cell count is below 200cells/ul Treatment:Double strength Cotrimoxazole i.e. Trimethoprim160mg + sulfamethoxazole800mg (continued till CD4 count is more than 200cells/ul.)