This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy: General Principles, Subject name: Pharmacology
[{'content': 'Antipseudomonals are all, except. \nSelect and explain. \nA. Cephalexin, B. Carbenicillin, C. Piperacillin, D. Ceftazidime', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (A) Cephalexin(Ref: KDT 8/e p773,774,776; Goodman & Gilman 10/e p1209)Cephalexin is an orally effective first generation cephalosporin active against gram positive but not against gram negative organisms like pseudomonas.', 'role': 'assistant'}]