This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
A 30-year old epileptic female, Kamla on Phenytoin therapy, developed weakness and fatigue. Blood examination revealed Hb= 4.6 gm. MCV=102 fl and MCH =40 pg/dl. What is the most probable diagnosis? 
Select and explain. 
A. Hea failure, B. Iron deficiency anemia, C. Phenytoin induced agranulocytosis, D. Megaloblastic anemia
D: Megaloblastic anemia
Answer: D: Megaloblastic anemia 
Explanation: Phenytoin can cause folic acid deficiency resulting in megaloblastic anemia. This is confirmed by raised MCV and MCH in the blood examination. REF: KD TRipathi 8th ed.