This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Pharmacology, Subject name: Pharmacology
Therapeutic drug monitoring is required in all except: 
Select and explain. 
A. Phenytoin, B. Metformin, C. Tacrolimus, D. Cyclosporine
B: Metformin
Answer: B: Metformin 
Explanation: Ans. (B) Metformin(Ref: KDT 8th/e p42)* We can easily monitor blood glucose levels as an effect of metformin, thus TDM is not required.* TDM is required for lithium, digitalis, phenytoin, immunosuppressants and anti-arrhythmics, etc.