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
Zero-order kinetics occur in the following drug with high dose 
Select and explain. 
A. Phenytoin and Theophylline, B. Digoxin and Propranol, C. Amiloride and Probenecid, D. Lithium and Theophylline
A: Phenytoin and Theophylline
Answer: A: Phenytoin and Theophylline 
Explanation: zero order kinetics -the rate of elimination remains constant irrespective of drug concentration, clearance decreases with increase in concentration, or a constant amount of drug is eliminated in unit time The elimination of some drugs changes from first order to zero order at higher doses eg ; Phenytoin, Tolbutamide, Theophylline, Warfarin, DIGOXIN, aspirin ref; KD Tripathi Pharmacology 7th edition (page no;31 )