This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Drugs which increase the level of theophylline include : 
Select and explain. 
A. Ciprofloxacin, B. Cimetidine, C. Allopurinol, D. All of these
D: All of these
Answer: D: All of these 
Explanation: Drugs which inhibit theophylline metabolism and increase its plasma level are:


Erythromycin
Ciprofloxacin
Cimetidine
OCP
Allopurinol


Agents which induce theophylline metabolism and decrease its plasma level are :


Smoking
Phenytoin
Rifampicin
Phenobarbitone