Drugs which increase the level of theophylline include :
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
Ciprofloxacin
Cimetidine
Allopurinol
All of these