Drugs which increase level of Theophylline include
Refer KDT 6/e p 221 Drugs which inhibit Theophylline metabolism and increase it's plasma level are Erythromycin Ciprofloxacin Cimetidine OCP Allopurinol
Ciprofloxacin
Cimetidine
Allopurinol
All of the above
Respiratory system