<prompt> Drugs which increase the level of theophylline include :CiprofloxacinCimetidineAllopurinolAll of these  <response>: Drugs which inhibit theophylline metabolism and increase its plasma level are:ErythromycinCiprofloxacinCimetidineOCPAllopurinolAgents which induce theophylline metabolism and decrease its plasma level are :SmokingPhenytoinRifampicinPhenobarbitone 