d) Theophylline tablets extended-release 12 hr formulation, 300 mg orally taken every 12 hr will be dispensed, and the subject will return one week later for Visit 2. The subject will be asked to refrain from using his/her long acting beta agonists and anticholinergics for one day (24 hours) prior to Visit 2, and not to use the short acting beta agonist or take any caffeine containing drinks on the morning of visit 2. The subject will be asked to inform the P. I. should there be any adverse event.