a patient with a history of bronchial asthma is seen in the clinic for increased episodes of difficulty breathing. he has been taking theophylline 100 mg po tid. he is 40 years old and obese with an 16-pack-year history of cigarette smoking and excessive intake of coffee daily. he eats a low-carbohydrate, high-protein diet. which identified factors decrease the therapeutic effects of the theophylline?