Answer to Question 1
A
Isoniazid, aspirin (acetylsalicylic acid), and cimetidine (Tagamet) all would cause an increase in serum phenytoin levels. Folic acid (response D) would not be affected. Responses B and C are incorrect.
Answer to Question 2
B
Theophylline is a bronchodilator. Responses A, C, and D are incorrect.