rug Interactions: Theophylline interacts with a wide variety of drugs. The interaction may be pharmacodynamic, i.e., alterations in the therapeutic response to Theophylline or another drug or occurrence of adverse effects without a change in serum Theophylline concentration. More frequently, however, the interaction is pharmacokinetic, i.e., the rate of Theophylline clearance is altered by another drug resulting in increased or decreased serum Theophylline concentrations. Theophylline only rarely alters the pharmacokinetics of other drugs.