Which substance must be discontinued for at least 24-36 hours before administering dipyridamole?

The appropriate substance to be discontinued for at least 24-36 hours before administering dipyridamole is theophylline. Dipyridamole is a vasodilator used in nuclear medicine stress testing; it works by inhibiting the reuptake of adenosine, which leads to increased coronary blood flow. Theophylline, a medication that acts as a bronchodilator and also has adenosine receptor antagonistic properties, can counteract the effects of dipyridamole. By inhibiting the action of adenosine, theophylline reduces the efficacy of dipyridamole in inducing vasodilation. Therefore, discontinuing theophylline is critical to ensure that dipyridamole can exert its full therapeutic effect during the test.

Other medications and substances do not have this specific interaction with dipyridamole that would necessitate their discontinuation prior to its administration. Water, insulin, and aspirin do not significantly affect the pharmacodynamics or pharmacokinetics of dipyridamole, allowing them to be continued as needed.