Xanthine interference with dipyridamole-thallium-201 myocardial imaging.

Both theophylline and caffeine have been shown to antagonize adenosine and are associated with false-negative test results with dipyridamole-T1-201 imaging. This has led to recommendations for theophylline and caffeine abstinence for at least 24 hours prior to dipyridamole-T1-201 imaging. Because pentoxifylline and its metabolites are structurally similar to theophylline and caffeine, and pentoxifylline has adenosine antagonistic properties, one might presume that pentoxifylline may also attenuate the diagnostic yield of dipyridamole-T1-201 imaging. To the best of our knowledge, the pharmacodynamic interaction between pentoxifylline and dipyridamole and its effects on dipyridamole-T1-201 imaging in patients have never been studied adequately. However, a single study in 7 dogs does suggest that there may be no significant interaction. In addition, we must also consider the nonacute nature of the clinical use of pentoxifylline in peripheral vascular disease and the critical need for accurate dipyridamole-T1-201 imaging results and the cost associated with this procedure. Until such information is available in humans, it would be prudent to discontinue pentoxifylline, in addition to caffeinated foods, caffeine-containing drug products, and theophylline, at least 24 hours prior to dipyridamole-T1-201 imaging.