Drug Interactions between bilberry / evening primrose / flax and dipyridamole

ADJUST DOSING INTERVAL: Caffeine and other xanthine derivatives (e.g., theophylline) are nonspecific, competitive antagonists of adenosine receptors. As such, they may interfere with the vasodilating effect of dipyridamole, an adenosine receptor agonist. In studies of healthy volunteers, caffeine has been shown to reduce the hemodynamic response (i.e., heart rate increases, vasodilation, blood pressure changes) to dipyridamole infusions, and both caffeine and theophylline have been reported to cause false-negative results in myocardial scintigraphy tests using dipyridamole.

MANAGEMENT: Patients should avoid consumption of caffeine-containing products for at least 24 hours prior to administration of dipyridamole for myocardial perfusion imaging.

ADJUST DOSING INTERVAL: Methylxanthines (e.g., caffeine, theophylline) are nonspecific, competitive antagonists of adenosine receptors. As such, they may interfere with the pharmacologic effects of adenosine and other adenosine receptor agonists such as dipyridamole and regadenoson. There have been case reports of patients receiving theophylline who required higher than normal dosages of adenosine for the treatment of paroxysmal supraventricular tachycardia. In studies of healthy volunteers, caffeine and theophylline have been shown to reduce the cardiovascular response to adenosine infusions (i.e., heart rate increases, vasodilation, blood pressure changes), and theophylline has also been shown to attenuate adenosine-induced respiratory effects and chest pain/discomfort. Similarly, caffeine has been found to reduce the hemodynamic response to dipyridamole, and both caffeine and theophylline have been reported to cause false-negative results in myocardial scintigraphy tests using dipyridamole. In a placebo-controlled study that assessed the effects of oral caffeine on regadenoson-induced increase in coronary flow reserve (CFR), healthy subjects who took caffeine 200 mg orally two hours prior to regadenoson administration exhibited a median CFR that was 92% that of subjects who took placebo. The study was done using positron emission tomography with radiolabeled water.

MANAGEMENT: Clinicians should be aware that adenosine and other adenosine receptor agonists may be less effective in the presence of methylxanthines. Methylxanthines including caffeine should be withheld for 12 to 24 hours (or five half-lives) prior to administration of adenosine receptor agonists for myocardial perfusion imaging. However, parenteral aminophylline should be readily available for treating severe or persistent adverse reactions to adenosine receptor agonists such as bronchospasm or chest pain.