Oral dipyridamole increases plasma adenosine levels in human beings.

Plasma adenosine levels in five healthy volunteers for 5 consecutive days showed far less intrasubject than intersubject variation (p less than 0.0001), indicating that plasma adenosine levels are relatively constant during this period. Plasma adenosine levels were then measured in a different group of five healthy subjects for a 5-day control period and during a 5-day course of oral dipyridamole at a dose of 100 mg every 6 hours. Intrasubject comparisons showed that plasma adenosine levels were significantly higher during the 5 days of dipyridamole administration than during the control period (p = 0.017) and that this increase was most significant after 48 hours of drug (p less than 0.001) administration. The average increase was 0.133 mumol/L (60%) with a range of 0.063 to 0.197 mumol/L (37% to 212%) during the last 3 days. A significant positive correlation was noted between plasma adenosine and dipyridamole levels (p = 0.001). We conclude that adenosine levels are relatively stable for an individual and are maximally increased after 2 days of oral dipyridamole.