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 < 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 < 0.001) administration. The average increase was 0.133 µmol/L (60%) with a range of 0.063 to 0.197 µmol/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. Clinical Pharmacology and Therapeutics (1989) 45, 80–84; doi: 10.1038/clpt.1989.12