This figure demonstrates the effects of grapefruit juice on felodipine pharmacokinetics and pharmacodynamics.{Dresser}   The top graph shows felodipine plasma concentrations at specific time points, up to 24 hours, following administration of a single dose of felodipine with 250 cc of  grapefruit juice or water.  The bottom graph shows systolic and diastolic blood pressure from the same time points.  Compared to water, there is an increase in felodipine plasma concentrations, as well as a decrease in systolic and diastolic blood pressure.  This demonstrates a potentially clinically significant effect of the grapefruit juice-felodipine interaction.

Dresser GK, Bailey DG, Carruthers SG (2000) Grapefruit juice--felodipine interaction in the elderly. Clin Pharmacol Ther 68: 28-34.