Determining the effects of grapefruit juice on pharmacokinetics of oral digoxin (a drug often prescribed for heart ailments) was the goal of a study by Parker et al. (A-1). Seven healthy nonsmoking volunteers participated in the study. Subjects took digoxin with water for 2 weeks, no digoxin for 2 weeks, and digoxin with grapefruit juice for 2 weeks. The average peak plasma digoxin concentration (Cmax) when subjects took digoxin with water is given in the first column of the following table. The second column gives the Cmax concentration when subjects took digoxin with grapefruit juice. May we conclude on the basis of these data that the Cmax concentration is higher when digoxin is taken with grapefruit juice? Let a ¼ :5.

Cmax Subject H2O GFJ 1 2.34 3.03 2 2.46 3.46 3 1.87 1.97 4 3.09 3.81 5 5.59 3.07 6 4.05 2.62 7 6.21 3.44 Source: Data provided courtesy of Robert B. Parker, Pharm.D.