Drug interaction potentials among different brands of grapefruit juice

The discrepancy of drug-interaction potential among different brands of grapefruit juice was estimated based on inhibition of CYP3A activity caused by furanocoumarin derivatives in the grapefruit juice. Heat treatment of the grapefruit juice at 95 degrees C for 1 h was utilized to degrade the furanocoumarins. Initial velocity of testosterone 6beta-oxidation using human liver microsomes was determined as an indicator of the CYP3A activities. Changes in the velocities of the reaction mixture were observed when 10% of each brand of untreated grapefruit juice or heat-treated grapefruit juice was added. The differences in the velocities between untreated and heat-treated grapefruit juice were defined as the potentials of furanocoumarin-caused CYP3A-inhibitions.