Effect of grapefruit juice on the pharmacokinetics of theophylline in healthy male volunteers

The effect of grapefruit juice (GFJ) on the pharmacokinetics of a single do se of theophylline was examined in an open crossover study. Healthy male vo lunteers were given sustained release theophylline (300 mg) along with 300 mi of either water or GFJ. Blood samples (2 ml) were collected at different time points Slam 0 to 48 h. Plasma was assayed for theophylline by HPLC an d various pharmacokinetic parameters were calculated. Theophylline levels w ere lower at all time points with GFJ coadministration as compared to water but were significantly lower only during the absorption phase from 1 to 4 h. Although the pharmacokinetic parameters were not significantly different between the two groups, all values were reduced except T-max which was sli ghtly increased. The results indicate that patients may be advised not to c onsume GFJ when taking slow-release theophylline and monitoring of plasma t heophylline levels in patients consuming GFJ might be helpful in better man agement of patient care. (C) 1999 Prous Science. All rights reserved.