Caffeine Grapefruit juice

Fuhr, U., Klittich, K. et al. (1993). Inhibitory effect of grapefruit juice and its bitter principal, naringenin, on CYP1A2 dependent metabolism of caffeine in man. Br. J. Clin. Pharmacol., 35(4), 431-6. 

Avoid consuming grapefruit or grapefruit juice and limit caffeine intake while taking verapamil... 

Maish WA, Hampton EM, Whitsett TL, Shepard JD, Lovallo WR. Influence of grapefruit juice on caffeine pharmacokinetics and pharmacodynamics. Pharmacotherapy 1996 16(6) 1046-1052. 

Grapefruit juice also inhibits the CYP1A2 enzyme system in vitro but not in vivo. This is consistent with the understanding that the effect of grapefruit juice occurs at the level of the intestinal wall where levels of CYP2A expression are low. These CYP2A substrates studied with grapefruit juice have included caffeine, theophylline, and coumarin (Table 34.1). 

There are isolated cases of apparent interactions between clozapine, and ampicillin, buspirone, caffeine, haloperidol, loperamide, modafinil, nefazodone, nicotinic acid, tryptophan, or vitamin C. Grapefruit juice, influenza vaccine mirtazapine, reboxetine, or venlafaxine do not appear to interact Cocaine levels may increase when taken with clozapine. 

Grapefruit juice does not interact with caffeine to a clinically relevant extent. 

Fuhr U, Klittich K, Staib AH, Inhibitory effect of grapefruit juice and the active component, naringenin on CYPl A2 dependent metabolism of caffeine in man. BrJ Clin Pharmacol (1993) 35,431-6, [Title corrected by erratum],... 

Drug-food interactions A systematic review evaluating interactions between CBZ and food [60 ] found that caffeine decreases oral bioavailability and impairs the anticonvulsant efficacy of CBZ in both human and animal studies. Grapefruit, kinnow, pomegranate, and star fruit juices cause an increase in the oral bioavailability of CBZ through inhibition of enteric CYP3A4 activity. 

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