Actually I was right.
Grapefruit + Xanax (alprazolam) = no difference
Grapefruit + Valium (diazepam) = potentiation
Studies:
1)
http://www.ncbi.nlm.nih.gov:80/entr...ve&db=pubmed&dopt=Abstract&list_uids=10907671
Psychopharmacology (Berl). 2000 Jun;150(2):185-90. Related Articles,Links
Effects of repeated ingestion of grapefruit juice on the single and multiple oral-dose pharmacokinetics and pharmacodynamics of alprazolam.
Yasui N, Kondo T, Furukori H, Kaneko S, Ohkubo T, Uno T, Osanai T, Sugawara K, Otani K.
Department of Neuropsychiatry, Hirosaki University School of Medicine, Japan.
The effects of repeated ingestion of grapefruit juice, an inhibitor of cytochrome P450 3A4 (CYP3A4), on the pharmacokinetics and pharmacodynamics of both single and multiple oral doses of alprazolam, a substrate of CYP3A4, were examined. In study 1, eight healthy volunteers ingesting 600 ml/day water or grapefruit juice for 10 days took a single oral 0.8-mg dose of alprazolam on the eighth day. Plasma drug concentrations were monitored up to 48 h after alprazolam dosing together with evaluation of psychomotor function. Grapefruit juice altered neither the plasma concentrations of alprazolam at any time points, any pharmacokinetic parameters, nor the majority of psychomotor function parameters in subjects. In study 2, 11 patients with anxiety disorders receiving alprazolam (0.8-2.4 mg/day) ingested grapefruit juice (600 ml/day) for 7 days. Blood samples were collected before and during grapefruit juice ingestion and 1 week after its discontinuation together with an assessment of clinical status. Grapefruit juice altered neither the steady-state plasma concentration of alprazolam nor the clinical status in patients. The present study shows that grapefruit juice is unlikely to affect pharmacokinetics or pharmacodynamics of alprazolam due to its high bioavailability.
2)
http://www.ncbi.nlm.nih.gov:80/entr...eve&db=pubmed&dopt=Abstract&list_uids=9625273
Eur J Drug Metab Pharmacokinet. 1998 Jan-Mar;23(1):55-9. Related Articles,Links
Interaction between grapefruit juice and diazepam in humans.
Ozdemir M, Aktan Y, Boydag BS, Cingi MI, Musmul A.
Department of Pharmacology, Medical Faculty, University of Osmangazi, Eskisehir, Turkey.
Grapefruit juice has been reported to markedly improve the bioavailability of triazolam, midazolam, terfenadine, cyclosporine and several dihydropyridine calcium channel blockers including felodipine, nifedipine, nitrendipine and nisoldipine. Because these drugs are metabolized by the hepatic cytochrome P450 isozyme (CYP) 3A4, the inhibitory effect of grapefruit juice is thought to results from inhibition of CYP3A4. In this study, our aim was to investigate the effects of grapefruit juice on plasma concentrations of diazepam. Eight healthy male and female subjects participated in this study. Oral (5 mg) diazepam was administered with either 250 ml water and grapefruit juice. Blood samples were collected for a 24 h period, and whole blood concentrations of diazepam were measured enzyme immunoassay. The mean AUC(0-24) of diazepam was increased 3.2-fold (P < 0.001) and Cmax was increased 1.5-fold (P < 0.05) by the grapefruit juice. Grapefruit juice postponed the tmax of diazepam from 1.50 h to 2.06 h (P < 0.01).