Grapefruit juice consumption

Fexofenadine and digoxin are both well-known substrates for OATP transport, though the relative contribution of OATP modulation on drug interactions involving these two agents is unclear, since both are also P-gp substrates. The 60-80% reduction in fexofenadine bioavailability that results from orange, apple, and grapefruit juice consumption, however, is likely the result of OATP inhibition, rather than of P-gp induction (94). 

In a pharmacokinetic study, grapefruit juice had little effect on the absorption of levothyroxine, suggesting a clinically relevant interaction is unlikely. However, there is one case of unexplained hypothyroidism in a patient taking levothyroxine, which resolved when grapefruit juice consumption was reduced. 

Specific concomitant medications or consumptions (check specific statin package insert for warnings) fibrates (especially gemfibrozil, but other fibrates too), nicotinic acid (rarely), cyclosporine, azole antifungals such as itraconazole and ketoconazole, macrolide antibiotics such as erythromycin and clarithromycin, protease inhibitors used to treat Acquired Immune Deficiency Syndrome, nefazodone (antidepressant), verapamil, amiodarone, large quantities of grapefruit juice (usually more than 1 quart per day), and alcohol abuse (independently predisposes to myopathy)... 

Fig. 18.6. Midazolam administration with and without grapefruit juice (CFJ) treatment [41]. Midazolam (15 mg tablet) was administered to eight male subjects (average body weight 82 kg) before and after consumption of two glasses (200 mL each) of CFJ, 1 h before drug administration. QMPRPIus was used to estimate human effective permeability (12 x 10 4 cm s 1), pure aqueous water...

Lilja JJ, Kivisto KT, Backman JT, Neuvonen PJ. Effect of grapefruit juice dose on grapefruit juice-triazolam interaction repeated consumption prolongs triazolam half-life. Eur J Clin Pharmacol 2000 56(5) 411-415. 

Lilja JJ, Neuvonen M, Neuvonen PJ. Effects of regular consumption of grapefruit juice on the pharmacokinetics of simvastatin. Br J Clin Pharmacol 2004 58(l) 56-60. 

Kivisto KT, Lilja JJ, Backman JT, Neuvonen PJ. Repeated consumption of grapefruit juice considerably increases plasma concentrations of cisapride. Clin Pharmacol Ther 1999 66(5) 448-153. 

Grapefruit juice does not specifically affect SSRIs, but the nurse should be aware that many medications interact negatively with grapefruit juice and its consumption should not be encouraged. 

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