Grapefruit Juice Can Interact With Medicines!
William C. Shiel Jr., MD, FACP, FACR
William C. Shiel Jr., MD, FACP, FACR
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
Medical and Pharmacy Editor:
A nutraceutical is a food or part of a food that allegedly provides medicinal or health benefits, including the prevention and treatment of disease. Grapefruit juice has been touted as containing many compounds that can reduce hardening of the arteries (atherosclerosis) and even the risk of cancer. Grapefruit juice can, therefore, be justifiably referred to as a classic nutraceutical. However, for many persons taking certain medications, grapefruit juice might actually better be termed a "nutrapollutical!"
It turns out that grapefruit juice can directly or indirectly interact in important ways with a number of medications. This is especially important since grapefruit juice is consumed by approximately one fifth of Americans for breakfast - a time of the day when medications also are commonly taken.
Grapefruit juice blocks special enzymes in the wall of the small intestine that actually destroys many medications and prevents their absorption into the body. Thus, smaller amounts of the drugs get into the body than are ingested. When the action of this enzyme is blocked, more of the drugs get into the body and the blood levels of these medications increase. This can lead to toxic side effects from the medications.
Amazingly, this remarkable food-drug interaction was discovered completely by accident over a decade ago! Researchers were investigating whether alcohol could interact with felodipine (Plendil) and used a solution of alcohol with grapefruit juice to mask the taste of alcohol for the study. Researchers discovered that blood levels of felodipine were increased several fold more than in previous studies. This increased blood level caused an increase in the effect and side effects of felodipine. Further research revealed that the grapefruit juice itself was actually increasing the amount of the study drug in the body.
Research about the interaction of grapefruit juice with drugs suggests that compounds in grapefruit juice, called furanocoumarins (for example, bergamottin), may be responsible for the effects of grapefruit juice. Researchers believe that furanocoumarins block the enzymes in the intestines that normally break down many drugs. One glass of grapefruit juice could elicit the maximum blocking effect, and the effect may persist for longer than 24 hours. Since the effects can last for such a prolonged period of time, grapefruit juice does not have to be taken at the same time as the medication in order for the interaction to occur. Therefore, unlike similar interactions, where the interaction can be avoided by separating the administration of the two interacting agents by a couple of hours, administration of grapefruit juice with susceptible drugs should be separated by 24 or more hours to avoid the interaction. Since this is not practical for individuals who are taking a medication daily, they should not consume grapefruit juice when taking medications that are affected by grapefruit juice.
The grapefruit juice-drug interaction can lead to unpredictable and hazardous levels of certain important drugs.
These are medications with which grapefruit juice should NOT be consumed unless advised by a doctor: