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Grapefruit Juice - Is It Always Healthy?

Meggan Weisberg
Doctor of Pharmacy Candidate, 2001
Ohio Northern University

Did you have a glass of grapefruit juice with breakfast this morning? Have you taken your morning medications? Do you know if grapefruit juice can interact with your medications?

Mr. X did not know. This healthy 29-year-old male woke up one morning and took his common allergy medicine, terfenadine. He had been taking this medicine twice a day for more than a year. He also liked drinking grapefruit juice 2 or 3 times a week and sometimes more often. On this day, he drank two glasses of grapefruit juice and went out to mow the lawn. Moments later, he collapsed and died due to a fatal heart problem.

Even though he had taken exactly the amount prescribed for him, the coroner found that the allergy medicine had reached a dangerous level in his blood. It appeared that grapefruit juice slowed down the body's ability to break down this drug. This may have led to the toxic amounts of the medicine that killed Mr. X.

The Food and Drug Administration (FDA) did not know about these side effects when the medicine was approved. The FDA removed this medicine from the market in 1997 because of the possibility of serious side effects on the heart.

While this problem has not been seen with other allergy medications, terfenadine is not the only medication affected by grapefruit juice! If we only knew then what we know now, Mr. X might still be alive. Every person who is taking medications should check to see if it is safe to drink grapefruit juice.

"Why does grapefruit juice interact with some medications and not others?"

It is not known exactly what grapefruit juice contains that causes these drug interactions. Some researchers think that narningenin, DHB, or both are the compounds in grapefruit juice that may be responsible for the interaction.1,2,3 What we do know is that some drugs need certain natural enzymes in the body to break them down so that medicine can be eliminated from the body.

Grapefruit juice interferes with one of these enzymes, CYP3A4. It may cause some medicine to build up in the body, leading to unwanted side effects. The amount of CYP3A4 found in a person will vary from person to person. People with higher amounts of the enzyme are affected when grapefruit juice is taken with medicine more often than people with lower amounts.

"Do other types of juices or eating a grapefruit interact with medications?"

Not all citrus juices contain narningenin or DHB. For this reason, citrus juices such as orange juice have not been shown to affect this enzyme.2

Different parts of the grapefruit also contain different amounts of these two substances. The peel of the grapefruit is thought to contain more than any other part of the fruit. It is uncertain if eating a grapefruit will cause the same effects as drinking grapefruit juice.

Even different brands of grapefruit juice may have different amounts of these two substances.2, 3 The way the grapefruit juice is processed may be one of the reasons for this. When companies make grapefruit juice, machines use enough pressure to squeeze these substances from all parts of the grapefruit. The consumer does not know how much of these compounds are in the different products. It would be helpful for consumers if the labels of grapefruit juice products contained a warning statement such as "This product contains substances that may interact with certain prescription drugs."

A common misconception is that it takes large amounts of grapefruit juice to interact with medications.1 An 8 oz glass of regular strength grapefruit juice has a similar effect as two or three glasses of double-strength grapefruit juice.

"Do my medications interact with grapefruit juice?"

Every time you are prescribed a new medicine check with your doctor or pharmacist about possible grapefruit juice interactions.

If you have not been drinking grapefruit juice, then do not add it to your diet until you know if it is safe for you. If you are already taking any of your medications with grapefruit juice, do not stop taking it without talking to your doctor first. When you stop drinking grapefruit juice, your doctor may need to adjust the dose of your medicine.

The following is a partial list of medication that interacts with grapefruit juice in some people.

atorvastatin (Lipitor)2
buspirone (Buspar)2
carbamazepine (Tegretol)2
cerivastatin (Baycol)2
cyclosporine (Sandimmune)1, 2, 3
diazepam (Valium)2
erythromycin (E-Mycin, Ery-Tab, E-base, E.E.S., Ery-Ped)
felodipine (Plendil)1, 2, 3, 4
lovastatin (Mevacor)2
methadone (Dolophine, Methadose )2
midazolam (Versed)1, 2, 4, 5
nifedipine (Adalat, Procardia )2, 3
nimodipine (Nimotop)2, 3
nisoldipine (Sular)1, 2, 3, 5
saquinavir (Fortovase, Invirase )3
sertraline (Zoloft)2
sildenafil (Viagra)2
simvastatin (Zocor)2
tacrolimus (Prograf)2
triazolam (Halcion)2

Not all of these medications in combination with grapefruit juice will produce as severe a reaction as the one described in the beginning of the article. Researchers continue to investigate grapefruit juice interactions to better predict which medicine should not be taken in combination with grapefruit juice.

Until all the facts are known, ask your pharmacist if your medicine interacts with the antibiotic erythromycin. If it does, then there is a high chance that the medicine will interact with grapefruit juice too.

Before you take your next pill, remember that grapefruit juice has the potential to interact with many prescription drugs. Grapefruit juice may not be healthy for everyone.

References:
1. Spence J.D. Drug interactions with grapefruit juice: Whose responsibility is it to warn the public? Clin Pharmacol Ther 1997;61: 395-200.

2. Kane GC, Lipsky JJ. Drug-grapefruit Juice Interactions. Mayo Clin Proc 2000;75:933-942.

3.Fuhr U. Drug Interactions with Grapefruit Juice. Drug Safety 1998 Apr; 18 (4): 251-272

.© 2001 Consumer Health Information Corporation. All rights reserved.