Grapefruit Juice -- The Facts About It Interactions with Certain Medications

Researchers have identified that chemical as the one that allows grapefruit juice to interact with certain medications. The furanocoumarins in the grapefruit juice are metabolized by the enzyme cytochrome P450 3A4. That enzyme exists in the cells of the intestine. Grapefruit juice can decrease its intestinal activity. The enzymes in the liver must then focus on breaking down the furanocoumarins in the grapefruit juice.

The liver also contains cytochrome P450. Because the liver contains that enzyme, it can breakdown many of the medications that enter the body. The liver metabolizes those medications, creating their disease-fighting or condition-preventing components.

Scientists have known for a while about the ability of grapefruit juice to interact with certain drugs. A clinical trial first brought such interactions to light. During a clinical trial for calcium blockers, the research team wanted to disguise the alcohol aftertaste left by the drug. They did not want trial participants to know whether or not they had received the drug.

Grapefruit and drug interactions The following drugs are known to have potentially serious interactions with grapefruit products, tangelos and Seville oranges.
Drug name	Type of drug
Carbamazepine (Carbatrol, Tegretol)	An anti-seizure medication
Buspirone (BuSpar), clomipramine (Anafranil) and sertraline (Zoloft)	Antidepressants
Diazepam (Valium), triazolam (Halcion)	Tranquilizers
Felodipine (Plendil), nifedipine (Adalat, Procardia), nimodipine (Nimotop), nisoldipine (Sular) and possibly verapamil (Isoptin, Verelan)	Calcium channel blockers used to treat high blood pressure
Saquinavir (Invirase) and indinavir (Crixivan)	HIV medications
Simvastatin (Zocor), lovastatin (Mevacor, Altoprev) and atorvastatin (Lipitor), simvastatin-ezetimibe (Vytorin)	HMG-CoA reductase inhibitors used to treat high cholesterol
Cyclosporine (Neoral, Sandimmune), tacrolimus (Prograf) and sirolimus (Rapamune)	Immunosuppressant drugs
Amiodarone (Cordarone)	A drug used to treat and prevent abnormal heart rhythms (arrhythmias)
Methadone	Pain relief medication
Sildenafil (Viagra)	Erectile dysfunction medication

Interaction with the calcium blockers

The clinical researchers decided to use grapefruit juice as the "cover-up substance." They then found that the grapefruit juice could interact with the calcium blockers. Scientists have since found dozens of other medications that can interact with grapefruit juice.

Interaction with certain drugs used to lower the blood level of cholesterol

As the liver works to breakdown the grapefruit juice, the drug builds-up in the body. That leads to a breakdown of the body muscles. The breakdown products flood the urinary system, and that can cause a catastrophic kidney failure.

Interaction with certain antibiotics

A patient on clanthromycin, erythromycin or troleandomycin should be counseled against drinking grapefruit juice. The combination of antibiotic and grapefruit juice can cause diarrhea. The interaction of the juice with the drug can slow the drug's ability to fight the infectious organism.

Usually the pharmacist puts a warning label on medications that interact with grapefruit juice. Unfortunately, a number of patients fail to heed or even read such labels. In a hospital setting, a person on erythromycin might be told not to order grapefruit juice. Still, an unknowing hospital volunteer might offer that patient a cup of juice-grapefruit juice.

Interaction with the antiepileptic drug carbamazeprine

Such a drug might be used as an alternative to a more common antiepileptic, such as phenytoin. That substitution might occur if a woman on phenytoin has chosen to become pregnant. Her doctor might warn her not to drink grapefruit juice, since juice would seem like a "good" drink for a pregnant woman.

Interaction with certain the treat high blood pressure drugs

That interaction can produce irregular heart rhythms. Ironically, some blood pressure medications lower the level of potassium in the body. That can be corrected by eating a different fruit-a banana.

Interaction with the drugs sisdenafil and tadalafil

Those names probably mean little to the average reader. The reader would certainly recognize the names on the medications that contain those two chemicals-Viagra and Cialis.

Men have yet another reason to keep in mind the ability of grapefruit juice to interact with certain drugs. Grapefruit juice interacts with finasteride, a drug used to treat benign prostatic hyperplasia.

Sugestion to Avoid Serious Interactions

If you take any of these drugs, you should completely avoid grapefruit products, tangelos and Seville oranges, unless otherwise directed by your doctor. Waiting to take these medications, ”even up to 24 hours”, after you drink grapefruit juice will not prevent an interaction.

Talk to your doctor or pharmacist if you have concerns about the effect of grapefruit products on any of the medications you take.

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