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Interactions With Drugs and
Medicines Grapefruit juice inhibits a special enzyme in the intestines that is responsible for the natural breakdown and absorption of many medications. When the action of this enzyme is blocked, the blood levels of these medications increase, which can lead to toxic side effects from the medications. Grapefruit juice research has suggested that flavonoids and/or furanocoumarin compounds are the substances that act to block the enzyme in the intestines that normally metabolizes many drugs. The grapefruit juice-drug interaction can lead to unpredictable and hazardous levels of certain important drugs. These medications should not be consumed with grapefruit juice unless advised by a doctor:
The following drugs may potentially have interactions with grapefruit juice, but this potential has not been scientifically studied. Use caution:
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Grapefruit juice Interactions with medicinesstatinsGrapefruit juice has been shown to increase levels of lovastatin, simvastatin, and atorvastatin, increasing the maximum concentration of unchanged simvastatin by ninefold, the mean area under the curve by 16-fold, and the maximum concentration and mean area underthe curve of simvastatin acid by sevenfold.Grape-fruit juice increased the HMG-CoA reductase inhibitionof lovastatin by 30% to 42% when the combination was administered for 3 consecutive days . Grapefruit juice also increased the maximum concentration and the areaunder the curve of atorvastatin acid by about threefold . |
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(Clinically Relevant Differences between the
Statins/Chong et al October 1, 2001 THE AMERICAN JOURNAL OFMEDICINE Volume 111393) |
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Grapefruit to blame
for side effect with Zocor Mar 02 (Reuters
Health) - Eating a grapefruit each morning may have triggered a serious
side effect in a woman taking the popular anticholesterol drug Zocor
(simvastatin), new research suggests. Although the case involved Zocor,
the authors note that similar drugs could also be influenced by grapefruit consumption.
The present case involved a 40-year-old woman who was admitted to the hospital with lower extremity weakness, study authors Dr. Jens P. Dreier and Dr. Matthias Endres, from Charite Hospital in Berlin, Germany, note. The report is published in the medical journal Neurology.
The woman reported exercising regularly at the gym and had apparently been healthy until 10 days prior when slight muscle weakness and pain were first noted. The patient had been taking Zocor for high cholesterol levels.
The laboratory findings suggested rhabdomyolysis and, given the patient's medication history, the researcher believed it was related to the Zocor. After discontinuation of the drug and vigorous fluid replacement, the patient's condition improved steadily and she was discharged from the hospital on day six.
Although Zocor was thought to be responsible for the rhabdomyolysis, the researchers were puzzled about the onset, since the patient had been taking the drug for more than two years. So, they questioned her about any recent triggers and that is when she revealed eating one grapefruit every day for the two weeks before admission. Rhabdomyolysis, a disorder involving muscle breakdown and kidney problems, is a rare but serious side effect of drugs like Zocor, known as statins. In August 2001, drug maker Bayer AG was forced to recall its statin Baycol (cerivastatin), after the drug was linked to an excessive number of rhabdomyolysis cases, including more than 100 fatalities.
Grapefruit contains a chemical that inactivates an enzyme in the liver that breaks down Zocor and many other statins. Therefore, regular consumption of the fruit can lead to body levels of Zocor that are too high.
Patients taking Zocor and most other statins should be advised not to eat grapefruit, the investigators conclude.
SOURCE: Neurology, February 24, 2004. |
calcium-channel blockersThe grapefruit juice-drug interaction seems to affect mainly the dihydropyridine family of calcium-channel blockers. Tachycardia and decreased diastolic blood pressure were noted when felodipine was given with double-strength grapefruit juice (GJ) in six hypertensive patients. Felodipine area under the curve (AUC) increased by 184%, and an increase in side effects (facial flushing, headache, dizziness) were noted. Patients in the same study taking nifedipine experienced an increase in AUC by 34%. In 12 healthy subjects amlodipine AUC was increased by 16% and patients experienced a slight reduction in diastolic blood pressure when amlodipine was given with single-strength GJ. |
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In most studies, the interactions were tested in healthy subjects. This is an important distinction, as patients with hypertension or other cardiac conditions may experience more pronounced effects on heart rate and blood pressure. GJ can cause substantial increases in bioavailability of certain calcium-channel blockers, primarily the dihydropyridine type. Patients receiving these medications and drinking grapefruit juice regularly should be monitored for increased response. A reasonable guideline for pharmacists and other health care professionals is to tell patients that if they are not currently taking their antihypertensive medications with grapefruit juice regularly, don’t start. If they are already taking their medications with grapefruit juice regularly, and are not experiencing adverse effects, don’t stop. if there is a concern for a drug interaction with GJ, it seems logical to avoid consumption of grapefruit segments as well during pharmacotherapy with the affected drug(s). Confectioneries, like marmalades, made from grapefruit peel may also cause a drug interaction. http://www.healthandage.com/Home/gm%3D20%21gsq%3Dgrapefruit%21gid7=617 July 15, 2003 Question I've heard mentioned a couple times in instructions or on labels that "grapefruit juice should not be used with this product". I believe calcium and Cipro were two of the items. Why is this? And does it mean you have to leave grapefruit totally out of your diet or just not have it in the same time frame - i.e. would a pill with breakfast and grapefruit at lunch be OK? Answer Research has shown that there is a component in grapefruit juice that appears to interfere with the liver's ability to clear some drugs from the body. Consequently the levels of the drugs in the blood could build to a toxic level. However, it is fine to drink grapefruit juice at times when you are not taking your medications - i.e. a few hours later. Neither calcium or Cipro appear to have an important grapefruit juice interaction. To learn more of the effects of grapefruit on drug absorbtion, go to the link below |
| 1. I don't drink grapefruit juice (GJ) but I do eat grapefruit pieces/sections or take grapefruit extract. Will this cause the same interactions with affected medication as the juice does ? |
| Recently, It has been shown that both grapefruit sections and an extract of grapefruit can cause interactions just the same way grapefruit juice can. The study was done with the blood pressure lowering drug felodipine (Plendil, Renedil). The blood levels of felodipine was increased equally whether it was given with juice, sections or grapefruit extract. This has not been confirmed with any other medications, but it does seem reasonable that since grapefruit juice is made from grapefruit, the pieces and sections could cause similar drug interactions. | 3. How does GJ cause drug interactions with medications ? |
| OK, this is the short answer. GJ is known to inhibit an enzyme system found in the small intestine that metabolizes some drugs prior to absorption into the bloodstream. This system is called CYP 3A4 and does play a role in the metabolism of certain drugs. Drugs that are affected by this interaction are metabolized less than usual when they are taken with GJ, allowing a higher amount to reach the bloodstream, and this will cause higher drug levels, sometimes with increases in clinical effects or side effects. GJ also affects a transporter called p-glycoprotein. The effects of this are less clearly defined, but p-glycoprotein is responsible for actively secreting some absorbed drugs back into the small bowel. |
| 4. I take a cholesterol lowering -statin drug known to interact with GJ. Can I have a glass of grapefruit juice in the morning, and then take my medication in the evening ? |
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concerns the -statin drugs lovastatin (Mevacor), atorvastatin (Lipitor),
simvastatin (Zocor) and cerivastatin (Baycol - now off the market). Pravastatin (Pravachol) and
fluvastatin (Lescol) do not appear to be affected by GJ.
A study that was done by Merck
(makers of Mevacor (lovastatin) gave the lovastatin dose in the evening after a single glass of GJ taken earlier that morning, and showed that the interaction was minimal, and that this practice could be done safely.
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| 5. Do oranges and other citrus fruits cause the same interaction as GJ ? |
| The answer is a qualified "no". The interaction is believed to be due to a chemical compound that is relatively specific to GJ, called 6',7'-dihydroxybergamottin. It is not due to vitamin C or citric acid. One variety of oranges called seville oranges contain 6',7'-dihydroxybergamottin, and did seem to cause a similar drug interaction to GJ, but these are not used for commercial juice production and are only seen in the marketplace as the main oranges used in marmalade production. Recently, studies with seville oranges have been done, and results will be available coming soon to this website. Grapefruit hybrids such as tangellos, have not been directly studied, and since they are not commonly seen in the marketplace, probably never will be studied. However, these products are genetically derived from grapefruit originally, and therefore may have potential for drug interactions. |
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| 6. Will grapefruit juice or pieces affect physiological functions of my body such as: lowering cholesterol, worsening body odor, increasing liver enzymes, make me lose weight, cause drowsiness, dizziness or other effects ? |
| Unfortunately, my field of research is very specifically limited to interactions that occur between grapefruit and medications. I do not study the physiological and/or nutritional functions of grapefruit. All of my recommendations about grapefruit juice-drug interactions are based on original research articles in the medical literature. These articles do not examine physiological effects of grapefruit other than with regard to how it may affect drug metabolism. I am unable to give you an answer to these types of questions, and would request that I not be sent email regarding the physiological/nutritional function(s) of grapefruit. For this type of information, the best person to ask would be a dietitian. Click here for an online dietitian's website. |
| 7. I tried searching for (specified drug) with the search engine on the main page. I am sure that the spelling of the drug was correct, but no results were found matching my query. Now what do I do ? |
| First,
re-check your spelling. Try entering the brand name (usually shorter,
easier to pronounce) and then the generic name (longer, harder to
pronounce). If you have a prescription that was filled outside of Canada
or the USA, use of the generic name is best. You can search the internet
to find the American brand name of your medication, and try entering that
into the search engine. If all of these attempts fail, then it means one
of two things: 1) There is no data regarding a grapefruit interaction with the medication you are searching for. 2) There is data regarding a grapefruit interaction, but it a relatively new article, and I have not added it to my website yet. I update the site regularly, but it may lag behind the medical literature by several months, due to delays in indexing services updating their databases, or delays on my part updating my website. |
Too Much Grape Juice Could Cause Iron DeficiencyThe same antioxidant compounds in dark grape juice that are noted for their health benefits in fighting heart disease may have a downside, according to new research in the Journal of Agricultural and Food Chemistry. In cell studies, scientists with the U.S. Department of Agriculture and Cornell University found that polyphenols in purple (also called red) grape juice can inhibit the uptake of iron, which could increase the risk of iron-deficiency anemia. |