Grapefruit in Your Diet may Interfere with Certain Medications

The Statue of Liberty on Liberty Island in New York Harbor. (Dr. Noorali Bharwani)
The Statue of Liberty on Liberty Island in New York Harbor. (Dr. Noorali Bharwani)

“Our research group discovered the interaction between grapefruit and certain medications more than 20 years ago,” says an article in the Canadian Medical Association Journal (CMAJ March 5, 2013) written by Dr. David Bailey, Ph.D and his colleagues from Ottawa.

Certain other citrus fruits and products can interfere with several kinds of prescription pills. You are advised to check with your pharmacist and/or doctor before consuming any citrus products, including grapefruit, if you take prescription medications. Taking your medication and grapefruit product at different times does not stop the interaction.

Chemicals in the fruit can interfere with the enzymes that break down the medication in the digestive system. As a result, the medication may stay in your body for too short or too long a time. A medication that’s broken down too quickly won’t have time to work. On the other hand, a medication that stays in the body too long may build up to potentially dangerous levels.

There is a long list of medications that is affected by grapefruit and other citrus food. Here are some examples:

Antibiotics: erythromycin

Cholesterol reducing pills: atorvastatin (Lipitor), lovastatin (Altoprev), others

High blood pressure pills: felodipine, carvedilol (Coreg), others

Pills for heart problems: amiodarone (Coradarone, Pacerone)

Antidepressants: diazepam (Valium, Diastat), fluvoxamine, others

Pills to prevent organ rejection in transplant recipients: cyclosporine (Sandimmune and others)

Play it safe with prescription drugs. Always ask your doctor or pharmacist when you get a new prescription if it interacts with any foods or other medicines.

Many of the drugs that interact with grapefruit are highly prescribed and are essential for the treatment of important or common medical conditions. Currently, more than 85 drugs have the possibility of interacting with grapefruit; of these drugs, 43 have interactions that can result in serious adverse effects.

The chemicals in grapefruit involved in this interaction are the furanocoumarins.

One whole grapefruit or 200 mL of grapefruit juice is sufficient to cause clinically relevant increased systemic drug concentration and subsequent adverse effect. Seville oranges, often used in marmalades, limes and pomelo also produce this interaction.

In spite of the scientific evidence from reliable sources regarding adverse effects as discussed earlier, in routine clinical practice physicians do not see too many complications. One reason could be that multiple factors likely need to combine to achieve a marked increase in systemic drug concentration. It is reasonable to assume that just exposure to any interacting combination would not be sufficient to cause a clinically important change in drug response in all, if not most, cases.

Having said that, the fact remains you have to be vigilant. Pharmacists are the best source of information when it comes medications.

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The Good and Ugly Sides of Grapefruit and Grapefruit Juice

Cross section of a grapefruit.
Cross section of a grapefruit.

There are many good things about grapefruit. According to the USDA, 100 grams of grapefruit contains 32 calories. Most of those calories come from carbohydrates and very few are from fat or protein. Micronutrients include vitamin C and potassium.

According to proponents of the “grapefruit diet”, grapefruit’s low glycemic index promotes fat burning. There are many other myths about the health benefits of grapefruit. How many of these are true remains to be seen.

Grapefruit is the bitter hybrid fruit of pomelo and sweet orange. It was first bred in Barbados in the 18th century and called the “forbidden fruit.” I could not find out why. However, there is new evidence to suggest it could be a “forbidden fruit.”

For years it has been shown that grapefruit interferes with absorption of medications, many of which are commonly used by people with serious health conditions. One-third of prescribed drugs in the US are taken by the elderly. Ambulatory and nursing home patients take an average of nine to 13 pills a day. This certainly increases their risk of adverse reactions. This can be from drug-drug interactions or caused by food.

A group of researchers have been tracking adverse reactions between medication and grapefruit for 20 years. The article was recently published in the Canadian Medical Association Journal. A disturbing trend was found between 2008 to 2012. The number of medications with the potential to interact with grapefruit, and cause serious adverse effects, increased from 17 to 43. This represents an average increase of more than six drugs per year. A portion of the new drugs entering the market each year.

It’s possible to die from an adverse reaction. Other complications range from kidney failure, respiratory failure, gastrointestinal bleeding, and bone marrow suppression in immunocompromised people.

The chemical compounds in grapefruit which cause these dangerous interactions are furanocoumarins. When we take a pill the whole amount is not absorbed from our intestine. An enzyme in the intestine destroys a portion of some drugs, thus reducing the amount entering the bloodstream. Furanocoumarins irreversibly inhibits the enzyme that normally inactivates an estimated 50 per cent of all medication. This allows more of the drug to enter the bloodstream and may cause damage to organs in the body.

Other citrus fruits like Seville oranges, used in marmalade, limes, and pomelos also contain this active ingredient. Drugs that undergo metabolism in the gastrointestinal tract by the enzyme CYP3A4 are affected. These drugs have to be taken orally and it does not matter when and how much grapefruit you have consumed before taking the pills.

Here are some examples of the pills you should avoid if you cannot do without grapefruit: statin drugs to lower cholesterol, blood pressure-lowering drugs, organ transplant rejection drugs, anti-anxiety drugs, antiarrhythmic drugs, and antihistamines. Visit Health Canada’s website for a complete list.

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