Grapefruit-medication interactions increasing

The number of prescription drugs that can have serious adverse effects from interactions with grapefruit are markedly increasing, yet many physicians may be unaware of these effects, states an article published in CMAJ (Canadian Medical Association Journal). The article, a review by the researchers who discovered the interactions more than 20 years ago, summarizes evidence to help clinicians better understand the serious effects this common food can have when consumed with certain prescription drugs.

"Many of the drugs that interact with grapefruit are highly prescribed and are essential for the treatment of important or common medical conditions," writes Dr. David Bailey, Lawson Health Research Institute, London, Ont., with coauthors. "Recently, however, a disturbing trend has been seen. Between 2008 and 2012, the number of medications with the potential to interact with grapefruit and cause serious adverse effects…has increased from 17 to 43, representing an average rate of increase exceeding 6 drugs per year. This increase is a result of the introduction of new chemical entities and formulations."

Adverse effects include sudden death, , , , bone marrow suppression in immunocompromised people, renal toxicity and other serious side effects.

"Unless are aware of the possibility that the adverse event they are seeing might have an origin in the recent addition of grapefruit to the patient's diet, it is very unlikely that they will investigate it," write the authors. "In addition, the patient may not volunteer this information. Thus, we contend that there remains a lack of knowledge about this interaction in the general healthcare community."

There are more than 85 drugs that may interact with grapefruit, and 43 can have serious side effects. Other such as Seville oranges, often used in marmalade, limes and pomelos also contain the (furanocoumarins). These chemicals are innate to the fruit and cause the interaction by irreversible inhibition of the metabolizing CYP3A4 enzyme that normally inactivates the effects of an estimated 50% of all medication. Drugs that interact with these chemicals have three characteristics: they are administered orally, they have very low to intermediate bioavailability (percentage of the oral dose of drug absorbed into the blood circulation unchanged) and they undergo drug metabolism in the gastrointestinal tract by CYP3A4. For drugs with very low bioavailability, ingestion of a single normal amount of grapefruit can be analogous to consuming multiple doses of the drug alone.

This interaction can occur even if grapefruit is consumed many hours before taking the medication. Thus, a modest solitary quantity of grapefruit can affect interacting drugs that are taken once a day at any time during the dosing interval. Frequent daily consumption of a regular amount can further augment the effect. For example, simvastatin, a commonly used statin, combined with a 200-mL glass of grapefruit juice once a day for 3 days, produced a 330% systemic concentration of the drug compared with water.

People older than 45 years are the prime purchasers of grapefruit and receive the most prescriptions for drugs. Because of the size of this population, substantial exposure to this interaction is likely. As well, older adults can have decreased ability to tolerate excessive systemic drug concentrations. Consequently, older people are especially vulnerable to these interactions.

"The current trend of increasing numbers of newly marketed -affected drugs possessing substantial adverse clinical effects necessitates an understanding of this interaction and the application of this knowledge for the safe and effective use of drugs in general practice," conclude the authors.

More information: www.cmaj.ca/lookup/doi/10.1503/cmaj.120951

add to favorites email to friend print save as pdf

Related Stories

Edible fungus foils dangerous grapefruit-drug interactions

Feb 02, 2009

Scientists in Florida report that adding an edible mushroom-like fungus to grapefruit juice may help to reduce the serious side effects that can occur when people taking certain prescription drugs drink grapefruit ...

Grapefruit juice lets patients take lower dose of cancer drug

Aug 07, 2012

A glass a day of grapefruit juice lets patients derive the same benefits from an anti-cancer drug as they would get from more than three times as much of the drug by itself, according to a new clinical trial. The combination ...

Recommended for you

FDA approves hard-to-abuse narcotic painkiller

Jul 25, 2014

(HealthDay)—A new formulation of a powerful narcotic painkiller that discourages potential abusers from snorting or injecting the drug has been approved by the U.S. Food and Drug Administration.

Race affects opioid selection for cancer pain

Jul 25, 2014

(HealthDay)—Racial disparities exist in the type of opioid prescribed for cancer pain, according to a study published online July 21 in the Journal of Clinical Oncology.

FDA approves tough-to-abuse formulation of oxycodone

Jul 25, 2014

(HealthDay)—Targiniq ER (oxycodone hydrochloride and naloxone hydrochloride extended release) has been approved by the U.S. Food and Drug Administration as a long-term, around-the-clock treatment for severe ...

Tough-to-abuse formulation of oxycodone approved

Jul 25, 2014

(HealthDay)—Targiniq ER (oxycodone hydrochloride and naloxone hydrochloride extended release) has been approved by the U.S. Food and Drug Administration as a long-term, around-the-clock treatment for severe pain when other ...

EU regulator: Morning-after pill OK for all women

Jul 24, 2014

(AP)—A commonly used morning-after pill is suitable for use by heavier women, the European Medicines Agency said Thursday after a review of the evidence sparked by the French manufacturer's declaration that the drugs didn't ...

Physicians warned about counterfeit medical devices

Jul 24, 2014

(HealthDay)—Physicians should be aware of the prevalence and serious consequences associated with use of counterfeit medical devices, according to a letter to the editor published online July 20 in Lasers in ...

User comments

Adjust slider to filter visible comments by rank

Display comments: newest first

Chromodynamix
not rated yet Nov 26, 2012
One deadly combination is Ephedra and grapefruit, which as you can imagine would be a popular breakfast combination.
I suspect this interaction is far more common than reported.
I personally ended up in a coma due to this interaction, but that's another story on Erowid.
mk_bruce_71697
not rated yet Nov 26, 2012
I get a Neurontin/gabapentin interaction with a beverage having less than 1% grapefruit juice. Drug documentation warns of grapefruit juice, but they do not go on to remind to watch out for products that contain grapefruit juice such as Squirt, Fresca, or Ting soda. Most people might know these sodas have grapefruit juice, but other products do NOT label grapefruit juice other than "citrus juice" in labeling. I think better product labeling for juices and expanded medication documentation is needed in this area. For MD's or pharmacists dealing with "side effect problems" with any of the 85 listed meds, I would rule out grapefruit juice hiding in a "citrus juice" labeled ingredient in a product the patient might be using. I know firsthand how a small amount of grapefruit juice can severely affect the medication I use. I learned the hard way.