Drug - Grapefruit Interaction Increasingly Common

The number of drugs that can be risky when taken with grapefruit is on the rise, largely due to the influx of new medications and chemical formulations, according to a new study.

Researchers at Lenox Hill Hospital (New York, NY, USA) reviewed medical literature for articles on grapefruit and drug interaction, as well as reviewing prescribing information for recently approved drugs in Canada. In all, they identified more than 85 drugs that may interact with grapefruit. Of these, the number of drugs that may result in potentially fatal side effects when mixed with grapefruit increased from 17 to 43 during the past four years; this equates to more than six new potentially risky drugs a year. The list includes some statins such as atorvastatin, lovastatin, and simvastatin, some antibiotics, cancer drugs, and cardiovascular medication.

The interaction can occur even if grapefruit is eaten many hours before taking the medication. For example, simvastatin, when taken with a medium glass of grapefruit juice once a day for three days, produced a 330% greater concentration of the drug compared to taking it with just water, which could cause rhabdomyolysis, a life-threatening damage to muscle tissue. With other drugs, just one serving of grapefruit can potentiate the effects, simulating taking multiple doses of the drug. The study was published early online on November 26, 2012, in the Canadian Medical Association Journal.

“If you consume grapefruit juice and take medications, be careful. If you need these drugs and there are not appropriate substitutes, you may need to limit or reduce your consumption of grapefruit juice and products,” said lead author Tara Narula, MD. “Some have more of an effect if you take them in close proximity to drinking grapefruit juice than if you space it out, but there can still be an interaction if you take the pill the night before or 12 hours before consuming grapefruit or grapefruit juice.”

Grapefruit contains furanocoumarins, potentially toxic organic compounds produced by plants as a defense mechanism against various types of predators, ranging from insects to mammals. In humans, the furanocoumarins bergamottin and dihydroxybergamottin are responsible for the "grapefruit juice effect" by affecting the hepatic and intestinal enzyme cytochrome P450 isoform CYP3A4, an enzyme that normally breaks down certain medications in the body. When it is left unchecked, medication levels can grow toxic in the body. Other citrus fruits such as Seville oranges, limes, and pomelos also contain furanocoumarins, but have not been as widely studied.

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