NEW ORLEANS — Primary care providers are encouraged to take dietary histories of their patients to specifically note the intake of grapefruit in light of increasing numbers of drugs that can adversely interact with the fruit, according to a poster presentation at the American Association of Nurse Practitioners 2015 meeting.
Mary Ann Whelan-Gales, DNP, ACNP, ANP-BC, CCRN, a nurse practitioner at Mount Sinai Hospital in New York City, stated that providers should consider persons older than age 45 years at higher risk, as they are the main consumers of grapefruit, receive the most prescription medications, and may have decreased capacity to compensate for excessive systemic drug concentrations.
She estimated that more than 85 medications that may adversely interact with grapefruit are on the market. These drugs are all administered orally, have very low to intermediate absolute bioavailability, and are metabolized by the cytochrome P450 3A4 (CYP3A4) enzyme.
A whole grapefruit or 200cc to 250cc of grapefruit juice has sufficient potency to create an average systemic drug concentration that is three-fold of that when the drug combines with water, according to Whelan-Gales.
The lower the oral bioavailability of a drug, the more likely it is to combine with grapefruit to increase systemic concentration. Although the greatest effects on pharmacokinetics occur when grapefruit is ingested simultaneously with a drug, the effects of grapefruit may last three to seven days after consumption.
Previous research has shown that the compound furanocoumarin (specifically, bergamottin) in grapefruit irreversibly inhibits CYP3A4, which can affect the metabolism of certain drugs and increase their bioavailability. Some serious adverse interactions linked to grapefruit include rhabdomyolysis, which can result with active forms of all statins (e.g., atorvastatin, lovastatin, simvastatin), nephrotoxity, which can occur with calcineurin inhibitors (e.g., cyclosporine, tacrolimus) , and torsade de pointes, which is a risk with some cardiovascular agents (e.g., amiodarone, dronedarone, quinidine).
Other fruits, such as Seville oranges, pomelos, cranberries, and Goji berries, also contain furanocoumarins, Whelan-Gales noted. Providers should advise patients not to consume grapefruit during treatment with drugs that have known or are likely to have adverse interactions or should prescribe noninteracting alternative medications, she suggested.
- Whelan-Gales MA. “A Forbidden Fruit.” Presented at: AANP 2015. June 9-14; New Orleans, Louisiana.