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The San Diego Union-Tribune

Grapefruit juice can turn a dose of some medicines into an overdose


February 26, 2008

QUESTION:In a past column you wrote that one should avoid grapefruit juice and grapefruit altogether while taking certain medications. One of the medications listed was the one I take: felodipine. The prescription bottle comes with an attached label that says, “Do not drink grapefruit juice or eat grapefruit within two to four hours of taking this medication.” This is confusing. Can you explain?

ANSWER:The short answer is that the label you refer to is outdated. At one time it was thought that separating the times you take the medication and ingest grapefruit could prevent a potential interaction. However, it's been known for years that the grapefruit effect can last for more than 24 hours. For this reason, spacing doses is not a workable option.

Felodipine is a calcium blocker prescribed for high blood pressure or angina pain. The grapefruit interaction, in fact, first came to light with felodipine and nifedipine, another calcium blocker. People who washed down these drugs with grapefruit juice were unaware that the juice was turning a normal dose into an overdose.

Enzymes in the intestines and liver break down drugs so the body can eliminate them. Grapefruit juice contains natural substances that block the action of some of these enzymes, primarily in the intestines. The result is that certain orally taken drugs can build up to excessive levels in the blood, increasing the risk of potentially serious adverse effects.

Besides calcium blockers, grapefruit interacts with some statin drugs (Lipitor, lovastatin, simvastatin; but not Crestor, fluvastatin, pravastatin) some benzodiazepines (including diazepam, midazolam, quazepam, triazolam), estrogens and various other drugs.

The prescribing information that comes with the statin drugs lovastatin and simvastatin implies that drinking up to a quart (four 8-ounce glasses) of grapefruit juice is OK, but other sources disagree.

With many drugs, one glass of grapefruit juice or one grapefruit can exert an effect. The extent of the effect depends on each person's particular physiology and other factors.

A note to pharmacists: If the label you attach to the prescription bottle carries the statement quoted above, consider marking through the phrase “within two to four hours of taking this medication,” leaving “Do not drink grapefruit juice or eat grapefruit.”

When ordering stick-on labels that call attention to the grapefruit interaction, look carefully at the wording. It may be confusing. For instance, one available label says “Do not drink grapefruit juice or eat grapefruit while taking this medication.” This sounds OK until you realize that many people may interpret “while taking” to mean “while they're swallowing the medication.” In such cases, pharmacist counseling will make the intent clear.

A better label: “Do not drink grapefruit juice or eat grapefruit while on this medication.”

The best label may be the simplest: “Do not drink grapefruit juice or eat grapefruit.”

Seville oranges may interact similarly to grapefruit. Other types of oranges, and tangerines and lemons, should not be a problem.

Richard Harkness is a consultant pharmacist, natural medicines specialist and author of eight books. Write him at 1224 King Henry Drive, Ocean Springs, MS 39564; or

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