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Wednesday, February 6, 2013

One Pill Becomes Twenty with a Sip of Grapefruit Juice

The title of this article is not hyperbole or fear-mongering exaggeration* according to clinical pharmacologist David Bailey who insists that there are a number of medications for which- "Taking one tablet with a glass of grapefruit juice is like taking 20 tablets with a glass of water.” Many, maybe most, people are familiar with the notion that grapefruit products can interact with certain drugs. You may have even seen the warning stickers on a medication.

 (*At least it isn’t exaggeration. I suppose an argument could be made for fear-mongering.)

Less well known, however, is how acute the reactions to those interactions can be, how many medications are reactive, how long after ingestion a dose of grapefruit products can interact with a medication and how small that dose needs to be.

Grapefruit. Courtesy of the National Cancer Institute http://www.cancer.gov/. Creator: Renee Comet (Photographer). http://visualsonline.cancer.gov/details.cfm?imageid=2630. Reuse Restrictions: None - This image is in the public domain and can be freely reused.
Grapefruit- Enemy of the Enzyme (at least the CYP3A4 enzyme)

In the normal physiological course of things, when someone takes a medication orally, that medication is metabolized in their gastrointestinal tract. The percentage of the active ingredient(s) in the swallowed medication that is absorbed to do its job- it’s “bioavailability”- is actually surprisingly small. The rates vary but drugs taken orally, pills in particular, have bioavailability rates that pretty much top out at 50-70%, with less than 10% not uncommon. Drugs are obviously formulated with that in mind- their dosage adjusted to the human body’s rate of absorption.

That bioavailability for the medications susceptible to grapefruit interaction is chiefly established in the gastrointestinal track by an enzyme called CYP3A4 which blocks and/or deactivates the bulk of an ingested drug. (That’s why dosages are different for drugs administered via needle, catheter or suppository- their bioavailability rates are much higher.) Grapefruit products contain organic chemicals called furanocoumarins which inhibit the CYP3A4 blocking enzymes, thereby increasing bioavailability.
Drug Conversion

Another dangerous interaction of CYP3A4 inhibition is actual chemical change in a drug. Opiate painkillers are a good example. Hydrocodone (Vicodin), a moderately powerful opiate, is converted by grapefruit’s interactivity into hydromorphone (Dilaudid), an extremely powerful opiate. Or, CYP3A4 converts a good deal of codeine into norcodeine- a metabolite that has little opioid activity. When that conversion is blocked, significantly more of the codeine is metabolized as morphine- which obviously has a lot of opioid activity. So as you can imagine, when a dose of hydrocodone that’s expected by the prescribing doctor to be metabolized at 40% is converted to hydromorphone that’s metabolized at 70%, the results can be damaging or even deadly.

Dose and Time

Furthermore, the dosages of grapefruit eaten or its juice drunk don’t need to be significant. A glass or half a fruit can be enough to facilitate dangerous drug-absorption rates. Nor does the ingestion need to have immediately preceded the taking of a medication. According to the earlier-cited specialist David Bailey, drinking a glass of grapefruit juice at breakfast can interact with the medication you take at dinner.

That high danger level at low doses combined with the long half-life of grapefruit’s enzyme-inhibiting chemicals can also increase toxicity by facilitating a cumulative buildup of a drug in your system. For instance, one example cited by Canadian researchers found that if someone taking simvastatin (Zocor) drank one seven-ounce glass of grapefruit juice a day for three days running, the concentration of simvastatin in their system would increase 330 percent.

The Risks and Avoiding Them

Statistically, people around 45 and up are most at risk. The middle aged and elderly are both more likely to be taking some kind of medication than those younger and the primary consumers of grapefruit products.

As for avoiding the risk of adverse furanocoumarin-drug reactions: if you’re not a fan of grapefruit, pomelo, tangelo or products containing these things, there is no risk. If you are a fan of one or all of those things, do some research on any meds you take. That research should definitely include talking with your doctor and/or pharmacist about any uncertainties. And uncertainty regarding the possibility of interaction is a reasonable one to harbor. In just the past decade or less, the number of drugs with the identifiable capacity for dangerous and even deadly furanocoumarin interactions rose from 17 to at least 85.

Many of those identified can be found on resources like Wikipedia’s page on the subject: http://en.wikipedia.org/wiki/Grapefruit_drug_interactions; or here: http://www.cbc.ca/news/health/story/2012/11/26/grapefruit-juice-drug-interactions.html.


This article is contributed by our guest author Jim Fox, a freelance writer who studied medicine for his undergraduate degree. He frequently writes about topics pertaining to the medical industry, including affordable RX drugs. When not typing the day away, he is either perfecting his wine recipes or lacing up his ice skates and heading for the nearest frozen water.
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