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Texas_wedge's picture
Posts: 2807
Joined: Nov 2011

Since I joined the forum, a few weeks ago, I've asked numerous questions. Some have met with helpful/informative/amusing answers but quite a few have been left hanging in the air. Of the latter, there is one on a topic I believe to be so important that I feel I should flag it again. In my first ever posting here, on 29th Nov, in the thread "Recovering from radical nephrectomy" I put the question:

4. Has anyone been warned of "The Grapefruit Effect" (that is the dramatic potentiation of some medicines and the attenuation of others by grapefruit juice - so that the effective dosage of your meds. gets screwed up)?

No-body seemed to be aware of this phenomenon - a little surprising since if you put a search into Google in terms like 'the grapefruit effect' you'll get something approaching 20 million sites - which should offer enough to even the most voracious reader. I offered a url for a succinct account of the key facts.


To save members the bother of hunting anything down, here are a couple of excerpts from different websites to give you the general idea.

PHILADELPHIA, Aug. 19, 2008 — Scientists and consumers have known for years that grapefruit juice can increase the absorption of certain drugs — with the potential for turning normal doses into toxic overdoses. Now, the researcher who first identified this interaction is reporting new evidence that grapefruit and other common fruit juices, including orange and apple, can do the opposite effect by substantially decreasing the absorption of other drugs, potentially wiping out their beneficial effects.
The study provides a new reason to avoid drinking grapefruit juice and these other juices when taking certain drugs, including some that are prescribed for fighting life-threatening conditions such as heart disease, cancer, organ-transplant rejection, and infection, the researcher says. These findings — representing the first controlled human studies of this type of drug-lowering interaction — were described today at the 236th National Meeting of the American Chemical Society.


Grapefruit juice boosts drug's anti-cancer effects

April 20, 2009

In a small, early clinical trial, researchers at the University of Chicago Medical Center have found that combining eight ounces of grapefruit juice with the drug rapamycin can increase drug levels, allowing lower doses of the drug to be given. They also showed that the combination can be effective in treating various types of cancer.

For two decades, pharmacists have pasted do-not-take-with-grapefruit-juice stickers on various pill bottles because it can interfere with the enzymes that break down and eliminate certain drugs. This interference makes the drugs more potent. In data presented at the AACR 100th Annual Meeting 2009, the Chicago researchers examine ways to exploit this fruit's medication-altering properties.

"Grapefruit juice can increase blood levels of certain drugs three to five times," said study director Ezra Cohen, MD, a cancer specialist at the University of Chicago Medical Center. "This has always been considered a hazard. We wanted to see if, and how much, it could amplify the availability, and perhaps the efficacy of rapamycin, a drug with promise for cancer treatment."

This trial was designed to test "whether we could use this to boost rapamycin's bioavailability to the patient's advantage, to determine how much the juice altered drug levels, and to assess its impact on anti-cancer activity and side effects," he said.

Later in the article this is stated:

"This study showed that substances known a furanocoumarins, plentiful in some forms of grapefruit juice, can decrease the breakdown of rapamycin. This makes the drug reach higher levels in the bloodstream, two to four times the levels seen without a juice boost, and thus increases the amount of the drug that reaches its targets.

"That means more of the drug hits the target, so we need less of the drug," said Cohen.

Many of the newer cancer medications, precisely focused on specific targets, are now taken as pills rather than intravenously. Some of these drugs, including rapamycin, can cost thousands of dollars a month. Hence, "this is an opportunity for real savings," Cohen said. "A daily glass of juice could lower the cost by 50 percent." "

It doesn't take much imagination to realise that drastically reducing the cost of an adjuvant therapy will make it much more likely that we can get it and that it will amplify the resources available for more R & D to make continuing progress - this at a time when AstraZeneca is announcing large job losses because, following Pfizer, it has disastrous pipeline problems (no drugs in the pipeline to replace the money-spinners on which their patents are about to run out). Eli Lilly is also, seemingly, approaching a potentially catastrophic patent cliff-edge.

I don't know whether the multiplier effect of the grapefruit juice, leading to lower drug doses, will also help reduce the side effects - wouldn't it be great if it does?

I am sure there are members here taking meds. that are affected by grapefruit juice and it would seem a smart move to consult appropriate experts to ensure that this effect is being taken into account.

Finally, another factor of truly huge importance for some drugs is the time of day they are taken. With some meds. the effect of diurnal/circadian rhythms (i.e. our body clocks) is such as to make a really large difference in their efficacy depending on when in the day they are taken. There is a burgeoning new area of science called chronopharmocology which addresses such issues.

I don't know how much variability there is between individuals in these phenomena and anyone who can educate me on the issue will command my gratitude.

lbinmsp's picture
Posts: 266
Joined: Jun 2006

and the only thing I can comment on definitively is, nearly every cancer drug warns against drinking or eating grapefruit during treatment. I've just started on Sutent and I think the pharmacist reminded me of that at least three times! I also remember that some antibiotics efficacy can be negatively affected by grapefruit as well. Since I'm not terribly fond of grapefruit, it isn't hard to avoid.


Texas_wedge's picture
Posts: 2807
Joined: Nov 2011

Thank goodness someone can confirm that I wasn't talking out of the back of my neck about this important topic. I began to fear everyone assumed it was pure confabulation on my part.

I've never seen a cancer drug, so far, so I wasn't aware how general is the advice to avoid grapefruit. It applies to many other types of drug too, for many major conditions, not least some psychiatric ones.

I believe that flagging this up will save lives - maybe even for some of us here! The fact is that with some of the new renal cancer meds we are still learning by trial and error what are appropriate doses for particular purposes and particular patients. Quite often larger doses are given than prove desirable and it's found that lower doses have the desired effect while considerably reducing side-effects. In such cases, the potentiation effect of grapefruit juice could well lead to a fatal overdose. By the same token, the reverse effect grapefruit has on some other drugs (attenuation) could lead to the life-saving propensity of the medicine being unnecessarily sacrificed.

Olsera's picture
Posts: 38
Joined: Dec 2011

Thank-you for this information I will keep it in mind for sure because I love grapefruit.

foxhd's picture
Posts: 2417
Joined: Oct 2011

I have always been aware of the caution associated with grapefruit and certain medications. I will bring this up next week when I see my doctor before my infusion. This MDX thing is a different animal. Thanks for the reminder Texas.

cww71964's picture
Posts: 97
Joined: Dec 2011

The 15 page paperwork I got for the trial I am considering specifically states No Grapefruit as it increases the medicine in your system.

Texas_wedge's picture
Posts: 2807
Joined: Nov 2011

Olsera, I believe a large proportion of the American population enjoys g. juice daily. I start my day with either 1/2 fresh grapefruit or, if in a hurry, a glass of the juice.

Fox, MDX-1106 is plainly something different so it will be interesting to hear the answer.

Wayne, thanks for the info. What a shame they can't quantify the multiplier effect so as to reduce the dose, save cost and possibly reduce any side-effects. I suppose Big Pharma won't be in any hurry to produce that information!

foxhd's picture
Posts: 2417
Joined: Oct 2011

MD said no issue with this drug.

Texas_wedge's picture
Posts: 2807
Joined: Nov 2011

Good to hear g. juice is no problem with MDX-1106 Fox.

This maze we're in gets ever more complex though. I was researching sodium/potassium balance and the supposed hazards for us of too much potassium in our diet. It appears that it's really of importance re CKD rather than RCC but the relationship between those two conditions is also complicated. There seems to be equivocation, in the literature, as to whether a surviving kidney is 'diseased' purely because it is performing less efficiently as per eGFR measures, simply due to age. A good explanation of this topic can be found here:


I was perplexed by data in this, seemingly authoritative, site:


I'm distressed to see quite a few of my favourite fruits and vegetables listed in the high potassium foods but there seem to be some strange anomalies. For instance, grapefruit juice is high potassium but 1/2 fresh grapefruit is low potassium!!! I use them as interchangeable at breakfast, depending solely on whether I'm in a hurry.

Similarly, raw apricots are high potassium but canned apricots in juice are low potassium, even though you are expressly instructed not to drink the juice of canned fruits!

I regularly eat several times the amount of high K fruits and veggies mentioned and I don't suppose there's been a day in the last 50 years when i haven't drunk at least 5 times the amount of tea and coffee recommended as an upper limit.

Perhaps I'm unwise but I don't intend to alter my diet on the basis of information i find highly implausible. Do we have any nutrition experts here who would like to comment?

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