grapefruit juice and bioavailability of cancer drugs. - 1246492

I'll ask her to respond but if my memory serves it's because the amount can't be regulated, reactions are too different from person to person. That's from a memory of a discussion about tarceva and grapefruit juice not other cancer treatment.

FYI, Dr. Walko wants to comment fully on this question so will wait until later this afternoon to tackle it.

This is an excellent question/idea: using an inhibitor of an enzyme that breaks down a particular drug to increase the amount of that drug in the body and thus take less of it, especially if the drug is expensive. In the case of some HIV medications, we actually do exactly this with a potent enzyme inhibitor called "ritonivir". Some of these medications even exist as a pill with both drugs in it to make it easier for patients.

The problem with doing the same with grapefruit juice is as Catdander alluded too...not everyone reacts exactly the same and the inhibitory properties can differ between people and types of grapefruit juice. (The actual substance in grapefruit juice is called "furanocoumarin").

If grapefruit juice were used to boost erlotinib (for example), the exact type of juice and quantity would have be recommended as well...and even then there would still be some variations between people. This is why some drugs are recommended to be taken on an empty stomach even though taking with food would cause more of the drug to be absorbed...there is less variation between people when taken without food and "without food" is a more reproducible direction to give to patients since different types of food may cause different amounts of the drug to be absorbed. Can you imagine being told that you had to take your lower dosed erlotinib with the fat equivalent of a McDonalds big Big Mac every day? A great question would be why not build a combination drug formulation (like I discussed above with the HIV medication) with a fixed amount of the inhibitor and the erlotinib in one tablet.

I will end with saying that this is a ongoing debate between the science side and drug companies that resulted in a series of commentaries and letters to the editor in the Journal of Clinical Oncology revolving around the drug lapatinib entitled: The Value Meal: How to save $1700 per month or more on lapatinib
http://jco.ascopubs.org/content/25/23/3397.full.pdf

Best,
Dr. Walko

I don't see a drug company spending money to do these kinds of studies in order to make it easier for people to do just as well with far less of the drugs they sell. The people with an incentive to do such a study would be the federal government or insurers, so that they could demonstrate equivalent efficacy with far lower expense...but I don't see that happening either.

-Dr. West

With this idea in mind perhaps a company studying a drug like afatinib would be interested. It shows a lot of promise but people quit the trial because of side effects.

Yes, but a dietary intervention that markedly increases efficacy would also almost certainly increase side effects to the same degree. It essentially makes a small amount of some drugs (+ grapefruit juice) as effective (and toxic) as a larger amount of drug.

The people with the most incentive to pursue this research are people who sell grapefruit juice. (Seriously)

-Dr. West

Interesting discussion - thanks to all. Intrigued by Dr Walko's suggestion of a combination drug, and will read the breast cancer link with interest.
Perhaps we need to find a country where grapefruit juice is not drunk or is in some way culturally unacceptable - then it might be easier to set up a trial!
Update: really interesting article which develops ssflxl's point in another context.