by Neil Bauman, Ph.D.
A lady asked:
Can a person drink grapefruit juice, or eat grapefruit without taking medications with it and be ok, or does grapefruit affect hearing loss period?
If you are not taking any medications, eat/drink as much grapefruit as your heart desires. It doesn’t affect ears. It’s not the grapefruit that is ototoxic.
What happens is that certain drugs (which can be ototoxic) can be absorbed into your bloodstream in much higher quantities than usual if you normally have high levels of an digestive enzyme called Cytochrome P-450 3A4 (CYP 3A4 for short) in your stomach and then eat grapefruit. The furanocoumarins in the grapefruit prevent this enzyme from breaking down the drug before it is all absorbed into your bloodstream—hence you get a much higher drug dose than otherwise.
Perhaps you don’t realize it, but many drugs are not completely absorbed by your body. For example, a given drug may typically only be 10% absorbed and 90% excreted. Doctors know this, so in effect they give you 10 times the dose you need—knowing that 90% is going to be wasted and only 10% absorbed.
Now, if you have high levels of CYP 3A4 in your stomach, the furanocoumarins bind to the CYP 3A4 and prevent it from breaking down certain drugs before they are absorbed. Thus, you could end up with 10 times the dosage. If the drug is ototoxic, you just got quite an ototoxic overdose, and that could affect your ears. The highest figures I have seen related to taking grapefruit juice were for Simvastatin (Zocor), which resulted in a 1,513% increase. That’s quite an overdose!
If you normally have very low levels of CYP 3A4 in your stomach, then taking grapefruit doesn’t make much difference. In this case, your body normally absorbs much more of these drugs—so your doctor has to give you a smaller dose than to people with high levels of CYP 3A4.
Here’s the rule of thumb. If you have high levels of CYP 3A4 in your stomach, you have to be consistent in your grapefruit intake—so either always take a same amount of grapefruit at the same time, or never take it. That way, the doctor can adjust the dose to fit how your body absorbs it.
If you have low levels of CYP 3A4 then it probably won’t make much difference whether you eat grapefruit or not.
Incidentally, there are a few drugs that also bind to CYP 3A4 so you don’t want to take them at the same time either.
If you want to learn more about this fascinating subject (and to learn which drugs are sensitive to grapefruit) read chapter 11 in “Ototoxic Drugs Exposed“.
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