I’m waiting to see it on CSI

…our intrepid investigaters find a young person dead from unknown causes…autopsy revealed an abnormally high level of drug X in the person’s system, so the original cause of death was listed as “accidental overdose”, but our intrepid CSI person finds the unwashed glass, analyzes it and finds residue of the substance that led to the person’s death, find the dangerous liquid in the refrigerator of the victim, and find the fingerprints of the killer.

And what was the cause of death? Death by Grapefruit juice.

Most people know about the lowly grapefruit, and most overweight people have tried the grapefruit diet (which works, but alas the average weight loss was 3.6 pounds over a 12 week period).

For years, we doctors knew to warn our patients on blood thinner not to drink grapefruit juice, but as the list of sophisticated medicines grew, so also did the list of medicines that were messed up by grapefruit juice.

The most common medicine are the “statins”, which people use to lower their cholesterol. If you take it with the grapefruit juice, the amount in your bloodstream goes up.

But the list is now endless: Statins (Lipetor, Zocor), Blood pressure medicine (Nifedipine/procardia but not Amlodipine/Norvasc), medicine for irregular hearts (Amiodarone and Quinidine), anti immune system drugs (cyclosporine/Sandimmune, tacrolimus/Prograf), and some HIV medicines (Fortovase, but not most of the others)..

Luckily for GP’s, most of our pharmacies have little lables on the pills and the Pharmacists often warn the patients of the problem. But although these drug interactions don’t usually kill people, they do make them sick, and the problem needs to be better publicized.

Here’s a longer list, but don’t sue me if I miss one. LINK 2 has a search engine…If you aren’t sure, ask your local pharmacist (which is why I don’t like mail pharmacies: they send a long complicated paper on what you should know, but they don’t know you like the guy at Walgreens’)
Drugs that Interact with Grapefruit Juice:

(from the December 2004 issue of the American Journal of Nursing)

Antibiotics: clarithromycin, erythromycin, troleandomycin

Anxiolytics: alprazolam, buspirone, midazolam, triazolam

Antiarrhythmics: amiodarone, quinidine

Anticoagulant: warfarin

Antiepileptic: carbamazepine

Antifungal: itraconazole

Anthelmintic: albendazole

Antihistamine: fexofenadine

Antineoplastics: cyclophosphamide, etoposide, ifosfamide, tamoxifen, vinblastine, vincristine

Antitussive: dextromethorphan

Antivirals: amprenavir, indinavir, nelfinavir, ritonavir, saquinavir

Benign prostatic hyperplasia treatment: finasteride

β-blockers: carvedilol

Calcium channel blockers: diltiazem, felodipine, nicardipine, nifedipine, nimodipine, nisoldipine, verapamil

Erectile dysfunction drugs: sildenafil, tadalafil

Hormone replacement: cortisol, estradiol, methylprednisolone, progesterone, testosterone

Immunosuppressants: cyclosporine, sirolimus, tacrolimus

HMG-CoA reductase inhibitors: atorvastatin, fluvastatin, lovastatin, simvastatin

Opioids: alfentanil, fentanyl, sufentanil

Selective serotonin reuptake inhibitors: fluvoxamine, sertraline

Xanthine: theophylline

Why do the drugs interact? It has something to do with the P450 oxidase system.

Grapefruit interferes with the enzyme in the intestine so you end up getting more drug in your body than without it. But since P450 is also in your liver, which is the garbage filtration system of the body, it probably has something to do with the enzyme there also.

Here’s a list of drugs
that mess up the enzymes that remove older medicine from your body.

Alas, the big problem is a lot of drugs interfere with that or other enzyme systems…so if you take a drug that turns off the system you end up with a higher level of the second medicine (example: If you take the antibiotic Erythromycin while on the seizure/pain medicine Tegretol, you end up getting a Tegretol (Carbamazepine) overdose.

On the other hand, if you take a medicine that stimulates the enzymes, you end up with the second medicine not working. (example: if you take Phenobarbital or Penicillin when on birth control pills, you can end up pregnant).

Wikipedia has an article, if you have a PhD in physiology and write papers on the P450 oxidase system you might be able to understand it.

And THIS ARTICLE is a nice summary of all sorts of things that can change how a medicine will work. It’s enough to make one paranoid. Heck, even oatmeal is dangerous: it interferes with digesting your Metformin. Luckily for most medicines, the amount needed to work can vary so a small amount of interferance doesn’t matter, and most medicines don’t poison you if the amount in your blood goes a little higher than normal.

As for grapefruit, the latest news on today’s BBC is that a survey of diet in California that found menopausal women who ate a lot of grapefruit had more breast cancer. Hmmm…

They think that something in grapefruit juice stops the body from taking out older estrogen molecules from your blood, so your estrogen level increases, and with the increase of estrogen, in the long term you could get an increase in breast cancer.

Sounds logical, but more study is needed until you panic. But if true, this brings up the possibility that grapefruit might also be associated with other estrogen effects, like decreasing hot flashes, keeping your tushie healthy, and increasing blood clotting and heart attacks.

In the meanwhile, don’t panic. If you aren’t taking any medicines, remember: grapefruit juice is a good source of vitamin C.


Nancy Reyes is a retired physician living in the rural Philippines. Her website is Finest Kind Clinic and Fishmarket, and she writes medical essays to HeyDocXanga Blog

Be Sociable, Share!