Today I had one of those moments, and it all started when this NCLEX prep professor said: "What else do you have to remember to teach regarding statins?" A student behind me chirped: "Don't drink grapefruit." My brain said, "Oh yeah..." and remembered when I told my mom, "Ah, just wait an hour or drink it an hour before you take your medicine." And just as that memory flashed in my mind the professor's voice zoomed back into the foreground with: "And you know, you can't just hold the medicine for an hour because the grapefruit stays in your system for 72 hours.**"
Thank God, my mom didn't listen to me. And this totally explains why, even though I regularly take a sleep aid, some days I wake up and am fine, but other days, if I've had grapefruit juice (which I juice and drink for the benefits of vit C and ribavirin) I feel like I'm wobbling around in a haze all day.
**Now, I haven't been able to verify that grapefruit stays in the body for 72 hours, but I've read one primary article (admittedly with a rather weak sample size) and several secondary articles that says scientists have found evidence that the grapefruit's effect on increasing certain medication to toxic levels does last at least 24 hours. [Edit: I've found an article that references studies supporting 72 hours as the upper threshold.]
Turns out, there's quite a few medications that interact with grapefruit. The classification of anti-cancer medications, anti-diabetic medications, antibiotics, anti-inflammatory medications, anti-lipemics, heart medications, centrally activating medications, estrogen supplements, GI medications, and immunosuppressant medications each have several specific medications that are known to have some reaction with grapefruit. I'm sure that's not a complete list, but, let's be honest, unless you have an eidetic memory you won't be memorizing all of those.
Now, as I said to my mentees, and as this professor said to us this morning, things are easier to remember if you understand why something happens. I knew that grapefruit competed with these medications. I knew that competing for binding sites meant the medication will reach a toxic level, but I didn't know that the enzyme responsible for the first pass effect was called "CYP3A4," and that it functioned both in the liver and in the small intestine. CYP3A4's job is to remove some of the medication from the body. But it has a high affinity for grapefruit so it will bind to the grapefruit juice first, allowing the medication to flow out of the liver and into the systemic circulation unaltered.
It is important to note, however, that I have read some clinicians are less inclined to be so stringent on withholding grapefruit juice because of debate on whether or the restrictions of patient lifestyle is necessary with less toxic medications when also taking into consideration the patient lifestyle. For example, in the case of simvastatin, minor side effects of drinking grapefruit juice were joint and muscle aches, but if the levels of medication become toxic, it's possible that cells could begin to break down, resulting in rhabdomyolysis. It should be stressed that this has only been reported once, and the prescription order of simvastatin is a dose that is now no longer standard practice.
Suffice it to say, per pharmacy warning and nursing teaching, we must teach our patients the risks--you're not just risking toxicity, you're also running the risk of amplifying any of those pesky side effects. If the patient is a grapefruit juice worshipper, perhaps there should be a change in medication. But if the patient normally abstains from grapefruit juice and accidentally forgets and drinks some, there's not likely a need for an ambulance. After all the discovery of the effect of grapefruit juice on medication absorption was completely accidental, and patients had been taking their medications in conjunction with grapefruit juice for years.
References:
http://www.cmaj.ca/content/suppl/2012/11/26/cmaj.120951.DC1/grape-bailey-1-at.pdf
http://www.drugs.com/article/grapefruit-drug-interactions.html
http://spectrum.diabetesjournals.org/content/19/4/202.full
http://health.clevelandclinic.org/2013/08/do-statins-and-grapefruit-safely-mix/
http://www.fda.gov/downloads/ForConsumers/ConsumerUpdates/UCM292839.pdf
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1873672/
http://www.ncbi.nlm.nih.gov/pubmed/11061578
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1884539/
http://www.nature.com/ejcn/journal/v58/n1/full/1601736a.html
http://www.ncbi.nlm.nih.gov/pubmed/6362950
http://www.ncbi.nlm.nih.gov/pubmed/11009051
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