Grapefruit

Well, I'm back (of course!). Don't think this is serious enough to call my doc, but I was dumb. I take tikosyn (dofetilide) and this morning I enjoyed a large glass of "mixed citrus" juice. Didn't know that grapefruit was one of them--duh--until my daughter turned down a serving saying she doesn't care for grapefruit. How bad is the interaction with the drug? No info on how much of the mix is grapefruit, but after it was pointed out, I can definitely taste it. Yikes.


3 Comments

Grapefruit juice is a nasty

by crustyg - 2022-12-06 13:25:05

Unhappily grapefruit juice inhibits some gut brush-border enzymes which are themselves responsible for the degradation of many orally administered drugs.  The usual doses are determined taking into account this first-pass loss, so if you manage to block these enzymes you can get a big overdose.  One of the best over-the-counter, non-sedative anti-histamines was withdrawn from the market (1990s) due to a couple of sad cases where folk developed Torsade-de-pointes cardiac arrhythmia and died by taking the drug with grapefruit juice.  Instead of putting a huge label across both sides of the pack, the manufacturer withdrew the drug completely.  No-one really cared about the many folk who crash their cars whilst taking the sedative anti-histamines, apparently.

I'd suggest missing your next dose of dofetilide and avoid grapefruit juice (in any form) while you're on it.  If necessary, for ever.  If you develop symptoms now, don't hesitate to go to your nearest ED.  But I think if you've only had one dose you should get through this without issues.

Lesson learned?

Grapefruit juice

by IAN MC - 2022-12-06 14:44:17

Dofetilide isn't alone in interacting with grapefruit.

As Crusty said, the commonest interactions are caused because grapefruit blocks a vital enzyme which helps to break down many drugs before they are excreted. If the  drug isn't broken down, the blood levels of the drug end up higher than they  should be so you are over-dosing  ! This may be very undesirable as most drug side-effects are dose dependent

Other commonly used drugs which are affected in  this way include some statiins, calcium channel blockers such as amlodipine and verapamil,  also older anti-coagulants like warfarin.

So I would recommend that you check the patient information leaflet before drinking grapefruit juice with ANY prescription drug.

Ian

Tikosyn and grapefruit

by AgentX86 - 2022-12-06 17:57:55

There seems to be some murky waters around tikosyn and grapefruit juice.  Many sites talk about enzime effects of the two but another says that no interaction is found in a meta-study of almost 12,000 people.  Who knows?

<https://www.ehealthme.com/drug-interaction/tikosyn/grapefruit/>

My guess would be that one instance wouldn't be a problem in any case.

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