Citrus clues

Checking product labels is important, because it’s not only grapefruit that interacts with some medications.

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Question:

Your October 29 column on grapefruit mentioned similar drug interactions with seville oranges. I take medication that stipulates I must avoid grapefruit, but this was the first time I'd seen other citrus fruits mentioned. I made seville marmalade this year for the first time, and my garden has what looks like a lemon tree but is actually a lemonade. Its fruit taste similar to the pomelos I had in China. Do you know if they are a problem with drug reactions?

Answer:

Seville oranges and certain lime varieties are related to grapefruit, all being hybrids of the pomelo, and therein lies the problem. The pomelo and its hybrids contain the group of compounds called furanocoumarins, which can interfere with our body's metabolism of certain medications. So, caution is warranted when using any medication that interacts with grapefruit, as it will likely interact with pomelos, seville oranges and certain limes, too.

A study published in 2001 found seville orange juice had a similar effect to grapefruit juice on drug metabolism. Drinking a 240ml glass of seville orange juice alongside felodipine (used to treat high  blood pressure and angina) resulted in a 76% increase in drug levels, comparable to what occurs with a glass of grapefruit juice. So, caution is warranted and seville orange juice and products (including marmalades) should be avoided when taking medication known to interact with grapefruit, because both the flesh and rind of this orange contain large quantities of furanocoumarins.