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Bitter Fruit
Written by Mark Siefring M.D. M.S.     
Tuesday, 13 April 2010 07:01
Bitter Fruit

 

Grapefruit and pomelos may be delicious, but they can have adverse health effects if you are taking medication. Mark Siefring M.D. M.S. reports.


Pomelos and grapefruit are enjoyed by many people, but many do not know that these fruits and their juice can seriously interact with several medications. It usually increases the drug’s level in the blood/serum. The ability of these fruit juices to increase drug concentrations was first discovered in 1989 when a study of the effect of grapefruit juice on a blood pressure (hypertension) medication called Felodipine was noted. The study was actually looking at the effect alcohol had on Felodipine and grapefruit juice just happened to be the flavouring mixer in the cocktail for volunteer trials. Serendipitously it was found that it was not the alcohol raising the level of this medication, but the grapefruit juice itself.

The results showed a huge increase in the levels of the blood pressure medication and it also showed that volunteers who drank the grapefruit juice cocktail and the medication had lower blood pressures and experienced more adverse side effects compared to those who had only taken the medication alone.

This phenomenon has now been recognised to affect many important drugs like those that lower cholesterol levels (Lipitor and Zocor as examples), blood pressure medications, anti-seizure medications, heart rhythm medications, and others. This phenomenon is caused by inhibition by grapefruit juice on the activity of one of the body’s most important detoxifying enzymes, called CYP3A4, which is involved in the metabolism of about half of all drugs currently prescribed. The results of several studies suggest that grapefruit and its juice affects the intestinal form of this enzyme greatly, but not as greatly the very same enzyme located in the liver. Repeated drinking of grapefruit juice (three times a day) in large amounts (200ml to 400 ml, double-strength), however, over several days can also inhibit this detoxifying enzyme in the liver as well.

 

Bitter Fruit

 

The Affects on Enzymes

Grapefruit juice is partly an irreversible inhibitor of these important enzymes, and thus the activity of the enzymes does not immediately return to normal after the juice has moved through the intestine. Interactions with drugs, therefore, cannot be fully avoided by taking your medication and the grapefruit juice at a different time. The recovery of half the enzyme’s activity to normal following a single glass of grapefruit juice appears to take about one day, but takes about three days to return to completely normal activity.

The amount of grapefruit ingested also substantially affects the magnitude of its effect on the body’s enzymes. One glass a day for 3 days doubles the blood levels of cholesterol-lowering medications; three glasses a day of double-strength grapefruit juice for 3 days results in 15-fold increases in blood levels of these medications. The capacity to inhibit these intestinal and liver enzymes may also vary depending on whether the grapefruit juice is white or pink, where and when it was harvested, and whether it is consumed in the form of a whole grapefruit or as fresh or frozen juice.

Not only grapefruit juice but some other citrus juices, like Seville (sour) oranges, can inhibit these enzymes. Sweet oranges and tangerines do not inhibit the CYP3A4 enzyme. Lemon juice does not appear to have any important interactions with this important enzyme (although there is evidence that lemon juice does decrease the levels of the antimalarial drug Chloroquine).

The list of medications that grapefruit juice can interefere with is too long to list here, therefore, it is very important if you are a regular connoiseur of grapefruit to seek your doctor’s advice if you are also taking a medication over a long period of time for any indication.

 

 

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