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We know now that the consumption of grapefruit or its juice (fresh or frozen) may cause an increase or, less frequently, a diminution of the effect of certain drugs. Grapefruit contains apparently substances capable of interfering with the absorption and the transformation of several drugs by inhibiting the fraction 3A4 of the cytochrome P450 (CYP 3A4) located in the small bowel. Products most susceptible to be affected have a weak oral bioavailability and an important pre-systemic metabolism (effect of first passage). A quantity as weak as 250 ml of grapefruit juice can provoke a significant increase of concentrations of certain drugs in the blood. The effects of grapefruit can last for 3 days or longer because the inhibition of the CYP 3A4 is irreversible. The body, thus, has to generate new enzymes to restore the normal level of activity The effect of interaction lastslast very long. It cannot be avoided by simply changing the interval between the drug’s intake and that of the grapefruit. So, drinking juice at lunch and taking the medicine in the evening, at bedtime, does not guarantee protection against the effects of the interaction. The consequences of the interaction vary according to the individual, the drug involved and the grapefruit itself. The intensity of the interaction varies obviously from one person to the other and on a day-to-dayday to day basis forto the same person. ThusSo, it is impossible to take the interaction into account, for example, by decreasing the dosage of medicine.
Drugs affected by grapefruit and grapefruit juice
To minimize the risks of unwanted effects, people who use one of the above listed medicines should refrain from consuming fresh grapefruit or grapefruit juice. Seville Oranges can present similar risk to that of grapefruit. Most of the other citrus fruits, such as lemon, lime, regular oranges and tangerines are not considered as dangerous. |