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The effects last because grapefruit-mediated inhibition of drug metabolizing enzymes, like CYP3A4, is irreversible; [30] that is, once the grapefruit has "broken" the enzyme, the intestinal cells must produce more of the enzyme to restore their capacity to metabolize drugs that the enzyme is used to metabolize. [19]
Cytochrome P450 3A4 (abbreviated CYP3A4) (EC 1.14.13.97) is an important enzyme in the body, mainly found in the liver and in the intestine, which in humans is encoded by CYP3A4 gene. It oxidizes small foreign organic molecules ( xenobiotics ), such as toxins or drugs, so that they can be removed from the body.
Grapefruit and grapefruit juice have been found to interact with numerous drugs, in many cases resulting in adverse effects. [4] This happens in two ways: one is that grapefruit can block an enzyme which metabolizes medication, [5] and if the drug is not metabolized, then the level of the drug in the blood can become too high, leading to an adverse effect. [5]
For example, when the blood pressure drug felodipine is taken with grapefruit juice rather than water, levels of the medication in the blood can more than double and result in headache, irregular ...
Grapefruit juice can act as an enzyme inhibitor, affecting the metabolism of drugs. In pharmaceutical sciences , drug interactions occur when a drug's mechanism of action is affected by the concomitant administration of substances such as foods, beverages, or other drugs.
Ritonavir. This antiretroviral medication inhibits CYP3A4 and may increase the effects of Cialis in the body. Alpha-blockers. When taken with Cialis, alpha-blockers can cause a drop in blood pressure.
Grapefruit–drug interactions are common, as the juice contains furanocoumarins that interfere with the metabolism of many drugs. This can prolong and intensify the effects of those drugs, leading to multiple side-effects such as abnormal heart rhythms, bleeding inside the stomach, low blood pressure, difficulty breathing, and dizziness.
Because of this risk, avoiding grapefruit juice and fresh grapefruits entirely while on drugs is usually advised. [13] Other examples: Saint-John's wort, a common herbal remedy induces CYP3A4, but also inhibits CYP1A1, CYP1B1. [14] [15] Tobacco smoking induces CYP1A2 (example CYP1A2 substrates are clozapine, olanzapine, and fluvoxamine) [16]