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Some substances, such as some drugs and furanocoumarins present in grapefruit juice, interfere with the action of CYP3A4. These substances will, therefore, either amplify or weaken the action of those drugs that are modified by CYP3A4. CYP3A4 is a member of the cytochrome P450 family of oxidizing enzymes. Several other members of this family ...
Ciclosporin (cyclosporine, Neoral): Blood levels of ciclosporin are increased if taken with grapefruit juice, orange juice, or apple juice. [12] A plausible mechanism involves the combined inhibition of enteric CYP3A4 and MDR1, which potentially leads to serious adverse events (e.g., nephrotoxicity).
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]
Grapefruit juice raises the bioavailability of carbamazepine by inhibiting the enzyme CYP3A4 in the gut wall and in the liver. [5] Lower levels of carbamazepine are seen when administered with phenobarbital , phenytoin , or primidone , which can result in breakthrough seizure activity.
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]
Under normal circumstances, the grapefruit juice effect is considered to be a negative interaction, and patients are often warned not to consume grapefruit or its juice when taking medication. However, some current research is focused on the potential benefits of cytochrome P450 inhibition. [ 3 ]
"INHIBITORS, INDUCERS AND SUBSTRATES OF CYTOCHROME P450 ISOZYMES". "The Life Raft Group: Long List of Inhibitors and Inducers of CYP3A4 and CYP2D6". "DRUGBANK Online: Cytochrome P-450 Enzyme Inhibitors". "MEDICATIONS METABOLIZED BY CYTOCHROME P450 3A4" (PDF)
The typical concentration of naringin in grapefruit juice is around 400 mg/L. [4] The reported LD50 of naringin in rodents in 2000 mg/kg. [ 5 ] Naringin inhibits some drug-metabolizing cytochrome P450 enzymes , including CYP3A4 and CYP1A2 , which may result in drug-drug interactions. [ 6 ]