Here is what Wikipedia has to say, and it is a daunting list that they note may be incomplete. It is quite a long list, but I don't see amoxicillin on it. To be certain, I would talk to the pharmacist.
From Wikipedia: ___________________________
Drugs found to be affected by grapefruit juice include, but are not limited to:
* Halcion, Versed, Valium, Xanax and quazepam * Norvir * Zoloft and Lustral * Statins such as Lipitor, Mevacor, Zocor, Simlup, Simcor, Simvacor, with the exception of Pravachol. Lescol and Crestor which are unaffected by grapefruit. * Dihydropyridines including Plendil, Cardene, nifedipine, Sular, Bayotensin * Cozaar * The cough suppressant dextromethorphan * modafinil (Provigil, Alertec, Modavigil, Modalert, Modiodal, Modafinilo, Carim, Vigia) * Prandin * Calan SR, Covera HS, Isoptin SR, Verelan * Buspar * Eltroxin, Levoxyl, Synthroid * Antiarrhythmics including Cordarone, Multaq, quinidine (Quinidex, Cardioquin, Quinora), Norpace, Rhythmol, and Coreg * Antihistamines Hismanal and Seldane (now removed from the US and Canadian markets) * cisapride (Prepuslid, Propulsid) (which treats GERD) - now removed from the US and Canadian markets * Erectile dysfunction drugs Viagra, Cialis, and Levitra * The anti-migraine drugs ergotamine (Cafergot, Ergomar), amitryptiline (Elavil, Endep, Vanatrip) and nimodipine (Nimotop) * Fluvoxamine (Luvox, Faverin, Fevarin and Dumyrox) * Codeine and Tramadol. It reduces the amount of codeine converted by CYP3A4 into norcodeine thus increasing the amount metabolized into morphine. Morphine itself, however, is not affected by grapefruit juice, as it is not metabolized by the cytochrome P450 system. * Cyclosporine (Neoral). Blood levels of cyclosporine are increased if taken with grapefruit juice. A plausible mechanism involves the combined inhibition of enteric CYP3A4 and P-glycoprotein, which potentially leads to serious adverse events (e.g., nephrotoxicity).Blood levels of tacrolimus (Prograf) can also be equally affected for the same reason as with cyclosporine. [both drugs are calcineurin inhibitors] * omeprazole (Losec, Prilosec) * oxycodone (Oxycodone is metabolized by the cytochrome P450 system, specifically CYP3A4, of which the bergamottin flavonoid is a strong inhibitor) * hydrocodone (The hepatic cytochrome P450 enzyme CYP2D6 converts it into hydromorphone, a more potent opioid.) * dihydrocodeine * quetiapine (Seroquel, Ketipinor) * methadone -- Inhibits the metabolism of methadone and raises serum levels. * buprenorphine Metabolized into norbuprenorphine by cytochrome-P450 isoenzyme 3A4 * Tyrosine kinase inhibitors, including Gleevec and Tasigna, used to treat chronic myelogenous leukemia and gastrointestinal tumors. * Anthelmintics (Used for treating certain parasitic infections, includes praziquantel albendazole and mebendazole) * carbamazepine (Tegretol) Grapefruit or grapefruit juice slows the breakdown of this drug, increasing the level of it in blood * Loperamide (Imodium), the anti-diarrhea drug * colchicine (Colcrys)
The CYP3A4 isoform of cytochrome P450 is located in both the liver and the enterocytes. Many oral drugs undergo first-pass (presystemic) metabolism by the enzyme. Several organic compounds found in grapefruit and specifically in grapefruit juice exert inhibitory action on drug metabolism by the enzyme. It has been established that a group of compounds called furanocoumarins are responsible for this interaction and not flavonoids as was previously reported.
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