Many medications interact with different foods, with grapefruit one of the worst food offenders. Whole grapefruit or grapefruit juice as well as similar foods such as Seville oranges, pomelos and tangelos interfere with medications broken down by certain enzymes in the liver. Grapefruit doesn't interfere with ramipril, an angiotensin-converting enzyme or ACE inhibitor used to lower blood pressure, but may interfere with combination medications that contain ramipril along with another drug.
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A chemical in grapefruit, possibly furanocoumarin, binds to an enzyme called CYP3A4 in the intestines. This enzyme also breaks down certain medications in your liver and decreases the amount of medication your body absorbs. When grapefruit juice chemicals block the action of the enzyme, you absorb more of the medication than you normally would. In the case of ACE inhibitors, which lower blood pressure, this could result in your blood pressure dropping lower than it should. Grapefruit juices affects the availability of CYP 3A4 by around 47 percent within the first four hours after ingestion, and continues to cause lower levels for 24 hours, according to the Harvard Medical School Family Health Guide.
Grapefruit juice doesn't affect most ACE inhibitors, including ramipril, according to an article published by Pakistani researchers in the October 2007 "Nutrition Journal." ACE inhibitors belong to a class of blood pressure-lowering medications that block production of angiotensin II, a hormone that narrows blood vessels and raises blood pressure. Grapefruit juice does affect other anti-hypertensive medications, including calcium channel blockers, which decrease the amount of calcium that enters the heart muscle, lowering blood pressure and slowing the heart rate.
The only time grapefruit juice shouldn't be taken when taking ramipril is when ramipril is mixed with another drug, like felopidine, a calcium channel blocker that is metabolized by the CYP 3A4 enzyme. A combination drug, Triapin, contains both medications. Because you may absorb an increased amount of felopidine when taking this drug, you may feel dizzy or lightheaded or even pass out from very low blood pressure if you take this drug while drinking grapefruit juice.
You don't have to worry about the effects of drinking grapefruit juice while taking ramipril. However, if your doctor changes your blood pressure medication or adds an additional medication, ask whether the new drug interacts with grapefruit.