Coreg is a beta-blocker prescribed for high blood pressure. Coreg works to lower blood pressure by relaxing your blood vessels and slowing the rate of your heart to make blood flow more easily. Grapefruit interferes with calcium channel blocker blood pressure medication, potentially causing grave side effects, but is not known to interfere with Coreg.
No Known Interference
The latest label for Coreg, known generically as carvedilol, was approved by the Food and Drug Administration in July 2011. The FDA label does not list grapefruit as a substance that could interfere with Coreg, and it does not list it as a substance that could cause side effects if combined with Coreg. MedlinePlus, a service of the National Institutes of Health, also does not list grapefruit warnings regarding Coreg. Many drugs remain untested for possible interactions with grapefruit, according to the People's Pharmacy. An absence of information about a drug interacting with grapefruit is simply an absence of information, not a guarantee that no interaction exists.
Metabolizing Drugs
The concern over grapefruit interfering with medication stems from the fact that grapefruit interferes with your CYP34A enzyme's ability to metabolize drugs. Not all medications are designed to be metabolized by your CYP34A enzyme. Coreg, for instance, is designed to be metabolized primarily by the CYP2D6 and CYP2C9 enzymes. According to the FDA, the CYP34A enzyme is only minimally involved in metabolizing Coreg. So grapefruit will not likely have much impact on your body's ability to metabolize Coreq.
Calcium Channel Blockers
Unlike Coreq, some types of blood pressure medications depend on your CYP34A enzyme. The calcium channel blockers nifedipine and felodipine should not be consumed with grapefruit. Calcium channel blockers work to lower blood pressure by preventing calcium from entering your blood vessels and heart. If consumed with grapefruit and not properly metabolized, they will be elevated in your system. Your blood pressure could drop to dangerously low levels, and your heart could stop beating.
Drug Interactions
Although it appears safe to eat grapefruit or drink grapefruit juice while taking Coreq, some medications interfere with your body's metabolism of the drug. Paroxetine, propafenone, quinidine and fluoxetine may increase the effectiveness of Coreg and cause adverse effects. Combining Coreg with the medications digoxin or cyclosporine may also elevate the effectiveness and the risk of side effects.Do not take Coreg with hypotensive drugs such as MAO inhibitors, as this can increase your risk of severe bradycardia or hypotension. For a full list of drugs and substances that interfere with Coreg, consult a medical professional.
References
- MedlinePlus: Carvedilol
- U.S. Food and Drug Administration: Carvedilol
- The People's Pharmacy; Graedons' Guide to Grapefruit Interactions; 2002
- The Harvard Medical School Family Health Guide: Grapefruit and Medication: A Cautionary Note
- "The New York Times"; Experts Reveal the Secret Powers of Grapefruit Juice; Nicholas Bakalar; March 2006
- MayoClinic.com; Calcium Channel Blockers; December 2010
