Question: why can you not take grapefruit with felodipine

Reference:
Felodipine: Felodipine is used to treat high blood pressure. Felodipine is in a class of medications called calcium channel blockers. It works by relaxing the blood vessels so your heart does not have to pump as hard.   High blood pressure is a common condition and when not treated, can cause damage to the brain, heart, blood vessels, kidneys and other parts of the body. Damage to these organs may cause heart disease, a heart attack, heart failure, stroke, kidney failure, loss of vision, and other problems. In addition to taking medication, making lifestyle changes will also help to control your blood pressure. These changes include eating a diet that is low in fat and salt, maintaining a healthy weight, exercising at least 30 minutes most days, not smoking, and using alcohol in moderation. Felodipine comes as an extended release tablet to take by mouth. It is usually taken once a day. To help you remember to take felodipine, take it around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take felodipine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.   Swallow the tablets whole; do not split, chew, or crush them.   Felodipine controls high blood pressure but does not cure it. Continue to take felodipine even if you feel well. Do not stop taking felodipine without talking to your doctor. This medication may be prescribed for other uses; ask your doctor or pharmacist for more information. Before taking felodipine,     - tell your doctor and pharmacist if you are allergic to felodipine, any other medications, or any ingredients in felodipine tablets. Ask your pharmacist for a list of the ingredients.   - tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: antiseizure medicines such as carbamazepine (Carbatrol, Equetro, Tegretol), phenytoin (Dilantin, Phenytek), and phenobarbital; cimetidine (Tagamet); erythromycin (E.E.S., Eryc, Ery-tab); itraconazole (Sporanox); ketoconazole (Nizoral); ranitidine (Zantac); and tacrolimus (Astagraf SL, Prograf).   - tell your doctor if you have or have ever had heart, liver, or kidney disease.   - tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking felodipine, call your doctor.   - if you are having surgery, including dental surgery, tell your doctor or dentist that you take felodipine. Talk to your doctor about drinking grapefruit juice or eating grapefruit while taking felodipine.   Talk to your doctor before using salt substitutes containing potassium. If your doctor prescribes a low-salt or low-sodium diet, follow these directions carefully. Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. Felodipine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:      - headache   - flushing   - dizziness or lightheadedness   - weakness   - fast heartbeat   - heartburn   - constipation   - enlargement of gum tissue around teeth    Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately or get emergency medical treatment:      - swelling of the face, eyes, lips, tongue, arms, or legs   - difficulty breathing or swallowing   - fainting   - rash     If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088). Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.   It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911. Keep all appointments with your doctor and the laboratory. Your blood pressure should be checked regularly to determine your response to felodipine.   Good dental hygiene decreases the chance and severity of gum swelling. Brush your teeth regularly and schedule dental cleanings every 6 months.   Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.   It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies. - Plendil® - Lexxel® (containing Enalapril, Felodipine)¶

Answer: Talk to your doctor about drinking grapefruit juice or eating grapefruit while taking felodipine.