Question: why can you not take grapefruit with felodipine

Reference:
 Felodipine Why is this medication prescribed? 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. How should this medicine be used? 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. Other uses for this medicine This medication may be prescribed for other uses; ask your doctor or pharmacist for more information. What special precautions should I follow? <h3>Before taking felodipine,</h3> /h3> 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. What special dietary instructions should I follow? 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. What should I do if I forget a dose? 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. What side effects can this medication cause? <h3>Felodipine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away: </h3> /h3> headache flushing dizziness or lightheadedness weakness fast heartbeat heartburn constipation enlargement of gum tissue around teeth <h3>Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately or get emergency medical treatment: </h3> /h3> 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). What should I know about storage and disposal of this medication? 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). 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 Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program. In case of emergency/overdose In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911. What other information should I know? 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. Brand names Plendil Brand names of combination products Lexxel (containing Enalapril, Felodipine) 

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