Prescription medications enter the body and work on a specific location, depending on the disease or condition. After a certain period of time, the medication is broken down, or metabolized, and eliminated from the body. The process of metabolism is performed by the liver and elimination is performed by the intestines and kidney. Prescription drugs may interact with other drugs and food. Grapefruit and grapefruit juice may interact with many drugs.
Enzymes
Cytochrome P450 is a large group of enzymes found in the liver. Cytochrome P450 3A4, or CYP 3A4, is a major enzyme involved in the breakdown of medications. Other medications and food may induce or inhibit CYP 3A4 and affect metabolism. An inducer causes an increase in the production of the enzyme. An inhibitor interferes with the ability of CYP 3A4 to metabolize a medication properly.
Grapefruit
Grapefruit contains chemicals called furanocoumarins, including quercetin, naringin and bergamottin that are potent inhibitors of CYP 3A4, according to "Pharmacotherapy: A Pathophysiologic." This decreases the rate at which the enzyme breaks down the medication, resulting in an exaggerated response.
Interactions
Grapefruit interacts with many medications and may cause high levels of the drug, states MayoClinic.com. A class of drugs known to interact with grapefruit is the "statins," which are popular cholesterol-lowering drugs. These drugs include simvastatin, atorvastatin, lovastatin and rosuvastatin. Calcium channel blockers are a class of drugs commonly used to treat high blood pressure. Felodipine, nifedipine, nimodipine and nisoldipine belong in this class and may reach toxic levels when administered with grapefruit. Cyclosporine, tacrolimus and sirolimus, which are immunosuppressant agents, are affected by grapefruit. Other medications include buspirone, sertraline, quetiapine, carbamazepine, amiodarone and saquinavir.
Consequences
Drug interactions with grapefruit and grapefruit juice may lead to harmful effects. If grapefruit is consumed while on a statin drugs, it may increase the risk of rhabdomyolysis, or the destruction of muscle cells. The patient may experience pain and muscle weakness. Grapefruit may also increase the appearance of side effects of medications. For example, cyclosporine has a boxed warning stating that it might cause high blood pressure and may increase the risk of infection, explains the "Drug Information Handbook." Grapefruit may produce a greater rise in blood pressure and increase the risk of infection further.
Prevention
The patient should inform his physician about all medical conditions he has and all the medication he currently takes. The physician can determine if there is an interaction with grapefruit. The patient may also speak the pharmacist when he fills the prescription. If a patient is taking a medication that interacts with grapefruit, he should avoid eating the fruit. According to MayoClinic.com, waiting to take a drug after drinking grapefruit juice does not prevent an interaction.
References
- "Pharmacotherapy: A Pathophysiologic Approach"; Joseph T. Dipiro, Robert L. Talbert, et al.; 2008
- MayoClinic.: Grapefruit juice: Can it cause drug interactions?
- "Drug Information Handbook"; Charles F. Lacy, Lora L. Armstrong, et al.; 2009
