Side Effects Of Grapefruit With Certain Medications

Grapefruit juice is known to interact with some medications. The offending agent in grapefruit juice thought to cause the interaction is a group of substances known as furanocoumarins. These substances are not present in orange juice. Furanocoumarins slow the metabolic breakdown of some drugs taken by mouth, therefore increasing the amount of medication in the body. In rare instances, this can lead to signs of drug toxicity. However, this interaction justifies avoidance of grapefruit juice with only a few medications. Though grapefruit juice may slow the metabolism of other drugs, according to David Greenblatt, MD in an article published in "Pharmacy Times", these interactions are not clinically important enough to recommend the widespread avoidance of grapefruit juice because the effect is either very modest, clinically irrelevant because of a wide safety margin with the drug, or occurs only with extremely large quantities of grapefruit juice unlikely to be consumed. Drinking grapefruit juice at a different time of day from when the medication is taken will not prevent an interaction. For the medications below, grapefruit juice should generally be avoided or the patient closely monitored for symptoms of toxicity.

Buspirone

Buspirone (BuSpar®) is used to treat anxiety. Consuming large quantities of grapefruit juice with buspirone has been found to increase blood levels of buspirone nine-fold in a study by JJ Lilja and colleagues, published in "Clinical Pharmacology and Therapeutics." Symptoms of toxicity with buspirone include nausea, dizziness and drowsiness.

Felodipine

Felodipine (Plendil®) is used to lower blood pressure. According to Dr. Greenblatt, it is more likely than other drugs in its class (calcium channel blockers) to interact with grapefruit juice. Symptoms of toxicity include low blood pressure, slow heart rate, confusion and nausea.

Simvastatin

Simvastatin (Zocor®) is used to treat high cholesterol. As above, simvastatin appears more likely than other drugs in its class to interact with grapefruit juice. Symptoms suggesting toxicity include nausea, vomiting and muscle soreness.

Cyclosporine

Blood levels of cyclosporine (Sandimmune®, Neoral®, Gengraf®), a drug used to prevent tissue rejection following transplantion among other uses, must be kept within a narrow range. While grapefruit juice only moderately increases blood levels, even a relatively small elevation may cause symptoms of toxicity. If grapefruit juice is consumed, cyclosporine blood levels should be monitored closely and the patient watched for signs of toxicity, such as nausea, tremor, or kidney or liver damage.

Carbamazepine

Carbamazepine (Tegretol®, Carbatrol®) is used for epilepsy and neuropathic pain. Like cyclosporine, blood levels must be kept within a narrow range. Thus, even modest elevations in blood levels caused by grapefruit juice could induce toxicity, characterized by dizziness, drowsiness, nausea, agitation or abnormal movements.