Moved Permanently. The document has moved here. 29 patient posts about Grapefruit and its potential interaction with Digoxin based on the insights of millions of patients and trusted online health resources. Study Objectives. To determine the effects of grapefruit juice on the pharmacokinetics of oral digoxin, a P‐glycoprotein substrate not metabolized by cytochrome P450 3A4, in healthy volunteers, and to assess whether polymorphic multidrug‐resistance‐1 (MDR1) expression contributes to interindividual variability in digoxin disposition. I am taking many meds for heart failure including digoxin, quinidex, mexitil and demadex. I have heard that grapefruit juice causes some of these drugs to be increased in their blood levels. Grapefruit seed extract is processed from grapefruit seeds and pulp obtained as a byproduct from grapefruit juice production. Vegetable glycerin is added to the final product to reduce acidity and. Examples of common medications that have a grapefruit juice interaction include felodipine (Plendil) and atorvastatin (Lipitor). If you drink grapefruit juice, always have your pharmacist run a drug interaction check with your medications to rule out an interaction before you combine them. Grapefruit juice is responsible for drug interactions mediated by intestinal cytochrome P4503A4 inhibition and possibly P-glycoprotein inhibition in enterocytes. Grapefruit juice: Grapefruit and grapefruit juice is often mentioned as a product that can interact negatively with drugs, but the actual number of drugs the juice can interact with is less well. Ibuprofen pharmacokinetics in preterm infants with patent ductus arteriosus Objective: Our objective was to study the pharmacokinetics of ibuprofen in premature infants with Grapefruit juice interaction studies with fexofenadine. Grapefruit and constituents were examined for decreased MDR1-mediated digoxin or vinblastine efflux using polarized epithelial cell monolayers. Grapefruit juice and homogenized unprocessed segments at 5% regular strength did not alter MDR1 activity.