Predicting clinical relevance of grapefruit-drug interactions: a complicated process

Grapefruit juice interacts with a number of drugs. This commentary provides feedback on a previously proposed approach for predicting clinically relevant interactions with grapefruit juice based on the average inherent oral bioavailability (F) and magnitude of increase in bioavailability with other CYP3A inhibitors of the drug.

Additional factors such as variability of the magnitude of the pharmacokinetic interaction among individuals, product monograph cautionary statements and vulnerability of the patient population should be considered.

A flow diagram is provided that should improve prediction of the pharmacokinetic interaction and clinical relevance for affected drugs and that recommends different courses of action for patient management. Forecasting the clinical importance of a particular drug interaction with grapefruit can be improved through consideration of additional readily available drug regulatory information.