Drug Interaction Report

Fosphenytoin may significantly reduce the blood levels of entrectinib, which may make the medication less effective in treating your condition. Using fosphenytoin with entrectinib may also increase the risk of an irregular heart rhythm that may be serious and potentially life-threatening, although it is a relatively rare side effect. You should seek immediate medical attention if you experience sudden dizziness, lightheadedness, fainting, shortness of breath, or heart palpitations during treatment with these medications, whether together or alone. Talk to your doctor if you have any questions or concerns. Your doctor may be able to prescribe alternatives that do not interact. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

Do not consume grapefruit, grapefruit juice, or Seville oranges during treatment with entrectinib. Doing so can significantly increase the blood levels of entrectinib and increase the risk and/or severity of side effects such as dizziness; confusion; hallucinations; problems with concentration, attention, thinking, and memory; mood changes; insomnia; drowsiness; liver problems; increased uric acid levels in the blood (hyperuricemia); congestive heart failure; fluid retention and swelling; changes in electrical activity of the heart (a condition known as QT prolongation, which may lead to irregular heart rhythm that can be life-threatening); vision problems; and low red or white blood cell counts. Talk to your doctor if you have any questions or concerns. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.