Drug Interaction Report

Before starting fingolimod, let your doctor know if you are currently receiving treatment with selpercatinib. Using fingolimod in this situation can increase the risk of an irregular heart rhythm that may be serious and potentially life-threatening, although it is a relatively rare side effect. This is most likely to occur early on after you start treatment with fingolimod, especially within the first 20 hours after the first dose. You may also be more susceptible if you have a heart condition called congenital long QT syndrome, other cardiac diseases, conduction abnormalities, or electrolyte disturbances (for example, magnesium or potassium loss due to severe or prolonged diarrhea or vomiting). On the other hand, it may be alright for you to use these medications together if you have been stable on fingolimod therapy for over a month while you start treatment with selpercatinib. Talk to your doctor if you have any questions or concerns. Your first dose of fingolimod must be taken at your doctor's office or a hospital, and you will need to be observed for 6 hours or more afterwards. In the event that you restart the medication after an interruption in treatment, you may need to take the first dose again under medical observation depending on how long you were on the medication before you stopped, and how many days the interruption lasted. You should seek immediate medical attention if you develop sudden dizziness, lightheadedness, fainting, shortness of breath, or heart palpitations during treatment with these medications, whether together or alone. 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.

You should limit or avoid consumption of grapefruit and grapefruit juice during treatment with selpercatinib unless directed otherwise by your doctor. Grapefruit juice may increase the blood levels of selpercatinib. High levels of selpercatinib can 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 may be more susceptible if you have a heart condition called congenital long QT syndrome, other cardiac diseases, conduction abnormalities, or electrolyte disturbances (for example, magnesium or potassium loss due to severe or prolonged diarrhea or vomiting). The risk and/or severity of other side effects may also increase, including nausea, vomiting, constipation, diarrhea, rash, muscle and joint pain, swelling of arms or legs, liver problems, high blood pressure, and bleeding complications. Talk to your doctor if you experience intolerable or troublesome side effects, or you have other questions or concerns. You should seek immediate medical attention if you develop sudden dizziness, lightheadedness, fainting, shortness of breath, or heart palpitations during treatment with selpercatinib. 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.