Drug Interaction Report

Tolvaptan may increase the blood levels and effects of vismodegib. This may increase the risk and/or severity of side effects such as muscle spasm, hair loss, taste disturbances, weight loss, fatigue, nausea, vomiting, diarrhea, decreased appetite, constipation, and joint pain. You may need a dose adjustment or more frequent monitoring by your doctor to safely use both medications. 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 avoid drinking grapefruit juice during treatment with tolvaptan. Grapefruit juice can cause too much of the medication to be in the blood. Serious nervous system side effects such as difficulty swallowing, trouble speaking, muscle weakness, trouble controlling body movements, confusion, mood changes, seizures, and coma may occur. 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.