Drug Interaction Report

Lapatinib may increase the blood levels of selumetinib in some patients. This may increase the risk and/or severity of serious side effects such as diarrhea; colitis (inflammation of the colon); skin rashes; cardiomyopathy (a condition that affects the heart muscle and its ability to pump blood); rhabdomyolysis (a rare condition involving the breakdown of skeletal muscle tissue that can cause kidney damage and death); and eye problems that can lead to blindness. Talk to your doctor if you have any questions or concerns. Your doctor may be able to prescribe alternatives that do not interact, or you may need a dose adjustment or more frequent monitoring to safely use both medications. You should seek prompt medical attention if you experience severe diarrhea; severe skin reactions (rash over a large area of the body, peeling skin, blisters); signs and symptoms of heart trouble (persistent coughing or wheezing, shortness of breath, swelling of ankles and feet, fatigue, increased heart rate); muscle problems (unexplained muscle pain, tenderness or weakness, especially with fever and/or dark colored urine); or vision problems (blurred vision, light sensitivity, dark spots or floaters, vision loss). 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.

Grapefruit juice can increase the blood levels of selumetinib. This may increase the risk and/or severity of serious side effects such as diarrhea; colitis (inflammation of the colon); skin rashes; cardiomyopathy (a condition that affects the heart muscle and its ability to pump blood); rhabdomyolysis (a rare condition involving the breakdown of skeletal muscle tissue that can cause kidney damage and death); and eye problems that can lead to blindness. Do not consume grapefruit, grapefruit juice, or any supplements that contain grapefruit extract during treatment with selumetinib. Talk to your doctor or pharmacist if you have any questions or concerns. You should seek prompt medical attention if you experience severe diarrhea; severe skin reactions (rash over a large area of the body, peeling skin, blisters); signs and symptoms of heart trouble (persistent coughing or wheezing, shortness of breath, swelling of ankles and feet, fatigue, increased heart rate); muscle problems (unexplained muscle pain, tenderness or weakness, especially with fever and/or dark colored urine); or vision problems (blurred vision, light sensitivity, dark spots or floaters, vision loss). 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.

Take lapatinib on an empty stomach 1 hour before or 1 hour after a meal unless otherwise directed by your doctor. This will make it easier for your body to absorb the medication. The lapatinib dose is administered once daily and should not be divided. The usual dose of lapatinib is equal to 5 tablets. You may swallow each tablet one at a time, but take the entire lapatinib dose at the same time each day. If you are receiving therapy with lapatinib you should be advised to avoid grapefruits and grapefruit juice. Grapefruit can raise the levels of lapatinib in your body and lead to dangerous side effects.