Drug Interaction Report

Lapatinib can increase the blood levels and effects of silodosin. This may cause blood pressure to fall excessively and heart rate to increase, especially when you rise from a sitting or lying position. The risk of other side effects such as dizziness, lightheadedness, fainting, headache, flushing, nasal congestion, heart palpitations, and priapism (prolonged and painful erection unrelated to sexual activity) may also increase. You may need a dose adjustment or more frequent monitoring by your doctor to safely use both medications. Let your doctor know if you develop these symptoms while using silodosin and they do not go away on their own or they become troublesome. Avoid driving or operating hazardous machinery until you know how the medication affects you, and use caution when getting up from a sitting or lying position. 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.

Taking silodosin with food can reduce the risk and/or severity of side effects. Therefore, silodosin should be administered with or immediately after a meal.