Posaconazole slows how your body clears Alectinib. In a study, Alectinib's peak blood level rose 1.18 times and total exposure rose 1.75 times. Its active by-product M4 went the other way: peak fell 71% and total exposure fell 25%.
These medicines are often taken together with some care. Your doctor may change a dose, space them apart or check on you more often. Make sure your doctor and pharmacist know you take both.
What to do: Ask your doctor or pharmacist before using both. They may check you more closely or change your plan.