Moderate. These medicines may cause some risk when taken together. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.
How the interaction occurs:
Calcium may bind to phenytoin in your digestive tract, preventing your body from absorbing your phenytoin.
What might happen:
The amount of phenytoin in your blood may decrease and it may not work as well.
What you should do about this interaction:
Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together. Your doctor may want to check the amount of phenytoin in your blood. Separate the times you take your phenytoin and your medicine that contains calcium by as much time as possible. Let your doctor know right away if you have any changes in the amount of seizures you have.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.
1.Garnett WR, Carter BL, Pellock JM. Effect of calcium and antacids on phenytoin bioavailability. Arch Neurol 1980 Jul;37(7):467.
2.Dilantin (phenytoin sodium) US prescribing information. Pfizer, Inc. November, 2012.