Reduce Your Risk For Thiopurine Drug Side EffectsIn some cases the expected response to thiopurine drugs is clear. For example, in individuals with low/absent TPMT activity, thiopurine drugs should be avoided because of the increased risk of developing severe, life-threatening bone marrow suppression when taking a standard dose of a thiopurine drug. Individuals with intermediate (reduced) TPMT activity may require a lower starting dose than is typically prescribed and may be at an increased risk for bone marrow suppression. In these cases, it is clear how genetic information can be used to reduce your risk of serious side effects. In other cases, it may not be possible to clearly predict response based on the available genetic information. For example, results may indicate that TPMT activity is either intermediate (reduced) or low/absent but the specific activity category cannot be predicted.
Thiopurine Drug-Drug Interactions
Some drugs (both prescription and over the counter) may decrease the effect of thiopurine drugs or increase the risk for side effects. Talk to your health care provider if you are taking a thiopurine drug in addition to any of the following drugs:
Allopurinol (Lopurin, Zyloprim) – Commonly prescribed to treat gout; can interfere with the breakdown of thiopurines drugs and cause a drop in white and red blood cells.
Warfarin (Coumadin, Jantoven) – When taken in combination with a thiopurine drug, warfarin (Coumadin), a blood thinner used to prevent blood clots, may not be as effective.
ACE Inhibitors (Lotensin, Capoten, Vasotec) – Often used to control hypertension, the use of ACE inhibitors with thiopurine drugs can cause anemia and low white blood cell counts.
Ribavirin (Copegus, Rebetol, RibaTab, RibaSphere) – An antiviral medication used to treat Hepatitis C, taking Ribavirin at the same time as a thiopurine drug can increase the risk for life-threatening bone marrow suppression. Bone marrow suppression is a severe decrease in cells responsible for providing immunity, carrying oxygen, and those responsible for normal blood clotting.
Aminosalicylates (Colazal, Asacol, Dipentum, Azulfidine) – Used to prevent inflammation in the colon, when taken with a thiopurine drug, aminosalicylates can increase the risk of bone marrow suppression in patients.
For a list of medications that interact with thiopurines, click here.
It is important that you talk to your healthcare providers about all of the medications (both over-the-counter and prescription) as well as supplements that you are taking, as they may interact with certain thiopurine drugs. Do not make changes to ANY medications without talking to your healthcare providers.
Thiopurines Drugs and Food Interactions
There are no known food interactions with thiopurine drugs.
Can TPMT Affect My Response to Any Other Drugs?
Other than the thiopurine drugs, TPMT is not known to affect your response to other drugs.
Talk to your healthcare providers about all of the medications (both over the counter and prescription) as well as any supplements that you are taking.