2017-08-24 15:42:24 UTC

IBD 115: Therapeutic Drug Monitoring in IBD

Learn more about Therapeutic Drug Monitoring, based on the AGA Clinical Guideline "Therapeutic Monitoring in Inflammatory Bowel Disease."

Clinical practice guidelines are developed under the guidance of the AGA Institute Clinical Guideline Committee and provide evidence-based recommendations for clinical practice in the field of gastroenterology. The clinical practice guidelines and related Clinical Decision Support Tools support evidence-based clinical decision-making by gastroenterologists and other health-care professionals at the point of care. The below information presents important content from those guidelines in a way that will help patients better understand AGA’s recommendations for evaluating, diagnosing or managing a condition.

AGA Clinical Guideline: Therapeutic Drug Monitoring in Inflammatory Bowel Disease

The information provided by the AGA Institute is not medical advice and should not be considered a replacement for seeing a medical professional.

Contents:

What is therapeutic drug monitoring?

What is the importance of therapeutic drug monitoring?

Individual reactions

Drug differences


What is therapeutic drug monitoring?

  • Therapeutic drug monitoring (or TDM, for short) is when your doctor looks at the amount of IBD drugs in your blood to make sure that you are getting optimal levels of the drug. 
  • TDM can also help make sure that your body is not breaking down the drug too quickly, which would make it not work as well.  
  • TDM is done through testing the patient’s blood on a regular basis while they are taking drugs for IBD.
  • TDM can check if you have developed antibodies to the drug. Antibodies are a type of immune cell that can destroy the drug and may cause the drug to not work.

What is the importance of therapeutic drug monitoring?

  • Using TDM in patients with active IBD helps guide treatment changes. 
  • Different patients may not have the same response to the same drug or to the same dose. TDM helps tailor the drug and dose to the body of each patient.
  • A drug can won’t work well if the drug concentration is too low or if you have developed antibodies to the drug.

Individual reactions

  • How a person’s body responds to a certain drug or dose depends on many things:
    • The severity of IBD or the amount of inflammation, or swelling, in the patient’s body.
    • The type of IBD (whether it is Crohn’s disease or ulcerative colitis).
    • Gender.
    • Weight.
  • There are three possible reasons why a certain drug might not be helpful for an IBD patient. 
    • Mechanistic failure 
      • This is when a patient does not respond to a specific drug even though that they have an acceptable amount of the drug in their blood.
      • This often means that the type of drug being given does not work for the specific type of IBD the patient has. 
      • Patients with mechanistic failure will likely not respond to other drugs of the same class. 
    • Immune-mediated pharmacokinetic failure 
      • This is when a patient’s immune system breaks down the drug in the body too quickly for it to effectively treat the disease.
      • Patients with this type of failure have low levels of the drug in their blood, and have a high amount of anti-drug antibodies.
    • Non-immune meditated pharmacokinetic failure
      • This is when the drug is cleared from the patient’s body too quickly for it to be helpful. 
      • This failure results from the drug moving throughout the body at a fast pace, often when the inflammation is intense.  
      • Patients with this type of failure will have low levels of the drug in their blood, but will not have high levels of anti-drug antibodies. This means that something else is breaking down the drug too quickly for it to work.

Your doctor can figure out which type of failure is happening by measuring the amount of drug in your blood right before the next dose is usually taken (also known as a trough level) and comparing it with the amount of anti-drug antibodies in your blood.

Drug differences

  • If you are taking a type of drug called anti-TNF agents (a type of biologic drug) for your IBD, TDM can help your doctor find the right drug and dose.
    • Reactive TDM is done on a patient who is currently having IBD symptoms to guide changes in the drug type or dose. 
      • If the trough level is at an acceptable amount, but you are still having IBD symptoms, your doctor may decide to switch you to a new type of drug.
      • If your trough levels are low and you do not have a high level of antibodies, your doctor may decide to increase the dose of the drug you are currently taking.
      • If your trough levels are low and you also have a high level of antibodies, your doctor may switch to another drug in the same class, or a completely new type of drug.
  • If you are taking a type of drug called a thiopurine for your IBD, TDM can help prevent serious side effects.
    • About one in every 10 patients is deficient in an enzyme called TPMT, which helps break down thiopurines so they do not become toxic. Your doctor can test your blood to see if you have this deficiency.
      • If you are deficient in TPMT, your doctor may start you at a lower level, see how your body responds, and increase the dose as needed.
      • Once you have started thiopurines, your doctor can use reactive TDM to test how well your body is breaking down the drug. 
      • If there are low levels of broken-down drugs in your body, your doctor may increase your dose.
      • If there are higher levels of broken-down drugs in your body, but your symptoms have not gotten better, your doctor may switch you to a different type of drug.
    • Even if you are not TPMT deficient, your doctor should still do regular blood tests as recommended by the maker of your drug.


For more information on Inflammatory Bowel Disease, visit gastro.org/IBD.
 

©AGA, July 2016

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