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Therapeutic drug monitoring uses lab tests to check the amount of medicine in your child’s body. These tests help your child’s care team know if:
Pharmacokinetics is an area of medicine that studies how drugs work in the body. Pharmacokinetic studies use patient samples to find out:
Each medicine works best at a certain level in the body. This is called the therapeutic drug level or therapeutic range. If the medicine level is too low, it will not work well. If the medicine level is too high, it might be harmful.
The right level of medicine depends on several factors, such as:
The correct dose of a medicine for a patient depends on factors such as:
Speak to your care team about the therapeutic range for your child’s medicine.
Your care team will tell you if medicine levels need monitoring. Follow their instructions about how and when your child should take their medicine and what to do when it is time for their drug level test.
Your child’s care team will take a blood sample from your child. The drug level is measured in the lab. The peak level is when the medicine is at its highest level in the body. This is usually shortly after your child takes their medicine. The lowest level, or trough, is usually right before the time for their next dose.
The time for testing depends on the kind of medicine. Many medicines have a trough (pre-dose) level checked before your child takes their next dose. But some levels are checked 4 to 6 hours after your child takes their medicine. Still other medicines have levels checked several times to make sure the body is removing the drug well.
When getting a drug level test, it is important to follow your health care provider’s instructions. Make sure that your child:
Your child’s test results will come back as a drug level. This level shows the amount of medicine in their blood. The level needs to be within a therapeutic range for their type of medicine. This range is where the medicine has the best chance of working without causing harm in most patients. Depending on the results, your care provider may change the amount of medicine your child takes.
Medical centers vary on how and when they monitor drug levels. Monitoring levels makes sure the drug stays at an acceptable level in the body, works well, and is safe. This amount may change, depending on a person and their health.
A drug may need monitoring if it:
|Type of Medicine
|Antibiotics, antifungals, antivirals
|Amikacin, gentamicin, meropenem, posaconazole, tobramycin, vancomycin, voriconazol
|Anticoagulant (stops blood clotting)
|Enoxaparin, heparin, warfarin
|Carbamazepine, lacosamide, lamotrigine, levetiracetam, phenobarbital, phenytoin, topiramate, valproic acid, zonisamide
|Methotrexate, mitotane, topotecan
|Digoxin, digitoxin, lidocaine, procainamide
|Immunosuppressants (reduce immune response for autoimmune disease, transplant)
|Azathioprine, cyclosporine, mycophenolate, sirolimus, tacrolimus
This list does not include all medicines that are monitored. Always follow the specific instructions of your health care provider for therapeutic drug monitoring of any medicines your child takes.
Many medicines do not need drug levels checked because:
Therapeutic drug monitoring helps your care team know that your child has the correct amount. When your child takes more medicine, or if they take the same amount more often, the drug level goes up. When they take less medicine, or take the same amount less often, the drug level goes down. Levels can also vary with how a patient’s body metabolizes and clears the drug, their health at that time, and other medicines they are taking.
Based on the test results, your health care provider might need to change your child’s dose.
Always follow your care team’s instructions on how to give and monitor medicines.
Reviewed: December 2023