Therapeutic drug levels


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How to prepare for the test

Some drug level tests require preparation. Ask your health care provider for preparation information related to the test ordered.

Infants and children:

The preparation you can provide for this test depends on your child's age, previous experience, and level of trust. For general information regarding how you can prepare your child, see the following:




How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.


Why the test is performed

Testing involves taking multiple measurements of blood levels of a drug over time. The main purpose is to determine the effective drug dosages and to prevent toxicity. Drug level testing is especially important in people taking drugs such as:

  • Procainamide or digoxin used to treat abnormal beating of the heart
  • Dilantin or valproic acid used to treat seizures
  • Gentamicin or amikacin, antibiotics used to treat infections

Often, these are drugs where the margin of safety between therapeutic levels and toxic levels is narrow. Testing may also be done to determine absorption, rate of metabolism, or interaction with other necessary drugs. Some drugs have more than one use.



Review Date: 10/27/2005
Reviewed By: Frank A. Greco, M.D., Ph.D., Director, Biophysical Laboratory, The LaheyClinic, Burlington, MA. Review provided by VeriMed Healthcare Network.

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