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Therapeutic drug levels
Alternative namesTherapeutic drug level tests are usually performed to look for the presence and the amount of specific drugs in the blood.
With most medications, you need a certain level of drug in the blood stream to obtain the desired effect. Some medications are toxic if the level rises too high and are ineffective if the levels are too low. Monitoring serum drug levels enables your health care provider to ensure that your drug levels are within an effective range.
How the test is performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to cause the vein to swell with blood.
A needle is inserted into the vein, and the blood is collected in air-tight vials or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
How to prepare for the testSome 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 feelWhen 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:
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.
Normal ValuesFollowing are some of the drugs that are commonly checked, and their therapeutic levels:
What abnormal results meanFollowing are some of the drugs that are commonly checked, and their toxic levels:
What the risks areRisks associated with venipuncture are slight:
Special considerationsVeins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Update Date: 11/3/2003Sherry Woodhouse, M.D., Department of Pathology and Laboratory Medicine, Cleveland Clinic Florida, Weston, FL. Review provided by VeriMed Healthcare Network.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT