Therapeutic drug levels are lab tests to look for the presence and the amount of a drug in the blood.
A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.
You will need to prepare for some drug level tests.
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
With most medicines, you need a certain level of the drug in your blood to get the proper effect. Some medicines are harmful if the level rises too high and do not work if the levels are too low.
Monitoring the amount of the drug found in your blood allows your health care provider to make sure the drug levels are in the proper range.
Drug level testing is important in people taking drugs such as:
Testing may also be done to determine how well your body breaks down the drug or how it interacts with other drugs you need.
Following are some of the drugs that are commonly checked and the normal target levels:
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
Values outside the target range may be due to minor changes or be a sign that you need to adjust your dosages. Your doctor may tell you to skip a dose if the values measured are too high. .
Following are toxic levels for some of the drugs that are commonly checked:
Therapeutic drug monitoring
Diasio RB. Principles of drug therapy. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 28.
Ford MD. Acute poisoning. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 110.
Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.
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