Home > Tests and Treatments > Therapeutic drug levels
  • We are sorry, but NCBI web applications do not support your browser and may not function properly. More information

PubMed Health. A service of the National Library of Medicine, National Institutes of Health.

A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

Therapeutic drug levels

Therapeutic drug monitoring

Last reviewed: April 29, 2013.

Therapeutic drug levels are lab tests to look for the presence and the amount of a drug in the blood.

How the Test is Performed

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.

How to Prepare for the Test

You will need to prepare for some drug level tests.

  • Your health care provider will tell you if you need to change the times you take any of your medicines.
  • Do not stop or change your medications without talking to your doctor first.

How the Test will Feel

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.

Why the test is performed

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.

Normal Results

Following are some of the drugs that are commonly checked and the normal target levels:

Note:

  • mcg/mL = microgram per milliliter
  • ng/mL = nanogram per milliliter
  • mEq/L = milliequivalents per liter
  • mcmol = micromole

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.

What Abnormal Results Mean

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:

References

  1. 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.
  2. Ford MD. Acute poisoning. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 110.

Review Date: 4/29/2013.

Reviewed 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.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial policy, editorial process and privacy policy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only — they do not constitute endorsementscof those other sites. © 1997–2011 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

Copyright © 2013, A.D.A.M., Inc.

What works?

  • Therapeutic drug monitoring of antiretroviral medications for people with HIVTherapeutic drug monitoring of antiretroviral medications for people with HIV
    Monitoring the levels of HIV medications (antiretrovirals) in the blood of patients can reveal if levels are too high or too low. High levels may lead to side effects and low levels may not prevent the virus from multiplying. Prevention of virus replication is important for the immune system to recover and to fight diseases. The results from our review show that there is not enough evidence to recommend that the drug levels should be checked in all patients who use antiretrovirals.
See all (29) ...

PubMed Health Blog...

read all...

Read More

MedlinePlus.gov links to free, reliable, up-to-date health information from the National Institutes of Health (NIH) and other trusted health organizations.

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...