Definition of Therapeutic drug levels:

Therapeutic drug level are laboratory tests to look for the presence and the amount of specific drugs in the blood.

How the test is performed:

A blood sample is needed. For information on how this is done, see:Venipuncture

How to prepare for the test:

Some drug level tests require preparation. Your health care provider will tell you how to prepare.

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:

With most medications, you need a certain level of drug in your bloodstream to obtain the desired effect. Some medications 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 within an effective range.

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

Testing may also be done to determine how well your body breaks down the drug ( metabolism), or how it interacts with other necessary drugs.