Medical Health Encyclopedia

Therapeutic drug levels

Infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

The sample is then taken to the laboratory, where it is evaluated for the particular drug specified by your health care provider.

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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:

• infant test or procedure preparation (birth to 1 year)
• toddler test or procedure preparation (1 to 3 years)
• preschooler test or procedure preparation (3 to 6 years)
• schoolage test or procedure preparation (6 to 12 years)
• adolescent test or procedure preparation (12 to 18 years)

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.

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