Information and Resources

Font Size

Medication Monitoring

Medication monitoring measures the level of a medicine in the blood to make sure the dosage of medicine is correct. Sometimes the amount of medicine that helps (therapeutic level) is very close to the amount that can cause harm (toxic level). Determining the correct dosage of a medicine for each person can be hard, because the dose needed to produce a therapeutic level in the blood varies from person to person. Things that affect medicine levels in the blood include age, weight, activity level, the speed at which the body breaks down the medicine, how the medicine was taken (such as by mouth, patch, or shot), and other medicines a person is using.

Medication monitoring is important for people whose bodies do not remove or break down (metabolize) medicines well because of poor function in the liver or kidneys. Also, some medicines can damage an organ (such as the liver or kidneys) or cause other problems at the dose used for treatment. If you are taking such a medicine, its amount in your blood may need to be checked regularly to ensure your dosage is at a safe and effective level.

Medication monitoring can also be useful for infants, older adults, people with heart failure or changes in heartbeat (arrhythmia), or people taking two or more medicines that may interfere with each other.

Medicine blood levels often depend on when the last dose was taken. The highest, or peak, level usually occurs 30 to 60 minutes after taking the medicine. The lowest, or trough, level occurs right before taking the next dose.

Monitoring can be done for nearly any type of medicine, but it is most often done for:

Certain antibiotics.
Medicines to treat heart problems.
Medicines to treat seizure disorders (epilepsy).
Medicines to treat bipolar disorder.
High doses of aspirin or similar medicines (salicylates).
Medicines used to prevent the body from rejecting an organ transplant.

A prothrombin time (PT) test is used to monitor the effects of the blood-thinning medicine warfarin (Coumadin).

Why It Is Done

Medication monitoring may be done to:

Confirm you are receiving an effective dose of medicine.
Determine whether you are receiving too much medicine.
Ensure that you are taking a medicine properly.

How To Prepare

It is important to know exactly when you took the last dose of the medicine for which you are being tested. Ask your doctor for instructions about the timing of the test.

Tell your doctor about all the prescription and nonprescription medicines you are taking and any drugs (such as alcohol, marijuana, or cocaine) you are using. Sometimes these can interfere with testing.

How It Is Done

The health professional drawing blood will:

Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
Clean the needle site with alcohol.
Put the needle into the vein. More than one needle stick may be needed.
Attach a tube to the needle to fill it with blood.
Remove the band from your arm when enough blood is collected.
Apply a gauze pad or cotton ball over the needle site as the needle is removed.
Apply pressure to the site and then a bandage.

1 | 2 | 3

Next Page >

WebMD Medical Reference from Healthwise

Last Updated: October 11, 2010

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.