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 difficult,
because the dose needed to produce a therapeutic level in the blood varies from
person to person. Factors 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 break down (metabolize) medicines effectively
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, such as amikacin (Amikacin), gentamicin,
or tobramycin (Nebcin). These antibiotics may cause hearing loss or kidney
damage if their level in the blood gets too high.
Medicines to
treat heart problems. These include digoxin (Lanoxin), quinidine (Cardioquin,
Quinidex, Quinaglute, Quin-Release), or procainamide.
Medicines to
treat seizure disorders (epilepsy). These include phenytoin
(such as Dilantin), carbamazepine (such as Tegretol),
barbiturates (such as phenobarbital), and valproic
acid (Depacon, Depakote, Depakene).
It is important to know exactly when you
took the last dose of the medicine for which you are being tested. Testing is
usually done right before you take another dose. Ask your health professional
for instructions about the timing of the test.
Tell your health
professional 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.
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.
You may feel nothing at all from the
needle puncture, or you may feel a brief sting or pinch as the needle goes
through the skin. Some people feel a stinging pain while the needle is in the
vein. But many people do not feel any pain (or have only minor discomfort) once
the needle is positioned in the vein. The amount of pain you feel depends on
the skill of the health professional drawing the blood, the condition of your
veins, and your sensitivity to pain.
There is very little risk of
complications from having blood drawn from a vein.
You may develop a small bruise at the
puncture site. You can reduce the risk of bruising by keeping pressure on the
site for several minutes after the needle is withdrawn.
In rare
cases, the vein may become inflamed after the blood sample is taken. This
condition is called phlebitis and is usually treated with a warm compress
applied several times daily.
Continued bleeding can be a problem
for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other
blood-thinning medicines can also make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your health professional before your blood is drawn.
Medication monitoring measures the level
of a medicine in the blood to make sure the dosage of medicine is correct. The
effective blood level for each medicine is different. Your health professional
will determine whether the dosage of the medicine needs to be adjusted based on
your blood test result.
Reasons you may not be able to
have the test or why the results may not be helpful include:
The time between when the medicine was first
taken and the blood test. For example, if the test should be done when the
medicine level is lowest, taking a dose of the medicine just before the blood
sample is taken can cause a falsely high result.
If you take
medicines other than the one(s) being monitored. This can include other
prescription and nonprescription medicines or drugs such as alcohol, marijuana,
and cocaine.
Medicine blood levels can be measured in a
person who may have taken an overdose.
The dose of a medicine may
need to be adjusted until the right blood levels are achieved. Dosage of a
medicine may also need to be changed if a person's lifestyle changes (such as
becoming more active) or if the person begins taking another medicine that can
affect the medicine being monitored.
A prothrombin time (PT) test
is a different type of monitoring test. It is used to monitor the effects of
the blood-thinning medicine warfarin (Coumadin). A PT test may also be called
international normalized ratio (INR). For more information, see the medical
test
Prothrombin Time.
Many medicines do not
have established therapeutic levels or methods to measure them. The therapeutic
level is determined either by how a person's symptoms are responding to the
medicine or by the onset of an adverse reaction.
This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.
